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					CS 352

         Prof. Richard P. Martin




                                   Introduction   1-1
Class web pages
 Main page on remus
    http://remus.rutgers.edu/cs352/F07/
    Check Thursday PM for the page
       • “read only”


 Sakai Web Site
   “write”
   Discussion board, handin,




                                           Introduction   1-2
Course Work
 2 Mid-terms (15% each)
   No electronic devices or notes allowed. No cheat sheets
    allowed
 Final (35%)
   You must send the instructor email at least 2 weeks
    before the final if you need to take the makeup!
 Project (35%)
   Part 1 (10%)
   Part 2 (10%)
   Part 3 (15%)




                                                    Introduction   1-3
Programming assignments
 Single long project
     Broken into three parts
 Can work in a group of 2
 Both program and write-up required
 Background needed to get started:
       • Java (112+ level)
          – Comfortable using data structures(stacks, trees, vector)
       • Unix (login, handin, permissions, javac)




                                                             Introduction   1-4
Programming Assignment
 2 Code reviews
   10-15 minute oral question and answer period.
   TA and instructor will critically review your assignment.
   “lost art” of program design.

 Make improvements for next level of the
  assignment.
     Grade depends on level of improvement in code quality as
      well as functionality.
 No late handin
   Failure to meet the deadline will result in a zero for all
    team members. No exceptions!


                                                        Introduction   1-5
Academic integrity
 No cheating on projects and exams
   Run code similarity detectors on the projects &
    code review
   Scrutinize exams for copying
 Department academic integrity policy
   http://www.cs.rutgers.edu/policies/academicint
    egrity/
   Acknowledge your awareness of this policy by
    the end of September to continue to access
    department computing facilities



                                            Introduction   1-6
Facilities
 “Cereal” machines and lab
   ~20 UltraSparc machines
   ~30+ Linux machines
   Cardkey Access: student ID card

 Romulus and remus for general use
   Create your accounts now!
   http://remus.rutgers.edu/newaccount.html




                                         Introduction   1-7
CS352 Fundamentals




                     Introduction   1-8
Why Study Networks?
 Integral part of society
     • Work, entertainment, community
 Pervasive
     • Home, car, office, school, mall …
 Huge impact on people and society




                                           Introduction   1-9
Impact of the Net on People
 Anytime access to remote information
     HW assignments from my server
 Person-to-person and group
 communication
     email, blogs, chat
 Form and strengthen communities
     chat rooms, MUDs, newsgroups




                                      Introduction   1-10
Impact of the Net on Society

 Huge impact!
     Continuation of technologies that reduce
      problems of time & space
       • (e.g. railroads,phone,autos,TV)
 Good, bad and ugly
     mirror of society
 Changes still on the horizon
     Commerce, services, entertainment, socializing



                                             Introduction   1-11
Example Impacts
 Economic impacts
    Productivity
    Nature of work
      • Open source movement
      • Vacation days?
 Leisure
    Music industy
 Social
   Who can contact me, and when?




                                    Introduction   1-12
Chapter 1: Introduction




                          Introduction   1-13
Chapter 1: Introduction


Our goal:
 get “feel” and terminology
 more depth, detail   later in course
 approach:
      use Internet as example




                                         Introduction   1-14
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
 1.8 History

                                    Introduction   1-15
Concepts for this chapter
 What is the Internet?
     Core and Edge of the Internet
     Core Network - Circuit, message and packet
      switching
 Network delay analysis
     Single link
     Multi-link
 Layering and encapsulation



                                             Introduction   1-16
What is the Internet?

 What is an internet?
   Network of networks

 What is the Internet?
   A global internet based on the IP protocol

 To what does the Internet technology
  refer?
     Architecture
     Services          Protocols


                                            Introduction   1-17
Architecture-wise




Network : Collection of interconnected machines

                                                  Introduction   1-18
Architecture-wise




Host: Machine running user application

                                         Introduction   1-19
 Architecture-wise




Media: Physical process used (copper wire, fiber optics, satellite link)

                                                                    Introduction   1-20
Architecture-wise




Channel: Logical line of communication

                                         Introduction   1-21
Architecture-wise




Router: decide where to send data next

                                         Introduction   1-22
 Architecture-wise

Company A




 Company B




   Edge Networks: Companies, organizations with a “default route”

                                                               Introduction   1-23
Architecture-wise
                            Internet Service Provider 1




