AT&T’s Common Architecture for Real-Time Services · PDF fileAT&T’s Common Architecture for Real Time Services, which you’ll read about in this paper, is one example of a forward-looking

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AT&T’s CommonArchitecturefor Real-TimeServices (CARTS)Based on 3GPP/IMS Standards

Prepared by AT&T Architecture and Network RealizationAT&T Architecture and Planning

Revised August 2010

AT&T Common Architecture for Real-Time Services __________________________________________________________________________________________ 2

AT&T Inc. is a premier communications holding company. Its subsidiaries and affiliates - AT&T operating companies - are the owners and operators of all network infrastructures, and the providers of AT&T services, in the United States and around the world.

Rethink PossibleSM with AT&T’s Network of theFuture

At AT&T, we are committed to continuous innovation to connectpeople everywhere they live and work and do it better than anyoneelse. In 2010 AT&T launched a new Brand Idea, “Rethink Possible.”Rethink PossibleSM asks people to imagine a world where it is pos-sible to do more, effortlessly, a world of more information, morepossibilities, enabled by AT&T and its network and services. AT&T’sCommon Architecture for Real Time Services, which you’ll readabout in this paper, is one example of a forward-looking multimedianetwork architecture which will enable businesses and consumersto take advantage of new generations of services, to truly “RethinkPossible” as they transact business and go about their daily lives,supported by AT&T.

AT&T’ vision describes a future where the limits of the traditionalwireless and wireline telephone networks as we’ve known them todate no longer apply. A world of effortless, seamless communica-tions has been unimaginable until now. This network of the futurewill enable any-time, any-distance, any-device communications.Furthermore, this vision enables the seamless creation of all kinds ofother services that people will want to use to enrich their lives andbe more productive. These services include the blending of enter-tainment and information with communications services, based oneach individual’s needs and requirements. AT&T”s network of thefuture will support mass customization of services of all kinds.

Integrated Service Delivery EnvironmentVoice MessagingConferencing Video Your App

Session Management

Common Network Capabilities

Access Technologies

End Devices

Other Apps

SharedInfrastructure

Proliferationof Services

Multiple AccessTechnologies

Multiple Personasper User

Access/DeviceIndependent Services

Multiple-UserDevices

Network of the Future



What are the key drivers for this transformation?

• Converged User Devices: PDAs and cell phones have alreadyconverged into today’s smart phones. Personal computers andnetbooks also can serve as soft phones. Televisions can be usedto access the Internet and to read email. Cellular phones can beused to view live television programs. We will be able to carry onedevice for all our on-the-go communications, entertainment andinformation needs.

• Converged Services: Services will converge not only in the senseof simultaneous and integrated support of multiple media, butalso in the sense of the functions they provide. For example, therewill be only one “contact list” where the user records informationabout people he or she needs to communicate with. This singlelist will be accessed via any devices-PC, netbook, PDA, wirelessphone, wireline phone, etc. And it will be seamlessly integratedwith other applications such as email, chat, and calendar.

• Multiple Access Technologies: Traditional TDM (wired) technolo-gy is only one of a suite of technologies that enable access tocommunication services. Today cellular, LTE, Ethernet, Wi-Fi,WiMAX, Broadband over Powerline (BPL), Cable, and DSL are alsobeing used now to reach a provider’s network. New and moreadvanced access technologies are bound to appear.

• “Access Agnostic” Services: Services will no longer be dedicat-ed or linked to a specific access technology. We will no longer talkabout “Voice over X”. There will be just services. A service can beinvoked using whatever access technology is available, or is lessexpensive, or is more powerful, at the time a session is initiated.

• Global Service Mobility: In the “global village” people are muchmore mobile than they used to be. As they travel the globe theyneed to be able to access a consistent set of services no matterwhere they are, what equipment they are using, or their means ofaccess. A business traveler, for instance, will be able to use thesame business services he or she has in the office while staying ina hotel thousands of miles away. Services associated with any ofa user’s “personas” will be available anywhere, limited only by thelimitations of the device or capabilities of the access network

• No Geographical Boundaries: The geographical boundaries ofthe public switched telephone network (PSTN) will no longer mat-ter. It will not make a difference whether a user calls a colleaguein the office next door or a friend thousands of miles away. Verylittle distinction will be made between a local, a long distance,and an international session.

• Blurred Boundaries between Consumer and BusinessServices: Even though we will continue to have services tailor-made for business users and for consumers, the distinctionbetween the two groups will gradually fade away – at least fromthe network architecture point of view. For example, both busi-nesses and consumers will benefit from a video conferencingservice or a find-me/follow-me service.

• Proliferation of Services: There will be a large and ever-growingnumber of services. The capabilities unleashed by a global, IP-based, and flexible communications infrastructure will unleashinnovation to a degree never experienced before.

• Flexible and Customer-Focused Network: Services will becomehighly “tunable”. Users will have the ability to customize their serv-ices easily without the need for intervention by the serviceprovider. It is even possible that mechanisms will be in place toenable a sophisticated user to design his or her own service bydefining the necessary service logic.

• Support of Multiple Personas: Each of us plays many roles inour lives: parent, friend, sports-enthusiast, employee, etc. In thenew language of multi-media communications, enabled by IMS,these aspects of our lives are called “personas.” Imagine that asingle person, using the same device, can simultaneously partici-pate in services in any of these multiple personalities or personas.No longer bound by traditional limitations of telephone numberand service, a user will be able to define various personas — eachhaving its own associated collection of communications services— and will be able to easily switch between them or use themfrom any device.

To achieve this vision, AT&T has designed its Common Architecturefor Real-Time Services, called simply CARTS throughout this docu-ment. CARTS, which in part relies on 3GPP/IMS standards for itssession layer, is an important component of the architecturalroadmap which will guide the development of AT&T’s network overthe next decade. The implementation of CARTS will be an evolutionof AT&T’s existing network, ensuring a smooth transition to the nextgeneration of services. Let us describe the technical underpinningsfor this rich multi-media architecture which will enable this vision tobecome a reality.

AT&T and IMS

AT&T has a long history of being the first major carrier to take a newtechnology and bring it to mainstream production. It was the firstcarrier to embrace MPLS in 1998, and assisted in the developmentof the IETF standard and to offer services based on the then-lead-ing-edge network architecture. With the emergence ofsoftswitching in the early years of the 21st century, AT&T foresawthe need for a layered multimedia architecture based on SIP, whereaccess capabilities were de-coupled from the core and service logicwas fully separated from transport. AT&T developed its own ses-sion-based (in contrast to call-based) multimedia architecture thatwas similar to IMS in principles and design; this architecture couldbe considered a precursor to IMS. As IMS matured, in keeping withAT&T’s preference for standards-based architectures, AT&T subse-quently embraced IMS for use within its multimedia architecture.

IMS is based on the principle that separation of access, sessionmanagement, and service logic layers is the most critical require-ment. The ability to support access technologies of the futurewithout impacting the rest of the architecture is critical. The ability



for application logic to be totally independent of the access tech-nology being used at the time of a call, the ability for an applicationto be applied to a session over various access technologies, and theability for several independent applications to be applied to a givensession are among other important required characteristics.

IMS standards and architecture specifications are now nearing alevel of industry acceptance in the global communications industry.It is predicted that IMS will become the de facto standard for real-time multimedia communications services over wired and wirelessnetworks. IMS is based on the Session Initiation Protocol, which isbetter known as SIP. This protocol, which acts as a session controllanguage, is flexible enough to handle the variety of multimedia ses-sions that will make up the communications of the future.

AT&T has selected IMS as the session management layer for its real-time network architecture, and plans to deploy IMS-compliantfunctions in its network as appropriate and as its business needsrequire. These plans are consistent with AT&T’s commitment to usestandards-based architectures in the design of its networks andinfrastructures.

The scope of the IMS specification itself is primarily limited to thesession control layer of the network. However, CARTS goes farbeyond the IMS specification itself and covers the entire networkincluding application structure, service delivery, service creation,service bundling and orchestration, generic support of variousaccess technologies, security, government-mandated capabilities,and more. IMS specifications and standards are used in CARTS forthe session control layer, but the architecture also includes a num-ber of additional key functional components and AT&T-developedenhancements in order to provide a complete network architecture.

AT&T believes that the inclusion of an IMS-based architecture inCARTS will provide tremendous value to our customers throughenabling lower cost solutions and quicker feature introduction builton a platform designed for new and evolving IP services. With itsgrowing acceptance by the communications industry and with workcurrently in progress to enhance and improve it, we are confidentthat IMS will become the session control standard architecture sup-porting the multi-access and multi-application networks of thefuture. Having such a standard architecture is a critical step in theevolution that is needed to transform the networks of the 20th cen-tury into those needed in the 21st century.

The present release of AT&T’s CARTS architecture, described withinthis document, is based on Release 9 of the 3GPP IMS Architecturestandards. This architecture is consistent with the work of a varietyof standards groups including 3GPP, ETSI, TISPAN, ATIS OMA, and theParlay Forum. AT&T is actively involved in these standards bodiesand is keenly interested in ensuring that the full range of accesstechnologies and wireline requirements will be addressed in futureenhancements to the architecture.

