1. Computer Networks

2. 6.1 NETWORKS, LARGE AND SMALL
A computer network is a combination of devices connected by transmission media.

3. 6.1
A computer network is a combination of devices connected by transmission media.
Transmission media include cable, wire, air.
A computer network can span a small, medium, or large geographical area.
Different networks form internet work (internet)
Model? Protocol?

4. 6.2
OSI MODEL

5. Note:
The Open Systems Interconnection (OSI) model is a theoretical model that shows how any two different systems can communicate with each other.
The OSI model was designed by the ISO (International Standard Organization)

6. Seven layers of the OSI model

7. Seven layers of the OSI model
The 7-layer OSI model gives network designers an idea
Of the functionality of each separate but related layer.
Not every computer need 7 layers to connect with other
Systems. The number of required layers depends on the
Functionality of the system and its location in the
network

8. Seven layers of the OSI model
Physical layer
transmitting raw bits over a communication channel, transform a stream of bits into signals

9. Seven layers of the OSI model
Data-link layer
To take a raw transmission facility and transform it into a line that appears free of undetected transmission errors to the network layer.
organize bits into logical units called frames
Responsible for delivery of a frame between 2 adjacent nodes
Two addresses added in the frame; one for sender node, another for receiver node
Error handling between 2 adjacent stations

10. Seven layers of the OSI model
Network layer
organize bits into logical units called packets
Responsible for delivery of a packet, from original
source to final destination
Two logical addresses (IP) added in the packet; one for sender node, another for receiver node
Logical addresses unchanged during the delivery

11. Seven layers of the OSI model
Transport layer
To accept data from the session layer, split it up into smaller units if need be, pass these to the network layer, and ensure that the pieces all arrive correctly at the other end.
Responsible for delivery of the whole message from source to destination
Packet ordering, re-transmission

12. Seven layers of the OSI model
Session layer
Allow users on different machines to establish sessions between them.
Synchronization points for backup in case of system or network failure
not used often in today’s network applications; usually bound in the application layer

13. Seven layers of the OSI model
Presentation layer
concerned with the syntax (format) and semantics (meaning) of the information exchanged between two systems
Compress/Decompress data for efficiency
Encrypt/Decrypt data for security
Functionality shifted to other layers, for example,
encryption/decryption in network layer (SSL)

14. Seven layers of the OSI model
Application layer
The application layer contains a variety of protocols that are commonly needed.
File transfer, , HTTP for www

15. The OSI model and protocols

16. Flow of data in the OSI model

17. Flow of data in the OSI model

18. 6.3
CATEGORIES OF
NETWORKS

19. Categories of networks

20. LAN
A local area network (LAN) allows resource sharing (hardware, software, and data) between computers.
A LAN can be configured in a bus, ring, or star topology.

21. MAN
A metropolitan area network (MAN) uses the services provided by a common carrier.

22. WAN
A wide area network (WAN) is the connection of individual computers or LANs over a large area. WANs are installed and run by common carriers.

23. 6.4
CONNECTING
DEVICES

24. Connecting devices

25. Repeater
A repeater is a connecting device that regenerates data and extends the physical length of a network.

26. Note:
Repeaters operate at the first layer of the OSI model.

27. Bridge
A bridge is a connecting device that filters traffic.

28. Note:
Bridges operate at the first two layers of the OSI model.

29. Switch
A switch is simply a sophisticated bridge with multiple interfaces, has better performance.

30. Routers in an internet
A router is a connecting device that routes packets.

31. Note:
Routers operate at the first three layers of the OSI model.

32. Gateway
A gateway allows two networks, each with a completely different protocol suite, to communicate.
The gateway understands the protocols used by each connected network and is therefore able to translate from one to another.
Today, however, the term gateway is used interchangeably with the term router.

33. Connecting devices and the OSI model

34. 6.5
THE INTERNET
AND
TCP/IP

35. The Internet and TCP/IP
An internetwork is two or more LANs, MANs, or WANs.
The most famous internetwork is the Internet
Transmission Control Protocol/Internet Protocol (TCP/IP) is the set of protocols used by the Internet, a worldwide internetwork of computers.

36. TCP/IP and OSI model
The TCP/IP is a suite or a stack of protocols that officially controls the Internet. TCP/IP was developed before the OSI model.

37. Network layer
The Internet Protocol (IP) is TCP/IP’s unreliable protocol at the network (internet) layer.
IP is a best-effort delivery service; no error checking/tracking/re-transmission
data unit at the IP layer is called an IP datagram (packet)
Datagrams may travel along different routes and may arrive out of sequence or duplicated

38. Network layer
An IP (Internet) address uniquely identifies each computer connected to the Internet.
Each Internet address consists of 4 bytes (32 bits).

39. IP addresses in dotted-decimal notation
For easier to read and remember, 32-bit IP
Address -> dotted-decimal format

40. Transport layer
User Datagram Protocol (UDP) and Transmission Control Protocol (TCP) are TCP/IP’s protocols at the transport layer.
UDP is an end-to-end transport level protocol that provides only the basic necessities for end-to-end delivery of a transmission.
TCP provides full transport layer services to applications. TCP is a reliable transport protocol.

41. Transport layer
TCP divides a message into a sequence of segments that are numbered sequentially.
The sequence numbers are used for re-transmission and re-ordering

42. Application layer
The TCP/IP application layer is equivalent to the combined session, presentation, and application layers of OSI model.
Communication on the Internet uses the client-server model.

43. FTP
A client, an application program running on a local machine, requests a service from a server, an application program running on a remote machine.
File Transfer Protocol (FTP) is a TCP/IP client-server application for copying files from one host to another.

44. SMTP
The protocol that supports electronic mail ( ) on the Internet is Simple Mail Transfer Protocol (SMTP).

45. SMTP
The SMTP coworks with Post Office Protocol (POP)

46. address
The local part defines the name of a special file, called
User mailbox
The domain name defines the computer that serves as
The SMTP server

47. TELNET (Terminal Network)
TELNET is a client-server application that allows a user to log on to a remote machine, giving the user access to the remote system.

48. TELNET Local login – access a computer directly
Remote login – access a computer remotely, through telnet service

49. Hypertext Transfer Protocol (HTTP)
Hypertext Transfer Protocol (HTTP) is a client-server program for accessing and transferring documents on the World Wide Web (WWW), a collection of multimedia documents.
The Uniform Resource Locator (URL) is a standard identifier for specifying information on the Internet.
URL:

50. Hypertext A concept, a document style Hypertext vs. linear
Hypertext documents contain links pointing to other documents (text, images, video, audio, etc.)
Homepage : the main page for an organization/individual

51. Browser A browser is needed to access a page on the WWW.
Usually consists of three parts: a controller, a method, and an interpreter.
Contents are displayed by interpreter

52. Types of Web documents
Static: fixed contents, stored in server side, use HTML (Hypertext Markup Language) for screen formatting
Dynamic: contents generated by server-side programs. Common gateway interface (CGI), servlets
Active: program run on client side, JavaScript, Applet.