Overview What s the Internet What s a protocol? Network edge Network core ccess nets, media Performance: loss, delay Protocol layers, service models ackbones, NPs, ISPs local ISP company regional ISP queuing Packets experience variable delays along the path from source to destination Four sources of delay at each hop» Nodal : Check for bit errors» Transmission Determine the output interface to forward packet on» Queuing:» Propagation Time spent waiting at outbound interface for Duration depends on the level of congestion at the interface 2 Transmission delay = time to put bits onto the = L/R» R = bandwidth (bps)» L = packet length (bits) queuing eware: s and R are very different quantities! Propagation delay = d/s» d = length of» s = signal speed in medium (~2x0 8 m/sec) Transmission & Propagation Example Transmission on a slow Time = 0 Time = 0 Time = 0,000,000 998,070 994,20,544,000 bps (T-) 9 bytes/ 0 latency,90 bytes in the 5,790 bytes in the Time = 5,8.4 andwidth-delay Product (DP) 0 5,790 bytes in the 994,20 bytes recv d 4
Transmission & Propagation Example Transmission on a fast Time = 0 Time = 0 Tme = 0 Time = 42.86,000,000 222,400 0 0 622,080,000 bps (OC-2) 77,760 bytes/ 0 latency 777,600 bytes in the,000,000 bytes in the 0 bytes in the,000,000 bytes recv d Typical delay: 20 µs»,0 byte packet on a 00 Mbps Ethernet Typical delay:» µs on a small campus» 25 to the West coast queueing Typical delay:»?? Typical queuing delay:»?? 6 Transmission Delay Telecommunications speed alphabet soup DS-/T- =.544 Mbps DS-/T- = 44.76 Mbps OC- = 5.84 Mbps OC-n = n OC-» OC- = OC- (55. Mbps)» OC-2 = 2 OC- (622.08 Mbps)» OC-48 = 48 OC- (2,488.2 Mbps/2.5 Gbps)» OC-92 = 92 OC- (9,95.28 Mbps/0 Gbps) Delay in Packet-Switched Networks Queuing delay (revisited) Understand queuing delay in ter of traffic intensity La/R» R = speed (bps)» L = packet length (bits/packet)» a = average packet arrival rate (packets/second) If La/R ~ 0: verage queuing delay small s La/R : Delays become large If La/R > : Work arrives faster than it can be serviced» verage delay goes to infinity! verage Queuing Delay La/R 7 8
9 queuing What dominates end-to-end delay? Transmission delay = 20 µs Propagation delay = 0 µs Queuing delay = k x 20 µs Processing delay = 00 µs What is is k? k? Note that,, and queuing delays are encountered at each hop» End-to-end delay is largely a function of the number of routers encountered along the path from source to destination Example: What was the delay from Michele s house? Tracing Tracing route route to to [0.27.48.4] [0.27.48.4] over over a a maximum maximum of of 0 0 hops: hops: traceroute from my house How can this be? 92.68.2.27 92.68.2.27 2 2 2 2 68..2.90 68..2.90 6 6 25 25 68..2.205 68..2.205 4 4 2 2 205..22.25 205..22.25 5 5 7 7 6 6 7 7 axr00asm-7-0-0-0.bellsouth.net axr00asm-7-0-0-0.bellsouth.net [65.8.27.20] [65.8.27.20] 6 6 7 7 6 6 pxr00asm-2-0-0.bellsouth.net pxr00asm-2-0-0.bellsouth.net [65.8.26.2] [65.8.26.2] 7 7 8 8 7 7 9 9 so-7-0-0-0.gar.tlanta.level.net so-7-0-0-0.gar.tlanta.level.net [67.72.8.4] [67.72.8.4] 8 8 8 8 8 8 7 7 so-6-0-0.gar2.tlanta.level.net so-6-0-0.gar2.tlanta.level.net [209.2.9.6] [209.2.9.6] 9 9 9 9 5 5 7 7 so-0--0.bbr2.tlanta.level.net so-0--0.bbr2.tlanta.level.net [209.2..225] [209.2..225] 0 0 0 0 ae-0-0.bbr2.washington.level.net ae-0-0.bbr2.washington.level.net [64.59.0.20] [64.59.0.20] so-7-0-0.edge.washington.level.net so-7-0-0.edge.washington.level.net [209.244..4] [209.244..4] 2 2 0 0 qwest-level-oc48.washington.level.net qwest-level-oc48.washington.level.net [209.244.29.82] [209.244.29.82] 2 2 5 5 205.7.25. 205.7.25. 