The Transport Layer

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Chapter 6 The Transport Layer 

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The Transport Service Services Provided to the Upper Layers Transport Service Primitives Berkeley Sockets An Example of Socket Programming: - An Internet File Server 

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Services Provided to the Upper Layers Host 1 Host 2 Application Application {orsession) Application’transport (or session} layer Transport | interface layer address TPDU Transport | Transport ‏تم‎ ‎entity | ‘Transport entity protocol + Network ‎Transporvinetwork‏ تیم ‎Network layer‏ سس ‎Network layer‏ ‎ ‎ ‎ ‎ ‎The network, transport, and application layers. ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ 

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Transport Service Primitives Primitive Packet sent Meaning LISTEN (none) Block until some process tries to connect CONNECT CONNECTION REQ. Actively attempt to establish a connection SEND DATA Send information RECEIVE (none) Block until a DATA packet arrives DISCONNECT | DISCONNECTION REQ. | This side wants to release the connection The primitives for a simple transport service. 

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Transport Service Primitives (2) Frame Packet TPDU header header header 7 ‏ص‎ TPDU payload 0 سم Frame payload The nesting of TPDUs, packets, and frames. 

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Transport Service Primitives (3) ات 7 Connection request TROU recelved i PASSIVE ACTIVE lesTAsLiSHNeNt| ESTABLISHMENT PENDING PENDING (Connect primitive Connection accepted ‘eects POU received Disconnect a ‘ACTIVE saci DISCONNECT | PENDING ‏تا‎ “| HE | -“Disconnestonreqoosr primitive executed TPOU racoWved A state diagram for a simple connection management scheme. Transitions labeled in italics are caused by packet arrivals. The solid lines show the client's state sequence. The dashed lines show the server's وج سم سس اوه 

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Berkeley Sockets Meaning Create a new communication end point Attach a local address to a socket ‘Announce willingness to accept connections; give queue size Block the caller until a connection attempt arrives Actively attempt to establish a connection Send some data over the connection Receive some data from the connection Release the connection Primitive SOCKET BIND LISTEN ACCEPT CONNECT SEND RECEIVE CLOSE The socket primitives for TCP. 

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(This page contains efent program that can request fle rom the server program * on the ext page. The server responds by sencing the whol te ‘include <systypes.h> finclude <sysisocket > ‎n>‏ مه ‎‘include <netdb hs ‎‘tootine SERVER_PORT 12345, ‘+ arbitrary, but clent& server must agree +) ‘#dotine BUF SIZE 4096 1+ Block ranster size +! ‎Int malik arge, char *"argv) ‎1 ‎inte, s, byes: char bufBUF size} 1 butler or incoming fle +! Stuck hostent sh "info about server»! struct sockaderin channet ‘+ holds I aaress */ ‎ ‎if (arge!= 3) fatal"Usage: cient server-name fle-name') | ‘+ ook up host's IP address «/ ‎if Qh fatal¢gothostbynamo failed’); ‎ockel(PF_INET, SOCK STREAM, IPPROTO TCP): ‎i (s-0) fatalsocket’ ‎] sizeot(channel) ‎channelsin famiy= AF_INET; ‎Imemepy(Gchannelsin adds ager, oh ade ht length ‎Channel ‏ی‎ ‎ ‎ ‎ ‎‘onnects (struct sockaddr ») channel, sizeot{channe) if{e-<0) fatal(connect fates: ‎/ Connection is now established. Send file name including 0 byte at end. +! ‎ ‎ ‎ ‎writs, argv2,srlon(argt2}+1) ‎Go get the fe and wre to standard ouput. ‏اه‎ ‎۷ 0 | A (oytas <= 0) ext} 1s check for end offi +! ito, ut, bytes) 1+ wre to standara output +! ‎ ‎) ‎1 ‎۳ ‎1 ‎rina", sing) ‎ext) ‎5 ‎Socket ‎Programmin ‎g Example: Internet File Server ‎Client code using sockets. 

