SoftSwitch

by

A S M Jayeed Bin Amin 062-424-056

Project report submitted to the Department of Computer Science and Engineering of

North South University

For

ETE 605 IP Telephony Spring 2008

Approved

_______________________________ Dr. Mashiur Rahman

15th April, 2008 Dhaka, Bangladesh

Acknowledgements

I acknowledge our Faculty Advisor Dr. Mashiur Rahman for providing me with the

opportunity to work on this project and learn all the tools, technologies used in it.

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Contents

Acknowledgements ii

1.1 Softswitch in general 1

1.2 Softswitch Advantages and Benefits 2

1.3 Three Factors Dominate New Softswitch Network Designs 2

2.1 Major Elements of a Softswitch 3

3. Features and Benefits of Softswitch Architecture in Wireless Networks 4

3.1 Distributed Switching 4

3.2 Deploy services of Softswitch 5

3.3 Deploy Services using IP-based Service Platforms via Softswitch 7

Reference 8

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1.1 Softswitch in General:

A softswitch is a central device in a telephone network which connects calls from one phone line

to another, entirely by means of software running on a computer system. This work was formerly

carried out by hardware, with physical switchboards to route the calls.

A softswitch is typically used to control connections at the junction point between circuit and

packet networks. A single device containing both the switching logic and the switching fabric can

be used for this purpose; however, modern technology has led to a preference for decomposing

this device into a Call Agent and a Media Gateway.

The Call Agent takes care of functions like billing, call routing, signalling, call services and so on

and is the 'brains' of the outfit. A Call Agent may control several different Media Gateways in

geographically dispersed areas over a TCP/IP link.

The Media Gateway connects different types of digital media stream together to create an end-to-

end path for the media (voice and data) in the call. It may have interfaces to connect to traditional

PSTN networks like DS1 or DS3 ports (E1 or STM1 in the case of non-US networks), it may

have interfaces to connect to ATM and IP networks and in the modern system will have Ethernet

interfaces to connect VoIP calls. The call agent will instruct the media gateway to connect media

streams between these interfaces to connect the call - all transparently to the end-users.

The softswitch generally resides in a building owned by the telephone company called a central

office. The central office will have telephone trunks to carry calls to other offices owned by the

telephone company and to other telephone companies (aka the Public Switched Telephone

Network or PSTN).

Looking towards the end users from the switch, the Media Gateway may be connected to several

access devices. These access devices can range from small Analog Telephone Adaptors (ATA)

which provide just one RJ11 telephone jack to an Integrated Access Device (IAD) or PBX which

may provide several hundred telephone connections.

Typically the larger access devices will be located in a building owned by the telephone company

near to the customers they serve. Each end user can be connected to the IAD by a simple pair of

copper wires.

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The medium sized devices and PBXs will typically be used in a business premises and the single

line devices would probably be found in residential premises.

In more recent times (i.e., the IP Multimedia Subsystem or IMS), the Softswitch element is

represented by the Media Gateway Controller (MGC) element, and the term "Softswitch" is rarely

used in the IMS context. [1]

1.2 Softswitch Advantages and Benefits

Reduce Costs

• Boost capacity of existing lines by offloading data to IP networks

• Lower cost commercial hardware and software

• Lower cost processing and connectivity expansion

• Smaller, higher-density packaging

Improve Services

• Roll out new services more quickly

• Differentiate services with value-added offerings

• Leverage familiar Internet and Web tools/programs

• Provide end users ability to maintain their own service preferences

Facilitate Migration to Data-Centric IP Networks

• Scale easily with new subscriber demand

• Quickly incorporate new protocols and connectivity

• Evolve networks and services through a distributed architecture

1.3 Three Factors Dominate New Softswitch Network Designs While lower cost has become the primary driver behind new softswitch network designs,

engineers must still pay attention to other major driving factors that dominate today’s design of

new systems -the “high-order-bits” in digital design parlance. For the new networks being built

for both wireless, wireline, and IP networks, three other factors dominate what must be

accommodated in the new designs, (1) massive scalability, (2) high-availability, and (3) enabling

rapid delivery of new services to customers, whether they be equipment builders or service

providers. Lower costs are assumed to be a major element in all three of these factors.

