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Integrated Circuits

by: Furman Breitenberg

Integrated Circuits EEC 189O

Furman Breitenberg
GPA 3.93


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This 44 page Class Notes was uploaded by Furman Breitenberg on Wednesday September 9, 2015. The Class Notes belongs to EEC 189O at University of California - Davis taught by Staff in Fall. Since its upload, it has received 54 views. For similar materials see /class/191946/eec-189o-university-of-california-davis in Engineering Electrical & Compu at University of California - Davis.

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Date Created: 09/09/15
EEC 189Q Computer Networks pp 39aztz39oiz Layer WorszYVzli 7136 fl fti wll39f Wazf Reading Appendix A Chuah Fall 2004 Application communicating distributed processes App licationlayer p rotocols Applications and applicationlayer protocols Running in network hosts in user space Exchange messages to implement application eg email file transfer the Web One piece of an application Define messages exchanged by apps and actions taken Use services provided by lower layer protocols Page 1 Clientserver paradigm 39 al network app has two p ce cl 11L and server Client Initiates contact With server speaks first Typically requests service from s For Web client is implemented in browser for e mail in mail reader Server Provides requested service to client eg Web server sends re uested Web page mail server delivers e mail Chuah Fall 2004 What transport service does an app need Data loss Some apps eg audio can tolerate some loss Other apps eg file transfer telnet require 100 reliable Timin data transfer g Some apps eg lnternet telephony interactive BandWIdth games require low delay to Some apps eg multimedia be effedive require minimum amount of bandwidth to be effective Other apps elastic apps make use of whatever bandwidth they get Chuah Fall 2004 Page 2 Transport service requirements of common apps Application Data loss Bandwidth Time Sensitive file transfer no loss elastic no email 0 loss elastic no Web 39 losstolerant elastic n realtime audiovideo losstolerant 0 audio SKbiMb yes 100 s msec video10Kb5Mb stored audiovideo losstolerant same as above yes few secs interactive games losstolerant few Kbps up yes 100 s msec financial apps no loss elastic yes and no Chuah F3112004 Internet apps their protocols and transport protocols Application Underlying Application layer protocol transport protocol email smtp RFC 821 Top remote terminal access telnet RFC 854 TCP Web http RFC 2068 TCP file transfer ftp RFC 959 Top streaming multimedia proprietary Top or UDP eg RealNetworks remote file server NSF TCP or UDP Internet telephony proprietary typically UDP eg Vocaltec Chuah F3112004 Page 3 The Web some jargon 39 Web Page User agent for Web is called Consists of objects a browser Addressed by a URL MS Internet Explorer Most Web pages consist Netscape Communicator Of Server for Web is called Web Base HTML page and server Several referenced Apache public domain MS Internet Information URL has two components Server host name and path name WWW someSchool edusomeDeptpic gif Chuah Fall 2004 The Web the http protocol Http hypertext transfer protocol Web s application layer protoco PC running Clientserver model Explorer client browser that requests receives displays Web objects server Web server sends objects in response to requests http10 RFC 1945 http11 RFC 2068 Navigator Chuah Fall 2004 Page 4 The http protocol more http TCP transport service http is quotstatelessquot Client initiates TCP connection Server maintains no creates socket to server port 80 information about past client requests Server accepts TCP connection from c ient a31de http messages applicationlayer protocol messages exchanged Protocols that maintain state between browser http client and are comp ex Web server http server Past history state must be maintained TCP connection closed If serverclient crashes their inconsistent must be reconciled Chuah Fall 2004 9 http example contains text references to 10 jpeg images Suppose user enters URL www 39 39edii nmelquot index 1a http client initiates TCP connection to http server process at 1b http server at host wwwsomeSchooledu Port 80 is WWW somesehooledu Waiting for default for http server TCP connection at por 80 accepts connection notifying client 2 http client