© 1998-1999 Marvin A. SirbuPage 1 Carnegie Mellon Voice Data Integration To date voice data integration in the enterprise has been minimal –separate logical

© 1998-1999 Marvin A. Sirbu Page 1

Carnegie Mellon

Voice Data Integration

• To date voice data integration in the enterprise has been minimal

– separate logical circuits on the mux network for voice and data.

• New technologies emerging to carry voice over

– ATM networks

– Frame relay networks

– Internet Protocol networks


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Basic Elements of Basic Elements of Voice over Networks Voice over Networks

• Gateway translates between 64 kbps PCM encoded telephony circuit and compressed, packetized voice.

• PC converts between packets and sound card with headset or microphone and speakers.

PSTN

Users

Internet PSTNGW GW

PBX

PhoneUser

Audio Equipped PC

Two Stage Dialing Public Interexchange Network

PBX

Local Switch

Packet / Circuit Gateway

PBX

Local Switch

LocalDS0

TransportNetwork

LocalDS0

TransportNetwork

Packet / Circuit Gateway

H.323 Gatekeeper

WideAreaData

Network

LEC #1

LEC #2

NextGenerationIXC

“1-888-NEXTGEN, ID6, PIN4, 1-234-555-1234”

T1

T1

Packets

Packets


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Voice Coding Standards

Compression Type Data Rate

G.711 – PCM 64 kbps

G.726 – ADPCM 32, 24, 16 kbps

G.728 – LD CELP 16 kbps

G.729 – CS ACELP 8 kbps

G.723.1 - MP-MLQ/ACELP 5.3, 6.3 kbps


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• Processing affects perceived quality (MOS Score)• Compression and packetization introduce delay

– for processing

– to accumulate speech for a packet.

Voice Quality and Delay

Compression MOS Score Delay (msec)

PCM (G.711) 4.4 0.75

32K ADPCM (G.726) 4.2 1

16K LD-CELP (G.728 4.2 3-5

8K CS-ACELP (G.729) 4.2 10

6K MP-MLQ/ACELP(G.723.1)

30


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Voice Quality and Delay

One way delay (msec) Perceived Quality

0-150 Acceptable for most users

150-250 Acceptable but perceptible

250 - 400 Typical of satellites; annoying

400+ Unacceptable for general network purposes.


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Sources of Delay

• Packetization at the source• Queuing delay at packet switches• Propagation delay

– 1 msec/100 miles• Dejitter buffer

– buffer packets at receiver to accommodate variable network delay (“jitter”)

NetworkGateway Gateway

(25 msec) (40 - 200 msec) (50-200 msec)


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Latency - T1 WAN Links

PBX

1 ms

Coder6.5 kbps

Compress

20 ms

SwitchRouting

1 ms

2048 byte MTUQueue Delay

11 ms

WAN Cloud

T1 WANUplink

HQ LAN

WAN Cloud

Branch Office

PBX

1 ms

Coder6.5 kbps

Decompress

20 ms

SwitchRouting

1 ms

2048 byte MTUQueue Delay

11 ms

T1 WANUplink

Branch Office

Worst case 292 ms round-trip latency

JitterBuffer

40 ms

40 msLA-NY


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Reducing Network Delay

• Controlling network delay and variability of network delay important.

• Solutions:

– Use ATM with guranteed quality of service. Low jitter because voice packets can’t get stuck behind large data packets

– Frame relay network with CIR. Some FR networks fragment all packets to reduce jitter.

– IP network route voice packets with higher priority (Differential service) reserve resources as with ATM (RSVP) run over lightly loaded or controlled load network, not public

Internet


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H.323

• A standard for multimedia communications over networks which do not provide a guaranteed Quality of Service

– (e.g. the Internet, or LAN)• Support for audio and video• Key elements

– H.323 terminals: capture/present audio or video

– H.323 Gatekeeper: provides call setup and control functions

– H.323 Gateway: converts between IP and PSTN style networks

– H.323 Multipoint Control Unit (MCU): Bridging functions


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H.323 Network ComponentsH.323 Network Components

H.323 Multimedia PC

PSTN

POTS Phone

Router

Gateway

H.323 Multimedia PC

GatekeeperFirewall

Multipoint ControlUnit

Internet/ Intranet

H.323 Multimedia

PC

H.323 Phone

H.323 Phone


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H.323 Interworking


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H.323 Protocol ArchitectureH.323 Protocol Architecture

