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Packet Switching and Computer Networks

Packet Switching and Computer Networks 31
P Pa ac ck ke et t S Sw wiit tc ch hiin ng g a an nd d C Co om mp pu ut te er r N Ne et tw wo or rk ks s Prof. Murat Torlak EE4367 Telecom. Switching TransmissionS Sw wiit tc ch hiin ng g  As computer networks became more pervasive, more and more data and also less voice was transmitted over telephone lines. Circuit Switching  The telephone network used circuit switching. Circuit switching operates by first reserving a complete route from the sender to the receiver. This bandwidth does not change during a call, and remains reserved even if the connection is not transmitting any data but is still active. An example follows:  A fixed bandwidth will be reserved at S1,S2,S4,S5, and S7 for the duration Prof. Murat Torlak EE4367 Telecom. Switching TransmissionP Pa ac ck ke et t S Sw wiit tc ch hiin ng g  Packet switching is similar to message switching using short messages. Any message exceeding a networkdefined maximum length is broken up into shorter units, known as packets, for transmission; the packets, each with an associated header, are then transmitted individually through the network.  T Th he e p pe er rf fo or rm ma an nc ce e o of f P Pa ac ck ke et t S Sw wiit tc ch hiin ng g iis s c ca alllle ed d B Be es st t E Ef ff fo or rt t performance. If you transmit from sender to receiver, all the network will do its best to get the packet to the other end as fast as possible, but there are no guarantees on how fast that packet will arrive. Prof. Murat Torlak EE4367 Telecom. Switching TransmissionP Pa ac ck ke et t F Fo or rm ma at ts s  A packet contains three major fields:  The header, the message, and redundancy check bits  Most popular technique uses cyclic redundancy checks (CRCs)  CRC is nothing more than a set of parity bits that cover overlapping fields of message bits.  CRC can detect small number of errors  A header typically contain numerous subfields in addition to the necessary address field Message Prof. Murat Torlak EE4367 Telecom. Switching TransmissionM Me es ss sa ag ge e S Sw wiit tc ch hiin ng g  Packet switching has its origin in message switching  A message switch typically operates in the storeand forward fashion  Message has to be completely received and stored by the switch before it can be forwarded to the next switch. Prof. Murat Torlak EE4367 Telecom. Switching TransmissionDe Della ay ys s iin n M Me es ss sa ag ge e s sw wiit tc ch hiin ng g  Minimum delay in message swicthing Prof. Murat Torlak EE4367 Telecom. Switching TransmissionDa Dat ta ag gr ra am m P Pa ac ck ke et t S Sw wiit tc ch hiin ng g  Each packet is routed independently through network  It is also called connectionless packetswitching  Routers in the internet are packet switches that operate in datagram mode Prof. Murat Torlak EE4367 Telecom. Switching TransmissionDe Della ay y C Ca allc cu ulla at tiio on ns s  Delay in datagram packet switching  Assume P=T/3 is required to transmit Prof. Murat Torlak EE4367 Telecom. Switching TransmissionV Viir rt tu ua all C Ciir rc cu uiit t P Pa ac ck ke et t S Sw wiit tc ch hiin ng g  VC packet switching involves the establishment of a fixed path, often called a virtual circuit or a connection Prof. Murat Torlak EE4367 Telecom. Switching TransmissionC Co on ng ge es st tiio on n  Congestion Prof. Murat Torlak EE4367 Telecom. Switching TransmissionR Re ef fe er re en nc ce e M Mo od de ells s The OSI Reference Model The TCP/IP Reference Model A Comparison of OSI and TCP/IP Prof. Murat Torlak EE4367 Telecom. Switching TransmissionL La ay ye er riin ng g  Layering Prof. Murat Torlak EE4367 Telecom. Switching TransmissionP Pr ro ot to oc co oll H Hiie er ra ar rc ch hiie es s  Layers, protocols, and interfaces. Prof. Murat Torlak EE4367 Telecom. Switching TransmissionO Op pe en n S Sy ys st te em ms s I In nt te er rc co on nn ne ec ct tiio on n ( (O OS SI I) )  OSI partioned the communication process into seven layers and provided a framework for talking about the overall communication process.  The OSI work also provided a unified view of layers, protocols, and services.  This unified view has provided the basis for the d de ev ve ello op pm me en nt t o of f n ne et tw wo or rk kiin ng g s st ta an nd da ar rd ds s t to o t th he e p pr re es se en nt t d da ay y. . Prof. Murat Torlak EE4367 Telecom. Switching TransmissionR Re ef fe er re en nc ce e M Mo od de ells s The OSI r re ef fe er re enc nce e model. Prof. Murat Torlak EE4367 Telecom. Switching TransmissionS Se er rv viic ce es s t to o P Pr ro ot to oc co olls s R Re ella at tiio on ns sh hiip p  The relationship between a service and a protocol. Prof. Murat Torlak EE4367 Telecom. Switching TransmissionO OS SI I R Re ef fe er re en nc ce e M Mo od de ell  The early network architectures developed by various vendors were not compatible with each other.  