NET 02 Network Architec

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1Electronic Engineering

ELE4NET: Network Arch +Protocols

Lecture 2:

Network Architecture and Protocols


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Protocols

Protocols are the rules or conventions for exchanging data. A protocol is used for communication between entities in

different systems.

Examples of entities are: User application programs

File transfer packages

e-mail programs

Examples of systems are: Computer systems

Terminals

The key features of a protocol: Syntax: data format

Semantics: control information and error handling

Timing: speed matching and sequencing


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Network Architecture

Communication between two entities can involve complexprocedures. Instead of a single module implementation, thecommunication task is better performed if broken intosubtasks.

In a network architecture, the modules are arranged in avertical stack. Each layer in the stack performs a related

subset of functions. Each layer relies on the next lower layer to perform more

primitive functions and conceal details of those functions.It provides services to the next higher layer.

Layers are functionally independent and have defined

interface to layers above and below. Structure designs are made up of layers, specified byprotocols.

Communication is achieved by having the correspondinglayers in two systems communicatepeer-to-peercommunication.


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Simple Three Layer Network

In general terms, communications involve three agents Applications (eg. file transfer)

Computers (eg. PCs & servers)

Networks

Communication tasks are organized into three layersNetwork access layer

Exchange of data between a computer and the network

Transport layer

Reliable data transfer Common layer shared by all applications

Application layer Contains logic to support user applications


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Simple Three Layer Network (contd)

Modules at the same level(peers) on different computers

communicate with each other

by means of a protocol


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Simple Three Layer Network (contd)

An application at

port 1 of computer A

wishes to send a

message to another

application at port 2

of computer B

Two levels ofaddressing: Each computer on

the network has aunique networkaddress

Each application ona computer has aunique addresswithin thatcomputer (serviceaccess points(SAPs) or ports)


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Protocol Data Unit (PDU)

The combination of data and control information

is a protocol data unit (PDU)

Typically control info is contained in a PDU

header Encapsulation

Addition of control info to data


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TCP/IP Protocol Architecture

Developed by US Defence Advanced Research ProjectsAgency (DARPA).

It is a research and development result on the

experimental packet-switched network, ARPANET.

Used as Internet standards.

TCP/IP does not have an official layer model but it

does have a working layer model:

Application layer

Host-to-host, or transport layer Internet layer

Network access layer

Physical layer


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The TCP/IP Layers (contd)

2. Network Access Layer

Exchange of data between an end system (server, work

station, etc) and attached network

Concerned with issues like :

destination address provision

invoking specific services like priority

access to & routing data across a network link between two

attached systems

Allows layers above to ignore link specifics


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3. Internet Layer

Routing functions across multiple networks to allow data

to traverse systems attached to different networks.

Using the Internet Protocol (IP)

The IP is implemented in end systems and routers.

A router is a processor that connects two networks and

whose primary function is to relay data between them.


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4. Transport Layer

Common layer shared by all applications

Provides reliable delivery of data (all of the data arrive at

the destination application and the data arrive in the same

order in which they were sent)

Using the Transmission Control Protocol (TCP)

5. Application Layer

Provides support for user applications

Needs a separate module for each different type of

application


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Operation of TCP/IP


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TCP/IP Addressing Requirements

Two levels of addressing required

Each host on a subnetwork needs a unique global network

address

its IP address

so as to allow data to be delivered to the proper host

Each process/application on a (multi-tasking) host needs a

unique address within the host

known as a port

so as to allow TCP to deliver data to the proper process

l i ( ) i h


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Protocol Data Units (PDUs) in the

TCP/IP Architecture

Protocol Data units

User

Data

Application

Data

TCP

Segment

Network Packet

IP Datagram

TCP

Header

IPHeader

Network

Header

Application Data Bit Stream

Data "Chunk"


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Transmission Control Protocol (TCP)

TCP is the transport layer protocol for most applications Provides a reliable connection (logical connection) for

transfer of data between applications

A TCP segment is the basic protocol unit

For the duration of the connection each entity tracks TCPsegments coming and going to the other entity

TCP header


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User Datagram Protocol (UDP)

An alternative to TCP No guaranteed delivery

No preservation of sequence

No protection against duplication

Minimum overhead Because it is connectionless, UDP has very little to do.

