Business Data Communications and Networking - Chapter 5: Network and Transport Layers

Business Data Communications and Networking 8th Edition Jerry Fitzgerald and Alan DennisJohn Wiley & Sons, Inc Prof. M. UlemaManhattan CollegeComputer Information Systems1Copyright 2005 John Wiley & Sons, IncChapter 5Network and Transport Layers2Copyright 2005 John Wiley & Sons, IncOutlineTransport & Network Layer ProtocolsTCP/IP, IPX/SPX, X.25, SNATransport Layer Functions Interacting with Application Layer PacketizingEnd-to-end delivery of application layer messagesNetwork Layer FunctionsAddressingRoutingTCP/IP Examples3Copyright 2005 John Wiley & Sons, IncIntroductionTransport and Network layersResponsible for moving messages from end-to-end in a networkClosely tied togetherTCP/IP: most commonly used protocolUsed in InternetCompatible with a variety of Application Layer protocols as well as with many Data Link Layer protocolsNetwork LayerData Link LayerApplication LayerTransport Layer4Copyright 2005 John Wiley & Sons, IncIntroduction - Transport layer Responsible for end-to-end delivery of messagesSets up virtual circuits (when needed) Responsible for segmentation and reassemblyBreaking the message into several smaller pieces at the sending endReconstructing the original message into a single whole at the receiving endInteracts with Application LayerTransport LayerApplication LayerNetwork Layer5Copyright 2005 John Wiley & Sons, IncIntroduction – Network LayerResponsible for addressing and routing of messagesSelects the best path from computer to computer until the message reaches destinationPerforms encapsulation on sending end Adds network layer header to message segmentsPerforms decapsulation on receiving end Removes the network layer header at receiving end and passes them up to the transport layerNetwork LayerTransport LayerData Link Layer6Copyright 2005 John Wiley & Sons, IncTCP/IP’s 5-Layer Network Model7Copyright 2005 John Wiley & Sons, IncTransport/Network Layer ProtocolsTCP/IP (Transmission Control Protocol / Internet Protocol)Most common, used by all Internet equipmentIPX/SPXSimilar to TCP/IPMainly used by Novell networks (Novell has since replaced it with TCP/IP)X.25Used mainly in EuropeSNA (System Network Architecture)IBM’s protocol suite8Copyright 2005 John Wiley & Sons, IncTCP/IPDeveloped in ‘74 by V. Cerf and B. Kahn As part of Arpanet (U.S. Department of Defense)Most common protocol suiteUsed by the Internet.Almost 70% of all backbone, metropolitan, and wide area networks use TCP/IP Most common protocol on LANs (surpassed IPX/SPX in ‘98)Reasonably efficient and error free transmissionPerforms error checkingTransmits large files with end-to-end delivery assuranceCompatible with a variety of data link layer protocols9Copyright 2005 John Wiley & Sons, IncTransmission Control ProtocolTCP Header: 192 bits (24 bytes)used in message reassemblyLinks the application layer to the network layerPerforms packetization and reassembly Breaking up a large message into smaller packets Numbering the packets and Reassembling them at the destination end Ensures reliable delivery of packets10Copyright 2005 John Wiley & Sons, IncInternet Protocol (IP)Responsible for addressing and routing of packetsTwo versions in current in useIPv4: a 192 bit (24 byte) header, uses 32 bit addresses. IPv6: Mainly developed to increase IP address space due to the huge growth in Internet usage (128 bit addresses)Both versions have a variable length data fieldMax size depends on the data link layer protocol.e.g., Ethernet’s max message size is 1,492 bytes, so max size of TCP message field: 1492 – 24 – 24 = 1444 bytesTCP headerIPv4 header11Copyright 2005 John Wiley & Sons, IncIP Packet FormatsIPv4 Header: 192 bits (24 bytes)IPv6 Header: 320 bits (40 bytes)12Copyright 2005 John Wiley & Sons, IncX.25Developed by ITU-T for use in WANsWidely used especially in EuropeSeldom used in North AmericaTransport layer protocols for X.25X.3 (performs packetization for ASCII terminals)TP (ISO defined), TCPNetwork Layer protocol for X.25Packet Layer Protocol (PLP) for routing and addressing Data Link Layer protocol for X.25LAP-B (Link Access Protocol-Balanced)Recommended packet size: 128 bytes But can support packet sizes up to 1024 bytes.13Copyright 2005 John Wiley & Sons, IncSNA - Systems Network ArchitectureDeveloped by IBMUsed on IBM and