Chap. 2 Network Models

2.1 Layered Tasks Sender, Receiver and Carrier

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

2.2 Internet Model Five Layer Internet Model

Internet Model Peer-to-peer Processes

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

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

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

Physical Layer

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

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

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

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

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

Network Layer Logical addressing Routing

Network Layer

Transport Layer

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

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

Transport Layer

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

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

Summary of Layers

2.3 OSI Model

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.

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

Model (cont’d) The OSI Model

OSI Layers

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

Applications for All Layers