Chapter 1: Introduction

Our goal:
get feel and

Overview:
whats the Internet? whats a protocol? network edge; hosts, access net,

terminology more depth, detail later in course approach: use Internet as example

physical media network core: packet/circuit switching, Internet structure performance: loss, delay, throughput security protocol layers, service models history
Introduction

1-1

What is the Internet

Meaning? Jargons? Components?

Introduction

1-2

Whats the Internet: nuts and bolts view

PC server

computing devices: hosts = end systems wireless laptop running network cellular handheld apps communication links fiber, copper, access points radio, satellite wired links transmission rate = bandwidth routers: forward router packets (chunks of data)

millions of connected

Mobile network Global ISP

Home network Regional ISP

Institutional network

Introduction

1-3

Whats the Internet: nuts and bolts view

protocols control sending, receiving of msgs

Mobile network Global ISP

e.g., TCP, IP, HTTP, Skype, Ethernet

Internet: network of networks

Home network Regional ISP

loosely hierarchical public Internet versus private intranet

Institutional network

Internet standards RFC: Request for comments IETF: Internet Engineering Task Force
Introduction 1-4

Whats 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
Introduction 1-5

Whats a protocol?
human protocols: whats the time? I have a question introductions specific msgs sent specific actions taken when msgs received, or other events network protocols: machines rather than humans all communication activity in Internet governed by protocols

protocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission, receipt
Introduction 1-6

Whats a protocol?
a human protocol and a computer network protocol:

Hi Hi
Got the time?

TCP connection request TCP connection response

Get http://www.awl.com/kurose-ross

2:00 time Q: Other human protocols?

<file>

Introduction

1-7

A closer look at network structure:

network edge:

applications and hosts access networks, physical media: wired, wireless communication links
network core: interconnected routers network of networks

Introduction

1-8

The network edge:

end systems (hosts):

client/server model

run application programs e.g. Web, email at edge of network

peer-peer

peer-peer model

client host requests, receives service from always-on server client/server e.g. Web browser/server; email client/server minimal (or no) use of dedicated servers e.g. Skype, BitTorrent
Introduction 1-9

Network edge: reliable data transfer service

Goal: data transfer
between end systems handshaking: setup (prepare for) data transfer ahead of time

TCP service [RFC 793]

reliable, in-order bytestream data transfer

Hello, hello back human protocol set up state in two communicating hosts

loss: acknowledgements and retransmissions sender wont overwhelm receiver senders slow down sending rate when network congested
Introduction 1-10

flow control:

TCP - Transmission

Control Protocol

congestion control:

Internets reliable data transfer service

Network edge: best effort (unreliable) data transfer service

Goal: data transfer

between end systems

same as before!

Apps using TCP:

HTTP (Web), FTP (file

UDP - User Datagram

Protocol [RFC 768]: connectionless unreliable data transfer no flow control no congestion control

transfer), Telnet (remote login), SMTP (email)

Apps using UDP:

streaming media,

teleconferencing, DNS, Internet telephony

Introduction 1-11

Access networks and physical media

Q: How to connect end systems to edge router? residential access nets institutional access networks (school, company) mobile access networks Keep in mind: bandwidth (bits per second) of access network? shared or dedicated?
Introduction 1-12

Residential access: point to point access

Dialup via modem

up to 56Kbps direct access to router (often less) Cant surf and phone at same time: cant be always on

DSL: digital subscriber line

deployment: telephone company (typically) up to 1 Mbps upstream (today typically < 256 kbps) up to 8 Mbps downstream (today typically < 1 Mbps) dedicated physical line to telephone central office

Introduction 1-13

Residential access: cable modems

HFC: hybrid fiber coax

asymmetric: up to 30Mbps downstream, 2 Mbps upstream network of cable and fiber attaches homes to ISP router homes share access to router deployment: available via cable TV companies