                                       ISP 2




               Core Networks (ISP tiers)
                Tier 1: Biggest ISPs
                Tier 2 and 3: Regional and very small.
                                        Introduction   1-24
Service-wise (applications)
 Electronic mail
 Remote terminal
 File transfer
 Newsgroups
 File sharing
 Resource distribution
 World Wide Web
 Video conferencing
 Games



                              Introduction   1-25
Service-wise (applications)



                          IP picture frame
                          http://www.ceiva.com/

         Web-enabled toaster +
         weather forecaster




                                        Internet phones


                                                      Introduction   1-26
Protocol wise
     Protocol
      • Architecture  Service
      • Rules of communication



         Hi
                                 TCP connection
                                 request
         Hi
                                 TCP connection
      Got the                    response
       time?
       2:00
                                     <file>
                        time
                                                  Introduction   1-27
Protocol wise
     Protocol
      • Architecture  Service
      • Rules of communication

     protocols define format, order of msgs sent and
      received among network entities, and actions
      taken on msg transmission, receipt




                                            Introduction   1-28
Protocol wise

     Protocol
      • Architecture  Service
      • Rules of communication


                   FTP       HTTP        RTP     TFTP

                         TCP               UDP

                                    IP

                  Ethernet     802.11     …      PPP

          CAT-5    Single-Mode                     RS-232
                      Fiber

                                                            Introduction   1-29
Core Networks
                             Internet Service Provider 1




                                        ISP 2




                Core Networks (ISP tiers)
                 Tier 1: Biggest ISPs
                 Tier 2 and 3: Regional and very small.
                                         Introduction   1-30
   Core Networks: ISP Tiers

                  local
                   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
ISPs
connecting
them to rest
                          Tier 1 ISP             Tier 1 ISP       Tier-2 ISP
of Internet
                                                                        local
                    Tier-2 ISP           Tier-2 ISP
                                                                         ISP
              local         local          local
               ISP           ISP            ISP


                                                                    Introduction   1-31
 Core Networks: ISP Tiers
 a packet passes through many networks!


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

                              Tier 1 ISP
                                                NAP


                   Tier 1 ISP              Tier 1 ISP       Tier-2 ISP
                                                                  local
              Tier-2 ISP           Tier-2 ISP
                                                                   ISP
        local         local          local
         ISP           ISP            ISP                     Introduction   1-32
Core Network Switching
Schemes




                         Introduction   1-33
Switching Schemes

(1) Circuit Switching
(2) Message Switching (Store-and-Forward)
(3) Packet Switching (Store-and-Forward)




                                    Introduction   1-34
Circuit Switching

 End-end resources reserved for
  transmission
 Example: Telephone network




                                   Introduction   1-35
Circuit Switching (cont’d)
1. Control message sets up a path from origin
   to destination
2. Return signal informs source that data
   transmission may proceed
3. Data transmission begins
4. Entire path remains allocated to the
   transmission (whether used or not)
5. When transmission is complete, source
   releases the circuit

                                       Introduction   1-36
 Circuit Switching (cont’d)
                      Call request signal



Propagation Delay
Time




                                                                     Transmission
                                                                     Delay

                                            Call accept signal



              Data
       Transmission
                                                                              Pros & Cons ?
              Time
                                               Data


                      A                B                    C    D    Routers/Switches

                                                                                    Introduction   1-37
Message Switching
 Each message is addressed to a destination
 When the entire message is received at a router,
  the next step in its journey is selected; if this
  selected channel is busy, the message waits in a
  queue until the channel becomes free
 Thus, the message “hops” from node to node
  through a network while allocating only one channel
  at a time
 Analogy: Postal service




                                               Introduction   1-38
  Message Switching (cont’d)
                              Entire message must arrive at router before it can
                              be transmitted on next link: store and forward


       Header
                    Msg
Time




                                                         Transmission
                                                         Delay

                               Msg
                                          Queueing
                                          Delay



                                             Msg



                A         B           C              D     Routers/switches

                                                                        Introduction   1-39
 Packet Switching

 Messages are split into smaller pieces called
  packets
 These packets are numbered and addressed and
  sent through the network one at a time
 Allows Pipelining
     Overlap sending and receiving of packets on multiple links




                                                       Introduction   1-40
Packet Switching (cont’d)


                      Pkt 1
         Header
  Time




                      Pkt 2

                                  Pkt 1
                      Pkt 3
                                                          Transmission
                                  Pkt 2
                                                          Delay
                                              Pkt 1
                                  Pkt 3