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Scalability - Tremendous growth in numbers of subscribers, who demand to be always on-line

and with higher speed links, is forcing bandwidth demands to double every nine months. Optical

fiber network technology is keeping pace, but Moore's law only predicts processor speeds to

double every eighteen months. This demands new architectural approaches to telecom networks,

by distributing intelligence out to the edges of the network, and designing new core network

switching and routing technologies. Building scalability into these new networks becomes one

major driving factor in new designs.

High Availability - As the content delivered over today's connection-based networks changes to

be predominantly data rather than voice, telecommunication operators and equipment suppliers

are transitioning their core networks to IP packet-switched technologies, optimized for delivery of

data, but also capable of handling Voice-over-IP (VoIP). A key challenge, however, for the

Network Equipment Providers (NEPs), is to deliver the same level of high availability with the

new packetswitched technologies as they currently deliver with existing, voice-optimized,

connection switched technologies. Continuous uptime, or high-availability, has become a second

major driving factor and a differentiator in offering services to customers.

Rapid delivery of new services - While dealing with these first two design factors, all three major

providers of service, wireless, wireline, and IP network vendors are being forced to deliver new

and improved services to customers, to keep existing customers, and to attract new ones as prices

for services are driven down by competition. To enable this, NEPs and their Telecom services

provider customers, ISPs and ASPs, are demanding more open, integrated, hardware and software

stacks in their platforms in order to deliver these new services to their customers more quickly.

Fortunately, addressing these four driving forces, lower cost, scalability, high availability, and

rapid delivery of new services, has become much easier with the definition of new industry

protocols and the availability of off-the-shelf standard hardware with modern processors and

software building blocks. Telecom equipment suppliers can now build carrier-grade high

performance, scalable, and highly available packet-switched core networks, including

softswitches with Voice-over-IP (VoIP) services using industry standard CompactPCI hardware

and software modules that leverage technologies developed for enterprise IP-based systems. [2]

2.1 Major Elements of a Softswitch Today the IETF and other standards bodies define the four basic building blocks of softswitch

architectures as shown in figure 2, (1) Media Gateway Controller (MGC), (2) Media Gateway

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(MG), (3) Signalling Controller, and (4) The IP/Internet Services Layer, such as media servers

handling voice recognition, SIP presence services, SIP proxy servers, etc. More and more these

are being defined as off-the-shelf, open standard, but highly available Internet servers. [2]

Figure 2.1: Typical Softswitch Architecture including Services Layer [2]

3. Features and Benefits of Softswitch Architecture in Wireless

Networks 3.1 Distributed Switching

Legacy circuit-switched networks utilize centrally located MSCs to provide the needed switching

of voice calls between the Radio Access Network (RAN) and the PSTN. Due to the significant

cost of operation and staffing of operational personnel to operate a MSC, Service Providers have

deployed large centrally located MSCs at the expense of backhauling the voice circuits from

RAN located in each city and likewise backhauling of the voice circuits to local PSTN

connections within each city. It should be noted that most local calls stay local, that is when a

mobile subscriber makes a call, they usually call someone within their own city or local area.

Since most calls stay local, this calls for double the circuits from the local RAN to the MSC and

from the MSC to the local PSTN. This is shown on the left side of the following diagram.

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As show on the right side of the above diagram, using the softswitch-based architecture of

centralized MSC Server/Softswitch with Media Gateways, call control and voice processing /

switching are separated allowing for Media Gateways to be placed where they can provide the

most value and the complex call control can still be centrally located. By deploying distributed

switching, Service Providers can significantly reduce the backhaul charges that they would have

to pay because the bearer voice stays local for local calls and does not require to be shipped back

to the central location only to be shipped back again to the local area for completion to the local

PSTN.

