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Transport Layer of TCP/IP Protocol


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The Transport layer transports data to and from the correct application. This process is known as end-to-end communication. In TCP/IP the Transport layer  provides a transport service for application data.

The Transport layer header includes a destination port number that identifies the destination application program on the remote machine and a source port number that identifies the application on the originating machine.

In addition, the Transport layer handles error detection, can handle recovery problems, and regulates the flow of information. The way in which the Transport layer handles error detection, the sequence of data,
and flow regulation depends on which protocol is used.

There are two main protocols that operate at the Transport layer, TCP and  UDP. The TCP/IP protocol stack features two Transport layer protocols, TCP and UDP:

Both are implemented as a part of the Solaris kernel. There three important binary properties that serve as the base of classification of transport layer protocols:

  1. connection-oriented vs. connectionless
  2. stateful vs. stateless
  3. reliable vs. unreliable

The first important distinction between transport layer protocols is connection-oriented vs. connectionless:

The second important distinction is "stateful vs. stateless" protocols:

The third important disctinction is "reliable vs. unreliable":

Based on this classification UDP and TCP looks like complete opposites:

Basic UDP information

UDP is a connectionless, stateless, and unreliable protocol.  It is faster and more efficient for many lightweight or time-sensitive purposes. Also, its stateless nature is useful for servers that answer small queries from huge numbers of clients. UDP is required for broadcast (send to all on local network) and multicast (send to all subscribers).

With UDP, the application is responsible for handling message loss, duplication, sequence (delivery out of order), and loss of connection. UDP receives incoming data from the application and encapsulates the data into UDP datagrams. UDP datagrams have a leading header section hat contains the source and destination port numbers, followed by the data section.

16 32 bits
Source port
Destination port


Basic TCP Information

TCP is a connection-oriented, stateful, and reliable protocol. TCP is suited for situations where large volumes of data must travel between systems, particularly across multiple routers and gateways. TCP
has four main features:

The TCP segment header has more fields then UDP header. The TCP header structure is as follows:

16 32 bits
Source port
Destination port
Sequence number
Acknowledgement number
Urgent pointer
Option + Padding
TCP header structure

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Transport layer - Wikipedia, the free encyclopedia


From Wikipedia

  • AEP, AppleTalk Echo Protocol
  • ATP, AppleTalk Transaction Protocol
  • CUDP, Cyclic UDP
  • DCCP, Datagram Congestion Control Protocol
  • FCP, Fiber Channel Protocol
  • FCIP, Fiber Channel over TCP/IP
  • IL, IL Protocol
  • iSCSI, Internet Small Computer System Interface
  • NBP, Name Binding Protocol
  • NetBEUI, NetBIOS Extended User Interface
  • SPX, Sequenced Packet Exchange
  • RTMP, Routing Table Maintenance Protocol
  • SCTP, Stream Control Transmission Protocol
  • SCSI, Small Computer System Interface
  • TCP, Transmission Control Protocol
  • UDP, User Datagram Protocol


    Q1.  What does the receiving host do with packets when it is using a connection-oriented  protocol ?

    a. acknowledges only the first and last packet, puts the packets in their proper order.

    b. acknowledges only the first and last packet, discards in any packet that have arrived out of sequence.

    c. acknowledges each packet and  puts the packets in their proper order.

    d. acknowledges each packet and discards in any packet that have arrived out of order

     A: C

    Q2. Which set has protocols of ONLY the Network layer ?





    A: B

    Q3. What are three purposes of ICMP :

    a. router discovery

    b. guarantee of transport

    c. estimate of bandwidth

    d. error messaging

    e. diagnostics/testing

    f. guarantee of uniqueness of node addresses

     A: A,D,E

    Q4. Connectionless protocols are implemented using ______.

    a. UDP

    b. TCP

    c. IP

    d. ICMP

    A: a

    Q5: Which layer in the TCP/IP Five-layer model performs end-to-end data transfers?

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