5 THE NETWORK LAYER 1

Transcription

1 5 THE NETWORK LAYER 1

2 FTP... TCP IP ATM Data link Physical Fig Running TCP/IP over an ATM subnet.

3 Issue Datagram subnet VC subnet Circuit setup Not needed Required Addressing Each packet contains Each packet contains a the full source and short VC number destination address State information Subnet does not hold Each VC requires subnet state information table space Routing Each packet is Route chosen when VC routed independently is set up; all packets follow this route Effect of router failures None, except for packets All VCs that passed lost during the crash through the failed router are terminated Congestion control Difficult Easy if enough buffers can be allocated in advance for each VC Fig Comparison of datagram and virtual circuit subnets.

4 Upper layer Connectionless Datagram UDP over IP Type of subnet Virtual circuit UDP over IP over ATM Connection-oriented TCP over IP ATM AAL1 over ATM Fig Examples of different combinations of service and subne structure.

5 A B C X X A' B' C' Fig Conflict between fairness and optimality.

6 B B F A G L D H E I J N C F A G L D H E I J N C K K M O M O (a) (b) Fig (a) A subnet. (b) A sink tree for router B.

7 B 7 C B (2, A) C (, ) A E 2 F D A E (, ) F (, ) D (, ) G (a) H G (6, A) (b) H (, ) B (2, A) C (9, B) B (2, A) C (9, B) A E (4, B) F (, ) D (, ) A E (4, B) F (6, E) D (,1) G (6, A) (c) H (, ) G (5, E) (d) H (, ) B (2, A) C (9, B) B (2, A) C (9, B) A E (4, B) F (6, E) D (, ) A E (4, B) F (6,E) D (, ) G (5, E) (e) H (9, G) G (5, E) (f) H (8, F) Fig The first five steps used in computing the shortest path from A to D. The arrows indicate the working node.

8 define MAX NODES 1024 / * maximum number of nodes * / define INFINITY / * a number larger than every maximum path * / int n, dist[max NODES][MAX NODES]; / * dist[i][j] is the distance from i to j * / void shortest path(int s, int t, int path[]) { struct state { / * the path being worked on * / int predecessor; / * previous node * / int length; / * length from source to this node * / enum {permanent, tentative} label; / * label state * / } state[max NODES]; int i, k, min; struct state * p; for (p = &state[0]; p < &state[n]; p++) { / * initialize state * / p->predecessor = 1; p->length = INFINITY; p->label = tentative; } state[t].length = 0; state[t].label = permanent; k = t; / * k is the initial working node * / do { / * Is there a better path from k? * / for (i = 0; i < n; i++) / * this graph has n nodes * / if (dist[k][i]!= 0 && state[i].label == tentative) { if (state[k].length + dist[k][i] < state[i].length) { state[i].predecessor = k; state[i].length = state[k].length + dist[k][i]; } } / * Find the tentatively labeled node with the smallest label. * / k = 0; min = INFINITY; for (i = 0; i < n; i++) if (state[i].label == tentative && state[i].length < min) { min = state[i].length; k = i; } state[k].label = permanent; } while (k!= s); / * Copy the path into the output array. * / i = 0; k = s; } do {path[i++] = k; k = state[k].predecessor; } while (k >= 0); Fig Dijkstra s algorithm to compute the shortest path through a graph.

9 Destination A B C D E F A 9 AB 4 ABC 1 ABFD 7 AE 4 AEF A B 20 C E 50 F (a) D Source B C D E F 9 BA 4 CBA 1 DFBA 7 EA 4 FEA 8 CB 3 DFB 2 EFB 4 FB 8 BC 3 DC 3 EC 2 FEC 3 BFD 3 CD 3 ECD 4 FD 2 BFE 3 CE 3 DCE 5 FE 4 BF 2 CEF 4 DF 5 EF (b) Fig (a) A subnet with line capacities shown in kbps. (b) The traffic in packets/sec and the routing matrix.

