CMPT 371 Chapter 1 by jianghongl


									       School of Computing Science
         Simon Fraser University

CMPT 371: Data Communications and

 Instructor: Dr. Mohamed Hefeeda

Course Objectives
 Understand principles of designing and
  operating computer networks,

 Understand the structure and protocols of
  the largest network of networks (Internet),

 Know how to implement network protocols
  and networked applications, and …

 Have fun!
Course Info
 Textbook
      Kurose and Rose, Computer Networking: A top-
      down Approach Featuring the Internet, 4th
      edition, 2008

 Course web page

  Or access it from my web page:
 Homework:            25%
      Several problem sets and programming

 Midterm exam:         25%

 Final exam:           50%

 Introduction
   Overview; Network types; Protocol layering;
    History of the Internet; Signals and Physical
 Network Applications
   Principles of network applications and protocols;
    Sample applications: HTTP, DNS; Socket
 Transport Layer
   Transport-layer services; Flow and congestion
    control; Internet transport protocols: UDP and

Topics (cont’d)
 Network Layer
      Routing algorithms (e.g., OSPF, RIP, BGP);
       Forwarding and addressing in the Internet (IP);
       Router design
 Link Layer and Local Area Networks
    Contention resolution and multiple access
     protocols; Error detection and correction;
     Ethernet; Bridges and switches
 Wireless Networks or Multimedia
  Networking (time permits)

Chapter 1: Overview

 Goal: Get a “feel” of the computer
 networking area

 Approach: we use the Internet as

Chapter 1: roadmap
 1.1 What is the Internet?
 1.2 Network edge
 1.3 Network core
 1.4 Network access and physical media
 1.5 Internet structure and ISPs
 1.6 Delay & loss in packet-switched networks
 1.7 Protocol layers, service models

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)

“Cool” Internet appliances

                                              Web-enabled toaster +
                                              weather forecaster

     IP picture frame

World’s smallest web server      Internet phones

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

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

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
What’s a protocol?
a human protocol and a computer network protocol:

                               TCP connection
                               TCP connection
     Got the                   response
      time?                    Get

Chapter 1: roadmap
 1.1 What is the Internet?
 1.2 Network edge
 1.3 Network core
 1.4 Network access and physical media
 1.5 Internet structure and ISPs
 1.6 Delay & loss in packet-switched networks
 1.7 Protocol layers, service models

A closer look at network structure

 network edge:
  applications and
 network core:
   routers
   network of
 access networks,
  physical media:
  communication links
 The network edge
 End systems (hosts):
     run application programs
      (e.g., email) at “edge of network”
 Two models
   client/server model
       • client requests, receives service
         from server, e.g. web browser/server
     peer-to-peer model
       • minimal (or no) use of dedicated servers
       • e.g., Gnutella, BitTorrent, …

 Two services from network
     Connection-oriented
     Connectionless
Network edge: Services from Network
Goal: Transfer data between end systems
 Connection-oriented          Connectionless
    Prepare for data             No connection set up,
     transfer ahead of time        simply send
    i.e., establish a            Faster, less overhead
     connection  set up          No reliability, flow
     “state” in the two            control, or congestion
     communicating hosts           control
    Usually comes with:
     reliability, flow and
                                    Internet: UDP—User
     congestion control
                                     Datagram Protocol
    Internet: TCP—
     Transmission Control

Chapter 1: roadmap
 1.1 What is the Internet?
 1.2 Network edge
 1.3 Network core
 1.4 Network access and physical media
 1.5 Internet structure and ISPs
 1.6 Delay & loss in packet-switched networks
 1.7 Protocol layers, service models

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”

Network Core: Circuit Switching

End-end resources
  reserved for “call”
 link bandwidth, switch
 dedicated resources: no
 circuit-like (guaranteed)
 call setup required

Network 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

Circuit Switching: FDM and TDM
                         4 users




Numerical example
 How long does it take to send a file of
  640,000 bits from host A to host B over a
  circuit-switched network?
   All links are 1.536 Mbps
   Each link uses TDM with 24 slots/sec
   500 msec to establish end-to-end circuit

Let’s work it out!

 NOTE: 1 Kb = 1000 bits, not 210 bits!