                                              Pkt 2


                                              Pkt 3



                                                              Pipelining

                  A           B           C           D
                                                            Introduction   1-41
Comparisons
(1) Header Overhead
      Circuit < Message < Packet
(2) Transmission Delay
      Short Bursty Messages:
             Packet < Message < Circuit
      Long Continuous Messages:
             Circuit < Message < Packet




                                          Introduction   1-42
Circuit Switching – still multiplexing
                            Example:
FDM
                            4 users

      frequency

                     time
TDM


      frequency

                     time
                                       Introduction   1-43
Packet Switching: Statistical Multiplexing
        100 Mb/s
A       Ethernet     statistical multiplexing   C

                          1.5 Mb/s
    B
          queue of packets
          waiting for output
                 link


                          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.
                                                    Introduction   1-44
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

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

 packet switching:
    with 35 users,
                                  Q: how did we get value 0.0004?
     probability > 10 active
     less than .0004

                                                      Introduction   1-45
Concepts for this chapter
 What is the Internet?
     Core and Edge of the Internet
     Core Network - Circuit, message and packet
      switching
 Network delay analysis
     Single link
     Multi-link
 Layering and encapsulation



                                             Introduction   1-46
Why Study Network
Performance like Delay Analysis
 Networks cost $
     OC-3 line ~= $10,000/month
     Cable modem: $40/month
     Are you getting your $/worth?
 Why is the network “slow”?
 Approach:
     Build abstract models of network performance
     Observe where real networks deviate from model
     Simple Models: Tells us average/best/worse cases->useful,
      practical
     Complex Models: Hard to understand -> useless




                                                           Introduction   1-47
Units
 Bits are the units used to describe an amount of data in a network
   1 kilobit (Kbit)        = 1 x 103 bits = 1,000 bits
   1 megabit (Mbit)        = 1 x 106 bits = 1,000,000 bits
   1 gigabit (Gbit)        = 1 x 109 bits = 1,000,000,000 bits
 Seconds are the units used to measure time
   1 millisecond (msec)   = 1 x 10-3 seconds = 0.001 seconds
   1 microsecond (msec)   = 1 x 10-6 seconds = 0.000001 seconds
   1 nanosecond (nsec)    = 1 x 10-9 seconds = 0.000000001 seconds
 Bits per second are the units used to measure channel
   capacity/bandwidth and throughput
      bit per second (bps)
      kilobits per second (Kbps)
      megabits per second (Mbps)




                                                              Introduction   1-48
Four sources of packet delay
 1. nodal processing delay:          2. queueing
        execute protocol code
                                         time waiting at output
        check bit errors
                                          link for transmission
        determine output link
                                         depends on congestion
                                          level of router


               transmission
 A                               propagation


     B
                  nodal
                processing    queueing

                                                         Introduction   1-49
Four sources of packet delay
 3. Transmission delay:          4. Propagation delay:
    Time to “get bits on            Time for bits to “move
     wires”                           across wires”
    R=link bandwidth (bps)          d = length of physical link
    L=packet length (bits)          s = propagation speed in
    Transmission delay =             medium (~2x108 m/sec)
     L/R                             propagation delay = d/s




           transmission
A                           propagation


    B
              nodal
            processing    queueing
                                                      Introduction   1-50
Transmission vs. Prop. delay

     A single transmission link as a water pipe




1.    The thicker the pipe, the more water it can carry from one end
      to the other in each unit time
2.    Water is carried from one end of the pipe to the other at
      constant speed, no matter how thick the pipe is

Water = Data bits
Thickness of the pipe = Channel capacity
Speed of water through the pipe = Propagation speed

                                                           Introduction   1-51
Transmission vs. Prop. Delay
(cont)
 pipe




        1.   Propagation delay is how long takes to cross
             the pipe, irrespective of volume
        2.   Transmission (bandwidth delay) is related to
             how much water can be pushed in through
             the opening per unit time




                                                  Introduction   1-52
 Transmission Time
How long does it take A to transmit an entire packet onto the link?


     Relevant information: packet length = 1500 bytes
                           channel capacity = 100 Mbps

     Another way to ask this question:
     If the link can transmit 10 million bits in a second, how
     many seconds does it take to transmit 1500 bytes (8x1500
     bits)?


                      1500 x 8 bits       Solving for t…
               t =                          t = 0.00012 sec (or 120 msec)
                       100 Mps


                                                             Introduction   1-53
 Propagation Delay
How long does it take a single bit to travel on the link from A to
   B?

