ISO-OSI.pdf

1 ISO-OSI 7-Layers Network Reference Model by MAZHAR IQBAL BUTT .

THE OSI REFERENCE MODEL The International Organization for Standardization (ISO (ISO)) developed the Open System Interconnection (OSI ( OSI)) Reference Model to promote communication between dissimilar computers as a guide for defining a set of open protocols. This model has served as one of the most basic and essential, elements of  computer networking since 1984. 2 ISO-OSI 7-Layers Network Reference Model by MAZHAR IQBAL BUTT .

The OSI model provides a framework (functional guideline) for defining standards to connect heterogeneous computers. The OSI model solves the complicated problem of communication between computer systems by dividing the communication into sub-tasks (layers). Each task executes a specific function by using the services of the task below it and providing services to above task. 3 ISO-OSI 7-Layers Network Reference Model by MAZHAR IQBAL BUTT .

OSI LAYER MODEL

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Most communication environments separate the communication functions and application processing. This separation of networking functions is called LAYERING. LAYERING. OSI divides the big task of host-to-host networking called INTERNETWORKING into a vertical stack. This OSI stack contains these seven numbered layers, these indicate distinct functions. 5 ISO-OSI 7-Layers Network Reference Model by MAZHAR IQBAL BUTT .

The layered approach to OSI offers several advantages to system implementers. By separating the job of  networking into logical smaller pieces, vendors can more easily solve network "problems" through divide-and-conquer divide-and-conquer.. The OSI layers afford extensibility. New protocols and other network services will generally be easier to add to a layered architecture. 6 ISO-OSI 7-Layers Network Reference Model by MAZHAR IQBAL BUTT .

7 ISO-OSI 7-Layers Network Reference Model by MAZHAR IQBAL BUTT .

Upper layers 7. application 6. presentation 5. session Lower layers 4. transport 3. network 2. data link 1. physical

Higher-level facilities Application Presentation Session Network communication Transport Network Physical medium Data Link Physical 8

ISO-OSI 7-Layers Network Reference Model by MAZHAR IQBAL BUTT .

ADVANTAGES •Divide the interrelated aspects of  network operation into less complex elements. •Define standard interfaces for "Plug and Plug" Compatibility and multi-vendor integration. •Divide the complexity of  internetworking into Discrete, more easily learned operations. 9 ISO-OSI 7-Layers Network Reference Model by MAZHAR IQBAL BUTT .

10 ISO-OSI 7-Layers Network Reference Model by MAZHAR IQBAL BUTT .

APPLICATION LAYER  The application layer provides different services to user applications. It interfaces directly to these services and provide conversion between associated application processes, after that it issues requests to the presentation layer. It contains a variety of  protocols that are commonly needed. Another application layer function is file transfer. Different file systems have different file naming conventions. Transferring a file between two different systems requires handling all incompatibilities. 11 ISO-OSI 7-Layers Network Reference Model by MAZHAR IQBAL BUTT .

Application Layer 7 protocols FTP

File Transfer Protocol

TFTP TFTP

Triv Trivia iall File File Tran Transf sfer er Prot Protoc ocol ol,, a simp simple le file file tran transf sfer er prot protoc ocol ol

HTTP HTTP

Hype HyperT rTex extt Trans ranspo port rt Prot Protoc ocol ol,, used used in the the Worl World d Wide Wide Web

POP3

Post Office Pro to to co col Version 3

SNM SNMP

Simp Simplle Netw Netwo ork Manage agement Prot rotocol ocol

SMTP

Simple Mail Transfer Prro ottocol

Teln Telnet et

A remo remote te term termin inal al acce access ss prot protoc ocol ol

Gnut Gnutel ella la

A peer peer-t -too-pe peer er file file-s -swa wapp ppin ing g prot protoc ocol ol

DNS

Domain Name Service

BOOTP

Boo ts tstrap Protocol

Rlogin gin

A UNIX remote login protoco l

MIME MIME

Mult Multip ipur urpo pose se Inte Intern rnet et Mail Mail Exte Extens nsio ions ns

AFP

Apple Filing Protocol

SSH

Secure SHell

IMAP IMAP

Int Intern ernet Message age Acce ccess Proto rotoco coll

NTP

Network Time Protocol

Goph Gopher er

A prec precu ursor rsor of web web searc earch h engi engine nes s

NCP

Netware Core Protocol

Fin Finger ger

Giv Gives use user profi rofile le info inform rma ation tion

NNTP NTP

New News Netw etwork ork Transf ansfe er Prot Protoc ocol ol

LDAP LDAP

Ligh Lightw twei eigh ghtt Dire Direct ctor ory y Acce Access ss Prot Protoc ocol ol

DHCP HCP

Dyn Dynamic Host ost Con Configu figura rattion ion Prot Protoc ocol ol

IRC

Internet Relay Chat

Jabb Jabbe er

An inst instan antt-me mess ssag agin ing g prot protoc ocol ol

WebD WebDAV AV

Web Web Dist Distri ribu bute ted d Auth Authori oring ng and and Vers Versio ioni ning ng

