Computer networks allow interconnected computers to work together. They can be used for business applications using a client-server model, home networking, by mobile users, and raise social issues. The document discusses different types of network hardware including local area networks (LANs), metropolitan area networks (MANs), wide area networks (WANs), wireless networks, home networks, and internetworks. It also covers network software including protocol hierarchies, connection-oriented vs. connectionless services, service primitives, and the relationship between services and protocols.

1. Introduction
By;
samiksha padgilwar
(ELECTRONICS ANDTELECOMMUNICATION
DEPARTMENT)
1
Computer Networks

2. Computer Networks
The old model of a single computer serving all of the
organization's computational needs has been replaced
by one in which a large number of separate but
interconnected computers do the job. These systems
are called computer networks.

3. Uses of Computer Networks
• Business Applications
• Home Applications
• Mobile Users
• Social Issues

4. Business Applications of Networks
A network with two clients and one server.
This whole arrangement is called the client-server model. It is
widely used and forms the basis of much network usage. It is
applicable when the client and server are both in the same building
(e.g., belong to the same company), but also when they are far apart.

5. Business Applications of Networks (2)
The client-server model involves requests and replies.

6. Home Network Applications
Some of the more popular uses of the Internet for home
users are as follows:
1. Access to remote information.
2. Person-to-person communication.
3. Interactive entertainment.
4. Electronic commerce.

7. Home Network Applications (2)
In peer-to-peer system there are no fixed clients and
servers.

8. Mobile Users
Mobile computers, such as notebook computers and
personal digital assistants (PDAs), are one of the
fastest growing segments of the computer industry.
Many owners of these computers have desktop
machines back at the office and want to be connected
to their home base even when away from home

9. Mobile Users (2)
Combinations of wireless networks and mobile
computing.

10. Social Issues
The widespread introduction of networking has
introduced new social, ethical, and political problems.
A lot of these problems could be solved if the
computer industry took computer security seriously. If
all messages were encrypted and
authenticated, it would be harder to commit mischief.

11. Network Hardware
• Local Area Networks (LANs)
• Metropolitan Area Networks (MANs)
• Wide Area Networks (WANs)
• Wireless Networks
• Home Networks
• Internetworks

12. Broadcast Networks
Types of transmission technology
Broadcast links:
Broadcast networks have a single communication channel that is
shared by all the machines on the network.
Point-to-point links:
Point-to-point networks consist of many connections between
individual pairs of machines.

13. Broadcast Networks (2)
Classification of interconnected processors by scale.

14. Local Area Networks
 Two broadcast networks
(a) Bus (b) Ring
In a bus (i.e., a linear cable) network, at any instant at most one machine is the
master and is allowed to transmit. All other machines are required to refrain from
sending.
In a ring, each bit propagates around on its own, not waiting for the rest of the
packet to which it belongs. Typically, each bit circumnavigates the entire ring in
the time it takes to transmit a few bits, often before the complete packet has even
been transmitted.
 Local area networks, generally called LANs, are privately-owned networks within a
single building or campus of up to a few kilometers in size.

15. Metropolitan Area Networks
A metropolitan area network based on cable TV.
 A metropolitan area network, or MAN, covers a city. The best-known example of a
MAN is the cable television network available in many cities.

16. Wide Area Networks
Relation between hosts on LANs and the subnet.
 A wide area network, or WAN, spans a large geographical area, often a country or
continent.

17. Wide Area Networks (2)
A stream of packets from sender to receiver.

18. Wireless Networks
Categories of wireless networks:
System interconnection
Wireless LANs
Wireless WANs

19. Wireless Networks (2)
(a) Bluetooth configuration (b) Wireless LAN

20. Wireless Networks (3)
(a) Individual mobile computers (b) A flying LAN

21. Home Network Categories
Some of the more obvious categories (with examples) are as follows:
Computers (desktop PC, PDA, shared peripherals
Entertainment (TV, DVD, VCR, camera, stereo, MP3)
Telecomm (telephone, cell phone, intercom, fax)
Appliances (microwave, fridge, clock, furnace, airco)
Telemetry (utility meter, burglar alarm, babycam).
The fundamental idea is that in the future most homes will be set up
for networking. Every device in the home will be capable of
communicating with every other device, and all of them will be
accessible over the Internet.

22. Network Software
Protocol Hierarchies
Design Issues for the Layers
Connection-Oriented and Connectionless Services
Service Primitives
The Relationship of Services to Protocols

23. Architecture of the Internet
Overview of the Internet

24. Protocol Hierarchies
To reduce their design complexity, most networks are
organized as a stack of layers or levels, each one built upon
the one below it.
The purpose of each layer is to offer certain services to the
higher layers, shielding those layers from the details of how
the offered services are actually implemented.
A protocol is an agreement between the communicating
parties on how communication is to proceed.
The interface defines which primitive operations and
services the lower layer makes available to the upper one.

25. Protocol Hierarchies (2)
Layers, protocols, and interfaces.

26. Protocol Hierarchies (3)
The philosopher-translator-secretary architecture.

27. Protocol Hierarchies (4)
Example information flow supporting virtual communication in layer 5.

28. Protocol Hierarchies (5)
A message, M, is produced by an application process running in layer 5
and given to layer 4 for transmission.
Layer 4 puts a header in front of the message to identify the message
and passes the result to layer 3.
Layer 3 must break up the incoming messages into smaller units,
packets, prepending a layer 3 header to each packet. In this example, M
is split into two parts, M1and M2. Layer 3 decides which of the
outgoing lines to use and passes the packets to layer 2.
Layer 2 adds not only a header to each piece, but also a trailer, and
gives the resulting unit to layer 1 for physical transmission.
At the receiving machine the message moves upward, from layer to
layer, with headers being stripped off as it progresses.

