Mike Whitehead

JANET & TELEPHONYaka Voice over IP

Tim Clark

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voice trafficon your network?

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Are youscared of

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What is Voice Traffic? Is Voice traffic special? Or just another network application like any

other? Will it require a radical change in

networking technology and practice?

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The Telephone Networka one minute description

Effectively it’s just a network of 64 kbps switched circuits

Telephonenetwork

analogue phone

digital phone

digital line (ISDN)

analogue line

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The Telephone NetworkInside the network

64 kbps 2 Mbps

34 Mbps

30 x

8 x

Time Division Multiplexing using the old PDH scheme to carry multiple circuits down a single higher speed circuit

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The Telephone NetworkSynchronous Digital Hierarchy

Switches pass data in fixed sized packets (cells) along links of different speeds

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Convergence Data networks are becoming

more reliable more affordable more flexible

Data networks can carry voice traffic in theory if not in practice

Telephone cabling can carry data networks Now well beyond the simple MODEM level Technologies like xDSL bring usable bandwidth.

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Convergence IP Telephony and other ways of getting voice

over the Data Network Carrying Voice over data networks

Variety of technologies Direct use of ATM for dedicated voice circuits is

one extreme Use of standard IP transactions over the Internet

at the other extreme. In between, are enhancements to existing circuits

such as Quality of Service extensions.

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What is Convergence? Payload convergence

• e.g. Voice typically uses Layer 1 but can now use Layer 3 for voice and for data

Protocol convergence • e.g. data over ATM networks, voice over data (VoIP)

Physical convergence • e.g. using the same cabling for voice and data

Device convergence • e.g. PABX with computer features (CTI, Voice Mail)

• e.g. Router with telephone capabilities

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What is IP Telephony? Between sites

aka “Toll Bypass” Keep the PABX and use the MAN/WAN

Within sites aka “The Full Monty” replace the PABX with LAN/MAN & PCs

Demonstrations at the Exhibition

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Voice as a bitstream Encoding and Compression Standards:

• G.711 PCM sampling 8,000 per sec, 8bit coding– 56 or 64Kbps 0.75ms coding time

• G.726 ADPCM (Adaptive Differential PCM) 4 bits– 16. 24, 32, 40Kbps 1ms coding time

• G.728 CELP (LD Code excited linear prediction)– 16Kbps 2.5ms coding time

• G.729 CS-ACELP Quality similar to 32Kbps ADPCM– 8Kbps 10ms coding time

• G.723.1 Multirate Coder– 5.3, 6.3Kbps 30ms coding time

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What are the problems? Delay caused by:

Encoding time - can be 30ms Network delay - say 100ms

Variable Delay = Jitter Congestion -> Dropped packets Delay causes problems

Echo - Talker overlap

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Overcoming the problems Delay:

Solutions involve interpolation & holdback

Prioritisation - Layer 2 Standards available: 802.1p - offers expedited traffic

• by priority tagging 802.1q - provides the tagging on VLANs

Layer 3 standards (IP) ToS = Type of Service

• old but little used until now

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H.323 Family H.320 (ISDN), H.324 (POTS), etc. H.323 runs over non-guaranteed packet

switched network (e.g. IP) Gateways to other systems Voice (G.711 mandatory), video optional Multimedia, multipoint, multicast support Gatekeepers

Bandwidth control, address translation Routing and billing control

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Quality of Service Phones do this with circuit switching Need to ensure

enough bandwidth from end to end enough bandwith at start of call enough available throughout the call

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SuperJANET 4 - The forces for change

“The network must respond to the migration of the learning process from its traditional base in the classroom, lecture theatre and laboratory, and into the home and the workplace”

- UKERNA / JISC, December 1999

How?

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Homes & Small Businesses Subscriber Loop The last few kilometres of the run Existing cable is not the ideal medium for

broadband communication But it is expensive to replace

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Digital Subscriber Loop Techniques for making the most of the

existing twisted pair retaining its use for ordinary analogue

telephony too

Not cat 5 twisted pair but “rusty old copper”

Not a new approach - but recent jargon latest techniques are sophisticated

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ADSLAsymmetric Digital Subscriber Loop

Asymmetric - different speed up and down BT is rolling it out Cable companies interested too Other companies want BT’s local loop Prices of the technology will fall

it is mass market

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ADSLWhat does it mean for us?

Delivery to home, SMEs and small outposts Not and end-to-end service - but telephone

exchange to subscriber So we can’t treat it as a new type of modem

service Establish relationships with telcos On campus residences

alternative to cat 5

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Video Conferencing Essentially a telephone call with pictures! Greedy bandwidth

Broadcast video needs oodles

Use compression as with voice M-JPEG over ATM uses 10-20MB ISDN-2 offers 128Kbps

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Video Conferencing Telephony based video conferencing: ISDN Data network based video conferencing:

Carried over ATM and IP

Offer different services Provide different qualities Need gateways to interwork

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Video Conferencing If your network can carry video

a very high bandwith application

Surely it can carry voice much less bandwidth hungry

Though voice far more susceptible to jitter

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The Role of ATM Use of ATM for crude interlinking of

PABX using 2Mbps circuit traffic (Mike)

Use of ATM by PABXes themselves with Mitel as an example (Tim)

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ATM network

2MbpsConstantBit Rate - CBR

30 channel privatenetwork using DPNSS

ATMG.703

ATMG.703

PABXG.703

PABXG.703

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ATM between sites

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ATM between sites Uses standard ATM circuit

Constant Bit Rate 2Mbps

PABX sees standard interface E1 G.703 2Mbps - 30 channels Can run standard DPNSS - private trunks