CARTS and IMS

IMS has been described as “enabling the promise of SIP.” IMS, basedon the work of several technical organizations including 3GPP, ETSI,TISPAN and ATIS, enables the control of multimedia forms of com-munication, including voice, using SIP as the signaling protocol. Butthe IMS architecture as defined in standards is not sufficient for acarrier to build and bill a complete set of end-to-end services. Thecarrier must add value at the access edge as well as from top tobottom with security, policy, billing and OSS support. In addition,the carrier may choose to build an application layer to enable thecreation of rich, blended forms of service that were difficult orimpossible to create using previous technologies.

In designing its CARTS architecture, AT&T has wrapped these addi-tional capabilities on top of an IMS core, as well as creating both aService Broker and a Web core to enable blended SIP-based andweb-based applications as well as composite SIP-Web services innew forms.

CARTS is based on a layered architecture comprising the followingbasic concepts:

• Each access technology communicates via a Border Controller,which provides a uniform internal view

• To provide a “service”, the corresponding Application Server (AS) is“plugged-in”.

• Once a new access technology is supported it can be used by allexisting and future Application Servers.

• Once a new AS is deployed it can support all compatible existingand future access technologies.

The diagram below illustrates these basic concepts.

Conceptual View of Architecture

Application

Session Controland Management

Infrastructure

InternetBorder

Controller

PSTNBorder

Controller Managed IPBorder

Controller

WirelessBorder

Controller

IP/MPLS Converged Network

VoiceApplication

Server

ConferencingApplication

Server Video

ApplicationServer

MessagingApplication

Server

CollaborationApplication

Server

PresenceApplication

Server

Managed IPAccess

PSTNAccess

InternetAccess

WirelessAccess



In defining the architecture, basic IMS architectural elements areused and then augmented with functions required to deploy com-plete end to end service.

This architecture, with its layered approach, does away with many ofthe standard notions that have been part of the communicationslandscape for a number of years.

For example, by abstracting the access layer, we can eliminate theidea of “over” terminologies like “Voice over DSL,” “Voice over cable,”Voice over IP.” “Voice” simply becomes a service that can be invokedand reached via a variety of access technologies. The service andthe access technology are no longer dependent upon each other.The goal of this architecture is to provide the same user experienceno matter what device or access technology is being used.

This architecture also enables the elimination of traditional distinc-tions such as “mobility service” or “international service.” There willsimply be services, and users will be able to access them whereverthey are, via any compatible access network or device.

One of CARTS’s important innovations is the idea of “SeamlessMobility.” This term has traditionally been interpreted as the ability tomove a wireless voice call between a cellular network and a Wi-Finetwork. But CARTS goes far beyond that definition and envisions afuture where a user can move not only a voice call but a multimediasession including voice, data and video, between any possible com-bination of access technologies and devices, not just wireless ones.From AT&T’s perspective, “Seamless Mobility” also incorporates theidea of Fixed Mobile Convergence, as the term is used in the indus-try to describe the ability to access services across both wirelineand wireless networks of all types.

Another important idea that CARTS enables is that users are nolonger identified by a line or a telephone number or a port number.Users are identified as people; people can use different accessmethodologies and devices. Going even further, individuals have dif-ferent aspects to their lives. Someone may be a family member or amember of a charitable organization or an employee of a company.Each aspect of a person’s life represents a potential “persona”. Theindividual has the ability to use and register for services based oneach different persona. We’ll discuss “personas” later in this docu-ment when we discuss the new end to end capabilities enabled byCARTS.

For the technically savvy, one of CARTS’ innovations is the extensiveuse of “enablers” or reusable “capabilities” throughout the architec-ture. Use of enablers or reusable capabilities is a new idea for amajor telecommunications carrier. Examples of such capabilities are“address book”, or “presence”. Historically a carrier would build indi-vidual capabilities for each individual service. The result of thisapproach was that it took a long time and was expensive to developservices. Since such capabilities were individually developed, theycould not be reused and the design would vary from product toproduct.

From a customer perspective, it meant that the address book popu-lated in a consumer service could not be accessed from a businessservice or vice versa, plus it had a different look and feel.

Fundamental to the CARTS architecture is the extensive use ofenablers or reusable capabilities as fundamental building blocks toenable rapid service development and the creation of modules thatcan be reused and accessed by more than one service. Truly seam-less services, based on enabler/capability building blocks, willprovide benefits to both consumers and businesses alike in terms ofefficiency and ease of use. Enablers are also discussed in theService Execution Runtime Framework (SERF) section later withinthis paper, in the context of customer access to these fundamentalbuilding blocks for their own applications.

But let’s return to the vision—what are some examples of futureservices that CARTS enables? How can this technical architectureenable businesses and consumers to communicate better and moreeffectively?

Anytime, Anywhere, Seamless Services

With IMS at its core, CARTS enables the creation of new servicesthat integrate innovative applications with the network itself, trans-forming the way people live and work as well as enhancing businessproductivity. Let’s look into the future and see what types of servicesmay be possible.

Peoples’ lives are rich and complex as they play many roles: busi-ness person, family member, sports enthusiast, to name a few.Global corporations are challenged to facilitate communicationsbetween employees around the world at any time of day or night,while being mindful of business hours and non-working hours. Thispicture illustrates one set of possible roles and situations; the com-plexity of communications is increased as locations span time zonesand countries. The hotel could be half-way across the world fromthe office or the home.

The Global Corporation has employees located around the world.Its technical experts and salespeople are frequently on the road,even traveling internationally to meet with clients. Historically theemail system, with its calendaring feature has been used to trackpeople’s availability for scheduling meetings and conference calls.But the email system doesn’t readily expose when it’s the middle ofthe night, or when people are not available because it’s after work-ing hours. It doesn’t know that it’s the middle of the night in Indiaand daytime in the United States. CARTS, with its support of blend-ed applications, potentially enables the integration of informationbetween the calendar and the network regarding people’s statusand availability to take a call on an immediate basis, or at somescheduled time in the future.

Let’s consider the case of Steve, the technical expert, who lives inCalifornia but is traveling to India for a week’s worth of client meet-ings for a major project. India is 13.5 hours ahead of California. Hecarries a single cellphone, but uses it for both business and person-al calls. The network knows which calls are to be billed to eachaccount based on his address book. He has configured his networkprofile for his work persona to be unavailable between 11 pm and 6am based on the local time of his location. Steve’s cellphone isturned on and it has transparently registered with the local network,


so the network knows what local time is. A client contacts Sally,the local technical support resource in California, with an urgentquestion at 4 pm PST. After speaking to the client, Sally realizesthat she needs to get the answer from Steve. It’s 5:30 am in India.She calls Steve’s cellphone and receives a message that says thathe’s traveling on business and will be available at 6 am local time,and that his availability will be in 30 minutes. She leaves a messagefor Steve to call her back as soon as possible. Steve’s cellphonedoes not ring but the message light comes on. When Steve arises,he sees the message and calls Sally back.

On day three of Steve’s trip to India, his 10 year old son Johncomes home from school grinning proudly and carrying a certifi-cate. His science fair project has won the prize for the bestsubmission. Steve had been working with John on the project forseveral weeks prior to the India trip and was anxious to hear theoutcome of their efforts. Even though it’s 3:30 am in India, Steve’swife calls him to tell him the exciting news. Since Steve’s personalprofile is set to allow calls from his wife at any hour of the day ornight, in this case Steve’s cellphone rings. Steve is tired, but happyto be waked up with such good news. His wife puts John on thephone and Steve gives him a hearty, “Congratulations.” They chatbriefly and then Steve goes back to sleep for another couple ofhours.

Consider the Road Warrior, or business traveler. You’ve just landedat a distant, unfamiliar city at about 6 p.m., and turned on your cell-phone. The first text message that greets you is from your airline,since you’ve opted into their frequent traveler program and askedfor alerts. “Welcome to Chicago, Mr. Jones. Baggage for flight 123is at carousel number 3.” The next text message is from the carrental company, as you’ve also opted into their frequent travelerprogram for alerts. “Welcome to Chicago, Mr. Jones. After you claimyour luggage, please proceed to the door marked “Shuttles” andtake the shuttle to our lot where your car will be waiting at stall 45.”You collect your bags and take the shuttle to the car rental.

As you drive to your hotel, a message from your son’s Little Leagueadvisor arrives, telling you when the next game will be. This mes-

sage was stored in the network since you had set your profile sothat such messages would only be sent after business hours or onweekends. Arriving at the hotel, logic using the GPS in your phonealerts the network as to where you are. As you turn into the parkinglot you receive a message from the hotel, “Welcome to the XYZHotel, Mr. Jones” and pointing out the choice of self-parking or valetparking and the daily charge for each. As you enter the building,you proceed to the priority check-in counter. You place your cell-phone near the scanner and it identifies you and asks if you’d liketo use the credit card on file. You indicate yes, and then input a PINyou’ve chosen as part of your opting in to use the hotel’s prioritycheck-in service; use of this code protects you in case your cellphone is lost or stolen. After you’ve authenticated, your cellphoneshows, “Welcome to the X Hotel; your room is 1123. For front deskplease dial 1, room service 2, etc.”

