Network Layer (OSI and TCP/IP)Lecture 9, May 2, 2003Data Communications and NetworksMr. Greg VoglUganda Martyrs University

Data Communications and Networks: Lecture 9: Network Layer

SourcesBITDCO lectures 18-20Hodson Ch. 12IU A247 lectures 5, 6, 8, 9, 11Chappell & Tittel, Guide to TCP/IP, Course Technology, 2002

Data Communications and Networks: Lecture 9: Network Layer

Functions of OSI Network LayerAddressing (sender and receiver machines)Routing (determining end-to-end path)Network control (sending/receiving status messages used to make routing decisions)Congestion control (monitor, reduce delays)

Data Communications and Networks: Lecture 9: Network Layer

Network AddressesDomain name e.g. yahoo.comHuman-friendly name of an Internet locationUsed in e-mail and web site addressesIP number e.g. 207.46.230.229Logical address of a computer, router, etc.Set by network administratorMAC address e.g. 00:00:C0:76:5A:26Physical address of a computer NIC

Data Communications and Networks: Lecture 9: Network Layer

Translating AddressesDomain Name System (DNS)Domain name IP numberType NSLOOKUP at DOS promptAddress Resolution Protocol (ARP)Local IP number MAC addressType ARP -A at DOS promptReverse ARP (RARP)MAC address local IP number

Data Communications and Networks: Lecture 9: Network Layer

RoutingIf packet destination is not on local subnetForward it to default gateway (router or server)Routing table in memory of each routerLists links to other network segments/subnetsGoalsFind the most efficient paths; avoid congestionConvergence: make all routing tables consistentAvoid routing loops, packets that live forever

Data Communications and Networks: Lecture 9: Network Layer

Centralised RoutingOne node is Network Routing Managerfinds over/under use of connectionscalculates optimal paths between nodesmakes, sends routing tables to all nodesDisadvantagesdelays to communicate with NRMdelays receiving tables --> inconsistenciesNRM performance/reliability, need backup

Data Communications and Networks: Lecture 9: Network Layer

Distributed Routinge.g. Routing Information ProtocolEach node calculates its own routing tablePeriodically transmit status to neighboursEvery 60 seconds, broadcast its routing tableEntries can be added, updated or discardedAvoids NRM bottleneckChanges take a long time to reach all nodes

Data Communications and Networks: Lecture 9: Network Layer

Static vs. Dynamic RoutingStatic routingAlways use one particular pathIf the path is unavailable use an alternativeRarely used (connections change; congestion)Weighted routing Randomly select a path from weighted alternativesDynamic or adaptive routingSelect best current message route using number of hops, speed and type of link, congestion/traffic

Data Communications and Networks: Lecture 9: Network Layer

Open Shortest Path First (OSPF)Link state routingOnly store table of directly connected linksAssumes routing tables rarely changeOnly send update info when link state changesRoutes based on network bandwidthReduced traffic; short convergence timeNow more widely used than RIPBetter for larger (enterprise) networks

Data Communications and Networks: Lecture 9: Network Layer

Internetworking Protocol SuitesTCP/IP (US Defense Dept, UNIX, etc.)OSI (ISO)XNS (Xerox, Ungermann-Bass)SNA/APPC (IBM)ATP (Apple)NetBEUI (Microsoft)IPX/SPX (Novell)

Data Communications and Networks: Lecture 9: Network Layer

OSI Model and Real Protocols

Data Communications and Networks: Lecture 9: Network Layer

TCP/IP Protocols and Layers

Data Communications and Networks: Lecture 9: Network Layer

OSI Model and Internet Protocols

Data Communications and Networks: Lecture 9: Network Layer

IP Datagram DeliveryUnreliable deliverydelivery, uniqueness, sequence not guaranteedreliability handled by higher layer (TCP)Connectionless Deliveryeach packet routed, delivered independently Best Effort Deliverydrop packets only if no resources (buffer space)

Data Communications and Networks: Lecture 9: Network Layer

IP Datagram Structure

Data Communications and Networks: Lecture 9: Network Layer

IP Address Classes

Data Communications and Networks: Lecture 9: Network Layer

Default Subnet Masks

Data Communications and Networks: Lecture 9: Network Layer

IP Version 6 (IPv6 or IPng)IPv4 32-bit addresses are almost all in useOnly 232 (4 billion) unique addressesProposed IPv6 uses 128-bit addressesMany addresses available (2128 = 1038)Not easily memorised like IPv4 addressesDisplayed in hexadecimal like MAC addressesCan contain IPv4 and MAC addressesSome addresses reserved for uni/multi/anycast

Data Communications and Networks: Lecture 9: Network Layer

Other IP Version 6 featuresRegistry service with 32 top level registriesFaster routing (addresses, simplified header)Quality of Service (reserve resources, request high performance for voice/video)Security (authentication/encryption)Auto-configuration (automatically choose an address; similar to BOOTP/DHCP)Mobile uses (cellphone/wireless)

Data Communications and Networks: Lecture 9: Network Layer