3rd Edition Chapter 1

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					Computer Networks
     Zenghua Zhao
  Based on the slides by
Jim Kurose and Keith Ross

                            Introduction   1-1
Chapter 1: Introduction
Our goal:              Overview:
 get “feel” and        what’s the Internet
  terminology           what’s a protocol?
 more depth, detail    network edge
  later in course       network core
 approach:
                        access net, physical media
    use Internet as
                        Internet/ISP structure
                        performance: loss, delay
                        protocol layers, service models
                        network modeling

                                              Introduction   1-2
Chapter 1: roadmap
 What   is the Internet?
 Network edge
 Network core
 Network access and physical media
 Internet structure and ISPs
 Network performance
 Protocol layers, service models
 History

                                    Introduction   1-3
What’s the Internet: “nuts and bolts” view
  millions of connected            router
     computing devices: hosts
   = end systems                      server
  running network apps          local ISP
  communication links
        fiber, copper, radio,
         satellite                             regional ISP
        transmission rate =
    routers: forward packets
     (chunks of data)

                                               Introduction   1-4
What’s the Internet: “nuts and bolts” view
   protocols control sending,             router     workstation
    receiving of msgs
       e.g., TCP, IP, HTTP, FTP, PPP                    mobile
   Internet: “network of               local ISP
       loosely hierarchical
       public Internet versus
        private intranet                              regional ISP
 Internet standards
    RFC: Request for comments
    IETF: Internet Engineering
     Task Force

                                                      Introduction   1-5
What’s the Internet: a service view
  communication
   infrastructure enables
   distributed applications:
       Web, email, games, e-
        commerce, file sharing
  communication services
   provided to apps:
       Connectionless unreliable
       connection-oriented

                                    Introduction   1-6
What’s a protocol?
human protocols:           network protocols:
 “what’s the time?”        machines rather than
 “I have a question”        humans
 introductions             all communication
                             activity in Internet
… specific msgs sent         governed by protocols
… specific actions taken   protocols define format,
  when msgs received,        order of msgs sent and
  or other events           received among network
                              entities, and actions
                                  taken on msg
                              transmission, receipt
                                           Introduction   1-7
What’s a protocol?
a human protocol and a computer network protocol:

       Hi                      TCP connection
                               TCP connection
     Got the                   response
      time?                    Get

 Q: Other human protocols?
                                                    Introduction    1-8
Chapter 1: roadmap
 What   is the Internet?
 Network edge
 Network core
 Network access and physical media
 Internet structure and ISPs
 Network performance
 Protocol layers, service models
 History

                                    Introduction   1-9
A closer look at network structure:

 network edge:
  applications and
 network core:
   routers
   network of
 access networks,
  physical media:
  communication links
                              Introduction   1-10
 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:
      host interaction symmetric
     e.g.: teleconferencing

                                       Introduction   1-11
Network edge: connection-oriented service

 Goal: data transfer              TCP service [RFC 793]
   between end systems               reliable, in-order byte-
  handshaking: setup                 stream data transfer
   (prepare for) data                    loss: acknowledgements
   transfer ahead of time                 and retransmissions
       Hello, hello back human      flow control:
        protocol                         sender won’t overwhelm
       set up “state” in two             receiver
        communicating hosts
                                     congestion control:
  TCP - Transmission                    senders “slow down sending
   Control Protocol                       rate” when network
       Internet’s connection-            congested
        oriented service
                                                        Introduction   1-12
Network edge: connectionless service

 Goal: data transfer          App’s using TCP:
   between end systems         HTTP (Web), FTP (file
       same as before!         transfer), Telnet
  UDP - User Datagram          (remote login), SMTP
   Protocol [RFC 768]:          (simple mail transfer
     connectionless            protocol--email)
     unreliable data
      transfer                App’s using UDP:
     no flow control          streaming media,
     no congestion control     teleconferencing, DNS,
                                Internet telephony
                                           Introduction   1-13
Chapter 1: roadmap
 What   is the Internet?
 Network edge
 Network core
 Network access and physical media
 Internet structure and ISPs
 Network performance
 Protocol layers, service models
 History

                                    Introduction   1-14
The Network Core
 mesh of interconnected
 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   1-15
Network Core: Circuit Switching