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۳ 3 ‏هه‎ esysenth> | ۳ ‘into enol he ‘cine SERVER_PORT 12345 arbiter, but ent & sewer must agree +) Adeline BUF_SiZE 4086 oc raster ie ‘eine QUEUE SZE 10 ivan are ca“) Int ‏فلا‎ 50 bytes, on = 1: ‏با از و مه‎ outgoing te»! Struct sockaddr In char ‘hls acess» 1+ But acess stro ta bind to socket. »/ memsetchannet 0, szel(channa), Ize channel +/ hanno. sin fay = AF_INET, ‘hanna shad adc» honiINADOA. ANY) ‘hanno sit_por = hlens(SERVER. PORT) ‘+ Passve open. Walt for connection, + ‎scoketAF-INET, SOCK STREAM, IPPROTO.TCP); + create sockot +‏ و ‎1g) fatal socket ale‏ ‎Setzockopfs, SOL-SOCKET, SO. REUSEADOR, (cher +) Son, casio): ‎= bins, (ctuct sockaddr») hanno, sizeo{channel 1 (20) faa be tea) ‎|etten(s, QUEUE. SIZE); J+ epeaty queue 1۱۱2 ۵( ‏ماه هه‎ ‎‘+ Sockot is now set up and Bound, Wal for connostion and procass ‏اه‎ ‎ ‎ ‎ ‎wn (1) sa aecepts 0,0 + blak for eanneton request »/ (ga <0) fata‘accapt fale reads, but, BUF SIZE) ‘tna te nam fom sockel + J» Got and return he He») t= open, ©. ADONLY}; ‘open te eto be sent back +! (Gd = 0 fataiepen tale) ‏ی‎ ‎bye = reals, bu, BUF SIZE) road om fe +) 1 ytes <= 0} break "sched frond a le */ vwrio(sa, bu, bles: Jn we bytes to sockot 0 ‏مجمه دز‎ 16 ‎ose) ‏مج‎ connection +! ‎Socket ‎Programmin ‎g Example: Internet File Server (2) ‎Client code using sockets. 

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Elements of Transport Protocols ° Addressing ¢ Connection Establishment * Connection Release ° Flow Control and Buffering ۰ Multiplexing ۰ Crash Recovery 

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Transport Protocol Router Router Subnet communication channel Host (a) (b) (a) Environment of the data link layer. (b) Environment of the transport layer. 

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Addressing Host 2 Server® \ TSAP i896 NSAP Sener Applicaton 35 مو سم layer “Transport layer Network layer Data ink layer Physical layer transport connections. Host 1 Application Oo” 1208 process سس ۳ TSAPs, NSAPs and 

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Connection Establishment Host 4 Host2 ime» ‏رهم‎ ‎server) © | سم @ How a user process in host 1 establishes a connection with a time-of-day server in host 2. 

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Connection Establishment (2) T 2 Forbidden ‏بح‎ ‎2 _| message Bor g 2 x g 5 s 8 3 Restart after 5 & Oe crash with 70 8 0 ‘Actual sequence é ‏رب بيك‎ numbers used 0 30 60 90 120 150 0 Time Time (a) 0 (a) TPDUs may not enter the forbidden region. (b) The resynchronization problem. 

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Connection Establishment (3) Three protocol scenarios for establishing a connection using a three-way handshake. CR denotes CONNECTION REQUEST. (a) Normal operation, (b) Old CONNECTION REQUEST appearing out of nowhere. (c) Duplicate CONNECTION REQUEST and duplicate ACK. 

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Connection Release Host 1 Host 2 | هس pack DATA DATA 08 ‏سح‎ ‎No data are delivered after a disconnect request Time Abrupt disconnection with loss of data. 

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Connection Release (2) & Wit army Ay The two-army problem. 

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Connection Release (3) Host 1 Host 2 Host 1 Host 2 Send DR DR Send DR OR + start timer a + start timer pe Seed DE Send DR 9۶ ‏و | ای‎ + sta ier Release Feleass connection ‏یتست‎ | گس همجمج ‎sensack LACK‏ | | مه ‏روف کش ‎connection‏ ‏مس ‎connection‏ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎(a) (b) ‎Four protocol scenarios for releasing a connection. (a) Normal case of a three-way handshake. (b) final ACK lost. ‎ ‎ ‎ ‎ ‎ ‎ 

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Connection Release (4) Host 2 Send DR & start timer ctimbout release connection ات | عفر کر (d) Host 1 Send DR + start timer (Tinfeout) send DR + start timer (N Tinfeouts)) release connection ost and Host 2 Send DR & start timer Send DR & start timer Release connection ponse ل — ‎ee |‏ »تفت Host 1 Send DR + start timer (Timeout) send DR + start timer’ Release connection Send ACK (co) (c) Response lost. (d) Res: subsequent DRs lost. 

