Computer Communication Networks Lecture 3 Layering and Protocol

Computer Communication & Networks Lecture 3 Layering and Protocol Stacks (contd. ) http: //web. uettaxila. edu. pk/CMS/coe. CCNbs. Sp 09/index. asp Waleed Ejaz waleed. ejaz@uettaxila. edu. pk 1

Seven layers of the OSI model 2

Network layer n End-to-End packet delivery q n From the original source to a destination Needed when 2 devices are attached to different networks q n Not a message What is the network definition here? Main duties: 1. 2. 3. 4. Logical addressing Routing Switching Congestion control and Qo. S 3

Source to destination delivery Data Link Network layer 4

Network layer - example - Network layer addresses Data Link layer addresses 5

Note The network layer is responsible for the delivery of individual packets from the source host to the destination host. 6

Transport layer n Process-to-Process delivery of the entire message q From the original source to a destination n Needed when several processes (running programs) active at the same time n Main tasks: q q q Port addressing Segmentation and reassembly Congestion control Flow control Error control 7

Transport Layer 8

Transport layer -an example of a reliable delivery - 9

Note The transport layer is responsible for the delivery of a message from one process to another. 10

Note The session layer is responsible for dialog control and synchronization. 11

Note The presentation layer is responsible for translation, compression, and encryption. 12

Application layer n n Enables user to access the network Provides services to a user q q q E-mail Remote file access and transfer (Telnet, FTP) Access to WWW (HTTP) 13

Note The application layer is responsible for providing services to the user. 14

OSI Reference Model n n A convenient aid for remembering the OSI layer names is to use the first letter of each word in the phrase: All People Seem To Need Data Processing 15

Summary of layers and protocols n Low-level protocols define the electrical and physical standards to be observed, bit- and byte-ordering and the transmission and error detection and correction of the bit stream n High-level protocols deal with the data formatting, including the syntax of messages, the terminal to computer dialogue, character sets, sequencing of messages 16

TCP/IP Protocol 17

TCP/IP Vs OSI Model 18

Four Level of Addresses 19

Relationship of Layers & Addresses in TCP/IP 20

Note The physical addresses will change from hop to hop, but the logical addresses usually remain the same. 21

Readings n Chapter 2 (B. A Forouzan) q Section 2. 3, 2. 4, 2. 5 22

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