Data Comm. & Networks Instructor: Ibrahim Tariq Lecture 3

2.2 Figure 2.2 Seven layers of the OSI model

3 Physical layer 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) physical connection

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

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

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

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

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

2.9 Figure 2.8 Network layer

10 Source to destination delivery Data Link Network layer

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

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

13 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

2.14 Figure 2.10 Transport layer

2.15 Figure 2.11 Reliable process-to-process delivery of a message

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

2.17 Figure 2.12 Session layer

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

2.19 Figure 2.13 Presentation layer

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

2.21 Figure 2.14 Application layer

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

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

24 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

2.25 Figure 2.15 Summary of layers