Arriving at your room, you hold the phone near the scanner by thedoor and the door unlocks. As you’re tired from a long trip, youchoose to order room service. After looking at the menu in theroom, you simply press a programmed key on your cellphone toplace your order. This particular hotel has also contracted for thefull range of AT&T voice, data, and video services, thus also givingyou the flexibility to access the services you’ve subscribed to in yourvarious personas using the hotel phone, computer, and television.

In addition to the challenges experienced by road warriors, manyindividuals are must spend long hours commuting and still be pro-ductive. Randy, a Commuting Professional, has a smartphone tokeep him connected and productive wherever he may be. At homehe subscribes to AT&T’s Uverse (IPTV) service. Although he likes thelatest technology, he still has an old-fashioned POTS line in his resi-dence. To prepare for an upcoming hands-on training class at work,Randy has decided to spend part of his commute time preparing bywatching a training video that his company has made available viathe Internet using his smartphone. The video is streamed to hissmartphone over the 3G/4G data channel from a network mediaserver on the Internet. He pauses the video when the train reacheshis stop and he then disembarks.

Arriving home, he uses his smartphone to disable his home securitysystem, open the garage door and unlock his front door. After get-ting settled at home, he wants to resume watching the video fromthe point where he paused it, but this time he indicates via hissmartphone that he wants to continue watching the video on histelevision, which is part of the Uverse service. The network knowsabout Randy’s Uverse service and asks him which TV he prefers towatch the rest of his video on. Randy chooses his living room TVwhich then starts streaming the rest of his video clip. As he getsclose to the end of the video, he receives a call from his son atschool on his residential POTS line. The caller’s number, name andpicture pop up in the corner of TV with options to answer the call,reject it, or send it to voice mail. Randy answers the call on hishome phone. The video is automatically paused. He finds out hisson needs a ride back home from school after his band practice isover. On the TV screen, using his smartphone as a remote, heaccesses his network services and creates an alarm to go off to


DrivingMy Car

DSL/Cable

Cellular

Home AwayFrom Home

On thePhone

In aMeeting

Or…

Office

Home

Office AwayFrom Office

Available(Except if...)

WiFi

Broadband

U

LimitedAccess

At theGame

Do Not Disturb(Except...)

On theBike

User’s view

remind him of the time he needs to leave to pick up his son. Hethen goes back and finishes watching the rest of his video clip.

In another scenario, the Investor is tracking a particular stock andwants to be alerted when it reaches a certain “strike” price so hecan buy it. His brokerage firm has an investing application hostedin the network that will alert him to the change of price dependingupon the preferences that he’s set up, such as his location. He hasset up his preferences that he is to be alerted of the stock price nomatter where he is: at work, at home, or traveling. He’s indicated hisnormal work hours and knows his location based on the GPS in hiscellphone. When the stock reaches the strike price, the networkknows to simultaneously ring his office telephone and his cellphoneif the event occurs during the business day. If he does not answerand the call goes to voicemail, the network also knows to send atext message to his cellphone with the stock price.

Parents are concerned about protecting their children fromstrangers, but even the youngest children today have cellphones toenable them to call home, call their friends, and enable their par-ents to reach them. A parental screening application can enableparents to be notified when children receive calls from unauthorizedindividuals, and can allow them to intercept those calls. Let’s takeJohn and his daughter Debbie. An unknown caller calls Debbie’scellphone. John receives a notification on his PDA that someone iscalling Debbie; the notification shows the both the caller ID of thecaller and their name (if calling name comes through). He hasthree ways of handling the call: 1) he can reject it, 2) he can allowthe call to go through, or 3) he can have it transferred to himself.Since he doesn’t recognize the name of the caller, he clicks on thelink on his PDA that says “Transfer Call to Me,” and his cellphonerings with the call from the person who had called his child.

Car accidents are distressing and costly to all involved, but CARTSpotentially enables faster handling of claims and documentation,saving time and effort for both the Consumer as well as the insur-ance company. On a dark, rainy night, a man’s car skids out ofcontrol and crashes into a tree on a country road. He’s shaken upand his car is not drivable. He first dials 911 and asks for assistance.The 911 dispatcher knows where he is because of the GPS trans-mitter in his cellphone, and immediately dispatches a tow truck. Thenext call the man makes is to his insurance company’s 24 hourclaims line. The agent first asks if he is all right. After finding out theman has not been injured, the agent confirms his location that wasprovided by GPS (“I see you’re on Highway 72, just south ofJohnstown”), and asks the man to use his cellphone camera totransmit a video of the environment around the accident—theimages show that it’s a forested area with a narrow country roadand that the roads are slick. The insurance claims agent also askshim to walk around the car and transmit the video of the damageto the car. The insurance agent then indicates they’ll have a rentalcar arranged for him at the town where the car will be towed. Thisapplication illustrates the potential to save time, money, and incon-venience both on the part of the consumer, and also the potentialto improve the productivity and responsiveness of the insurancecompany.

It’s always challenging for Friends to get together due to the prob-lem of coordination between busy schedules and the obstacle ofgeographic distance. Mary is on the phone with Julie, discussinggoing to see a movie; Julie suggests inviting Jane. Mary adds Janeonto the conversation, creating a 3 way call. They all live and workin various parts of the large metropolitan area and are willing tomeet at the theatre that’s most convenient to all. Each has an ideaabout what film she’d like to see, and starts downloading movietrailers to see what looks interesting. Mary’s in her office on a wiredtelephone, Julie’s just completed a meeting with a client and is hav-ing coffee at a nearby Starbuck’s, and Jane is at home.

After discussing the various options, they agree to see a particularfilm. Now the challenge is finding which theatre is showing the filmand is most convenient to the three of them. Mary has signed upfor a movie locater service; she accesses the website and puts inthe telephone number of her cellphone plus her friends’ cellphonenumbers. The application knows where they are each located basedon the GPS in their cellphones. The movie locater application tellsthem which theatre has the film and is most convenient; it also pro-vides the show times and offers to reserve e-tickets. Mary agrees,and inputs the PIN she created for the e-ticket application, which isalready populated with her credit card number. The applicationasks if all the attendees would like turn by turn directions to thetheatre. Mary says yes and text messages with directions are sent toall three parties (via SMS to the Julie and Jane, and via email toMary, who is in her office). They meet up later and pass an enjoy-able evening together having dinner and seeing the film.

These have been just a few examples of how the CARTS architec-ture enables new and innovative services that can improve personaland business productivity and help customers connect to anyone,anywhere, anytime. Now let’s look at the technical architecturewhich makes this possible.



Find nearby movie theatersPresence and location

Scheduling movies with friendsiCalendar and instant messaging

Purchase e-ticketseCommerce

Preview moviesStreaming video

Movie Locator Service

Five simultaneousSIP sessions


AT&T’s CARTS Architecture

The diagram below shows the complete view of CARTS:


We’ll go through each component or “layer” of the architectural dia-gram, starting from the bottom, describing its purpose andfunctions, then return to the sides at the end. Any acronyms notspecifically addressed in the text are listed in the Acronyms sectionat the end.

Devices and Access Networks:

At the very bottom of the CARTS architecture diagram we finddevices of various kinds and the access networks to which thesedevices connect. In reality customers and businesses use “services“which today are typically combinations of devices and servicestightly wedded together. CARTS breaks this long-accepted para-digm and creates a more flexible environment, because it is “accessagnostic. ”, This means that all of the components in layers abovethe devices and access networks don’t care about how the user isconnected and what device the user is using. In order to appreciatethe services that CARTS supports, we need to remember the manytypes of devices that are in use today and see how CARTS enables

them all to take advantages of this rich new service environment.

The purple boxes represent various types of devices commonly usedtoday: 1) Unmanaged IP devices such as an IP-PBX or a PC; 2)Devices that can be managed by AT&T, including devices to be pro-vided as part of AT&T’s Digital Home initiative, cellphones, androuters/gateways; and 3) Unmanaged TDM devices such as tradi-tional PBXs and traditional TDM wired telephones, sometimes called“black phones.” All of these types of devices can take advantage ofCARTS and use its applications, with the nature of the usagedepending upon the capabilities of the devices themselves.

The green boxes represent the access networks that the devicesuse. CARTS enables many different forms of access to utilize itsservices. Access networks include two basic types: IP-based,including dedicated Internet access like AT&T’s Managed InternetService; and TDM Circuit Switched, such as the traditional TDM voicenetwork or the Wireless Circuit Switched (CS) Network. Over time, asthe TDM-based public switched telephone network is retired, thelatter type of access will no longer be needed.

Policy

Man

ag

em

en

tan

d Q

oS

OSS/BSS

Pro

vider/A

pp M

gm

t.