     Relevant information: link distance = 500 m
                           prop. delay factor = 5 msec/km

     Another way to ask this question:
     If it takes a signal 5 msec to travel 1 kilometer, then how
     long does it take a signal to travel 500 meters?

                 500 m                Solving for t…
         t   =             * 5 msec           t = 2.5 msec
                 1000 m


                                                             Introduction   1-54
 Caravan analogy
                          100 km               100 km
      ten-car     toll                toll
      caravan    booth               booth
 Cars “propagate” at            Time for last car to
  100 km/hr                       propagate from 1st to
 Toll booth takes 12 sec to      2nd toll both:
  service a car                   100km/(100km/hr)= 1 hr
  (transmission time)            Time to “push” entire
 car~bit; caravan ~ packet       caravan through toll
                                  booth onto highway =
 Q: How long until caravan
                                  12*10 = 120 sec
  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
 Cars now “propagate” at       at 2nd booth and 3 cars
  1000 km/hr                    still at 1st booth.
 Toll booth now takes 1       1st bit of packet can
  min to service a car          arrive at 2nd router
 Q: Will cars arrive to        before packet is fully
  2nd booth before all          transmitted at 1st router!
  cars serviced at 1st
  booth?

                                               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
Single Link Example
                     A                   B
                             500 m


               Protocol Processing Time = 40 msec
                   packet length = 1500 bytes
                  channel capacity = 100 Mbps
              propagation delay factor = 5 msec/km

1.   How long to format the data (execute protocol)?
2.   How long does it take a single bit to travel on the link
     from A to B?
3.   How long does it take A to transmit an entire packet
     onto the link?
                                                     Introduction   1-58
 Timeline Method
             Host A         Host B
       40                        Protocol Delay
               1st bit
       2.5                        Propagation delay

Time
       120                       Transmission time
                last bit



       40                         Protocol Delay

       Total time: 40+120+2.5+40 = 202.5 msec
                                                Introduction   1-59
Single Link Delay Modeling
    A            B




    Processing delay              T1
    Message Size (bits, bytes)    N
    Link bandwidth (bps)           B
    Propagation delay (seconds)    T2

                T1+N/B+T2

                                   Introduction   1-60
Multiple Link Delay Modeling
     A     B    C               P    Q




 Processing delay                  T1
 Message Size (bits, bytes)        N
 Link bandwidth (bps)               B
 Propagation delay (seconds)        T2



                                          Introduction   1-61
Multiple Link Delay Modeling
       A        B       C              P     Q




 Processing delay                               T1
 Message Size (bits, bytes)                     N
 Per-Link bandwidth (bps)                       B
 Propagation delay (seconds)                    T2
 Number of switches (in-between stations)        s
 Time to set up circuit:                         c
 Size of the packet:                             p
 Size of the header:                             h

                                                 Introduction   1-62
Circuit Switching Time


 Set-up cost + bandwidth delay




                 N
              C
                 B


                                  Introduction   1-63
 Packet switching

                  Host A   Switch 1 Switch 2 Host B

       Packet 1
                                                        Propagation
       Packet 2                                         Delay
       Packet 3
Time
       Packet 4
                                                        Bandwidth
                                                        Delay




                                                      Introduction   1-64
Packet Switching Time
 Delay = Transmission + “Propagation” delays

 “Propagation” delay:
         Time for a single packet to cross
                   - not really prop. delay in the traditional sense

    + Transmission delay (also bandwidth delay):
            Time to push all the packets into the network


                  ( p  h)  N          ( p  h)
       ( S  1) *          (    1) *
                      B       P            B


                                                                 Introduction   1-65
Packet Switching Time

                                         Transmission delay
 “Propagation” delay

                                        Number of packets
 Number of links/hops


              ( p  h)  N          ( p  h)
   ( S  1) *          (    1) *
                  B       P            B
                        Time for each packet to
                        go through each link

                                                            Introduction   1-66
Note on Pipelining
 The above analysis is very general:
     Packets in a computer network
      • Messages/packets are the unit of work.
     Instructions in a processor
      • Instructions are the unit of work.
     Jobs through a batch Q in an operating system.
      • Processes are the unit of work.




                                                 Introduction   1-67
Switching schemes Comparison
 Given choice of 2 switching schemes, how
  would you compare their performance?
     Eg. Circuit switching or packet switching?
 Goal: Determine which is faster
     Formal definition: Least time to move a fixed
      amount of data
 Could you come up with a closed form
  expression based on your choices?



