CHAPTER 3 : OSI MODEL - Universiti Putra Malaysiacsnotes.upm.edu.my/kelasmaya/web.nsf/0269bceb436307ce... · OSI Layer TCP/IP Protocol Suite ... Lecture notes SKR 3200 Idawaty Ahmad

Lecture notes  SKR 3200

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CHAPTER 3 : OSI MODEL

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OSI Layer

TCP/IP Protocol Suite

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CHAPTER 3 : THE OSI MODEL

Established in 1947, the ISO is a multinational bodydedicated to worldwide agreement on international

d d

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standard ISO standard which covers all aspects of network

communications – OpenOpen SystemsSystems InterconnectionInterconnection (OSI)(OSI)model

OpenOpen SystemSystem – a model that allows any two differentsystems to communicate regardless of their underlyingarchitecture

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OSI is not a protocol Model for understanding and designing a network

architecture that is flexible, robust, and interoperable

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3.1 THE MODEL

OSI – a layered framework for design of networksystems that allows for communication across allt f t t

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types of computer system 7 layer architecture Intermediate nodes – involve only the first three

layers Peer-to-Peer Process?

Layer n, use the services provided by layer n-1 andprovides services for layer n+1Th h hi th t i t t

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The process on each machine that communicate at agiven layer are called peer-to-peer process

Use protocol

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3.1 THE MODEL

At sending machine: headers added to the message at L6,5,4,3,2

7/26/2009g Trailer is added at only L2

At receiving machine The message is unwrapped layer by layer, received

process and removing the data meant for it.(reverse ofsending machine)

Interfaces between layers – control the passing of

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the data and network information down/up throughthe layers of sending/receiving machine

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3.1 THE MODEL

The 7L can grouped into three subgroup L1,2,3 – the network support layer – deal with the physical

7/26/2009pp y p yaspects of moving data from one device to another

L5,6,7 – the user support layer –allow interoperabilityamong unrelated software systems

L4 – ensures end-to-end reliable data transmission After pass through L1 of sending machine, the data

unit is changed into electromagnetic signal andt t d l h i l li k

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OSI Model

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MODEL RUJUKAN OSI7/26/2009

Presentation

Session

Transport

Application

Connection/less multiplexConnection/less multiplex flowflow dandan error controlerror control

Aplikasi Web, SMTP, FTP,Telnet,IRC,News dllAplikasi Web, SMTP, FTP,Telnet,IRC,News dll

Komunikasi yang selamat: Secure Socket Layer (SSLKomunikasi yang selamat: Secure Socket Layer (SSL))

Data compression,encryption, character representationData compression,encryption, character representation

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Network

Data Link

Physical FDDI,ATM, Ethernet, Token Ring, Dialup,wirelessFDDI,ATM, Ethernet, Token Ring, Dialup,wireless

Topologi Rangkaian,Pengalamatan, Topologi Rangkaian,Pengalamatan, ErrorError, , flow controlflow control

Penghantaran paket ke destinasiPenghantaran paket ke destinasi

Connection/less, multiplexConnection/less, multiplex,,flowflow dan dan error controlerror control

Network card

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OSI Layers

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An Exchange Using the OSI Model

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KONSEP HEADER DALAM MODEL OSI

Pelayan Pelanggan

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Presentation

Session

T t

Application

Presentation

Session

Transport

Applicationdatadata

TCPheader

datadata

segment

packet

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Transport

Network

Data Link

Physical

Network card

Transport

Network

Data Link

Physical

TCPheader

datadata IPheader

p

TCPheader

datadata IPheader

frame

Ethernet header

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3.2 FUNCTION OF EACH LAYER Physical layer (L1)

Coordinates the function required to transmit a bit streamover a physical medium

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over a physical medium Deal with the mechanical/electrical spec of the interface

and transmission medium Defines the procedures and functions that physical

devices and interfaces have to perform for transmission tooccur

Concerned with: Physical characteristics of interfaces and media Representation of bits

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Representation of bits Bits must be encoded into signals –electrical or optic

Data rate –the number of bits sent each second Synchronization of bits Line configuration – connection of devices to the medium

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3.2 FUNCTION OF EACH LAYER

Concerned with:

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Physical topology How devices are connected to form a network

Transmission mode Direction of signal transmission between two devices

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The physical layer is responsible for transmitting individual bits from one

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node to the next.