IBM-compatible mainframesBased on non-standard proprietary protocolsDifficult to integrate with non-SNA networksRequires special equipment, gateways (to route messages between SNA and non-SNA networks)Likely disappear over timeIBM now offers TCP/IP on its networks14Copyright 2005 John Wiley & Sons, IncTransport Layer FunctionsLinking to Application LayerPacketization and ReassemblyEstablishing connection (virtual)Connection OrientedConnectionlessQuality of Service (QoS)15Copyright 2005 John Wiley & Sons, IncLinking to Application LayerTCP may serve several Application Layer protocols at the same timeProblem: Which application layer program to send a message to?Solution: Port numbers located in TCP header fields; 2-byte each (source, destination)Standard port numbersUsual practiceNonstandard port numbersPossible, but requires configuration of TCPTCPHTTPFTPSMTP80212516Copyright 2005 John Wiley & Sons, IncApplication Layer Services17Copyright 2005 John Wiley & Sons, IncPacketization and ReassemblyreceiverTCPIPFTPTCPIPFTPsenderApplication layer sees message as a single block of dataBreaks a large message into smaller pieces (packetization) Delivers incoming packets as they arrive (e.g., Web pages) or to wait until entire message arrives (e.g., e-mail)Puts them back together at the destination (reassembly)What size packet to use? Done through negotiations18Copyright 2005 John Wiley & Sons, IncSetting up Virtual ConnectionsABSYNSYNACK 2not busyData 1Data 2Data 3Data 4FINRequests a virtual circuit (TCP connection) and negotiates packet size with BSends data packets one by one (in order) using continuous ARQ (sliding window)Closes virtual circuit19Copyright 2005 John Wiley & Sons, IncRouting Implied by Transport LayerConnection Oriented (provided by TCP)Setting up a virtual circuit (a TCP connection)TCP asks IP to route all packets in a message by using the same path (from source to destination) Packet deliveries are acknowledgedUsed by HTTP, SMTP, FTPConnectionless Routing (provided by UDPSending packets individually without a virtual circuitEach packet is sent independently of one another (routed separately and can follow different routes and arrive at different times)QoS Routing (provided by RTP)A special kind connection oriented routing with priorities20Copyright 2005 John Wiley & Sons, IncUDP - User Datagram ProtocolProtocol used for connectionless routing in TCP/IP suite (no acks, no flow control)Uses only a small packet header Only 8 bytes containing only 4 fields:Source portDestination portMessage lengthHeader checksumCommonly used for control messages that are usually small, such as DNS, DHCP, RIP and SNMP.21Copyright 2005 John Wiley & Sons, IncQoS - Quality of ServiceQoS parametersAvailability, Reliability, TimelinessTimeliness - timely delivery of packets Packets be delivered within a certain period of time (to produce a smooth, continuous output Required by some applications, especially real time applications (e.g., voice and video frames)(e-mail doesn’t require this)QoS routing Defines classes of service, each with a different priority:Real-time applications - highestA graphical file for a Web page - a lower priorityE-mail - lowest (can wait a long time before delivery)22Copyright 2005 John Wiley & Sons, IncProtocols Supporting QoSAsynchronous Transfer Mode (ATM)A high-speed data link layer protocolTCP/IP protocol suiteResource Reservation Protocol (RSVP)Sets up virtual circuits for general purpose real-time applicationsReal-Time Streaming Protocol (RTSP)Sets up virtual circuits for audio-video applicationsReal-Time Transport Protocol (RTP) Used after a virtual connection setup by RSVP or RTSPAdds a sequence number and a timestamp for helping applications to synchronize deliveryUses UDP (because of its small header) as transport IPRTSPRSVPUDPRTP23Copyright 2005 John Wiley & Sons, IncNetwork Layer FunctionsAddressingEach equipment on the path between source and destination must have an addressInternet AddressesAssignment of addressesTranslation between network layer addresses and other addresses (address resolution)RoutingProcess of deciding what path a packet must take to reach destinationRouting protocols24Copyright 2005 John Wiley & Sons, IncAddress TypeExampleExample AddressApplication LayerNetwork LayerData Link LayerTypes of AddressesIP addressURLMAC addresswww.manhattan.edu149.61.10.22 (4 bytes)00-0C-00-F5-03-5A (6 bytes)NameStreet #Apt #AnalogyTry “ping”ing a URL; translation (corresponding IP address) will be given by the answer.These addresses must be translated from one type to another (for a message to travel from sender to receiver). This translation process is called address resolution.25Copyright 2005 John Wiley & Sons, IncAssignment of AddressesApplication Layer address (URL)For servers only (clients don’t need it)Assigned by network managers and placed in configuration files. Some servers may have several application layer addressesNetwork Layer Address (IP address)Assigned by network managers, or by programs such as DHCP, and placed in configuration filesEvery network on the Internet is assigned a range of possible IP addresses for use on its networkData Link Layer Address (MAC address)Unique hardware addresses placed on network interface cards by their manufacturers ( based on a standardized scheme)Servers have permanent addresses, clients usually do not26Copyright 2005 John Wiley & Sons, IncInternet AddressesManaged by ICANNInternet Corporation for Assigned Names and NumbersManages the assignment of both IP and application layer name space (domain names)Both assigned at the same time and in groupsManages some domains directly (e.g., .com, .org, .net) and Authorizes private companies to become domain name registrars as wellExample: Indiana University URLs that end in .indiana.edu and iu.eduIP addresses in the 129.79.x.x range (where x is any number between 0 and 255)27Copyright 2005 John Wiley & Sons, IncIPv4 Addresses4 byte (32 bit) addressesStrings of 32 binary bitsDotted decimal notation Used to make IP addresses easier to understand for human readersBreaks the address into four bytes and writes the digital equivalent for each byteExample: 128.192.56.1 1 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 1 1 1 0 0 0 0 0 0 0 0 0 0 128Copyright 2005 John Wiley & Sons, IncClassfull AdressingClass AClass BClass CClass DClass E2^31 = 2 Billion addresses2^30 = 1 Billion addresses2^29 = 536 Million addresses2^28 = 268 Million addresses01 01 1 01 1 1 01 1 1 12^28 = 268 Million addressesNet IDHost ID7 bits24 bitsNet IDHost ID14 bits16 bits21 bits8 bitsNet IDHost ID0 -127128 -191192 -22329Copyright 2005 John Wiley & Sons, IncIPv6 AddressingNeedIPv4 uses 4 byte addresses:Total of one billion possible addressesIP addresses often assigned in (large) groups Giving out many numbers at a time  IPv4 address space has been used up quickly e.g., Indiana University: uses a Class A IP address space (65,000 addresses; many more than needed) IPv6 uses 16 byte addresses:3.2 x 1038 addresses, a very large numberLittle chance this address space will ever be used up30Copyright 2005 John Wiley & Sons, IncSubnetsGroup of computers on the same LAN with IP numbers with the same prefixAssigned addresses that are 8 bits in lengthFor example: Subnet 149.61.10.x Computers in Business (x is between 0 & 255)Subnet 149.61.15.xComputers in CS department Assigned addresses could be more or less than eight bits in lengthFor example: If 7 bits used for a subnetSubnet 1: 149.61.10.1-128Subnet 2: 149.61.10.129-25531Copyright 2005 John Wiley & Sons, IncSubnets: ExampleSchool of Business 149.61.10.X149.61.10.50 149.61.10.51 149.61.10.52GWSchool of Engineering 149.61.15.X149.61.15.50 149.61.15.51 149.61.15.52149.61.10.6149.61.254.4149.61.254.x149.61.254.5149.61.15.8GWBackbone32Copyright 2005 John Wiley & Sons, IncSubnet MasksUsed to make it easier to separate the subnet part of the address from the host part. ExampleSubnet: 149.61.10.x Subnet mask: 255.255.255.000 or in binary 11111111.11111111.11111111.00000000ExampleSubnets: 149.61.10.1-128, Subnet mask 255.255.255.128 or, in binary: 11111111.11111111.11111111.1000000033Copyright 2005 John Wiley & Sons, IncDynamic AddressingGiving addresses to clients (automatically) only when they are logged in to a networkEliminates permanent addresses to clientsWhen the computer is moved to another location, its new IP address is assigned automaticallyMakes efficient use of IP address space Example:A small ISP with several thousands subscribersMight only need to assign 500 IP addresses to clients at any one timeUses a server to supply IP addresses to computers whenever the computers connect to network34Copyright 2005 John Wiley & Sons, IncPrograms for Dynamic