Another key benefit of using the softswitch-based distributed architecture is to share the core

network between voice traffic and GPRS data. The Service Provider now has one network to

maintain instead of 2 networks as they do in 2.5G networks. [3]

3.2 Deploy services of Softswitch

Wireless operators are deploying standards-based services using mobile Intelligent Network (IN).

The GSM standard for the mobile IN is Customized Application for Mobile Enhanced Logic

(CAMEL). Similarly, the U.S. CDMA & TDMA markets are standardizing on Wireless

Intelligent Network (WIN). Though many services, such as prepaid, today are deployed using

proprietary extensions to the IN protocol, extending these services to roaming partners requires

the implementation of standards-based CAMEL & WIN services.

Both CAMEL and WIN architectures utilize a centralized intelligent network node known as the

Service Control Point (SCP). A MSC that has been upgraded to provide support for CAMEL and

WIN, at certain points in a call, passes control of the call to the SCP. The SCPs then execute the

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service logic. As new services are deployed, operators must upgrade all their MSCs and arm them

with these triggers. The disadvantages of this approach are:

• Provisioning Cost – Upgrading each MSCs and provisioning the service can be expensive and

time consuming.

• MSC real-time processing cost – These triggers may take up 5 to 20% of the MSC processing

capacity. This means that the operator will be able to pack 5 – 20% fewer wireless subscribers per

MSC compared with MSCs, which do not have to process these triggers. This is a huge cost to the

operator.

• Software cost - There is a capital expense associated with software upgrades on the MSCs

• Market Timing of Service Delivery – Software development on traditional circuit switched

MSCs is longer.

A better and more economical solution is to offload these triggers onto a Softswitch. As Mobile

originated/terminated calls are routed through the softswitch, the softswitch launches the queries

to SCPs based on the provisioned triggers. This allows centralizing the provisioning of service

triggers at the softswitch and unburdens the MSC from processing these triggers.

A good example is Wireless Number Portability (WNP). WNP, mandated by the FCC in the U.S.,

allows subscribers to change the operator they use for service but still retain the same PSTN

directory number. As the PSTN directory number no longer indicates the physical home network

switch, every call must be intercepted at the MSC, and a WNP query is launched to the SCP to

obtain a Location Routing Number (LRN) and ultimately the call is routed to the destination

indicated by the Location Routing Number. As queries are launched on every call, the processing

burden on the MSC could be significant.

The following figure compares the architecture of doing the LNP triggers on an MSC versus

doing it on a softswitch.

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Other examples of IN Services, which can be launched from a Softswitch, are Number Pooling,

Prepaid Roaming, Toll Free service, Location based Services etc. Number Pooling, which allows

multiple operators to share a block of NPA-NXX also, requires processing very similar to LNP.

Number Pooling is mandated by several state regulators. Most of the prepaid platforms deployed

today use proprietary IN solution. CAMEL & WIN based solutions allow seamless roaming

prepaid across partner networks. CAMEL Phase 2 and Phase 3 define the prepaid & prepaid

roaming capabilities where as WIN Package 2 defines the prepaid solution for the roaming

networks. [3]

3.3 Deploy Services using IP-based Service Platforms via Softswitch

The International Softswitch Consortium’s Applications Working Group has developed an

Applications Framework, in which Softswitches can use SIP or LDAP to access services from IP-

based Application Servers. These IP-enabled Service Platforms operate in a similar fashion as

SCP’s, but they are available at a much lower cost and offer more flexibility. Once the databases

are moved to a more modern platform, they can be queried by the Softswitch using SIP or LDAP.

More information on this Application Framework is available from the Application Working

Group. [3]

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References:

[1] www.wikipedia.org

[2] Peter Palm, New Softswitch Architectures help to manage the Network Industry turmoil, Sun Microsystems [3] Softswitch Applications in Wireless Core Networks, Version: 1.1 - April 18, 2002, International Softswitch Consortium, Wireless Working Group

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