                                               Introduction   1-68
Circuit switching vs. packet
switching


       N       p  h   N      
    C      ?          P   S 
                                  
       B       B              




                                       Introduction   1-69
Questions
 How does packet switching reduce the
  impact of increasing s?
 Show, using an equation, how reducing the
  packet size and packet switching reduces
  the impact of increasing s.
 Where does the approach of reducing
  packet size fail to give any benefit?




                                      Introduction   1-70
Queuing Delay



  A


      B
                queueing




                           Introduction   1-71
Queueing delay

 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   1-72
Queuing Delay  Packet Loss
 queue (aka 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
A


    B
                  queueing
                                       Introduction   1-73
Concepts for this chapter
 What is the Internet?
     Core and Edge of the Internet
     Core Network - Circuit, message and packet
      switching
 Network delay analysis
     Single link
     Multi-link
 Layering and encapsulation



                                             Introduction   1-74
Why Layering?
 Networks are complex!
     Hosts, routers, links of various media,
      applications, protocols, hardware, software
 Layering provides separation of concerns
   Different vendors and organizations responsible
    for different layers
   Testing and maintenance is simplified
   Easy to replace a single layer with a different
    version



                                              Introduction   1-75
Protocol Hierarchy
 Use layers to hide complexity
     Each layer implements a service
      • Layer N uses service provided by layer N-1
      • layer N-1 provides a service to layer N
     Protocols
      • Each layer communicates with its peer by a set of rules




                                                      Introduction   1-76
Protocol Hierarchy         (cont’d)
   Host A                             Host B
    Layer 7
              Layer 7 Protocol        Layer 7


              Layer 6 Protocol
    Layer 6                           Layer 6

              Layer 5 Protocol
    Layer 5                           Layer 5

              Layer 4 Protocol
    Layer 4                           Layer 4

              Layer 3 Protocol
    Layer 3                           Layer 3


              Layer 2 Protocol
    Layer 2                           Layer 2

              Layer 1 Protocol
    Layer 1                           Layer 1
              Physical Medium
                                      Introduction   1-77
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



                                                                                 Introduction      1-78
Different Layering
Architectures
 ISO OSI 7-Layer Architecture
 TCP/IP 4-Layer Architecture
   + application layer = 5 layers in Kurose

 Novell NetWare IPX/SPX 4-Layer
  Architecture




                                               Introduction   1-79
Standards Making
Organizations
ISO = International Standards Organization
ITU = International Telecommunication Union
  (formerly CCITT)
ANSI = American National Standards Institute
IEEE = Institute of Electrical and Electronic
  Engineers
IETF = Internet Engineering Task Force
ATM Forum = ATM standards-making body

...and many more

                                           Introduction   1-80
Why So Many Standards
Organizations?
 Multiple technologies
 Different areas of emphasis and history
   Telecommunications/telephones
      • ITU,ISO,ATM
     Local area networking/computers
      • IETF, IEEE
     System area networks/storage
      • ANSI




                                        Introduction   1-81
ISO OSI Layering
Architecture
    Host A                                     Host B
    Application        Application Protocol    Application
      Layer                                      Layer


   Presentation       Presentation Protocol    Presentation
      Layer                                       Layer


     Session             Session Protocol       Session
      Layer                                      Layer


    Transport           Transport Protocol     Transport
      Layer                                      Layer

     Network      Network           Network     Network
      Layer        Layer             Layer       Layer


     Data Link    Data Link        Data Link   Data Link
      Layer        Layer            Layer       Layer


     Physical     Physical          Physical    Physical
      Layer        Layer             Layer       Layer
                    Router            Router   Introduction   1-82
ISO’s Design Principles
 Each layer should perform a well-defined
  function
 The layer boundaries should be chosen to
  minimize information flow across the
  interfaces
 The number of layers should be large
  enough that distinct functions need not be
  thrown together in the same layer out of
  necessity, and small enough that the
  architecture does not become unwieldy
                                      Introduction   1-83
Layer 1: Physical Layer
 Functions:
   Transmission of a raw bit stream
   Forms the physical interface between devices
 Issues:
   Which modulation technique (bits to pulse)?
   How long will a bit last?
   Bit-serial or parallel transmission?
   Half- or Full-duplex transmission?
   How many pins does the network connector
    have?
   How is a connection set up or torn down?

