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ali.dmohammadi@ gmail.comali.dmohammadi@ gmail.com OrientationOrientation 1-1-11

Orientation

Computer NetworksComputer Networks

Shahrood University of TechnologyShahrood University of TechnologyDepartment of Computer Engineering & ITDepartment of Computer Engineering & IT


Chapter 1: OrientationChapter 1: Orientation

1.0 Why Networking1.1 What is the Internet?1.2 Network Structure

Network edge

Network coreNetwork access and physical media

1.3 Internet structure and ISPs 1.4 Delay & loss in packet-switched networks1.5 Protocol layers, service models1.6 History


Distributed Software Application (will be discussed): WEB, email, 3-tier appl., … Database Directory

Resource Sharing File, Software, Data, … (Network File System, File

Transfer, …) CPU, Memory, Peripherals, …

Communication Email, Chat, TV, Radio, Video Conference,

Telephone, . Virtual Terminal (Remote Login)

Why Networking !Why Networking !


Platform (OS + Hardware)

Application Program Interface (API)

Application Software

Platform (OS + Hardware)


Application process

Application process

Application process

Application process

Inter-process Communication

Platform Services Graphics Data Interchange Data Management User Interface Software Engineering Communication

Services

Application AgentApplication Agent

Application SoftwareApplication Software


Distributed Applications or Network Application: Distributed Applications or Network Application: Client/ServerClient/Server

Application Software (Client Part)

Application Software (Client Part)

Networking Software & HardwareNetworking Software & Hardware

Application Software (Server Part)

Application Software (Server Part)

Client (user) AgentClient (user) Agent Server AgentServer Agent

CommunicationCommunicationNetworkNetwork

Client Agents Examples: Internet Explorer + http,

Opera + http MS’s Outlook + SMTP,

Netscape’s Messenger + SMTP, Eudora + SMTP

… next slide

Application Program Interface (API) Application Program Interface (API)Syste

mA

pplica

tion

Platform (OS + Hardware)Platform (OS + Hardware)


Application process

Application process

Client/Server ApplicationsClient/Server Applications

Application Program Interface (API) Application Program Interface (API)

Networking Software & HardwareNetworking Software & Hardware


Platform (OS + Hardware) Platform (OS + Hardware)

Application Process(Client Side)

Application Process(Client Side)

Application Process(Server Side)

Application Process(Server Side)

Server Agents Examples: Internet Information

Sever + http, Appachi + http

SQL query engines + http Communication Software

Examples: TCP, UDP; IP…


Application Software

Presentation

User Interface

Business (Application Logic)

Data (Database Access)

Layered Application ModelLayered Application Model

Client Part

Server Parts


Presentation: The client agent remains focused

on presenting information to or receiving

input from the user.

User Interface: User’s access to the application

logic via client agent. It can be dynamic and

configured by user. It is build on the top of the

user interface control. Dynamic User Interface:

• Customizing the look (example: www.cstore.com

• Customizing the content ( examples:

my.yahoo.com , www.exite.com )

Client PartClient Part


Business Rules (Application Logic) Units of processing or algorithms that

represents concept of importance to the organization using database.

Data (Database Access) Logic to connect to database; access/manipulate data

held within databases.

Server PartsServer Parts


User InterfaceUser Interface

Presentation Presentation Business

(Application Logic)

Business (Application

Logic)

Database

Layered Application: Layered Application: 3-Tier Client/Server Model3-Tier Client/Server Model

Client Workstation(rich client)

Application Sever

Data (Data Access and Storage)

Data (Data Access and Storage)


Mobile ClientWorkstation (thin client)

User InterfaceUser Interface

Presentation Presentation

Data Server

Run by Client AgentRuns by Application

Server Agent

Runs by Database Server Agent

Run by Client Agent

user

user


““Logical Tiers vs Physical TiersLogical Tiers vs Physical Tiers

Application Model Logical Tiers

• Presentation• User Interface• Business• Data

Physical Tiers• Client workstation• Application server• Data Base

Application Model Logical Tiers

• Presentation• User Interface• Business• Data

Physical Tiers• Client workstation• Application server• Data Base

PresentationClient WorkstationUser Interface

Business (Application Logic)

Application Server

Data (Database Access)

Database


Chapter 1 OutlineChapter 1 Outline


Network edge




Local ISP (LAN)Local ISP (LAN)

hub

Client

Printer

Server

Client

LAN Switch

Client

Remote Access ServerModem pools

TelephoneLines

Router

External Link

Serversmodem

modem

Client

modem

modem External LinkRouter


internet: network of networksinternet: network of networks

modem

modem

local ISP

companynetwork

mobile station

workstation

router

servermodem

regional ISP

local ISP

Base Station

links


InternetInternet

millions of connected computing devices: hosts, end-systems PCs workstations, servers, … Personal Data Assistances, phones, … running network apps

communication links fiber, copper, radio, satellite transmission rate = bandwidth

routers: forward packets

Networking Hardware and Software Protocols, Hubs, LAN Switches, Repeaters,


protocols control sending, receiving of messages e.g., TCP, IP, HTTP, FTP, PPP, …

Internet: “network of networks” loosely hierarchical public Internet versus private intranet

Internet standards (IAB) RFC: Request for comments IETF: Internet Engineering Task Force

InternetInternet


human protocols: “what’s 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

What’s a protocol?


a human protocol and a computer network protocol:

Q: Other human protocols?

Hi

Hi

Got thetime?

2:00

TCP connection req

TCP connectionresponseGet http://www.awl.com/kurose-ross

<file>time

What’s a protocol?


Examples? Search Engines (Google) Email (Hotmail) Shopping (Amazon) Auctions (eBay) Chat (AOL)

Internet ServicesInternet Services

Goals? Fast service (low latency) Service all users (scalability) Always available (fault tolerance)


the Internetthe Internetintranet

router

Intranet: access is denied from outside

firewall

A private corporate network consisting of hosts, routers, and networks that use TCP/IP technology. An intranet may or may not connect to the global Internet.

intranetintranet


Extranet: an internet of networkseach of which is belong to

individual company or organization

Company 1

Company 2

Company 3

extranetextranet


IP addressing: ICANNIP addressing: ICANN

Q: How does an ISP get block of addresses and Names?