Essentially, it adds port addressing to IP

UDP header


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IP and IPv6

IP header

IPv6 header

32-bit source and

destination addresses

128-bit source and

destination addresses


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IPv6

Provides enhancements over existing IP

Designed to accommodate higher speeds and the

mix of data streams, including graphic and video

Driving force was the need for more addressesdue to the growth of the Internet and of private

networks attached to the Internet

IPv6 includes 128-bit source and destination

address fields


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ELE4NET: Network Arch +

Protocols

TCP/IP Applications

A number of standard applications operating on top of TCP,

for example,

Simple Mail Transfer Protocol (SMTP)

A basic electronic mail transport facility for transferring messages among

separate hosts. The target SMTP module will store the incoming messagein a user's mailbox.

File Transfer Protocol (FTP)

Send files from one system to another under user command. Both text

and binary files are accommodated.

Telnet

Provides a remote logon capability, which enables a user at a

terminal or PC to logon to a remote computer and function as if

directly connected to that computer.


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Protocols

Some TCP/IP Protocols


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Protocols

TCP/IP Layers and Example Protocols


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Protocols

Open Systems Interconnection (OSI) Model

The InternationalOrganisation for

Standardisation (ISO)

recognised the

importance of the needfor a universal network

architecture and

developed the OSI model

in the early 80s.

The OSI model consists

of seven layers.

Application

Physical

Data Link

Network

Transport

Session

Presentation

User Software

Physical Interconnect Medium

Layer

7

1

2

3

4

5

6

System 1

Application

Physical

Data Link

Network

Transport

Session

Presentation

User Software Unit

Exchanged

Message

System 2

Packet

Message

Message

Message

Bit

Frame

Application Protocol

Presentation Protocol

Session Protocol

Transport Protocol

Network Protocol

D.L. Protocol

Communications Path


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Protocols

The OSI Layers

1. Physical Layer Provides transparent bit transmission of data over physical medium

Signal encoding/modulation

There are 4 important properties:

a) Procedural

Sequence of events by which bit streams exchange

b) Functional

Specifies the functionality of the hardware in interface

c) Electrical

Specifies the electrical levels representing bits, data rate, etc.d) Mechanical

Indicates the mechanical connection to the physical transmissionmediumconnector type, pin connections, etc.


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Protocols

The OSI Layers (contd)

2.Data Link Layer Transmits/receives the raw bit stream to/from the physical

layer.

Provides error correction and control service for higherlayers

Must provide the functions: flow control

error handling

framing of data

Examples of data link protocols are: High-level Data Link ControlHDLC

Link Access ProtocolBalancedLAPB (used in packet switching)

Logical Link ControlLLC (used in LAN protocol architecture)


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Protocols


3. Network Layer Provides for the transfer of information across

some sort of network

Vast range of possibilities for network layer

Simple point-point system Single network

Complex connection across multiple networks(internetworking)

Provides the upper layers with independence fromdata transmission and switching technologies

Responsible for establishing, maintaining andterminating connections


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Protocols


Layers 1,2 & 3 are sometimesgrouped together as thecommunications subnet.

One example of this groupingis the X.25 packet switchingstandard whose functionality is

specified on 3 levels: Physical level (standard used:

e.g., X.21, EIA-232)

Link level (standard used:LAPB)

Packet level (providing a

virtual circuit service)

Another example is the LANarchitecture, described by theIEEE 802 model.


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Protocols


4. Transport Layer Provides end-to-end transport of data that shields

upper layers from the details of the interveningnetwork(s). It is a connection oriented service:

maps transport addresses to network addresses

multiplexes transport connections onto the network(s)

end-to-end error recovery

segmentation and blocking

flow control of individual transport connection oftransport layer to network layer

expedited data transfer


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Protocols


5. Session Layer The lower layers provide reliable exchange of data in an

expedited service. The session layer provides a means of

controlling the data flow.

Establishes, manages and terminates connections(sessions) between cooperating applications.

6. Presentation Layer

Provides data transformation services:

Compression

Encryption

Peripheral device coding (device drivers)


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Protocols


7. Application Layer

Specifies the user interface so a user program can

interface to the application layer

Provides the definition for a user application to access

the lower layers

General programs such as file transfer, mail and

terminal access reside in this layer

P l A hi F k


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Protocols

Protocol Architecture as a Framework

for Standardisation The overall

communicationsfunction isdecomposed intomodules.

Info hiding: Lower layers

are concernedwith greaterlevels of detail.

Upper layers areindependent ofthese details.

Each layerprovides services

to the nexthigher layer andimplements a

protocol to thepeer layer inother systems.


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OSI vs TCP/IP

There are a number of reasons why

the TCP/IP architecture has come to

dominate The key TCP/IP protocols were mature

and well tested at a time when similar

OSI protocols were in the development

stage. When businesses began to

recognize the need for interoperability

across networks, only TCP/IP was

available and ready to go. The OSI model is unnecessarily complex.

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