Computer networks

Session conducted by Maya Ma'am

Layers in networking

  1. Application layer

  2. Presentation layer

-Authorisation: privileges are given

-Authentication: login/password


  • Encryption

  • Compression

  • Translation

  1. Session layer (start, end, stop)

  2. Transport layer

  • TCP – connection-oriented(when u send a message and expect a reply back,eg email)(slower)

  • UDP – connectionless(no acknowledgement required, eg: video streaming)(faster)

  1. Physical layer (wire): Converts into 0s and 1s


Repeater- repeats (layer1)

Hub-multi port repeater(layer 1)(many ports)(sends across multiple devices)

Switch-layer2-(mac address) filter according to mac address


router-layer3-(IP address)filter according to IP address

gateway- an entrance/exit point of a network

Classes of IP addressing:- at the first octet)

  • Class A- 1-126(Check first octet)(Last 3 are hosts)(

  • Class B- 128-191(Check first two octets)(Last 2 are hosts)(

  • Class C- 192-223(Check first three octets)(Last 1 is hosts)(

Loopback address- testing)

World Route- (To send the information across all the networks)

  • and are different networks

  • and are the same networks

  • and are different networks(class B)

  • and are different networks(class C)

Host is like roll no and network is like classroom

A subnet is like a classification inside a network(To make communication efficient, class C). A subnet mask is used to divide an IP address into two parts. One part identifies the host (computer), and the other part identifies the network to which it belongs. No. of subnets - 2^x, where x is the number of 1's in binary, 2^x-2 is the no. of hosts(no. of zeroes) Eg: 192 -11000000, 4 subnets and 62 hosts. , 240- 11110000, has 16 subnets and 14 hosts. Block size: 256-Host.

Cisco Packet Tracer:

The software allows users to simulate the configuration of Cisco routers and switches using a simulated command line interface.


Router(config)# hostname <hostname>

Router# config term

Router(config)# int gi0/0

Router(config_if)# ip add

Router(config_if)#  no shut
  • Two routers are connected together in the same network(but idle)

  • When two routers are active

  • To test whether two networks are working, we can ping it and if the reply is given back.

  router(config_if)# exit
  router(config)# do ping <next_router_ip>

Serial Interface:

A serial interface is a communication interface between two digital systems that transmits data as a series of voltage pulses down a wire.

DCE: Decides who is sending at what rate(Synchronization of clock rates)

Router0 is DCE and Router1 is DTE, the clock rate is specified only in the DCE. Now check if the interface is working by pinging the other router.


Telnet is a client/server application protocol that provides access to virtual terminals of remote systems on local area networks or the Internet.