A: ICANN: (Internet Corporation For Assigned Names and Numbers) The organization that took over the IANA

duties after Postel’s death. IANA: (Internet Assigned Number Authority)

Essentially one individual (Jon Postel). IANA was originally responsible for assigning IP addresses and the constants used in TCP/IP protocols. Replaced by ICANN in 1999.

Q: How does an ISP get block of addresses and Names?

A: ICANN: (Internet Corporation For Assigned Names and Numbers) The organization that took over the IANA

duties after Postel’s death. IANA: (Internet Assigned Number Authority)

Essentially one individual (Jon Postel). IANA was originally responsible for assigning IP addresses and the constants used in TCP/IP protocols. Replaced by ICANN in 1999.


IP addressing: ICANNIP addressing: ICANN

ICANN coordinates the assignment of identifiers that must be globally unique for the Internet to function. allocates addresses manages DNS assigns domain names, resolves disputes assigns default port numbers sets protocol parameter


(b)(b) USC-ISI Marina del Rey, CA

(l)(l) ICANN Marina del Rey, CA

(e) (e) NASA Mt View, CA(f)(f) Internet Software C. Palo Alto, CA

(i)(i) NORDUnet Stockholm, Sweden

(k)(k) RIPE London, UK

(m)(m) WIDE Tokyo, Japan

(a)(a) NSI Herndon, VA(c)(c) PSInet Herndon, VA

(d)(d) U Maryland College Park, MD(g)(g) DISA Vienna, VA

(h)(h) ARL Aberdeen, MD(j)(j) NSI (TBD) Herndon, VA

DNS Root ServersDNS Root Servers


communication infrastructure enables distributed applications: Web, email, games,

e-commerce, database., file (MP3) sharing

communication services provided to apps: connectionless connection-oriented

modem

modem

local ISP

companynetwork

regional ISP

What’s the Internet: a service viewWhat’s the Internet: a service view


Chapter 1: OutlineChapter 1: Outline


Network edgeNetwork coreNetwork access and physical media



Network StructureNetwork Structure

network edge: applications and hosts

network core: routers

access networks, physical media: communication

links

modem

modem

local ISP

companynetwork

regional ISP


The network edge:The network edge:

end systems (hosts): run application programs e.g. Web, email at “edge of network”

client/server model client host requests, receives

service from always-on server e.g. Web browser/server;

email client/server

peer-peer model: minimal (or no) use of

dedicated servers e.g. Gnutella, KaZaA

modem

modem

local ISP

companynetwork

regional ISP


Client-ServerClient-Server

Application Softwaremodem

modem

1. Client-ServerClient Side SoftwareServer Side Software

2. Peer-to-Peer ! (chapter 2)

Client SideSoftware

Server SideSoftwarePeer Side

Peer Side


Server TypesServer Types

Web server File Server (example: Network File System) Database Server Application Server Groupware Server Software Server Object Server Proxy Server DNS Server


Network edge: connection-oriented serviceNetwork edge: connection-oriented service

Goal: data transfer between end systems

handshaking: setup (prepare for) data transfer ahead of time set up “state” in two

communicating hosts TCP - Transmission

Control Protocol Internet’s connection-

oriented service

TCP service [RFC 793] reliable, in-order byte-

stream data transfer loss: acknowledgements

and retransmissions flow control:

sender won’t overwhelm receiver

congestion control: senders “slow down

sending rate” when network congested


Network edge: connectionless serviceNetwork edge: connectionless service

Goal: data transfer between end systems same as before!

UDP - User Datagram Protocol [RFC 768]: Internet’s connectionless service unreliable data

transfer no flow control no congestion

control

App’s using TCP: HTTP (Web), FTP (file

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

App’s using UDP: streaming media,

teleconferencing, DNS, Internet telephony




Network edge




The Network CoreThe 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”

modem

modem

local ISP

companynetwork

regional ISP


Network Core: Circuit SwitchingNetwork Core: Circuit Switching

End-end resources reserved for “call”

link bandwidth, switch capacity

dedicated resources: no sharing

circuit-like (guaranteed) performance

call setup required

modem

modem

local ISP

companynetwork

regional ISP


Network Core: Circuit SwitchingNetwork Core: Circuit Switching

network resources (e.g., bandwidth) divided into “pieces”

pieces allocated to calls

resource piece idle if not used by owning call (no sharing)

dividing link bandwidth into “pieces” frequency division time division


FDMA

frequency

time

TDMA

frequency

time

4 users

Example:

Circuit Switching: TDMA and TDMA


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

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 transmit over link wait turn at next

link

Bandwidth division into “pieces”

Dedicated allocationResource reservation

Network Core: Packet Switching


Packet Switching: Statistical MultiplexingPacket Switching: Statistical Multiplexing

Sequence of A & B packets does not have fixed pattern statistical multiplexing.

In TDM each host gets same slot in revolving TDM frame.

Sequence of A & B packets does not have fixed pattern statistical multiplexing.

In TDM each host gets same slot in revolving TDM frame.

A

B

C10 MbsEthernet

1.5 Mbs

D E

statistical multiplexing

queue of packetswaiting for output

link

emptybuffer


Packet switching versus circuit switchingPacket switching versus circuit switching

Each user: sends 100 kbps when

“active” is active p=10% of time

Each user: sends 100 kbps when

“active” is active p=10% of time

Packet switching allows more users to use network!Packet switching allows more users to use network!

User: 1

1 Mbps link

User: N

Switch

Circuit-Switch ≤ 10 simultaneous usersCircuit-Switch ≤ 10 simultaneous users


How many Users?

)!(!

!

)1(),;(

kNk

N

k

N: whichin

ppk

NpNkP kNk

)!(!

!

)1(),;(

kNk

N

k

N: whichin

ppk

NpNkP kNk

binomial distribution: The probability that k users be active together:

35

11

( 10) ( ;35,0.1) 0.0017

( 10) 1 0.0017 0.9983k

P k P k

P k

Packet-Switch if N=35 users, for active users > 10

there is: probability < 0.0017 for active users <=

10 there is: probability > 0.9983


Packet Switching UsersPacket Switching Users

Switch supports 35 simultaneous users (connections) Up to 10 users be active: no queue, packet

switching has almost the same delay performance as circuit switching.

More than 10 users be active: output queue begin to grow and the connections experience queuing delay.

Because the probability of having 11 or more simultaneous active users is 0.0017,almost the same delay performance as circuit switching.

Packet switching allows more than 3 times the number of users.


