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
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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 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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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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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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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
M
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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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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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
M
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
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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
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
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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E-mail and voicemail
2. E-mail
Many useful facilities developed:
Distribution Lists
Automatic filtering
…etc.
MIME allows audio attachments
More intuitive user interface
T
(perhaps)
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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!
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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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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
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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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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
T
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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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 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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Reliability - before
Telephones
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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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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When your PC becomes
your phone ....
and it breaks down ...
how do you
phone the
Help Desk
M
?
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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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