10 i Line λ i (pkts/sec) C i (kbps) µc i (pkts/sec) T i (msec) Weight 1 AB BC CD AE EF FD BF EC Fig Analysis of the subnet of Fig. 5-8 using a mean packet size of 800 bits. The reverse traffic (BA, CB, etc.) is the same as the forward traffic.

11 I H H I I I H A A Router A B C D F G E H I J K L (a) New estimated delay from J To A I H K Line A B C D E F G H I J K L JA delay JI delay JH delay JK delay is is is is Vectors received from J's four neighbors (b) K K New routing table for J Fig (a) A subnet. (b) Input from A, I, H, K, and the new routing table for J.

12 A B C D E (a) Initially After 1 exchange After 2 exchanges After 3 exchanges After 4 exchanges A B C D E (b) Initially After 1 exchange After 2 exchanges After 3 exchanges After 4 exchanges After 5 exchanges After 6 exchanges Fig The count-to-infinity problem.

13 A B C Router D Fig An example where split horizon fails.

14 H Router B D E D E G I G H B A C F A C F I LAN (a) N (b) Fig (a) Nine routers and a LAN. (b) A graph model of (a).

15 West East G B C F A H E I D J Fig A subnet in which the East and West parts are connected by two lines.

16 A B 2 C E 8 F D A Seq. Age B 4 E 5 Link State Packets B C D E F Seq. Seq. Seq. Seq. Seq. Age Age Age Age Age A 4 B 2 C 3 A 5 B 6 C 2 D 3 F 7 C 1 D 7 F 6 E 1 F 8 E 8 (a) (b) Fig (a) A subnet. (b) The link state packets for this subnet.

17 Send flags ACK flags Source Seq. Age A C F A C F Data A F E C D Fig The packet buffer for router B in Fig.5-15.

18 Full table for 1A Hierarchical table for 1A Dest. Line Hops Region 1 Region 2 1A 1B 1A 1C 2A 2B 1B 1B 1 1C 1C 1 2C 2D 2A 2B 2C 2D 3A 4A 5B 5C 3A 5A 3B 4B 3B 4C 5D 4A 5E 4B Region 3 Region 4 Region 5 4C 5A 5B 5C 5D 5E 1B 2 1B 3 1B 3 1B 4 1C 3 1C 2 1C 3 1C 4 1C 4 1C 4 1C 5 1B 5 1C 6 1C 5 Dest. Line Hops 1A 1B 1B 1 1C C 1B 1C 1C 1C (a) (b) (c) Fig Hierarchical routing.

19 Wireless cell Home agent Mobile host Home LAN Foreign agent Foreign LAN WAN MAN Fig A WAN to which LANs, MANs, and wireless cells are attached.

20 1. Packet is sent to the mobile host's home address 4. Subsequent packets are tunneled to the foreign agent 3. Sender is given foreign agent's address 2. Packet is tunneled to the foreign agent Fig Packet routing for mobile users.

21 I F H J N A D G K E O M O G C D N B H L L B A E H B C D F J G O M K L N I (a) A B C D G J O F I E H K L M N (b) (c) K E Fig Reverse path forwarding. (a) A subnet. (b) A spanning tree. (c) The tree built by reverse path forwarding.

22 , 2 1, , 2 1, (a) (b) (c) (d) Fig (a) A subnet. (b) A spanning tree for the leftmost router. (c) A multicast tree for group 1. (d) A multicast tree for group 2.

23 Perfect Packets delivered Maximum carrying capacity of subnet Desirable Congested Packets sent Fig When too much traffic is offered, congestion sets in and performance degrades sharply.

24 Layer Policies Transport Retransmission policy Out-of-order caching policy Acknowledgement policy Flow control policy Timeout determination Network Virtual circuits versus datagram inside the subnet Packet queueing and service policy Packet discard policy Routing algorithm Packet lifetime management Data link Retransmission policy Out-of-order caching policy Acknowledgement policy Flow control policy Fig Policies that affect congestion.