29. Design Issues for the Layers
 Addressing
 consequence of having multiple destinations
 Error Control
 The receiver should be able to inform sender which data was received
correctly
 Flow Control
 Keep sender from swamping slow receiver with data
 Keep the sender from swamping with data slow networks
 Multiplexing
 Use same communication channel for multiple, unrelated
conversations
 Routing
 When multiple paths between source and destination, one path must
be chosen

30. Connection-Oriented and Connectionless
Services
Connection-oriented
Connection-oriented services includes the steps of setting up a call from one computer to
another, transmitting/receiving data, and then releasing the call, just like a voice phone call.
However, the network connecting the computers is a packet switched network, unlike the
phone system's circuit switched network.
Connection-oriented communication is done in one of two ways over a packet switched network: with and without virtual circuits.
Connectionless:
Connectionless services is just packet switching where no call establishment
and release occur. A message is broken into packets, and each packet is transferred
separately. Moreover, the packets can travel different route to the destination since
there is no connection. Connectionless service is typically provided by the UDP
(User Datagram Protocol), which we will examine later.
The packets transferred using UDP are also called data grams.
With Virtual circuit: A virtual circuit is one which appears to the user as equivalent to a
dedicated point-point service but is maintained by computers.
Without virtual circuits: This is what TCP does in the Internet. The only two machines in
the Internet that are aware a connection is established are the two computers at the
endpoints. The Internet itself--its routers and links--have no information about the presence
of a connection between the two computers.

31. Difference: Connection-Oriented and Connectionless Services
Feature Connectionless Connection-oriented
How is data sent? one packet at a time as continuous stream of packets
Do packets follow same route? no
virtual circuit: yes
without virtual circuit: no
Are resources reserved in network? no
virtual circuit: yes
without virtual circuit: no
Is connection establishment done? no yes
Is state information stored at
network nodes?
no
virtual circuit: yes
without virtual circuit: no
What is impact of node/switch
crash?
only packets at node are lost all virtual circuits through node fail
What addressing information is
needed on each packet?
full source and destination address
virtual circuit: a virtual circuit
number
without virtual circuit: full source
and destination address

32. Service Primitives
Five service primitives for implementing a simple connection-
oriented service.

33. Service Primitives (2)
Packets sent in a simple client-server interaction on a connection-
oriented network.

34. Services to Protocols Relationship
The relationship between a service and a protocol
A protocol, in contrast, is a set of rules governing the format and meaning of the
packets, or messages that are exchanged by the peer entities within a layer.
A service is like an abstract data type or an object in an object-oriented language. It
defines operations that can be performed on an object but does not specify how these
operations are implemented. A protocol relates to the implementation of the service and
as such is not visible to the user of the service.

35. Reference Models
The OSI Reference Model
The TCP/IP Reference Model
A Comparison of OSI and TCP/IP
A Critique of the OSI Model and Protocols
A Critique of the TCP/IP Reference Model

36. The OSI Reference Model

37. The TCP/IP reference model.

38. The TCP/IP reference model (2)
Protocols and networks in the TCP/IP model initially.
On top of the transport layer is the application layer. It contains all the higher-level protocols.
The early ones included virtual terminal (TELNET), file transfer (FTP), and electronic mail

39. Comparison between OSI and TCP/IP
Reference Models
OSI
1)It has 7 layers
2)Transport layer guarantees delivery of
packets
3)Separate presentation layer
4)Separate session layer
5)Network layer provides both
connectionless and connection oriented
services
6)It defines the services, interfaces and
protocols very clearly and makes a clear
distinction between them
7)It has a problem of protocol filtering into
a model
TCP/IP
1)Has 4 layers
2)Transport layer does not guarantees
delivery of packets
3)No presentation layer, characteristics
are provided by application layer
4)No session layer, characteristics are
provided by transport layer
5)Network layer provides only
connection less services
6)It does not clearly distinguishes
between service interface and
protocols
7)The model does not fit any protocol
stack.

40. A Critique of the OSI Model and
Protocols
Why OSI did not take over the world:
Bad timing
Bad technology
Bad implementations
Bad politics

41. A Critique of the TCP/IP Reference
Model
Problems:
 Service, interface, and protocol not distinguished
 Not a general model
 Host-to-network “layer” not really a layer
 No mention of physical and data link layers
 Minor protocols deeply entrenched, hard to replace

42. EXAMPLE NETWORKS:
Internet
The ARPANET
NFSNET
Connection-Oriented Network
X.25
ATM
Ethernet
Wireless LANs: 802.11

43. ATM (Asynchronous Transfer Mode)
ATM virtual circuits
ATM virtual circuits

44. ATM Virtual Circuits (2)
An ATM cell

45. The ATM Reference Model
The ATM reference model

46. The ATM Reference Model (2)
The ATM layers and sublayers and their functions.

47. References
Computer Networks,Tanenbaum, 4th Edition.
Data Communications and Networking,
Behrouz A. Forouzan, 4th
Edition.
Computer Networks, A Systems Approach,
Larry L. Peterson & Bruce S. Davie,
4th Edition.