Catalo

gs

Charg

ing &

Billin

g

Service D

elivery

Core Fu

ctions

Service A

ssuran

ce

Quality o

f Service

Policy M

anag

emen

t

Circuit Access Networks(POTS, PSTN, 3GPP CS networks)

IP Access Networks(Internet, Managed IP Services, 3GPP PS Network

Managed Devices(Digital Home MAG, Cell Phones, Gateway/Routers)

Unmanaged IP Devices(PC, IP-PBX)

Unmanaged TDM Devices(PBX, Black Phones)

Media Servers

Content Delivery

DRM Functions

Media Resources

Content Management

SIP Access

InterconnectSessionBorder

Controller

AccessSessionBorder

Controller

Web Access

Real-TimeAccess

Management

WebSecurityGateway

ExternalApplication

Access

SIP Core

ENUM

TransitFunction

I/S-CSCF

BGCF

SupportFunctions

Circuit Access

CircuitSwitch

Gateway

LineAccess

Gateway

Service Creation & DeliveryFramework

Service Syndication

Services Marketplace

Service Metadata

Application Creation Environment

Service Execution Runtime Framework

Runtime Execution Environment

CARTS Applications

Service Brokering Enablers and Enabler Access

ConsolidatedNetwork

Repository

ApplicationRepositories

HSS(CS/PS)

HSS(IMS)


Connecting the IP access networks to the CARTS access layer isAT&T’s IP /MPLS network. On the diagram this is represented by theblack line separating the access networks from the CARTS layers,CARTS does not “own” or control the IP/MPLS network (i.e., it is anindependent AT&T architecture with its own architecture definition),but simply uses it for transport. AT&T has been a leader in thedevelopment and implementation of IP/MPLS technology and has arobust, automated systems infrastructure supporting its global IPnetwork. CARTS will take advantage of AT&T’s mature globalIP/MPLS network for transporting its rich set of services, as well asinterconnect various components of CARTS.”

Border Controllers, Device Support and CircuitAccess

Moving up from the access networks layer, we come to three bluerectangles. This layer represents the actual “access” layer of theCARTS architecture and is where the access networks describedabove connect to CARTS.

We described how the architecture supports various types of accesswhich communicate via a Border Controller or other gateway func-tion. The Border Controller is the first entry point in the AT&Tnetwork and includes both security and transport functions, withSIP being a signaling protocol. Once a given type of access is“plugged in,” it has access to the core and higher layers of thearchitecture, including the application layer. AT&T’s deployment willinclude geo-redundancy, resilient designs, and diversity of the vari-ous network elements to ensure the high reliability that ourcustomers require for multimedia and voice services.

At present the CARTS architecture includes three types of access:Web Access, SIP Access, and Circuit Access. The individual yellowboxes represent these specialized edge or border functions:

• Web Security Gateway (WSG) - Entry point to web/HTTP/por-tal services. CARTS supports various types of services, andincludes the ability to authenticate and blend various combina-tions of these services; Web/HTTP/portal services are described inthe SERF Core section.

• External Application Access (EAA): The EAA proxies communi-cations between externally-developed applications and CARTSresources. When an application developed by a Third Party or anEnterprise Customer wants to access enablers or other resourcesin CARTS, this access is mediated by the EAA.

• Real-Time Access Management (RAM): In the Access Layer, theWSG and EAA perform the security and authentication functions,and the Real-time Access Manager performs the authorizationfunctions. RAM is the policy decision and enforcement point forgranting user access to services based on user role, subscription,and service access policies.

• Access Session Border Controller (A-SBC) – Today’s smart IPtelephones automatically “register” the phone and its user withthe network; this is called SIP User Agent functionality. This type

of SBC communicates with such devices. The standard IMS func-tion within the A-SBC which handles this function is called theProxy Call Session Control Function (P-CSCF). AT&T has integratedthe P-CSCF into the A-SBC architectural element in CARTS.

• Interconnect SBC (I-SBC) – This capability supports the abilityfor other carriers to exchange SIP/VoIP traffic with AT&T via SIP orVoIP peering (note that this is not the same as traditional ISPpeering).

• Circuit Switch Gateway (CSG) The CSG provides access to/fromthe PSTN, Wireless Mobile Switching Centers (MSCs, similar toswitching centers for the TDM network), and Enterprise TDM end-points such as TDM PBXs: these are typically high-capacitytelephone trunk connections.

• Line Access Gateway - Access for individual POTS lines: theseare the typical two-wire connections to individual traditional tele-phones.

Media Resources

Adjacent to the Web Access area of the architecture is the MediaResources area. One of the important principles of CARTS is that“content” in any form (voice, data, text, video) should be deployedas close as possible to the access layer This principle is illustrated inthe location of the Media Resources section of the architecture(adjacent to the access layer).

In the context of traditional telephony Media Servers are used tosupport such things as interactive response announcements, ordi-nary announcements such as “The number you have called is not inservice, please check the number,” and network announcementsused in mass calling events such as the popular American televisionshow American Idol. As the forward-looking architecture that couldsome day support an entire voice network based on IP using SIPsignaling, the CARTS architecture includes media servers of thisnature within its core. These types of media servers are not specifi-cally called out in the simplified picture above, taken from theoverall CARTS architecture picture, but are simply part of the arsenalof media servers of various types. However, as the architecture isdesigned to support all forms of media, CARTS goes beyond the tra-ditional telephony use of media servers described previously andincludes media servers to support what most people think of whenthey hear the term “media”–video, both flowing from the networkand uploaded by consumers.

Another important principle of CARTS is that content should beaccessible from any type of access network and from any applica-tion to any device ranging from cell phones to digital home tocorporate IP PBX, via the Internet or wireless network. To supportthis flexibility, Media Servers and resources must be shareable byservices and applications. The CARTS architecture enables applica-tions to call upon these resources and use them as needed, withouthaving such servers dedicated to specific applications. The ability todeploy and use media servers by multiple applications makes it pos-sible to deploy new services more rapidly and with less cost.


AT&T Common Architecture for Real-Time Services ________________________________________________________________________________________ 10

Enterprises who may wish to host their applications in AT&T’s net-work may use these resources for their applications since theresources are shared.

CARTS Media Servers can be shared across any number of servic-es. CARTS Media servers consolidate the functions ofannouncement servers, interactive voice response (IVR) servers, con-ferencing bridges, messaging platforms, and platforms providingspeech recognition and related technologies into a multi-service,open standards-compliant solution for network and enhanced serv-ices media processing. Media Servers provide reusablefunctionality that is decoupled from services and does not requireconfiguration on a per-service basis; each service simply makes useof media server functionality that it needs. Adding the media pro-cessing required by a new service only requires scaling the existingmedia servers and possibly adding new media servers to supportnew functionality. Changing or augmenting functionality of existingmedia servers or replacing existing media servers with new types isnot required.

To allow the efficient sharing of resources, and maximize mediaresource availability and utilization, AT&T has included a new func-tion in the CARTS architecture called the Media Resource Broker(MRB). This is a new common architecture component for theassignment of resources to services from a common pool of MediaServers. The MRB is required by large service providers to efficientlyassign resources to many multimedia services in support of millionsof users. The MRB also performs load distribution and site manage-ment functions as well as resource brokering to meet AT&T’soperation requirements. However, the industry has not yet devel-oped Media Resource Brokers that meet AT&T’s requirements. Whilethe concept of a Media Resource Broker is not new, AT&T is taking aleadership role in its development from two perspectives—first, byactively contributing to the standards bodies who are developingspecifications for such an entity, and second, by engaging in dia-logue with vendors regarding the technical requirements and needsfor this type of device. AT&T strongly supports use of standardizedinterfaces within its network architecture and is currently active in anumber of standards bodies to develop open standards. To datework on the MRB concept has been done in ATIS-PTSC, ITU-T NGN,and the IETF Media Control Working Group.

CARTS Media Resources can be accessed from both the SIP Coreand the CARTS applications layer (SERF), which is described later inthis document. The power of this architecture is that it enables AT&Tto create blended services that can be accessed from any device,with the nature of the service delivery varying according to thedevice’s capabilities. In addition to media servers of various types,CARTS also includes a common set of media-processing functionsthat can be shared and used independently by individual networkservices to support service innovation and differentiation. This func-tional area has been designed to maximize use of commonfunctions, to enable streamlined service development and fastertime-to-market for new services, to enable content to be sharedacross channels and devices, and to support both user-generatedas well as licensed content. As one would expect, it’s critical to beable to manage media from a licensing perspective, to distribute it

efficiently to customers everywhere, and to keep track of copyrightstatus and licensing agreements (i.e., the capabilities comprisingContent Management).

In addition to providing support for traditional voice applications,CARTS supports Multimedia Conferencing. This capability enablesthe blending of multiparty audio, video, messaging, and applicationsharing, thus enabling the development of rich media conferencingexperiences. The CARTS Multimedia Conferencing architecture isbased on the IETF XCON Working Group design. MultimediaConferencing can leverage the Media Resource Broker architecture,extending the XCON model to include the MRB.

