WELCOME to COMP 421 /CMPET 401 COMMUNICATIONS and NETWORKING Class 1

WELCOME to WELCOME to COMP 421 /CMPET 401COMP 421 /CMPET 401

COMMUNICATIONS and NETWORKING

Class 1

COURSE OUTLINECOURSE OUTLINE

Overview of Communications– Introduction

– Protocols and Architecture Data Communications

– Data Transmission

– Transmission Media

– Data Encoding

– Data Link Control

– Multiplexing

COURSE OUTLINE (continued)COURSE OUTLINE (continued) Local and Wide Area Networks

– LAN & WAN Protocols

– Switching Techniques

– Bridges and Routers

– High Speed Networks

– Internetworking

– Internet Resources

Network Operating Systems

TELECOMMUNICATIONSTELECOMMUNICATIONS

The elements of a telecommunication system are:•Transmitter •Channel •Line •Receiver

The transmitter is a device that transforms or codes the message into a physical phenomenon called the transmission channel, by its physical nature it is likely to modify or degrade the signal on it path from the transmitter to the receiver.

Telecommunications is the technique of transmitting a message from one point to anotherknowing how much information, if any, is likely to be lost in the process. Hence the term TELECOMUNICATIONS covers all forms of distance communications including:

•Radio•Telegraph•Television•Telephony•Data Communications•Computer Networking


The receiver has a decoding mechanism capable of recovering the message within certain limits of signal degradation by the communication channel. Telecommunication can be point-to-point or point-to-multipoint in which case it is called conferencing. Broadcasting is a particular form of telecommunication that is point-to-multipoint

and goes predominantly from the transmitter to the receivers.

Possible imperfections in a communication channel are: Shot noise Thermal noise Latency Non linear channel transfer function Sudden signal drops Bandwidth limitations Signal reflections


The art of the telecommunications engineer is to analyze the physical properties of the transmission channel, and the statistical properties of the message, in order to design the most effective coding and decoding mechanisms.

Information theory enables us to evaluate the capacity of a communication channel according to its bandwidth and signal-to-noise ratio.

W orkstation

Cloud

Modem ModemW orkstation

HubW orkstationW orkstation

Hub

Cloud

The Communications Model

output information

Input deviceInput device TransmitterTransmitter Transmission

mediumTransmission

medium ReceiverReceiver Output DevicesOutput

Devices

input information

input data

transmitted signal

receivedsignal

output data

Communication TasksCommunication Tasks Communication Tasks Include:

– Transmission System Utilization– Interfacing– Signal Generation– Synchronization– Exchange Management– Error Correction and Detection– Flow Control– Addressing– Routing– Recovery– Message Formatting– Security– Network Management

Data Communication NetworkData Communication Network

Communication Network

Communication Network Node

Network Station

Data Communication NetworkingData Communication Networking

Networks are used to link devices together– Distant - Network is called a Wide Area Network (WAN)

Circuit Switched Packet Switched Frame Relay ATM Public Switched Telephone Network (PSTN) Leased lines Public switched data network (PSDN) Integrated services digital network (ISDN)

– Local - Network is called a Local Area Network (LAN)– Intermediate - Network is called a Metropolitan Area Network (MAN)

PSTNPSTN

modem modem

modem link via PSTN

PSTN

LANLANhubhub

hubhub

hubhub

hubhub

1st floor1st floor

2nd floor2nd floor

3rd floor3rd floor

4th floor4th floor

routerrouter

confined geographical areaconfined geographical area under single managementunder single management high data ratehigh data rate

serverserver

stationstation

stationstation

stationstation

Leased linesLeased lines• Lease pubic circuits to connect different sites• Communication channel is private

LAN

Voice

LAN

Voice

LAN

Voice

leased circuit

PSDNPSDN

PSDN= Public Switched Data Network

LAN

LAN

LAN

PSDN

• PSDN is designed specifically for the transmission of data rather than voice• Communication is shared

ISDNISDNISDN is an acronym for integrated Services Digital NetworkISDN provides integrated voice and data over the Telephone

company facilities.