25 Faucet Host computer Packet Unregulated flow Leaky bucket Water Interface containing a leaky bucket The bucket holds packets Water drips out of the hole at a constant rate Regulated flow Network (a) (b) Fig (a) A leaky bucket with water. (b) A leaky bucket with packets.

26 (a) 25 MB/sec for 40 msec 0 Time (msec) 500 (b) 2 MB/sec for 500 msec 0 Time (msec) MB/sec for 11 msec (c) 2 MB/sec for 364 msec 0 Time (msec) 500 (d) 25 MB/sec for 22 msec 2 MB/sec for 228 msec 0 Time (msec) MB/sec for 33 msec (e) 2 MB/sec for 92 msec 0 Time (msec) MB/sec for 62 msec (f) 2 MB/sec for 190 msec 0 Time (msec) 500 Fig (a) Input to a leaky bucket. (b) Output from a leaky bucket. (c) - (e) Output from a token bucket with capacities of 250KB, 500KB, and 750KB. (f) Output from a 500KB token bucket feeding a 10 MB/sec leaky bucket.

27 Host computer Host computer One token is added to the bucket every T The bucket holds tokens Networks (a) Networks (b) Fig The token bucket algorithm. (a) Before. (b) After.

28 Characteristics of the Input Service Desired Maximum packet size (bytes) Loss sensitivity (bytes) Token bucket rate (bytes/sec) Loss interval (µsec) Token bucket size (bytes) Burst loss sensitivity (packets) Maximum transmission rate (bytes/sec) Minimum delay noticed (µsec) Maximum delay variation (µsec) Quality of guarantee Fig An example flow specification.

29 A Congestion A B B Virtual circuit Congestion (a) (b) Fig (a) A congested subnet. (b) A redrawn subnet that eliminates the congestion and a virtual circuit from A to B.

30 A Packet C Finishing time 8 B B 16 C 3 8 O D 17 D E 18 E A 20 (a) (b) Fig (a) A router with five packets queued for line O. (b) Finishing times for the five packets.

31 B C B C A D A D E F E F Heavy flow Choke Choke Choke Choke Reduced flow Choke Choke Reduced flow Flow is still at maximum rate Flow is reduced (a) (b) Fig (a) A choke packet that affects only the source. (b) A choke packet that affects each hop it passes through.

32 Senders A B C A B C A B C D E F D E F D E F G H I G H I G H I J K L J K L J K L Receivers (a) (b) (c) Fig (a) A network. (b) The multicast spanning tree for host 1. (c) The multicast spanning tree for host 2.

33 A D B E C F A D B E C Bandwidth reserved for source 2 F A D B E C F Bandwidth reserved for source 1 G H I G H I G H I J K L J K L J K L (a) (b) (c) Fig (a) Host 3 requests a channel to host 1. (b) Host 3 then requests a second channel, to host 2. (c) Host 5 requests a channel to host 1.

34 Host LAN Multiprotocol router WAN-WAN LAN Bridge B LAN M M X.25 WAN M M SNA WAN LAN LAN-LAN LAN-WAN LAN-WAN-LAN Fig Network interconnection.

35 Network 1 packets here Network 2 packets here Full gateway Network 2 packets here Network 1 G Network 2 G Network 2 Network 1 Network 1 packets here (a) (b) Half-gateway Neutral packets here Network 1 Network 2 (c) Fig (a) A full gateway between two WANs. (b) A full gateway between a LAN and a WAN. (c) Two half-gateways.

36 Item Some Possibilities Service offered Connection-oriented versus connectionless Protocols IP, IPX, CLNP, AppleTalk, DECnet, etc. Addressing Flat (802) versus hierarchical (IP) Multicasting Present or absent (also broadcasting) Packet size Every network has its own maximum Quality of service May be present or absent; many different kinds Error handling Reliable, ordered, and unordered delivery Flow control Sliding window, rate control, other, or none Congestion control Leaky bucket, choke packets, etc. Security Privacy rules, encryption, etc. Parameters Different timeouts, flow specifications, etc. Accounting By connect time, by packet, by byte, or not at all Fig Some of the many ways networks can differ.