sends http request message containing URL into TCP comecnon SOCket 3 http server receives request message forms response message containing requested object someDepamnenthomeindex sends message into socket time Chuah Fall 2004 10 Page 5 http example cont 5 http client receives response ontaining htrnl file displays htrnl Parsing htrnl file finds 10 referenced jpeg objects 6 Steps 15 repeated for each of 10 jpeg tun objects Chuah Fall 2004 4 http server closes TCP connection Nonpersistent and persistent connections Nonpersistent HTTP10 Serverparses request responds and closes TCP connection 2 RTTs to fetch each object Each object transfer suffers from slow start But most 10 browsers use parallel TCP connections Chuah Fall 2004 Persistent Default for HTTP11 On sarne TCP connection server parses request responds parses new request Client sends requests for all referenced objects as soon as it receives base HTML Fewer RTTs and less slow start Page 6 Electronic Mail Three major components User agents Mail servers Simple mail transfer protocol smtp aka mail reader Composing editing reading mail messages e g Eudora Outlook elm Netscape Messenger 0mg01 g message queue Outgoing incoming messages V stored on server user mz box Chuah Fall 2004 13 Electronic Mail mail servers Mail Servers Mailbox contains incoming messages yet to be read for user Message queue of outgoin to be sent mail messages smtp protocol between mail servers to send emai messages Client sending mail server Server receiving mail server Chuah Fall 2004 14 Page 7 Electronic Mail smtp RFC 821 Chuah Fall 2004 Uses tcp to reliably transfer email msgfrom client to server port 25 Direct transfer sending server to receiving server Three phases of transfer IIandshaking greeting Transfer of messages Closure Commandresponse interaction Commands ASCII text Response status code and phrase Messages must be in 7bit ASCII Sample smtp interaction MOMOOOMOMOMOMOM Chuah Fall 2004 220 hamburgeredu HELO crepesfr 250 Hello crepesfr pleased to meet you MAIL FROM ltalicecrepesfrgt 250 alicecrepesfr Sender ok RCPT TO ltbobhamburgeredugt 250 bobhamburgeredu DATA 354 Enter mail end with Do you like ketchup How about pickles Recipient ok quotquot on a line by itself 250 Message accepted for delivery QUIT 221 hamburgeredu closing connection Page 8 above lets you send email without using email client reader Try smtp interaction for yourself telnet servername 2 5 see 220 reply from server enter HELO MAIL FROM RCPT TO DATA QUIT commands Chuah Fall 2004 17 smtp final words Smtp uses persistent Comp aris on with http connections http pull Smtp requires that message header amp body be in 7bit 39 Emall Pugh as Both have ASCII Certain character strings are commandresponse net Perm th m message interaction status codes eg CRLF CRLF Thus message has to be encoded http each object is usually into either base64 encapsulated in its own or quoted printable response message Smtp server uses smtp multiple objects CRLF CRLF to determine message sent in a multipart end of message message is Chuah Fall 2004 Page 9 Mail message format RFC 822 standard for text message format Header lines eg To From s b Body the message characters onl II Chuah Fall 2004 smtp protocol for exchanging 39 s u 39ect di erent um smtp cumman header Message form at multimedia extensions MIME version method used A to encode data multimedia data type subtype parameter declaration MIME multimedia mail extension RFC 2045 2056 Additional lines in rnsg header declare MIME content type From alicecrepes fr To bobhamburgeredu Subject Picture of yummy crepe MIME Version 0 gtContent Transfer Encoding base64 7Content Type imagejpeg base64 encoded data base64 encoded data encoded data Chuah Fall 2004 Page 10 M ContenteType typesubtype parameters Text Video 39 Example 5let P951 Example subtypeszmpeg Plain I hth quicktime Image Application Other data that must be processed by reader before Viewable Example subtypes jpeg gif Audio E xample subtypes Example subtypes basic ms rd octet Bbit mulaw encoded stream 32kadpcm 32 kbps coding Chuah Fall 2004 Multipart Type F om alicecrepesfr To bob urgeredu Subject Picture of yummy crepe MIME Version 10 quot quot 3 mn39lt39ih 14 mi ri 1 766789 98766789 A A m a 5 a r u Content Type textplain Dear Bob Please find a picture of a crepe 98766789 Content Transfer Encoding base64 Content Type imagejpeg base64 