Transcript voip

JANET & TELEPHONY
aka Voice over IP
Tim Clark
Mike Whitehead
Are you
scared of
voice traffic
on your
network?
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Networkshop
2000
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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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Networkshop
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The Telephone Network
a one minute description
Effectively it’s just a network of 64 kbps switched circuits
analogue phone
analogue line
Telephone
network
digital line (ISDN)
digital
phone
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Networkshop
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The Telephone Network
Inside the network
64 kbps
2 Mbps
30 x
34 Mbps
8x
Time Division Multiplexing using the old PDH scheme to carry
multiple circuits down a single higher speed circuit
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The Telephone Network
Synchronous 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


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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




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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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Networkshop
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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
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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


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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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Networkshop
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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
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Bandwidth control, address translation
Routing and billing control
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Quality of Service
Phones do this with circuit switching
Need to ensure
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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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Networkshop
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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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Networkshop
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ADSL
Asymmetric 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

T
it is mass market
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ADSL
What 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

T
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
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
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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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Networkshop
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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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Networkshop
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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

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with Mitel as an example (Tim)
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ATM between sites
PABX
30 channel private
network using DPNSS
G.703
ATM
G.703
ATM
network
2Mbps
Constant
Bit Rate - CBR
ATM
G.703
PABX
G.703
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ATM between sites
Uses standard ATM circuit

Constant Bit Rate 2Mbps
PABX sees standard interface

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E1 G.703 2Mbps - 30 channels
Can run standard DPNSS - private trunks
Simple standards - no compression
Permanent 2Mbps bandwidth assigned
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Networkshop
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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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Networkshop
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Distributed site PABX
Peripheral
node
cabinets
Mitel SX2000
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Node to peripheral cabinet can be ATM
node
ATM network
Peripheral cabinets
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Mitel SX2000
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Node to Node - conventional 2 Mbps links
node
2Mbps
link
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Mitel SX2000
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Ideally would be:
node
155 Mbps
link
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not Mitel SX2000
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 voicemail
1. 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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Networkshop
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E-mail and voicemail
2. E-mail
Many useful facilities developed:

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Distribution Lists
Automatic filtering
…etc.
MIME allows audio attachments
More intuitive user interface

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(perhaps)
Networkshop
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E-mail and voicemail
E-mail user interface
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E-mail and voicemail
Voicemail user interface
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E-mail and voicemail
ripe 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
[email protected] ?

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Without re-recording it on your PC!
Networkshop
2000
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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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Networkshop
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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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Networkshop
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Charging
1. 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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Networkshop
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Charging
2. 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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Networkshop
2000
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Telephony over
SuperJANET 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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Networkshop
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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

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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:



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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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Networkshop
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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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Networkshop
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Policy, Regulation and Charging
Technological 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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Networkshop
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Reliability - before
Telephones

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
little to go wrong
seen as important
PABXes never “rebooted”
Data Networks


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not seen as vital
temperamental “high tech” equipment
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2000
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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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Networkshop
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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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Networkshop
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So why Voice over IP?
Data networks must be ever more reliable
Convergence growing:

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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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Networkshop
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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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Networkshop
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When your PC becomes
your phone ....
and it breaks down ...
how do you
phone the
Help Desk
M
?
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2000
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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


M
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?


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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
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