Introduction 1-1 Chapter 1 Introduction Computer Networking: A Top Down Approach , 4 th edition. Jim Kurose, Keith Ross Addison-Wesley, July 2007. A note on the use of these ppt slides: We’re making these slides freely available to all (faculty, students, readers). They’re in PowerPoint form so you can add, modify, and delete slides (including this one) and slide content to suit your needs. They obviously represent a lot of work on our part. In return for use, we only ask the following: If you use these slides (e.g., in a class) in substantially unaltered form, that you mention their source (after all, we’d like people to use our book!) If you post any slides in substantially unaltered form on a www site, that you note that they are adapted from (or perhaps identical to) our slides, and note our copyright of this material. Thanks and enjoy! JFK/KWR All material copyright 1996-2007 J.F Kurose and K.W. Ross, All Rights Reserved Introduction 1-2 Chapter 1: Introduction Our goal: get “feel” and terminology more depth, detail later in course approach: use Internet as example Overview: what’s the Internet? what’s a protocol? network edge; hosts, access net, physical media network core: packet/circuit switching, Internet structure performance: loss, delay, throughput security protocol layers, service models history Introduction 1-3 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 wireless laptop cellular handheld wired links access points communication links fiber, copper, radio, satellite transmission rate = bandwidth routers: forward packets (chunks of data) Introduction 1-4 “Cool” internet appliances World’s smallest web server http://www-ccs.cs.umass.edu/~shri/iPic.html IP picture frame http://www.ceiva.com/ Web-enabled toaster + weather forecaster Internet phones Introduction 1-5 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 private intranet Internet standards RFC: Request for comments IETF: Internet Engineering Task Force Home network Institutional network Mobile network Global ISP Regional ISP Introduction 1-6 What’s the Internet: a service view communication infrastructure enables distributed applications: Web, VoIP, email, games, e-commerce, file sharing communication services provided to apps: reliable data delivery from source to destination “best effort” (unreliable) data delivery
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Introduction 1-1
Chapter 1Introduction
Computer Networking: A Top Down Approach ,4th edition. Jim Kurose, Keith RossAddison-Wesley, July 2007.
A note on the use of these ppt slides:We’re making these slides freely available to all (faculty, students, readers).
They’re in PowerPoint form so you can add, modify, and delete slides
(including this one) and slide content to suit your needs. They obviously
represent a lot of work on our part. In return for use, we only ask the
following:
� If you use these slides (e.g., in a class) in substantially unaltered form,
that you mention their source (after all, we’d like people to use our book!)
� If you post any slides in substantially unaltered form on a www site, that
you note that they are adapted from (or perhaps identical to) our slides, and
note our copyright of this material.
Thanks and enjoy! JFK/KWR
All material copyright 1996-2007
J.F Kurose and K.W. Ross, All Rights ReservedIntroduction 1-2
Chapter 1: Introduction
Our goal:� get “feel” and terminology
� more depth, detail later in course
� approach:� use Internet as example
Overview:� what’s the Internet?
� what’s a protocol?
� network edge; hosts, access net, physical media
� network core: packet/circuit switching, Internet structure
� performance: loss, delay, throughput
� security
� protocol layers, service models
� history
Introduction 1-3
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)
Introduction 1-4
“Cool” internet appliances
World’s smallest web server
http://www-ccs.cs.umass.edu/~shri/iPic.html
IP picture frame
http://www.ceiva.com/
Web-enabled toaster +
weather forecaster
Internet phones
Introduction 1-5
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 private intranet
� Internet standards� RFC: Request for comments
� IETF: Internet Engineering Task Force
Home network
Institutional network
Mobile network
Global ISP
Regional ISP
Introduction 1-6
What’s the Internet: a service view
� communication infrastructure enables distributed applications:
• Datagram network is not either connection-oriented or connectionless.• Internet provides both connection-oriented (TCP) and connectionless services (UDP) to apps.
Introduction 1-45
Internet structure: network of networks
� roughly hierarchical
� at center: “tier-1” ISPs (e.g., Verizon, Sprint, AT&T, Cable and Wireless), national/international coverage
� treat each other as equals
Tier 1 ISP
Tier 1 ISP
Tier 1 ISP
Tier-1 providers interconnect (peer) privately
Introduction 1-46
Tier-1 ISP: e.g., Sprint
…
to/from customers
peering
to/from backbone
…
.
