network models.ppt

7/30/2019 Network Models.ppt

1/38

2.1

2 LAYERED TASKS

We use the concept of layers in our daily life.

As an example, let us consider two friends who

communicate through postal mail. The process of

sending a letter to a friend would be complex if

there were no services available from the postoffice.

NETWORK MODELS

LAYERED TASK


2/38

2-1 LAYERED TASKS

Figure 2.1 Tasks involved in sending a letter2.2


3/38

2-2 THE OSI MODEL

1. Established in 1947, the International Standards

Organization (ISO) is a multinational bodydedicated to worldwide agreement on international

standards.

2. An ISO standard that covers all aspects of

network communications is the Open SystemsInterconnection (OSI) model. It was first

introduced in the late 1970s.

3. ISO is the organization. OSI is the model.

4. Topics to be covered:1. Layered Architecture

2. Peer-to-Peer Processes

3. Encapsulation

2.3


4/38

Figure 2.2 Seven layers of the OSI model

2.4


5/38

2-2 THE OSI MODEL

Why use a layered approach ?

Data communications requires complex procedures

Sender identifies data path/receiver

Systems negotiate preparedness

Applications negotiate preparedness

Translation of file formats

For all tasks to occur, a high level of cooperation is

required Provide framework to implement multiple specific

protocols per layer

2.5


6/38

2-2 THE OSI MODEL

Advantages of Layering

Easier application development

Network can change without all programs being

modified

Breaks complex tasks into subtasks Each layer handles a specific subset of tasks

Communication occurs

between different layers on the same node or stack(INTERFACES)vertical communications

between similar layers on different nodes or stacks

(PEER-TO-PEER PROCESSES) horizontal

communications2.6


7/38

Figure 2.3 The interaction between layers in the OSI model

Network

support

layers

User

support

layers

2.7


8/382.8

Figure :


9/38

Figure 2.4 An exchange using the OSI model

2.9


10/38

2-3 LAYERS IN THE OSI MODEL

Figure 2.5 Physical layer

The physical layer is responsible for movements of

individual bits from one hop (node) to the next.

2.10


11/382.11

Function of The Physical layer H/W Specifications

Physical representation of Interfaces & media - Fibre/ CAT etc

Encoding and Signalling

Representation of bits Data rate Transmission Rate

Data Transmission and Reception

Synchronization of bits Clock thing Line configuration Point to Point / Multi etc /

shared or dedicated

Topology and N/W Design


12/38

Figure 2.6 Data link layer

The data link layer is responsible for moving

frames from one hop (node) to the next.

2.12


13/382.13

Function of The Data link layer

Framing

Physical addressing

Acknowledgement

Sequence Numbering

Flow control

Error control Retransmission

Access control


14/38

Figure 2.7 Hop-to-hop delivery

2.14


15/38

Figure 2.8 Network layer

The network layer is responsible for the delivery of

individual packets from the source host to the

destination host.

2.15


16/382.16

Function of The Network layer

Logical addressing

Internetworking

Routing


17/38

Figure 2.9 Source-to-destination delivery

2.17


18/38

Figure 2.10 Transport layer

The transport layer is responsible for the delivery

of a message from one process to another.

2.18


19/382.19

Function of The Transport layer

Service point addressing

Segmentation & reassembly

Connection control Flow control

Error control


20/38

Figure 2.11 Reliable process-to-process delivery of a message

2.20


21/38

Figure 2.12 Session layer

The session layer is responsible for dialog

control and synchronization.

2.21


22/38

2.22

Function of The Session layer

Dialog control

Synchronization


23/38

Figure 2.13 Presentation layer

The presentation layer is responsible for translation,

compression, and encryption.

2.23


24/38

2.24

Function of The Presentation layer

Translation

Encryption

Compression


25/38

2.25


26/38

Figure 2.14 Application layer

The application layer is responsible for

providing services to the user.

2.26


27/38

2.27

Function of The Application layer

Network virtual terminal

File transfer, access management (FTAM)

Mail services Directory services


28/38

Figure 2.15 Summary of layers

2.28


29/38

2.29

Comparison of the OSI & TCPreference Models The OSI has seven layers while TCP/IP has five layers.

The OSI supports both connectionless and connection-oriented communication in the network layer but onlyconnection-oriented in the transport layer which is

visible to the user. TCP/IP supports only connectionlessservices on the network layer but gives options in thetransport layer for both connectionless and connection-oriented services. The later option is a very important

and useful factor.Network layer Transport layer

OSI C.O. & C.L C.O.

TCP/IP C.O. C.O. & C.L


30/38

2.30

Comparison of the OSI & TCP reference Models

The OSI reference model was devised beforethe protocols wereinvented while The TCP/IP the reverse was true: the protocol came

first, and the model was really just a description of the existingprotocols. Three concepts are central to the OSI model: 1.Services 2. Interfaces 3. Protocols

The servicedefine what the layer does, not how entities above itaccess it or how the layer works.

The Interfacetells the process above it how to access it.The Protocolsused in the layer are the layers own business. It canuse any protocols it wants to , as long as it gets the job done. It canalso change them at will without affecting software in higher layers.While The TCP/IP model did not originally clearly distinguishbetween services, interfaces and protocols.

The protocols in the OSI model are better hidden than in the TCP/IPmodel and can be replaced relatively easily as the technologychanges.

2 4 C / O OCO S


31/38

2-4 TCP/IP PROTOCOL SUITE

1. The layers in the TCP/IP protocol suite do not

exactly match those in the OSI model. The originalTCP/IP protocol suite was defined as having four

layers: host-to-network, internet, transport, and

application.

2. However, when TCP/IP is compared to OSI, we can

say that the TCP/IP protocol suite is made of five

layers: physical, data link, network, transport, and

application.3. Topics covered:1. Physical and Data Link Layers

2. Network Layer3. Transport Layer

4. Application Layer2.31


32/38

Figure 2.16 TCP/I P and OSI model

2.32

2 5 ADDRESSING


33/38

2-5 ADDRESSING

Four levels of addresses are used in an internet

employing the TCP/IP protocols: physical, logical, port,and specific.

Topics discussed in this section:

Figure 2.17 Addresses in TCP/I P

2.33


34/38

Figure 2.18 Relationship of layers and addresses in TCP/I P

2.34


35/38

1. A node with physical address 10 sends a frame to a

node with physical address 87. The two nodes are

connected by a link (bus topology LAN).

2. The computer with physical address 10 is thesender, and the computer with physical address 87

is the receiver.

3. In most data link protocols, the destination address

(87) comes before the source address (10).

Figure 2.19 Physical addresses

2.35


36/38

Most local-area networks use a 48-bit (6-byte) physicaladdress written as 12 hexadecimal digits; every byte (2

hexadecimal digits) is separated by a colon.

07:01:02:01:2C:4B

A 6-byte (12 hexadecimal digits) physical address.

2.36


37/38

Figure 2.20 I P addresses

2.37


38/38

Figure 2.21 Por t addresses

Read k in place

of a

network models.ppt

Documents