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Flow Control and Buffering ۱ J 0 ۱ Trou 4 Unused space \ (a) Chained fixed-size buffers. (b) Chained variable- sized buffers. (c) One large circular buffer per connection. 

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Flow Control and Buffering (2) ‘Comments, A wants 8 buffers B grants messages 0-3 only Anas 3 buffers left now Anas 2 buffers left now Message lost but A thinks it has 1 left B acknowledges 0 and 1, permits 2-4 Anas 1 buffer left Abas 0 buffers left, and must stop A times out and retransmits Everything acknowledged, but A still locked ‘A may now send 5 B found a new buffer somewhere Abas 1 buffer left Ais now blocked again Ais still blocked Potential deadlock B ۱14 ۱۱۱۱۱۱۱ ۱ ۱ The arrows show the direction of transmission. An ellipsis (...) indicates a lost TPDU. A Message 1 + «request 8 bufters> 2 ‏سم‎ <ack=15,buf=4> 3 ‏حت‎ «seq=0, data = mo> 4 + <seq=1,data=mt> ‏عد و‎ «seq=2, data =m2> 6 - <ack = 1, buf =3> 7 + <seq=3, data =m3> ‏و‎ —+ — «seq=4,data=m4> ‏و‎ —~ — <seq=2, data =m2> 10 ‏لم‎ <ack=4, buf = 0> "+ ack = 4, buf = 1> 12 ‏اله‎ <ack=4, buf=2> 18 —* — <seq=5, data = m5> 14 ‏حا‎ <seq=6, data = mé> 15 -— — <ack=6, buf =0> 16 +++ <ack=6, buf=4> Dynamic buffer allocation. 

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Multiplexing Transport address ۰ ۰ ۰ Network ‎matters‏ سر ‎ ‎۰ ‎Se ge ‎Router lines ‎ ‎ ‎ ‎ ‎ ‎ ‎To router (a) (b) ‎(a) Upward multiplexing. (b) Downward multiplexing. ‎ ‎ ‎ ‎ ‎ 

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Crash Recovery Strategy used by receiving host First ACK, then write First_write, then ACK Strategy used by sending host ACWW) AWC —CAW) = CWA), = WAC WEA) Always retransmit ok uP OK 9 pup | ‏عنام‎ ‎Never retransmit Lost | ok | Lost ۱8۲ | Ok OK Retransmit in SO OK ‏ملام‎ | 1057 Lost | DUP 9 Retransmit in St Lost | 0k OK OK 0 DUP OK _ = Protocol functions correctly DUP_ = Protocol generates a duplicate message LOST = Protocol loses a message Different combinations of client and server strategy. 

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A Simple Transport Protocol ¢ The Example Service Primitives ¢ The Example Transport Entity ° The Example as a Finite State Machine 

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The Example Transport Entity Network packet Meaning CALL REQUEST Sent to establish a connection CALL ACCEPTED Response to CALL REQUEST CLEAR REQUEST Sent to release a connection CLEAR CONFIRMATION | Response to CLEAR REQUEST DATA Used to transport data CREDIT Control packet for managing the window The network layer packets used in our example. 

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The Example Transport Entity (2) Each connection is in one of seven states: Idle - Connection not established yet. Waiting - CONNECT has been executed, CALL REQUEST sent. Queued - A CALL REQUEST has arrived; no LISTEN yet. Established - The connection has been established. Sending - The user is waiting for permission to send a packet. Receiving - A RECEIVE has been done. DISCONNECTING - a DISCONNECT has been done locally. 1 2 

