1: Introduction 1 Chapter I: Introduction Course on Computer Communication and Networks, CTH/GU The slides are adaptation of the slides made available by the authors of the course’s main textbook: Computer Networking: A Top Down Approach , 5th edition. Jim Kurose, Keith Ross Addison-Wesley, July 2007.
Course on Computer Communication and Networks, CTH/GU The slides are adaptation of the slides made available by the authors of the course’s main textbook: Computer Networking: A Top Down Approach , 5th edition. Jim Kurose, Keith Ross Addison-Wesley, July 2007. Chapter I: Introduction. - PowerPoint PPT Presentation
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1: Introduction1
Chapter I: Introduction
Course on Computer Communication and Networks, CTH/GU
The slides are adaptation of the slides made available by the authors of the course’s main textbook:
Computer Networking: A Top Down Approach ,5th edition. Jim Kurose, Keith RossAddison-Wesley, July 2007.
1: Introduction2
Chapter I: IntroductionThe slides are
adaptation of the slides made available by the authors of the course’smain textbook
Overview: what’s the Internet
types of service ways of information transfer,
routing, performance, delays, loss-------------------------------------------- protocol layers, service models access net, physical media backbones, NAPs, ISPs
(history) quick look into ATM networks
Introduction1-3
What’s the Internet: “nuts and bolts” view
millions of connected computing devices: hosts = end systems running network
apps
Home network
Institutional network
Mobile network
Global ISP
Regional ISP
router
PC
server
wirelesslaptop
cellular handheld
wiredlinks
access points
communication links fiber, copper,
radio, satellite transmission
rate = bandwidth
routers: forward packets (chunks of data)
Introduction1-4
What’s the Internet: “nuts and bolts” view protocols control
sending, receiving of msgs e.g., TCP, IP, HTTP, Skype,
Ethernet Internet: “network of
networks” loosely hierarchical public Internet versus
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! Queues may grow unlimited, packets can be lost
1: Introduction19
… “Real” Internet delays and routes (1)… 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
1: Introduction20
…“Real” Internet delays and routes (2)…
1 cs-gw (128.119.240.254) 1 ms 1 ms 2 ms2 border1-rt-fa5-1-0.gw.umass.edu (128.119.3.145) 1 ms 1 ms 2 ms3 cht-vbns.gw.umass.edu (128.119.3.130) 6 ms 5 ms 5 ms4 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 ms7 nycm-wash.abilene.ucaid.edu (198.32.8.46) 22 ms 22 ms 22 ms8 62.40.103.253 (62.40.103.253) 104 ms 109 ms 106 ms9 de2-1.de1.de.geant.net (62.40.96.129) 109 ms 102 ms 104 ms10 de.fr1.fr.geant.net (62.40.96.50) 113 ms 121 ms 114 ms11 renater-gw.fr1.fr.geant.net (62.40.103.54) 112 ms 114 ms 112 ms12 nio-n2.cssi.renater.fr (193.51.206.13) 111 ms 114 ms 116 ms13 nice.cssi.renater.fr (195.220.98.102) 123 ms 125 ms 124 ms14 r3t2-nice.cssi.renater.fr (195.220.98.110) 126 ms 126 ms 124 ms15 eurecom-valbonne.r3t2.ft.net (193.48.50.54) 135 ms 128 ms 133 ms16 194.214.211.25 (194.214.211.25) 126 ms 128 ms 126 ms17 * * *18 * * *19 fantasia.eurecom.fr (193.55.113.142) 132 ms 128 ms 136 ms
traceroute: gaia.cs.umass.edu to www.eurecom.frThree delay measurements from gaia.cs.umass.edu to cs-gw.cs.umass.edu
* means no reponse (probe lost, router not replying)
trans-oceaniclink
1: Introduction21
Packet switching versus circuit switching(2)
Great for bursty data resource sharing no call setup
Excessive congestion: packet delay and loss protocols needed for reliable data transfer,
congestion control Q: How to provide circuit-like behavior?
bandwidth guarantees needed for audio/video apps
still not entirely solved problem…
Is packet switching a “slam dunk winner?”
1: Introduction22
Packet-switched networks: routing
Goal: move packets among routers from source to destination we’ll study several path selection algorithms
Important design issue: datagram network:
• destination address determines next hop• routes may change during session
virtual circuit network: • each packet carries tag (virtual circuit ID), tag
determines next hop• fixed path determined at call setup time, remains fixed
thru call• routers maintain per-call state
1: Introduction23
Network Taxonomy
Telecommunicationnetworks
Circuit-switchednetworks
FDM TDM
Packet-switchednetworks
Networkswith VCs
DatagramNetworks
• Datagram network cannot be charecterized either connection-oriented or connectionless.
• Internet provides both connection-oriented (TCP) and connectionless services (UDP) to apps.
Introduction1-24
Packet loss
queue (aka buffer) preceding link 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 allA
B
packet being transmitted
packet arriving tofull buffer is lost
buffer (waiting area)
Introduction1-25
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
server, withfile of F bits
to send to client
link capacity
Rs bits/sec
link capacity
Rc bits/sec pipe that can carry
fluid at rate
Rs bits/sec)
pipe that can carryfluid at rate
Rc bits/sec)
server sends bits
(fluid) into pipe
Introduction1-26
Throughput (more)
Rs < Rc What is average end-end throughput?
Rs bits/sec Rc bits/sec
Rs > Rc What is average end-end throughput?
Rs bits/sec Rc bits/sec
link on end-end path that constrains end-end throughput
bottleneck link
Introduction1-27
Throughput: Internet scenario
10 connections (fairly) share backbone bottleneck link R
protocols define format, order of msgs sent and received among network entities and actions taken on msg transmission, receipt
1: Introduction51
The OSI Reference Model
ISO (International Standards Organization) defines the OSI (Open Systems Inerconnect) model to help vendors create interoperable network implementation
Reduce the problem into smaller and more manageable problems: 7 layers a layer should be created where a different level of
abstraction is needed; each layer should perform a well defined function)
The function of each layer should be chosen with an eye toward defining internationally standardized protocols
``X dot" series (X.25, X. 400, X.500) OSI model implementation (protocol stack)