Physical Layer

Link Layer

Network Layer (IP)

Unreliable Transport (UDP)Reliable Transport (TCP)

T.123(ISO+TCP)

T.124GCC

T.125MCS

Real-Time Protocol(RTP)

RTCP

G.7XXAudio

H.26XVideo RAS

Term. <->GW

H.225.0Call

Signal

H.245Call

Signal

AV Appl. Q.931 Terminal Control and Mgmt

Data Appl. orT.126/T.127


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H.232 Layered Architecture


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Early Internet TelephonyEarly Internet Telephony

• Long Distance Bypass, Fueled by International Tariffs, Domestic Access Charges- Arbitrage opportunity

• Often proprietary Internet protocols• Audio only

PSTN

Users

Internet PSTNGW GW

PBX

PhoneUser

Audio Equipped PC


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Enterprise VoN Bypass

• Company has existing Data network between locations.• Put voice traffic on existing data network and save phone

charges• Network can be any of

– IP

– Frame Relay

– ATM• Private ATM, FR nets mostly have PVCs• Treat PVC between two PBXs same as a leased line.


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PBX to Gateway VoIP Signalling

PBX

CorporateNetwork PBX

Trunk Signaling

Step 1-- the PBX seizes a trunk line to the gateway, and forwards dial digits

527-3845


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PBX


Q.931

H.323 agent H.323 agent

Step 2 -- The Gateway uses a dial plan to map dial digits into the IP addressof the remote gateway. H.323 agent software initiates a call using Q.931signaling protocol to remote gateway


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PBX


Trunk Signaling

Step 3 -- The remote H.323 agent seizes a PBX trunk, returns a Q.931acknowledgement to the origin, and forwards dial digits to the PBX

Step 4 -- Voice traffic flows between PBXs over the H.323 session established between the two gateways.


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Future Directions

• Phase 1: wide area bypass

– corporate intranet

– interexchange carriers access charges key

• Phase 2: IP PBX

– easier integration of voice and data

– integration with data for ACD applications• Phase 3: IP based Local Exchange Carriers

Yesterday’s PBX

Proprietary Ckt switch

Card(s)Proprietary

interface

Applications (Voicemail/IVR)

Voice Path (TDM)

Signaling Path

PSTN

Proprietaryterminals

Proprietary interface

Proprietary Line

Card(s)

Proprietary Trunk Card(s)

Mainframe cabinet

Standard interface

Proprietary Processor

Card(s)Proprietary

interface

IntelProcessor Standard

OR Proprietary Interface

Windows NT Server PC

Call Control Application

Tomorrow’s PBX - the IP PBX

Voice Path (TDM)

Signaling Path

PSTN

Standard interface

TCP/IPNetwork

StandardOR Proprietary

interface

Ethernet phonesand

PC applications

IP to PSTNGateway

Standardinterface

Applications Server

(Voicemail/IVR)


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Call ManagerIP Phone

PSTN

IP/PSTN GatewaysIP/PSTN Gateways• PSTN trunk interface• Analog fax/phone/modemUser InstrumentUser Instrument

• Ethernet IP telephone• Wireless H.323 handset• PC with H.323 softphone

Call ProcessingCall Processing• NT server• PBX functionality

PSTN/IP Gateway

3 Core Components of an IP PBX

Source: Selsius, Corp


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PBX servicesPBX services

EtherPhoneServer

EtherPhoneEtherPhone

EtherPhoneBranch


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PhoNetwork TopologyPhoNetwork Topology

EtherPhone

EtherPhoneBranch

PhoNetwork Server

Gateway

PacketPhone

Area code“8”


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IP Phones Product Characteristics

• Ethernet connectivity• IP Address and signaling(TCP/IP)• Audio via RTP/IP (Conforms to H.323 RTP format)• Built-in Compression: G.711, G.723

Managed on a call-by-call basis• Configuration

DHCP or static Config via browser I/F

• Built-in encryption for privacy protection• 3rd-pair powered for wired devices

Call-Manager / gatekeeper Product Characteristics

• Provides intelligent call processing and PBX functionality• H.323 standard-based• Standard PC hardware with only a Ethernet NIC• Signalling support for gateways (Q.931, H.245, H.225, RAS)• Call processing engine

Features: hold, transfer, forward, display messaging, speed dial, call waiting, park, pickup, multi-cast conferencing etc.