End-end resources
  reserved for “call”
 link bandwidth, switch
 dedicated resources: no
  sharing among apps.
 circuit-like: (guaranteed)
 call setup required
      Admission control,
       resource allocation

                               Introduction   1-16
Network Core: Circuit Switching
network resources              dividing link bandwidth
  (e.g., bandwidth)             into “pieces”
  divided into “pieces”           frequency division
 pieces allocated to calls        multiplexing (FDM)
 resource piece   idle if        time division (TDM)
  not used by owning call
  (no sharing)

                                               Introduction   1-17
Circuit Switching: FDM and TDM
                         4 users




                                    Introduction   1-18
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
   500 msec to establish end-to-end circuit

Work it out!
          Rate 1.536 Mbps /24 = 64,000 bps
          Total time 500ms+ 640/64s=10500 ms
                                               Introduction   1-19
Network Core: Packet Switching
each end-end data stream           resource contention:
  divided into packets              aggregate resource
 user A, B packets share            demand can exceed
  network resources                  amount available
 each packet uses full link        congestion: packets
  bandwidth                          queue, wait for link use
 resources used as needed,         store and forward:
                                     packets move one hop
                                     at a time
Bandwidth division into “pieces”
                                       transmit over link
     Dedicated allocation
                                       wait turn at next
    Resource reservation
                                                 Introduction   1-20
Network Core: Packet Switching
         10 Mbs
A        Ethernet     statistical multiplexing      C

                           1.5 Mbs
           queue of packets                      45 Mbs
           waiting for output

                           D                       E

    Packet-switching versus circuit switching: human
      restaurant analogy
     other human analogies?

                                                          Introduction   1-21
Packet-switching: store-and-forward
                    R          R       R

 Takes L/R seconds to             Example:
  transmit (push out)               L = 7.5 Mbits
  packet of L bits on to
  link or R bps                     R = 1.5 Mbps
 Entire packet must                delay = 15 sec
  arrive at router before
  it can be transmitted
  on next link: store and           Assume the propagation
  forward                           delay is ignored
 delay = 3L/R
    3 is the number of hops

                                                      Introduction   1-22
Network Core: Packet Switching
                 store and forward behavior
                   break message into
                    smaller chunks:
                   Store-and-forward:
                    switch waits until chunk
                    has completely arrived,
                    then forwards/routes
                   Q: what if message was
                    sent as single unit?

                                  Introduction   1-23
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 p=10% of time

                                N users
 circuit-switching:                                           1 Mbps link
    10 users

 packet switching:
    with 35 users, probability > 10 active less than .0004
    With n users, probability >10 active is        n
                                               10  i  (1  p)ni p i
                                              0i  

                                                              Introduction   1-24
Packet switching versus circuit switching
Is packet switching a “slam dunk winner?”

 Great for bursty data
    resource sharing
    no call setup
 Excessive congestion: packet delay and loss
    protocols needed for reliable data transfer,
     congestion control
 Q: How to provide circuit-like behavior?
    bandwidth guarantees needed for audio/video
    still an unsolved problem (chapter 6)

                                            Introduction   1-25
Packet-switched networks: routing
   Goal: move packets among routers from source to
       we’ll study several path selection algorithms (chapter 4)
 datagram network:
    destination address determines next hop
    routes may change during session
    analogy: driving, asking directions

 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

                                                         Introduction   1-26
Network Taxonomy

     Circuit-switched                    Packet-switched
         networks                           networks

 FDM                                Networks          Datagram
                                    with VCs          Networks

 • Datagram network is not either connection-oriented
 or connectionless.
 • Internet provides both connection-oriented (TCP) and
 connectionless services (UDP) to apps. (using datagram)
                                                    Introduction   1-27
Chapter 1: roadmap
 What   is the Internet?
 Network edge
 Network core
 Network access and physical media
 Internet structure and ISPs
 Network performance
 Protocol layers, service models
 History

                                    Introduction   1-28
Access networks and physical media
 Q: How to connect end
   systems to edge router?
  residential access nets
  institutional access
   networks (school,
  mobile access networks

 Keep in mind:
  bandwidth (bits per
   second) of access
  shared or dedicated?
                                 Introduction   1-29
Residential access: point to point access

 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
                                                 Introduction   1-30
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   1-31
Residential access: cable modems

