integrated voice
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Integrated
Voice/ Data
SwitchingThomas M. ChenDavid G. Messerschmitt
(June 1988) 1
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Introduction
AIM- Basic understanding of technical
problems in integration of voice and data
services in a single network basically at switch
level.
BENEFITS????
PROBLEMS???
Merits and Demerits of Different Switching
Techniques.
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Benefits
Efficiency
Complexity
Cost Person to Machine communication.
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PROBLEMS
What was the reason to use different network
for Voice and Data communication ?
-> Separate application for data and voice.
-> Different characteristics of V and D signal.
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Voice Signal V/S Data signal
V D-> Real time -> non real time
-> Analog -> Digital
-> Human generated -> Machine gen..
-> Spectral density -> Bit rate & Datawell known & consistent length varies.
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Types of Traffic
Class I - Voice and Video (real time)
Class II - Interactive Data (Person to Machineor possibly Machine to Machine)e.g. Videotex
Class III- Bulk Data (Machine to Machine)
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Class I - Voice and Video (real time)
One direction usually active at any time.
Can tolerate
-> a certain amount of degradation (e.g.,noise, clipping, compression)
-> occasional blocking (i.e., the connection
of a call is refused) without becomingobjectionable.
* But Delay as minimum as possible (in ms)
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Class II & Class III
Class II can tolerate some delay (Fraction of
second) and some blocking but no error.
Class III can tolerate only delay.
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Level of Integration
First level ( Integrated access )
->single user access interface -> common
network interface
* Traffic within the network routed to different
transport network.
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Second Level ( Integrated Transmission )
-> Transport networks share common
transmission facilities between switches
-> but maintain separate switching facilities
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Third Level (Integrated Switching)
-> Switching facility as well as transmission links
and network access are shared.
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Different Switching
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Terminal interface handles signaling function.
Switching network provides transmission path.
Controller guard the activity of TI and SN.
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Circuit Switching
Direct electrical path.
Blocking based Traffic.
Efficient if setup and disconnect times - small. Channel with full bandwidth through out call.
Minimum transmission delay.
BUT
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Continue
Disadvantage for most Data application
-> Information except signaling message is not
processed -> error
-> no error detection/correction within network.
-> less efficient for Data
-> fixed bandwidth is not good idea for variabledata rate.
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Continue
Modification in Circuit Switching
-> For bandwidth efficiency - statistical
multiplexing techniques such as Time
Assignment Speech Interpolation (TASI)
-> Or Digital Speech Interpolation (DSI)
-> Discarding some message when congestion.
-> Reduction in call setup and disconnect time.
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Packet Switching
Message switching
Or store & forward
switching.But Messages are divided
into smaller segments of
limited length Packetseach having its Header .
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Continue
Traffic is handled on delay basis.
No signaling (in Datagram) but packets headeroverhead.
Dynamic bandwidth allocation.
Processing of packets within network make itto detect and correct error before delivery of
message. Need modification for Voice applications b/c
of reconstruction problem in random delay
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PS in voice transmission
Need additional delay at voice decoder.
Flexibility provides copying, broadcasting etc.
Efficient for burst traffic.-> neglect silence interval means uses channel
capacity only when voice is active.
-> provides facility to discard some messagewhen congestion.
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Modification
To reduce the transit delays for voice packets.
shorter packet lengths or by virtual cut throughswitching.
Voice packets can be given higher priority(pre-emptive) than data packets.
Reduce its encoding rate by means of feedbackcontrol when excessive delays.
encoded information is placed or embedded inpackets of different priority or lower prioritypackets can be discarded .
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Burst Switching
Form of message switching that combinesdifferent features of fast circuit switching.
A burst is a variable length message consisting
of a 4-byte header followed by an informationfield and an end-of-burst flag.
-> In a data burst, the information is the data.
-> In a voice burst, the information is a talkspurt.
-> In command burst, is used to carry network
information between burst switches.
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A burst can begin to be forwarded before it is bufferedcompletely because a burst is always transmitted at thesame rate.
Control is partially distributed to numerous small link
switches so less sensitive to node failures andoverloads.
Local destinations can be handled by the appropriatelink switch.
Longer distance routes involve accessing a Translation& Routing (T&R) processor for the routing information.
Priority Command -> voice-> data.
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Hybrid Switching
To provide both circuit and packet switchingfeature.
Accomplished by time-multiplexing voice and
data as shown in fig.
Voice slots are circuit switched while the dataslots are packet switched.
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fixed voice/data boundary is inefficient due to thestatistical fluctuations in voice and data traffic.
For more efficiency, the voice/data boundary can bemovable.
->Voice allotted up to a maximum number of
time slots.
->Data is allowed to use temporarily silent voice
slots as well as slots allocated just to data.
Increased efficiency is achieved at the cost ofcomplicated analysis and switch operations.
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Fast Packet Switching
It is an advanced version of packet switching
based on fiber optic links and simplified
protocols.
Also called Asynchronous Time Division (ATD)
or Asynchronous Transfer Mode (ATM).
A protocol is the set of rules .
Conventional protocols are structured
hierarchically as a set of layers.
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The most well-known network architecture is
the Open Systems Interconnection (OSI)
developed by the International Standards
Organization (ISO) as shown in fig.
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The key aspect of fast packet switching is
simplification of the lower layer protocols.
Specifically, the functions of error correction
and flow control.
A fast packet format in fig.
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Comparisons of switching focused on circuit andpacket switching for many reasons.
->Predominant ones at that time.
->Today switching techniques be base on it.->Another reason for their dominance is their
proven efficiency and effectiveness for voice or
data.
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A Comparative Discussion of Switching
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->Final reason is that circuit and packet switching be
implemented in the worldwide ISDN
Harrington analysed circuit switching and
concluded that its not the preferable approach
for data services.
Coviello compared circuit and packet switching
for voice and concluded that conventional packetswitching was inadequate without major
modifications.
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Comparison between burst and fast packet
indicated that both techniques performed
roughly equivalently for both voice and data.
Hybrid seems to be a practical short-term
approach and capable of effectively handling a
wide mix or different types of traffic.
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Conclusions
We have presented a discussion of the technical
problem of integrating voice and data, while
focusing on the switching level.
Conventional circuit and packet switching havedifferent regions or usefulness and neither is
suitable without significant modification.
Burst switching suffers from the disadvantagesof incompatibility with present network.
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Hybrid switching is promising as a short-term
approach with some technical difficulties.
Finally fast packet switching is a promising
solution to the integration problem, but more
research and development is needed.
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