CARTS also provides support for Digital Rights Management (DRM)which enables the definition of and the enforcement of secure con-tent transport as well as secure content licensing, includingprotection and control of the viewing of content that is deliveredover IP transport and rights management for the delivered content.AT&T will support a single DRM system for AT&T content, with inter-operability with other DRMs only as required.

SIP Core

Moving to the right from the Media Resources box is the SIP Corearea of CARTS. The SIP Core is responsible for session control forIMS connections in the architecture. This portion of the CARTS archi-tecture is what could be considered “IMS,” thus illustrating howmuch functionality a carrier must add in order to create a completearchitecture.

Another part of the SIP core is a group of functions that providetransit and routing capabilities. In the context of CARTS, “transit”means the efficient transport of calls that do not require the use ofthe IMS core capabilities; these arrangements are typically used bywholesale customers and represent low-feature traffic.

Overall the SIP Core consists of four groups of functions:

• IMS Core – contains the Interrogating-Call Session ControlFunction (I-CSCF) and Serving-Call Session Control Function (S-CSCF). The IMS Core also supports important interfaces to theHome Subscriber Server (HSS) and the Subscriber LocationFunction (SLF) although these elements are implemented outsideof the SIP Core in the Consolidated Network Repository (CNR)which will be described next.

• Transit Related Functions – These include the Transit Function (TF)and Breakout Gateway Control Function (BGCF).

- TF - By directly routing to/from border elements bypass-ing the IMS Core the transit function allows particularcalls to avoid the IMS Core overhead when required.

- BGCF - The Breakout Gateway Control Function is theintelligent PSTN/Wireless routing element in CARTS. Thisfunction performs routing of IMS-originated calls to adestination gateway towards the PSTN, based on thetelephone number of the called party.



The SIP Core also includes what are called Support Functions –As voice traffic is increasingly shifted to IP networks, carriers mustdesign their IP and IMS-based architectures to be compliant withall requirements of law enforcement and emergency services.Thus, the CARTS core architecture includes support for E911 andCommunications Assistance for Law Enforcement Act (CALEA)functions required by law in the United States. E911 support forVoice over IP service providers was mandated by the FCC in 2005;CALEA was originally enacted by Congress in 1994; in 2005 theFCC decreed that broadband and interconnected Voice over IPservice providers also are subject to CALEA. Similar requirementsalso exist in other countries.

ENUM - Maps a telephone number to a Uniform ResourceIdentifier (URI) specifying a host that can be resolved via DNS. Inthe initial deployment, ENUM will be used for number mappinginternal to the AT&T network.

Consolidated Network Repository

Moving to the right of the SIP core, the Consolidated NetworkRepository (CNR) provides a single logical database to store sub-scriber information. It will be implemented in a highly-scalable andgeo-redundant configuration to insure high availability to criticalnetwork and application access. The CNR will be used withinCARTS as the primary subscriber data repository with interfaces tothe access, SIP Core, SERF, Policy and BSS/OSS functions of CARTS.

Implementing a common repository simplifies sharing of subscriberprofile information between various network access elements andapplications. The CNR supports the standard network repositoriesused for access and IMS via an integrated logical model.

In the CNR architecture, the HSS (Home Subscriber Server), whichoften presented as a monolithic entity, is divided logically into theparts that support mobility access and IMS based services. The for-mer is designated the HSS (CS/PS) for circuit switched/packetswitched mobile access. The latter is designated the HSS(IMS) forIMS services and is used for the new IP based voice, messaging andvideo services based on IMS standards. The following describesthese parts in additional detail:

• The HSS(CS/PS) is the evolution of the Home Location Register(HLR) used in 2G and 3G networks. It contains the subscriberinformation to control access via the cellular network. It includesthe information required for users to gain Long Term Evolution(LTE) access.

• The HSS(IMS) is the master database for IMS subscribers. An IMSSubscriber is a subscriber to the new IP based voice, messaging,and video services AT&T will be offering. It stores the Initial FilterCriteria (iFC) which is the mechanism for determining which appli-cation servers should be invoked on a call for a particular useridentity, as well as the authentication credentials for authorizingnetwork access.

The CNR can also support the Subscriber Location Function(SLF). The SLF is required when subscriber data are stored in multi-ple HSS elements in an IMS network..

Service Execution Runtime Framework

The very top layer of the CARTS architecture represents the applica-tion layer and its two components, These two componentsrepresent the Integrated Services Delivery Environment as shown inthe “Network of the Future” diagram on page 1. These represent theapplication layer. The left-hand side (yellow box) is the ServiceExecution Runtime Framework (SERF). This is the part of theapplication layer in AT&T’s CARTS architecture that is concernedwith the actual execution of services. The right-hand side is theService Creation and Delivery Framework (SCDF), which sup-ports service creation design, provisioning, testing, portal testing,and other non-run-time activities. We’ll discuss SERF first.

SERF provides a comprehensive set of capabilities that the enter-prise customer can leverage with the assurance that their serviceshave access to all necessary network connectivity capabilities andservice support resources, have the necessary reliability and per-formance, and can be seamlessly blended as needed with othercommunications, content delivery, and information services.

Applications have access to a complete catalog of Enablers.Enablers represent capabilities which provide well-defined inter-faces to common network functions, or shared data, and supportthe reuse of particular modules of program logic that are useful to– but independent of – any particular application. Availability ofthese enablers simplifies application development for enterprisesand their developers, since many ancillary functions needed byapplications are made available in a transparent fashion. Theenabler functionalities go beyond traditional telephony (voice) appli-cations to include support of multimedia applications such as musicand video. It is envisioned enterprises will have access to theseenablers via the External Application Access function for their ownapplications. Enterprises can be assured that the enabler architec-ture aligns with the emerging industry view (e.g., in the Open MobileAlliance); however, AT&T’s approach provides a more coherent viewof the set of enablers by bundling key capabilities that are likely tobe used together.

The common shared environment for hosting CARTS applicationsand enablers provided by the Runtime Execution Environment(REE) provides several types of benefits to enterprise customerapplication developers in situations where the applications are host-ed by AT&T whether on AT&T or customer premises. The commonshared platform frees the customer’s application developer fromproviding complicated platform and infrastructure components. Thisallows them to focus on meeting business needs and thereforereducing time to market for new services. The efficient sharing ofcommon platform infrastructure/services and simplification of oper-ations tasks and procedures reduces the overall costs of supportingservices. Finally, the enterprise customer benefits from increased



overall service availability and reliability since common manage-ment paradigms are leveraged and operational automation isimproved as a result of carefully limiting technology choices in theimplementation of the REE.

Service Brokering is a key component of SERF that enables theblending of basic services from several different domains includingIMS, traditional landline/mobile services (such as 800 calls), IPTV,and Web Services applications into new offerings. Enterprises bene-fit in two ways depending on their relationship to AT&T: (1) Theirbasic services can be integrated with services from other providersto provide new experiences for business and residential subscribers;and (2) Enterprises can take advantage of the capability of buildingcomplex services that can be offered to their own subscribers. Theenterprise is able to capitalize on blending that can occur at variouslevels in the AT&T architecture, including subscriber devices, applica-tion servers, a stand-alone service broker element, and the businessprocess level (i.e., Service Oriented Architecture). In addition, vari-ous service broker architecture technologies can be brought to bearon behalf of the customer, such as an IMS Service CapabilityInteraction Management (SCIM) and JSR 289 SIP Servlet containers.

The OSS/BSS area of CARTS will be discussed later in this docu-ment, but SERF’s capabilities provide a preview of their breadth andrichness. Specifically, a number of new SERF-specific OSS/BSScapabilities can be used by the enterprise in support of new func-tionality and applications. Fulfillment area capabilities include (1)Extending the capability for subscribers to activate a new service orfeature on demand in a real time mode; (2) The ability to exposenew customer services or upgrades to subscriber devices based onservice discovery or subscriber preference plus network-derivedintelligence on their usage patterns; and (3) The capability todynamically provision and de-provision resources to match the serv-ice delivery requirements. Charging capabilities that can beleveraged by customers include emerging real time and complexdynamic charging models; integration of charging with policy defini-tion and enforcement at various levels, supporting bothcustomer-defined and AT&T defined policies; SLA-based charging tosupport a variety of new business models such asadvertisement/sponsorship based charging and micro-payments;and integration of charging/billing with service assurance to accu-rately reflect charging based on the delivered QoS.

Service Creation and Delivery Framework (SCDF)

To the right of SERF in the CARTS application layer is the ServiceCreation and Delivery Framework (SCDF). This innovative archi-tecture serves the needs of five key actors in the global servicesecosystem: Application Creators, Advertisers, Service Providers,OSS/BSS Providers and End Users. While SERF supports run-timeactivities, SCDF enables rapid service creation, testing and moneti-zation of applications developed by AT&T or third parties.

