CS 4470 Computer Networking Protocols 2 Introduction 2

CS 4470 Computer Networking Protocols 2. Introduction 2 Huiping Guo Department of Computer Science California State University, Los Angeles

Outline r Protocols and layering r Internet architecture r Network performance 2. Introduction 2 2 -2

Protocols and layering r What is layering m Modular approach to network functionality r Example Application-to-application channels Host-to-host connectivity Link hardware 2. Introduction 2 2 -3

Why layering? r Networks are complex! r We need a way to organize the structure of network functionalities and to reduce the design complexities r Benefits of layering m m m Interoperability Reuse Hiding underlying details 2. Introduction 2 2 -4

Many many Network Components Application Operating System Application Router Software (many protocols) Operating System Links Computer Protocol Software Router Hardware 2. Introduction 2 Network Interface Computer Bridge HW/SW 2 -5

Protocols and layering r What is a Protocol m Module in layered structure m Set of rules governing communication between network elements (applications, hosts, routers) r Protocols define: m Interface to higher layers (API) m Interface to peer • Format and order of messages • Actions taken on receipt of a message 2. Introduction 2 1 -6

A human protocol and a computer network protocol TCP connection request Hi Hi TCP connection response Got the time? Get http: //www. abc. com/img 1. jpg 2: 00 <file> time 2. Introduction 2 2 -7

Protocol interfaces r Each protocol offers an interface to its users, and expects one from the layers on which it builds m Syntax and semantics • Data formats • Interface characteristics, e. g. IP service model r Protocols build upon each other m Add value • E. g. , a reliable protocol running on top of IP m Reuse • E. g. , OS provides TCP, so apps don’t have to rewrite 2. Introduction 2 2 -8

Outline r Protocols and layering r Internet model r Network performance 2. Introduction 2 2 -9

TCP/IP Model: the Internet model r Each layer relies on services from layer below r Each layer exports services to layer above r Interface between layers defines interaction m Hides implementation details m Layers can change without disturbing other layers 5 Application 4 Transport 3 Network 2 Data link 1 Physical 2. Introduction 2 2 -10

TCP/IP Model: the Internet model r application: supporting network applications m FTP, SMTP, HTTP r transport: application-application data transfer m TCP, UDP r network: routing of datagrams from source to destination. Node-node data transfer m IP, routing protocols r link: data transfer between neighboring network elements m PPP, Ethernet r physical: bits “on the wire” 2. Introduction 2 2 -11

TCP/IP protocols suite FTP HTTP NV TCP TFTP Applications UDP TCP UDP Waist IP Data Link NET 1 NET 2 … NETn Physical The Hourglass Model The waist facilitates interoperability 2. Introduction 2 2 -12

Protocols for Interoperability r Many implementations of many technologies: m Hosts running Free. BSD, Linux, Windows, Mac. OS, m People using Mozilla, Explorer, Opera, … m Routers made by cisco, juniper, … m Hardware made by IBM, Dell, Apple, … r And they change all the time. r But they can all talk together because they use the same protocol(s) m m Application level protocols: HTTP, SMTP, POP, IMAP, etc. Hardware protocols (ethernet, etc) 2. Introduction 2 2 -13

Protocols for Abstraction & Reuse r Multiple choices of protocol at many layers m Physical: copper, fiber, air, carrier pigeon m Link: ethernet, token ring, SONET, FDDI m Transport: TCP, UDP, SCTP r But we don’t want to have to write “a web (HTTP) browser for TCP networks running IP over Ethernet on Copper” and another for the fiber version… m m m Reuse! Abstraction! Protocols provide a standard interface to write to Layers hide the details of the protocols below 2. Introduction 2 2 -14

TCP/IP protocols suite B A HTTP message HTTP TCP segment TCP router IP Ethernet interface HTTP IP packet IP Ethernet interface TCP router IP packet SONET interface 2. Introduction 2 SONET interface IP IP packet Ethernet interface IP Ethernet interface 2 -15

Layer Encapsulation User A User B Get index. html Connection ID Source/Destination Link Address 2. Introduction 2 2 -16

Outline r Protocols and layering r Internet architecture r Network performance 2. Introduction 2 2 -17

