Computer Networks Foundation Concepts

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					                        Computer Networks
                         Foundation Concepts-IV

                                     Dr. Rahul Banerjee
              Birla Institute of Technology & Science
                             Pilani, Rajasthan – 333 031, INDIA
                    Home Page: http://www.bits-pilani.ac.in/~rahul/
            Email: Rahul@bits-pilani.ac.in / RahulBanerjeeBITS@Gmail.com

Wednesday 27 February 2008        (c) Dr. Rahul Banerjee, BITS-Pilani, INDIA   1
                             Interaction Points
•   Introduction to Computer Networks
•   Types of Networks
•   Topologies of Computer Networks
•   Interconnection of basic elements
•   Performance Evaluation, QoS
•   Protocol Implementation Aspects
•   Simulation Tools for this course
•   Concluding remarks

Wednesday 27 February 2008      (c) Dr. Rahul Banerjee, BITS-Pilani, INDIA   2
           Elements involved in a Network /
      •    Nodes
                    Internetwork
            – Regular computing nodes
            – Network extension / interconnection devices
      • Network Interfaces
            – NICs / On-board Chips
            – Wireless interfaces
            – Wireline interfaces
      • Links
            – Wireline links
            – Wireless links
      • Strategies, Algorithms & Protocols:
            – H/W, S/W, (c) Dr. RahullevelBITS-Pilani, INDIA
                         F/W Banerjee, implementations
Wednesday 27 February 2008                                     3
                              Network Building Blocks
• Nodes: where processing and communication capabilities
  co-exist
• Physical Links: those entities that provide physical path
  (direct paths between neighbouring nodes (point-to-point / point-
  to-multi-point) for data delivery over guided or unguided
  media
• Logical Links: an abstraction showing the logical path of
  data delivery at layers higher than the physical layer
• Hosts: end / intermediate nodes where all levels / layers
  including those belonging to applications exist



  (c) Dr. Rahul Banerjee, BITS, Pilani, India   4
                             Network Building Blocks
• Repeaters: where L1 layer / level exist with L1-
  protocol data unit (raw bits) regeneration and
  onward transmission
• Gateways: where two or more different
  networks meet and may require protocol /
  message translation capabilities
• Routers: where L1, L2 and L3 layers / levels exist
  with L3-protocol data unit (packet) processing,
  routing and forwarding
• Clouds: abstraction of node connectivity in the
  networking context <details hidden>
 (c) Dr. Rahul Banerjee, BITS, Pilani, India   5
                    Interconnection of nodes /
                            interfaces
• Media-based interconnection
      – Guided / Unguided
      – Noisy / Noiseless
      – Broadcast / Non-broadcast

• Link-based interconnection
      – Secure / Insecure
      – Logical / Physical
      – Point-to-Point / Multi-point

Wednesday 27 February 2008   (c) Dr. Rahul Banerjee, BITS-Pilani, INDIA   6
The TCP / IP Architecture


          Application Layer



                TCP Layer


             Internet Layer


     Host-to-Network Interface


                   Raw Hardware

       (c) Dr. Rahul Banerjee, BITS-Pilani, INDIA   7
A Look at the TCP/IP Family of the
            Protocols

                              RTP RTCP RTSP
           SSL/TLS




                     IEEE 802.2 LLC Sub-layer


            IEEE 802.x or equivalent MAC Sub-layer




                           Physical Layer



                          8
               The TCP/IP Network Architecture




Source: Peterson & Davie: Computer Networks, 4e, Elsevier, 2007.
                              Network Topologies
• Bus Topology
       – Shared
       – Switched
• Tree Topology
• Ring Topology
       – Single
       – Double
• Star Topology
• Irregular Topology
• Complete Topology

(c) Dr. Rahul Banerjee, BITS, Pilani, India   10
A Bus Topology based Computer
           Network

   PC        PC                      PC              PC


         SHARED                      BUS
          PC                               PC             PC
   PC




        (c) Dr. Rahul Banerjee, BITS-Pilani, INDIA             11
A Ring Topology based Computer
            Network
        C
                                                      C
C




    C                                                        C

            C



                (c) Dr. Rahul Banerjee, BITS-Pilani, INDIA       12
A Tree Topology based
  Computer Network
       N                                             N




                                                         N
N


                      N                          N



                              N




    (c) Dr. Rahul Banerjee, BITS-Pilani, INDIA               13
A Star Topology based Computer
           Network
                         C




                   Switch
C                                                    C




        (c) Dr. Rahul Banerjee, BITS-Pilani, INDIA       14
                        Concluding remarks
•   A network is …
•   An internetwork is …
•   A vertical Layer ‘n’ to Layer ‘m’ service is …
•   A horizontal Layer ‘n’ to Layer ‘n’ service is …
•   A Service Access Point is …
•   A Protocol is …
•   A Protocol Stack is …
•   A Protocol Family / Suite is …
•   A Cloud is ….
Wednesday 27 February 2008   (c) Dr. Rahul Banerjee, BITS-Pilani, INDIA   15
        Applications of Computer Networks
• Numerous applications of computer
  networking are possible.
• Some of the most popular ones include:
       – Electronic Mail
       – Web-browsing
       – Digital Libraries
       – Video-on-Demand
       – File Transfer
       – Video / Audio Conferencing
(c) Dr. Rahul Banerjee, BITS,
                                16
Pilani, India
        Types of Computer Networks                  1 of 2