Multiple line appearances/single number distribution Bandwidth (Compression) Manager Interface to voice mail

– Manageable using web interface Real-time/historical performance monitor CDR reporting

– Architected for fault-tolerant and redundant operations for scalable/reliable operations

Source: Selsius

An outside caller or ext 8560 calls ext 8565. 8565 is traveling and 8660 is supposed to answer the call. 8660 is at lunch. However, since 8565 is now logged into the network running her virtual phone, she can answer the call herself, by selecting the ringing and blinking line appearance.

PSTN

PBX Phones

PBX

EthernetGateway

Analog orDigitalLine (s)

Call Manager

Ethernet Switch

Ethernet Hub

PC

VoiceMail

Travelerin other

city EXT 8565EXT 8565

EXT 8560

Shared/Switched/10/100/1000

Ethernet

EXT 8660

Multi-line Appearances

Call Coverage Flexibility


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IP Network

PSTN

PSTN

Call ManagementServers

IP Phone

IP Phone

IP Phone

IP Phone IP Phone

IP Phone

IP Phone

PSTN

Remote IPSites

Remote IPSites

Consolidated Phase

Source: Selsius


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The Death of Distance

• Any phone connected to the Internet can be part of the “domain” of a paticular Gatekeeper (“call server”)

• Can create a citywide “PBX” by linking all remote offices to a common Gatekeeper over the Internet

– even worldwide


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Economics of Premises IP Telephony• An IP-PBX enables the use of Internet telephony over a LAN -

allowing a complete integration of voice and data networks.• What does it Cost?

– Develop a cost model to estimate the impact of installing an IP-PBX on the cost of premises, local, and long distance calling.

– Compare with Centrex.

• Joint work with Kanchana Wanichkorn


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Network Architecture

Backbone Fast EthernetSwitch

Router CSU/DSU

Gateway

Gatekeeper

Leased Linesto ISP’s POP

Trunk Linesto PSTN’s CO

Corporate Office

10 Mbps Switched Ethernet

100 Mbps Fast Ethernet

DesktopEthernet Switch

To eachemployee’sPC andTelephoneHandset




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End User Configuration

Voice over IPAdapter


Type 1: Traditional Telephone with Voice over IP Adapter DesktopEthernet Switch

Each PC equipped withVoice over IP Interface card

Type 2: Computer Telephone


Micro HubIP Telephone HandsetType 3: IP Telephone


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Centrex Scenario• Two choices of long distance call routing via

1. a traditional Interexchange Carrier (IXC)

2. an Internet Telephony Interexchange Carrier (ITXC)

IXC

LEC LEC

ITXC

1

2

Dial-in Gateway

Circuit Switched

IP


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IP-PBX Scenario • Three choices of long distance call routing via

1. a traditional Interexchange Carrier (IXC)

2. an Internet Telephony Interexchange Carrier (ITXC)

3. an Internet Service Provider (ISP) - intra-corporate calls

Circuit Switched

IP

IXC

LEC LEC

ITXC

1

3

2 Remote Gateway

ISP


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Key Assumptions

• 15 kbps per voice channel.• Where the infrastructure exists, corporations always

choose to route toll calls over an Internet Telephony Interexchange Carrier (ITXC).

• The ITXC provides an additional discount for net to phone service, which saves the ITXC the costs of an originating gateway.


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Results

Centrex IP-PBX IP-PBX IP-PBX (200 lines) (100 lines) (20 lines)

Equipment $5 $21 $24 $40LEC service $52 $21 $24 $34Long distance calling $27 $19 $21 $34Maint., move, and change $4 $10 $11 $16Total monthly cost per line $89 $71 $80 $124


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IP-PBX Cost Breakdown

$0

$20

$40

$60

$80

$100

$120

$140

Large(200 lines)

Medium(100 lines)

Small(20 lines)

IP-P

BX

Mo

nth

ly C

ost

pe

r L

ine IXC and ITXC

Maintenance,move, and change

LAN upgrade

ISP access andservice

PSTN trunk linesand local usage

Gateway andgatekeeper

Handset(computertelephone)


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Optimal Choices

LEC Cost Small Medium Large(20 lines) (100 lines) (200 lines)

Low Centrex Centrex IP-PBX

Base Centrex IP-PBX IP-PBX

High Centrex IP-PBX IP-PBX


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Cost Comparison among Different Scenarios

$0

$20

$40

$60

$80

$100

$120

$140

$160

Large Medium Small

(20 lines)

To

tal

Mo

nth

ly C

ost

per

Lin

e Centrex with IXC

IP-PBX with IXC(no IP intra-corporate)

Centrex with ITXC

IP-PBX with ITXC (IP intra-corporate)

IP-PBX withdiscount ITXC

(IP intra-corporate)(100 lines)(200 lines)


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Economic Implications

• The major saving of an IP-PBX over Centrex comes from the saving in intra-corporate long distance calls.

