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It is connection less (No Acknowledgment) and unreliable approach .It is iterative compared to concurrent TCP and It is used for broadcasting and multi-casting , all real time application  (or) services utilities UDP with help of RTP (video conference , live Telecast)because it has fixed header size.It is a message oriented and there is no flow control.Pseudo-header of UDP is same as TCP.

UDP Format 
 Application that require bulk data transfer and fastness (than reliability) uses UDP.
Protocols which takes services of UDP are


It is reliable , port to port , byte/stream transport layer protocol and support full duplex , connection oriented (cumulative acknowledgment) approach.Not useful for broadcasting and multi casting.

It is a slow start protocol and uses sliding window protocol for flow control,the window size is set and controlled by receiver.
TCP connection have three phases.
(i) Connection establishment
(ii) Data Transmission 
(iii) Connection Termination

TCP Format:
  TCP uses random initial sequence number.Probability of getting a number = 1/232

Protocols which takes services of TCP are:
HTTP(80) , FTP(Data (20) , Control (21) , Telnet (23) , SMTP (25) , POP3 (110)

TCP congestion Control: Two approaches are used
(a) Slow Start and Additive Increase
(b) Multiplicative Decrease: Congestion window always starts MSS = 1 and increases exonentially upto threshold value, then increases linearly upto sender window size (SWS) and when timeout occurs.congestion window reduced to 1 MSS and threshold value reduced to half of congestion window size.

TCP Error Control: 3 parameters are used

(a) Checksum:It detects errors.
(b) ACK: There is no negative acknowledgment in TCP, as well as there is No ACK for received ACK.If any segment is corrupted (found through checksum),such segment are not acknowledge.
(c) Time-out: Transport layer uses dynamic RTT for time out calculation.Different timers are deployed for error control like Time Awaited Timer , Keep-Alive Timer,Persistence Timer , Re transmission Timer.

Purpose of Pseudo-header: It is used to identify whether packet is received by the correct destination or not.It is prepared at the source with source values, again it is prepared at destination with destination values.

TCP State Transition Diagram: The functionality of TCP connection setup communication phases and termination phase can be easily depicted by the state transition diagram where the TCP will be only at one state at a time w.r.t server or client.

1. Error control procedures are not depicted.
2. Retransmission's are not shown.

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