AddressingBootstrap Protocol (bootp)Dynamic Host Control Protocol (DHCP)Different approaches, but same basic operations:A program residing in a client establishes connection to bootp or DHCP serverA client broadcasts a message requesting an IP address (when it is turned on and connected)Server (maintaining IP address pool) responds with a message containing IP address (and its subnet mask)IP addresses can also be assigned with a time limit (leased IP addresses)When expires, client must send a new request35Copyright 2005 John Wiley & Sons, IncAddress ResolutionServer Name ResolutionTranslating destination host’s domain name to its corresponding IP addresse.g., www.yahoo.com  204.71.200.74)Uses one or more Domain Name Service (DNS) servers to resolve the addressData Link Layer Address ResolutionIdentifying the MAC address of the next node (that packet must be forwarded t) Uses Address Resolution Protocol (ARP)36Copyright 2005 John Wiley & Sons, IncDNS - Domain Name ServiceUsed to determine IP address for a given URLProvided through a group of name serversDatabases containing directories of domain names and their corresponding IP addressesLarge organizations maintain their own name serverssmaller organizations rely on name servers provided by their ISPsWhen a domain name is registered, IP address of the DNS server must be provided to registrar for all URLs in this domainExample: Domain name: indiana.edu URLs: www.indiana.edu, www.kelly.indiana.edu, abc.indiana.edu37Copyright 2005 John Wiley & Sons, IncHow DNS WorksDesired URL in client’s address table:Use the corresponding IP addressEach client maintains a server address table containing URLs used and corresponding IP addressesDesired URL not in client’s address table:Use DNS to resolve the addressSends a DNS request packet to its local DNS serverURL in Local DNS server Responds by sending a DNS response packet back to the client38Copyright 2005 John Wiley & Sons, IncHow DNS Works (Cont.)URL NOT in Local DNS server Sends DNS request packet to the next highest name server in the DNS hierarchyUsually the DNS server at the top level domain (such as the DNS server for all .edu domains)URL NOT in the name serverSends DNS request packet ahead to name server at the next lower level of the DNS hierarchy39Copyright 2005 John Wiley & Sons, IncHow DNS WorksClient computerDNS ServerDNS RequestLANLANInternetDNS RequestDNS ServerRoot DNS Server for .EDU domainUniversity of TorontoIndiana UniversityDNS RequestDNS ResponseDNS ResponseDNS ResponseAsks for a web page on Indiana University’s server40Copyright 2005 John Wiley & Sons, IncMAC Address ResolutionProblem:Unknown MAC address of the next node (whose IP address known)Solution:Uses Address Resolution Protocol (ARP) OperationBroadcast an ARP message to all nodes on a LAN asking which node has a certain IP addressHost with that IP address then responds by sending back its MAC addressStore this MAC address in its address table Send the message to the destination nodeExample of a MAC address: 00-0C-00-F5-03-5A41Copyright 2005 John Wiley & Sons, IncRoutingProcess of identifying what path to have a packet take through a network from sender to receiverRouting TablesUsed to make routing decisionsShows which path to send packets on to reach a given destinationKept by computers making routing decisionsRoutersSpecial purpose devices used to handle routing decisions on the Internet Maintain their own routing tables Dest.BCDEFGNextBBDDDB42Copyright 2005 John Wiley & Sons, IncRouting Example Dest.BCDEFGNextBBDDDBRouting Table for APossible paths from A to G:ABCGABEFCGADEFCGADEBCGBEach node has its own routing tableA43Copyright 2005 John Wiley & Sons, IncTypes of Routing Centralized routingDecisions made by one central computerUsed on small, mainframe-based networks Decentralized routing Decisions made by each node independently of one another Information need to be exchanged to prepare routing tablesUsed by Internet44Copyright 2005 John Wiley & Sons, IncTypes of Decentralized RoutingStatic routing: Uses fixed routing tables developed by network managersEach node has its own routing tableChanges when computers added or removedUsed on relatively simple networks (with few routing options that rarely change)Dynamic routing (aka. Adaptive routing): Uses routing tables (at each node) that are updated dynamicallyBased on routing