The Fundamental Purpose Of Data Communications Is To .

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Introduction to NetworkingThe fundamental purpose of data communications is toexchange information between user's computers, terminalsand applications programs.Simplified Communications System Block DiagramCopyright January 19, 2005 by Chaim Ziegler, Ph.D.2-1

Data Communications Networking!In its simplest form data communications takes placebetween two devices that are directly connected bysome form of point-to-point transmission medium.!Often it is impractical for two devices to be directlyconnected:a)b)!The devices are far apart,There is a large setinterconnected.ofdevicestobeThe solution is to connect each device to aCOMMUNICATIONS NETWORK.Interconnection via a Communications NetworkCopyright January 19, 2005 by Chaim Ziegler, Ph.D.2-2

Switched Communications NetworksCommunications between stations is accomplished viatransmission and switching.A Generic Switched Communications Network! Common Switching Methods:- Circuit Switching- Message Switching- Packet SwitchingCopyright January 19, 2005 by Chaim Ziegler, Ph.D.2-3

Switching Methods1. Circuit Switching:! Prior to the start of data transmission, an end-to-end(station-to-station) physical path must beestablished.! During data transmission, all channels in the path areused simultaneously.! The entire path remains dedicated to the pair ofcommunicating stations until circuit release.! Three phased operation:- Circuit Establishment (Allocation of Resources)- Data Transfer (Use of Resources)- Circuit Termination (Deallocation of Resources)2. Message Switching:! A MESSAGE represents a logical unit of informationthat one station wishes to send to another station.! No dedicated path is established prior to datatransfer. Instead, the message will travel over onechannel at a time.! A message travels (hops) through the network fromnode-to-node, in a store-and-forward fashion, untilit reaches its final destination.Copyright January 19, 2005 by Chaim Ziegler, Ph.D.2-4

3. Packet Switching:! Messages are decomposed into smaller units of datacalled PACKETS and then sent outpacket-by-packet.! Many packets of the same message can be in transitat the same time.! Reassembly of the original message is required at thedestination.Copyright January 19, 2005 by Chaim Ziegler, Ph.D.2-5

Packet Switching AlternativesA. Virtual Circuit Packet Switching:! A LOGICAL CONNECTION (virtual circuit) isestablished between communicating stations priorto the transmission of data packets.! The logical connection establishes the route overwhich all data packets will travel between stations.! Packet delivery across the virtual circuit will be insequential order.! Connection-Oriented Operation:- Connection Establishment Phase- Data Transfer Phase- Connection Termination PhaseVirtual Circuit Packet SwitchingCopyright January 19, 2005 by Chaim Ziegler, Ph.D.2-6

B. Datagram Packet Switching:! Each data packet is treated independently from oneanother.! Each packet finds its own route through the network.! Packets may arrive at the destination out ofsequential order.! Connectionless Operation:- Data Transfer PhaseDatagram Packet SwitchingCopyright January 19, 2005 by Chaim Ziegler, Ph.D.2-7

Broadcast Communications NetworksA transmission from one station can be received by all otherstation within the network.Sample Networks:! Satellite Networks! Radio Networks! Local Area NetworksCopyright January 19, 2005 by Chaim Ziegler, Ph.D.2-8

Sample Broadcast Network TopologiesSatellite Network TopologyRadio Network TopologyBus TopologyRing Topology! Common Access Methods:- Contention (e.g., CSMA/CD, etc.)- Reservation- Token PassingCopyright January 19, 2005 by Chaim Ziegler, Ph.D.2-9

Type of NetworksLocal Area Network (LAN):A Local Area Netw ork is a communications netw orkthat provides interconnection of a variety of datacommunicating devices w ithin a small area.(Ethernet, Token Ring, 10BaseT, 100BaseT, .)Typical Characteristics! High Data Rates (0.1 to 1000 Mbps)! Short Distances (0.1 to 25 km)! Low Error Rate (10 -8 to 10 -1 1 )Wide Area Network (WAN):A Wide Area Netw ork is a communications netw orkthat provides interconnection of a variety of datacommunicating devices over long distances.Copyright January 19, 2005 by Chaim Ziegler, Ph.D.2-10

Shared Media vs. Switching LAN ArchitecturesCopyright January 19, 2005 by Chaim Ziegler, Ph.D.2-11

The InternetThe Internet is an interconnected collection of netw orks.Copyright January 19, 2005 by Chaim Ziegler, Ph.D.2-12

Internetworking! Communications Netw ork:!!!!A facility that provides a data transfer service amongstations attached to the netw ork.Internet:A collection of interconnected communicationsnetw orks.Subnetw ork:A constituent netw ork of an internet.Intermediate System (IS) or Interw orking Unit (IWU):A device used to interconnect tw o subnetw orks andpermit communications betw een end systemsattached to different subnetw orks. (e.g., Router,Bridge, .)Communications Protocol:A set of rules used for regulating communicationsbetw een entities on different systems.Copyright January 19, 2005 by Chaim Ziegler, Ph.D.2-13