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Physical Layer

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3.2 FUNCTION OF EACH LAYER Data Link Layer (L2):

Responsible for node-to-node delivery Makes appear error free to the network layer

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Makes appear error free to the network layer Responsibilities include:

Framing – divides the stream data to manageable data units –frame

Physical addressing – adds a header to the frame –to define thephysical address of sender( source address) and receiver(destination address)

Flow control – to prevent overwhelming at the receiver Error control – provides reliability – to detect and retransmit

damaged or lost frames, also prevent duplication of frames -

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Access control – require a protocol to determine which devicehas control over the link at any given time –> same link with twoor more devices connected.

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The data link layer is responsible for transmitting frames from

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one node to the next.

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Data Link Layer7/26/2009

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Example 1Example 1

In the next figure, a node with physical address 10 sends a frame to a node with h i l dd 87 Th t d

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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

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Data Link Layer Example7/26/2009

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3.2 FUNCTION OF EACH LAYER

Network Layer (L3): Responsible for the sourcesource--toto--destinationdestination deliverydelivery of a

7/26/2009p yypacket possibly across multiple networks (links)

If two systems are attached to different networks, we needthe network layer protocol to accomplish source-to-destination delivery

Specific responsibility: Logical addressing – to distinguish the source and

destination systems when a packet passes the networkboundary also known network address

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ester 1 :boundary – also known network address Routing – internetwork/large network – route the packet to

the final destination

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NN

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The network layer is responsible for the delivery of packets from the

original source to the

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Network Layer

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Network Layer Example

Example 2Example 2

In the next figure, we want to send data from a node with network address A and physical

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node with network address A and physical address 10, located on one LAN, to a node with a network address P and physical address 95, located on another LAN. Because the two devices are located on different networks, we cannot use physical addresses only; the

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physical addresses only have local jurisdiction. What we need here are universal addresses that can pass through the LAN boundaries. The network (logical) addresses have this characteristic.

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Network Layer Example

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3.2 TRANSPORT LAYER

Transport Layer (L4): Review of a network layer responsibility:

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Review of a network layer responsibility: Responsible for source-to-destination (end-to-end) delivery of

the entire message Individual packet – treats each packet independently

transport layer Ensures the whole (entire) message arrives intact and in order Oversee both error control and flow control at source-to-

destination levelTo added security transport layer create a connectionconnection

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To added security, transport layer create a connectionconnectionbetween the two end ports Connection - Single logical path between the source and

destination

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3.2 TRANSPORT LAYER

Creating connection involves 3 steps:

7/26/2009g p Connection establishment Data transfer Connection release

Has more control over sequencing, flow,error correction and detection

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3.2 TRANSPORT LAYER Specific responsibilities:

Service-point addressing Computers often run several programs at the same time

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From a specific process (running program) on one computer to aspecific process (running program) on the other

TL header must include a serviceservice--pointpoint addressaddress or portport addressaddress Segmentation and reassembly

Segment – add a sequence number into message segment Connection control

Can be either connectionless (independent packet) orconnection oriented

Flow control

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End-to-end flow control ( across multiple networks) Error control

End-to-end error control ( across multiple networks)

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The transport layer is responsible for delivery of a message from one process

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Figure : Reliable process-to-process delivery of a message

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Transport Layer

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Example 3Example 3

Figure shows an example of transport layer communication Data coming from the upper

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communication. Data coming from the upper layers have port addresses j and k (j is the address of the sending process, and k is the address of the receiving process). Since the data size is larger than the network layer can handle, the data are split into two packets, each

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Transport Layer Example

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Transport Layer Example

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3.2 SESSION LAYER

Session Layer (L5) The network dialogdialog controllercontroller

7/26/2009gg EstablishesEstablishes, maintainsmaintains, and synchronizessynchronizes the interaction

between communicating systems Responsibilities:

Dialog control allows two systems to enter into a dialog communication between two process – half-duplex or full-

duplex Synchronization

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into a stream of data E.g.: sending a file..