The functionality of SCDF can be grouped into three main compo-nents which are delivered in the context of a ServicesMarketplace as shown in the diagram:

The Application Creation Environment component of SCDF sup-ports the creation and distribution of applications for mass marketand enterprise customers. It includes a developer portal providinginformation about AT&T’s application programs and provides accessto the following:

• Widget, Java, web and native development frameworks and asso-ciated interactive development environments (IDEs).

• Enabler SDKs and associated test facilities providing access toreusable network and OSS/BSS functions.

• An “eventing” framework supporting the loose coupling of appli-cations across end user devices. “Eventing” is an emerging termthat refers to publish-subscribe notification via events. Registeredevent types, called Marketplace Events, are sent and received viathe Publish Subscribe Notify (PSN) component of the SERF ServiceBroker. The use of Marketplace Events enables applications to pro-vide an integrated three-screen experience by simply generatingevents that are subscribed to by other applications operating inthe end user’s three-screen (i.e., computer, TV and mobile screen)environment. Marketplace Events also support the Monetization ofService Metadata strategy described below.

• Mash-ups and Service Blends which are developed on an acceler-ated timeline by a Service Broker Development Organization onbehalf of other developers

• Functions for Network Late Binding: a library of generic Web 2.0functions (e.g., Photo Sharing or cloud storage) which developerscan leverage in their applications rather than coding to the everchanging implementations of specific providers (e.g., Picasa orFlickr). This also enables end-users to establish their preferencesfor specific function providers in one place, rather than with eachapplication incorporating those functions.

• UI component libraries, also known as graphical widgets, certifiedwith Service Marketplace user interface and usability standards.These libraries may be used by any application but are primarilyaimed at applications seeking to design presentation layer viewscompliant with Easy Service Syndication standards.

• An app store supported by app on-boarding and certificationprocesses.

The Service Metadata component of SCDF monetizes the cus-tomer insight metadata generated by third party services in a waythat is a win-win for Application Creators, Customers and AT&T:

• Customers opt-in to usage collection on an application-by-appli-cation basis in exchange for something of value (usually a lowerapplication price at point of purchase).

• Based on the customer’s opt-in, applications are authorized tosend Marketplace Events to AT&T containing insight metadataabout those customers.

• The information from a single application may not be of muchvalue by itself, but when integrated across thousands of applica-



tions, a profile emerges that can be used to provide ad and pro-motional advice to advertisers and service providers.

• Advertisers and service providers never actually access the insightdata themselves, but based on the data, AT&T can select end-users that would be most receptive to a set of promotionalcriteria, or select ads that would be most appealing to a givenend-user.

• The revenue generated by this advice is shared with the applica-tions that enabled the advice. Thus, Application Creators are ableto participate in advertising without having to set up relationshipswith advertisers and without even having to serve ads in conjunc-tion with their applications. The data they provide may bemonetized in many different contexts, over and over again, provid-ing them with a continuing stream of income that greatly exceedsthe revenue they would have earned from the typical sale in anapp store.

• Customers benefit by getting lower prices for the apps they want,and by interacting with ads that are actually relevant to theirinterests.

This strategy is not limited to AT&T services and devices. Any appaccessible to the Web can provide customer insight as part of thisstrategy and any service provider can benefit from the insightafforded by AT&T’s ad and promotional advice services.

The Service Syndication component of SCDF provides a way forservice providers to easily brand, customize and offer applicationscreated by third party Application Creators. In particular, theSyndication Component Model and syndication component of theServices Marketplace make it easy to:

• Provide customer self-service functionality through existing man-agement portals in the Web and on mobile devices. This includesordering, test, trouble, SLA, usage, inventory and other customerself-service functionality that may be available from applications.

• Expose attributes that enable Product Managers to configureapplications into branded products and offers complete with mar-keting collateral, customization of functionality, association ofbillable rates, and creation of bundles associated with promotionsand discounts.

• Integrate with third Party OSS/BSS Providers via standardizedevents. OSS/BSS Providers are a new class of partners facilitatedby the syndication model. They support both Application Creatorsand Service Providers who may wish to reduce their complexity byusing OSS/BSS Provider services.

• Provide settlement functions between all partners participating inthe Marketplace.

Policy Management and Quality of Service (QoS)

On the left-hand side of the overall CARTS architecture diagram wefind a vertical bar with Policy Management and QoS within it. Inorder to support rich, multi-media, flexible, and innovative services,Policy Management is required in addition to a Quality of Servicearchitecture that can communicate with the underlying IP/MPLSnetwork and determine if a service can be supported with theappropriate performance, and reserve resources when necessary.

Policy Management focuses on Resource and Admission Controlin the broadest sense. Resources can include items such as net-work, middleware and applications / services. Admission controltypically includes a variety of authorization scenarios. These capa-bilities support various types of services (e.g., QoS, security, etc.) in amore real-time manner, but also enable various other operationalefficiencies.

The CARTS architecture incorporates Quality of Service (QoS)capabilities and functionality across the entire vertical left-hand sideof the overall CARTS diagram. As illustrated, QoS potentially impactsall aspects of a call or service supported via CARTS, including theaccess line, the IP/MPLS network, the CARTS core, and the CARTSapplication layer.

In the context of CARTS and AT&T’s IP/MPLS network, QoS describesindividual mechanisms that can be used to affect the performanceof particular data flows in the network. With the convergence ofservices to a common IP layer service infrastructure, these IP layer,network-centric QoS capabilities become an important tool toenable the service designer to specify the IP network performancerequired by particular traffic flows. These network QoS mechanismsprovide capabilities to prioritize the specified traffic flows (e.g. atraffic class) in terms of loss, delay, jitter, admission priority, or rout-ing. In IP networks, QoS mechanisms provide improved performancefor high priority applications during times of network congestionbut have no effect during periods of time with no congestion. TheCARTS QoS architecture includes the support of video services aswell as voice over IP, thus including additional traffic classes, differ-ent behavior requirements, and desired network performancecharacteristics. Admission control capabilities (e.g., policy-enabled)are also extended to support the complexity of resource consump-tion required for VBR traffic and multicast video streams.

Network layer QoS can be applied in multiple ways: statically (e.g.,provisioned similar to a PVC); re-provisioned under policy (manage-ment) control (e.g., like a soft-PVC); or dynamically (e.g., like an SVC).Most of the currently deployed IP routing equipment is designed tosupport static QoS definitions, with limited policy control capabilitiesthat are seldom used. However, policy-based capabilities areexpected to be developed to support some forms of dynamic QoSin the future.

CARTS QoS capabilities utilize the underlying network QoS capabili-ties of the IP/MPLS core, in the wireless and wireline accessnetworks, at the intelligent edge devices (e.g., Residential Gateway(RG), Set Top Box (STB), Mobile Endpoint (UE), etc.), as well as sup-porting CARTS applications’ QoS requests. To support the different



types of access networks, QoS functionality will require that therebe a mapping or alignment function between the various accessnetworks’ QoS mechanisms and the desired QoS treatment byCARTS applications. Thus a related effort, AT&T’s QoS TargetArchitecture, (separate from CARTS, but used by CARTS) has focusedeffort on defining the mapping between Ethernet QoS, IP QoS, andthe 3GPP QoS and how these mechanisms interwork to provide endto end QoS treatment to customers across all of AT&T’s networks,including CARTS.

Operations Support Systems/Business SupportSystems (OSS/BSS)

On the far right-hand side of the overall CARTS diagram is a verticalbar running the length of the architecture (turned 90 degreesabove). Its location displays its important role in the architecture-theability to connect to any layer and obtain information to deliver theservices and render accurate billing and perform service assuranceactivities.

Besides supporting the traditional OSS/BSS capabilities to managethe IMS network infrastructure, the CARTS OSS/BSS definesenhanced system functions to support real-time services. One sig-nificant innovation in the CARTS OSS/BSS architecture is to be ableto provide “Real-time” OSS/BSS Application/Service Control func-tions to dynamically manage the Customer and Applicationinteractions in the CARTS environment. These are real-time func-

tions that co-exist with the application services in the Run-timeExecution Environment (REE), which was described in the SERF sec-tion earlier in this document. These functions include:

• Real-time Access Management functions for fine-grained userauthorization based on user subscriptions and service policies.

• Application Menu Control functions for a user-friendly portal environment that is customized based on user context and servicecontext. It provides a consistently orchestrated customer experience.

• Real-time Provisioning functions for on-demand user registrationand configuration of the application services and devices.

• Real-time Charging functions including On-line Charging (prepaid),Credit Control (preset credit limit), Real-time Rating, and Real-timeBalance Management to support the CARTS services.

• Service Quality Management functions for proactive monitoring ofnetwork resources and service quality.

The BSS/OSS applications, Network applications, Customer Serviceapplications and Service Control functions should all operate basedon common information models to optimize interoperability andflexibility of capabilities and services AT&T offers to customers.

The following diagram gives a high level overview of the BSS/OSSfunctions we’ve just described and the architecture framework inrelation to the CARTS infrastructure and applications.


