Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge end - PowerPoint PPT Presentation

Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge � end systems, access networks, links 1.3 Network core � circuit switching, packet switching, network structure 1.4 Delay, loss and throughput in packet-switched networks 1.5 Protocol layers, service models 1.6 Networks under attack: security 1.7 History Introduction 1-1 Introduction

How do loss and delay occur? packets queue in router buffers � packet arrival rate to link exceeds output link capacity � packets queue, wait for turn packet being transmitted (delay) ‏ A B packets queueing (delay) ‏ free (available) buffers: arriving packets dropped (loss) if no free buffers Introduction 1-2 Introduction

Four sources of packet delay � 1. nodal processing: � 2. queueing � check bit errors � time waiting at output link for transmission � determine output link � depends on congestion level of router transmission A propagation B nodal queueing processing Introduction 1-3 Introduction

Delay in packet-switched networks 3. Transmission delay: 4. Propagation delay: � d = length of physical link � R=link bandwidth (bps) ‏ � s = propagation speed in � L=packet length (bits) ‏ medium (~2x10 8 m/sec) ‏ � time to send bits into link = L/R � propagation delay = d/s Note: s and R are very different quantities! transmission A propagation B nodal queueing processing Introduction 1-4 Introduction

Caravan analogy 100 km 100 km ten-car toll toll caravan booth booth � Time to “push” entire � cars “propagate” at caravan through toll 100 km/hr booth onto highway = � toll booth takes 12 sec to 12*10 = 120 sec service car (transmission � Time for last car to time) ‏ propagate from 1st to � car~bit; caravan ~ packet 2nd toll both: � Q: How long until caravan 100km/(100km/hr)= 1 hr is lined up before 2nd toll � A: 62 minutes booth? Introduction 1-5 Introduction

Caravan analogy (more) ‏ 100 km 100 km ten-car toll toll caravan booth booth � Yes! After 7 min, 1st car � Cars now “propagate” at at 2nd booth and 3 cars 1000 km/hr still at 1st booth. � Toll booth now takes 1 � 1st bit of packet can min to service a car arrive at 2nd router before packet is fully � Q: Will cars arrive to transmitted at 1st router! 2nd booth before all cars serviced at 1st � See Ethernet applet at AWL booth? Web site Introduction 1-6 Introduction

Nodal delay d nodal = d + d + d + d proc queue trans prop � d proc = processing delay � typically a few microsecs or less � d queue = queuing delay � depends on congestion � d trans = transmission delay � = L/R, significant for low-speed links � d prop = propagation delay � a few microsecs to hundreds of msecs Introduction 1-7 Introduction

Queueing delay (revisited) ‏ � R=link bandwidth (bps) ‏ � L=packet length (bits) ‏ � a=average packet arrival rate traffic intensity = La/R � La/R ~ 0: average queueing delay small � La/R -> 1: delays become large � La/R > 1: more “work” arriving than can be serviced, average delay infinite! Introduction 1-8 Introduction

“Real” Internet delays and routes � What do “real” Internet delay & loss look like? � Traceroute program: provides delay measurement from source to router along end-end Internet path towards destination. For all i: � sends three packets that will reach router i on path towards destination � router i will return packets to sender � sender times interval between transmission and reply. 3 probes 3 probes 3 probes Introduction 1-9 Introduction

“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 1 ms 2 ms 2 border1-rt-fa5-1-0.gw.umass.edu (128.119.3.145) 1 ms 1 ms 2 ms 3 cht-vbns.gw.umass.edu (128.119.3.130) 6 ms 5 ms 5 ms 4 jn1-at1-0-0-19.wor.vbns.net (204.147.132.129) 16 ms 11 ms 13 ms 5 jn1-so7-0-0-0.wae.vbns.net (204.147.136.136) 21 ms 18 ms 18 ms 6 abilene-vbns.abilene.ucaid.edu (198.32.11.9) 22 ms 18 ms 22 ms trans-oceanic 7 nycm-wash.abilene.ucaid.edu (198.32.8.46) 22 ms 22 ms 22 ms 8 62.40.103.253 (62.40.103.253) 104 ms 109 ms 106 ms link 9 de2-1.de1.de.geant.net (62.40.96.129) 109 ms 102 ms 104 ms 10 de.fr1.fr.geant.net (62.40.96.50) 113 ms 121 ms 114 ms 11 renater-gw.fr1.fr.geant.net (62.40.103.54) 112 ms 114 ms 112 ms 12 nio-n2.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 r3t2-nice.cssi.renater.fr (195.220.98.110) 126 ms 126 ms 124 ms 15 eurecom-valbonne.r3t2.ft.net (193.48.50.54) 135 ms 128 ms 133 ms 16 194.214.211.25 (194.214.211.25) 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 Introduction 1-10 Introduction

