bent 3173 chapter 2.pdf

8/18/2019 BENT 3173 Chapter 2.pdf

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Chapter Contents

Protocol architecture & operation

TCP/IP

OSI

Standards

2BENT 3173 DATA COMMUNICATIONS & NETWORKING


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BENT 3173 DATA COMMUNICATIONS & NETWORKING


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How to Communicate ?

Dr Wong

Interested in XY

Speaks only Chinese

Dr Raymond Expert in XY

Speaks only French

Ms Leong

Chinese-English

translator

Mr Henry

French-English

translator

Chinese

document

Exchanging

documents

in English

French

document

Discussing XY

research in China



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Why Need Protocol Architecture?

• File transfer

• Source must activate communication path or inform network of the identity of

the desired destination

• Source must ascertain that the destination is prepared to receive data

• File transfer application on source must ascertain that the destination’s filemanagement program is prepared to accept and store file

• May need file format translation if file format used on source & destination are

incompatible

• Instead of implementing in single module, the task is broken into

subtasks

• Each subtask is implemented separately



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Protocol Architecture

• Modules arranged in vertical stack

• Each layer performs a subset of the

functions required to communicate with

another system

• Relies on the next lower layer to perform

more primitive functions & to conceal the

details of those functions

• Provides services to the next higher layer

• Changes in one layer should not requirechanges in other layers

Subtask A

Subtask B

Subtask C

Layer 3

Layer 2

Layer 1



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Protocol

• Data communication usually occurs between entities in different

system

• Entities : anything capable of sending or receiving information

• Different entities can’t simply send data to each other & expect to be understood

• For communication to occur, the entities must agree on a protocol

• Protocol : set of rules or conventions that allow peer layers to

communicate



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Key Elements of a Protocol

• 3 elements of a protocol are :

• Syntax

• Refers to structure/format of the data

•Semantics

• Refers to the meaning of each section of bits

• Includes control information for coordination & error handling

• Timing

• Refers to when data should be sent & how fast they can be

sent

• Includes sequencing and speed matching



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Protocol Architecture

• The same set of layered functions must exist in two systems if those systems

want to communicate

• Communication is achieved by having the peer layers in the two systems

communicate

• The peer layers communicate by means of formatted blocks of data that obey aset of rules conventions known as a protocol

Subtask A

Subtask B

Subtask C Layer 3

Layer 2

Layer 1

Subtask A

Subtask B

Subtask C

Communications

network



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Standardized Protocol Architectures

• Required for devices to communicate

• Vendors have more marketable products

• Customers can insist on standards based equipment

• Two standards:

• TCP/IP protocol architecture

• OSI model

• Also:

• Internetwork Packet eXchange/Sequenced Packet eXchange

(IPX/SPX),• NetBIOS Enhanced User Interface (NetBEUI)

• AppleTalk

• IBM Systems Network Architecture (SNA)



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TCP/IP Model

• Transmission Control Protocol / Internet Protocol

• Result of protocol research & development conducted on the

experimental packet-switched network, ARPANET, funded by

Defence Advanced Research Projects Agency (DARPA)• Generally referred as the TCP/IP protocol suite

• Consists of a large collection of protocols that have been issued

as Internet standards by the Internet Architecture Board (IAB)

• Most widely used interoperable network protocol architecture



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TCP/IP Model

Physical

Network access

Internet

Layer 1

Transport

Application

Layer 2

Layer 3

Layer 4

Layer 5



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TCP/IP Layers

Physical

Network access

Internet

Transport

Application

Physical layer

Covers the physical interface between a data

transmission device (e.g. workstation, computer) &

transmission medium or network

Concerns with specifying the characteristics of the

transmission medium, nature of the signals, data

rate etc



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TCP/IP Layers

Physical

Network access

Internet

Transport

Application

Network Access layer

Concerns with the exchange of data between end

system (server, workstation, etc) and the network

to which it is attached

Concerns with access to and routing data across a

network for two end systems attached to the same

network



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TCP/IP Layers

Physical

Network access

Internet

Transport

Application

Internet layer

Implements procedures needed to allow data to

travel across multiple interconnected networks

Internet Protocol (IP) is used to provide routing

function across multiple networks

Implemented in end systems and routers


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TCP/IP Layers

Physical

Network access

Internet

Transport

Application

Transport layer

Concerns about the reliability requirement of

exchanged data

E.g. Data arrive at destination application, in thesame order in which they were sent

Transmission Control Protocol (TCP) is the most

commonly used protocol to provide reliability


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TCP/IP Layers

Physical

Network access

Internet

Transport

Application

Application layer

Responsible for providing services to the user

Contains the logic needed to support various user

applications

Example of applications :

Simple Mail Transfer Protocol (SMTP)

File Transfer Protocol (FTP)

TELNET




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TCP/IP Layers and Protocol Examples


Provides ccess to the

TCP/IP environment for

users and also provides

distributed information

services.