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The Example Transport Entity £23. fidefine MAX_CONN 32 J* max number of simultaneous connections */ define MAX_MSG_SIZE 8192 J+ largest message in bytes */ define MAX_PKT SIZE 512 J+ largest packet in bytes +/ tidefine TIMEOUT 20, fidefine CRED 1 define OK 0 fidefine ‏لالع همع‎ fidefine ERR_REJECT -2 fidefine ERR_CLOSED -3 fidefine LOW_ERR -3 typedef int transport_address; typedef enum {CALL_REQ,CALL_ACC,CLEAR_REQ,CLEAR_CONF,DATA_PKT,CREDIT) pkt type; typedef enum (IDLE, WAITING, QUEUED,ESTABLISHED,SENDING RECEIVING, DISCONN) cstate; * Global variables. */ transport_address listen_address; ‘I local address being listened to */ int listen_conn; J connection identifier for listen */ unsigned char data[MAX PKT SIZE]; _/* scratch area for packet data */ struct conn { transport_address local_address, remote_address; cstate stat ‘state of this connection +/ unsigned char *user_but_addr; J» pointer to receive buffer */ int byte_count; J sendireceive count »/ int cr_req_received; J set when CLEAR_REQ packet received */ int timer I used to time out CALL_REQ packets */ int credits; ‘J number of messages that may be sent +/ } conn[MAX_CONN + 1]; + slot 0 is not used */ 

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The Example Transport Entity (4) void sleep(void); * prototypes */ void wakeup(void); void to_net{int cid, int q, int m, pkt_type pt, unsigned char tp, int bytes): void from_net(int *cid, int +g, int *m, pkt type *pt, unsigned char «p, int *bytes); int listen(transport_address t) {/* User wants to listen for a connection. See if CALL_REQ has already arrived. */ inti, found for (i = 1; 1 <= MAX_CONN; i++) + search the table for CALL_REQ */ if (conn{i].state == QUEUED && connfij.local address == 1) { found break; } ‎(found == 0) )‏ از ‎No CALL_REQ is waiting. Go to sleep until arrival or timeout. +/‏ */ ‎listen_address =; sleep(); i= listen_conn ;‏ 1 ‎connfi}.state‏ ‎connfilimer‏ ‎:STABLISHED; /* connection is ESTABLISHED */ : /* timer is not used */ ‎ ‎ 

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The Example Transport Entity fe) listen_conn, / is assumed to be an invalid address */ to_net(i, 0,0, CALL_ACC, data, 0); Js tell net to accept connection */ return(i; ‏ع‎ return connection identifier */ 1 int connect(transport_address |, ransport_address r) (User wants to connect to a remote process; send CALL_REQ packet. */ inti: struct conn “cptr; data[0]=*; datalt] J» CALL_REQ packet needs these ‏اه‎ ‎MAX_CONN; J» search table backward +/ while (conn[i].state != IDLE && i> 1)i=i 15 if (connfi} state == IDLE) { ‘/* Make a table entry that CALL_REQ has been sent. */ ptr = 806001: cptr->local address = I; cptr->remote_address optr->state = WAITING; cptr->clr_req_ received cptr->credits = 0; cpt->timer = 0; to_net(, 0, 0, CALL_REQ, data, 2); sleep() ‘+ wait for CALL_ACC or CLEAR. REQ +/ if (cptr>state == ESTABLISHED) retumn(); if (optr>clr_teq_received) { 1+ Other side refused call. +/ cptr->stato = IDLE; J» back to IDLE stato */ to neti, 0, 0, CLEAR CONF, data, 0); roturn(ERR_ REJECT); } else return(ERR_FULL); Js reject CONNECT: no table space */ ۱ 

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The Example Transport Entity (6) int send(int cid, unsigned char bufptr(), int bytes) {/* User wants to send a message. */ inti, count, m; struct conn *cptr = &conn{cid); /* Enter SENDING state. 7 optr->state = SENDING; cptr->byte_count = 0; J+ # bytes sent so far this message */ if (cptr->clr_req_received == 0 && cptr->credits == 0) sleep(); if (cptr->clr_req_received == 0) { / Credit available; split message into packets if need be. */ do{ if (bytes — cptr->byte_count > MAX_PKT_SIZE) {/* multipacket message */ count = MAX_PKT_SIZE; m= 1; /* more packets later */ Jelse { J+ single packet message */ count = bytes - cptr->byte_count; m=0; _/* last pkt of this message */ 1 for (i = 0; i < count; i++) datafi] = bufptr{cptr->byte_count + i]; to_net(cid, 0,m, DATA_PKT, data, count); /* send 1 packet */ cptr->byte_count = cptr->byte_count + count; /* increment bytes sent so far */ } while (cptr->byte_count < bytes); _/* loop until whole message sent */ 