Network Core: Packet Switching
each end-end data stream           resource contention:
  divided into packets              aggregate resource
 packets from different             demand can exceed
  users share network                amount available
  resources                         congestion: packets
 each packet uses full link         queue, wait for link use
  bandwidth                         store and forward:
 resources used as needed           packets move one hop
                                     at a time
                                         Node receives complete
Bandwidth division into “pieces”          packet before forwarding
     Dedicated allocation
    Resource reservation
Packet Switching: Statistical Multiplexing
        10 Mb/s
A       Ethernet     statistical multiplexing   C

                          1.5 Mb/s
          queue of packets
          waiting for output

                          D                     E

Sequence of A & B packets does not have fixed pattern,
  shared on demand  statistical multiplexing.
TDM: each host gets same slot in revolving TDM frame.
Packet switching versus circuit switching
Packet switching allows more users to use network!
 1 Mb/s link
 each user:
    100 kb/s when “active”
    active 10% of time

 circuit-switching:           N users
    10 users
                                                        1 Mbps link
 packet switching:
    with 35 users,
     probability > 10 active
     less than .0004
                                 Q: how did we get the value 0.0004?

Packet switching versus circuit switching

 Advantages
   no call setup  simpler
   resource sharing (statistical multiplexing) 
       • better resource utilization
       • more users or faster transfer (a single user can use
         entire bw)
       • Well suited for bursty traffic (typical)
 Disadvantages
     Congestion may occur 
       • packet delay and loss
       • need protocols to control congestion and ensure
         reliable data transfer

Packet-switched networks: forwarding
   Goal: move packets through routers from source to
       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
    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
Network Taxonomy


   Circuit-switched                  Packet-switched
       networks                         networks

 FDM                            Networks        Datagram
                                with VCs        Networks

Chapter 1: roadmap
 1.1 What is the Internet?
 1.2 Network edge
 1.3 Network core
 1.4 Network access and physical media
 1.5 Internet structure and ISPs
 1.6 Delay & loss in packet-switched networks
 1.7 Protocol layers, service models

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

 Keep in mind:
  bandwidth (bits per
   second) of access network?
  shared or dedicated?

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
Residential access: cable modems

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

Residential access: cable modems

 Diagram:   1-35
Institutional access: local area
 company/univ local area network
  (LAN) connects end system to
  edge router
 Ethernet:
    shared or dedicated link
     connects end system and
    10 Mbs, 100Mbps, Gigabit
 LANs: chapter 5

Wireless access networks
 shared    wireless access network
  connects end system to router
      via base station aka “access point”   router
 wireless LANs:
    802.11b (WiFi): 11 Mbps                   base
 wider-area wireless access                 station
    provided by telco operator
    3G ~ 384 kbps
      • Will it happen??
    WAP/GPRS in Europe                                mobile

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

   to/from                                       laptops
              cable   router/
             modem    firewall
                           Ethernet    point

Physical Media

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

Physical Media: coax, fiber
 Coaxial cable:                   Fiber optic cable:
  two concentric copper           glass fiber carrying light
   conductors                       pulses, each pulse a bit
  bidirectional                   high-speed operation:
                                         high-speed point-to-point
  baseband:
                                         transmission (e.g., 10’s-
       single channel on cable          100’s Gps)
        legacy Ethernet
                                   low error rate: repeaters

  broadband:                       spaced far apart; immune
     multiple channels on          to electromagnetic noise
     HFC

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, 54 Mbps

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

       reflection                satellite
       obstruction by objects       Kbps to 45Mbps channel (or
       Interference                  multiple smaller channels)
       fading                       270 msec end-end delay
                                     geosynchronous versus low
Chapter 1: roadmap
 1.1 What is the Internet?
 1.2 Network edge
 1.3 Network core
 1.4 Network access and physical media
 1.5 Internet structure and ISPs
 1.6 Delay & loss in packet-switched networks
 1.7 Protocol layers, service models

 Internet structure: network of networks

 roughly hierarchical
 at center: “tier-1” ISPs (e.g., MCI, Sprint, AT&T, Cable
  and Wireless), national/international coverage
    treat each other as equals

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

Tier-1 ISP: e.g., Sprint
       POP: point-of-presence

           to/from backbone

       …                …


          to/from customers

                                 Introduction   1-44
   Internet structure: Tier-2 ISPs
  “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
                                                            at NAP
Tier-2 ISP is
customer of           Tier 1 ISP        Tier 1 ISP      Tier-2 ISP
tier-1 provider
                   Tier-2 ISP        Tier-2 ISP

   Internet structure: Tier-3 ISPs
  “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                                 1-46
 Internet structure: packet journey
 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                                 1-47
A snapshot of the Internet in 1999 showing major ISPs