 Diagram:   Introduction   1-32
Cable Network Architecture: Overview

                                   Typically 500 to 5,000 homes

   cable headend

             cable distribution
            network (simplified)

                                                      Introduction   1-33
Cable Network Architecture: Overview

   cable headend

             cable distribution
            network (simplified)

                                          Introduction   1-34
Cable Network Architecture: Overview


   cable headend

                cable distribution

                                            Introduction   1-35
Cable Network Architecture: Overview

                                     V    V   V   V   V   V           N
                                     I    I   I   I   I   I   D   D   T
                                     D    D   D   D   D   D   A   A   R
                                     E    E   E   E   E   E   T   T   O
                                     O    O   O   O   O   O   A   A   L

                                     1    2   3   4   5   6   7   8   9


   cable headend

              cable distribution

                                                                          Introduction   1-36
Company 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
  LANs: chapter 5

                                  Introduction   1-37
Wireless access networks
 shared    wireless access
  network connects end system
  to router
      via base station aka “access
       point” AP
 wireless LANs: (802.11)               base
    802.11b (WiFi): 11 Mbps          station
    802.11, 802.11a, 802.11g

 wider-area wireless access
    provided by telco operator
    3G ~ 384 kbps
      • Will it happen??
    WAP/GPRS in Europe

                                                Introduction   1-38
Home network components
 ADSL or cable modem
 router/firewall/NAT (Network Address Translation)
    NAT enables a LAN to use one set of IP addresses for
     internal traffic and a second set of addresses for external
     traffic. It makes all necessary IP address translations.
 Ethernet
 wireless access point
     to/from                                                laptops
                 cable    router/
                modem     firewall
                               Ethernet           point

                                                      Introduction   1-39
Physical Media
                                    Twisted Pair (TP)
 Bit: propagates between            two insulated copper
  transmitter/rcvr pairs              wires
 physical link: what lies                Category 3: traditional
  between transmitter &                    phone wires, 10 Mbps
  receiver                                 Ethernet
                                           Category 5:
 guided media:
                                           100Mbps Ethernet
      signals propagate in solid
       media: copper, fiber, coax
 unguided media:
    signals propagate freely,
     e.g., radio

                                                     Introduction   1-40
Physical Media: coax, fiber
 Coaxial cable:                   Fiber optic cable:
                                   glass fiber carrying light
  two concentric copper
                                    pulses, each pulse a bit
                                   high-speed operation:
  bidirectional
                                        high-speed point-to-point
  baseband:                             transmission (e.g., 5 Gps)
       single channel on cable    low error rate: repeaters
       legacy Ethernet             spaced far apart ; immune
  broadband:                       to electromagnetic noise
     multiple channel on cable
     HFC

                                                       Introduction   1-41
Physical media: radio
  signal carried in             Radio link types:
   electromagnetic                terrestrial microwave
   spectrum                          e.g. up to 45 Mbps channels

  no physical “wire”             LAN (e.g., Wifi)
  bidirectional                     2Mbps, 11Mbps

  propagation                    wide-area (e.g., cellular)
   environment effects:              e.g. 3G: hundreds of kbps

       reflection                satellite
       obstruction by objects       up to 50Mbps channel (or
       interference                  multiple smaller channels)
                                     270 msec end-end delay
                                     geosynchronous versus low
                                                   Introduction   1-42
Chapter 1: roadmap
 What   is the Internet?
 Network edge
 Network core
 Network access and physical media
 Internet structure and ISPs
 Network performance
 Protocol layers, service models
 History

                                    Introduction   1-43
 Internet structure: network of networks

 roughly hierarchical
 ISP: Internet Service Providers
 at center: “tier-1” ISPs (e.g., UUNet, BBN/Genuity,
  Sprint, AT&T), national/international coverage
    treat each other as equals: no payment among them
                                              Tier-1 providers
                                              also interconnect
                         Tier 1 ISP           at public network
                                      NAP     access points
  interconnect                                (NAPs)
                 Tier 1 ISP      Tier 1 ISP

                                               Introduction   1-44
Tier-1 ISP: e.g., Sprint
Sprint US backbone network
                                                              DS3 (45 Mbps)
                                                              OC3 (155 Mbps)
                                                              OC12 (622 Mbps)
                                                              OC48 (2.4 Gbps)

                                                                           New York
   Stockton             Cheyenne         Chicago                          Pennsauken
  San Jose                                   Roachdale                   Wash. DC
                           Kansas City