Com puter

Fax

Telephone

TelcoCentralOffice

Telephone

Fax Com puter

TelcoCentralOffice

3 TelephoneLines

1 ISDNLine

StandardsStandards

Standards are required in the telecommunications industry to governthe physical, electrical and procedural characteristics of communications equipment.

Some organizations whom exist, at least partially, to create thesestandards are:

•The Internet Society•ISO•ITU-T (formerly CCITT)•The ATM Forum•IEEE

RFC - Request for Comment

StandardsStandards

Integrated computer andtelecommunications industry

Integrated computer andtelecommunications industry

ISOITU-T

International Standards(Open Systems Interconnection)

TelecommunicationsIndustry

TelecommunicationsIndustry

ITU-TCEPTANSI

Interface standards(multi-vendor systems)

ComputerIndustry

ComputerIndustry

Proprietary standards(closed systems)

ECMAEIA

IEEE

StandardsStandards

The Standardization Process of the Internet Organizations is•Be stable & well understood•Be technically competent•Have multiple independent and interoperable

implementations with substantial operational experience•Enjoy significant public support•Be recognizable useful in some or all parts of the Internet

The key difference between theses criteria and this used for the international standards from ISO and ITU-U is the emphasis on operational experience

StandardsStandards

Proposed Standard

DraftStandard

InternetStandard

Experimental International

InternetDraft

Historic

The process a specification goes through to become a standard is defined by RFC 2026

An Example – 802.11 Wireless LANAn Example – 802.11 Wireless LAN

802.11 Initial 1 & 2 Mbps802.11a High Rate 5.7Ghz802.11b 5.5 and 11 Mbps802.11c MAC Bridge802.11d Regulating Domains802.11e Quality of Service802.11f Multi-Vendor Inter-Access Port802.11g High Rate 2.4Ghz802.11h Power Control/Frequency Selection802.11i Enhanced Security802.11j 4.9-5Ghz in Japan802.11k Radio Resonance Management

TOPOLOGIESTOPOLOGIES

A network topology is the geometric arrangement of nodes and cable links in a LAN, and is used in two general configurations: bus and star. These two topologies define how nodes are connected to one another. A node is an active device connected to the network, such as a computer or a printer. A node can also be a piece of networking equipment such as a hub, switch or a router.

A bus topology consists of nodes linked together in a series with each node connected to a long cable or bus. Many nodes can tap into the bus and begin communication with all other nodes on that cable segment. A break anywhere in the cable will usually cause the entire segment to be inoperable until the break is repaired. Examples of bus topology include 10BASE2 and 10BASE5.

TOPOLOGYTOPOLOGY

Bus topology.

Mesh topology A network topology in which there are at least two nodes with two

or more paths between them.

Ring topology: A network topology in which every node has exactly two branches

connected to it.

Star topology: A network topology in which peripheral nodes are connected to a

central node, which rebroadcasts all transmissions received from any peripheral

node to all peripheral nodes on the network, including the originating node. .

Hybrid topology A hybrid network accrues only when two basic networks are

connected and the resulting network topology fails to meet one of the basic

topology definitions. For example, two star networks connected together exhibit

hybrid network topologies.

Tree topology: A network topology that, from a purely topologic viewpoint,resembles an interconnection of star networks in that individual peripheralnodes are required to transmit to and receive from one other node only,toward a central node, and are not required to act as repeaters orregenerators.

Computer NetworksComputer NetworksA computer network is a system for communication among two or more computersComputer network may be categorized by Range:

PANLANMANWAN

Computer network applications may be categorized with respect to the functional relationships between components:

•Client-server•Multi-tier architecture•peer to peer

PANsPANs

A personal area network (PAN) is a computer network used forcommunication among computer devices (including telephones andpersonal digital assistants) close to one person. The devices may ormay not belong to the person in question. The reach of a PAN istypically a few meters. PANs can be used for communication amongthe personal devices themselves (intrapersonal communication), orfor connecting to a higher level network and the Internet (an uplink).

