Network StandardOSI MODEL

BY TREVOR KAPUSA

OSI Model

Functions

Summary to Physical Layer

The Physical Layer has two responsibilities; → it sends bits and receives bits.All wiring, power, cabling and connections are part of the physical layer

Without the physical layer functioning properly none of the upper layers will respond correctly

OSI Model

2. Data Link Layer

Purpose Manages the flow of data over the physical media

Responsible for error-free transmission over the physical media Assures error-free data submission to the Network Layer The physical address defines how devices are labelled in the data link

layer. This physical address is most commonly called the Media Access

Control (MAC) address. The MAC address is a unique number assigned by the manufacturer

•Physical addressing•Network topoloty•Error notification•Access to the physical medium•Flow control

Data Link Devices

Switches and bridges

Devices that use MAC addressing to make networking decisions function on the data link layer.Example: Do ipconfig /all on command Line (cmd)

Physical Address. . . . . . . . . : 48-D2-24-8A-3D-9E

Data Link Layer Subdivision

Improvement to ISO Model Logical Link Control (LLC) sub-layer

Manages service access points (logical link) Managing frames to upper and lower layers Error and flow control

Media Access Control (MAC) sub-layer Applies directly to network card communication Access control

Address Resolution Protocol

ARP (Address Resolution Protocol) ARP maintains a small database in memory, called the ARP cache, that

cross-references physical and logical addresses. on CMD do arp –aInterface: 192.168.43.175 --- 0x4 Internet Address Physical Address Type 192.168.43.1 02-90-4c-14-43-19 dynamic 224.0.0.22 01-00-5e-00-00-16 static 239.255.255.250 01-00-5e-7f-ff-fa static

Media Access Control Application

Network Interface Card driver

NETWORKSOFTWARE

NETWORKCARD

NIC Driverfacilitates data transfer

3. Network Layer

Basically defines logical addressing and the ways that packets are moved from source to destination on a network

Purpose Addressing and routing the packets

Example application at the router If the packet size is large, splits into small packets

Cont….

Network Layer Function

Address messages Path determination between source and destination nodes on different

networks Address translation from logical to physical

Example: Gil-llw-noc ----------> 154.66.120.129 Routing of data (path determination)

Based on priority Best path at the time of transmission

Congestion control

Logical Address Construction

A routing protocol used to pass messages between routers for maintaining and updating routing tables Example: RIP, IGRP, OSPF, EIGRP.

Routed Protocolsused to carry end-user traffic across the internetworkExample: IP and IPX**Routing protocols support routed protocols

Lower Layers Application Areas

Special significance to network card design Applies to general LAN hardware design

Exceptions Routers etc.

802. standards Centered around the lower layers Applies to networks

Layer Operations

At each layer, additional information is added to the data packet An example would be information related to the IP protocol that is

added at Layer 3

Formatting of Data Through the Layers

Application Header Presentation Header Session Header

Transport HeaderNetwork Header

Data Link Header and Trailer Physical Frame Preamble

Packet : General Format

Header Trailer

Data

A general concept of packets serves as a prerequisite tothe understanding of the ISO-OSI model.

Some Header Information Added at Various Layers Packet arrival information Receiver’s address Sender’s address Synchronization character

Some of the Major Components of the Data Packet

Sender’sAddress

Receiver’sAddress Control

Data

Data

ErrorCorrectionProtocol

Start/synchInformation

Standardizing Packet Formatting

Packets must conform to a standard in order for the nodes in a network to be able to communicate with one another

The International Standards Organization (ISO) has provided a reference model

Standards are established for operations at each layer of the ISO/OSI model in the form of protocols

Layered Model Summary