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Program Name :B.Tech
Semester :ECE 6th Sem
Course Name: Computer Network
Course Code:EC 602
Facilitator Name: Megha Dewan
Topic Name:- Transport Layer
Contents of Topic: Behrouz A. Forouzan Learning Outcome: Students get to know about basics of Transport Layer UNIT No. 1
What a Network layer actually does?
It oversees source-to-destination delivery of individual packets , it does not recognize any relationship between those packets. It treats each one independently , as though each piece belongs to a separate message.
How transport layer differ from network layer?
- (^) The transport layer , ensures that the whole message arrives intact and in order , overseeing both error control and flow control at the source –to-destination level.
Transport layer protocol
- (^) A transport layer protocol can be either connectionless or connection-oriented.
- (^) UDP-Connectionless protocol-Simple
- (^) TCP-Connection oriented protocol-Complex
- (^) SCTP-Connection oriented protocol-Designed for Multimedia application
- (^) (Stream control transport protocol)
PDU(SEGMENT)
- (^) In the Transport layer a message is normally
divided into transmittable segment.
- (^) UDP treats each segment separately
- (^) TCP creates a relationship between
the segments using sequence numbers.
Connection –oriented transport layer
- (^) A connection oriented transport layer makes a
connection with the transport layer at the
destination machine first before delivering the
packets.
- (^) After all the data is transferred , the
connection is terminated.
- (^) TCP and SCTP are Connection
oriented…
Reliable versus unreliable
Transport layer service can be reliable or unreliable
- (^) If the application layer program needs reliability, TCP &SCTP protocol will implement flow and error control at the transport layer. But it is slower and more complex service.
- (^) If the application layer program does not need reliability, it means most real-time application does not demand flow and error control,but it demand fast service. So unreliable protocol UDP is used.
Question arises?
- (^) If the data link layer is reliable and has flow
and error control , do we need this at
transport layer too?
Answer
YES
- (^) Reliability at the data link layer is between two nodes ;
- (^) we need reliability between two ends.
- (^) Because the network layer in the internet is unreliable.
- (^) So we need to implement reliability at the transport layer.
Addressing
- (^) At the Data link layer, we need a MAC address to choose ONE node among SEVERAL node.
- (^) At the Network layer we need an IP address to choose one Host among Millions.
- (^) At the Transport layer we need a transport layer address called a PORT NUMBER ,to choose among multiple processes running on the destination host.
- (^) Destination port number for delivery; source port no for the reply
Port number
- (^) Port number for a client host program defines
itself randomly by the transport layer. at this is
called ephemeral port number ranging from
49,152 to 65,
- (^) Port number for servers are universally
assigned by (internet assigned number
authority) called well-known port number
ranging from0 to 1023
Socket address
It is a 48 bit address. It is a combination of both IP Address and port number.
UDP
- (^) The User Datagram Protocol (UDP) is called a connectionless , unreliable transport protocol.
- (^) UDP is so powerless , it perform process to process communication with very limited error checking.
- (^) If a process wants to send a small message and does not care much about reliability , it can use UDP