condition information exchanged between routing devices45Copyright 2005 John Wiley & Sons, IncDynamic Routing AlgorithmsDistance Vector Uses the least number of hops to decide how to route a packetUsed by Routing Information Protocol (RIP)Link StateUses a variety of information types to decide how to route a packet (more sophisticated)e.g., number of hops, congestion, speed of circuitLinks state info exchanged periodically by each node to keep every node in the network up to dateProvides more reliable, up to date paths to destinationsUsed by Open Shortest Path First (OSPF)BACDEFGEx: From A to G  ABCG46Copyright 2005 John Wiley & Sons, IncRouting ProtocolsUsed to exchange info among nodes for building and maintaining routing tablesAutonomous System (AS)A network operated by an organization (e.g., Indiana U.)Protocols classified based on autonomous systemsTypes of Routing ProtocolsInterior routing protocols (RIP, OSPF, EIGRP, ICMP)Operate within a network (autonomous system)Provide detailed info about each node and pathsExterior routing protocols (BGP)Operate between networks (autonomous systems)47Copyright 2005 John Wiley & Sons, IncRouting Information Protocol (RIP)A dynamic distance vector interior routing protocolOnce popular on Internet; now used on simple networks Operations:Manager builds a routing table by suing RIPRouting tables broadcast periodically (every minute or so) by all nodesWhen a new node added, RIP counts number of hops between computers and updates routing tables48Copyright 2005 John Wiley & Sons, IncOpen Shortest Path First (OSPF)A dynamic link state interior routing protocol Became more popular on InternetMore reliable pathsIncorporates traffic and error rate measuresLess burdensome to the network Only the updates sent (not entire routing tables) and only to other routers (no broadcasting)49Copyright 2005 John Wiley & Sons, IncOther Interior Routing ProtocolsEnhanced Interior Gateway Routing Protocol (EIGRP)A dynamic link state protocol (developed by Cisco)Records transmission capacity, delay time, reliability and load for all pathsKeeps the routing tables for its neighbors and uses this information in its routing decisions as wellInternet Control Message Protocol (ICMP)Simplest and most basicAn error reporting protocol (report routing errors to message senders)Limited ability to update routing tables50Copyright 2005 John Wiley & Sons, IncExterior Routing Protocols Border Gateway Protocol (BGP)Used to exchange routing info between autonomous systemsBased on a dynamic distance vector algorithmFar more complex than interior routing protocolsProvide routing info only on selected routes (e.g., preferred or best route) Privacy concernToo many routes; can’t maintain tables of every single rout51Copyright 2005 John Wiley & Sons, IncInternet Routing using BGP, OSPF and RIPRouter 1Router 4Router 3OSPFDesignated RouterBorder RouterRouter 2Autonomous System A(using OSPF)Router 1Router 4Router 3BorderRouterRouter 2Autonomous System B(using RIP)Router 1Router 4Border RouterRouter 3Router 2Autonomous System C(using OSPF)BGPBGPOSPFDesignated RouterAutonomous System EAutonomous System DAutonomous System FBGPBGPBGPBGPRouter 5Router 552Copyright 2005 John Wiley & Sons, IncMulticastingCastingUnicast message: one computer  another computerBroadcast message: one computer  all computers in the networkMulticast message: one computer  a group of computers (e.g., videoconference)Internet Group Management Protocol (IGMP)Provides a way for a computer to report its multicast group membership to adjacent routersA special IP address assigned to identify the groupRouting node sets MAC address to a matching MAC addressWhen multicast session ends, IGMP sends a message to the organizing computer( or router) to remove multicast group53Copyright 2005 John Wiley & Sons, IncSending Messages using TCP/IPRequired Network layer addressing informationComputer’s own IP addressIts subnet maskTo determine what addresses are part of its subnetLocal DNS server’s IP addressTo translate URLs into IP addressesIP address of the router (gateway) on its subnetTo route messages going outside of its subnetObtained from a configuration file or provided by a DHCP serverServers also need to know their own application layer addresses (domain names)54Copyright 2005 John Wiley & Sons, IncTCP/IP Configuration Information55Copyright 