………
POP: point-of-presence
Introduction 1-47
Internet structure: network of networks
� “Tier-2” ISPs: smaller (often regional) ISPs� Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs
Tier 1 ISP
Tier 1 ISP
Tier 1 ISP
Tier-2 ISPTier-2 ISP
Tier-2 ISP Tier-2 ISP
Tier-2 ISP
Tier-2 ISP pays tier-1 ISP for connectivity to rest of Internet� tier-2 ISP is customer oftier-1 provider
Tier-2 ISPs also peer privately with each other.
Introduction 1-48
Internet structure: network of networks
� “Tier-3” ISPs and local ISPs � last hop (“access”) network (closest to end systems)
Tier 1 ISP
Tier 1 ISP
Tier 1 ISP
Tier-2 ISPTier-2 ISP
Tier-2 ISP Tier-2 ISP
Tier-2 ISP
localISPlocal
ISPlocalISP
localISP
localISP Tier 3
ISP
localISP
localISP
localISP
Local and tier-3 ISPs are customers ofhigher tier ISPsconnecting them to rest of Internet
Introduction 1-49
Internet structure: network of networks
� a packet passes through many networks!
Tier 1 ISP
Tier 1 ISP
Tier 1 ISP
Tier-2 ISPTier-2 ISP
Tier-2 ISP Tier-2 ISP
Tier-2 ISP
localISPlocal
ISPlocalISP
localISP
localISP Tier 3
ISP
localISP
localISP
localISP
Introduction 1-50
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
A
B
packet being transmitted (delay)
packets queueing (delay)
free (available) buffers: arriving packets dropped (loss) if no free buffers
Introduction 1-51
Four sources of packet delay
� 1. nodal processing:� check bit errors
� determine output link
A
B
propagation
transmission
nodalprocessing queueing
� 2. queueing� time waiting at output link for transmission
� depends on congestion level of router
Introduction 1-52
Delay in packet-switched networks
3. Transmission delay:
� R=link bandwidth (bps)
� L=packet length (bits)
� time to send bits into link = L/R
4. Propagation delay:
� d = length of physical link
� s = propagation speed in medium (~2x108 m/sec)
� propagation delay = d/s
A
B
propagation
transmission
nodalprocessing queueing
Note: s and R are very different quantities!
Introduction 1-53
Packet Processing inside switches
ForwardingDecision
ForwardingDecision
ForwardingDecision
Forwarding
Table
Forwarding
Table
Forwarding
Table
Interconnect
OutputScheduling
Introduction 1-54
Switching Fabric
Introduction 1-55
Switching InterconnectsTwo basic techniques
Input Queuing Output Queuing
Usually a non-blocking
switch fabric (e.g. crossbar)
Usually a fast bus
Introduction 1-56
Caravan analogy
� cars “propagate” at 100 km/hr
� toll booth takes 12 sec to service car (transmission time)
� car~bit; caravan ~ packet
� Q: How long until caravan is lined up before 2nd toll booth?
� Time to “push” entire caravan through toll booth onto highway = 12*10 = 120 sec
� Time for last car to propagate from 1st to 2nd toll both: 100km/(100km/hr)= 1 hr
� A: 62 minutes
toll booth
toll booth
ten-car caravan
100 km 100 km
Introduction 1-57
Caravan analogy (more)
� Cars now “propagate” at 1000 km/hr
� Toll booth now takes 1 min to service a car
� Q: Will cars arrive to 2nd booth before all cars serviced at 1st booth?
� Yes! After 7 min, 1st car at 2nd booth and 3 cars still at 1st booth.
� 1st bit of packet can arrive at 2nd router before packet is fully transmitted at 1st router!� See Ethernet applet at AWL Web site
toll booth
toll booth
ten-car caravan
100 km 100 km
Introduction 1-58
Nodal delay
� dproc = processing delay� typically a few microsecs or less
� dprop = propagation delay� a few microsecs to hundreds of msecs
proptransqueueprocnodal ddddd +++=
Introduction 1-59
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 1-60
“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 1-61
“Real” Internet delays and routes
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 response (probe lost, router not replying)
trans-oceaniclink
Introduction 1-62
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
A
B
packet being transmitted
packet arriving tofull buffer is lost
buffer (waiting area)
Introduction 1-63
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 capacityRs bits/sec
link capacityRc bits/sec
pipe that can carryfluid at rateRs bits/sec)
pipe that can carryfluid at rateRc bits/sec)
server sends bits (fluid) into pipe
Introduction 1-64
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
Introduction 1-65
Throughput: Internet scenario
10 connections (fairly) share backbone bottleneck link R bits/sec
� transport: process-process data transfer� TCP, UDP
� network: routing of datagrams from source to destination� IP, routing protocols
� link: data transfer between neighboring network elements� PPP, Ethernet
� physical: bits “on the wire”
application
transport
network
link
physical
Introduction 1-75
ISO/OSI reference model
� presentation: allow applications to interpret meaning of data, e.g., encryption, compression, machine-specific conventions
� session: synchronization, checkpointing, recovery of data exchange
� Internet stack “missing” these layers!