Runtime Execution Environment (REE)

App

SLF BGCF

CSCFMRFC-PHSS

App App

IP/MPLS Core Network

Transport NetworkInternetAccess

WI-MAXAccess

WirelessAccess

PSTNAccess

SERF Video Conf.Voicemail

ContentStreamingLocation

CCPIDM

ServiceBroker

Presence

NetworkAddress Book

CustomerService

Applications

AlarmMonitoring

Perf.CollectionActivation

OnlineCharging

Real-timeBalance mgmt.

PolicyMgmt.App/feature

ConfigCredit Control

App AccessAuthorization

App MenuControl

CARTSReal-time

ApplicationManagement

UsageCol. & Med

BSS

OSS

Mediation

Real-timeBSS/OSSFunctions

ServiceControlEnablers

SIPCall Control

Account

Portal

Sales

Billing Ordering

Trouble TicketingProductCatalog SLA Reporting

Testing Surveil PerformanceRating

Rea

l-tim

e

Pro/Config. Mgmt (e.g., SPP)Repository

NetworkInventory

Preferences

WorkflowMgmt.

B.I.

Security


In AT&T’s network of the future with its anytime, anywhere, con-verged services, it’s important to be able to provision and bill forthese services, as well as to ensure that they are performing asadvertised and promised via service level agreements.

The picture to the left gives an idea of the richness of the newbilling environment. Both customers and Customer Care have theability to obtain information via a portal. Subscribers have the abilityto order service or to change it in real-time. Analysis of a cus-tomer’s usage habits may generate a recommendation to them topurchase additional services or modify the rate plan they’re using.

The Billing System architecture will support a converged masterbilling account structure which allows all service charges from AT&Tto be posted in a single account. The customer will also have thecapability to manage services and devices with multiple personaprofiles and have charges posted in different accounts based on thepersona used. Later in this document we’ll discuss what “persona”means and how the CARTS architecture supports it.

For example, an employee for an Enterprise customer may use acompany provided cell phone for business calls and personal callsby logging into the corresponding persona profile. The charges forbusiness calls will be aggregated to the Enterprise customer’saccount, and the personal calls will be posted into employee’s per-sonal account. The CARTS Online Charging function will enablereal-time service charging. The customer will be able to view thecharges immediately after the service is rendered without waitingfor the end of a full billing cycle. The CARTS Credit Control func-tions will support the pre-paid model as well as real-time balancemanagement where customer can set up credit limits or replenishfunds in real-time.

Another important function of OSS/BSS is Service Assurance,which comprises the functions of monitoring, managing and main-taining AT&T’s networks, services and devices (user) services anddevices (user) so that they provide the levels of service, availabilityand performance that meet the customer’s expectations and com-mitted Service Level Agreements.

The CARTS Service Assurance domain includes enhancements tothe monitoring plane, including passive and active monitoring,incorporation of service and device (user) management, and thepossibility for third party management. The Service Assurancearchitecture will also enable a Service view of applications /enablers with drilldowns. The architecture also supports policy andSLA management at all layers, including resource, service, enabler,customer, persona, etc.

Two key considerations have been made for interfacing with therest of CARTS: 1) Service Oriented Architecture (SOA) has beenincorporated throughout the architecture to enable modularizationand reuse of system functionalities. and 2) dynamic resource man-agement has been incorporated to manage logical and virtualresources based on policies in real-time.

The OSS infrastructure will also correlate and support the ability todrill down into service and device performance information includ-ing base protocol analysis such as latency, jitter, dropped packets,and multimedia service performance as measured by Mean OpinionScores (MOS), and applications / devices involving logic and context


Customer Customer Care

Real-timeBalance Mgmt.

OCS

CCF

Billing

Rating

Usage Collection & Mediation

QoS/Event based

Adjustment

Usage Storage &IntelligentAnalysis

Online Charging& Credit Control

Charging Rulesas Policy

ProactiveSales

Portal - External/Internal Users

Inven

tory &

Data M

gm

t

Perf. Mgmt.

Fraud Mgmt.

Billing AccountIncluding

Persona Option

UserInteligence

CARTS Core, IP Core, Access Domains,and End Points

CARTS C IP C A D i

Applications/SERF

Customer Customer Care Network Care

PerformanceManagement

Test Platform

Incident,Change, Traffic Mgmt., andDisaster Recovery

Workforce Scheduling& Dispatch

Management

FaultManagement

Business Process

Automation

Portal - External/Internal Users

Service Oriented Architecture

XML e-Bond

CustomerNotification

Dat

a B

ase

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Rec

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TroubleMgmt.

CARTS Core, IP Core, Access Domains,and End Points

CARTS Core IP Core Access Domains

Applications/SERF

ServiceQualityMgmt.


End to End Architecture Capabilities

We’ve described all the components in the various layers of theoverall CARTS diagram and how they combine to support new, rich,multi-media applications. But the CARTS architecture also supportsspecific innovative end to end capabilities where the architecturecomponents described previously are seamlessly interwoven toenable end to end capabilities. These capabilities include Personas,Wireless-Wireline Convergence, Integrated Video Capabilities, and, inkeeping with AT&T’s historic and ongoing technical leadership rolein IP network security, a comprehensive security architecture basedon the principle of “defense in depth.” We’ll discuss these end toend capabilities now.

One of the most innovative capabilities supported by CARTS is thenew concept of “Personas.” A Persona is a new type of identity,going beyond our traditional notions of identity being tied to deviceor telephone number. Persona support allows services to be pro-vided based on these new types of identities that refer to Users,that is, human beings, rather than devices or lines (e.g., telephonenumbers in traditional telephony). Different personas (e.g. friend,family member, fellow gamer) could get different treatments from aset of network applications (e.g. call forwarding, Answer Tones,photo sharing, location sharing).

The support for Personas is built upon CARTS’ device and accessindependence and CARTS’ identity management. Because servicesare provided based on the Persona, many new services and userexperiences are enabled. The same user can get the same services

from multiple devices. Multiple users may share a device and getdifferent services and treatments. A single user may have multiplepersonas, belonging to the same or different billing accounts.Multiple people may share a persona when they function as a singleuser such as a family or a call center agent. Personas may be cre-ated for limited purposes such as selling a car or meeting someoneonline allowing services to be tailored to a specific purpose or topreserve the user’s anonymity from another party.

There has been an evolution in how identities (e.g., telephone num-bers and usernames) are used in the delivery of network services.The CARTS Persona Network Architecture extends this evolution toenhance the AT&T user experience of network services. Before thisarchitecture, there had been an evolution of telephone numberidentities from line-based (PSTN) to device-based (wireless andISDN). In the Internet, there is currently an evolution from useridentities that only have meaning to specific applications, to identi-ties that have a network meaning and are passed on toapplications.

With CARTS, a user can get the same services from the networkfrom any device that can support those services. Single Sign Onand Federation of Identities are driving the movement towards a“network” concept of identity. Because both web identities andIMS identities are becoming network-managed user identities,CARTS can have a single set of identities representing the sameuser in multiple domains (web and IMS) facilitating AT&T’s ability toserve and understand the customer and making simpler the devel-opment and deployment of converged services.


Four Categories of Persona Services

Special Purpose Personas

BuyMyCarPhone

BuyMyCarWeb Site

BuyMyCarAnnouncements

Separate Business and Consumer Personas

Accounting & Services

Multiple Personas

Separate Personalization

Ring Music Go team

Single Persona Capabilities

Multiple Devices Shared Devices


These new network-managed identities enable the customer tohave multiple personas. Each persona could have different serviceprofiles and, therefore, get different services. This is important toour customers because it allows their communications to be tai-lored to different contexts and roles that are meaningful in theirlives. For example, the network could serve the customer differentlyfor business use, when family is involved, for best friends, or whenan item has to be advertised and sold.

The CARTS Persona Network Architecture adds persona-basedcapabilities to CARTS. Additionally, it ensures that network capabili-ties designed for a network without personas continue to work in anew network environment where each user may have multiple per-sonas. Because email is an important mode of user communicationsthat has developed its own application-specific architecture, theCARTS Persona Network Architecture also incorporates email intothe persona paradigm.

Another one of CARTS’ end to end capabilities is enabling the abilityto seamlessly roam between wired and wireless networks of alltypes, including Wi-Fi and GSM/3GPP (and ultimately LTE), both withvoice calls as well as data sessions. The CARTS architecture includessupport for Wireline-Wireless Convergence (WWC). In this con-text “convergence” implies a common and consistent service offeringacross a wide variety of access networks and user devices. Subscriberswill be able to receive a unified offering of formerly unrelated serv-ices such as wireless and wireline, enterprise and consumercommunications, entertainment, video, data, and telephony services,across a wide variety of access networks including circuit switched,packet switch, broadband, etc. To accomplish this convergence, theCARTS WWC architecture includes these important areas:

• Service Continuity and Consistency (SCC): Service Continuityand Consistency enables uniform service delivery to the UE, byinterworking changes in underlying resources which left alonewould otherwise cause the service to behave inconsistently or fail.New capabilities found in 3GPP’s IMS Service Continuity and IMSCentralized Services provide the interworking necessary to survivethese kinds of underlying changes in a way that also provides theuser with a consistent service experience.