DICT

Dictionary protocol

BACn BACnet et

Buil Buildi ding ng Auto Automa mati tion on and and Cont Control rol Netw Networ ork k prot protoc ocol ol

RADIUS RADIUS

An authen authentic ticati ation, on, author authoriza izatio tion n and accoun accountin ting g protoco protocoll

DIAME DIAMETE TER R

An authen authentic ticati ation, on, author authoriza izatio tion n and accoun accountin ting g prot protoco ocoll

SIP

A signaling protocol

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PRESENTATION LAYER  This layer provides data representation and code formatting. It provides a uniform means for a remote host to inform the local client how to present the data to the application or client. It ensures that the data that arrives from the network can be used by the application, and it ensures that information send by the application can be transmitted on the network. In some cases, the presentation layer directly translates data from one format to another. Other functions that may correspond to the presentation layer are data encryption/decryption and compression/decompression. 13 ISO-OSI 7-Layers Network Reference Model by MAZHAR IQBAL BUTT .

The presentation layer is responsible for the delivery and formatting of information to the application layer for further processing or display. It relieves the syntactical differences in data representation within the end-user systems. Note: An example of a presentation service would be the conversion of an EBCDIC-coded text file to an ASCII-coded file. In many widely used applications and protocols, no distinction is made between the presentation and application layers. For example, HTTP is an application layer protocol, also identify character encoding for proper conversion in the presentation layer. 14 ISO-OSI 7-Layers Network Reference Model by MAZHAR IQBAL BUTT .

SESSION LAYER  The session layer establishes, manages and terminates session between application. It responds to service requests from the presentation layer and issues service requests to the transport layer. It provides the mechanism for managing enduser, host, application process operations and establishes check pointing, termination, and restart procedures. This layer is responsible for dialog control between nodes. Dialog is a formal conversation in which two nodes agree to exchange data. 15 ISO-OSI 7-Layers Network Reference Model by MAZHAR IQBAL BUTT .

The communications between applications across a network can take place and controlled in one of three dialog modes, are Simplex, Half-duplex, and Full-duplex.Sessions can allow traffic to go in both directions at the same time, or in only one direction at a time. Testing for out-of-sequence packets is handled also. Sessions, enable nodes to communicate in an organized manner. Each session has three phases as Connection establishment, Data transfer, Connection release. 16 ISO-OSI 7-Layers Network Reference Model by MAZHAR IQBAL BUTT .

Session Layer 5 protocols NCP

Network Control Protocol

SMB

Server Message Block

NFS

Network File System

ASP

AppleTalk Session Protocol

ADSP

AppleTalk Data Stream Protocol

DLC

Data Link Control

NP

Named Pipes

NetBIOS NWLink PAP

Printer Access Protocol

ZIP

Zone Information Protocol

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TRANSPORT LAYER  It translates system names into addresses and divides messages into fragments that fit within the size limitations established by the network. This layer is responsible for addressing, determining routes for sending, managing network traffic problems, packet switching, routing, data congestion, and reassembling data at the receiving end to recover the original message. Ensure that segments delivered will be acknowledge back to sender. 19 ISO-OSI 7-Layers Network Reference Model by MAZHAR IQBAL BUTT .

It provides retransmission of segments those are not acknowledged. Put segments back into their correct sequence at the destination. To enable packets reassembly in their original order, this layer includes a messages sequence number in its header. It allows users to segment/reassemble several upper layer application on to the same transport data stream. It insures host-to-host session connection. 20 ISO-OSI 7-Layers Network Reference Model by MAZHAR IQBAL BUTT .

In some protocol suites this layer also provides multiple conversations (multiplex) between the same two end-points. Delivery may be 'guaranteed' (streams, like TCP) or 'best effort' (datagram, like UDP). The transport layer also is responsible for delivering messages from a specific process on one computer to the corresponding process on the destination computer. In OSI terms the transport layer assigns a service access point (SAP ID) to each packet. In TCP/IP terms that is called a port port.. 21 ISO-OSI 7-Layers Network Reference Model by MAZHAR IQBAL BUTT .

One more responsibility of the transport layer is detecting errors in transmitting data. Two general categories of error detection can be performed by the transport layer: Reliable delivery : Reliable delivery does not mean that errors cannot occur, only that errors are detected if they do occur. Unreliable delivery : Unreliable delivery does not mean that errors are likely to occur, but rather indicates that the transport layer does not check for errors. 22 ISO-OSI 7-Layers Network Reference Model by MAZHAR IQBAL BUTT .