encoded data 98766789 Chuah Fall 2004 Page 11 Mail access protocols i SMTP SMTP v POP3 or b is 7 MAP V U I sender39 s mail receiver39s mail server SMTP deliverystmage to receives serve Mail access pxotoml retrieval cmse nex POP Posto ice Protocol RFC 1969 Authorization agent ltgtserver and download IMAP Interneth Access Pmtocol RFC 1730 More features more complex Mampulatron of stored msgs on server HTTP Hmmail Yahool Mail etc quahfa zood 23 POPS protocol OK papa serve ready useralice Authorization phase ox Client commands 555 hungry K use successfully logged on 7 user declare usemame 7 pass password Server responses s ox s ERR Transaction phase cheg bv list list message 11 ers zetz retrieve message by number et 1 ltmesssge 1 contentsgt dele 1 et 2 ltmesssge 1 contentsgt delede1ete quit dele 2 it OK PHYS mm signing at mushmzom 24 Page 12 EEC 189Q Computer Networks hwr hmvay RQ Stopamisz go za Emf fe dz39w R mt Z a un gZ K2227 nk gy Reading 5152 Error Recovery Reliable deliver over unreliable channel How to recover from corruptedlost packets Error detection and retransmission With acknowledgements and timeouts Also called Automatic Repeat Request ARQ Retransmission incurs round trip delay Error correcting codes Also called Forward Error Correction FEC No sender retransmission required Chuah Fall 2004 Page1 Error Control Automatic Repeat Request ARQ Basic concept detect error and request retransmission of those erroneous frames Different retransmission strategies 0 Stopandwait GobackN Selective repeat Two factors 1 Correctness Do we succeed in releasing each packet once and only once without errors 2 Efficiency How much BW is wasted by unnecessary waiting and unnecessary retransmission Chuah Fall 2004 Assumptions we make the following assump ion The receiver knows when frames start and end To analyze different retransmission strategies t s 2 All frames containing transmission errors are detected 3 Each transmitted frame experiences nonzero delay before arriving at receiver Some frames might e lost Those that arrive are assumed to arrive in the same order as transmitted with or without errors Node A Node B A Error detected Chuah Fall 2004 Page 2 StopandWait Basic idea Sender A transmits a packet then wait lf frame is errorfree B sends acknowledgement ACK else B sends a negative acknowledgement NACK Senderl sends next packet or retransmit when it receives ACK or NACK Problem 1 ACKNACK could get lost too Solution Timer at sender When node A times out it retransmits the packet Chuah Fall 2004 Potential problems with the basic scheme Unnumbered frames have problems l Node A times out and resends frame Node A ACK Node B Does this frame contain packet 0 or 1 Release 1 packet to higher layer Solution Add sequence number in the frame a er Chuah Fall 2004 Page 3 Potential problems with the basic scheme Not good enough gt Unnumbered ACKs also have problems I Node A times out and resends frame Sequence Number Node A E E W Release Discard duplicate Packet 0 Solution Return Sequence of the next packet expected instead of ACKNACK Chuah Fall 2004 StopandWait ARQ Timeout Timeout Sequence Number I SN NodeA III III RN1 RN1 Node B n Request Number 1 RN Release Discard duplicate Packet 0 Note Node A delays retransmitting packet l on the second request of it to avoid unnecessary retransmission Chuah Fall 2004 Page 4 Chuah Fall Alternating Bit Protocol StopAndWait principles Uses timers seqno s 01 error detection bits Frames and Ack s are numbered with Alternating 0 and 1 At each instant the receiver Expects a particular seqno Discards frames with wrongunexpected seqno 2004 Chuah Fall 2004 StopandWait ARQ Remaining problem SN amp RN can become arbitrarily large with increasing time Send number modulo an integer Module 2 is sufficient Node A Node B Timeout IIl kN RN RNw RN1 L l 1 Release Discard Packet 0 Release Packet 1 Il gt Page 5 Problem with StopandWait Sender Rec eiver Can t keep the pipe full Utilization is low When bandwidthdelay product is large very eff1c1ent Example 15Mbps link X 45ms RTT 675Kb 8KB 1KB frames implies 18 h link utilization Can we do something else while wuitingfor an ACK Chuah Fall 2004 Pipelining Allow multiple outstanding unACKed frames Upper bound on unACKed frames called window Sender Receiver Time Chuah Fall 2004 Page 6 Pipelined Protocols Sender allows multiple inflight yettob eacked plltts Range