Personal area networks may be wired with computer buses such asUSB and Firewire. Wireless PANs can also be made possible withnetwork technologies such as IrDA and Bluetooth.

MANsMANs

Metropolitan area networks or MANs are large computernetworks usually spanning a campus or a city. Common technologiesused for this purpose are Asynchronous Transfer Mode, Fiberdistributed data interface and Switched multimegabit data service andmore recently gigabit Ethernet.

Distances between 5 and 50 kmDistances between 5 and 50 km

Data rate above 1 MbpsData rate above 1 Mbps

Standards: IEEE 802.6 DQDB, FDDI, and ATMStandards: IEEE 802.6 DQDB, FDDI, and ATM

LANs (Local Area Networks)Maximum distance not more than a few kmsMaximum distance not more than a few kms

Ownership by a single organizationOwnership by a single organization

Transmission speed of at least several Mbps (tens to hundreds are Transmission speed of at least several Mbps (tens to hundreds are economical)economical)Some widely used standards include:Some widely used standards include:

IEEE 803.3 - EthernetIEEE 803.3 - Ethernet

IEEE 803.5 - Token ringIEEE 803.5 - Token ring

FDDIFDDI

ATM ATM

An important issue in broadcast LANs is the allocation of the shared channel An important issue in broadcast LANs is the allocation of the shared channel (media access control)(media access control)

Control may be static (time division multiplexing) or dynamic (contention or Control may be static (time division multiplexing) or dynamic (contention or arbitration)arbitration)

WANs (Wide Area Networks)

Often a network is located in multiple physical locations. Wide area networking combines multiple LANs that are geographically separate. This is accomplished by connecting the different LANs using services such as dedicated leased phone lines, dial-up phone lines both synchronous and asynchronous, satellite links, and data packet carrier services. Wide area networking can be as simple as a modem and remote access server for employees to dial into, or it can be as complex as hundreds of branch offices globally linked using special routing protocols and filters to minimize the expense of sending data sent over vast distances.

WANWANWAN (Wide Area Network)WAN (Wide Area Network)

Spans entire states or countriesSpans entire states or countries

Data rate of 1.544 (T1), and 45 (T3) Mbps Data rate of 1.544 (T1), and 45 (T3) Mbps common common

Higher data rates are available with the wide Higher data rates are available with the wide deployment of ATM backbone networksdeployment of ATM backbone networks

Often owned by multiple organizationsOften owned by multiple organizations

WANWANUsually separate communications functions from application Usually separate communications functions from application functionsfunctions

Transmission lines: Transmission lines: circuitscircuits, , channelschannels or or trunkstrunks

Switching elements: Switching elements:

Specialized computers connecting two or more circuitsSpecialized computers connecting two or more circuits

Intermediate SystemsIntermediate Systems, , Packet SwitchingPacket Switching NodeNode, , Data Data Switching ExchangeSwitching Exchange, , RouterRouter, etc., etc.

Intermediate systems store a complete Intermediate systems store a complete packetpacket before before forwarding itforwarding it

•store-and-forwardstore-and-forward; ; packet switchedpacket switched; ; point-to-pointpoint-to-point networknetwork

Computer NetworksComputer NetworksComputer Networks may be implemented using a variety of network protocolstack architectures computer buses or combinations of media and protocol layersincorporating one or more of the following:

ARCNETDECNETEthernetIPTCPAppleTalkToken RingIPXFDDIHSSIATMRS-232USBFirewireX.25Blue Tooth WiFiFrame Relay

Network SoftwareNetwork Software

Network software is Network software is highlyhighly structuredstructured

This technique has been immensely successfulThis technique has been immensely successful

The key is The key is LayeredLayered design design

Each layer provides a Each layer provides a serviceservice to the layer above to the layer above

Each layer hides details of how the service is provided to Each layer hides details of how the service is provided to the layer abovethe layer above

