Computer Networks

Marwan Al-Namari

Week 4

7 Layers

OSI Layer Communication

OSI 7-Layer Model logical view

Physical Path

ApplicationApplication

PresentationPresentation

SessionSession

TransportTransport

NetworkNetwork

Data LinkData Link

PhysicalPhysical

ApplicationApplication

PresentationPresentation

SessionSession

TransportTransport

NetworkNetwork

Data LinkData Link

PhysicalPhysical

Physical Medium

Logical Path

The interaction between layers in the OSI model

EncapsulationEach layer add its own header (and maybe trailer ) to the portion of the packet and pass it to the next layer without knowing which part is data and header( and maybe trailer ).it treat it as one integral unit. The concept is called encapsulation.In the way back each layer will take-off the header ( and maybe trailer ) from the incoming packet and pass it to the next layer . The concept is called decapsulation.

Packet Components

The Complete Packet

Cyclical Redundancy Check

Packet Creation Process

OSI vs. TCP/IP Model

TCP/IP standardsThe Internet Engineering Task Force (IETF) is the body that defines standard internet operating protocolsThese standards are specified in documents called RFCs ( Requests for comments)

e.g. RFC 821 is about SMTP ( e-mail) protocols

TCP/IPTCP/IP : Transmission Control Protocol /Internet Protocol.It is a suite of protocols providing communications in a heterogeneous environment.It is used for interoperability among many different types of computers.Almost all networks support TCP/IP.Support routing.Used as internetworking protocol.

Other Protocols in the SuiteThese protocols were written specifically for TCP/IP:SMTP(Simple Mail Transfer Protocol) : EmailFTP (File Transfer Protocol) : For exchanging files .SNMP(Simple Network Management Protocol) :Network Management.