Requirements for Internetworking! Provide a link betw een netw orks.! Provide for routing and delivery of data betw eenprocesses on different netw orks.! Provide an accounting service that keeps track of theuse and status of the various netw orks and IWUs.! Accommodate differences among netw orks:-netw ork serviceaddressingroutingquality of servicemaximum packet sizeflow and congestion controlerror reportingCopyright January 19, 2005 by Chaim Ziegler, Ph.D.2-14

Connectionless Internetworking - The IP ApproachThe Internet Protocol (IP) is a DoD standard. Itprovides connectionless service betw een stations.A connectionless internet facility is flexible in that itrequires very little of its constituent netw orks.Copyright January 19, 2005 by Chaim Ziegler, Ph.D.2-15

IP Address Structure! IP addresses are communicated as four bytes usingdotted decimal notation. e.g.,00001010 00000000 00000000 00000000 10.0.0.0(Class A netid 10 (ARPANET))10000000 00000011 00000010 00000011 128.3.2.3 (Class B netid 128.3 hostid 2.3)11000000 00000000 00000001 11111111 192.0.1.255 (Class C netid 192.0.1 all hostsbroadcast)(BC - IP Address: 146.245.XXX.YYY)Copyright January 19, 2005 by Chaim Ziegler, Ph.D.2-16

Addressing! Network Service Access Point (NSAP):- Uniquely identifies a station w ithin the internet(global internet address).- A station may have more than one NSAP.- Usually has the form (network, host).! Subnetwork Attachment Point Address (Network Pointof Attachment):- Each subnetw ork must maintain a unique addressfor each station attached to that subnetw ork.- One must assume that the subnetw ork attachmentpoint address has significance only w ithin aparticular subnet.- The interw orking facility must translate betw eenthe global address and the locally significantaddress.Copyright January 19, 2005 by Chaim Ziegler, Ph.D.2-17

Internet Routing ExampleCopyright January 19, 2005 by Chaim Ziegler, Ph.D.2-18

Transport Protocols! Transmission Control Protocol (TCP)Connection-Oriented! User Datagram Protocol (UDP)Connectionless! TCP Services:- Provides reliable communications across reliableand unreliable netw orks and internets.- Designed specifically and exclusively to w ork w ithIP.! UDP Services:- Provides a transport-level, unreliable, datagramservice.- Delivery and duplicate detection are notguaranteed.Copyright January 19, 2005 by Chaim Ziegler, Ph.D.2-19

Client-Server Model for Applications!Client-Server Model defines a paradigm forcommunications betw een tw o programs called theclient and the server.! Server:Any application that provides a service to a netw orkuser.-File ServerPrint ServerCommunications ServerTelephony ServerFax ServerWeb Server! Client:Any program that makes a request to the server.Copyright January 19, 2005 by Chaim Ziegler, Ph.D.2-20

TCP/IP Application Layer SchematicCopyright January 19, 2005 by Chaim Ziegler, Ph.D.2-21

TCP/IP Application ProtocolsCopyright January 19, 2005 by Chaim Ziegler, Ph.D.2-22

Directory Services - Address Resolution ServiceTCP/IP Adress Composition! Within real system environments users (people andAPs) are know n by symbolic names.! Directory Services are used to find the addresses of anamed destination user.! Addresses can consist of:- Netw ork Point-of-Attachment (physical address)- IP address- TCP/UDP port numberCopyright January 19, 2005 by Chaim Ziegler, Ph.D.2-23

TCP/IP Domain Name System (DNS)! The total directory system in a TCP/IP suite is know nas the Domain Name System (DNS).! It uses a hierarchial structure for naming entities.! The Internet uses a partition of Domains at the highestlevel of its hierarchy:- COM commercial organizations- EDU educational institutions- GOV government institutions- MILmilitary groups- NET (Internet) netw ork support centers- ORG other organizations- country code (e.g., .us, .ca, .uk, .il)- etc.Sample Domain Name HierarchyCopyright January 19, 2005 by Chaim Ziegler, Ph.D.2-24

The Domain Name Server! Associated w ith each institution netw ork is a host thatruns an AP know n as the Domain Name Server.! Associated w ith the DNS server is a DirectoryInformation Base (DIB) w hich contains all thedirectory related information for that institution.! Each host has a client process know n as the NameResolver w hich communicates the DNS server.Name-to-Address Resolution Protocols and SequenceCopyright January 19, 2005 by Chaim Ziegler, Ph.D.2-25

Uniform Resource Locators (URL)! A Uniform Resource Locator (URL) is a compactrepresentation of the location and access method fora resource available via the Internet.! General form of a URL: scheme : scheme-specific-part ! URL Schemes:http://w w w lyn.cuny.edu/ myfile.txtmailto:w [email protected] January 19, 2005 by Chaim Ziegler, Ph.D.2-26

Copyright © January 19, 2005 by Chaim Ziegler, Ph.D. 2-4 Switching Methods 1. Circuit Switching