The NThe Nthth layer on one machine “talks to” or interacts with layer on one machine “talks to” or interacts with the Nthe Nthth layer on another machine layer on another machine

Understanding Services and ProtocolsUnderstanding Services and Protocols

Protocol is set of rules about the format and meaning of data Protocol is set of rules about the format and meaning of data units exchanged by peersunits exchanged by peers

Protocol is used by entities to implement servicesProtocol is used by entities to implement services

Protocol and/or its implementation can change and as long as Protocol and/or its implementation can change and as long as the Service (interface) remains unchanged, higher layers are the Service (interface) remains unchanged, higher layers are happy and continue to workhappy and continue to work

Like in abstract data types or object orientation, we Like in abstract data types or object orientation, we decoupledecouple interface and implementationinterface and implementation

Protocols

Although each network protocol is different, they all share the same physical cabling. This common method of accessing the physical network allows multiple protocols to peacefully coexist over the network media, and allows the builder of a network to use common hardware for a variety of protocols. This concept is known as "protocol independence," which means that devices that are compatible at the physical and data link layers allow the user to run many different protocols over the same medium.

Protocols

File TransferApplication

CommunicationsService Module

Network AccessModule

File TransferApplication

CommunicationsService Module

Network AccessModule

Comms\Network

NetworkInterface Logic

Network

Interface Logic

Communications related data units

Files and file transfer commands

A Structured Set of Modules implements the communications function

That structure is referred to as a Protocol Architecture

Protocols

The Key Elements of Protocols are:

•SYNTAX - Data format and signal levels

•SEMANTICS- Control information for coordination & error handling

•TIMING - speed matching and sequencing

Network Software - ProtocolsNetwork Software - Protocols

Conventions and rules governing this interaction are specified by Conventions and rules governing this interaction are specified by the Layer N the Layer N ProtocolProtocol

A protocol is an agreement about how communications are to A protocol is an agreement about how communications are to proceedproceed

Without a protocol, communication can be difficult or even Without a protocol, communication can be difficult or even impossibleimpossible

E.g. Telephone conversation, Postal addressesE.g. Telephone conversation, Postal addresses


The set of protocols and layers together make up the The set of protocols and layers together make up the Network Network ArchitectureArchitecture

A Network Architecture A Network Architecture SpecificationSpecification must provide enough must provide enough information to allow implementation in hardware/softwareinformation to allow implementation in hardware/software

Implementation specific details are Implementation specific details are notnot part of the part of the architecture and should be architecture and should be irrelevantirrelevant for inter-operation for inter-operation

With one protocol per layer we have a With one protocol per layer we have a Protocol StackProtocol Stack


Information is Information is notnot actually transferred directly actually transferred directly between between peerpeer layer N layer N entitiesentities

Peer layer N entities carry on a virtual Peer layer N entities carry on a virtual communication using the services of the layers communication using the services of the layers belowbelow

Layer N passes data and control information down Layer N passes data and control information down to (or receives data and control from) Layer N-1 to (or receives data and control from) Layer N-1 until the physical medium is reacheduntil the physical medium is reached

The benefits of Layered ProtocolsThe benefits of Layered Protocols

Network Architectures, Protocols and Protocol stacks are the Network Architectures, Protocols and Protocol stacks are the Fundamentals of Computer NetworksFundamentals of Computer Networks

They form the foundation for the very considerable They form the foundation for the very considerable success of computer networks in the real worldsuccess of computer networks in the real world

Multilayer communications protocols allow Multilayer communications protocols allow

ready adaptation of successful protocols to new ready adaptation of successful protocols to new technology (prevent obsolescence)technology (prevent obsolescence)

migration of protocols from software implementation migration of protocols from software implementation (slow) to hardware (fast) as they evolve(slow) to hardware (fast) as they evolve

More Benefits of Layered ProtocolsMore Benefits of Layered Protocols

Separate data and control informationSeparate data and control information

Support differing levels of abstraction (message, packet, Support differing levels of abstraction (message, packet, frame) with different sizesframe) with different sizes