4 4 2 2 2 2 dca-core-02.inet.qwest.net dca-core-02.inet.qwest.net [205.7.8.22] [205.7.8.22] 5 5 4 4 5 5 5 5 atl-core-02.inet.qwest.net atl-core-02.inet.qwest.net [205.7.8.5] [205.7.8.5] 6 6 2 2 atl-edge-9.inet.qwest.net atl-edge-9.inet.qwest.net [205.7.2.22] [205.7.2.22] 7 7 57 57 26.207.6.42 26.207.6.42 8 8 54 54 0.27..25 0.27..25 9 9 48 48 0.27.2.4 0.27.2.4 20 20 78 78 46 46 [0.27.48.4] [0.27.48.4] 0 Overview Protocol Layers What s the Internet What s a protocol? Network edge Network core ccess nets, media Performance: loss, delay Protocol layers, service models ackbones, NPs, ISPs local ISP company regional ISP Networks are complex!» Composed of many pieces Hosts, routers, s of various media, s, protocols, hardware, software Is there any hope of organizing the structure of the?» Or at least organizing our discussion of s? Solution!» Decompose functions into a stack of function layers» Each layer provides welldefined services to the layer above it in the stack» and uses the services provided by the layer below it Each layer can treat everything below it in the stack as a black box 2
Internet protocol layers ( stack ) pplication layer» Supporting s ftp, SMTP, HTTP Transport layer» Host-host transfer TCP, UDP Network layer» Routing of packets from source to destination IP, routing protocols Link layer Different services» Data transfer between directly specified at each connected elements layer interface Ethernet, 802., SONET, Physical layer» The insertion of individual bits on the wire Internet protocol layers ( stack ) Each layer implements a protocol with its peer layer in a distributed system End system pplication protocol Transport protocol Network protocol Link protocol Physical (signaling) protocol End system 4 Logical communication The implementation of each layer is distributed throughout the» Some layers just distributed on the end-syste The distributed components perform actions, exchange messages with peers 5 Logical Communication Example The layer Receive from dd layer protocol information Send to peer layer Wait for peer layer to respond Peer delivers to its layer ack 6
7 Data flow through protocol layers Protocol layering and formats t er, each layer takes from above» dds header information to create new unit» Passes new unit to layer below Process reversed at receiver H Send Message H trans M Source Destination Segment H net H trans M H net H trans M Datagram H net M H H net H trans M Frame H trans M Receive Message M Message H trans M 8 Common logical functions in most layers Error control» Make the logical channel between layers reliable (or simply more reliable) Flow control» void overwhelming a peer with Segmentation and reassembly» Partitioning large messages into smaller ones at the er and reassembling them at the receiver Multiplexing» llowing several higher-level sessions to share a single lower-level connection Connection setup» Handshaking with a peer Overview What s the Internet What s a protocol? Network edge Network core ccess nets, media Performance: loss, delay Protocol layers, service models ackbones, NPs, ISPs local ISP company regional ISP 9 20
2 The rchitecture of the Internet The Internet as a of s The Internet is roughly hierarchical National/international backbone providers (NPs) at the root» MCI, Sprint, Level, Qwest, NP Local ISP Regional ISP National ackbone Provider NP National ackbone Provider Regional ISP Local ISP NPs interconnect ( peer ) with each other privately, or at public Network ccess Point (NPs) Regional ISPs connect into NPs Local ISPs connect into regional ISPs Summary Covered a ton of material» Internet overview» What s a protocol?» Network edge, core, access» Performance: loss, delay» Layering and service models» ackbones, NPs, ISPs You now hopefully have:» Context, overview, feel of ing» More depth, detail later in course Something dangerous to mumble at parties! 22