                            Fort Worth

                                                                       Introduction    1-45
   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 ISPs
Tier-2 ISP pays         Tier-2 ISP                          also peer
                                          Tier-2 ISP        privately with
tier-1 ISP for
connectivity to                 Tier 1 ISP                  each other,
rest of Internet                                  NAP       interconnect
 tier-2 ISP is
                                                            at NAP
customer of
tier-1 provider       Tier 1 ISP        Tier 1 ISP      Tier-2 ISP

                   Tier-2 ISP        Tier-2 ISP

                                                          Introduction   1-46
   Internet structure: network of networks

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

                   ISP     Tier 3                   local
                                         local            local
                            ISP                      ISP
                                          ISP              ISP
Local and tier-            Tier-2 ISP            Tier-2 ISP
3 ISPs are
customers of                        Tier 1 ISP
higher tier                                           NAP
them to rest
                          Tier 1 ISP             Tier 1 ISP       Tier-2 ISP
of Internet
                    Tier-2 ISP           Tier-2 ISP
              local         local          local
               ISP           ISP            ISP                     Introduction   1-47
 Internet structure: network of networks

 a packet passes through many networks!

            ISP     Tier 3                    local
                                   local            local
                     ISP                       ISP
                                    ISP              ISP
                    Tier-2 ISP             Tier-2 ISP

                              Tier 1 ISP

                   Tier 1 ISP              Tier 1 ISP       Tier-2 ISP
              Tier-2 ISP           Tier-2 ISP
        local         local          local
         ISP           ISP            ISP                     Introduction   1-48
Different ISPs
 wireless ISP
   limited localized areas known as "hotspots”
   attract a wide variety of business

 satellite ISP
    own specialized equipment
    pretty expensive

                                              Introduction   1-49
Chapter 1: roadmap
 What   is the Internet?
 Network edge
 Network core
 Network access and physical media
 Internet structure and ISPs
 Network performance
 Protocol layers, service models
 History

                                    Introduction   1-50
Network Performance
We study different protocols and how they work, how they
Performane Metrics
 Delay (sec)
 Throughput (bits/sec)
 Loss rate (% of packets lost)

 Cost of running the protocol/algorithm
    Computation time (can contribute to delay)
    Storage (state)
    Messaging (can reduce throughput)
   (These all contribute to “scalability”)
 Things we have a hard time measuring
      Manageability
      Security

                                                    Introduction   1-51
 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)


                              packets queueing (delay)
                free (available) buffers: arriving packets
                dropped (loss) if no free buffers
                                                             Introduction   1-52
Four sources of packet delay
 1. nodal processing:            2. queuing
    check bit errors                time waiting at output
    determine output link            link for transmission
                                     depends on congestion
                                      level of router

 A                           propagation

            processing    queueing

                                                     Introduction   1-53
Delay in packet-switched networks
3. Transmission delay:         4. Propagation delay:
 R=link bandwidth (bps)        d = length of physical link
 L=packet length (bits)        s = propagation speed in
 time to send bits into          medium (~2x108 m/sec)
   link = L/R                   propagation delay = d/s

                               Note: s and R are very
                                 different quantities!
A                         propagation

          processing    queueing
                                                 Introduction   1-54
 Caravan analogy
                          100 km               100 km
      ten-car     toll                toll
      caravan    booth               booth
 Cars “propagate” at            Time to “push” entire
  100 km/hr                       caravan through toll
 Toll booth takes 12 sec to      booth onto highway =
  service a car                   12*10 = 120 sec
  (transmission time)            Time for last car to
 car~bit; caravan ~ packet       propagate from 1st to
                                  2nd toll both:
 Q: How long until caravan
                                  100km/(100km/hr)= 1 hr
  is lined up before 2nd toll
  booth?                         A: 62 minutes

                                               Introduction   1-55
Caravan analogy (more)
                           100 km                     100 km
     ten-car    toll                       toll
     caravan   booth                      booth
                               Yes! After 7 min, 1st car at 2nd
 Cars now “propagate” at       booth and 3 cars still at 1st
  1000 km/hr                    booth.
                               1st bit of packet can arrive at
 Toll booth now takes 1        2nd router before packet is
  min to service a car          fully transmitted at 1st router!
 Q: Will cars arrive to               See Ethernet applet at AWL
                                        Web site
  2nd booth before all
  cars serviced at 1st