Allow segmentation of large messagesAllow segmentation of large messages

Peer process abstraction facilitates reduction of difficult Peer process abstraction facilitates reduction of difficult design task (a network architecture) into smaller manageable design task (a network architecture) into smaller manageable tasks (protocol layer architecture)tasks (protocol layer architecture)

Typically lower layer protocols of “network software” are Typically lower layer protocols of “network software” are implemented in silicon (hardware)implemented in silicon (hardware)

Network Software - Interfaces & ServicesNetwork Software - Interfaces & Services

InterfacesInterfaces exist between each layer exist between each layer

Interface defines which Interface defines which primitiveprimitive functions and functions and servicesservices layer N-1 layer N-1 provides to layer Nprovides to layer N

Want layers to:Want layers to:

Perform a well defined, logically related set of functionsPerform a well defined, logically related set of functions

Minimize the amount of information needed to pass between Minimize the amount of information needed to pass between layerslayers

Keep interfaces “clean” to allow easy and Keep interfaces “clean” to allow easy and transparenttransparent replacement of layersreplacement of layers

The 3 Layer ModelThe 3 Layer Model

This layer is concerned with the exchange of data between the computer and the network

•Network access Layer -

•Transport Layer -

•Application Layer -

This layer is concerned with reliable and orderly exchange of data

This layer provides the logic required to support the various user applications

A Simple ArchitectureA Simple ArchitectureApplication

Transport

NetworkAccess

Application

Transport

NetworkAccess

Application

Transport

NetworkAccess

•Each computer contains software at all three layers.•Every entity on the network must have a unique address•Actually two layers of addressing are required

•A unique network address•Each application of the computer must have a unique address

•This application address allows the transport layer to supportapplications on each computer and are known as Service Access Points (SAPs)

SAPs

NetworkAddress Comms

Network

( ) ( ) ( ) ( )

( ) ( ) ( ) ( )

( ) ( ) ( ) ( )

Simplified ArchitectureSimplified Architecture

Application

Transport

NetworkAccess

Application

Transport

NetworkAccess

Comms\Network

NetworkAccessProtocol

Transport Protocol

Application Protocol

NetworkAccessProtocol

Computer AComputer B

PDUsPDUsProtocol Data Unit (PDU) - is the combination of data from the next

higher layer and control information

Application data

Applicationdata

Transportheader

Transportheader

Transportheader

Transportheader

Networkheader

Networkheader

Transport protocoldata unit (TPDU)

Network protocoldata unit (NPDU)

Applicationdata

Applicationdata

Applicationdata

control info + data in each layer = protocol data unit (PDU)

Network OperationNetwork Operation

Destination SAP - Tells the destination Transport layer to whom to deliver the message

Sequence Number - Tells the destination what order the PDU was sent by numbering them

Error-Detection Code - The sending transport sends a code that is a function of the contents of the PDU. The receiving entity performs the same calculation and compares the two numbers.

Information in Transport Header


Information in Network Header

Destination Computer Address - Tells the network to which computer the data is to be delivered

Facilities Requests - Tells the network to make use of certain facilities (i.e. Priority)

Operation of Protocol ArchitectureOperation of Protocol Architecture

NetworkAccess

Transport

Application Application

Transport

NetworkAccess

Source X Destination Y

Record

Record

DSAP DSAP

DHost DHost

Packet

Transport PDU


•Computer X desires to send a record to computer Y•Computer X hands the record via a procedure call to the Transport layer•The Transport layer adds its header creating the Transport PDU•This is passed down to the Network layer •The Network layer adds its header creating the Network PDU•The Network accepts the network PDU from X and delivers it to Y•The network access module in Y receives the PDU and strips off the header•It transfers the transport PDU to its transport layer•The Transport layer examines the transport header and on the basis of the SAP field delivers the enclosed record

