Network protocols It describes the different topologies used in computer networks. for more info, contact: electron3011@gmail.com

1. Computer Communication Networks
BTech 3rd Year EXTC
Re-presented by-
Rehan Ahmad,
Assistant Professor,
Dept of EXTC,
MPSTME,
Shirpur Campus
[Academic Year 2015-16]
rehan.ahmad@nmims.edu
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2.  What is a Network?
 A set of entities connected by communication link-
- telephone networks.
- Ethernet.
- internet.
- hardware circuits.

3. What is a Computer Network?
A network consists of 2 or more computers connected
together, and they can communicate and share resources
(e.g. information).

4.  Why Networking?
• Sharing information — i.e. data communication
• Do you prefer these?
• Or this?

5. • Sharing hardware or software
• Centralize administration and support
• E.g. print document
• E.g. Internet-based, so everyone can access the same
administrative or support application from their PCs

7. How many kinds of Networks?
• Depending on one’s perspective, we can classify
networks in different ways
• Based on transmission media:
• Wired (UTP, coaxial cables, fiber-optic cables) and
Wireless.
• Based on network size:
• LAN and WAN (and MAN).
• Based on management method:
• Peer-to-peer and Client/Server
• Based on topology (connectivity):
• Bus, Star, Ring …
:
:

8.  Topology
 3 basic types

9.  Bus Topology

10. CSMA/CD
[Carrier sense Multiple Access/Collision detection]
 With CSMA, collision occupies medium for duration of
transmission of full frame
 Instead “CD”= collision detect:
 Stations listen whilst transmitting
 If medium idle, transmit
 If busy, listen for idle, then transmit (and listen)
 If collision detected, jam (send noise) then cease
transmission
 Even if collision happens at the station next to the
transmitting station, collision will be detected after
>= RTT
 After jam, wait random time then start again.

11. Collision detection
Collision detection can still take as long as 

12.  Bus Topology
 Merits:
 1. Easy to understand, install and use for small networks.
 2. The cabling cost is less as the topology requires least
amount of cable for connection.
 3. Easy to expand by joining two cables with a BNC
connector.
 4. Use of repeaters is possible for signal boosting.
 Demerits:
 1. Heavy network traffic slows down speed.
 2. Use of BNC connector attenuates the signal.
 3. Cable break and loose BNC connector will cause
reflections and may bring down entire network.

13.  Star Topology

14.  Star Topology
 Merits:
 1. Connection of multiple node does not hamper network
speed as the information routing is through independent
Hub.
 2. Multiple hub are connected together for easy
expansion.
 Demerits:
 1. If the central Hub fails entire network fails to operate.
 2. Many star networks require a deice at the central point
to rebroadcast or switch the network traffic.
 3. Cabling cost is more, since cables must be pulled from
all computers to the central hub.

15.  Ring Topology
 Token ring

16.  Ring Topology
 Merits:
 1. No one computer can monopolize the network as every
computer is given equal access to the network.
 2. The fair sharing of the network allows the network to
continue function in a useful manner rather than fail.
 Demerits:
 1. Failure of one computer on the ring can affect the entire
network.
 2. It is difficult to trouble shoot the ring.
 3. Adding or removing the nodes disturbs the network
activities.

17.  Mesh Topology

18.  Mesh Topology
 Merits:
 1. Use of dedicated link guarantees that each connection
can carry its own data load , thus eliminating traffic issues.
 2. Robust, because failure of one computer does not bring
down entire network.
 3. Provide security, because every message travels along
a dedicated link.
 4. Point to point link make fault diagnose easy.
 Demerits:
 1. Installation and reconfiguration is difficult due to nature
of connection.
 2. Cabling cost more.

19.  TreeTopology

20.  TreeTopology
 Merits:
 1. it allows more devices to be attached to a single hub and
can therefore increase the distance of signals travelling from
device to device.
 2. It allows the network to isolate and prioritize communication
from different computers.
 Demerits:
 1. if the central hub fails, entire network brings down.
 2. cabling cost is more

21.  LogicalTopology

22.  Hybrid Topology

23.  Switching
 3 types
 Circuit Switching
 Message Switching
 Packet Switching

24.  Circuit Switching

25.  Merits:
 1. Major advantage is presence of dedicated transmission channel,
because of which high data transfer rate is achieved.
 2. No delay in data flow because of dedicated channel.
 Demerits:
 1. Dedicated channel cannot be used for any other communication,
event though it is free.
 2. Dedicated channel requires ore bandwidth.
 3. It takes more time to establish connection.