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Session Layer7/26/2009

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3.2 PRESENTATION LAYER

Presentation Layer (L6) Concerned with the syntax and semantics of the

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Concerned with the syntax and semantics of theinformation exchanged between two systems.

Responsibilities: Translation

The process (running programs) in two systems are usuallyexchanging information

Different computers use different encoding systems Responsible for interoperabilityinteroperability between different

encoding methods

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dependentdependent formatformat into aa commoncommon formatformat Receiver machine change the commoncommon formatformat into its

receiverreceiver--dependentdependent formatformat36

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3.2 PRESENTATION LAYER

Encryption Encryption - transform the original information to

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Encryption transform the original information toanother form and sends it over the network

Decryption - reverse process at the receiver side assure privacy - to carry a sensitive data/information

Compression Reduces the number of bits to be transmitted multimedia data transmission – such as text, audio and

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video

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Presentation Layer

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3.2 APPLICATION LAYER Application Layer (L7)

EnablesEnables useruser , whether human or software toto accessaccess thethenetworknetwork

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networknetwork Provides user interfaces and support for services such as

email, remote file access, shared database mgmt andtransfer etc

No trailer or header are added here Specific services

Network virtual terminal File transfer, access, and management (FTAM) –

access/manage/control files in a remote computer

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sources

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Application Layer

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

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Summary of Layer Functions (OSI model)

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3.3 TCP/IP PROTOCOL SUITE

Developed prior to the OSI model5 l l k I t t d l

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5 layers – also known Internet model The three topmost layers in the OSI model

are represented in TCP/IP by a single layer –applicationapplication layerlayer

TCP/IPTCP/IP is a hierarchical protocol – theupper-level protocol is supported by one or

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E.g.: @ TL – TCP, UDP; @NL - IP

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Summary of Layer Functions (TCP/IP)

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PROTOKOL SUIT TCP/IP

TCP: Transmission Control ProtocolIP I t t P t l

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IP: Internet ProtocolMenggunakan dan mendefinasi hanya 4 paras1974 Dua tujuan utama senibina TCP/IP adalah:

Untuk membentuk sambungan antara rangkaian yang berbeza pada sambungan rangkaian dan juga

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Untuk menyembunyikan segala details tentang sambungan, jenis rangkaian daripada paras aplikasi.

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TCP/IP

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Transport

ApplicationHTTP, SMTP, FTP,Telnet, POP3,IMAP, ping dllHTTP, SMTP, FTP,Telnet, POP3,IMAP, ping dll

TCP, UDP, SNMPTCP, UDP, SNMP

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Network

Link

IP, UDPIP, UDP

ATM,FDDI,Ethernet,PPP dan jenis ATM,FDDI,Ethernet,PPP dan jenis Rangkaian yang lain Rangkaian yang lain

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REVISION… Q&AS

What is peer-to-peer process?

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What is the difference between a service-point-address, a logical address, and aphysical address?

What is the purpose of translation by thepresentation layer?

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PEER-TO-PEER PROCESS

The process on each machine that communicate at a given layer.

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at a given layer.

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DIFFERENT

Service point address identifies the application process on the station at L4

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application process on the station at L4Logical address/LNA defines the sender

and receiver at L3 and is used to deliver message across multiple networks

Physical address is the local address of a node is used by L2 to deliver data from

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Definition :Specifications for the physical components

THE PHYSICAL LAYER

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Specifications for the physical components of the network

What Physical Layer Components do: Specifications for: Cabling Interconnection Methods Data Encoding Electrical Properties

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Examples Ethernet (IEEE 802.3) Token Ring (IEEE 802.5) FDDI (ANSI X3T9.5) IEEE 802.11b (Wireless)

