1. CECS 474 Computer Network Interoperability CHAPTER1 Network Protocols Tracy Bradley Maples, Ph.D. Computer Engineering & Computer Science Cal ifornia State University, Long Beach Notes for Douglas E. Comer, Computer Networks and Internets (5th Edition)

2. Protocol Suites and Layering Models • Defn:Protocolsareagreements abouthowcommunicationshouldtake place. • Theyspecify: • Formatofmessages • Meaning ofmessages • Rules for exchangingmessages • Procedures forhandling problems • Network hardwarefunctions ata verylowlevel. • Hardware related problemscan occurthatneedto be addressed byprotocols: • Bits can becorrupted ordestroyed • Entirepackets can belost • Packets can beduplicated • Packets can be delivered outoforder

3. Protocols canalso be usedto distinguishamong: • Multiple computerson anetwork • Multiple applicationson a computer • Multiple copiesofa single application on a computer • Sets of Protocols • Setsof protocols are designedtoworktogether. • Each protocol solvesa smallpartofthe communicationsproblem • Setsofprotocols are knownas: • --ProtocolSuites • --Protocol families • Theyaredesignedinlayers.

4. Protocol Design • Protocols are dividedintolayers • Eachlayerisdevotedto one sub-problem Example:TheISO(InternationalStandardsOrganization)OSI (OpenSystemInterconnection)7-layerReferenceModel • The OSI7-Layer Model • The7-LayerModel: • Wasdefinedfairlyearlyinthedevelopmentofnetworks • Isnowsomewhatdated • Doesnotincludetheinternetlayer

5. The OSI7-Layers • Layer 1:Physical • Theunderlying hardware • Layer 2:DataLink(media access) • Hardware framedefinitions • Layer 3:Network • Packet forwarding • Layer 4:Transport • Reliability • Layer 5:Session • Loginand passwords • Layer 6:Presentation • Data representation • Layer 7:Application • Individual applicationprograms

6. The Layering Model • Protocol softwarefollowsthelayeringmodel, with: • One softwaremoduleperlayer • Modulesthat worktogether • Incoming oroutgoing datapassingfrom onemoduletoanother The entire set of protocol layers (or modules)is known as a stack.

7. Layers andPacket Headers • Eachlayer: • Prependsa headertothe outgoing packet • Removesa header from theincoming packet • Thisprocessisknownasdata encapsulation.

8. Layering Principle SoftwareimplementinglayerN at the destinationreceives exactlythemessagesentbysoftware implementinglayerN atthesource. --Comer

9. TCP/IP Layering NotwithstandingthepushbyresearcherstoadopttheOSImodel,itbecameclearthatTCP/IP wastechnically more flexible and superior. TCP/IP is the primary protocol stack used today. Note:ThisTCP/IPlayeringis anactualimplementation ofprotocols,unliketheISO model.

10. TCP/IP Layers • Layer 1:Physical • Basic networkhardware • SimilartoOSILayer 1 • Layer 2:NetworkInterface • MAC frameformat • MAC addressing • Interfacebetweencomputer andthenetwork(i.e.,theNIC) • SimilartoOSILayer 2 • Layer 3: Internet • Formatofpackets • Mechanismsforforwarding packets • NotintheOSIModel • Layer 4:Transport • Specifies howto providereliabletransferfromoneapplication on onecomputertoanapplication onanother • SimilartoOSILayer 4 • Layer 5:Application • Everythingelse (i.e.,how one application usesthe Internet) • SimilartoOSILayer 6 and7