                                                       Introduction   1-56
Nodal delay
           d nodal  d proc  d queue  d trans  d prop

 dproc = processing delay
    typically a few microsecs 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

                                                           Introduction   1-57
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   1-58
Packet 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

                                       Introduction   1-59
Queuing loss

                                   Introduction   1-60
Chapter 1: roadmap
 What   is the Internet?
 Network edge
 Network core
 Network access and physical media
 Internet structure and ISPs
 Network performance
 Protocol layers, service models
 History

                                    Introduction   1-61
Protocol “Layers”
Networks are complex!
 many “pieces”:
   hosts                      Question:
   routers               Is there any hope of
   links of various      organizing structure of
    media                        network?
   applications
   protocols           Or at least our discussion
   hardware,                   of networks?

                                         Introduction   1-62
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
    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?
    Sometimes yes: sensor networks

                                              Introduction   1-63
Internet protocol stack
 application: supporting network applications
      ftp, smtp, http
 transport: host-host data transfer             application
      tcp, udp
 network: routing of datagrams from source      transport
  to destination
      ip, routing protocols
 link: data transfer between neighboring
  network elements
      ppp, ethernet                                link
 physical: bits “on the wire”
  At least some of the protocol stack runs on
  every node/element/box that is connected
  to the network

                                                    Introduction   1-64
Network-wide view of layering
Each layer:         application
 distributed        network
 “entities”           link
  implement          physical
  layer functions                          network
  at each node      application              link
                    transport              physical
 entities           network
  perform              link
  actions,           physical
                                  application       application
  exchange                        transport         transport
  messages with                    network           network
  peers                              link              link
                                   physical          physical

                                                Introduction   1-65
Transport layer view
 take data from app   application
 add addressing,      transport
  reliability check
  info to form          physical
                                        ack      network
 send datagram to     application                 link
  peer                 transport     data        physical
 wait for peer to      network
  ack receipt             link
 analogy: post                         application       application
  office                                transport         transport
                                         network           network
                                           link              link
                                         physical          physical

                                                      Introduction   1-66
  Network layer view:
 Receive       application
  packet, check transport
  for errors     network
 Look at          link
  address to                           network
  decide where application               link
                 transport             physical
  to forward
  pkt               link
 Pass to         physical                        data
                              application     application
  MAC/DL to
                              transport       transport
  put on link or               network         network
  sit in buffer                  link            link
                               physical        physical

                                                     Introduction   1-67
  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

               source      destination
        M    application   application             M      message
     Ht M    transport     transport        Ht     M      segment
   Hn Ht M    network       network       Hn Ht    M      datagram
Hl Hn Ht M      link          link     Hl Hn Ht    M       frame
              physical      physical

                                                  Introduction   1-68
      message         M   application
    segment Ht        M   transport
 datagram Hn Ht       M    network
frame      Hl Hn Ht   M      link
                                         Hl Hn Ht       M      link       Hl Hn Ht     M


                destination                Hn Ht    M       network        Hn Ht   M
           M     application            Hl Hn Ht    M         link      Hl Hn Ht   M
     Ht    M     transport                                  physical
   Hn Ht    M     network
Hl Hn Ht    M       link                                                           router

                                                                        Introduction       1-69
ISO/OSI Reference Model
ISO: International Standard Orgnization

OSI: Open System Interconnection

7     Application                  Application
5       Session

4     Transport                     Transport

3          IP                             IP
       Data link                    Data link
1      physical                      physical

    ISO/OSI RM                     TCP/IP RM     Introduction   1-70
Chapter 1: roadmap
 What   is the Internet?
 Network edge
 Network core
 Network access and physical media
 Internet structure and ISPs
 Network performance
 Protocol layers, service models
 History

                                    Introduction   1-71
Internet History
1961-1972: Early packet-switching principles
 1961: Kleinrock - queueing    1972:
  theory shows                       ARPAnet demonstrated
  effectiveness of packet-            publicly
                                     NCP (Network Control
 1964: Baran - packet-               Protocol) first host-
  switching in military nets          host protocol
 1967: ARPAnet conceived            first e-mail program
  by Advanced Research
                                     ARPAnet has 15 nodes
  Projects Agency
 1969: first ARPAnet node