Delay A B 2. Introduction 2 2 -18

Delay r Queuing r Processing m m check bit errors determine output link m m time waiting at output link for transmission depends on congestion level of router transmission A propagation C B nodal processing 2. Introduction 2 D queueing 2 -19

Delay r Transmission delay m m m R=link bandwidth (bps) L=packet length (bits) time to send bits into link = L/R r Propagation delay m m m d = length of physical link s = propagation speed in medium (~2 x 108 m/sec) propagation delay = d/s transmission A propagation B nodal processing 2. Introduction 2 queueing 2 -20

Nodal Delay r dproc = processing delay m typically a few microsecs or less r dqueue = queuing delay m depends on congestion r dtrans = transmission delay m = L/R, significant for low-speed links r dprop = propagation delay m = distance/propagation speed m a few microsecs to hundreds of msecs http: //mediaplayer. pearsoncmg. com/_ph_cc_ecs_set. title. Propagation _Delay_and_Transmission_Delay_(Chapter_01)__/aw/streaming/ecs_ kurose_compnetw_6/Prop. And. Transmit. m 4 v 2. Introduction 2 2 -21

Queueing delay r R=link bandwidth (bps) r L=packet length (bits) r a=average packet arrival rate traffic intensity = La/R r La/R ~ 0: average queueing delay small r La/R -> 1: delays become large r La/R > 1: more “work” arriving than can be serviced, average delay infinite! 2. Introduction 2 2 -22

Packet loss r queue (aka buffer) preceding link in buffer has finite capacity r when packet arrives to full queue, packet is dropped ( lost) r lost packet may be retransmitted by previous node, by source end system, or not retransmitted at all 2. Introduction 2 2 -23

Traceroute r Diagnostic tool r http: //www. traceroute. org/ m m m sends three packets that will reach router i on path towards destination router i will return packets to sender times interval between transmission and reply. 3 probes 2. Introduction 2 2 -24

“Real” Internet delays and routes traceroute: gaia. cs. umass. edu to www. eurecom. fr Three delay measurements from gaia. cs. umass. edu to cs-gw. cs. umass. edu 1 cs-gw (128. 119. 240. 254) 1 ms 2 border 1 -rt-fa 5 -1 -0. gw. umass. edu (128. 119. 3. 145) 1 ms 2 ms 3 cht-vbns. gw. umass. edu (128. 119. 3. 130) 6 ms 5 ms 4 jn 1 -at 1 -0 -0 -19. wor. vbns. net (204. 147. 132. 129) 16 ms 11 ms 13 ms 5 jn 1 -so 7 -0 -0 -0. wae. vbns. net (204. 147. 136) 21 ms 18 ms 6 abilene-vbns. abilene. ucaid. edu (198. 32. 11. 9) 22 ms 18 ms 22 ms 7 nycm-wash. abilene. ucaid. edu (198. 32. 8. 46) 22 ms trans-oceanic 8 62. 40. 103. 253 (62. 40. 103. 253) 104 ms 109 ms 106 ms link 9 de 2 -1. de. geant. net (62. 40. 96. 129) 109 ms 102 ms 104 ms 10 de. fr 1. fr. geant. net (62. 40. 96. 50) 113 ms 121 ms 114 ms 11 renater-gw. fr 1. fr. geant. net (62. 40. 103. 54) 112 ms 114 ms 112 ms 12 nio-n 2. cssi. renater. fr (193. 51. 206. 13) 111 ms 114 ms 116 ms 13 nice. cssi. renater. fr (195. 220. 98. 102) 123 ms 125 ms 124 ms 14 r 3 t 2 -nice. cssi. renater. fr (195. 220. 98. 110) 126 ms 124 ms 15 eurecom-valbonne. r 3 t 2. ft. net (193. 48. 50. 54) 135 ms 128 ms 133 ms 16 194. 211. 25 (194. 211. 25) 126 ms 128 ms 126 ms 17 * * means no response (probe lost, router not replying) 18 * * * 19 fantasia. eurecom. fr (193. 55. 113. 142) 132 ms 128 ms 136 ms 2. Introduction 2 2 -25