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The Example Transport Entity (7) optr->credits / * each message uses up one credit */ optr>state return(OK); Jelse ( optr->state = ESTABLISHED; return(ERR_CLOSED); /* send failed: peer wants to disconnect */ 1 1 int receive(int cid, unsigned char bufptr[], int +bytes) {/" User is prepared to receive a message. */ struct conn *cptr = &conn|cid]; it (optr->olr_req_received == 0) { /* Connection stil established; try to receive. */ optr->state = RECEIVING; optr->user_but_addr = bufptr; optr->byte_count = 0; data[0] = CRED; datalt to_net(cid, 1,0, CREDIT, data, 2); /* send credit »/ sleep); + block awaiting data */ *bytes = optt->byte_count; 1 cptr->state = ESTABLISHED; return(cptr->clr_req_received ? ERR_CLOSED : OK); } 

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The Example Transport Entity (8) int disconnect(int cid) {/ User wants to release a connection. */ struct conn *cptr = &conn{cid]; if (cptr->cir_req_received) { J+ other side initiated termination +/ optr-astate = IDLE; J+ connection is now released */ to_net(cid, 0, 0, CLEAR_CONF, data, 0); }else { J we initiated termination */ cptr->state = DISCONN; J+ not released until other side agrees */ to_net(cid, 0, 0, CLEAR_REQ, data, 0); 1 return(OK); } Void packet_arrival(void) {A packet has arrived, get and process it. */ int cid; J connection on which packet arrived +/ int count, i, q, m; pkt_type ptype;_/* CALL_REQ, CALL ACC, CLEAR_REQ, CLEAR_CONF, DATA PKT, CREDIT */ unsigned char data[MAX_PKT_SIZE]; _/* data portion of the incoming packet */ struct conn *eptr; from_net(&cid, &q, &m, &ptype, data, &count); /* go get it */ ‘&connicid]; 

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The Example Transport Entity CON J remote user wants to establish connection #/ datal1}; switch (ptype) ( ‘case CALL_RE ‘optr->local_address = datal0]; optr->remote_addres: if (cptr-slocal_address == listen_address) { listen_conn = cid; cptr->state = ESTABLISHED; wakeup(): ( ‏)اه‎ ‏عمجم‎ ‎1 optr->clr_req_receiver break: ‘case CALL_ACC: ] remote user has accepted our CALL_REQ */ optr-state = ESTABLISHED; wakeup(): break: case CLEAR_REQ: Js remote user wants to disconnect or reject call */ IMEOUT; UEUED; optr->timer 0; cptr->credits = 0; = IDLE; /* clear collision */ RECEIVING II cptr->state if (eptr->state it (eptr-sstate SENDING) wakeup(); J+ remote user agrees to disconnect +/ break: case CREDIT: /* remote user is waiting for data */ ptr-scredits += datal1}: it (cptr->state == SENDING) wakeup(); break; ‘case DATA_PKT: Js remote user has sent data +/ for (i = 0; | < count; i++) eptr->user_buf_addrfeptr-=byte_count + i] = datali); optr-sbyte_count += count; it (m == 0) wakeup); 

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The Example Transport Entity (10) } void clock (void) {/* The clock has ticked, check for timeouts of queued connect requests. */ inti struct conn *optr; for (i = 1; i <= MAX_CONN; i++) { ptr = 00 if (cptr->timer > 0) ) /+ timer was running ‏اه‎ ‎cptr->timer— ‎if (optr->timer == 0) { J timer has now expired */ cptr->state = IDLE; to_net(i, 0, 0, CLEAR_REQ, data, 0); 

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The Example as a Finite State Riva to __Wating _Quoued_Esabished Sending Recaiing comoting ۳۳" At Sod Ga ae AF Seats Viste Cal.feq A Walt tar ret 8: Son al 1: St ‘0: Set Cr rq. recive tag 2s: Send Czar cont At Record erect | 5000 90 212 ‏و ا‎ عم Pt: connection tabi امس مركن ‘SEND RECEWE مه مه مرسمه سس nein pets 81 The example protocol as a finite state machine. Each entry has an optional predicate, an optional action, and the new state. The tilde indicates that no major action is taken. An overbar above a predicate indicate the negation of the predicate. Blank entries correspond to 

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The Example asa Finite State connect ‏هد‎ ‎oe ‎GER RES CALL REG warn ‏مه‎ ‎CALL ACC. uisreN | estan. creo, | USHeD | receve 6 ‘CLEAR REQ. 1 5 seno_)$) ‏مس‎ ‏ممص وريد | هو‎ 1 oiscon NecTING CLEAR REO, CLEAR CONE The example protocol in graphical form. Transitions that leave the connection state mnnhannroan Katia Aoan Amittand far oimmnlinitr 

