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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.

    2

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    Benefits

    Efficiency

    Complexity

    Cost Person to Machine communication.

    3

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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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