Introduction

1-14

Residential access: cable modems

Diagram: http://www.cabledatacomnews.com/cmic/diagram.html

Introduction

1-15

Cable Network Architecture: Overview

Typically 500 to 5,000 homes

cable headend cable distribution network (simplified) home

Introduction

1-16

Cable Network Architecture: Overview

server(s)

cable headend cable distribution network home

Introduction

1-17

Cable Network Architecture: Overview

cable headend cable distribution network (simplified) home

Introduction

1-18

Cable Network Architecture: Overview

FDM (more shortly):
V I D E O 1 V I D E O 2 V I D E O 3 V I D E O 4 V I D E O 5 V I D E O 6 D A T A 7 D A T A 8 C O N T R O L 9

Channels

cable headend cable distribution network home

Introduction

1-19

Company access: local area networks

company/univ local area

network (LAN) connects end system to edge router Ethernet: 10 Mbs, 100Mbps, 1Gbps, 10Gbps Ethernet modern configuration: end systems connect into Ethernet switch LANs: chapter 5

Introduction

1-20

Wireless access networks

shared

wireless access network connects end system to router

via base station aka access point

router base station

wireless LANs: 802.11b/g (WiFi): 11 or 54 Mbps wider-area wireless access

provided by telco operator ~1Mbps over cellular system (EVDO, HSDPA) next up (?): WiMAX (10s Mbps) over wide area

mobile hosts
Introduction

1-21

Home networks
Typical home network components: DSL or cable modem router/firewall/NAT Ethernet wireless access point
to/from cable headend cable modem router/ firewall Ethernet wireless laptops wireless access point
Introduction 1-22

Physical Media
Bit: propagates between

transmitter/rcvr pairs physical link: what lies between transmitter & receiver guided media:

Twisted Pair (TP) two insulated copper wires

signals propagate in solid media: copper, fiber, coax

Category 3: traditional phone wires, 10 Mbps Ethernet Category 5: 100Mbps Ethernet

unguided media: signals propagate freely, e.g., radio

Introduction

1-23

Physical Media: coax, fiber

Coaxial cable:
conductors bidirectional baseband:

Fiber optic cable:

glass fiber carrying light

two concentric copper

pulses, each pulse a bit high-speed operation:

broadband: multiple channels on cable HFC

single channel on cable legacy Ethernet

high-speed point-to-point transmission (e.g., 10s100s Gps)

low error rate: repeaters

spaced far apart ; immune to electromagnetic noise

Introduction

1-24

Physical media: radio

signal carried in

Radio link types:

terrestrial microwave e.g. up to 45 Mbps channels LAN (e.g., Wifi)

electromagnetic spectrum no physical wire bidirectional propagation environment effects:

11Mbps, 54 Mbps

reflection obstruction by objects interference

wide-area (e.g., cellular) 3G cellular: ~ 1 Mbps satellite

Kbps to 45Mbps channel (or multiple smaller channels) 270 msec end-end delay geosynchronous versus low altitude
Introduction 1-25

The Network Core

mesh of interconnected

routers the fundamental question: how is data transferred through net? circuit switching: dedicated circuit per call: telephone net packet-switching: data sent thru net in discrete chunks
Introduction 1-26

Network Core: Circuit Switching

End-end resources reserved for call
link bandwidth, switch

capacity dedicated resources: no sharing circuit-like (guaranteed) performance call setup required

Introduction

1-27

Network Core: Circuit Switching

network resources (e.g., bandwidth) divided into pieces
pieces allocated to calls resource piece dividing link bandwidth

idle if not used by owning call (no sharing)

into pieces frequency division time division

Introduction

1-28

Circuit Switching: FDM and TDM

FDM frequency time TDM Example: 4 users

frequency time

Introduction

1-29

Numerical example
How long does it take to send a file of

640,000 bits from host A to host B over a circuit-switched network?

All links are 1.536 Mbps Each link uses TDM with 24 slots/sec 500 msec to establish end-to-end circuit

Lets work it out!