Transport Layer 4 protocols SPX

Sequenced Packet Exchange

TCP

Transmission Control Protocol

UDP

User Datagram Protocol

SCTP

Stream Control Transmission Protocol

RTP

Real-time Transport Protocol

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NETWORK LAYER  The network layer operates independently of  the physical medium, which is a concern of the physical layer.Since routers are network layer devices, they can be used to forward packets between physically different networks. When the network layer receives a message from upper layers, the network layer adds a header to the messages that includes the source and destination network address. This combination of data plus the network layer is called a packet packet.. 24 ISO-OSI 7-Layers Network Reference Model by MAZHAR IQBAL BUTT .

It translates logical addresses and names into physical addresses for Packets delivery. The addressing which makes this delivery possible can be thought of as a universal address as compared to the local addressing of  the MAC. It determines routes for sending, managing network traffic problems, packet switching, routing, data congestion, and reassembling data. 25 ISO-OSI 7-Layers Network Reference Model by MAZHAR IQBAL BUTT .

This layer may also be concerned with end-toend flow control and the segmentation and reassembly (SAR) functions for the transmission of large packets of data which exceed the maximum transmission unit (MTU) of the data link layer. The Internet Protocol (IP) is the most common example, and Novell's Internetwork Packet eXchange (IPX) is another popular implementation. 26 ISO-OSI 7-Layers Network Reference Model by MAZHAR IQBAL BUTT .

Network Layer 3 protocols IP

Internet Protocol version 4

IPv6

Internet Protocol version 6

ARP

Address Resolution Protocol

RARP

Reverse Address Resolution Protocol

ICMP

Internet Control Message Protocol

IGMP

Internet Group Management Protocol

MPLS

Multi-Protocol Label Switching

RIP

Routing Information Protocol

OSPF

Open Shortest Path First

EGP

Exterior Gateway Protocol

BGP

Border Gateway Protocol

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DATA LINK LAYER  The data link layer sends data from network layer to physical layer. Manages physical layer communications between connecting systems. It is responsible for providing node-to-node communication on a single, local network. To provide this service, the data link layer must perform two functions. 1.It must provide an address mechanism that enables messages to be delivered to the correct nodes, Also, it must translate messages from upper layer into bits that the physical layer can transmit. 2.Data units at the Data Link layer are most commonly called frames, although the term packet is used with some protocols. 28 ISO-OSI 7-Layers Network Reference Model by MAZHAR IQBAL BUTT .

The Data Link layer is comprised of a single layer in the OSI model but actually incorporates two sub-layers when viewed from the perspective of the IEEE Logical Link Control (LLC) model. The lower of the two sublayers is called the media access control (MAC) and the upper sub-layer is the LLC layer. The MAC layer provides local addressing, error correction, and in some cases includes a field to distinguish the frame type from other frame types. This component determines who is allowed to access the media at any one time. The LLC provides Service Access points (SAP) for passing off the frame to higher level. This component determines where one frame of data ends and the next one starts. Examples of data link standards include frame relay, ETHERNET, token ring, and FDDI. 29 ISO-OSI 7-Layers Network Reference Model by MAZHAR IQBAL BUTT .

Data link Layer 2 protocols ARP

Address Resolution Protocol

CDP

Cisco Discovery Protocol

DCAP

Data Link Switching Client Access Protocol

Ethernet FDDI

Fiber Distributed Data Interface

HDLC

High Level Data Link Control

L2F

Layer 2 Forwarding Protocol

L2TP

Layer 2 Tunneling Protocol

PPP

Point-to-Point Protocol

PPTP

Point-to-Point Tunneling Protocol

SLIP

Serial Line Internet Protocol

Token ring X.25 Frame relay

A simplified version of X.25

ATM

Asynchronous Transfer Mode

MPLS

Multi-Protocol label switching

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PHYSICAL LAYER  This transmits data over a physical medium or on network hardware, like cables, cards, etc. This layer relates the electrical, optical, mechanical and functional interface to the cable. It is responsible for transmitting bits (zero & ones) from one computer to another. This layer is concerned with the signaling of the message and the interface between the sender or receiver and the medium. It is defined by one of the standards bodies and carries a designation that indicates the characteristics of the connection. Among frequently used physical layers standards are EIA-232D, ITU V.35, and some of the X series (X.21/X.21bis). 31 ISO-OSI 7-Layers Network Reference Model by MAZHAR IQBAL BUTT .

Physical Layer 1 protocols ISDN

Integrated Services Digital Network

PDH

Plesiochronous Digita ital Hierarchy, T-c T-carrie rier (T1, T3 etc)

RSRS-232 232

A seri erial line line inter nterfa face ce orig riginal inally ly deve develloped oped to connec nnectt modems and computer terminals

SDH

Synchronous Digital Hierarchy

SONET

Synchronous Optical NETworking

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MNEMONICS The following mnemonics may help you remember the layers sequence and names: 1."People Design Networks To Send Packets Accurately" 2."Please Do Not Take Sales People's Advice" 3."Always Put Some Thought Into Designing Programs" 34 ISO-OSI 7-Layers Network Reference Model by MAZHAR IQBAL BUTT .