37 SNA Multiprotocol router 1 X. 25 M M ATM Router M OSI M End-to-end concatenated virtual circuits 2 Host Fig Internetworking using concatenated virtual circuits.

38 1 M M Packets travel individually and can take different routes Router M M Multiprotocol router 2 Host Fig A connectionless internet.

39 Ethernet in Paris Multiprotocol router Acts like a serial line WAN Tunnel 1 2 Ethernet in London Header IP Ethernet frame IP IP packet inside payload field of the WAN packet IP Ethernet frame Fig Tunneling a packet from Paris to London.

40 Car English channel Paris Railroad carriage London Railroad track Fig Tunneling a car from France to England.

41 2 B 3 A B A 1 C Gateway D C D E Network 4 F 5 E F (a) (b) Fig (a) An internetwork. (b) A graph of the internetwork.

42 Packet Network 1 Network 2 G 1 G 2 G 3 G 4 G 1 fragments a large packet G 2 reassembles the fragments G 3 fragments again G 4 reassembles again (a) Packet G 1 G 2 G 3 G 4 G 1 fragments a large packet The fragments are not reassembled until the final destination (a host) is reached (b) Fig (a) Transparent fragmentation. (b) Nontransparent fragmentation.

43 Number of the first elementary fragment in this packet Packet number End of packet bit 1 byte A B C D E F G H I J Header (a) A B C D E F G H I J Header (b) Header A B C D E F G H I J Header Header Header (c) Fig Fragmentation when the elementary data size is 1 byte. (a) Original packet, containing 10 data bytes. (b) Fragments after passing through a network with maximum packet size of 8 bytes. (c) Fragments after passing through a size 5 gateway.

44 Packet filtering router Application gateway Packet filtering router Backbone Connections to outside networks Corporate network Security perimeter Inside LAN Outside LAN Firewall Fig A firewall consisting of two packet filters and an application gateway.

45 Leased lines to Asia US backbone Leased transatlantic line European backbone Regional network C SNA network IP Router National network A Tunnel D B Host 1 2 IP token bus LAN IP token ring LAN IP Ethernet LAN Fig The Internet is an interconnected collection of many networks.

46 32 Bits Version IHL Type of service Total length Time to live Identification Protocol D F Source address M F Destination address Fragment offset Header checksum Options (0 or more words) Fig The IP (Internet Protocol) header.

47 Option Description Security Specifies how secret the datagram is Strict source routing Gives the complete path to be followed Loose source routing Gives a list of routers not to be missed Record route Makes each router append its IP address Timestamp Makes each router append its address and timestamp Fig IP options.

48 32 Bits Class A B C D E 0 Network Host 10 Network Host 110 Network Host 1110 Multicast address Reserved for future use Range of host addresses to to to to to Fig IP address formats.

49 Host Network 127 (Anything) This host A host on this network Broadcast on the local network Broadcast on a distant network Loopback Fig Special IP addresses.

50 32 Bits Subnet mask 10 Network Subnet Host Fig One of the ways to subnet a class B network.

51 Message type Description Destination unreachable Packet could not be delivered Time exceeded Time to live field hit 0 Parameter problem Invalid header field Source quench Choke packet Redirect Teach a router about geography Echo request Ask a machine if it is alive Echo reply Yes, I am alive Timestamp request Same as Echo request, but with timestamp Timestamp reply Same as Echo reply, but with timestamp Fig The principal ICMP message types.

52 Router has 2 IP addresses To WAN Router has 2 IP addresses F2 1 2 F1 F3 3 4 E1 CS Ethernet E2 E3 E4 E5 E6 Campus FDDI ring EE Ethernet Ethernet addresses Fig Three interconnected class C networks: two Ethernets and an FDDI ring.

53 WAN 1 A B C D E WAN 2 F LAN 1 H I J LAN 2 G (a) WAN 3 W A B C 4 D 6 8 W2 F H L2 2 J G L1 W3 (b) Fig (a) An autonomous system. (b) A graph representation of (a).