Introduction

1-30

Network Core: Packet Switching

each end-end data stream divided into packets user A, B packets share network resources each packet uses full link bandwidth resources used as needed

Bandwidth division into pieces Dedicated allocation Resource reservation

resource contention: aggregate resource demand can exceed amount available congestion: packets queue, wait for link use store and forward: packets move one hop at a time

Node receives complete packet before forwarding

Introduction

1-31

Packet Switching: Statistical Multiplexing

A B
100 Mb/s Ethernet

statistical multiplexing
1.5 Mb/s

queue of packets waiting for output link

Sequence of A & B packets does not have fixed pattern, bandwidth shared on demand statistical multiplexing. TDM: each host gets same slot in revolving TDM frame.
Introduction 1-32

Packet-switching: store-and-forward
L R R R

takes L/R seconds to

transmit (push out) packet of L bits on to link at R bps store and forward: entire packet must arrive at router before it can be transmitted on next link delay = 3L/R (assuming zero propagation delay)

Example: L = 7.5 Mbits R = 1.5 Mbps transmission delay = 15 sec

more on delay shortly

Introduction 1-33

Packet switching versus circuit switching

Packet switching allows more users to use network!
1 Mb/s link each user: 100 kb/s when active active 10% of time

Circuit switching:

N users 1 Mbps link

10 users with 35 users, probability > 10 active at same time is less than .0004

Packet switching:

Q: how did we get value 0.0004?

Introduction

1-34

Packet switching versus circuit switching

Is packet switching a slam dunk winner?
great for bursty data

resource sharing simpler, 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 an unsolved problem (chapter 7)
Q: human analogies of reserved resources (circuit switching) versus on-demand allocation (packet-switching)?
Introduction 1-35

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 providers interconnect (peer) privately

Tier 1 ISP Tier 1 ISP

Tier 1 ISP

Introduction

1-36

Tier-1 ISP: e.g., Sprint

POP: point-of-presence

to/from backbone

peering

to/from customers

Introduction

1-37

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-2 ISP pays tier-1 ISP for connectivity to rest of Internet tier-2 ISP is customer of tier-1 provider

Tier-2 ISP

Tier-2 ISP

Tier 1 ISP Tier 1 ISP

Tier-2 ISP

Tier-2 ISPs also peer privately with each other.

Tier 1 ISP
Tier-2 ISP

Tier-2 ISP

Introduction

1-38

Internet structure: network of networks

Tier-3 ISPs and local ISPs last hop (access) network (closest to end systems)

local ISP Local and tier3 ISPs are customers of higher tier ISPs connecting them to rest of Internet

Tier 3 ISP Tier-2 ISP

local ISP

local ISP Tier-2 ISP

local ISP

Tier 1 ISP Tier 1 ISP

Tier-2 ISP local ISP

Tier 1 ISP

Tier-2 ISP local ISP

Introduction 1-39

Tier-2 ISP local local ISP ISP

Internet structure: network of networks

a packet passes through many networks!

local ISP

Tier 3 ISP Tier-2 ISP

local ISP

local ISP Tier-2 ISP

local ISP

Tier 1 ISP Tier 1 ISP

Tier-2 ISP local ISP

Tier 1 ISP
Tier-2 ISP local local ISP ISP

Tier-2 ISP local ISP

Introduction 1-40

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

1-41

Four sources of packet delay

1. nodal processing: check bit errors determine output link 2. queueing time waiting at output link for transmission depends on congestion level of router

A B

transmission propagation

nodal processing

queueing
Introduction 1-42

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 Note: s and R are very different quantities!
propagation

A B

transmission

nodal processing

queueing

Introduction

1-43

Caravan analogy
100 km ten-car caravan toll booth toll booth
Time to push entire

100 km

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?

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
Introduction 1-44

Caravan analogy (more)

100 km ten-car caravan toll booth toll booth
Yes! After 7 min, 1st car at

100 km

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?