Packet loss � queue (aka buffer) preceding link in buffer has finite capacity � packet arriving to full queue dropped (aka lost) ‏ � lost packet may be retransmitted by previous node, by source end system, or not at all buffer packet being transmitted (waiting area) ‏ A B packet arriving to full buffer is lost Introduction 1-11 Introduction

Throughput � throughput: rate (bits/time unit) at which bits transferred between sender/receiver � instantaneous: rate at given point in time � average: rate over longer period of time link capacity link capacity server, with pipe that can carry server sends bits pipe that can carry R c bits/sec R s bits/sec file of F bits fluid at rate (fluid) into pipe fluid at rate to send to client R s bits/sec) ‏ R c bits/sec) ‏ Introduction 1-12 Introduction

Throughput (more) ‏ � R s < R c What is average end-end throughput? R s bits/sec R c bits/sec � R s > R c What is average end-end throughput? R s bits/sec R c bits/sec bottleneck link link on end-end path that constrains end-end throughput Introduction 1-13 Introduction

Throughput: Internet scenario R s � per-connection R s R s end-end throughput: R min(R c ,R s ,R/10) ‏ � in practice: R c or R s R c R c is often bottleneck R c 10 connections (fairly) share backbone bottleneck link R bits/sec Introduction 1-14 Introduction

Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge � end systems, access networks, links 1.3 Network core � circuit switching, packet switching, network structure 1.4 Delay, loss and throughput in packet-switched networks 1.5 Protocol layers, service models 1.6 Networks under attack: security 1.7 History Introduction 1-15 Introduction

Protocol “Layers” Networks are complex! � many “pieces”: � hosts Question: � routers Is there any hope of � links of various organizing structure of media network? � applications � protocols Or at least our discussion of networks? � hardware, software Introduction 1-16 Introduction

Organization of air travel ticket (complain) ‏ ticket (purchase) ‏ baggage (claim) ‏ baggage (check) ‏ gates (unload) ‏ gates (load) ‏ runway landing runway takeoff airplane routing airplane routing airplane routing � a series of steps Introduction 1-17 Introduction

Layering of airline functionality ticket (purchase) ‏ ticket (complain) ‏ ticket baggage (check) ‏ baggage (claim baggage gates (load) ‏ gates (unload) ‏ gate runway (takeoff) ‏ runway (land) ‏ takeoff/landing airplane routing airplane routing airplane routing airplane routing airplane routing departure intermediate air-traffic arrival airport control centers airport Layers: each layer implements a service � via its own internal-layer actions � relying on services provided by layer below Introduction 1-18 Introduction

Why layering? Dealing with complex systems: � explicit structure allows identification, relationship of complex system’s pieces � layered reference model for discussion � modularization eases maintenance, updating of system � change of implementation of layer’s service transparent to rest of system � e.g., change in gate procedure doesn’t affect rest of system � layering considered harmful? Introduction 1-19 Introduction

Internet protocol stack � application: supporting network applications application � FTP, SMTP, HTTP � transport: process-process data transport transfer network � TCP, UDP � network: routing of datagrams from link source to destination � IP, routing protocols physical � link: data transfer between neighboring network elements � PPP, Ethernet � physical: bits “on the wire” Introduction 1-20 Introduction

ISO/OSI reference model � Presentation: allow applications to interpret meaning of data, e.g., Application encryption, compression, machine- Presentation specific conventions Session � Session: synchronization, checkpointing, recovery of data Transport exchange Network � Internet stack “missing” these Datalink layers! Physical � these services, if needed, must be implemented in application � needed? Introduction 1-21 Introduction

The OS I Reference Model � A standard "test" question on j ob interviews – memorize the layers! • Application • Presentation • S ession • Transport • Network • Datalink • Physical � Mnemonics: � All Programmers S eem To Need Data Processing Introduction