This desire led to an effort to develop a reference model for open system interconnection (OSI)  OSI reference model partitioned the communications process into seven layers provided a framework for talking a ab bo ou ut t t th he e o ov ve er ra allll c co om mm mu un niic ca at tiio on ns s p pr ro oc ce es ss s a an nd d h he en nc ce e w wa as s intended to facilitate the development standards. The OSI work also provided a unified view of layers, protocols, and services. Prof. Murat Torlak EE4367 Telecom. Switching TransmissionT Th he e s se ev ve en n lla ay ye er r O OS SI I M Mo od de ell  OSI reference model Prof. Murat Torlak EE4367 Telecom. Switching TransmissionO OS SI I L La ay ye er rs s  Physical layer deals with transfer of bits over a communication channel  Data link layer provides for the transfer of frames across a transmission link (dialup modems use PPP)  Network layer provides for transfer of data in the form of packets across a communication network. Addresing and c co on ng ge es st tiio on n a ar re e d de ea allt t w wiit th h n ne et tw wo or rk k lla ay ye er r  Transport layer is responsible for the endtoend transfer of messages from a process in the source machine to aprocess in the destination machine.  TCP/IP networks, access the transport layer  Setting up and releasing connections across the network Prof. Murat Torlak EE4367 Telecom. Switching TransmissionO OS SI I L La ay ye er rs s  Session layer can be used to control the manner in which data are exchanged. Certain applications require a half duplex dialog where the two parties take turns transmitting information  Presentation layer is intended to provide the application layer with independence from differences in the r re ep pr re es se en nt ta at tiio on n o of f d da at ta a. . F Fo or r e ex xa am mp plle e, , d diif ff fe er re en nt t c co om mp pu ut te er rs s use different codes for representing characters and integers, and also different conventions as to whether the first bit or last bit is the most significant bit.  Application layer provides services that are frequently required by the applications involve communications. Ex: HTTP, FTP, email Prof. Murat Torlak EE4367 Telecom. Switching TransmissionH He ea ad de er rs s a an nd d T Tr ra aiille er rs s Prof. Murat Torlak EE4367 Telecom. Switching TransmissionT TC CP P/ /I IP P R Re ef fe er re en nc ce e M Mo od de ell  The TCP/IP reference model. Prof. Murat Torlak EE4367 Telecom. Switching TransmissionT TC CP P/ /I IP P P Pr ro ot to oc co oll G Gr ra ap ph h Prof. Murat Torlak EE4367 Telecom. Switching TransmissionR Ro ou ut tiin ng g  Routing the packets Prof. Murat Torlak EE4367 Telecom. Switching TransmissionH HT TT TP P E Ex xa am mp plle e Prof. Murat Torlak EE4367 Telecom. Switching TransmissionA Ap pp plliic ca at tiio on n Prof. Murat Torlak EE4367 Telecom. Switching TransmissionR Re ef fe er re en nc ce e M Mo od de ells s  Protocols and networks in the TCP/IP model initially. Prof. Murat Torlak EE4367 Telecom. Switching TransmissionN Ne et tw wo or rk k S St ta an nd da ar rd diiz za at tiio on n I IT TU U  Main sectors • Radiocommunications • Telecommunications Standardization • Development  C Clla as ss se es s o of f M Me em mb be er rs s • National governments • Sector members • Associate members • Regulatory agencies Prof. Murat Torlak EE4367 Telecom. Switching TransmissionI IE EE EE E 8 80 02 2 S St ta an nd da ar rd ds s The 802 working groups. The important ones are marked with . The ones marked with  are hibernating. The one marked with † gave up. Prof. Murat Torlak EE4367 Telecom. Switching TransmissionB Bu us siin ne es ss s A Ap pp plliic ca at tiio on ns s o of f N Ne et tw wo or rk ks s  A network with two clients and one server. Prof. Murat Torlak EE4367 Telecom. Switching TransmissionH Ho om me e N Ne et tw wo or rk k A Ap pp plliic ca at tiio on ns s Access to remote information Persontoperson communication Interactive entertainment Electronic commerce Prof. Murat Torlak EE4367 Telecom. Switching TransmissionN Ne et tw wo or rk k H Ha ar rd dw wa ar re e Local Area Networks Metropolitan Area Networks Wide Area Networks Wireless Networks Home Networks Internetworks Prof. Murat Torlak EE4367 Telecom. Switching TransmissionL Lo oc ca all A Ar re ea a N Ne et tw wo or rk ks s  Two broadcast networks  Bus  Ring Prof. Murat Torlak EE4367 Telecom. Switching TransmissionM Me et tr ro op po olliit ta an n A Ar re ea a N Ne et tw wo or rk ks s  A metropolitan area network based on cable TV. Prof. Murat Torlak EE4367 Telecom. Switching TransmissionW Wiid de e A Ar re ea a N Ne et tw wo or rk ks s  Relation between hosts on LANs and the subnet. Prof. Murat Torlak EE4367 Telecom. Switching TransmissionW Wiid de e A Ar re ea a N Ne et tw wo or rk ks s ( (2 2) )  A stream of packets from sender to receiver. Prof. Murat Torlak EE4367 Telecom. Switching TransmissionW Wiir re elle es ss s N Ne et tw wo or rk ks s Categories of wireless networks: System interconnection Wireless LANs W Wiir re elle es ss s W WA AN Ns s Prof. Murat Torlak EE4367 Telecom. Switching TransmissionW Wiir re elle es ss s N Ne et tw wo or rk ks s ( (2 2) )  Bluetooth configuration  Wireless LAN Prof. Murat Torlak EE4367 Telecom. Switching TransmissionW Wiir re elle es ss s N Ne et tw wo or rk ks s ( (3 3) )  Individual mobile computers  A flying LAN Prof. Murat Torlak EE4367 Telecom. Switching Transmission