26.  Message Switching

27.  Merits:
1. It provides efficient traffic management by assigning priorities
to the messages to be switched.
2. Reduces network traffic congestion because it is able to store
messages until a free communication channel is available.
3. Network devices share the data, which avoids traffic over the
network.
4.Provides asynchronous communication across the time zones.
Demerits:
1. Store & forwarding introduces delay hence cannot used for
real time audio video transmission.
2. Intermediate devices requires a large storage capacity since
it has to store the message unless a free path is available.

28. A message Switched Network

29.  Features of Store & Forward Message Switching:
1. Store and forward service is unidirectional.
2. For switch to switch transfer of message, the network may employ
some error control mechanism.
3. Message is stored into switch at each stage of transmission.
4. Delay in delivery is the sum of -
time required to send the message to the entry switch
+ switch delay
+ transmission time at each switch.

30.  Packet Switching

31. Datagram Packet Switching

32.  Virtual Packet Switching
 Packet Switching’s
 Merits:
1. It increases the bandwidth of the network by allowing
many devices to communicate through the same network
channel.
2. A switching node can route the packet as and when
required.
3. Because of small sized packets the transmission delay is
reduced as the switching node, does not write the packets
into its memory before forwarding it.

33.  Demerits:
1. Switching nodes for packet switching require large
amount of RAM to handle large quantities of packets.
2. The switching nodes requires more processing power
because the packet switching protocols are more
complex.
3. Packet are more easily lost on their route , hence
sequence numbers are required to identify the missing
packets.

34. Parameters Message Switching Circuit Switching Packet Switching
EndTerminal Telegraph,Teletype Telephone modem Computer
Information type Morse code,ASCII code,
Baudot code
AnalogVoice or PCM
digital voice
Binary information
Addressing scheme Geographical addresses Hierarchical numbering
plan
Hierarchical address
space
Routing scheme manual Route selected during
call set up
Each packet routed
independently
Multiplexing scheme Character or message
multiplexing
Circuit multiplexing Packet multiplexing
shared media access
network.
Transmission system Digital data over
different transmission
media
Analog & Digital data
over different
transmission media
Digital data over
different transmission
media
Application Telegraph network for
transmission of telegram
Telephone network for
bi-directional, real time
transfer of voice signal
Internet for datagram &
reliable stream service
between computers

35. Reference Models
• The OSI Reference Model
• The TCP/IP Reference Model
• A Comparison of OSI and TCP/IP

37.  OSI Model

38. Reference Models
The OSI
reference
model.

39. Reference Models (2)
 TheTCP/IP reference model.

40.  Merits of OSI model:
1. It distinguishes very clearly between services, interfaces
and protocols.
2. The protocols in OSI model are better hidden, so they
can be easily replaced by new protocols as the
technology changes.
3. OSI is a general model.
4. This model supports connection oriented as well as
connection less services.

41. A Critique of the OSI Model and
Protocols
 Why OSI did not take over the world
• Bad timing
• Bad technology
• Bad implementations
• Bad politics
• Session and presentation layers are not of much
use.
• This model was derived before the protocols
were invented, so in practice, the problem is
fitting protocol into a model.

42. Reference Models (3)
 Protocols and networks in theTCP/IP model initially.

43. A Critique of the TCP/IP Reference Model
1. The model does not clearly distinguish the concepts of service,
interface, and protocol.
2. The model is not general and is poorly suited to describing
and other protocol stack.
3. The model does not distinguish (or even mention) the
physical and data link layer.
4. Only TCP and IP are carefully thought out and implemented.
Many other protocols are ad hoc.
5. The host to network layer is not a layer at all, it is simply an
interface.

44. References:
1. Data Communication and Networking by Beherouz A
Forouzan, 4th Edition, TMH.
2. Computer Networks by Andrew S Tennanbaum , 4th Edition,
TMH.
3. Communication Networks, Fundamental concept and key
architectures, by Alberto Leon-Garcia, Indra Widjaja, TMH.