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The Internet Transport Protocols: UDP ٠ Introduction to UDP ۰ Remote Procedure Call ¢ The Real-Time Transport Protocol 

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Introduction to UDP Destination port UDP checksum, 32 Bits The UDP header. Source port UDP length 

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Remote Procedure Call Client CPU Server CPU 7 Client Server, 1 stub stub Client Server — 2 4 Operating system ¥ 4 Operating system ‏له سا‎ Network Steps in making a remote procedure call. The stubs are shaded. 

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The Real-Time Transport Protocol Ethernet IP UDP ۳ Multimedia application| ‏ا‎ header pester header RTP Socket interface RTP payload UDP ‏م‎ |+—— UDP payload ——+| Ethernet + ۱۳ payload ‏أحج‎ |+—— Ethernet payload ——_——+| (a) (b) User space os Kernel (a) The position of RTP in the protocol stack. (b) Packet nesting. 

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The Real-Time Transport Protocol (2) 32 bits 1 1۱۱۱۲۱ ۱۱۱۱۲۲۲۷۱۱۱۲۱۲۳۱ ۱۲۱ Ver. |P|x| Cc |M| Payload type ‘Sequence number Timestamp Synchronization source identifier Contributing source identifier The RTP header. 

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The Internet Transport Protocols: TCP duction to TCP [CP Service Model [CP Protocol [CP Segment Header Intro The 7 The 1 The 7 TCP Connection Establishment TCP Connection Release TCP Connection Management Modeling TCP Transmission Policy TCP Congestion Control TCP Timer Management Wireless TCP and UDP Transactional TCP 

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The TCP Service Model Port _| Protocol Use 21 FIP File transfer 23 Telnet. Remote login 25 SMTP. E-mail. 69 TFTP Trivial File Transfer Protocol] 9 Finger Lookup info about a user 80 HTTP World Wide Web 110 POP-3 emote e-mail access 119 NNTP USENET news Some assigned ports. 

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The TCP Service Model (2) ABCD IP header TCP header ‏يا‎ 8 ۸ (a) Four 512-byte segments sent as separate IP datagrams. (b) The 2048 bytes of data delivered to the application in a single READ CALL. 

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The TCP Segment Header 32 Bits Source port Destination port Sequence number ‘Acknowledgement number Tor ۸/۴ header 8۱55| ۷|۱ Window size length ۵۲۱۷۸ Checksum Urgent pointer Options (0 or more 32-bit words) 2 1 Data (optional) TCP Header. ۳ 

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The TCP Segment Header (2) 32 Bits ‏ربا یبا نير‎ Source address Destination address 00000000 Protocol = 6 TCP segment length The pseudoheader included in the TCP checksum. 

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TCP Connection Establishment Host 2 Host2 Host 1 SYN (SE0~ 5 Host 1 Seon [| sea =¥) snes 5 نو هر em seo Time SAA HACK ey 41) 0 (a) (a) TCP connection establishment in the normal case. (b) Call collision. 

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TCP Connection Management Modeling State Description CLOSED No connection is active or pending LISTEN The server is waiting for an incoming call SYN RCVD ‘A connection request has arrived; wait for ACK SYN SENT The application has started to open a connection ESTABLISHED | The normal data transfer state FIN WAIT 1 The application has said it is finished FIN WAIT 2 The other side has agreed to release TIMED WAIT _| Wait for all packets to die off CLOSING Both sides have tried to close simultaneously CLOSE WAIT _| The other side has initiated a release LAST ACK Wait for all packets to die off The states used in the TCP connection management finite state machine. 