of sequence numbers must be increased Buffering at sender andor receiver data packet a a stopandwoit protocol in operation b a pipelined protocol in operation Two generic forms of pipelined sliding window protocols GoBaCkN and SelectiveRepeat Chuah Fall 2004 13 Windowbased ARQs Idea Allow Sender to keep transmitting a window of packets while waiting for ACKs Another function of sliding window protocols gt Flow Control What happens if the sender tries to transmit faster than the receiver can accept Data will be lost unless flow control is implemented We will get back to this when we talk about TCP Chuah Fall 2004 14 Page 7 Sliding Window Protocols Some Definitions Sequence Number SN each frame is assigned a SN that is incremented as each frame is transmitted Sender Window Keeps track of SNs for frames that have been sent but not yet acknowledged Receiver Window Keeps track of sequence numbers for frames that the receiver is allowed to accept Maximum Sender Window Size W5 The maximum number of frames the sender can transmit without receiving any ACKs Maximum Receiver Window Size The maximum number of frames the receiver may receive before returning an ACK to the sender Chuah Fall 2004 Maximum Sender Window Size With maximum window size of 1 the sender waits for an ACK before sending another frame With maximum window size of Ws the sender can transmit up to Ws frames before being blocked allows sender to transmit several frames before receiving an A also a form of pipelining gt keeps the link from being idle Chuah Fall 2004 Page 8 Maximum Receiver Window Size Chuah Fall 2004 With a maximum window size of 1 the receiver must receive and process every frame in sequence With a maximum window size of WK the receiver can receive and process up to frames before acknowledging them The receiver can still accept and buffer frames received after a frame that is losterroneous Allow piggybacking of ACK onto the header of an outgoing data frame in the reverse direction 0 Full duplex transmission Sliding Window Protocol General Remarks Chuah Fall 2004 The sending and receiving windows do not necessarily have the same maximum size Any frame whose SN falls outside of the receiver window is discarded by the receiver The sender window s size grows and shrinks as frames are transmitted and acknowledged Unlike the sender window the receiver window always remains at its maximum size Page 9 What About Errors What if a data or acknowledgement frame is lost when using a sliding window protocol GoBackN Selective Repeat Chuah Fall 2004 19 GoBackN Protocol Sender keeps copy of up to W5 outstanding packets k bit sequence number SN in packet header When the receiver notices a missingerroneous frame It discards ALL frames with greater SNs and sends no ACK Sender timeout 139 retransmit all the frames in its sending window packet i and all frames after that with higher SNs Cumulative ACK ACKi ACKs all packets up to including SN i send base nexfseqnum 1 i aired IIIIIIHHHHHHHHIIIlIIH HHHH awed win ize Chuah Fall 2004 usable not yet sen r I not usable 20 Page 10 GoBackN Example Consider WS 4 Sender keeps copy of up to 4 outstanding packets 0 0 1 2 Node A i 0 1 0 1 x LnkwN LIIAKA 01 D gtqu Node B OK OK OK OK Chuah Fall 2004 GoBackN Example 1 Rule when error occurs retransmit packet plus all subsequent packets I I Time out 0 I 0 0 0 0 0 0 0 1 1 1 1 1 1 2 2 2 2 t NodeA 3 3 I 0 1 2 3 1 2 3 NodeB H Discard Receiver does not need to buffer packets VNR1 Chuah Fall 2004 Page11 GoBackN Example 2 Rule when error occurs retransmit packet plus all subsequent packets Time out 0 H 0 0 0 1 2 2 2 1 1 1 2 3 3 2 2 3 4 t Node A 3 4 I 0 1 2 3 2 3 4 Node B 0 Discard Chuah Fall 2004 23 GoBackN with Negative ACKs 0 0 0 1 2 2 2 1 1 1 2 3 3 2 2 3 4 t NodeA 3 4 0 1 2 3 2 3 4 N NodeB Discard Chuah Fall 2004 24 Page 12 Remarks on GoBackN Go BackN can recover from missing frames But It is wasteful If there are errors the sender will spend time retransmitting frames the receiver has already seen Chuah Fall 2004 Selective Repeat Receiver individually acknowledges all correctly received packets buffers all the correct frames that arrive following the bad one for eventual inorder delivery to upper layer When receiver notices a skipped SN it keeps acknowledging the last good SN Sender only resends packets for which ACK not received but not all its successors Sender timer for each