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THE PHYSICAL LAYER

What Physical Layers Components do: Specifications for the physical components

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Specifications for the physical components of the network

Examples (What Defined) Ethernet (Physical Spec) Token Ring (Physical Spec) FDDI 802.11b (Physical Spec) T Carrier (T1)

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THE DATA LINK LAYER

What Data Link Layer Components do: Media Access Control (MAC) and Logical

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Media Access Control (MAC) and Logical Link Control (LLC)

Addresses network devices (MAC Address)

Places data in a Data Frame (packet) Gives the data bits to the NIC card (MAC)

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Controls the Network Interface Card’s (NIC) Access to the Media (MAC)

Detects transmission errors (LLC)52

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THE NETWORK LAYER

Definitions: Provides network-wide addressing and mechanism to move packets

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addressing and mechanism to move packets between multiple networks

What Networking Layer Components do: Network Addressing Move of packets between different networks – routing

Examples Internet Protocol (TCP/IP) IPX (Netware)

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packets between different networks –routing

Where is it on my computer: TCP/IP Software

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THE TRANSPORT LAYER

Definitions: Provides end-to-end communication and reliable data delivery

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communication and reliable data delivery Examples Transport Control Protocol

(TCP/IP), User Datagram Protocol (UDP) What Transport Layer Components do: Receives data from application and

segments it

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Can provide transmission error detection and correction

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THE SESSION LAYER

Definitions: Allows application to maintain an ongoing communication (session)

7/26/2009g g ( )Examples NetBIOS Netware Core Protocol What Session Layer Components do: Manage user sessions

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and Server Service Software (Windows) ,Redirector or Requestor (Netware), Windows Client for Netware (Netware)

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THE PRESENTATION LAYER

Definitions: Provides common data formatting

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Provides common data formatting between communicating devices

Examples Multipurpose Internet Mail Extensions (MIME)

What Presentation Layer Components do: Make sure the receiving station can read

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the transferred data Where is it on my computer: Workstation

or server service Email client56

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THE APPLICATION LAYER

Definitions: Gives end-user applications access to network resources

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access to network resources Examples Workstation and Server Service

Software (Windows) Windows Client for Netware (Netware)

What Application Layer Components do: Gives end-user applications access to

t k

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network resources Where is it on my computer: Workstation

or server service (Session, Presentation and Application) 57

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JENIS ALAMAT DI ANTARA RANGKAIAN

Tiga jenis alamat yang digunakan antararangkaianAlAl k k

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AlamatAlamat ParasParas Data LinkData Link:: Alamat yang membezakan tiap-tiap perkakasan dalam

rangkaian Dikenali sebagai physical atau hardware address

AlamatAlamat MACMAC :: Alamat MMedia AAccess CControl: MACMAC LebihLebih kurangkurang samasama fungsinyafungsinya dengandengan AlamatAlamat ParasParas Data Data

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AlamatAlamat IP:IP: Lanjutan tentang ini dalam kuliah yang lain kemudian

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ALAMAT MAC Panjangnya 48bits 12 digit dalam bentuk hexadecimal

Di l i l h IEEE

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Di pelopori oleh IEEE 6 digit pertama:mengenalpasti vendor atau

pembuat perkakasan tersebut (OUI: Organizationally Unique Identifier)

6 digit terakhir : Nombor siri untuk perkakasantersebut dan ditentukan oleh vendor tersebut: (Intel dsb)

Dikenali juga sebagai burned-in-address (BIAs)

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ALAMAT PARAS DATA LINK DAN ALAMATMAC

LAN 4FDDI

LAN 37/26/2009

TokenRing

LAN 2FDDIPenghala APenghala A

FDDI

T rd p t 5 l m t MACT rd p t 5 l m t MAC

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Hakcipta: Idawaty Ahmad FSKTM UPM

U N I V E R S I T YU N I V E R S I T Y

Dialup

Ring

Ethernet LAN 1

Terdapat 5 alamat MAC Terdapat 5 alamat MAC pada Penghala Apada Penghala A

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