Chapter 1: roadmap
 1.1 What is the Internet?
 1.2 Network edge
 1.3 Network core
 1.4 Network access and physical media
 1.5 Internet structure and ISPs
 1.6 Delay & loss in packet-switched networks
 1.7 Protocol layers, service models

 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)


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


                processing    queueing

Delay in packet-switched networks
3. Transmission delay:           4. Propagation delay:
 Time to “push” the entire       Time for last bit of packet to
   packet on link                   propagate from src to dst
 R=link bandwidth (bps)          d = length of physical link
 L=packet length (bits)          s = propagation speed in
 Transmission delay = L/R          medium (~2x108 m/sec)
                                  propagation delay = d/s

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

            processing    queueing
 Transmission vs. propagation: Caravan analogy

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

                   See applet at textbook web site          1-53
Total 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

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!
“Real” Internet delays and routes

 What do “real” Internet delay & loss look like?
 Traceroute program: provides delay measurement
  from source to router along end-end Internet path
  towards destination. For all i:
      sends three packets that will reach router i on path
       towards destination
      router i will return packets to sender
      sender times interval between transmission and reply.

       3 probes        3 probes

            3 probes

“Real” Internet delays and routes
traceroute: to
                                    Three delay measurements from
1 cs-gw ( 1 ms 1 ms 2 ms
2 ( 1 ms 1 ms 2 ms
3 ( 6 ms 5 ms 5 ms
4 ( 16 ms 11 ms 13 ms
5 ( 21 ms 18 ms 18 ms
6 ( 22 ms 18 ms 22 ms
7 ( 22 ms 22 ms 22 ms trans-oceanic
8 ( 104 ms 109 ms 106 ms
9 ( 109 ms 102 ms 104 ms
10 ( 113 ms 121 ms 114 ms
11 ( 112 ms 114 ms 112 ms
12 ( 111 ms 114 ms 116 ms
13 ( 123 ms 125 ms 124 ms
14 ( 126 ms 126 ms 124 ms
15 ( 135 ms 128 ms 133 ms
16 ( 126 ms 128 ms 126 ms
17 * * *
18 * * *              * means no response (probe lost, router not replying)
19 ( 132 ms 128 ms 136 ms

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

    throughput: rate (bits/time unit) at which
      bits transferred between sender/receiver
        instantaneous: rate at given point in time
        average: rate over longer period of time

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

                                                       Introduction   1-59
 Throughput (more)
  Rs   < Rc What is average end-end throughput?

              Rs bits/sec              Rc bits/sec

  Rs   > Rc What is average end-end throughput?

              Rs bits/sec              Rc bits/sec

 bottleneck link
link on end-end path that constrains end-end throughput
                                                Introduction   1-60
Throughput: Internet scenario

 per-connection
                          Rs                        Rs
 in practice: Rc or      Rc                          Rc
  Rs is often                       Rc

                          10 connections (fairly) share
                       backbone bottleneck link R bits/sec
                                               Introduction   1-61
Chapter 1: roadmap
 1.1 What is the Internet?
 1.2 Network edge
 1.3 Network core
 1.4 Network access and physical media
 1.5 Internet structure and ISPs
 1.6 Delay & loss in packet-switched networks
 1.7 Protocol layers, service models

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?

Layering of airline functionality

ticket (purchase)                                            ticket (complain)   ticket

baggage (check)                                              baggage (claim      baggage

  gates (load)                                                gates (unload)     gate

runway (takeoff)                                              runway (land)      takeoff/landing

airplane routing    airplane routing      airplane routing   airplane routing    airplane routing

   departure                intermediate air-traffic              arrival
    airport                     control centers                   airport

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

Why layering?
Dealing with complex systems:
 explicit structure allows identification,
  relationship of complex system’s pieces
 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
 What is the downside of layering?

Internet protocol stack
 application: supporting network
  applications                         application
      FTP, SMTP, HTTP
 transport: process-process data      transport
      TCP, UDP                         network
 network: routing of datagrams from
  source to destination                   link
      IP, routing protocols
 link: data transfer between           physical
  neighboring network elements
      PPP, Ethernet
 physical: bits “on the wire”
                                           Introduction   1-66
ISO/OSI reference model
 presentation: allow applications to
  interpret meaning of data, e.g.,      application
  encryption, compression, machine-
  specific conventions
 session: synchronization,               session
  checkpointing, recovery of data        transport
 Internet stack “missing” these
  layers!                                     link
    these services, if needed, must      physical
     be implemented in application
    needed?

