1. Chap. 2 Network Models

2. 2.1 Layered Tasks
Sender, Receiver and Carrier

3. Layered Tasks Hierarchy Services Higher Layer Middle Layer Lower Layer
The Each layer uses the services of the layer immediately below it.

4. 2.2 Internet Model
Five Layer Internet Model

5. Internet Model
Peer-to-peer Processes

6. Peer-to-peer Processes
Interfaces between Layers
Each interface defines what information and services a layer must provide for the layer above it.
Well defined interfaces and layer functions provide modularity to a network
Organizations of the layers
Network support layers : Layers 1, 2, 3
User support layer : Layer 5
It allows interoperability among unrelated software systems
Transport layer (Layer 4) : linking two subgroups

7. Peer-to-peer Processes
An exchange using the Internet model

8. Physical Layer
coordinates the functions required to transmit a bit stream over a physical medium.
(deal with the mechanical and electrical specification of the primary connections: cable, connector)
Physical characteristics of interfaces and media
Representation of bits
Data rate : transmission rate
Synchronization of bits
 is responsible for transmitting individual bits from one node to the next node

9. Physical Layer

10. Data Link Layer
The data link layer is responsible for transmitting frames from one node to the next.

11. Data Link Layer Major duties Framing Physical addressing Flow control
Error control
Access control

12. Data Link Layer
Hop-to-hop (node-to-node) delivery

13. Data Link Layer
In Figure 2.8 a node with physical address 10 sends a frame to a node with physical address 87. The two nodes are connected by a link. At the data link level this frame contains physical addresses in the header. These are the only addresses needed. The rest of the header contains other information needed at this level. The trailer usually contains extra bits needed for error detection

14. Network Layer
The network layer is responsible for the delivery of packets from the original source to the final destination.

15. Network Layer
Logical addressing
Routing

16. Network Layer

17. Transport Layer

18. Transport Layer
The transport layer is responsible for delivery of a message from one process to another.

19. Transport Layer Port addressing Segmentation and ressemblt
Connection control
Flow control
Error control

20. Transport Layer

21. Application Layer
The application layer is responsible for providing services to the user.

22. Application Layer The major duties of the application Mail services
File transfer and access
Remote log-in
Accessing the World Wide Web

23. Summary of Layers

24. 2.3 OSI Model

25. OSI Reference Model OSI : Open System Interconnection by ISO
Basic Reference Model : ISO-7498
Purpose of OSI Model
~ is to open communication between different systems without requiring changes to the logic of the underlying hardware and software.

26. The Model
OSI Model
~ is layered framework for the design of network systems that allows for communication across all types of computer systems
Layered Architecture
~ shows the layers involved when a message is sent from device A to device B

27. Model (cont’d)
The OSI Model

28. OSI Layers

29. Model (cont’d) Peer-to-peer process
~ process on each machine that communicate at a given layer
Interfaces between Layers
~ defines what information and services a layer must provide for the layer above it

30. Applications for All Layers