unACKedpacket Sender window N consecutive SN s limits SN s of sent unACKedpkts Chuah Fall 2004 Page 13 Selective Repeat ARQ As in GoBackN Packet sent When available up to Window limit Unlike GoBackN Outoforder but otherwise correct is AC Ked Receiver buffers outoforder packets Sender on timeout of packet k retransmit just k Comments More receiver buffering than GoBack N More complicated buffer management by both sides Saves bandwidth 0 no need to retransmit correctly received packets Chuah Fall 2004 27 Selective Repeat Example 1 Packet 11 must not be sent until packet 117 W5 has been acknowledged to avoid overloading receiver buffer I I Timeout 0 0 0 0 0 0 0 4 7 7 7 7 2 2 2 2 t NodeA 3 3 3 3 I 3 0 1 2 Node B OK OK OK OK Receiver Buffer 3 Chuah Fall 2004 Release packet 0123 to upper layer Page14 Selective Repeat Example 2 I Timeout I 0 0 0 1 2 2 2 2 1 1 1 2 3 2 2 3 4 4 NodeA 3 45 5 5 Assign sequence number to each frame SeqNum Maintain three state variables send window size SW5 last acknowledgment received LAR last frame sent LES Maintain invariant LFS LAR lt sws S SWS l I t l LAR LFS Advance LAR when ACK arrives Buffer up to sws frames Chuah Fall 2004 NodeB OK OK OK OK OK OK 3 3 ReleaseL l 3 5 Release 2345 Chuah Fall 2004 29 SW Sender Page 15 SW Receiver Maintain three state variables receive window size RWS largest frame acceptable LAP last frame received LFR Maintain invariant LAF LFR lt RWS S vas LFR LAF Frame SeqNum arrives if LFR lt SeqNum lt LA gt accept gt if SeqNumlt LFR or SeqNumgt LAF discarded Send cumulative ACKs Chuah Fall 2004 Summary Data Link Control DLC Layer takes care of Framing Error detection Error correction or retransmission ARQ Retransmission Strategies Stopandwait GoBankN Selective Repeat Two important factor a Correctness safety amp liveness b Efficiency Chuah Fall 2004 Page 16 Analyzing E iciency ofARQ Protocols Let rpm time to process a packet N 0 at a node Imp one way propagation time rpm transmission time of a packet Ef ciency or Utilization E time spent 39 39 useful data total time spent incl waiting amp retransmissions Efficiency Without Errors n I Pr oa I Node A 1 H Prop Proc r Ef dmy TransP 2Prop Proc TransA TransP S Chuah Fall 2004 34 Page 17 Efficiency with Error Timeout T P S A 1p B Let p Prob error amp 139 time to send a packet ET 1705 p TET Eh plpT S I E l llg iTransP HT ChooseTS gt iff k l e g 172211111ng S Chuah Fall 2004 35 Efficiency of StopandWait ARQ Without error 7amp tpk 2 2ampme Let a thP tpkt 112a With Error p 25 fig Nr tpkt 2 tprop where N expected of transmission for a frame Nr 11P 50 f stoprandwait p LL 12u Chuah Fall 2004 35 Page18 Selective Repeat Protocol Efficiency Analysis I N S W Node A l39 W Without error Zif k l e g min WX TrunsPS l wuueu Chuah Fall 2004 Analysis Cont d Id D39 I s w W 39 A I Let p Proberror W infinity 1 Expected number of attempts to send a packet LP i mi 1 1 TrunsPl 7 Node A Nuu Efficiency Chuah Fall 2004 Page19 Chuah Fall 2004 Efficiency of Sliding Window Protocol Let W window size S timeout and assume S gt tpkt 2t So if Wtpktgttpkt 2t prop prop the link is always full With packets Without error 7 1 if W gt2a1 ifW lt2a1 Chuah Fall 2004 Efficiency of Selective Repeat SR With Error p the error free equation needs to be divided by Nr which is 11p 5SRp1 P SR p ifWgt2a1 W17 2 ifWlt2a1 2u1 Page 20 EEC189Q Computer Networks ayeraf rczzi ecture Reference Chapter 2122 231 Recap from last lecture Circuit vs Packet switching Multiplexing strategies Deterministic vs statistical multiplexing Fundamental issues in networking Communication network is a complex distributed system How do we implement it How do we control it Chuah Fall 2004 Page 1 What is The Internet The Internet Collection ofnetworks and routers that span the network intranet private may use leased lines firewa Chuah Fall 2004 use the TCPIP protocols toforrn a single cooperative virtual connection ofdi erent LANs within an organization usually small but possibly hundreds of routers may be connected to the Internet or not often by 11 world and Hosts end systems 7 pc s workstations servers 7 PDA s phones toasters router server running network apps Communication links 7 Pointtopoint multiaccess 7 fiber copper radio satellite Routers forward packets chunks of data thru network Internet network of networks compan Internetis a specific internet network I Chuah Fall 2004 Elements of