54 AS 1 AS 2 Backbone Backbone router Area Internal router BGP protocol connects the ASes AS 3 AS 4 Area border router AS boundary router Fig The relation between ASes, backbones, and areas in OSPF.

55 Message type Description Hello Used to discover who the neighbors are Link state update Provides the sender s costs to its neighbors Link state ack Acknowledges link state update Database description Announces which updates the sender has Link state request Requests information from the partner Fig The five types of OSPF messages.

56 B C A E F G D H Information F receives from its neighbors about D From B: "I use BCD" From G: "I use GCD" From I: "I use IFGCD" From E: "I use EFGCD" I J (a) (b) Fig (a) A set of BGP routers. (b) Information sent to F.

57 32 Bits Version Priority Flow label Payload length Next header Hop limit Source address (16 bytes) Destination address (16 bytes) Fig The IPv6 fixed header (required).

58 Prefix (binary) Usage Fraction Reserved (including IPv4) 1/ Unassigned 1/ OSI NSAP addresses 1/ Novell NetWare IPX addresses 1/ Unassigned 1/ Unassigned 1/ Unassigned 1/ Unassigned 1/8 010 Provider-based addresses 1/8 011 Unassigned 1/8 100 Geographic-based addresses 1/8 101 Unassigned 1/8 110 Unassigned 1/ Unassigned 1/ Unassigned 1/ Unassigned 1/ Unassigned 1/ Unassigned 1/ Link local use addresses 1/ Site local use addresses 1/ Multicast 1/256 Fig IPv6 addresses

59 Extension header Description Hop-by-hop options Miscellaneous information for routers Routing Full or partial route to follow Fragmentation Management of datagram fragments Authentication Verification of the sender s identity Encrypted security payload Information about the encrypted contents Destination options Additional information for the destination Fig IPv6 extension headers.

60 Next header Jumbo payload length Fig The hop-by-hop extension header for large datagrams (jumbograms).

61 Next header 0 Number of addresses Next address Bit map 1 24 Adresses Fig The extension header for routing.

62 Virtual! circuit Virtual path Transmission path Fig A transmission path can hold multiple virtual paths, each of which can hold multiple virtual circuits.

63 40 Bits C GFC VP I VC I PTI L HEC P (a) C VP I VC I PTI L HEC P GFC: General Flow Control VPI: Virtual Path Identifier VCI: Virtual Channel Identification PTI: Payload Type CLP: Cell Loss Priority HEC: Header Error Check (b) Fig (a) The ATM layer header at the UNI. (b) The ATM layer header at the NNI.

64 "" " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " Payload type Meaning "" " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " 000 User data cell, no congestion, cell type 0 "" " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " 001 User data cell, no congestion, cell type 1 "" " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " 010 User data cell, congestion experienced, cell type 0 "" " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " 011 User data cell, congestion experienced, cell type 1 "" " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " 100 Maintenance information between adjacent switches "" " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " 101 Maintenance information between source and destination switches "" " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " 110 Resource Management cell (used for ABR congestion control) "" " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " 111 Reserved for future function "" " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " Fig Values of the PTI field.

65 " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " Message Meaning when sent by host Meaning when sent by network " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " SETUP Please establish a circuit Incoming call " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " CALL PROCEEDING I saw the incoming call Your call request will be attempted " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " CONNECT I accept the incoming call Your call request was accepted " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " CONNECT ACK Thanks for accepting Thanks for making the call " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " RELEASE Please terminate the call The other side has had enough " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " RELEASE COMPLETE Ack for RELEASE Ack for RELEASE " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " Fig Messages used for connection establishment and release.

66 $ % ) & ( ' + * Source host Time Setup Call proceeding Connect Switch 1 Switch 2 Setup Call proceeding Connect Connect ack Setup Connect Connect ack Destination host Connect ack (a) Release Release complete Release Release complete Release Release complete (b ) Fig (a) Connection setup in an ATM network. (b) Connection release.

