CMPE 150 Winter 2009 Lecture 7 Januaryy 27 2009 PE P E Mantey CMPE 150 Introduction to Computer Networks Instructor Patrick Mantey mantey soe ucsc edu htt http www soe ucsc edu mantey d t Office Engr 2 Room 595J Office hours Tues 3 5 PM Mon 5 6 PM TA Anselm Kia akia soe ucsc edu Web site http www soe ucsc edu classes cmpe150 Winter09 Text Tannenbaum Computer p Networks 4th edition available in bookstore etc Syllabus Today s Agenda Flow Control Protocols continued Link Layer y Point to point Protocols Standards Data Link HDLC PPP MAC Sub layer Link Sharing Aloha Ethernet Sliding Window Protocols Supports bi directional data transfer Full Full duplex duplex piggy backing of acks Sliding Window Protocols A One Bit Sliding Window Protocol A Protocol Using Go Back N A Protocol Using Selective Repeat A Protocol Using Go Back N Pipelining and error recovery Effect on an error when Figure 3 16 a Receiver s window size is Tannenbaum 1 Sliding Window Protocol Using Go Back N Simulation of multiple timers in software Tannenbaum Figure 3 18 A Sliding Window Protocol Using Selective Repeat a Initial situation with a window size seven b After seven frames sent and received but not acknowledged c Initial situation with a window size of four d After Aft ffour fframes sentt and d received i d b butt nott acknowledged k l d d Tannenbaum Figure 3 20 Protocol Verification Finite State Machine Models Petri Net Models Finite State Machine Models a State S di diagram for f protocoll 3 3 b Transmissions Petri Net Models A Petri net with two places and two transitions Petri Net Models 2 A Petri net model for protocol 3 Transparency Transparency Dictionary Transparency p y the quality q y or state of being g transparent Transparent Function adjective d Etymology Middle English from Medieval Latin transparent transparens transparent transparens present participle of transparEre to show through from Latin trans parEre to show oneself 1 a 1 having h the h property off transmitting light without appreciable scattering so that http www m w com cgi bin dictionary va transparency bodies lying beyond are seen clearly Packet Switching A comparison of circuit switched and packet packetTannenbaum Figure 2 40 switched networks Tannenbaum page 153 Another difference is that circuit switching is completely transparent The sender and receiver can use any bit rate format or framing method they want The carrier does not know or care It is this transparency that allows voice data and fax to coexist within the phone system ARQ Protocols Automatic Repeat ReQuest Protocols that wait for ACK before sending more data ACKs now are used for flow AND error control What can happen pp At receiver frame arrives correctly frame arrives damaged g frame does not arrive At sender ACK arrives correctly ACK arrives damaged ACK does not arrive ARQ Protocols Sender Send frame 0 Start timer If ACK 0 arrives send d frame f 1 1 If timeout re send frame 0 Receiver Waits for frame If frame arrives check if correct sequence number number Then send ACK for that frame Go to Sliding Window Protocol Using Go Back N Simulation of multiple p timers in software Tannenbaum Figure 3 18 Animations Simulation http netbook cs purdue edu othrpags page15 htm http www humboldt edu 7Eaeb3 telecom SlidingWindow html http media pearsoncmg com aw aw kurose network 2 applets go back n go back n html Data Link Protocols HDLC High Level Data Link Control The h Data Link i k Layer in i the h Internet High Level Data Link Control Derived from SDLC of IBM Synchronous Data Link Control Protocol Frame format for bit oriented protocols High Level Data Link Control 2 High Level Control field of a An information frame b A supervisory frame An c A unnumbered b d fframe DLL Protocols SLIP Serial Line IP Dial up Di l protocol t l No error control Not N standardized d di d PPP Point to Point Protocol Internet standard for dial up connections Provides framing similar to HDLC The Data Link Layer in the Internet A home personal computer acting as an internet host PPP Point to Point Protocol The PPP full frame format for unnumbered mode operation PPP Point to Point Protocol 2 A simplified phase diagram for bring a line up and down PPP Point to Point Protocol 3 The LCP frame types Other DLL Protocols LLC Logical Link Control Part of the 802 protocol family for LANs LANs Link control functions divided between the MAC layer and the LLC layer layer LLC layer operates on top of MAC layer Dst Dst MAC MAC control addr Src Src MAC addr Src LLC Dst Src Dst LLC LLC ctl Data addr addr FCS Medium Access Control Sublayer Chapter 4 Shared Media Broadcast Network Multiaccess Channel Random Access Channel Local Area Networks LANS Link Sharing Issues Traffic separation from different users Link utilization Examples p Ethernet 802 11 Multiplexing Sharing a link channel among multiple source destination pairs i Example high capacity long distance trunks fiber microwave links carry multiple connections at the same time Multiplexing Techniques 3 basic types yp Frequency Division Multiplexing FDM Time Division Multiplexing p g TDM Statistical Time Division Multiplexing STDM FDM High bandwidth medium when compared to signals to be transmitted Widely used e g e g TV TV radio radio Various signals carried simultaneously where each one modulated onto different carrier frequency or channel Channels separated by guard bands unused to prevent interference FDM 1 2 N Frequency Time TDM TDM or synchronous TDM TDM High data rate medium when compared to signals to be transmitted N 2 1 Frequency Time TDM Time divided into time slots slots Frame consists of cycle of time slots In each frame frame 1 or more slots assigned to a data source source U1 U2 1 2 frame UN N 1 2 N Time TDM No control info at this level level Flow and error control To be provided on a per per channel channel basis basis Use DLL protocol such as HDLC Examples E l SONET S Synchronous h O Optical ti l Network for optical fiber s simple simple fair fair s inefficient Statistical TDM Or asynchronous TDM Dynamically allocates time slots on demand N input lines in statistical multiplexer but onlyy k slots on TDM frame where k n Multiplexer scans input lines collecting data until frame is filled Demultiplexer receives frame and distributes data accordingly STDM Data rate on mux ed line sum of data rates from all i input t lines li Can support more devices than TDM using same link Problem bl peakk periods i d Solution multiplexers have some buffering
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