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

Introduction 1-45

Nodal delay
d nodal = d proc + d queue + d trans + d prop
dproc = processing delay

typically a few microsecs or less depends on congestion = L/R, significant for low-speed links a few microsecs to hundreds of msecs
Introduction 1-46

dqueue = queuing delay

dtrans = transmission delay

dprop = propagation delay

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

1-47

Real Internet delays and routes

What do real Internet delay & loss look like? traceroute : 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

1-48

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 7 nycm-wash.abilene.ucaid.edu (198.32.8.46) 22 ms 22 ms 22 ms trans-oceanic 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 1-49

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
buffer (waiting area) packet being transmitted

packet arriving to full buffer is lost

Introduction 1-50

Throughput
throughput: rate (bits/time unit) at which

bits transferred between sender/receiver

instantaneous: rate at given point in time average: rate over long(er) period of time

link capacity server, with server sends bits pipe that can carry fluid at rate file into pipe (fluid) of F bits Rs bits/sec to send to client Rs bits/sec)

link capacity pipe that can carry Rfluid at rate c bits/sec Rc bits/sec)
Introduction

1-51

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

bottleneck link
link on end-end path that constrains end-end throughput
Introduction 1-52

Throughput: Internet scenario

per-connection
Rs Rs R Rc Rc Rc Rs

end-end throughput: min(Rc,Rs,R/10)

in practice: Rc or Rs

is often bottleneck

10 connections (fairly) share backbone bottleneck link R bits/sec

Introduction 1-53

Protocol Layers
Networks are complex! many pieces: hosts routers links of various media applications protocols hardware, software

Question:
Is there any hope of organizing structure of network? Or at least our discussion of networks?

Introduction

1-54

Organization of air travel

ticket (purchase) baggage (check) gates (load) runway takeoff airplane routing ticket (complain) baggage (claim) gates (unload) runway landing airplane routing airplane routing

a series of steps
Introduction 1-55

Layering of airline functionality

ticket (purchase) baggage (check) gates (load) runway (takeoff) airplane routing
departure airport

ticket (complain) baggage (claim gates (unload) runway (land) airplane routing airplane routing airplane routing
arrival airport

ticket baggage gate takeoff/landing airplane routing

intermediate air-traffic control centers

Layers: each layer implements a service via its own internal-layer actions relying on services provided by layer below

Introduction

1-56

Why layering?
Dealing with complex systems:
explicit structure allows identification,

relationship of complex systems pieces layered reference model for discussion modularization eases maintenance, updating of system change of implementation of layers service transparent to rest of system e.g., change in gate procedure doesnt affect rest of system layering considered harmful?
Introduction 1-57

Internet protocol stack

application: supporting network applications FTP, SMTP, HTTP transport: process-process data transfer TCP, UDP network: routing of datagrams from source

application transport network link physical

to destination

IP, routing protocols

link: data transfer between neighboring

network elements

PPP, Ethernet

physical: bits on the wire

Introduction

1-58

ISO/OSI reference model

presentation: allow applications to

interpret meaning of data, e.g., encryption, compression, machinespecific 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

1-59

source
message segment Ht datagram Hn Ht frame Hl Hn Ht
M M M M

application transport network link physical

Encapsulation

link physical switch

destination
M Ht Hn Ht Hl Hn Ht M M M

Hn Ht Hl Hn Ht

M M

application transport network link physical

network link physical

Hn Ht

router

Introduction

1-60

Network Security
attacks on Internet infrastructure:

infecting/attacking hosts: malware, spyware, worms, unauthorized access (data stealing, user accounts) denial of service: deny access to resources (servers, link bandwidth)

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

1-61

What can bad guys do: malware?

