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Packet Switching and Computer Networks

Packet Switching and Computer Networks 31
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EdwardCage,Bahamas,Professional
Published Date:08-07-2017
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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 network-defined 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 store-and- 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 packet-switching  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 end-to-end 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 & Transmission