Packet switching versus circuit switchingPacket switching versus circuit switching

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 applications.

still an unsolved problem (chapter 6)


Packet-switching: store-and-forwardPacket-switching: store-and-forward

Takes L/R seconds to transmit (push out) packet of L bits on to link or R bps

Entire packet must arrive at router before it can be transmitted on next link: store and forward

delay = 3L/R

Example: L = 7.5 Mbits;

message size R = 1.5 Mbps; link

bandwidth message

transmission time = L/R = 5 sec

delay = 3L/R = 15 sec

R R R

L


Packet Switching: Message SegmentingPacket Switching: Message Segmenting

Now break up the message into 5000 packets

Each packet 1,500 bits

1 msec to transmit packet on one link

pipelining: each link works in parallel

Delay reduced from 15 sec to 5.002 sec


Packet-switched networks: forwardingPacket-switched networks: forwarding

Goal: move packets through routers from source to destination we’ll study several path selection (i.e.

routing)algorithms (chapter 4) datagram network:

destination address in packet 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


Network TaxonomyNetwork Taxonomy

Telecommunicationnetworks

Telecommunicationnetworks

Circuit-switchednetworks

Circuit-switchednetworks

FDMFDM TDMTDM

Packet-switchednetworks

Packet-switchednetworks

Networkswith VCsNetworkswith VCs

DatagramNetworksDatagramNetworks

Datagram network is not either connection-oriented or connectionless. Internet provides both connection-oriented (TCP) and connectionless services (UDP) to applications.




Network edge




Access networks and physical mediaAccess networks and physical media

Q: How to connection 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?

modem

modem

local ISP

companynetwork

regional ISP


Residential access: point to point Residential access: point to point accessaccess

Dialup via modem up to 56Kbps direct access

to router (often less) Can’t surf and phone at

same time: can’t be “always on”

ADSL: asymmetric digital subscriber line up to 1 Mbps upstream (today typically < 256

kbps) up to 8 Mbps downstream (today typically < 1

Mbps) FDM: 50 kHz - 1 MHz for downstream 4 kHz - 50 kHz for upstream 0 kHz - 4 kHz for ordinary telephone

modem

modem


Company access: local area networksCompany access: local area networks

company/univ local area network (LAN) connects end system to edge router

Ethernet: shared or dedicated

link connects end system and router

10 Mbs, 100Mbps, Gigabit Ethernet

deployment: institutions, home LANs happening now

LANs: chapter 5

modem

modem


Wireless access networksWireless access networks

shared wireless access network connects end system to router via base station aka

“access point” wireless LANs:

802.11b (WiFi): 11 Mbps wider-area wireless

access provided by telco operator 3G ~ 384 kbps

• Will it happen?? WAP/GPRS in Europe

shared wireless access network connects end system to router via base station aka

“access point” wireless LANs:

802.11b (WiFi): 11 Mbps wider-area wireless

access provided by telco operator 3G ~ 384 kbps

• Will it happen?? WAP/GPRS in Europe

basestation

mobilestations (hosts)

router


Home networksHome networks

Typical home network components: ADSL or cable modem router/firewall/NAT Ethernet wireless access point

(Network Address Translation) A technology that allows hosts with private addresses to communicate with an outside network such as the global Internet.

wireless access point

wirelesslaptops

router/Firewall/NAT

cable modem

to/fromInternet

Ethernet (switched)


Physical (Transmission) Media-LinkPhysical (Transmission) Media-Link

Physical Media (link) : what lies between transmitter & receiver.Physical Media (link) : what lies between transmitter & receiver.


Twisted PairTwisted Pair

Twisted Pair (TP) Unshielded/Shielded UTP/STP

Category 3: traditional phone wires, 10 Mbps Ethernet

Category 5 TP: 100Mbps Ethernet

…


Physical Media: coax, fiberPhysical Media: coax, fiber

Coaxial cable: two concentric copper

conductors bidirectional baseband:

single channel on cable legacy Ethernet

broadband: multiple channel on

cable HFC

Fiber optic cable: glass fiber carrying

light pulses, each pulse a bit

high-speed operation: high-speed point-to-point

transmission (e.g., 5 Gps) low error rate:

repeaters spaced far apart ; immune to electromagnetic noise


Physical media: radioPhysical media: radio

signal carried in electromagnetic spectrum

no physical “wire” bidirectional propagation

environment effects: reflection obstruction by objects interference

Radio link types: terrestrial microwave

e.g. up to 45 Mbps channels

LAN (e.g., WaveLAN) 2Mbps, 11Mbps

wide-area (e.g., cellular) e.g. 3G: hundreds of

kbps satellite

up to 50Mbps channel (or multiple smaller channels)

270 msec end-end delay geosynchronous versus

LEOS


Delay Latency for propagating data along the link Corresponds to the “length” of the link Typically measured in seconds

Bandwidth (Capacity) Amount of data sent (or received) per unit time Corresponds to the “capacity” of the link Typically measured in bits per second

Bandwidth(Bps)

Delay(sec)

delay x bandwidth(bit)

Links: Delay and BandwidthLinks: Delay and Bandwidth




Network edge




Tier Definition-Tier 1Tier Definition-Tier 1

Tier 1 providers make settlement-free interconnection arrangements with other Tier 1 providers, in which the two networks agree to carry each other's traffic (so-called "peering" with one another) at no cost.

No Tier 1 carriers have to pay for IP transit to any other Tier 1, and in general all other ISPs directly or indirectly pay the Tier 1s for access to their networks.

Tier 1 providers own the physical medium over which information is carried, as well as the network equipment which manages that information.


Tier 1 IPv4 ISPsTier 1 IPv4 ISPs

The following are believed to be the only Tier 1 ISPs worldwide:1. AOL Transit Data Network (ATDN)-AS 1668 2. AT&T-AS 7018 (not 2685, 2686, 2687, 2688 or 7132) 3. Global Crossing (GX)-AS 3549 4. Level 3-AS 3356 5. Verizon Business (UUnet)-AS 701 (not 702, 703 or 19262) 6. Nippon Telegraph and Telephone Corp. (NTT)-AS 2914 7. Qwest-AS 209

8. SAVVIS (Cable & Wireless America)-AS 3561

9. Sprint Nextel Corporation-AS 1239 • In the Internet, an autonomous system (AS) is a collection of IP

networks and routers under the control of one entity (or sometimes more) that presents a common routing policy to the Internet. See RFC 1930 for additional detail on this updated definition.