a Network E workstation new 4a mo bile Page 2 Internet Architecture Chuah Fall 2004 Internet Structure Network of Networks Roughly hierarchical Internet backbone core Tier1ISlseg ATampT Sprint UUNet BBNGenuity providing nationalinternational coverage Regional lSPs Tier2 Tier3 Access networks at the edge Residential enterprise campus network small local ISPs Chuah Fall 2004 Page 3 Chuah Fall 2004 NAPS NSPs ISPs NSF National Service Provider Tier 1 Backbones Example Inlemel MCI Sprint Link UUNET NAP National Access Point customers Chuah Fall 2004 Private Peering Private Peering Private Peering Page 4 Click here for a closer look at the Click here for Sprint network in Washington state a closer look at the Sprint network on the East Coast ir I New York 39ennsauken Relay 39 Wash DC Click here for a closer look at the Sprint network in Northern California Sprint Pearl Cityin Hawaii is a I a future network location a Chuah Fall 2004 litililET39S North Jamaican internet Backbone mum ElliTilquot h mrm r quota Elm mm HH T H rm Turning mmmw Hem mm ruminant Luis I mmquot AHEELE Hutu a 39 smugE Mimi i a Single hub Sin l m ltl le 5 1 A Elngloimultlpluim 3 Elwin43L I L d bpsj mumps rumpus I Multiple huh mlemltipte D5 1 39Slnglwmultilplq at 4 Jimmy5 QEIEths HI Will all llHl lIllili links are IMer Chuah Fall 2004 10 Page5 minim UUNET39s Glnhal Internet Bazkhnne Types of links 7 951 r Dssm a w E evels ofservices o ered commerciall r 2 Relay minim 39n 1 544 Mbps 24x 54Kbps 44 735 Mb 5 Links for Long Haul Transmission Possibilities r FwerSONET 7 moer 7 PW 7 P TM er Frame Relay we WDM Page 6 How do we study this cloud of network How was it designed Why is the Internet the way it is today Can we reduce its complexity to something tractable Chuah Fall 2004 13 Layered Architecture Layering simplifies the architecture of m lb e SamCV complex s s em Layer N relies on services from layer N1 to provide a service to layer N1 Layer N1 Interfaces define the services offered SerVice required from a lower layer is independent of it39s implementation Layer N 7 Informationcomplexity hiding 7 Layer N change doesn39t affect other layers 4 7 Similai ject Chuah Fall 2004 14 Page 7 Protocols Protocol rules by which network elements communicate Protocols define the agreement between peering entities The format and the meaning of messages exchanged Protocols in everyday life Examples traffic control open roundtable discussion etc JILL a G g Q 9 O jog g x Traf c Carma Flam Carma Chuah Fall 2004 Protocols and Services Protocols are used to implement services Peering entities in layer N provide service by communicating with each other using the service provided by layer Nl Logical vs physical communication Physicuicomm Rumquot Physicnlcnmm Emilia mam PM Pm Chuah Fall 2004 Page 8 ISO 081 Reference Model 1974 Chuah Fall 2004 ISO International Standard Organization OSI Open System Interconnection Started to 1978 first standard 1979 ARPANET started in 1969 TCPIP protocols ready by Goal a general open standard Allow vendors to enter the market by using their own implementation and protocols 081 Reference Model Application Presentation Session Transport Network Datalink Physical OSI Protocol Stack Chuah Fall 2004 OSI conceptually define service interface amp protocol Service says what a layer does Interface says how to access the service Protocol says how is the service implemented A set ofrules and formats that govern the communication between two peers Page 9 ISO 081 Reference Model Seven layers Lower three layers are peertopeer Next four layers are endtoend Layerto layer communication Session Network Data i nk Network Datalink Network Datalink medium Chuah Fall 2004 Data Transmission A layer can use only the service provided by the layer immediate below it Each layer may change and add a header to data packet liar data QF E 39 Chuah Fall 2004 data lit E N o Page 10 Protocol Packets Protocol data units PDUs paclltets exchanged between peer entities Service data units SDUs packets handed to a layer by an upper layer Data at one layer is encapsulated in packet at a lower layer 7 Envelope within Envelope PDU SDU optional header or trailer Protocol Packet my Layer 2 Tmile 93 etgt Hm Request Message HIP eg 9 3 Ethernet quotD 599mm F Packet reme Ginah Fa 2004 Implementation of Layers Ginah Fa 2004 Page 11


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