2005 John Wiley & Sons, IncTCP/IP Network Example56Copyright 2005 John Wiley & Sons, IncCase 1a: Known Address, Same SubnetCase:A Client (128.192.98.130) requests a Web page from a server (www1.anyorg.com)Client knows the server’s IP and Ethernet addressesOperations (performed by the client)Prepare HTTP packet and send it to TCPPlace HTTP packet into a TCP packet and sent it to IPPlace TCP packet into an IP packet, add destination IP address, 128.192.98.53 Use its subnet mask to see that the destination is on the same subnet as itselfAdd server’s Ethernet address into its destination address field, and send the frame to the Web server57Copyright 2005 John Wiley & Sons, IncCase 1b: HTTP response to clientOperations (performed by the server)Receive Ethernet frame, perform error checking and send back an ACKProcess incoming frame successively up the layers (data link, network, transport and application) until the HTTP request emergesProcess HTTP request and sends back an HTTP response (with requested Web page)Process outgoing HTTP response successively down the layers until an Ethernet frame is createdSend Ethernet frame to the clientOperations (performed by the client)Receive Ethernet frame and process it successively up the layers until the HTTP response emerges at browser58Copyright 2005 John Wiley & Sons, IncCase 2: Known Address, Different SubnetSimilar to Case 1aDifferencesUse subnet mask to determine that the destination is NOT on the same subnetSend outgoing frames to the local subnet’s GWLocal gateway operationsReceive the frame and remove the Ethernet headerDetermine the next node (via Router Table) Make a new frame and send it to the destination GWDestination gateway operationsRemove the header, determine the destination (by destination IP address)Place the IP packet in a new Ethernet frame and send it to its final destination.59Copyright 2005 John Wiley & Sons, IncCase 3: Unknown AddressOperations (by the host)Determine the destination IP address Send a UDP packet to the local DNS server Local DNS server knows the destination host’s IP addressSends a DNS response back to the sending hostLocal DNS server does not know the destination IP address Send a second UDP packet to the next highest DNS host, and so on, until the destination host’s IP address is determined Follow steps in Case 260Copyright 2005 John Wiley & Sons, IncTCP ConnectionsBefore any data packet is sent, a connection is establishedUse SYN packet to establish connectionUse FIN packet to close the connectionHandling of HTTP packetsOld version: a separate TCP connection for each HTTP RequestNew version: Open a connection when a request (first HTTPP Request) send to the serverLeave the connection open for all subsequent HTTP requests to the same serverClose the connection when the session ends61Copyright 2005 John Wiley & Sons, IncTCP/IP and LayersHost ComputersPackets move through all layersGateways, RoutersPacket moves from Physical layer to Data Link Layer through the network LayerAt each stop along the wayEthernet packets is removed and a new one is created for the next nodeIP and above packets never change in transit (created by the original sender and destroyed by the final receiver)62Copyright 2005 John Wiley & Sons, IncMessage Move Through Layers63Copyright 2005 John Wiley & Sons, IncImplications for ManagementMost organizations moving toward a single standard, TCP/IPDecreased cost of buying and maintaining network equipmentDecreased cost of training networking staffTelephone companies (having large non-TCP/IP networks) moving toward TCP/IPSignificant financial implications for telcosSignificant financial implications of networking equipment manufacturers64Copyright 2005 John Wiley & Sons, IncCopyright 2005 John Wiley & Sons, Inc. All rights reserved. Reproduction or translation of this work beyond that permitted in section 117 of the 1976 United States Copyright Act without express permission of the copyright owner is unlawful. Request for further information should be addressed to the Permissions Department, John Wiley & Sons, Inc. The purchaser may make back-up copies for his/her own use only and not for distribution or resale. The Publisher assumes no responsibility for errors, omissions, or damages caused by the use of these programs or from the use of the information herein. 65Copyright 2005 John Wiley & Sons, Inc