TCP/IP Model

TCP/IP is an abbreviation used for transmission control protocol/Internet Protocol.

It was developed by Defence Advance Research Projects Agency (ARPA, later DARPA) in late 1970's.

The layers in the TCP/IP protocol suitedo not exactly match those in the OSI model.

TCP/IP and OSI Model

• Host-to-network : Physical and data link layer– No specific protocol

• Network layer– IP(Internet Protocl), ARP(Address Resolution Protocol),

RARP(Reverse ARP), ICMP(Internet Control Message Protocol), IGMO(Internet Group Message Protocol)

• Transport layer– TCP(Transmission Control Protocol), UDP(User Datagram Protocl),

SCTP(Stream Control Transmission Protocol),

• Application Layer– Combined session, presentation, and application layers

TCP/IP Protocol Suite

(a) FTP (File Transfer Protocol)

FTP is used for file transfer between inter network nodes.

b) SMTP (Simple Mail transfer Protocol)

It is used for exchanging e-mail.

c)Telnet

Telnet provides connectivity between dissimilar operating systems. Telnet is a general purpose client-server application program.

d) DNS (Domain Name Systems)

The DNS is used to convert the domain name into the IP addresses. People prefer to use name instead of addresses. Therefore DNS maps a name to an address and conversely.

(e) HTTP (Hypertext Transfer Protocol)

HTTP is an internet protocol designed for a specific application, the World Wide Web (WWW).

Addressing

• Four levels of addresses in TCP/IP protocols• Physical (link), logical (IP, network), port, and specific addresses

Relationship of Layers and Addresses

Physical Address : (Link Address)

•Address of node as defined by the network.•Size and format of these addresses vary depending on the network. E.g Ethernet (48 bits)•Each system having a NIC(Network Interface Card)through which two systems physically connected with each other with cables.• The address of the NIC is called Physical address or mac address.• This is specified by the manficture company of the card.

Logical Address : necessary for universal communications, independent of underlying physical network.

(IP address of the system)  Combination of Net ID and Host ID.  This address can be changed by changing the host position on the network. 

Port Address:

There are many application running on the computer. Each application run with a port no.(logically) on the computer.

The physical addresses will change from hop to hop, but the logical addresses and port addresses usually remain the sameIn computer networking, a port is an application- specific or process-specific software construct serving as a communications endpoint.

 The well-known ports are defined by convention overseen by the Internet Assigned Numbers Authority (IANA)

Examples of well known ports include:

21: File Transfer Protocol (FTP)

22: Secure Shell (SSH)

23: Telnet remote login service

25: Simple Mail Transfer Protocol (SMTP)

53: Domain Name System service

80: Hypertext Transfer Protocol (HTTP) used in the World

Wide Web

119: Network News Transfer Protocol (NNTP)

161: Simple Network Management Protocol (SNMP)

Specific Address

• Some application have user-friendly addresses that are designed for that specific address

• Example 1: e-mail address: kchung@kw.ac.kr– Defines the recipient of an e-mail

• Example 2: URL (Universal Resource Locator) : www.kbs.co.kr– Used to find a document on the WWW

Summary1.The OSI model originally distinguishes between service,interface and protocols.1.The TCP/IP model doesnt clearly distinguish between service,interface and protocol.2.The OSI model is a reference model.2.The TCP/IP model is an implementation of the OSI model.3.In OSI model,the protocols came after the model was described.3.In TCP/TP model, the protocols came first and the model was really just a description of theexisting protocols.4.In OSI model,the protocols are better hidden.4.In TCP/IP model ,the protocols are not hidden.5.The OSI model has 7 layers.5.The TCP/IP model has only 4 layers.6.The OSI model supports both connectionless and connection-oriented communication in thenetwork layer,but only connection -oriented communication in transport layer.6.The TCP/IP model supports both connectionless and connection-oriented communication in the transport layer,giving users the choice.