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Chapter: Computer Networks : Transport Layer

Important Short Questions and Answers: Computer Transport Layer

Computer Networks - Transport Layer - Important Short Questions and Answers: Computer Transport Layer

1. What is function of transport layer?


The protocol in the transport layer takes care in the delivery of data from one application program on one device to an application program on another device. They act as a link between the upper layer protocols and the services provided by the lower layer.


2. What are the duties of the transport layer?

The services provided by the transport layer End-to-end delivery, Addressing, Reliable delivery, Flow control & Multiplexing


3. What is the difference between network layer delivery and the transport layer delivery?

Network layer delivery


The network layer is responsible for the source-to-destination delivery of packet across multiple network links.


Transport layer delivery

The transport layer is responsible for source-to-destination delivery of the entire message.


4. What are the four aspects related to the reliable delivery of data?

The four aspects are,


Error control, Sequence control, Loss control & Duplication control


5. What is meant by segment?


At the sending and receiving end of the transmission, TCP divides long transmissions into smaller data units and packages each into a frame called a segment.


6. What is meant by segmentation?


When the size of the data unit received from the upper layer is too long for the network layer datagram or data link layer frame to handle, the transport protocol divides it into smaller usable blocks. The dividing process is called segmentation.


7. What is meant by Concatenation?


The sizes of the data unit belonging to a single session are so small that several can fit together into a single datagram or frame, the transport protocol combines them into a single data unit. The combining process is called concatenation.


8. Explain the main idea of UDP.


UDP is called a connectionless, unreliable transport protocol. It does not add anything to the services of IP except to provide process-to-process communication instead of host-to-host communication. Also, it performs very limited error checking.


9. What are the two possible transport services?

Two basic types of transport services are,


Connection service

Connectionless services


10. The transport layer creates the connection between source and destination. What are the three events involved in the connection?

For security, the transport layer may create a connection between the two end ports. A connection is a single logical path between the source and destination that is associated with all packets in a message. Creating a connection involves three steps:

·Connection establishment

·Data transfer & Connection release.


11. Name the parameters of quality of services in a network.

Reliability, Delay, Jitter & Bandwidth.


12. What is meant by congestion? Why the congestion occur in network?


Congestion in a network occurs if user sends data into the network at a rate greater than that allowed by network resources. Congestion occurs because the switches in a network have a limited buffer size to store arrived packets.


13. What is Three-way Handshaking?


The connection establishment in TCP is called three-way handshaking. The process starts with the server. The server program tells its TCP that it ready to accept a connection. This is called a request for a passive open. Although the server TCP is ready to accept any connection from any machine in the world, it cannot make the connection itself.


The client program issues a request for an active open. A client that wishes to connect to an open server tells its TCP that it needs to be connected to that particular server. TCP can now start the three-way handshaking process.


14. How will the congestion be avoided?

The congestion may be avoided by two bits


BECN - Backward Explicit Congestion Notification

FECN - Forward Explicit Congestion Notification


15. What is the function of BECN BIT?


The BECN bit warns the sender of congestion in network. The sender can respond to this warning by simply reducing the data rate.


16. What is the function of FECN?


The FECN bit is used to warn the receiver of congestion in the network. The sender and receiver are communicating with each other and are using some types of flow control at a higher level.


17. What is meant by quality of service? What are the two categories of QoS attributes?


The quality of service defines a set of attributes related to the performance of the connection. For each connection, the user can request a particular attribute each service class is associated with a set of attributes.


The two main categories are

·           User Oriented

·           Network Oriented


18. What is TCP?


TCP guarantees the reliable, in order delivery of a stream of bytes. It is a full-duplex protocol, meaning that each TCP connection supports a pair of byte streams, one flowing in each direction.


19. List out the user related attributes?

User related attributes are

SCR – Sustainable Cell Rate

PCR – Peak Cell Rate

MCR- Minimum Cell Rate

CVDT – Cell Variation Delay Tolerance


20. What are the networks related attributes?

The network related attributes are,


Cell loss ratio (CLR)

Cell transfer delay (CTD)

Cell delay variation (CDV)

Cell error ratio (CER)


21. What is frame? What is framing bits?


A frame consists of one complete cycle of time slots, including one or more slot dedicated to each sending device. One or more synchronization bits are usually added to the beginning of each frame. These bitts are called framing bits.


22. What is interleaving?


The switch moves from device to device at a constant rate and fixed order. This process is called interleaving.


23. Give the difference between service point address, logical address & physical address? Service point addressing


The transport layer header includes a type of address called a service point address or port address, which makes a data delivery from a specific process on one computer to a specific process on another computer.


Logical addressing


If a packet passes the network boundary we need another addressing to differentiate the source and destination systems. The network layer adds headers, which indicate the logical address of the sender and receiver.


Physical addressing

If the frames are to be distributed to different systems on the network, the data link layer adds the header, which defines the source machine’s address and the destination machine’s address.




Congestion: Excessive network or internetwork traffic causing a general degradation of service


First-In, First-Out (FIFO) Queue: A queue in which the first item in is the first item out.


Forward Explicit Congestion Notification (FECN): A bit in the Frame Relay packet thatnotifies the destination of congestion.


Internet Assigned Numbers Authority (lANA): A group supported by the U.S. governmentthat was responsible for the management of Internet domain names and addresses until October 1998.


Leaky Bucket Algorithm: An algorithm to shape bursty traffic.


Priority Queueing: A queuing technique in which packets are assigned to a priority class, eachwith its own queue.


Pseudoheader: Information from the IP header used only for checksum calculation in the UDPand TCP packet.


Quality of Service (QoS): A set of attributes related to the performance of the connection.


Socket Address: A structure holding an IP address and a port number.


Token: A small packet used in token-passing access method.


Token Bucket: An algorithm that allows idle hosts to accumulate credit for the future in theform of tokens.


Token Passing: An access method in which a token is circulated in the network. The station thatcaptures the token can send data.


Transmission Control Protocol (TCP): A transport protocol in the TCP/IP protocol suite.


User Datagram Protocol (UDP): A connectionless TCP/IP transport layer protocol.


Weighted Fair Queuing: A packet scheduling technique to improve QoS in which the packetsare assigned to queues based on a given priority number.


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