McGraw-Hill ©The McGraw-Hill Companies, Inc., 2000

Computer Communication and Networks

Muhammad Waseem Iqbal

Lecture # 07

TCP/IP PROTOCOL SUITETCP/IP PROTOCOL SUITE

The layers in the The layers in the TCP/IP protocol suiteTCP/IP protocol suite do not exactly do not exactly match those in the OSI model. The original TCP/IP match those in the OSI model. The original TCP/IP protocol suite was defined as having four layers: protocol suite was defined as having four layers: host-to-host-to-networknetwork, , internetinternet, , transporttransport, and , and applicationapplication. However, . However, when TCP/IP is compared to OSI, we can say that the when TCP/IP is compared to OSI, we can say that the TCP/IP protocol suite is made of five layers: TCP/IP protocol suite is made of five layers: physicalphysical, , data linkdata link, , networknetwork, , transporttransport, and , and applicationapplication..

Physical and Data Link LayersNetwork LayerTransport LayerApplication Layer

Topics discussed in this section:Topics discussed in this section:

Figure-1 TCP/IP and OSI model

ADDRESSINGADDRESSING

Four levels of addresses are used in an internet employing Four levels of addresses are used in an internet employing the TCP/IP protocols: the TCP/IP protocols: physicalphysical, , logicallogical, , portport, and , and specificspecific..

Physical AddressesLogical AddressesPort AddressesSpecific Addresses

Topics discussed in this section:Topics discussed in this section:

Figure -2 Addresses in TCP/IP

Physical address:

• When referring to computers in general or computer memory, the physical address is the computer memory address of a physical hardware device.

• When referring to a network address, physical address is sometimes used to describe the MAC address.

• This is specified by the manufacture company of the card.

• This address is used by data link layer.

MAC address: • A hardware address that uniquely identifies each node of a network. • In IEEE 802 networks, the Data Link Control (DLC) Layer of the OSI.

Model is divided into two sub-layers 1.Logical Link Control (LLC) layer 2.Media Access Control (MAC) layer

•The MAC layer interfaces directly with the network medium. Consequently, each different type of network medium requires a different MAC layer.•The chance to see the MAC address is very difficult for any of your equipment.

• Software that helps your computer communicate with a network takes care of matching the MAC address to a logical address.

• If you'd like to see the MAC address and logical address used by the Internet Protocol (IP) for your Windows computer, you can run a small program that Microsoft provides.• Go to the "Start" menu, click on "Run," and in the window that appears, type WINIPCFG (IPCONFIG/ALL for Windows 2000/XP). • When the gray window appears, click on "More Info" and you'll get information.

Logical address: •An IP address of the system is called logical address.• This address is the combination of Net ID and Host ID.• This address is used by network layer to identify a particular network (source to destination) among the networks. •This address can be changed by changing the host position on the network. So it is called logical address. •The IP address is the logical address assigned to your connection by your ISP or network administrator. •The logical address is what the network uses to pass information along to your computer.

Port Address: There are many application running on the computer.

Each application run with a port no.(logically) on the computer. This port no. for application is decided by the Karnal of the OS. This port no. is called port address.

Figure-3 Relationship of layers and addresses in TCP/IP

In Figure-4 a node with physical address 10 sends a frame to a node with physical address 87. The two nodes are connected by a link (bus topology LAN). As the figure shows, the computer with physical address 10 is the sender, and the computer with physical address 87 is the receiver.

Example-1

Figure -4 Physical addresses

Most local-area networks use a 48-bit (6-byte) physical address written as 12 hexadecimal digits; every byte (2 hexadecimal digits) is separated by a colon, as shown below:

Example-2

07:01:02:01:2C:4B

A 6-byte (12 hexadecimal digits) physical address.

Figure-5 shows a part of an internet with two routers connecting three LANs. Each device (computer or router) has a pair of addresses (logical and physical) for each connection. In this case, each computer is connected to only one link and therefore has only one pair of addresses. Each router, however, is connected to three networks (only two are shown in the figure). So each router has three pairs of addresses, one for each connection.

Example-3

Figure-5 IP addresses

Figure-6 shows two computers communicating via the Internet. The sending computer is running three processes at this time with port addresses a, b, and c. The receiving computer is running two processes at this time with port addresses j and k. Process a in the sending computer needs to communicate with process j in the receiving computer. Note that although physical addresses change from hop to hop, logical and port addresses remain the same from the source to destination.

Example-4

Figure-6 Port addresses

The physical addresses will change from hop to hop,but the logical addresses usually remain the same.

Example-5

As we will see in Chapter 23, a port address is a 16-bit address represented by one decimal number as shown.

753

A 16-bit port address represented as one single number.