UUNET US backbone network


Tier-1 ISPs InterconnectionTier-1 ISPs Interconnection

9

11

22

33

4

Topology: Full MeshData Rates: 622Mbps, 2.5-10Gbps

▪▪▪

▪▪▪

▪▪▪

▪▪▪

▪▪▪

NAPs

NAPs

NAPs

NAPs

NAPs

NA

P:

Netw

ork

Acc

ess

Poin

t

Tier-2 ISPsTier-2 ISPs

High Speed Link from Telecom Companies

1. NSF 1988 ,T12. ANS 1993 ,T3


Tier Definition-Tier 2, 3Tier Definition-Tier 2, 3

There is no formal interconnection hierarchy, lower-tier companies are divided into two categories: Tier 2 - A network who peers with other networks,

but still pays for transit to reach some portion of the Internet.

Tier 3 - A network who solely purchases transit from other networks to reach the Internet.

Many of Tier 2 and 3 companies are very large Internet providers, but since they purchase IP transit from other networks they are not considered Tier 1.


▪▪▪▪NAPs

Tier-2 Tier-2 ISPISP Tier-2 Tier-2

ISPISP

Tier-1 Tier-1 ISPISP

Access ISP

Access ISP

Servers modem

Com3

RAS+

Modem Pool

modem

Tier-2 ISPs / Access ISPsTier-2 ISPs / Access ISPs

Remote Clients

Clients

▪▪▪ To Tier-1 ISP


Tier-1 ISP: e.g., UUNETTier-1 ISP: e.g., UUNET


Internet structure: network of networksInternet structure: network of networks

roughly hierarchical at center: “tier-1” ISPs (e.g., UUNet, BBN/Genuity,

Sprint, AT&T), national/international coverage treat each other as equals

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

Tier-1 providers interconnect (peer) privately

NAP

Tier-1 providers also interconnect at public network access points (NAPs)



“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

NAP

Tier-2 ISPTier-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, interconnect at NAP

Tier-2 ISP



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

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

NAP


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

Internet Internet Connection Connection Providers Providers (ICPs)(ICPs)For local ISPsFor local ISPs


End to End CommunicationEnd to End Communication

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

NAP


Tier-2 ISP Tier-2 ISP

Tier-2 ISP

AccessISPAccess

ISPAccess

ISP

AccessISP

AccessISP Tier 3

ISP

AccessISP

AccessISP

AccessISP

a packet passes through many networks!




Network edge




How do loss and delay occur?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 queue (delay)

free (available) buffers: arriving packets dropped (loss) if no free buffers


Four sources of packet delayFour sources of packet delay

1. nodal processing: check bit errors determine output link

A

B

propagation

transmission

nodalprocessing queue

2. queueing time waiting at output

link for transmission depends on

congestion level of router


Delay in packet-switched networksDelay in packet-switched networks

3. Transmission delay: R=link bandwidth (bps) L=number of bits in

packet (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 queue

Note: s and R are verydifferent quantities!

Note: s and R are verydifferent quantities!

bit length: s/R [m]packet length: Ls/R

[m]

bit length: s/R [m]packet length: Ls/R

[m]


Caravan analogyCaravan analogy

car=bit caravan = packet cars speed (km/hr) = propagation speed (m/sec) service rate at toll booth (car/sec) = bandwidth

(bit/sec)

ten-car caravan 120

km

toll booth22331010

11 toll booth


Caravan Analogy (cont.)Caravan Analogy (cont.)

cars speed = 120 km/hr = 2km/mintoll booth takes 12 sec to service a car ( car/sec)

Q: How long until caravan is lined up before 2nd toll booth?

Time to “push” entire caravan through toll booth onto highway = 12*10 = 120sec = 2min

Time for last car to propagate from 1st to 2nd toll both: 120km/(120km/hr)= 1 hr

A: 62 minutes

121

120 km

toll booth22331010

11toll booth

4km


Caravan Analogy (cont.)Caravan Analogy (cont.)

Q: Will cars arrive to 2nd booth before all cars serviced at 1st booth?

After (1+6) 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!

cars speed = 1200 km/hr = 20km/mintoll booth takes 1min to service a car ( 1

car/min)

120 km 2233

99

11toll booth6688 77

toll booth

20km20km

1010


Bit LengthBit Length

bit length = s/R Packet length = Ls/R

s = propagation speed of energy in the link (medium) [m/sec]

R = link bandwidth [bps] L = number of bits in packet [bits]

Example : s= 200m/µs; R=10Mbps [Tbit =0.1 µs]; L= 250 Byte = 2000 bit

20m

linksource destination

Propagation direction

20

00 1

99

9

1234

20×2000 m


Nodal delayNodal delay

dproc = processing delay typically a few msecs or less

dqueue = queuing delay depends on congestion

dtrans = transmission delay = L/R, significant for low-speed links

dprop = propagation delay a few microsecs to hundreds of msecs

proptransqueueprocnodal ddddd


Queuing delay (revisited)Queuing delay (revisited)

R=link bandwidth (bps) L=packet length (bits) a=average packet

arrival rate

traffic intensity = La/R

La/R ~ 0: average queuing delay small La/R —> 1: delays become large La/R > 1: more “work” arriving than can

be serviced, average delay infinite!

La/R

Avera

ge q

ueuin

g d

ela

y

1


““Real” Internet delays and routesReal” 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


““Real” Internet delays and routesReal” 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 measements from gaia.cs.umass.edu to cs-gw.cs.umass.edu

* means no reponse (probe lost, router not replying)

trans-oceaniclink


Packet LossPacket Loss

queue (aka buffer) preceding link in buffer has finite capacity

when packet arrives to full queue, packet is dropped (aka lost)

lost packet may be retransmitted by previous node, by source end system, or not retransmitted at all




Network edge




Network ModelsNetwork Models

The network model is defined in 3-D space.

App. Software (User) Plane: Data Communication.

Control Plane: Connection setup and

connection Maintenance, Resources access control

and access level control. Management Plane: Measurement and

management of network performance.

App. Software (User) Plane:Data Communication.

App. Software (User) Plane:Data Communication.

App. SoftwareApp. Software(User)(User)PlanePlane

Figure: Network Model.

We study this part only!We study this part only!


Why layering?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?


What’s a protocol?What’s a protocol?human protocols: “what’s 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 defines: format, order of msgs sent

and received among network entities, and

actions taken on msg transmission, reception.