67 SF Original path New path Minneapolis 0 Denver 4 Omaha Virtual path DC NY LA Dallas Fig Rerouting a virtual path reroutes all of its virtual circuits.

68 " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " Incoming Incoming Outgoing Outgoing Source line VPI Destination line VPI Path: " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " NY 1 1 SF 4 1 New " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " NY 1 2 Denver 4 2 New " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " LA 3 1 Minneapolis 0 1 New " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " DC 1 3 LA 3 2 New " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " NY 1 1 SF 4 1 Old " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " SF 4 3 DC 1 4 New " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " DC 1 5 SF 4 4 New " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " NY 1 2 Denver 4 2 Old " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " SF 4 5 Minneapolis 0 2 New " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " NY 1 1 SF 4 1 Old " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " Fig Some routes through the Omaha switch.

69 VPI_table for Minn. VPI_table for DC VPI_table for Dallas VPI_table for LA VPI_table for Denver Incoming VPI 0 Outgoing Line VPI Outgoing Line VPI Outgoing Line VPI Outgoing Line VPI Outgoing Line VPI Line 0 Line 1 Line 2 Line 3 Line 4 Fig The table entries for the routes of Fig

70 Class Description Example CBR Constant bit rate T1 circuit RT-VBR Variable bit rate: real time Real-time videoconferencing NRT-VBR Variable bit rate: non-real time Multimedia ABR Available bit rate Browsing the Web UBR Unspecified bit rate Background file transfer Fig The ATM service categories.

71 Service characteristic CBR RT-VBR NRT-VBR ABR UBR Bandwidth guarantee Yes Yes Yes Optional No Suitable for real-time traffic Yes Yes No No No Suitable for bursty traffic No No Yes Yes Yes Feedback about congestion No No No Yes No Fig Characteristics of the ATM service categories.

72 " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " Parameter Acronym Meaning " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " Peak cell rate PCR Maximum rate at which cells will be sent " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " Sustained cell rate SCR The long-term average cell rate " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " Minimum cell rate MCR The minimum acceptable cell rate " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " Cell delay variation tolerance CDVT The maximum acceptable cell jitter " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " Cell loss ratio CLR Fraction of cells lost or delivered too late " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " Cell transfer delay CTD How long delivery takes (mean and maximum) " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " Cell delay variation CDV The variance in cell delivery times " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " Cell error rate CER Fraction of cells delivered without error " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " Severely-errored cell block ratio SECBR Fraction of blocks garbled " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " Cell misinsertion rate CMR Fraction of cells delivered to wrong destination " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " Fig Some of the quality of service parameters.

73 Probability 1-α α Minimum CTD CDV Transfer time Cells lost or delivered too late Fig The probability density function for cell arrival times.

74 , Time T L (a) t 1 Cell 1 2 t 2 Maximal case. Cell 2 arrives T sec after Cell 1 cell 3 expected T at t 2 + T (b) 1 2 Slow sender. Cell 2 arrives > T sec after cell 1 t 1 t 2 T Cell 3 expected at t 2 + T (c) 1 2 Fast sender. Cell 2 arrives up to L sec early t 1, t2 T Cell 3 expected at t 1 + 2T (d) 1 2 Very fast sender. Cell 2 arrives prior to t 1 + T L. Cell is nonconforming. t 1 Cell 3 expected at t 1 + T Fig The generic cell rate algorithm.

75 Time 0 T 2T 3T 4T 5T T-ε 1 T-ε 2 T-ε T-ε 3 T-ε ε 2ε 3ε (a) 4 5 4ε Non- conforming cell 6 5ε Bucket limit Fluid level T 0 (b) Fig (a) A sender trying to cheat. (b) The same cell arrival pattern, but now viewed in terms of a leaky bucket.

76 Direction of data flow Sender Receiver Path taken by RM cells ATM Switch Fig The path taken by RM cells.

77 -. 1 Host 1 2 LES does address lookup LES / BUS does 0 broadcasting / BUS 2 3 Fig ATM LAN emulation.