Application

Transfer of data between

end points. May provide

error control, flow control,

congestion control, reliable

delivery.

Transport

Shield higher layers from

details of physical network

configuration. Provides

routing. May provide QoS,

congestion control.

Internet

Logical interface to actual

network hardware. May be

stream or packet oriented.

May provide reliable

delivery.

Network Access

Transmission of bit stream;

specifies medium, signal

encoding technique, data

rate, bandwidth, and

physical connector.

Physical

Twisted pair, optical fiber, satellite,

terrestrial microwave

Ethernet, WiFi, ATM, frame relay

IPv4, IPv6

TCP, UDP

SMTP, FTP, SSH, HTTP

ARP

ICMP,

OSPF,

RSVP



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Operations of TCP/IP

• For successful communication, two levels of addressing are

needed

• Each host on a subnetwork must have a unique global

internet address IP address• Each process with a host must have an address that is

unique within the host to allow TCP to deliver data to proper

process ports




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Router J

TCP

IP

Physical Physical

IP

NAP 1 NAP 2

Physical Physical

Network Access

Protocol #1

Host A

App XApp Y

TCP

IP

Network Access

Protocol #2

Host B

App YApp X

Network 1 Network 2

Global internet

address

1 2 2 4 63

Subnetwork attachment

point address

Logical connection

(e.g., virtual circuit)

Logical connection

(TCP connection)

Port

A process associated with

port 3 at host A wishes to

send a message to another

process, associated with port

2 at host B



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Router J

TCP

IP

Physical Physical

IP

NAP 1 NAP 2

Physical Physical

Network Access

Protocol #1

Host A

App XApp Y

TCP

IP

Network Access

Protocol #2

Host B

App YApp X

Network 1 Network 2

Global internet

address

1 2 2 4 63


point address

Logical connection


Logical connection

(TCP connection)

Port

The process at A hands the

message down to transport

layer with instructions to

send it to port 2 host B



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Router J

TCP

IP

Physical Physical

IP

NAP 1 NAP 2

Physical Physical

Network Access

Protocol #1

Host A

App XApp Y

TCP

IP

Network Access

Protocol #2

Host B

App YApp X

Network 1 Network 2

Global internet

address

1 2 2 4 63


point address

Logical connection


Logical connection

(TCP connection)

Port

TCP in transport layer

hands the message down

to Internet layer with

instructions to send it to

host B

IP in Internet layer need not be

told the identity of the

destination port, it only needs

to know that the data are

intended for host B



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Router J

TCP

IP

Physical Physical

IP

NAP 1 NAP 2

Physical Physical

Network Access

Protocol #1

Host A

App XApp Y

TCP

IP

Network Access

Protocol #2

Host B

App YApp X

Network 1 Network 2

Global internet

address

1 2 2 4 63


point address

Logical connection


Logical connection

(TCP connection)

Port

IP hands the message

down to network

access layer with

instructions to send it

to router J



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To control this operation, control information as

well as user data must be transmitted

The sending process generates a block of data &

passes this to transport layer

TCP may break this block into smaller pieces to

make it more manageable

To each of these pieces, TCP appends control

information known as TCP header, forming a TCP

segment

The control information is to be used by the peer

TCP protocol entity at host B


TCP

IP

Physical

Network Access

Protocol #1

Host A

App XApp Y

1 2 3



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Items in the TCP header include the following :

Destination port

Sequence number

Checksum

Next TCP hands each segment to Internet layer with

instructions to transmit it to host B

Application byte stream

TCP segmentCPheader

User data


TCP

IP

Physical

Network Access

Protocol #1

Host A

App XApp Y

1 2 3



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IP appends a header of control information to each

segment to form IP datagram

IP header contains the destination host address (inthis example is host B)

Each IP datagram is presented to the network access

layer for transmission across the first subnetwork in its

journey to the destination


TCP segment

IP

header

IP datagram

TCP

header

User data


TCP

IP

Physical

Network Access

Protocol #1

Host A

App XApp Y

1 2 3



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NA layer appends its own header, creating a packet or frame The packet is transmitted across the subnetwork 1 to router J

Items that may be contained in network access header :

Destination subnetwork address

Facilities requests, e.g. priority


TCP segment

IP

header

IP datagram

Network

header

Network-level packet

TCP

header

User data


TCP

IP

Physical

Network Access

Protocol #1

Host A

App XApp Y

1 2 3



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Router J

TCP

IP

Physical Physical

IP

NAP 1 NAP 2

Physical Physical

Network Access

Protocol #1

Host A

App XApp Y

TCP

IP

Network Access

Protocol #2

Host B

App YApp X

Network 1 Network 2

Global internet

address

1 2 2 4 63


point address

Logical connection


Logical connection

(TCP connection)

