Circuit Switching and Packet Switching-Data Communication and Computer Networks-Lecture Slides, Slides of Data Communication Systems and Computer Networks

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Data and Computer Communications Chapter 10 – Circuit Switching and Packet Switching Docsity.com a — le) = = ® = Xe) ® <= Oo — = ep) Public Circuit Switched Network Long-distance Long-distance office office .Telelelore) End Office oo Lrws ooooooocopoo 3 3° 3° x oO oO 3° o Oo 0 o0c000 1 I 1 Cc ctine Trunk Intercity Trunk ca sesesess Snngesng am Connecting Trunk Circuit Establishment “., Intermediate .’ exchange Control Unit Circuit Switch ma (seats) ay ey Digital Switch #2 8 5 a 2 ao | 3 a § 3 a 3 & Network Interface 3 Stage Space Division Switch FIRST STAGE SECOND STAGE THIRD STAGE 2x5 switch 2x2 switch 2x 2 switch Time Division Switching modern digital systems use intelligent control of space & time division elements  use digital time division techniques to set up and maintain virtual circuits  partition low speed bit stream into pieces that share higher speed stream  individual pieces manipulated by control logic to flow from input to output Docsity.com Softswitch Media gateway controller Supervisory events teg., off-hook, on-hook) Circuit- or packet- Media. Circuit- or packet- switched falcway switched aDOSS. trunks. (b) Softswitch architecture Packet Switching a fsa Packet-Switching com ation (packet otha as ") Advantages  line efficiency  single link shared by many packets over time  packets queued and transmitted as fast as possible  data rate conversion  stations connects to local node at own speed  nodes buffer data if required to equalize rates  packets accepted even when network is busy  priorities can be used Docsity.com Switching Techniques  station breaks long message into packets  packets sent one at a time to the network  packets can be handled in two ways  datagram  virtual circuit Docsity.com Virtual Circuits v Datagram  virtual circuits  network can provide sequencing and error control  packets are forwarded more quickly  less reliable  datagram  no call setup phase  more flexible  more reliable Docsity.com (a) 1-packet message (b) 2-packet message Header Packet Size | velo Circuit v Packet Switching  performance depends on various delays  propagation delay  transmission time  node delay  range of other characteristics, including:  transparency  amount of overhead Docsity.com 9.5 The following table illustrates the operation of a FHSS system using the same PN sequence as Problem 94. Time Input data Frequency PN sequence Time Input data Frequency PN sequence What ts the pentod of the PN sequence? The system makes use of a form of PSK. What form of PSK is it? What is the number of bits per signal element? What ts the number of FSK frequencies? What is the lenzth of a PN sequence per hop? Is this a slow or fast FH system? What is the total number of possible carrier frequencies? Show the vanation of the base, or demodulated, frequency with time. X.25  ITU-T standard for interface between host and packet switched network  almost universal on packet switched networks and packet switching in ISDN  defines three layers  Physical  Link  Packet Docsity.com X.25 - Physical  interface between station node link  two ends are distinct  Data Terminal Equipment DTE (user equipment)  Data Circuit-terminating Equipment DCE (node)  physical layer specification is X.21  can substitute alternative such as EIA-232 Docsity.com X.25 Use of Virtual Circuits Mainframe Personal computer i Personal computer Solid line = physical link Dashed line = virtual circuit Packet-Switching Network Personal computer Personal computer rs User Data and X.25 Protocol Control Information X.25 packet LAPB frame Issues with X.25  key features include:  call control packets, in band signaling  multiplexing of virtual circuits at layer 3  layers 2 and 3 include flow and error control  hence have considerable overhead  not appropriate for modern digital systems with high reliability Docsity.com Protocol Architecture Control Plane User Plane User Plane Control Plane Q.931/0.933 Q.931/0.933 User-selectable functions LAPD (Q.921) LAPF core LAPF core (Q.922) (Q.922) 1.430/1.431 1.430/1.431 User (TE) S Network (NT) LAPF Functionality  LAPF (Link Access Procedure for Frame Mode Bearer Services) defined in Q.922  only core functionality used:  frame delimiting, alignment and transparency  frame mux and demux using addressing field  ensure frame is integral number of octets  ensure frame is neither too long nor short  detection of transmission errors  congestion control functions  form sub-layer of data link layer  data transfer between subscribers only Docsity.com Frame Relay Data Link Connections  logical connection between subscribers  data transferred over them  not protected by flow or error control  uses separate connection for call control  overall results in significantly less work in network Docsity.com