GATE CS & IT Engineering Computer Networks Syllabus

Computer Networks syllabus — full chapter and topic list

Expand any chapter to see its topics and sub-topics. This is the whole examinable outline for Computer Networks in GATE CS & IT Engineering, not a summary of it.

1. 1

   Concept of Layering

   2 topics

   • OSI and TCP/IP Protocol Stacks
   • Basics of Packet, Circuit and Virtual Circuit-Switching
2. 2

   Data Link Layer

   4 topics

   • Framing
   • Error Detection
   • Medium Access Control
   • Ethernet Bridging
3. 3

   Routing Protocols

   4 topics

   • Shortest Path
   • Flooding
   • Distance Vector Routing
   • Link State Routing
4. 4

   Fragmentation and IP Addressing

   2 topics

   • IPv4
   • CIDR Notation
5. 5

   Basics of IP Support Protocols

   3 topics

   • ARP
   • DHCP
   • ICMP
6. 6

   Network Address Translation (NAT)

   1 topic

   • NAT
7. 7

   Transport Layer

   5 topics

   • Flow Control
   • Congestion Control
   • UDP
   • TCP
   • Sockets
8. 8

   Application Layer Protocols

   5 topics

   • DNS
   • SMTP
   • HTTP
   • FTP
   • Email

Computer Networks flashcards for GATE CS & IT Engineering

22 of 51 cards from the Computer Networks deck — real questions with worked answers.

1. How many layers are in the OSI reference model, and what are they from top to bottom?

   7 layers: Application, Presentation, Session, Transport, Network, Data Link, Physical (top to bottom).

2. How do the layers of the TCP/IP model map onto the OSI model?

   TCP/IP has 4 layers: Application (OSI Application+Presentation+Session), Transport, Internet/Network (OSI Network), and Network Access/Link (OSI Data Link+Physical).

3. Which OSI layer is responsible for end-to-end reliable delivery, and what is its Protocol Data Unit (PDU)?

   The Transport layer; its PDU is the segment (TCP) or datagram (UDP). It handles end-to-end error control, flow control, and multiplexing via port numbers.

4. Name the Protocol Data Unit (PDU) at the Network, Data Link, and Physical layers.

   Network layer: packet (datagram); Data Link layer: frame; Physical layer: bit.

5. Compare circuit switching and packet switching on resource reservation and delay.

   Circuit switching reserves a dedicated path before transfer (constant delay, no congestion once set up, but wastes idle capacity). Packet switching forwards packets independently with no reservation (statistical multiplexing, efficient, but variable/queuing delay possible).

6. What distinguishes a virtual-circuit network from a datagram (pure packet-switched) network?

   A virtual circuit sets up a connection and a fixed path; each packet carries a small Virtual Circuit Identifier (VCI), packets arrive in order. A datagram network is connectionless; each packet carries the full destination address and is routed independently, so packets may take different paths and arrive out of order.

7. In circuit switching, what are the three phases of a communication session?

   Circuit establishment (setup), data transfer, and circuit teardown (disconnection).

8. What is framing, and what problem does it solve at the data link layer?

   Framing groups the stream of bits from the physical layer into discrete units (frames) so the receiver can identify where each frame begins and ends, enabling per-frame error and flow control.

9. Describe byte/character stuffing used in framing.

   A special FLAG byte marks frame boundaries. If the FLAG (or the ESC byte) appears in the data, an ESC byte is inserted before it (stuffed). The receiver removes the stuffed ESC bytes to recover the original data.

10. Explain bit stuffing as used in HDLC framing.

    The flag is the bit pattern $01111110$. To prevent this pattern appearing in data, the sender inserts a $0$ after every five consecutive $1$s in the payload; the receiver removes a $0$ that follows five consecutive $1$s.

11. For a single parity bit, what error-detection capability does it provide?

    A single parity bit detects all odd numbers of bit errors but fails to detect any even number of bit errors; it cannot correct errors.

12. In CRC error detection, how is the codeword formed from a message $M(x)$ and generator $G(x)$ of degree $r$?

    Append $r$ zeros to the message: compute $M(x)\cdot x^{r}$, divide by $G(x)$ modulo-2 to get remainder $R(x)$, and transmit $T(x)=M(x)\cdot x^{r}+R(x)$, which is exactly divisible by $G(x)$. The receiver flags an error if $T(x)\bmod G(x)\neq 0$.

13. What is the minimum Hamming distance of a code, and how many errors can it detect and correct?

    For minimum Hamming distance $d$: it detects up to $d-1$ errors and corrects up to $\left\lfloor \frac{d-1}{2} \right\rfloor$ errors.

14. What does the Internet checksum (used in IP/TCP/UDP) compute?

    The 16-bit one's complement of the one's complement sum of all 16-bit words in the data; the receiver sums all words including the checksum and the result should be all $1$s if no error.

15. What is the purpose of Medium Access Control (MAC), and name the three broad categories of MAC protocols.

    MAC arbitrates which station may use a shared broadcast channel to avoid/handle collisions. Categories: (1) Channel partitioning (TDMA, FDMA, CDMA), (2) Random access (ALOHA, CSMA/CD, CSMA/CA), (3) Taking turns (polling, token passing).

16. What are the maximum channel utilizations of pure ALOHA and slotted ALOHA?

    Pure ALOHA: maximum efficiency $\frac{1}{2e}\approx 18.4\%$ at offered load $G=0.5$. Slotted ALOHA: maximum efficiency $\frac{1}{e}\approx 36.8\%$ at $G=1$.

17. In CSMA/CD, what is the relation between frame transmission time and propagation delay, and why?

    Transmission time must satisfy $T_{frame}\geq 2T_{prop}$ (one round-trip time), so a sender is still transmitting when a collision signal returns and can detect it. Hence minimum frame size $=2\times$ (propagation delay) $\times$ (bandwidth).

18. What is the difference between CSMA/CD and CSMA/CA, and where is each used?

    CSMA/CD detects collisions while transmitting (used in wired Ethernet). CSMA/CA avoids collisions using backoff, interframe spacing, and optionally RTS/CTS, since wireless cannot reliably detect collisions (used in 802.11 Wi-Fi).

19. In Ethernet's binary exponential backoff, after the $n$-th collision how is the backoff time chosen?

    The station waits $k$ slot times where $k$ is chosen uniformly at random from $\{0,1,\dots,2^{m}-1\}$ with $m=\min(n,10)$; the number of collisions is capped at 16 attempts before aborting.

20. What is a transparent bridge and how does it learn forwarding entries?

    A transparent bridge connects LAN segments at the data link layer and is invisible to hosts. It uses backward learning: it associates a frame's source MAC with the incoming port to build a filtering table, and floods frames whose destination is unknown.

21. Why do bridged/switched Ethernet networks run the Spanning Tree Protocol (STP)?

    To eliminate loops in a topology with redundant links. Loops would cause broadcast storms and multiple frame copies; STP disables redundant ports to create a single loop-free active topology (a spanning tree) while keeping backups for failover.

22. Contrast a collision domain and a broadcast domain in switched Ethernet.

    Each switch/bridge port is its own collision domain (full-duplex switching eliminates collisions). All ports of a switch are in one broadcast domain; a router (or VLAN boundary) separates broadcast domains.

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