Port


At router J, the packet

header is stripped off and

the IP header is examined

Base on destination

address info in the IP

header, the IP module inthe router directs the

datagram out across

subnetwork to host B

To do this, the datagram is

again encapsulated with a

network access header




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Router J

TCP

IP

Physical Physical

IP

NAP 1 NAP 2

Physical Physical

Network Access

Protocol #1

Host A

App XApp Y

TCP

IP

Network Access

Protocol #2

Host B

App YApp X

Network 1 Network 2

Global internet

address

1 2 2 4 63


point address

Logical connection


Logical connection

(TCP connection)

Port


When the data are

received at B, the

reverse process occurs

At each layer, the

corresponding header is

removed, and the remainder is

passed on to the next higher

layer until the original userdata are delivered to the

destination process




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OSI Reference Model

• Open System Interconnection OSI) reference model

• Designed by International Organization for Standardization

(ISO)

• A seven-layer model

• Never seriously implemented as a protocol stack

• A theoretical model designed to show how a protocol stack

should be implemented



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OSI Reference Model

Physical

Data Link

Network

Layer 1

Transport

Session

Presentation

Application

Layer 2

Layer 3

Layer 4

Layer 5

Layer 6

Layer 7



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OSI vs TCP/IP

Physical

Data Link

Network

Transport

Session

Presentation

Application

Physical

Transport

Application

Internet

Network access



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OSI Reference Model

Physical

Data Link

Network

Transport

Session

Presentation

Application

Application layer Provides access to the OSI

environment for users and also

provides distributed information

services



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OSI Reference Model

Physical

Data Link

Network

Transport

Session

Presentation

Application

Presentation layer Provides independence to the

application processes from

difference in data representation

(syntax)


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OSI Reference Model

Physical

Data Link

Network

Transport

Session

Presentation

Application

Transport layer Provides reliable, transparent

transfer of data between end

points; provides end-to-end error

recovery and flow control



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OSI Reference Model

Physical

Data Link

Network

Transport

Session

Presentation

Application

Network layer

Provides upper layers with

independence from the data

transmission and switching

technologies used to connect

systems; responsible for

establishing, maintaining and

terminating connection


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OSI Reference Model

Physical

Data Link

Network

Transport

Session

Presentation

Application

Physical layer

Concerned with transmission of

unstructured bit stream over

physical medium; deals with the

mechanical, electrical, functional

& procedural characteristics to

access the physical medium



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OSI Environment



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OSI Environment

• Each system contains the 7 layers

• Communications is between applications in the two computers, labeled

application X and application Y

• If application X wishes to send a message to application Y , it invokes the

application layer (layer 7)

• Layer 7 establishes a peer relationship with layer 7 of the target

computer using layer 7 protocol (application protocol)

• This protocol requires services from layer 6, so the two layer 6 entities

use a protocol of their own, and so on down to the physical layer, whichactually transmits bits over a transmission medium.



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OSI Environment

• No direct communication between peer layers except at the

physical layer

• Use of protocol data unit (PDU) within OSI architecture

•

PDU – combination of data from the next higher layer and control information

• When X has a message to send to Y, it transfers those data to

application layer (layer 7)

• A header is appended to the data that contains requiredinformation for the peer layer application protocol –

Encapsulation



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OSI Environment

• The original data plus header are now passed as a unit to presentation

layer (layer 6)

• The layer treats the whole unit as data and appends its own header

(second encapsulation)

• This process continues down through data link layer (layer 2) which

generally adds both a header & trailer

• This layer 2 unit, called a frame, is then passed onto the transmission

medium by the physical layer



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OSI Environment

• When the frame is received by the target system, the reverse process

occurs

• As the data ascend,

• each layer strips off the outermost header

• acts on the protocol information contained therein

• and passes the remainder up to the next layer



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Standards

• Required to allow for interoperability between equipment

• Provide guidelines to manufacturers, vendors, government agencies &

other service providers to ensure interconnectivity in international

communications

• Advantages

• Ensures a large market for equipment and software

• Allows products from different vendors to communicate

• Disadvantages

• Freeze technology

• May be multiple standards for the same thing



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Standards Organizations

• International Organization for Standardization (ISO)

• Multinational body

• Membership drawn mainly from standards creation committees of various governments

throughout the world

• Active in developing cooperation in the realms of scientific, technological and economic

activity

• International Telecommunication Union – Telecommunication

Standards Sector (ITU-T)

• Formerly Consultative Committee for International Telegraphy and Telephony (CCITT)

•UN agency

• Research & establishment of standards for telecommunications



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Standards Organizations

• Institute of Electrical & Electronics Engineers (IEEE)

• Largest professional engineering society in the world

• One of its goal : Oversees development & adoption of international standards for

computing & communications

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