Data Comm Networks Instructor Ibrahim Tariq Lecture 3

Data Comm. & Networks Instructor: Ibrahim Tariq Lecture 3

Figure 2. 2 Seven layers of the OSI model 2. 2

Physical layer physical connection Transporting bits from one end node to the next - type of the transmission media (twisted-pair, coax, optical fiber, air) - bit representation (voltage levels of logical values) - data rate (speed) - synchronization of bits (time synchronization) 3

Note The physical layer is responsible for movements of individual bits from one hop (node) to the next. 4

Data Link layer logical connection Transporting frames from one end node to the next one - framing - physical addressing - flow control - error control - access control 5

Data Link layer - hop-to-hop delivery- 6

Note The data link layer is responsible for moving frames from one hop (node) to the next. 7

Network layer Not a message n End-to-End packet delivery q n Needed when 2 devices are attached to different networks q n From the original source to a destination What is the network definition here? Main duties: 1. 2. 3. Logical addressing Routing Congestion control and Qo. S 8

Figure 2. 8 Network layer 2. 9

Source to destination delivery Data Link Network layer 10

Network layer - example - Network layer addresses Data Link layer addresses 11

Note The network layer is responsible for the delivery of individual packets from the source host to the destination host. 12

Transport layer • Process-to-Process delivery of the entire message – From the original source to a destination • Needed when several processes (running programs) active at the same time • Main tasks: – – – Port addressing Segmentation and reassembly Congestion control Flow control Error control 13

Figure 2. 10 Transport layer 2. 14

Figure 2. 11 Reliable process-to-process delivery of a message 2. 15

Note The transport layer is responsible for the delivery of a message from one process to another. 16

Figure 2. 12 Session layer 2. 17

Note The session layer is responsible for dialog control and synchronization. 18

Figure 2. 13 Presentation layer 2. 19

Note The presentation layer is responsible for translation, compression, and encryption. 20

Figure 2. 14 Application layer 2. 21

Application layer • Enables user to access the network • Provides services to a user – E-mail – Remote file access and transfer (Telnet, FTP) – Access to WWW (HTTP) 22

Note The application layer is responsible for providing services to the user. 23

OSI Reference Model • 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 24

Figure 2. 15 Summary of layers 2. 25