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TCP Connection Management Modeling (2) \CONNECTISYN (Sep ofthe ay handel) close sent {Sip St he Say Fresh) 022-50 همه (ata vance state) ESTABLISHED 50-1 {evoane | iw سم همه [ 0 مه کر ‎sens‏ م سلیم ‎ ‎ ‎ ‎ ‎ ‎۸ ‏همه ‎TCP connection management finite state machine. The heavy solid line is the normal path for a client. The heavy dashed line is the normal path for a server. The light lines are unusual events. Each transition is labeled by the event causing it and the action resulting from it, ‎ ‎ ‎ ‎ ‎ 

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Sender Receiver Receivers buter 9 4k Empty Se Se |-_——{nox = 28 Wi = 2088} 7 Te : Ful Senders Posted متهم اميم 2 Window management in TCP. pplication ‘oes 82 ‏أ‎ TCP Transmission Policy ۳ ‘does a2 ‏أ‎ a wet Sender may. send up to2K — 

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TCP Transmission Policy (2) 56061605 is full Application reads 1 byte [== Roam for ane more byte ‎Reader Window update segment sent‏ سم ‎ ‎ ‎ ‎ ‎New byte arrives ‎ ‎Receivers buffer is full ‎ ‎Silly window syndrome. ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ 

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TCP Congestion Control Fate agustment ‎Lagecapacty‏ = رت ‎~ ‎3 0 ‎(a) A fast network feeding a low capacity receiver. (b) A slow network feeding a high-capacity receiver. 

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TCP Congestion Control (2) Timeout x ‘Threshold Threshold Congestion window (kilobytes) o 2 4 6 8 0 2 14 16 18 2 22 2 Transmission number An example of the Internet congestion algorithm. 

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TCP Timer Management 9 1 93 9 Te 92 Probability Probability 8 2 o 10 2 30 40 50 °o “qo 20 30 0 Round-trip time (msec) Round-trip time (msec) 8 (b) (a) Probability density of ACK arrival times in the data link layer. (b) Probability density of ACK arrival times for TCP. 

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Wireless TCP and UDP Sender TCP #1 Base station TCP #2 کار host Router Antenna Splitting a TCP connection into two connections. 

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Transitional TCP Client Server Client Server 1 1 |] sw. ‘SYN, request, Fin y— 2 |. —svn, ACKISYN 2 gy, ACK(FIN), ro: FIN 3 3 لب ۸0165۷۸۷ Time ‏لب أ‎ Time | |. ackiveauest + FN) fa) (b) (a) RPC using normal TPC. (b) RPC using T/TCP. 

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Performance Issues Performance Problems in Computer Networks Network Performance Measurement System Design for Better Performance Fast TPDU Processing Protocols for Gigabit Networks 

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Performance Problems in Computer Networks The state of transmitting one megabit from San Diego to Boston (a) Att =0, (b) After 500 psec, (c) After 20 msec, (d) after 40 msec. 

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Network Performance Measurement The basic loop for improving network performance. 1. Measure relevant network parameters, performance. 2. Try to understand what is going on. 3. Change one parameter. 

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System Design for Better Performance Rules: 1. CPU speed is more important than network speed. 2. Reduce packet count to reduce software overhead. Minimize context switches. Minimize copying. You can buy more bandwidth but not lower delay. Avoiding congestion is better than recovering from it. 7. Avoid timeouts. Soe S 

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System Design for Better Performance (2) o of 02 08 04 05 06 07 08 09 10 Load Response as a function of load. 

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System Design for Better Performance (3) User process running at the Network Receiving time of the packet arrival manager process User space ol 5/19 9 — OK Four context switches to handle one packet with a user-space network manager. 

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Fast TPDU Processing |= Sending Receiving process —. “ay 9 process ‘TPDU passed to the receiving process 1 |+— Trap into the kernel to send TPDU ‏مر‎ | The fast path from sender to receiver is shown with a heavy line. The processing steps on this path are shaded. Network 

صفحه 64:
Fast TPDU Processing (2) Source port Destination port ver. | IHU] TOs Total length Sequence number Identification Fragment offset ‘Acknowledgement number TTL | Protocol || Header checksum Len |Unused Window size Source address, Checksum Urgent pointer Destination address. 2 (b) (a) TCP header. (b) IP header. In both cases, the shaded fields are taken from the prototype without change. 

صفحه 65:
Fast TPDU Processing (3) Slot Pointer to list of timers for T + 12 =—— Current time, T Pointer to list of timers for T +3 Pointer to list of timers for T + 10 A timing wheel. 

صفحه 66:
Protocols for Gigabit Networks 1000 sec 100 sec 10sec 1 sec 100 msec 10 msec 1 msec 10? 104 105 1058 107 10810 109 1010 02 Data rate (bps) Time to transfer and acknowledge a 1-megabit file over a 4000-km line.