                                                   Introduction   1-72
    Internet History
    1972-1980: Internetworking, new and proprietary nets
 1970: ALOHAnet satellite        Cerf and Kahn’s
    network in Hawaii               internetworking principles:
   1973: Metcalfe’s PhD thesis        minimalism, autonomy -
    proposes Ethernet                   no internal changes
   1974: Cerf and Kahn -               required to
    architecture for                    interconnect networks
    interconnecting networks           best effort service
   late70’s: proprietary               model
    architectures: DECnet, SNA,        stateless routers
                                       decentralized control
   late 70’s: switching fixed
                                  define today’s Internet
    length packets (ATM
   1979: ARPAnet has 200 nodes
                                                       Introduction   1-73
Internet History
1990, 2000’s: commercialization, the Web, new apps
 Early 1990’s: ARPAnet             Late 1990’s – 2000’s:
                                     more killer apps: instant
 1991: NSF lifts restrictions on     messaging, P2P file sharing
  commercial use of NSFnet
                                     network security to
  (decommissioned, 1995)
 early 1990s: Web
                                     est. 50 million host, 100
    hypertext [Bush 1945, Nelson     million+ users
                                     backbone links running at
    HTML, HTTP: Berners-Lee          Gbps
    1994: Mosaic, later Netscape
    late 1990’s:
     commercialization of the Web

                                                      Introduction   1-74
The Internet History (1) -
 Evolved from ARPANET, 1969 Advanced Research
    Projects Agency (ARPA),U.S. Department of
   First operational packet-switching network
   Began in four locations: UCLA, University of Santa
    Barbara, the University of Utah, and SRI
    (Stanford Research Institute)
   Today tens of millions of hosts
   Hundreds of millions of users
   Nearly 200 countries
   Number of connections growing exponentially
   Allowed devices from different manufacturers
    and with different data rates to communicate
   Used adaptive routing                                      1-75
Number of
Internet Hosts

                 Introduction   1-76
The Internet History (2) -
 Telnet provided common denominator terminal
    Software written support “Telnet terminal,”
    Any terminal could interact with any computer

 File Transport Protocol (FTP) offered similar open
      Transparent transfer of files from one computer to
      Overcomes different word sizes, different bit orders
       and different word formats
 First “killer app” was electronic mail
    Previously all single computer systems
    1972, Ray Tomlinson of Bolt Beranek and Newman (BBN)
    Distributed mail service across network using multiple
    1973 three quarters of all ARPANET traffic wasIntroduction   1-77
The Internet History (3) –
 Packet-switching applied to tactical radio communication
    (packet radio) and satellite communication (SATNET)
       Different communication environments
       Certain parameters, e.g. maximum packet size, different
 Vint Cerf and Bob Kahn of ARPA developed protocols for
    communicating across arbitrary, multiple, packet-switched
    networks (internetting)
   May 1974 Transmission Control Protocol
   Refined by ARPANET community
   Major contributions from participants from European
    Networks, such as Cyclades (France), and EIN
   Leading to TCP and IP
   Basis for TCP/IP protocol suite
   1982-1983, ARPANET switched from NCP to TCP/IP
   Many networks connected using TCP/IP
   Use of ARPANET restricted to ARPA contractors Introduction    1-78
The Internet History (4) –
National Science Foundation
 Extended support to other computer research
      CSNET in 1980-1981
 1986, extended Internet support to general
  research community
      NSFNET backbone
      Originally designed to interconnect six NSF funded
       supercomputer centers across USA and to
       supercomputer users
 Eventually, interconnection through NSF backbone
  to regional packet switched networks across USA
 In 1990 ARPANET was shut down

                                                      Introduction   1-79
The Internet History (5) –
Acceptable Use Policies
 In many countries (including United States
  until 1995) national governments subsidized
  the Internet backbone
 Acceptable use policies limited commercial
   Research and educational (and of course
    government) use only
   The “culture” of the Internet imposed
    additional informal limitations on commercial

                                             Introduction   1-80
The Internet History (6) –
Internet Interconnection Points
 1991 almost all commercial TCP/IP service in USA
  provided by:
      General Atomics
        • Operated CERFnet (a California regional network)
      Performance Systems International
        • PSINet (commercial spin-off from New York’s NYSERnet)
      UUNET Technologies
        • Commercial Internet service provider that owned Alternet
 Did not use NSF backbone on own networks
    Not subject to Acceptable Use Policy

