OSI model explanation

OSI and TCP/IP DOD Model

Physical Layer:

List of services:

-moving bits from source to destination

-providing a standardized interface to physical transmission media

Hardware equipment

-Cables, connectors, pin outs, Fiber Media Converter

Protocols and standards

- RS 232(serial port) -v.35 -Cat5 - RJ45, RJ11 connectors

Data link Layer:

List of services:

-Involved in converting bits into bytes and bytes into frames

-This is subdivided into two layers 1) LLC 2) MAC

LLC: Provides flow control, acknowledgment, and error notification on data link (the physical medium connecting two devices)

MAC: Determines who is allowed to access the media at any one time (CSMA/CD), provides physical addressing (mac), store and forward or cut through switching

Protocols:

-LAN side: 802.3 (Ethernet), ARP, STP

-WAN side: HDLC, PPP, FR, ATM, CDP

Network layer:

-The network layer is responsible for packet forwarding

-For outgoing packets, select the next-hop host and transmit the packet to this host by passing it to the appropriate link layer implementation; for incoming packets, capture packets and pass the packet payload up to the appropriate transport-layer protocol

Protocol: IP (ipv4, ipv6), icmp (error and diagnostics function)

Transport Layer:

-This layer defines how data is sent. Provides reliable and unreliable mode transport of segments. The application decides which mode to send data

-This layer also defines well know port numbers

-flow and error control on logical link (logical link traverses a series of data links - end2end)

Protocol: TCP (reliable), UDP (unreliable)

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Layers Application, Presentation, Session are handled by OS that is running on the host

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Application Layer:

Provides and interface that allows applications to interact across the network.

Protocols: Telnet, FTP, TFTP, HTTP

BGP is an application layer protocol as it uses TCP to transport its messages.

RIP is an application layer protocol as it uses UDP to transport its messages.

Presentation Layer:

As soon as application starts sending data it passes through presentation layer, where data is formatted in a format that is understandable by the server the application is communicating to.

Protocols: jpg, mpeg, avi

Session Layer:

The session layer provides the mechanism for opening, closing and managing a session between end-user application processes. Responsible for keeping sessions separate.

The session layer responds to service requests from the presentation layer and issues service requests to the transport layer.