Simple standards - no compression Permanent 2Mbps bandwidth assigned

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ATM: intra-campus PABXes Single site, but distributed PABX Once it was thought ATM would be the

unifying technology for voice and data But: PABX move to ATM not as fast as had

been hoped Meanwhile data networks using alternative

technologies - like Gigabit Ethernet

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Distributed site PABX

node Peripheral

cabinets

Mitel SX2000

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Node to peripheral cabinet can be ATM

node

ATM network

Peripheral cabinets

Mitel SX2000T

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Node to Node - conventional 2 Mbps links

Mitel SX2000

node

2Mbps link

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Ideally would be:

node

155 Mbps

link

not Mitel SX2000T

ATM network

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Intra-campus PABXes Data Network mixed technology

Fast Ether, Gigabit Ether ATM - especially to remote campuses

PABX manufacturers are using PC servers as PABXes

Data Network switch manufacturers are interfacing to telephones

Is IP the new unifying protocol?

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E-mail and voicemail1. Voicemail Now more like E-mail than an answering

machine Voicemail servers are “ordinary” computers

they often store messages on disks in the same format as

“ordinary computers” communicate using standard LAN protcols

Sometimes even allow desktop PCs access as clients

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E-mail and voicemail2. E-mail Many useful facilities developed:

Distribution Lists Automatic filtering …etc.

MIME allows audio attachments More intuitive user interface

(perhaps)

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E-mail and voicemailE-mail user interface

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E-mail and voicemailVoicemail user interface

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E-mail and voicemailripe for convergence But it is only just starting to happen. How many have a voicemailbox which

telephone callers can leave messages in? How many of you could forward a message

from that voicemailbox to T.Clark@warwick.ac.uk ? Without re-recording it on your PC!

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Policy Policy itself is more a matter for the

Network Strategy workshop But: the opportunities and obstacles which

regulatory and charging policies present often pose technical challenges

What are they?

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Charging Challenges arise due to the way which IP

networks on the one hand, and telephony on the other, have approached charging

As the technologies merge, the differences present both opportunities and obstacles

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Charging1. IP Traditionally - pay for leased line /

bandwidth Without usage based charging:

runaway costs or cap the supply

Pay per byte would seem the way But with IP you can’t tell who caused a

particular packet to flow.

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Charging2. Telephony Charge by circuit occupancy

i.e. calls charged by time

Running costs not as strongly related to use as charges suggest

High standing charge socially unacceptable Can stifle Internet access by phone Rapid changes taking place

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Telephony overSuperJANET I, II and III Greater difference between “local” and

“long distance” charges Potential for huge savings But:

regulatory issues made it difficult providers’ terms made it impossible UKERNA had no remit

It didn’t happen

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Telephony over SuperJANET4 Operational requirement states:

“The supplier must place no restriction on UKERNA’s use of the facilities provided”

Differential between “local” and “long distance” call charges narrowed So major incentive gone

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Telephony over SuperJANET4 SuperJANET4 is an IP network

no major additional infrastructure needed on SuperJANET if we use voice over IP.

Gradual change: voicemail / e-mail video “conferencing” (video phone calls) IP voice traffic will just happen

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Telecommunications Licensing All telecommunications need a licence

Telecommunications Act 1984

Widely applicable Voice and data traffic are both regulated

You can operate under standard licences SPL = Self Provision Licence TSL = Telecommunications Service Licence

Most MANs and HEI networks violate rules

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Licensing Issues Current situation

Problems recognised by Oftel & DTI no enforcement

• (perhaps voice traffic could precipitate it)

EU directives require issues to be addressed JISC, UK MANs group, etc. working on it Oftel assisting DTI have plans for new class licences for

education

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Policy, Regulation and ChargingTechnological Impact Swift changes in policy (e.g. Charges) make

sudden demands on the technology. What was impractical, becomes practical,

and vice versa. So some technology which is out of

favour today may be in favour tomorrow. Keep abreast of what technology can

deliver to meet changes in policy.

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Reliability - before Telephones

little to go wrong seen as important PABXes never “rebooted”

Data Networks not seen as vital temperamental “high tech” equipment

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Reliability - now PABX runs software - it does “go down” Data network equipment often more reliable

than before (but there is more of it) Data network outages have larger impact

than before Have we got convergence of reliability and

importance too?

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So why Voice over IP? Why run two systems?

Two networks, cables and staff?

Avoid (high) call charges Multimedia PCs make good phones

Featurephones are expensive Standard handsets lousy for PABX features but features via a GUI are much easier

Unified messaging (Voice mail & email) Collaborative working growing

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So why Voice over IP? Data networks must be ever more reliable Convergence growing:

Interoperability good Quality is good

Licensing is same for voice and data and many more IP is the protocol of choice

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Organisation & Culture Who runs telephone services?

Often within administration or estates.

Staff have different backgrounds & culture Telecomms staff treasure their heritage Data network staff treat voice as “dirty”

Even end-users have different cultural approach to voice and data networks

Organisations merging the operations Must co-operate and converge

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how do you phone the Help Desk

When your PC becomes your phone ....

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and it breaks down ...

?

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Will it really happen? Technology is definitely converging What are the real drivers?

Probably not really the cost savings

Facilities are the big driver Key could be collaborative working

That’s what the telephone is good at That’s a great use for multimedia PCs

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What to do next..... Understand how to run a voice service Persuade your organisation to prepare

Especially management issues

Get your networks ready Build in resilience and QoS Savings on PABX may pay for this!

When? Heroic to go wholly VoIP today Reprehensible to ignore it in 2 years time

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Time for Discussion

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Thank you for coming