Protocols (stack)Protocols (stack)

Distributed Systems relies on communicating elements.

Communicating elements follow a set of rules, syntax and semantics, i.e. Protocol.

In other words: A protocol governs the co-operation of two remote

parties (elements), or Two elements, remote to each other, do together a

task using a predefined rules, syntax, and semantics. Protocol Stack: It is a set of protocols,

designed to govern entire network.


Internet Layering Model and Internet Layering Model and ProtocolsProtocols

Application: supporting network applications FTP, SMTP, HTTP

Transport: host-host 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: Putting bits “on the wire”

application

transport

network

link

physical


Layers and AddressesLayers and Addresses

Application Layer domain name e.g. www.shahroodut.ac.ir

Transport Layer the identity of the application in the

destination host Port number: 2 bytes e.g. 80

Network Layer the network identity of the destination

host IP address: 4 bytes for IPv4 e.g. 202.156.1.78

Link Layer the identity of network interface card MAC address (physical address): 6 bytes e.g. 00-04-23-5E-6A-93

Application Layer domain name e.g. www.shahroodut.ac.ir

Transport Layer the identity of the application in the

destination host Port number: 2 bytes e.g. 80

Network Layer the network identity of the destination

host IP address: 4 bytes for IPv4 e.g. 202.156.1.78

Link Layer the identity of network interface card MAC address (physical address): 6 bytes e.g. 00-04-23-5E-6A-93

application

transport

network

link

physical


Open Systems Interconnection model (International Standard Organization-ISO, UN)

OSI model vs TCP/IP modelOSI model vs TCP/IP model

application

transport

network

link

physical

application

transport

network

networkinterface

application

presentation

Session

transport

network

Link

physical


Layering and DataLayering and Data

Each layer takes data from above adds header information to create new data unit passes new data unit to layer below

PDUs: frame, datagram (packet), segment, messagePDUs: frame, datagram (packet), segment, message

applicationtransportnetwork

linkphysical

Source process


linkphysical

Destination process

message

segment

datagram

frame

M

M HtHnHl Tl

M HtHn

M Ht

M

M HtHnHl Tl

M HtHn

M Ht


Layering and ProtocolLayering and Protocol

Appl. Soft. Appl. Soft.

App. Layer Protocols(ftp, http, SMTP, …)

Transport LayerProtocol (TCP, UDP)

Network LayerProtocols (IP, OSPF, RSVP)

Link LayerProtocols (Ethernet, FDDI, …)

application

transport

network

link

physical

application

transport

network

link

physicalPhysical Layer

Protocols (Ethernet, FDDI, …)

Physical Communication Channel

NETWORKNETWORK


Protocol layering and dataProtocol layering and data

Ht

Message App. ProcessApp. Process

applicationHa

Message

transport Ht Ht

Ht

network

App. Process decides to send a message to its counterpart

App. Layer adds its header, sends the message to transport layer

Transport layer breaks down the message into several parts, add its header to each part And makes segments.It sends one-by-one segments to network layer


Protocol Data UnitsProtocol Data Units

message[mes/sec]

Segment[seg/sec]

Datagram[Packet/sec]

Frame[frame/sec]

application

transport

network

link

physical

Appl. Soft.

application

transport

network

link

physical

Appl. Soft.[tps], [HTTPops/s],[NFS IOPS]

1st layer PDU(physical frame)

[bps]

Physical Communication Channel[Baud], [Hz]

Bau

d =

ch

an

ges

in s

ign

al/se

cB

au

d =

ch

an

ges

in s

ign

al/se

c


Network Network BandwidthBandwidth, , ThroughputThroughput and and GoodputGoodput

Application Layer

Transport Layer

Network Layer

Link Layer

Physical layer

Bandwidth Throughput Goodput

Tps, HTTPops/s,

…

Segmant/s

Packet/s Frame/s

Bit/s

Bandwidth: The rate at which the data units can be transmitted.

Throughput: The rate at which the data units are delivered (transferred).

It is a function of load. Its upper-band is Bandwidth.

Goodput: The rate at which the useful data units are delivered (transferred).

Its upper-band is the Throughput.

Bandwidth: The rate at which the data units can be transmitted.

Throughput: The rate at which the data units are delivered (transferred).

It is a function of load. Its upper-band is Bandwidth.

Goodput: The rate at which the useful data units are delivered (transferred).

Its upper-band is the Throughput.


Throughput, Goodput vs LoadThroughput, Goodput vs Load

Goodput

Throughput


Example: Network Layer GoodputExample: Network Layer Goodput

Goodput:

Efficiency:

link. congestion-no and packet, corupted-no packet, loss-no

:of condition in goodput goodput Optimum

[bps] goodput optimum

[bps] goodputEfficiency

[sec] duration time recieving

[bit] packet per length payloadreplica) recieved - packets recievedsbGoodput

100

(]/[


Protocols/ServicesProtocols/Services

application

transport

network

link

physical

Data Transport Services

Application Program Services

Hop-to-Hopprotocols

End-to-Endprotocols


From Application ViewpointFrom Application Viewpoint


Communication Software & HardwarePlatform (OS + Hardware)

Application SoftwareApplication Software

APIAPI

App. SoftwareApp. Software

transportnetwork

linkphysical

application

Controlledby OS

Controlledby App. Soft.


Layering: Physical Communication Layering: Physical Communication


linkphysical

modem

modem

networklink

physical


linkphysical


linkphysical


linkphysical

data

data

Host A

Host B

Router R


Layering: Logical Communication-1 Layering: Logical Communication-1

Each layer: distributed “entities”

implement layer functions at each node

entities perform actions, exchange messages with peers


linkphysical

modem

modem

networklink

physical


linkphysical


linkphysical


linkphysical


Layering: LogicalLayering: Logical Communication Communication

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


linkphysical

modem

modem

networklink

physical


linkphysical


linkphysical


linkphysical

data

data

transport

data

transport

ack


TCP/IP protocol stackTCP/IP protocol stack

mimemime

ftpftp httphttp smtpsmtp telnettelnet snmpsnmp tftptftp rtprtp dnsdns ……

Transmission Control Pr. (TCP)

Transmission Control Pr. (TCP)

User Datagram Pr. (UDP)User Datagram Pr. (UDP)

icmpicmp ospfospfrsvprsvp igmpigmp

Ethernet, token ring, FDDI, ATM, Frame relay, SNA, X25Ethernet, token ring, FDDI, ATM, Frame relay, SNA, X25

domain name service

real time pr.trival file transfer pr.

simple network management pr.

ftp: file transfer protocolhttp; hypertext transfer protocolSmtp: simple mail transfer protocolMime: multipurose Internet mail extensionstelnet=virtual terminal

icmp: Internet control message protocolospf: open shortest path first protocolrsvp: resource reservation protocoligmp: Internet group management protocol

arparp rarprarpInternet Protocol (IP)Internet Protocol (IP)

arp: address resolution protocolrarp: reverse address resolution protocol




Network edge




Internet Host CountInternet Host Count

Internet Systems Consortium, Inc. (ISC) is a nonprofit corporation

dedicated to supporting the infrastructure of the universal connected self-organizing Internet and

has autonomy to participates by developing and maintaining core production quality software, protocols, and operations.