� these services, if needed, must be implemented in application
� needed?
application
presentation
session
transport
network
link
physical
Introduction 1-76
Layering: logical communication
applicationtransportnetworklink
physical
applicationtransportnetworklink
physicalapplicationtransportnetworklink
physical
applicationtransportnetworklink
physical
networklink
physical
Each layer:
� distributed
� “entities”implement layer functions at each node
� entities perform actions, exchange messages with peers
Introduction 1-77
Layering: logical communication
applicationtransportnetworklink
physical
applicationtransportnetworklink
physicalapplicationtransportnetworklink
physical
applicationtransportnetworklink
physical
networklink
physical
data
data
E.g.: transport� take data from app
� add addressing, reliability check info to form “datagram”
� send datagram to peer
� wait for peer to ack receipt
� analogy: post office
data
transport
transport
ack
Introduction 1-78
Layering: physical communication
applicationtransportnetworklink
physical
applicationtransportnetworklink
physicalapplicationtransportnetworklink
physical
applicationtransportnetworklink
physical
networklink
physical
data
data
Introduction 1-79
An Network Example
Introduction 1-80
Addressing level
� Level in architecture at which entity is named
�Unique address for each end system (computer) and router
�Network level address � IP or internet address (TCP/IP)
� Network service access point or NSAP (OSI)
� Process within the system� Port number (TCP/IP)
� Service access point or SAP (OSI)
Introduction 1-81
Address Concepts
Introduction 1-82
Addressing Scope
�Global non-ambiguity� Global address identifies unique system
� There is only one system with address X
�Global applicability� It is possible at any system (any address) to identify any other system (address) by the global address of the other system
� Address X identifies that system from anywhere on the network
� e.g. MAC address on IEEE 802 networks
Introduction 1-83
Connection Identifiers
� Connection oriented data transfer (virtual circuits)
�Allocate a connection name during the transfer phase� Reduced overhead as connection identifiers are shorter than global addresses
� Routing may be fixed and identified by connection name
� Entities may want multiple connections -multiplexing
� State informationIntroduction 1-84
Addressing Mode
�Usually an address refers to a single system� Unicast address
� Sent to one machine or person
�May address all entities within a domain� Broadcast
� Sent to all machines or users
�May address a subset of the entities in a domain� Multicast
� Sent to some machines or a group of users
Introduction 1-85
Multiplexing
�Supporting multiple connections on one machine
�Mapping of multiple connections at one level to a single connection at another� Carrying a number of connections on one fiber optic cable
� Aggregating or bonding ISDN lines to gain bandwidth
Introduction 1-86
Protocol layering and data
Each layer takes data from above
� adds header information to create new data unit
� passes new data unit to layer below
applicationtransportnetworklink
physical
applicationtransportnetworklink
physical
source destination
M
M
M
M
Ht
HtHn
HtHnHl
M
M
M
M
Ht
HtHn
HtHnHl
message
segment
datagram
frame
Introduction 1-87
source
applicationtransportnetworklink
physical
HtHn M
segment Ht
datagram
destination
applicationtransportnetworklink
physical
HtHnHl M
HtHn M
Ht M
M
networklink
physical
linkphysical
HtHnHl M
HtHn M
HtHn M
HtHnHl M
router
switch
Encapsulationmessage M
Ht M
Hn
frame
Introduction 1-88
Network Security
�The field of network security is about:� how bad guys can attack computer networks
� how we can defend networks against attacks
� how to design architectures that are immune to attacks
� Internet not originally designed with (much) security in mind� original vision: “a group of mutually trusting users attached to a transparent network” ☺
� Internet protocol designers playing “catch-up”
� Security considerations in all layers!
Introduction 1-89
Bad guys can put malware into hosts via Internet� Malware can get in host from a virus, worm, or trojan horse.
� Spyware malware can record keystrokes, web sites visited, upload info to collection site.
� Infected host can be enrolled in a botnet, used for spam and DDoS attacks.
� Malware is often self-replicating: from an infected host, seeks entry into other hosts
Introduction 1-90
Bad guys can put malware into hosts via Internet� Trojan horse