Spyware: Worm: infection by downloading infection by passively web page with spyware receiving object that gets records keystrokes, web itself executed sites visited, upload info self- replicating: propagates to collection site to other hosts, users Virus Sapphire Worm: aggregate scans/sec

infection by receiving object (e.g., e-mail attachment), actively executing self-replicating: propagate itself to other hosts, users

in first 5 minutes of outbreak (CAIDA, UWisc data)

Introduction

1-62

Denial of service attacks

attackers make resources (server, bandwidth)

unavailable to legitimate traffic by overwhelming resource with bogus traffic

1.

select target

2. break into hosts

around the network (see malware) 3. send packets toward target from compromised hosts

target

Introduction

1-63

Sniff, modify, delete your packets

Packet sniffing:
broadcast media (shared Ethernet, wireless) promiscuous network interface reads/records all packets (e.g., including passwords!) passing by

src:B dest:A

payload

Wireshark software used for end-of-chapter labs is a (free) packet-sniffer more on modification, deletion later Introduction

1-64

Masquerade as you
IP

spoofing: send packet with false source address

A
src:B dest:A payload

Introduction

1-65

Masquerade as you
IP

spoofing: send packet with false source address record-and-playback: sniff sensitive info (e.g., password), and use later
password holder is that user from system point of view

src:B dest:A

user: B; password: foo

B
Introduction 1-66

Masquerade as you
IP

spoofing: send packet with false source address record-and-playback: sniff sensitive info (e.g., password), and use later
password holder is that user from system point of view

later ..
A

src:B dest:A

user: B; password: foo

B
Introduction 1-67

Network Security
more throughout this course chapter 8: focus on security crypographic techniques: obvious uses and

not so obvious uses

Introduction

1-68

Internet History
1961-1972: Early packet-switching principles
1961: Kleinrock - queueing

theory shows effectiveness of packetswitching 1964: Baran - packetswitching in military nets 1967: ARPAnet conceived by Advanced Research Projects Agency 1969: first ARPAnet node operational

1972:

ARPAnet public demonstration NCP (Network Control Protocol) first host-host protocol first e-mail program ARPAnet has 15 nodes

Introduction

1-69

Internet History
1972-1980: Internetworking, new and proprietary nets
1970: ALOHAnet satellite

network in Hawaii 1974: Cerf and Kahn architecture for interconnecting networks 1976: Ethernet at Xerox PARC late70s: proprietary architectures: DECnet, SNA, XNA late 70s: switching fixed length packets (ATM precursor) 1979: ARPAnet has 200 nodes

Cerf and Kahns internetworking principles: minimalism, autonomy - no internal changes required to interconnect networks best effort service model stateless routers decentralized control define todays Internet architecture

Introduction

1-70

Internet History
1980-1990: new protocols, a proliferation of networks
1983: deployment of new national networks:

TCP/IP 1982: smtp e-mail protocol defined 1983: DNS defined for name-to-IPaddress translation 1985: ftp protocol defined 1988: TCP congestion control

Csnet, BITnet, NSFnet, Minitel 100,000 hosts connected to confederation of networks

Introduction

1-71

Internet History
1990, 2000s: commercialization, the Web, new apps
Early 1990s: ARPAnet

decommissioned 1991: NSF lifts restrictions on commercial use of NSFnet (decommissioned, 1995) early 1990s: Web hypertext [Bush 1945, Nelson 1960s] HTML, HTTP: Berners-Lee 1994: Mosaic, later Netscape late 1990s: commercialization of
the Web

Late 1990s 2000s:

more killer apps: instant

messaging, P2P file sharing network security to forefront est. 50 million host, 100 million+ users backbone links running at Gbps

Introduction

1-72

Internet History
2007: ~500 million hosts Voice, Video over IP P2P applications: BitTorrent (file sharing) Skype (VoIP), PPLive (video) more applications: YouTube, gaming wireless, mobility

Introduction

1-73

Introduction: Summary
Covered a ton of material! Internet overview whats a protocol? network edge, core, access network packet-switching versus circuit-switching Internet structure performance: loss, delay, throughput layering, service models security history You now have: context, overview, feel of networking more depth, detail to follow!

Introduction

1-74