Internet Systems Consortium, Inc. (ISC) is a nonprofit corporation

dedicated to supporting the infrastructure of the universal connected self-organizing Internet and

has autonomy to participates by developing and maintaining core production quality software, protocols, and operations.


Internet Standard: RFCsInternet Standard: RFCs

Introduction Year

RF

C N

umbe

rs


Internet HistoryInternet History

1961: Kleinrock - queueing theory shows effectiveness of packet-switching

1964: Baran - packet-switching in military nets

1967: ARPAnet conceived by Advanced Research Projects Agency

1969: first ARPAnet node operational

1972: ARPAnet

demonstrated publicly

NCP (Network Control Protocol) first host-host protocol

first e-mail program ARPAnet has 15

nodes

1961-1972: Early packet-switching principles1961-1972: Early packet-switching principles



1970: ALOHAnet satellite network in Hawaii

1973: Metcalfe’s PhD thesis proposes Ethernet

1974: Cerf and Kahn - architecture for interconnecting networks

late70’s: proprietary architectures: DECnet, SNA, XNA

late 70’s: switching fixed length packets (ATM precursor)

1979: ARPAnet has 200 nodes

Cerf and Kahn’s internetworking principles: minimalism, autonomy

- no internal changes required to interconnect networks

best effort service model

stateless routers decentralized control

define today’s Internet architecture

1972-1980: Internetworking, new and proprietary nets1972-1980: Internetworking, new and proprietary nets



1983: deployment of TCP/IP

1982: SMTP e-mail protocol defined

1983: DNS defined for name-to-IP-address translation

1985: FTP protocol defined

1988: TCP congestion control

new national networks: Csnet, BITnet, NSFnet, Minitel

100,000 hosts connected to confederation of networks

new national networks: Csnet, BITnet, NSFnet, Minitel

100,000 hosts connected to confederation of networks

1980-1990: new protocols, a proliferation of networks1980-1990: new protocols, a proliferation of networks



Early 1990’s: ARPAnet decommissioned

1991: NSF lifts restrictions on commercial use of NSFnet (decommissioned, 1995)

early 1990s: Web hypertext [Bush 1945,

Nelson 1960’s] HTML, HTTP: Berners-Lee 1994: Mosaic, later

Netscape late 1990’s:

commercialization of the Web

Late 1990’s – 2000’s:

more killer apps: instant messaging, peer2peer file sharing (e.g., Naptser)

network security to forefront

est. 50 million host, 100 million+ users

backbone links running at Gbps

1990, 2000’s: commercialization, the Web, new apps1990, 2000’s: commercialization, the Web, new apps


References & LinksReferences & Links

Complimentary Hyperlinks This part provides hyperlinks to interesting

(and hopefully useful) computer-networking resources. Most of these resources provide complimentary information to the material in chapter 1. If you're asked to write a paper pertaining to a specialized topic in computer networking, these resources should serve as a good starting point for your research.

References and Hyperlinks


Complimentary Hyperlinks 1Complimentary Hyperlinks 1

IEEE History Center http://www.ieee.org/organizations/history_center/oral_histories/comsoc_oh.html.

Oral Histories that have been collected to commemorate the 50th Anniversary of the IEEE Communications Society. A number of interesting interviews with pioneers in the field.

International Engineering Consortium: Web ProForum Tutorials http://www.iec.org/online/tutorials/

More than 150 tutorials on communications and networking topics, with a focus on cutting edge technology. The tutorials vary in terms of their technical depth, but many are outstanding, and all are extremely well-written and very readable. This is the first place we look when looking for an on-line survey or tutorial.


Broadband: Bringing home the bits http://www.nap.edu/html/broadband Extensive report on the importance and future of

residential broadband access from the Computer Science And Telecommunications Board, National Research Council, January 2002

Webopedia http://www.pcwebopaedia.com/ Online dictionary for computer and Internet

technology

Internet Economics http://china.si.umich.edu/telecom/net-economics.html Comprehensive index for resources relating to

Internet economics, including regulation and pricing.



traceroute.org http://www.traceroute.org/ As discussed in Section 1.6, Traceroute provides routes and packet

delays between pairs of hosts in the Internet. This site gives you direct access to hundreds of source hosts from which you can trace routes to arbitrary destination hosts. Choose a country, a source host in that country, and any destination host -- then see how the packets weave their way through the Internet.

Internet Engineering Task Force (IETF) http://www.ietf.org/

The IETF is an open international community concerned with the development and operation of the Internet and its architecture. The IETF was formally established by the Internet Architecture Board (IAB), http://www.isi.edu/iab, in 1986. The IETF meets three times a year; much of its ongoing work is conducted via mailing lists by working groups. Typically, based upon previous IETF proceedings, working groups will convene at meetings to discuss the work of the IETF working groups. The IETF is administered by the Internet Society, http://www.isoc.org/, whose Web site contains lots of high-quality, Internet-related material.



Henning Schulzrinne's Internet Technical Resources http://www.cs.columbia.edu/~hgs/internet Henning Schulzrinne has an extensive - although not

always current - index of online resources for the Internet.

The Association for Computing Machinery (ACM) http://www.acm.org/ A major international professional society that has

technical conferences, magazines, and journals in the networking area. The ACM Special Interest Group in Data Communications (SIGCOMM), http://www.acm.org/sigcomm, is the group within this body whose efforts are most closely related to networking



The Institute of Electrical and Electronics Engineers (IEEE) http://www.ieee.org/

The other major international professional society that has technical conferences, magazines, and journals in the networking area. The IEEE Communications Society, http://www.comsoc.org/, and the IEEE Computer Society, http://www.computer.org/, are the groups within this body whose efforts are most closely related to networking.