• Even without a discount in the ITXC rate, an IP-PBX costs less than Centrex as long as there are some calls made directly from one IP-PBX to another.

• The incremental cost of allocating more voice traffic to IP is less than the incremental cost of allocating more voice traffic to the PSTN.

• An IP-PBX is not yet economical for small corporations.


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Additional Considerations

• IP-PBX simplifies construction of Call Center applications

– speech is already digitized and compressed

– IVR applications can be constructed entirely in software without need for DSP boards to digitize voice or generate call control signals.


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Features

• Compared Current VoIP PBX product features to CMU’s most recent premises RFP (1989)

• Many capabilities not available• Availability standards not met

– Move entire LAN to telephony availability standards? 99.991% uptime

• Fault logging and notification standards not met


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Moves, Adds and Changes

• In theory, can move phone to new office, plug it in and have all features.

– Limitations works within bridged subnet within routed subnets, must use DHCP to automatically assign

appropriate IP address to phone


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Security Issues

• If you swap handsets with the President, you can highjack all the President’s calls

• Must have voice traffic encryption

– CMU has many hackers• Security of NT Server OS?


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Electric Power

• Must provide uninterruptible 48V DC power via 10BaseT cable to handsets

– CMU is largely wired with IBM Type 3 cable containing two shielded twisted pair for data and 4 pair for voice.

STP doesn’t have power pair

– CMU moving to 100BaseT as standard either ethernet phones would need to support 100BaseT ports, or would

need separate ports in each office for computing and phones.

• Emergency Phone Power– All wiring closets would need UPS.

– Conducted preliminary analysis of cost of acquiring 4 hour UPS for all LAN equipment and uninterruptible 48V DC power for 7,000 phones.

Estimated cost at $500,000 for the entire campus.


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Conclusions• An IP-PBX is more expensive than Centrex when only

premises telephony costs are considered. • When the impact of premises voice system choice on toll

calling costs is included, an IP-PBX is shown to provide a significant cost savings for medium and large firms.

• These savings are largely obtained on intra-corporate calls.• Regulatory policies which reduce access charges for all IXCs

or impose them on phone-to-phone ITXCs will likely slow the growth of ITXCs. However, it is likely that IP-PBX users may continue to benefit from an access charge exemption.


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2nd Century Product


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RouterCMTS

VoIP over Cable Modem

PSTN

TelephonyGateway

BTI CM

Tap Fiber Node

Local hub

PrimaryHub

Internet

VOIP Telephony & Cable Modem Architecture

Full Service Packet Based NetworkEnd-user Applications

Network and Service ManagementNetwork

ManagementInternetServers

NetworkDatabases

FeatureServers

Core Network

STM/Optical

Gateway

PSTN

Broadband AccessServer/MUX

Wired

Large BusinessAccess

Wireless AccessServer

IP

FixedWireless

Residence/Small Business Access

AccessServer

Wireless Mobility Access

ResourceServers

Cable Access

AccessServer

HFCPlant

xDSL

PacketPhone

Adapter

CableModem

SettopBox

Public Internet

Source: Lucent


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Summary• Voice data integration is finally beginning to appear practical• Cost savings realizable today by moving some voice to corporate

data networks.• IP-based IXCs cheaper largely because they don’t pay access

charges• Technology is still fairly new. Features more limited than

traditional telephone switches• Increased pressure for QoS features in data networks.

– New economic models needed to pay for QoS• Data networks and PCs not as reliable as telephone today.

– Will phone still work when the power goes out?• Radical paradigm shift underway throughout the telephone

industry

Documents

© 1998-1999 Marvin A. SirbuPage 1 Carnegie Mellon Voice Data Integration To date voice data integration in the enterprise has been minimal –separate logical