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Unit 6 transport layer
 

Unit 6 transport layer

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The transport layer...TCP VS IP , TCP HEADER , UDP , And transport layer functionalists............

The transport layer...TCP VS IP , TCP HEADER , UDP , And transport layer functionalists............

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    Unit 6 transport layer Unit 6 transport layer Presentation Transcript

    • Prof. CHINTAN PATEL chintan.patel@marwadieducation.edu.in MEFGI , Rajkot
    • Flow control Error control Multiplexing and de-multiplexing Segmentation and Reassembly Service point addressing
    • • Service provided to upper layer. Transport service primitives • Transport layer protocols : TCP and UDP •
    • • • • • • Transport entity to make efficient use of network services. Many services of transport layer and network layers are similar but “ The transport codes runs entirely on user machine , but network layer mostly runs on the routers” User does not have control over network layer so only possibility is to put on top of the network layer another layer that improves quality of services. Transport service provider :     • Physical layer Data link layer Network layer Transport layer Transport service users :  Application , presentation and session layer.
    • The nesting of TPDUs, packets, and frames.
    • • A network socket is an endpoint of an inter-process communication flow across a computer network. Today, most communication between computers is based on the Internet Protocol; therefore most network sockets are Internet sockets. • A socket API is an application programming interface(API), usually provided by the operating system, that allows application programs to control and use network sockets. Internet socket APIs are usually based on the Berkeley sockets standard. • A socket address is the combination of an IP address and a port number, much like one end of a telephone connection is the combination of a phone number and a particular extension. Based on this address, internet sockets deliver incoming data packets to the appropriate application process or thread.
    • • • • • • • Addressing Connection Establishment Connection Release Flow Control and Buffering Multiplexing Crash Recovery
    • (a) Environment of the data link layer. (b) Environment of the transport layer.
    • Note: The transport layer is responsible for process-to-process delivery.
    • Normally servers must have a known port number, while clients can have ephemeral(temporary) port numbers (Port numbers 0..2^16-1 = 0..65,535)
    • IP addresses versus port numbers
    • • • • • There are two styles of terminating a connection: asymmetric release and symmetric release. asymmetric release is the way the telephone system works: when one party hangs up, the connection is broken symmetric release treats the connection as two separate unidirectional connections and requires each one to be released separately. asymmetric release may result in loss of data:
    • The two-army problem.
    • (c) Response lost. (d) Response lost and subsequent DRs lost.
    • (a) Chained fixed-size buffers. (b) Chained variable-sized buffers. (c) One large circular buffer per connection.
    • • • • Introduction to UDP Remote Procedure Call The Real-Time Transport Protocol
    • Note: UDP is a connectionless, unreliable protocol that has no flow control and error control (except checksum calculation). •If packet loss during transmission it can not recover by UDP . It can recover error only in arrived packet using check sum •It uses port numbers to multiplex data from the application layer.
    • Popular Application Port Protocol 7 Echo 9 Discard Description Echoes a received datagram back to the sender Discards any datagram that is received 11 Users Active users 13 Daytime 17 Quote 19 Chargen 53 Nameserver 67 Bootps Server port to download bootstrap information 68 Bootpc Client port to download bootstrap information 69 TFTP Trivial File Transfer Protocol Returns the date and the time Returns a quote of the day Returns a string of characters Domain Name Service 111 RPC Remote Procedure Call 123 NTP Network Time Protocol 161 SNMP Simple Network Management Protocol 162 SNMP Simple Network Management Protocol (trap)
    • Steps in making a remote procedure call. The stubs are shaded.
    • • • • • • • • • • • RPC : When a process on M/C 1 calls a procedure on M/C 2, the calling process on 1 is suspended and execution of the called procedure takes place on 2. Calling procedure is known as a Client. Called procedure is known as a server. Client stub : Represents server procedure in client address space. Server stub : Represent reply to client in server address space. 1: client calling client stub(Local procedure call). 2 : Marshaling : Client stub packing the parameter in message and making a system call to send a message. 3: Kernel sends a message from a client m/c to server stub. 4: Kernel passing in coming parameter to server stub. 5 : server stub calls server procedure with unmarsheled parameter.
    • (a) A fast network feeding a low capacity receiver. (b) A slow network feeding a high-capacity receiver.
    • • TCP has a mechanism for congestion control. The mechanism is implemented at the sender • The window size at the sender is set as follows: Send Window = MIN (flow control window, congestion window) where • flow control window is advertised by the receiver • congestion window is adjusted based on feedback from the network
    • Source Add one packet each RTT Destination
    • • • • • Too slow. Reacts aggressively. Wastage of bandwidth at initial stage. Congestion is detected when time out occurs.
    • • The sender has two additional parameters:   • Congestion Window (cwnd) Initial value is 1 MSS (=maximum segment size) counted as bytes Slow-start threshold Value (ssthresh) Initial value is the advertised window size) Congestion control works in two modes:   Slow start (cwnd < ssthresh) Congestion avoidance (cwnd >= ssthresh)
    • Slow start, exponential increase
    • Note In the slow start algorithm, the size of the congestion window increases exponentially until it reaches a threshold.
    • Note In the congestion avoidance algorithm the size of the congestion window increases additively until congestion is detected.
    • Window management in TCP.
    • • • • When a segment is sent, a retransmission timer is started. If the segment is acknowledged before the timer expires, the timer is stopped. If, on the other hand, the timer goes off before the acknowledgement comes in, the segment is retransmitted (and the timer os started again).
    • • • • It is designed to prevent the following deadlock. The receiver sends an acknowledgement with a window size of 0, telling the sender to wait. Later, the receiver updates the window, but the packet with the update is lost. Now the sender and the receiver are each waiting for the other to do something. When the persistence timer goes off, the sender transmits a probe to the receiver. The response to the probe gives the window size. If it is still 0, the persistence timer is set again and the cycle repeats. If it is nonzero, data can now be sent.
    • • • When a connection has been idle for a long time, the keep-alive timer may go off to cause one side to check whether the other side is still there. If it fails to respond, the connection is terminated.
    • • It runs for twice the maximum packet lifetime to make sure that when a connection is closed, all packets created by it have died off.