The SETI@home Project http://setiathome.ssl.berkeley.edu/ As discussed in Section 1.2, the SETI@home project is a scientific

experiment that uses Internet-connected computers to search for extraterrestrial intelligence. You can download the SETI program directly from this site.

Nerds 2.0.1 A Brief History of the Internet http://www.pbs.org/opb/nerds2.0.1

This is the Web site for the highly entertaining and informative PBS video on the history of the Internet. The PBS video, Triumph of the Nerds, about the history of personal computers, is also recommended.



Leonard Kleinrock's Personal History of the Internet http://www.lk.cs.ucla.edu/LK/Inet/birth.html

Professor Leonard Kleinrock made numerous important contributions to Internet technology and to the field of computer networking. This page provides his own interesting and highly entertaining description of the early history of the Internet.

The DSL Forum http://www.dslforum.org/ DSL Forum is a consortium of nearly 250 leading industry players

covering telecommunications, equipment, computing, networking and service provider companies. The site is rich in information about developments in digital subscriber loop and broadband access to the home.

Cable-modems.org http://www.cable-modems.org/ This site has many tutorials on cable modems, hybrid fiber-coax,

and related topics. Also includes reviews of cable modem products.



A note on Internet Request for Comments (RFCs): Copies of Internet RFCs are maintained at multiple sites. The RFC URLs below all point into the RFC archive at the Information Sciences Institute (ISI), maintained the the RFC Editor of the Internet Society (the body that oversees the RFCs). Other RFC sites include http://www.faqs.org/rfc, http://www.pasteur.fr/other/computer/RFC (located in France), and http://www.csl.sony.co.jp/rfc/ (located in Japan).

Internet RFCs can be updated or obsoleted by later RFCs. We encourage you to check the sites listed above for the most up-to-date information. The RFC search facility at ISI, http://www.rfc-editor.org/rfcsearch.html, will allow you to search for an RFC and show updates to that RFC.



References and Hyperlinks 1References and Hyperlinks 1

[@Home 1998] @Home, "Frequently Asked Questions," http://www.home.com/qa.html.

[Abramson 1970] N. Abramson, "The Aloha System--Another Alternative for Computer Communications," Proceedings of Fall Joint Computer Conference, AFIPS Conference, p. 37, 1970.

[ADSL 1998] ADSL Forum, "ADSL Tutorial," http://www.adsl.com/adsl_tutorial.html

[Almanac 1998] Computer Industry Almanac, http://www.c-i-a.com/



[AT&T Apps 1998] AT&T, "Killer Apps," http://www.att.com/technology/forstudents/brainspin/networks/killerapps.html

[AT&T Bandwidth 1999] AT&T, "Bandwidth: The Need for Speed," http://www.att.com/technology/forstudents/brainspin/networks/bandwidth/game.html

[AT&T Optics 1999] AT&T, "What are fiber optics?," http://www.att.com/technology/forstudents/brainspin/fiberoptics/

[Baran 1964] P. Baran, "On Distributed Communication Networks," IEEE Transactions on Communication Systems, Mar. 1964. Rand Corporation Technical report with the same title (Memorandum RM-3420-PR, 1964). http://www.rand.org/publications/RM/RM3420/



[Berners-Lee 1989] T. Berners-Lee, CERN, "Information Management: A Proposal," Mar. 1989, May 1990. http://www.w3.org/History/1989/proposal.html

[Bertsekas 1991] D. Bertsekas and R. Gallagher, Data Networks, 2nd Ed. , Prentice Hall, Englewood Cliffs, NJ, 1991.

[Bush 1945] V. Bush, "As We May Think," The Atlantic Monthly, July 1945. http://www.theatlantic.com/unbound/flashbks/computer/bushf.htm

[Cable 1998] Cable Data News, "Overview of Cable Modem Technology and Services," 1998. http://www.cabledatacomnews.com/cmic/cmic1.html



[Cerf 1974] V. Cerf and R. Kahn, "A Protocol for Packet Network Interconnection," IEEE Transactions on Communications Technology, Vol. COM-22, No. 5, pp. 627-641.

[Cisco LAN 1998] Cisco Systems Inc., "Designing Switched LAN Internetworks," http://www.cisco.com/univercd/cc/td/doc/cisintwk/idg4/nd2012.htm

[Clark 1988] D. Clark, " The Design Philosophy of the DARPA Internet Protocols, Proceedings of ACM SIGCOMM'88, (Stanford, CA), Aug. 1988, Vol. 18, No. 4, http://www.acm.org/sigcomm/ccr/archive/1995/jan95/ccr-9501-clark.html

[Cusumano 1998] M.A. Cusumano and D.B. Toffle, Competing on Internet Time: Lessons from Netscape and its Battle with Microsoft, Free Press, 1998



[Daigle 1991] J. N. Daigle, Queuing Theory for Telecommunications, Addison-Wesley, Reading, MA, 1991.

[DEC 1990] Digital Equipment Corporation, "In Memoriam: J. C. R. Licklider 1915-1990," SRC Research Report 61, Aug. 1990. http://gatekeeper.dec.com/pub/DEC/SRC/research-reports/abstracts/src-rr-061.html

[Dertouzos 1999] M. Dertouzos, "The Future of Computing," Scientific American, August 1999, pp.52-55.

[Fraser 1983] A. G. Fraser, "Towards a Universal Data Transport System," IEEE Journal on Selected Areas in Communications, Vol. SAC-1, No 5, pp. 803-816.



[Fraser 1993] A. G. Fraser (1993). "Early Experiments with Asynchronous Time Division Networks," IEEE Network Magazine, Vol. 7, No. 1, pp. 12-27.