The components of a basic NetworkThe components of a basic Network

Why establish a computer networkWhy establish a computer network

•Program and file sharing

•Network resource sharing

•Database sharing

•Economical expansion of the PC base

•Workgroup capabilities

•Centralized management

•Security

•Interconnectivity

•Enhancement of corporate structure

Distributed computingDistributed computing

Access methods in a distributed Access methods in a distributed computing environmentcomputing environment

A local area network (LAN) and an A local area network (LAN) and an internetworkinternetwork

A network communication modelA network communication model

Circuit SwitchingCircuit Switching

Circuit-switched is a type of network in which a physical path is obtained forand dedicated to a single connection between two end-points in the networkfor the duration of the connection. Ordinary voice phone service is circuit-switched. The telephone company reserves a specific physical path to thenumber you are calling for the duration of your call. During that time, noone else can use the physical lines involved.


That's a vulnerability that circuit-switched networks share with Ethernet, IP,data-only and sometimes even cable networks. If a tornado, earthquake, icestorm or terrorist attack disables that shared central office or the linesleading to it, all data and voice communications for miles around could stopdead in their routes.

Circuit-switched networks have been rapped for not having theresiliency and redundancy to reroute traffic that runs into a fiber orwire cut, because they don't have as many dispersed points ofpresence as IP networks have.

But the big problem for enterprises running circuit-switched networksis that first stretch that connects them to the public network - avulnerable mile, or two or three, that links them to a solitary centraloffice shared by several carriers and service providers


Packet SwitchingPacket Switching

Packet switching is a communications paradigm in which packets(messages or fragments of messages) are individually routedbetween nodes, with no previously established communication path

Packet-switched describes the type of network in which relativelysmall units of data called packets are routed through a networkbased on the destination address contained within each packet.Breaking communication down into packets allows the same datapath to be shared among many users in the network. This type ofcommunication between sender and receiver is known asconnectionless (rather than dedicated). Most traffic over the Internetuses packet switching and the Internet is basically a connectionlessnetwork.


Another type of digital network that uses packet-switching is the X.25network, a widely-installed commercial wide area network protocol.Internet protocol packets can be carried on an X.25 network. TheX.25 network can also support a virtual circuit in which a logicalconnection is established for two parties on a dedicated basis forsome duration. A permanent virtual circuit (PVC) reserves the path onan ongoing basis and is an alternative for corporations to a system ofleased lines. A permanent virtual circuit is a dedicated logicalconnection but the actual physical resources can be shared amongmultiple logical connections or users.


Analogous to a physical packet sent through the post with theaddress written on the outside, this provides the information thenetwork (the postal service) needs to get the packet to the correctdestination.

Packets are routed to their destination through the most expedientroute (as determined by some routing algorithm). Not all packetstravelling between the same two hosts, even those from a singlemessage, will necessarily follow the same route.

The destination computer reassembles the packets into theirappropriate sequence. Packet switching is used to optimize the useof the bandwidth available in a network and to minimize the latency.Ethernet, X.25 and Frame relay are international standard layer 2packet switching networks.The Internet is a packet-switched network, running the Internetprotocol layer 3 protocol over a variety of other network technologies.

Also called connectionless.

Internet

The Internet is a system of linked networks that are worldwide in scope and facilitates data communication service such as remote login, file transfer, electronic mail, the World Wide Web and newsgroups.

With the meteoric rise of demand for connectivity, the Internet has become the communications highway for millions of users. The Internet was initially restricted to military and academic institutions in its infancy but now it is a full-fledged information channel for any and all forms of information and commerce. Internet websites now provide personal, educational, political and economic resources to every corner of the planet.

Intranet

With the advancements made in browser-based software for the Internet, there is now a phenomenon developed by private organizations called an intranet. An intranet is a private network utilizing Internet-type tools, but available only within that organization. For large organizations, an intranet provides an easy access mode to corporate information for employees.

Documents

WELCOME to COMP 421 /CMPET 401 COMMUNICATIONS and NETWORKING Class 1