                                            Introduction   1-84
Layer 2: Data Link Layer
 Functions:
     Provides reliable transfer of information
      between two adjacent nodes
     Creates frames from bits and vice versa
     Provides frame-level error control
     Provides flow control
 In summary, the data link layer provides
  the network layer with what appears to be
  an error-free link for packets


                                                  Introduction   1-85
Layer 3: Network Layer

 Functions:
   Responsible for routing decisions
      • Dynamic routing
      • Fixed routing
     Performs congestion control




                                        Introduction   1-86
Layer 4: Transport Layer

 Functions:
   Hide the details of the network from the session
    layer
      • Example: If we want replace a point-to-point link with a
        satellite link, this change should not affect the behavior
        of the upper layers
     Provides reliable end-to-end communication




                                                       Introduction   1-87
    Transport Layer (cont’d)
              Host A                                     Host B
              Application        Application Protocol    Application
                Layer                                      Layer
   first
end-to-end
             Presentation       Presentation Protocol    Presentation
  layer         Layer                                       Layer


               Session             Session Protocol       Session
                Layer                                      Layer


              Transport           Transport Protocol     Transport
                Layer                                      Layer

               Network      Network           Network     Network
                Layer        Layer             Layer       Layer


               Data Link    Data Link        Data Link   Data Link
                Layer        Layer            Layer       Layer


               Physical     Physical          Physical    Physical
                Layer        Layer             Layer       Layer
                            Router            Router     Introduction   1-88
Transport Layer (cont’d)

 Functions (cont’d):
   Perform end-to-end flow control
   Perform packet retransmission when packets
    are lost by the network




                                          Introduction   1-89
Layer 5: Session Layer
 May perform synchronization between
  several communicating applications or
  logical transmissions
 Groups several user-level connections into
  a single “session”
 Examples:
     Banking session
     Network meetings



                                       Introduction   1-90
Layer 6: Presentation Layer
 Performs specific functions that are
  requested regularly by applications
 Examples:
     encryption
     ASCII to Unicode, Unicode to ASCII
     LSB-first representations to MSB-first
      representations




                                               Introduction   1-91
Layer 7: Application Layer
 Application layer protocols are application-
  dependent
 Implements communication between two
  applications of the same type
 Examples:
     FTP
     HTTP
     SMTP (email)



                                        Introduction   1-92
TCP/IP Layering Architecture
                      A simplified model
                      The network layer
  Application
                        Hosts drop packets into
                         this layer, layer routes
   Transport             towards destination-
                         only promise- try my
                         best
  Internet/Network
                      The transport layer
                        reliable byte-oriented
  Host-to-Net            stream




                                         Introduction   1-93
TCP/IP Layering Architecture
(cont’d)




       Host A                                               Host B
       Application             Application Protocol         Application
         Layer                                                Layer

       Transport           Transport Protocol (TCP)         Transport
         Layer                                                Layer

        Network
                     IP   Network
                                      IP    Network
                                                       IP    Network
         Layer             Layer             Layer            Layer


        Host-to-           Host-to-         Host-to-         Host-to-
       Net Layer          Net Layer        Net Layer        Net Layer




                                                            Introduction   1-94
Internet “Hourglass”
Architecture
   • Defined by Internet Engineering Task Force (IETF)
   • “Hourglass” Design


                FTP       HTTP        RTP     TFTP

                      TCP               UDP

                                 IP

               Ethernet     802.11     …      PPP

       CAT-5    Single-Mode                     RS-232
                   Fiber



                                                         Introduction   1-95
Encapsulation
Treat the neighboring layer’s information as
  a “black box”, can’t look inside or break
  message
 Sending: add information needed by the
  current layer “around” the higher layers’
  data
     headers in front
     trailers in back
 Receiving: Strip off headers and trailers
  before handing up the stack
                                       Introduction   1-96
Encapsulation
                   Data

    Application
                  AH   Data

                                                     Headers
      Layer


   Presentation
                  PH      Data
      Layer


     Session
                  SH       Data
      Layer


    Transport
                  TH          Data                   Trailer
      Layer

     Network
                  NH             Data
      Layer


     Data Link
                  DH              Data         DT
      Layer


     Physical
                  PH                    Data
      Layer
                                                            Introduction   1-97
     message        M
                          source
                        application
                                                 Encapsulation
  segment      Ht   M   transport
datagram Hn Ht      M    network
frame Hl Hn Ht      M      link
                         physical
                                                        link
                                                      physical

                                                                           switch



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

                                                                 Introduction   1-98
Concepts for this chapter
 What is the Internet?
     Core and Edge of the Internet
     Core Network - Circuit, message and packet
      switching
 Network delay analysis
     Single link
     Multi-link
 Layering and encapsulation



                                             Introduction   1-99

				
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