 Communication between their networks did use
  NSF backbone
      Under the policy

                                                             Introduction   1-81
The Internet History (7) –
 Commercial Information Interchange
 Originally mechanism to interchange traffic at a West Coast
 Each network’s customers access customers on others’
  networks at no extra charge
 1996, CIX had 147 member networks
 No settlements
      No traffic based fees for use
 Similar interconnection point (1994) in England
      London Internet Exchange (LINX)
      1996, it had 24 member networks
 1991, U.S. government said it would no longer subsidize
  Internet after 1995
 Mandated network access points
      Now three, New York, Chicago, and San Francisco
 Metropolitan area exchanges, MAE East and MAE West
 U.S. part of Internet opened to commercial activity Introduction   1-82
U.S. Internet Access Points

                          Introduction   1-83
The Internet History (8) –
The World Wide Web
 Spring 1989, at CERN (the European Laboratory
    for Particle Physics)
   Englishman Tim Berners-Lee proposed a
    distributed hypermedia technology to exchange
    research findings over Internet
   1991 prototype World Wide Web developed at
    CERN using NeXT computer as a platform
   End of 1991, limited release of line-oriented
    browser or reader
   Explosive growth came with first graphically
    oriented browser, Mosaic, 1993
       NCSA Center, University of Illinois
       Mark Andreasson and others
       Two million copies delivered over Internet
       Now ubiquitous                               Introduction   1-84
The Internet History (9) –
What is the Web
 Internationally distributed collection of multimedia files
  supported by clients (users) and servers (information providers)
 Each file addressed in consistent manner using its Uniform
  Resource Locator (URL)
 Viewed by clients using browsers
      E.g. Netscape Navigator, Microsoft’s Internet Explorer
      There are others!
      Usually graphical display and support for multimedia
      Move from file to file by clicking with mouse highlighted text or
       image (link)
      Layout of display controlled by Hypertext Markup Language (HTML)
      Embedded commands in text files
      Specify fonts, colors, images and their placement and links
 Hypertext Transfer Protocol (HTTP)
      Protocol used in TCP/IP networks for fetching WWW files
      More later
                                                          Introduction   1-85
The Internet History (10) –
The Internet Today
 Users connect through an Internet service provider
 Home users
   Major online services such as America Online and Compuserve
   Connect to ISPs over phone lines using modems at 56.6 kbps
   OK for e-mail but marginal for graphics-intensive Web
   New alternatives include ISDN, ADSL, and cable modem

 Work users
   Workstations or PCs connected to LANs
   LAN connects through trunks to ISP
   T-1 or T-3 connection for large organizations
   Smaller organizations may use 56 kbps or ISDN connections

 ISPs connected by "wholesalers,“
    Network service providers

 They interconnect using Internet connection points
 T-3 rates or ATM connections                     Introduction   1-86
The Internet History (11) –
Commercial Use
 Acceptable Use Policy limited early commercial use
  to research and educational
      Some informational activities that could be considered
       marketing went on
 First commercial applications were mainly
      Sales, marketing, public relations
 Electronic data interchange (EDI)
    Intercompany invoices, billing, etc.
    Designed for dedicated WAN

 America Online, bulletin board type services
  dealing with technical and usage problems
                                                       Introduction   1-87
The Internet History (12) –
Direct Sales
 Initially Internet did not support online
  transactions well
      No easy to use graphical user interface
        • World Wide Web not commonly available until 1993
        • Initially little support for submitting information (forms) to
      No security; No effective payment systems; Credit card?
      People uncomfortable sending credit card numbers over
      If information not encrypted it is easy to “listen in”
      Several files of customer's credit card numbers on
       merchant’s computers have been compromised
 Privacy concerns
    “data mining,”
        • Collecting customer transaction information to improve
          targeting of marketing
                                                              Introduction   1-88
Introduction: Summary
Covered a “ton” of material!   You now have:
 Internet overview             context, overview,
 what’s a protocol?             “feel” of networking
 network edge, core, access    more depth, detail to
  network                        follow!
    packet-switching versus
 Internet/ISP structure
 performance: loss, delay
 layering and service
 history

                                            Introduction   1-89

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