[Goodman 1997] D. Goodman (Chair), The Evolution of Untethered Communications, National Academy Press, Washington DC, Dec. 1997. http://www.nap.edu/readingroom/books/evolution/index.html

[Green 1992] P. Green, Fiber Optics Networks, Prentice Hall, 1992

[Greenberg 1997] I. Greenberg, "The Future of the Living Room." http://www.cnet.com/Content/Features/Dlife/Living/index.html



[Haynal 1999] R. Haynal, "Internet Backbones," http://navigators.com/isp.html

[Huston 1999a] G. Huston, "Interconnection, Peering, and Settlements - Part I," The Internet Protocol Journal, Vol. 2, No. 1, (June 1999). http://www.cisco.com/warp/public/759/ipj_2-1/ipj_2-1_ps1.html

[Huston 1999b] G. Huston, "Interconnecting, Peering, and Settlements - Part II," The Internet Protocol Journal, Vol. 2, No. 2 (June 1999). http://www.cisco.com/warp/public/759/ipj_2-2/ipj_2-2_ps1.html

[Iren 1999] S. Iren, P. Amer, P. Conrad, "The Transport Layer: Tutorial and Survey," ACM Computing Surveys, Vol 31, No 4, (Dec 1999). http://www.cis.udel.edu/~amer/PEL/survey/

[Jacobson 1988] V. Jacobson, "Congestion Avoidance and Control," Proceedings of ACM SIGCOMM '88, pp. (Stanford, CA, Aug. 1988), 314-329, ftp://ftp.ee.lbl.gov/papers/congavoid.ps.Z



[Kegel 1999] Dan Kegel's ISDN Page, http://alumni.caltech.edu/~dank/isdn/

[Kleinrock 1961] L. Kleinrock, "Information Flow in Large Communication Networks," RLE Quarterly Progress Report, July 1961.

[Kleinrock 1964] L. Kleinrock, 1964 Communication Nets: Stochastic Message Flow and Delay, McGraw-Hill, NY, NY, 1964.

[Kleinrock 1975] L. Kleinrock, Queuing Systems, Vol. 1, John Wiley, New York, 1975.

[Kleinrock 1976] L. Kleinrock, Queuing Systems, Vol. 2, John Wiley, New York, 1976.

[Kleinrock 1998] L. Kleinrock, "The Birth of the Internet," http://www.lk.cs.ucla.edu/LK/Inet/birth.html

[Leiner 1998] B. Leiner, V. Cerf, D. Clark, R. Kahn, L. Kleinrock, D. Lynch, J. Postel, L. Roberts, and S. Woolf, "A Brief History of the Internet," http://www.isoc.org/internet/history/brief.html

[List 1999] "The List: The Definitive ISP Buyer's Guide," http://thelist.internet.com/



[Lucky 1997] R. Lucky, "New Communication Services - What Do People Want?", Proceedings of the IEEE, Oct. 1997, pp 1536-1543.

[Metcalfe 1976] R. M. Metcalfe and D. R. Boggs. "Ethernet: Distributed Packet Switching for Local Computer Networks," Communications of the Association for Computing Machinery, Vol. 19, No. 7, (July 1976), pp. 395 - 404. http://www.acm.org/classics/apr96/

[Mills 1998] S. Mills, "TV set-tops set to take off," CNET News.com, Oct. 1998. http://news.cnet.com/news/0-1006-200-334433.html

[NAS 1995] National Academy of Sciences, The Unpredictable Certainty: Information Infrastructure Through 2000, National Academy of Sciences Press, 1995. http://www.nap.edu/readingroom/books/unpredictable/chap4.html



[Network 1996] Network Wizards, "Internet Domain Survey", July 1996, http://www.nw.com/zone/WWW-9607/report.html

[Network 1999] Network Wizards, "Internet Domain Survey," Jan. 1999, http://www.isc.org/ds/

[Pacific Bell 1998] Pacific Bell, "ISDN Users Guide," http://www.pacbell.com/Products_Services/Residential/ISDNuserguide/0,1078,20,00.html

[Perkins 1994] A. Perkins, "Networking with Bob Metcalfe," The Red Herring Magazine, Nov. 1994. http://www.herring.com/mag/issue15/bob.html

[Quittner 1998] J. Quittner, M. Slatalla, Speeding the Net: The Inside Story of Netscape and How it Challenged Microsoft, Atlantic Monthly Press, 1998.



[Ramaswami 1998] R. Ramaswami, K. Sivarajan, Optical Networks: A Practical Perspective, Morgan Kaufman Publishers, 1998

[RFC 001] S. Crocker, "Host Software," RFC 001 (the very first RFC!).

[RFC 793] J. Postel, "Transmission Control Protocol," RFC 793, Sept. 1981. http://www.rfc-editor.org/rfc/rfc793.txt

[RFC 801] J. Postel, "NCP/TCP Transition Plan," RFC 801 Nov. 1981. http://www.rfc-editor.org/rfc/rfc801.txt

[RFC 1034] P. V. Mockapetris, "Domain Names--Concepts and Facilities," RFC 1034, Nov. 1987. http://www.rfc-editor.org/rfc/rfc1034.txt

[Roberts 1967] L. Roberts, T. Merril, "Toward a Cooperative Network of Time-Shared Computers," AFIPS Fall Conference, Oct. 1966.

[Ross 1995] K. W. Ross, Multiservice Loss Models for Broadband Telecommunication Networks, Springer, Berlin, 1995.

[Segaller 1998] S. Segaller, Nerds 2.0.1, A Brief History of the Internet, TV Books, New York, 1998.



[Thinplanet 2000] Thinplanet homepage, http://www.thinplanet.com/

[Turner 1986] J. Turner, "New Directions in Communications (or Which Way to the Information Age?)," Proceedings of the Zürich Seminar on Digital Communication, (Zurich, Switzerland, Mar. 1986), pp. 25-32,.

[W3C 1995] The World Wide Web Consortium, "A Little History of the World Wide Web," 1995. http://www.w3.org/History.html

[Wakeman 1992] Ian Wakeman, Jon Crowcroft, Zheng Wang, and Dejan Sirovica, "Layering Considered Harmful," IEEE Network, Jan. 1992, p. 20-24.


References and Hyperlinks 13

[Waung 1998] W. Waung, "Wireless Mobile Data Networking The CDPD Approach," Wireless Data Forum, 1998. http://www2.wirelessdata.org/public/whatis/whatis.html

[Wireless 1998] Wireless Data Forum, "CDPD System Specification Release 1.1," 1998. http://www2.wirelessdata.org/public/specification/index.html

[Wood 1999] L. Wood, "Lloyds Satellites Constellations," http://www.ee.surrey.ac.uk/Personal/L.Wood/constellations/iridium.html

[Ziff-Davis 1998] Ziff-Davis Publishing, "Ted Nelson: Hypertext pioneer," 1998. http://www.zdnet.com/zdtv/screensavers_story/0,3656,2127396-2102293,00.html© 2000-2001 by Addison Wesley Longman A division of Pearson Education.

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