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    Lec 3 - Transport Layer - I

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    Hamna Younis
    TCP is better for applications that require reliable data delivery and flow control. It establishes connections, performs error checking and retransmits lost packets. UDP is a simpler protocol that does not establish connections or perform error checking, making it faster but unreliable. It is better for real-time applications like streaming media where lost packets are not re-sent and speed is important. So in summary, TCP is more reliable while UDP is faster. The choice depends on an application's requirements for reliability vs speed.

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    Lec 3 - Transport Layer - I

    Uploaded by

    Hamna Younis
    11 views18 pages
    TCP is better for applications that require reliable data delivery and flow control. It establishes connections, performs error checking and retransmits lost packets. UDP is a simpler protocol that does not establish connections or perform error checking, making it faster but unreliable. It is better for real-time applications like streaming media where lost packets are not re-sent and speed is important. So in summary, TCP is more reliable while UDP is faster. The choice depends on an application's requirements for reliability vs speed.

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    TCP is better for applications that require reliable data delivery and flow control. It establishes connections, performs error checking and retransmits lost packets. UDP is a simpler protocol that does not establish connections or perform error checking, making it faster but unreliable. It is better for real-time applications like streaming media where lost packets are not re-sent and speed is important. So in summary, TCP is more reliable while UDP is faster. The choice depends on an application's requirements for reliability vs speed.

    Copyright:

    © All Rights Reserved
    Download as PPTX, PDF, TXT or read online from Scribd
    Download as pptx, pdf, or txt
    11 views18 pages

    Lec 3 - Transport Layer - I

    Uploaded by

    Hamna Younis
    TCP is better for applications that require reliable data delivery and flow control. It establishes connections, performs error checking and retransmits lost packets. UDP is a simpler protocol that does not establish connections or perform error checking, making it faster but unreliable. It is better for real-time applications like streaming media where lost packets are not re-sent and speed is important. So in summary, TCP is more reliable while UDP is faster. The choice depends on an application's requirements for reliability vs speed.

    Copyright:

    © All Rights Reserved
    Download as PPTX, PDF, TXT or read online from Scribd
    Download as pptx, pdf, or txt
    of 18

    Computer and

    Communication Networks
    EE-357
    By Dr Mir Yasir Umair
    Associate Professor, MCS, NUST
    Transport Layer
    Chap 03
    Chapter 3: Transport Layer
    our goals:
     understand principles behind transport layer
    services:
     multiplexing, demultiplexing
     reliable data transfer
     flow control
     congestion control

    Transport Layer 3-3


    Chapter 3: Transport Layer
     learn about Internet transport layer protocols:
     UDP: connectionless transport
     TCP: connection-oriented reliable transport
     TCP congestion control
    Transport services and protocols
    application
    transport
    network

     provide logical communication between data link


    physical

    app processes running on different hosts

    lo
     transport protocols run in end systems

    gi
    ca
    enl
     send side: breaks app messages into segments, passes to

    d-
    network layer

    en
    d
     rcv side: reassembles segments into messages, passes to

    tra
    ns
    app layer

    po
    rt
     more than one transport protocol
    available to apps application
    transport
    network
     Internet: TCP and UDP data link
    physical

    Transport Layer 3-5


    Transport Layer
    Sender’s side: - breaks application layer messages into segments,
    appends header and passes them to network layer – Multiplexing

    Receiving side: - Reassembles segments into messages, use header to


    deliver data to the correct process/ service - Demultiplexing
    Transport vs. network layer
    network layer: logical communication between
    hosts
    transport layer: logical communication between
    processes
     relies on, enhances, network layer services

    Transport Layer 3-7


    Household analogy
    12 kids in Ann’s house sending letters to 12 kids in Bill’s house:
    • hosts = houses
    • processes = kids
    • app messages = letters in envelopes
    • transport protocol = Ann and Bill who demux to in-house siblings
    • network-layer protocol = postal service
    Internet transport-layer protocols
    application
    • reliable, in-order delivery transport
    network
    data link
    (TCP) physical
    network
    o congestion control network data link

    lo
    data link physical

    gi
    o flow control physical

    ca
    network

    l
    o connection setup data link

    en
    physical

    d-
    • unreliable, unordered

    en
    network

    d
    data link

    tra
    delivery: UDP physical

    ns
    po
    network
    o no-frills extension of “best-effort” IP

    rt
    data link
    physical
    • services not available: network
    data link application
    physical transport
    o delay guarantees network
    network
    data link
    o bandwidth guarantees physical data link
    physical

    Transport Layer 3-9


    Telephone Analogy
    A telephone call over a “telephony network” works as follows:

    • Both parties have a telephone installed.


    • A phone number is assigned to each telephone.
    • Turn on ringer to listen for a caller.
    • Caller lifts telephone and dials a number.
    • Telephone rings and the receiver of the call picks it up.
    • Both Parties talk and exchange data.
    • After conversation is over they hang up the phone.
    In the world of sockets……
    • Socket() – Endpoint for communication
    • Bind() - Assign a unique telephone number.
    • Listen() – Wait for a caller.
    • Connect() - Dial a number.
    • Accept() – Receive a call.
    • Send(), Recv() – Talk.
    • Close() – Hang up.
    Dissecting the Analogy
    A network application works as follows:

    • An endpoint (telephone) for communication is created on both ends.


    • An address (phone no) is assigned to both ends to distinguish them
    from the rest of the network.
    • One of the endpoints (caller) initiate a connection to the other.
    • The other end (receiver) point waits for the communication to start.
    • Once a connection has been made, data is exchanged (talk).
    • Once data has been exchanged the endpoints are closed (hang up).
    Major Transport-layer Protocols
    • UDP - (User Datagram Protocol)
    o Connectionless Protocol
    o Unreliable Delivery No acknowledgments & retransmissions
    o Integrity Checking To detect corrupted data

    • TCP – (Transmission Control Protocol)


    o Connection Oriented Set-up and tear-down of TCP session
    o Reliable Delivery
    o Integrity Checking
    o Congestion Control Adapt to network congestion
    o Flow Control Prevent overflow of the receiver’s buffer space

    Services not available: Delay and Bandwidth guarantees


    TCP vs. UDP
    Q: Which protocol is better ?
    A: It depends on the application.

    TCP provides a connection-oriented, reliable byte stream


    service (lots of overhead).

    UDP offers minimal datagram delivery service (as little


    overhead as possible).
    Why Would Anyone Use UDP?
    • Finer control over what data is sent and when
    o As soon as an application process writes into the socket, UDP packages the data and forwards
    the segment to next layer.
    o TCP throttles the sender incase the link is excessively congested. TCP will also continue to
    resend a segment until destination acknowledges the receipt.
    o Real-time applications use UDP since they do not want to overly delay segment and can tolerate
    some data loss

    • No delay for connection establishment


    o UDP just blasts away without any formal preliminaries which avoids introducing any
    unnecessary delays

    • No connection state
    o Unlike TCP, there is no allocation of buffers, parameters, sequence #s etc, hence making it
    easier to handle many active clients at once.

    • Small packet header overhead (UDP 8-bytes long, TCP 20 bytes)


    Internet Applications and
    Underlying Protocols
    Before we Go further
    • Transport Layer has four major tasks –

    1. Delivery service to the processes


    2. Reliability
    3. Flow rate
    4. Congestion control
    Thank you

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