                                          Introduction   1-67
      message         M
    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

Network Security
 The field of network security is about:
   how bad guys can attack computer networks
   how we can defend networks against attacks
   how to design architectures that are immune to
 Internet not originally designed with
  (much) security in mind
     original vision: “a group of mutually trusting
    users attached to a transparent network” 
   Internet protocol designers playing “catch-up”
   Security considerations in all layers!

                                                  Introduction   1-69
Bad guys can put malware into
hosts via Internet
 Malware can get in host from a virus, worm, or
  trojan horse.

 Spyware malware can record keystrokes, web
  sites visited, upload info to collection site.

 Infected host can be enrolled in a botnet, used
  for spam and DDoS attacks.

 Malware is often self-replicating: from an
  infected host, seeks entry into other hosts

                                                   Introduction   1-70
Bad guys can put malware into
hosts via Internet
 Trojan horse                  Worm:
    Hidden part of some          infection by passively
     otherwise useful              receiving object that gets
     software                      itself executed
    Today often on a Web         self- replicating: propagates
     page (Active-X, plugin)       to other hosts, users
 Virus                                  Sapphire Worm: aggregate scans/sec
    infection by receiving
                                 in first 5 minutes of outbreak (CAIDA, UWisc data)

     object (e.g., e-mail
     attachment), actively
    self-replicating:
     propagate itself to
     other hosts, users
                                                                 Introduction   1-71
     Bad guys can attack servers and
     network infrastructure
  Denial of service (DoS): attackers make resources
      (server, bandwidth) unavailable to legitimate traffic
      by overwhelming resource with bogus traffic
1.   select target
2. break into hosts
   around the network
   (see botnet)
3. send packets toward
   target from                               target
   compromised hosts

                                                      Introduction   1-72
The bad guys can sniff packets
Packet sniffing:
   broadcast media (shared Ethernet, wireless)
   promiscuous network interface reads/records all
    packets (e.g., including passwords!) passing by

       A                              C

                       src:B dest:A   payload
      Wireshark software used for end-of-chapter
       labs is a (free) packet-sniffer
                                                    Introduction   1-73
The bad guys can use false source
 IP   spoofing: send packet with false source address
        A                               C

               src:B dest:A   payload


                                              Introduction   1-74
The bad guys can record and
 record-and-playback: sniff sensitive info (e.g.,
  password), and use later
    password holder is that user from system point of


                              src:B dest:A   user: B; password: foo


                                                         Introduction   1-75
Network Security
 more throughout this course
 chapter 8: focus on security
 crypographic techniques: obvious uses and
  not so obvious uses

                                       Introduction   1-76
Internet History
1961-1972: Early packet-switching principles
 1961: Kleinrock - queueing    1972:
  theory shows                       ARPAnet public demonstration
  effectiveness of packet-
                                     NCP (Network Control Protocol)
                                      first host-host protocol
 1964: Baran - packet-
                                     first e-mail program
  switching in military nets
                                     ARPAnet has 15 nodes
 1967: ARPAnet conceived
  by Advanced Research
  Projects Agency
 1969: first ARPAnet node

                                                       Introduction   1-77
    Internet History
    1972-1980: Internetworking, new and proprietary nets
 1970: ALOHAnet satellite        Cerf and Kahn’s internetworking
    network in Hawaii                principles:
   1974: Cerf and Kahn -              minimalism, autonomy - no
    architecture for                     internal changes required
    interconnecting networks             to interconnect networks
   1976: Ethernet at Xerox            best effort service model
    PARC                               stateless routers

   ate70’s: proprietary               decentralized control

    architectures: DECnet, SNA,   define today’s Internet
    XNA                              architecture
   late 70’s: switching fixed
    length packets (ATM
   1979: ARPAnet has 200 nodes

                                                           Introduction   1-78
Internet History
1980-1990: new protocols, a proliferation of networks

 1983: deployment of       new national networks:
    TCP/IP                   Csnet, BITnet,
   1982: smtp e-mail        NSFnet, Minitel
    protocol defined        100,000 hosts
   1983: DNS defined        connected to
    for name-to-IP-          confederation of
    address translation      networks
   1985: ftp protocol
   1988: TCP congestion
                                              Introduction   1-79
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   1-80
Internet History

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

                                 Introduction   1-81
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 models
 History (self reading)


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