• Packet access continuity: Packet access Continuity providesseamless Data session continuity between access networks fordata related real-time applications such as VPN.

• Session Continuity: Session Continuity allows a UE session or amedia component thereof to be transferred, if needed, to a differ-ent network element or different UE without disrupting theend-to-end session.

The third end to end capability is CARTS’ Integrated VideoCapabilities (IVC). The IVC architecture describes how video serv-ices (e.g., mobile video, PC video, IPTV, etc.) are provided withinCARTS utilizing the principles of device and service independence.The scope of IVC includes communication and entertainment videocapabilities as well as converged services across video and otherCARTS applications such as telephony. Convergence, though com-mon Enablers and service blending, is built into the architecture

instead of depending on pair-wise interworking between services ashas traditionally been done by many carriers. IVC describes howstandard CARTS functions such as Media Resources, Enablers, andService Broker are used to support end-to-end video services. Thearchitecture promotes cost efficiency and service rationalization.

The IVC architecture “virtualizes” video-capable devices to encour-age service / device independence and enables a decoupling ofdevice from service. For example IVC treats a home gateway, PCand mobile device in the same way, and makes the same videoservices available to all of them, subject to their video capabilities.This is accomplished by standardized interfaces between the videodevice and the CARTS network.

The IVC architecture supports both SIP and Web interactionsbetween the IVC end-user video device and network services. TheIVC architecture does not dictate the use of SIP and Web interfacesfor specific applications. However, SIP interfaces are expected beused for communications services (e.g., video call), and Web inter-faces can be used for application control functions (e.g., channelchange). This approach supports flexible device and applicationdesign.

The IVC architecture supports flexible video media paths betweenthe video device and the CARTS network and is standards-based sothat it can leverage industry trends for vendor products. This allowsfor lower cost and increased availability. Standardization alsoimproves prospects for interoperability with other services/products.

AT&T, with its deep security expertise, exemplifies the due diligenceand discipline of a service provider that successfully protects its net-work and computing infrastructures with a ComprehensiveSecurity Architecture. The fundamental concepts and principlesof security are designed into the CARTS architecture. The objectivesof security are to protect the confidentiality, integrity, and availabili-ty of communications. Basic principles of security used by AT&Tinclude defense in depth using multiple mechanisms, prevention(such as access control and perimeter security), management (suchas operations security), logging and auditing, and innovation trans-fer (that is, a commitment to continual improvement andinnovation).

It is well known that applications using the SIP protocol, such asVoIP, pose particular security challenges to carriers due to the pro-tocol design itself. With VoIP, both the signaling as well as theactual voice messages (called media) are carried in-band, thus mak-ing signaling vulnerable to the same security risks as other Internettraffic. Recognizing these security challenges, CARTS functionsas an overlay network on top of AT&T’s converged IP/MPLS network.The CARTS security architecture has been designed with multiplelayers, consistent with AT&T’s “Defense in Depth” principles in orderto ensure the security of these communications. The design princi-ple of layers is consistent with the general architecture used inprotecting corporate assets in the Internet and includes three secu-rity domains, each with its own security requirements. To furtherenhance the security of communications carried by CARTS, AT&T



has deliberately departed from the “any to any” Internet communi-cations model in that strict boundaries are defined regarding whatdevice can communicate with what device, thus providing additionalcontrol.

An additional challenge with VoIP is that SIP servers and associateddevices have not been designed and built with security asa priority. Most of them do not include firewall functionality as partof their configuration. Therefore, in order to ensure the security ofour Services over IP infrastructure and our customers’ traffic, theSession Border Controller (SBC) is used to establish the first line ofdefense from a security perspective. The SBC serves as the interme-diary between the trusted domain and the untrusted domain, andthus provides an additional layer of security over that providedinherently within VoIP devices.

CARTS takes a holistic approach towards perimeter security in itsBorder Security Functions framework. Security gateways such asSession Border Controllers (SBCs), firewalls and application/webfirewalls work together with Intrusion Detection/IntrusionPrevention Systems (IDS/IPS) and Security Information and EventManagement Systems (SIEMS) to detect attacks that may be occur-ring over a wide span and a period of time (“low and slow” or“stealth” attacks). These systems are then linked to IdentityManagement and Policy Management for improved coordinationand faster incident response.

The CARTS Security architecture describes guidelines and mecha-nisms designed to safeguard customer data, the AT&T CARTSinfrastructure, as well as voice services, multimedia services, andapplications against internal and external threats including Denial-of-Service (DoS) and Distributed DoS (DDoS) attacks. AT&T CARTSSecurity architecture is designed to ensure proper availability, confi-dentiality, and integrity of user information while providing solutionsthat are flexible and do not impose requirements that may beuneconomical or too constraining.

As discussed in the Core section, CARTS includes both a SIP coreand Web core. To improve the customer experience, AT&T has beenworking towards a Single Sign-on (SSO) environment for its cus-tomers in the web domain, so that customers need only log in onceto have access to all AT&T services to which they have subscribed.CARTS extends that SSO and Identity Management environment tointegrate identities between Web and SIP domains, as well as toleverage the existing authentication of the mobile device. As anexample, just by powering up one’s wireless device one could haveaccess to customized services such as weather reports for a particu-lar zip code, sports scores for one’s favorite teams, and stock quotesfor one’s favorite stocks. Of course, sensitive transactions will stillrequire a PIN or password.

Where services involve the delivery of media content, the conceptof Digital Rights Management (DRM) applies. DRM enables encryp-tion of content for IP transport and licensing of that content. AT&T’s

DRM approach includes real-time and off-line encryption, key andlicensing information management, and the use of secure servers.

As stated throughout this paper, the CARTS architecture providesthe roadmap to an infrastructure that supports the creation of richand compelling applications and services. AT&T is taking measuresto increase the security of its web applications by reducing theavailability of means that hackers and attackers could employ.Applications are restricted in the resources they can contact andthere are restrictions on the types of data structures used. AT&Tadheres to the Web Services Security standards. In addition, AT&Tdevelopers receive training in secure coding techniques such asalways validating user input. Penetration testing is also performedto ensure that AT&T web applications offer a secure customer expe-rience.

AT&T’s IMS Strategy

AT&T as a corporation is strongly committed to a standards-basedapproach to new technologies. Use of industry standards enablesAT&T to select best of breed vendors to supply components to buildits networks and services. AT&T has a long legacy of involvementwith standards bodies and is highly involved with the standardsbodies that continue to evolve the IMS architecture. AT&T’s role inthese standards bodies is to provide input to ensure that the evolv-ing standards meet the needs of businesses and consumers alike interms of resiliency and feature functionality. In addition to workingwith and in standards bodies, AT&T is working with key vendors toencourage them to build their equipment to support the evolvingIMS standards and to avoid the use of proprietary interfaces.

In working with the business community at large, AT&T sees its roleas an educator in helping businesses to understand this new tech-nology and its potential as well as demonstrating how AT&T willtake a leadership role in implementing it. Business customers willnot see much impact of IMS in the short term as vendors build andcarriers implement the appropriate interfaces to support the existingenvironment as well as the emerging service environment. In thenear term, business customers purchasing IP-PBXs would do well toconsider making investments in equipment that is built with indus-try-standard interfaces, particularly SIP.

To conclude, AT&T is committed to evolving its network to beingbased on IMS. However the move to IMS will be evolutionary, notrevolutionary, and will take place over a period of years. The firstphases, which began in 2007 and have continued since then, haveseen the creation of new and innovative services such asVideoShare and U-verse Voice, with more expected to follow. Thesephases will be followed by wireless/wireline convergence andseamless mobility. Ultimately the promise of CARTS, with IMS at itscore, is to support all AT&T’s multi-media services in one highlyflexible and resilient platform.



Acronyms:

CCF = Charging Collection FunctionCS = Circuit SwitchedLTE = Long Term EvolutionOCS = Online Charging SystemOSS = Operations Support SystemsPOTS = Plain Old Telephone ServicePS = Public SwitchedPSTN = Public Switched Telephone Network-

the traditional network that has been providing voiceservices for almost 100 years

SBC = Session Border ControllerSDK = Software Development KitTCAP = Transaction Capabilities Application PartUE = Mobile Endpoint (User Equipment)

August 2010 AB-2071

© 2010 AT&T Intellectual Property. All rights reserved. AT&T and the AT&T logo are trademarks of AT&T Intellectual Property.AT&T Inc. is a premier communications holding company. Its subsidiaries and affiliates - AT&T operating companies - are the owners and operators of all network infrastructures, and the providers of AT&T services, in the United States and around the world.

Documents

AT&T’s Common Architecture for Real-Time Services · PDF fileAT&T’s Common Architecture for Real Time Services, which you’ll read about in this paper, is one example of a forward-looking