• Class One: Function-based classification
            • Data Networks
            • Voice Networks
            • Multimedia Networks
• Class Two: Location-and-Distance-based
  classification
            •   Personal Area Networks (PANs)
            •   Local Area Networks (LANs)
            •   Metropolitan Area Networks (MANs)
            •   Wide Area Networks (WANs)
 (c) Dr. Rahul Banerjee, BITS,
                                     17
 Pilani, India
        Types of Computer Networks                2 of 2



• Class Three: Forwarding-based classification
            • Switched Networks
                    – Circuit-Switched Networks
                    – Packet-Switched Networks
            • Shared Networks
            • Hybrid Networks
• Class Four: Ownership-based classification
            • Public Networks
            • Private Networks
            • Virtual Private Networks

 (c) Dr. Rahul Banerjee, BITS,
                                             18
 Pilani, India
        Types of Computer Networks                  1 of 2



• Class One: Function-based classification
            • Data Networks
            • Voice Networks
            • Multimedia Networks
• Class Two: Location-and-Distance-based
  classification
            •   Personal Area Networks (PANs)
            •   Local Area Networks (LANs)
            •   Metropolitan Area Networks (MANs)
            •   Wide Area Networks (WANs)
 (c) Dr. Rahul Banerjee, BITS,
                                     19
 Pilani, India
        Types of Computer Networks                2 of 2



• Class Three: Forwarding-based classification
            • Switched Networks
                    – Circuit-Switched Networks
                    – Packet-Switched Networks
            • Shared Networks
            • Hybrid Networks
• Class Four: Ownership-based classification
            • Public Networks
            • Private Networks
            • Virtual Private Networks

 (c) Dr. Rahul Banerjee, BITS,
                                             20
 Pilani, India
Comparing Computer Networks with
      Distributed Systems
• Terms Computer Network and Distributed
  System must NOT be used interchangeably since:
    – In the former, locations and elements of network
      remain visible to the user; whereas
    – in the latter, the underlying network remains
      transparent to the user who sees the system as a uni-
      processor.
• Similar differences can be cited in case of
  Network Operating Systems and Distributed
  Operating Systems.
 (c) Dr. Rahul Banerjee, BITS,
                                 21
 Pilani, India
    Some More Terms Related to Networks
• Channel <application-level logical communication
  path>
• Services
• Interfaces: Peer-to-Peer / Layer-to-Layer
• Service Access Points
• Interoperability <applies to different
  implementations of the same specification>
• Compatibility <applies to independent
  implementations of the different specifications>
• Tunneling <Encapsulation & Decapsulation>
  (c) Dr. Rahul Banerjee, BITS,
  Pilani, India
                                  22
                      Network Building Blocks
• Bridges: where L1 and L2 layers / levels exist with
  L2-protocol data unit (frame) processing and
  forwarding
• Hubs: where L1 and L2 layers / levels exist with
  ability to handle and deliver L2-protocol data
  unit (frame) over a shared medium
• Switches: where L1 and L2 and / or L3
  (sometimes even higher) layers / levels exist
  with L2 and / or L3-protocol data unit (frame /
  packet) processing, switched routing /
  forwarding
 (c) Dr. Rahul Banerjee, BITS,
 Pilani, India
                                 23
                                LANs
• The term LAN stands for Local Area Network.
• The term ‘local area’ in the world of
  networking usually refers to a geographically
  contiguous area in which the inter-computer
  distance is lesser than or equal to one
  kilometer.



(c) Dr. Rahul Banerjee, BITS,
                                 24
Pilani, India
                       Local Area Networks ...
• It is wholly owned by a single organization /
  entity, is locally installed (i.e. in a single
  contiguous geographic location like an office,
  a laboratory, a building or a campus) is called
  a Local Area Network (LAN).
• Although, normally, in a LAN, the inter-node
  distance does not exceed a kilometer; in most
  of the real-life situations, it is far less than this
  ceiling.

 (c) Dr. Rahul Banerjee, BITS,
                                  25
 Pilani, India
    Circuit-Switching Vs. Packet Switching
• Circuit-Switching
       – Establish-connection-before-transfer + Pay-as-per-time,
         not-as-per-traffic
               • Example: Telephone networks
• Packet Switching
       – Variable-size + Store-in-entirety-first-and-Forward-later
               • Example: IP networks
       – Fixed-size (cells) + Store-header-first-and-begin-
         forwarding-without-wait-for-payload
               • Example: ATM networks



(c) Dr. Rahul Banerjee, BITS,
                                         26
Pilani, India
    Hierarchical Switched Networks

                                 Core
                                Switch


Distribution                                                 Distribution
   Switch                                                       Switch
                     Distribution
                        Switch



Access                        Access                           Access
Switch                        Switch                           Switch

               (c) Dr. Rahul Banerjee, BITS, Pilani, India                  27
Local Area Networks using Hierarchical
         Switched Networks
                               Core Switch




Distribution Switch            Distribution Switch                    Distribution Switch




     Access Switch                 Access Switch                          Access Switch




PC / Laptop /Tablet /
Network Printer
                        (c) Dr. Rahul Banerjee, BITS, Pilani, India                         28
                                 MANs
• The term MAN stands for Metropolitan Area
  Network.
• A computer network that is not usually owned by
  a single organization / entity and that is spread
  over a metropolitan city area is called a
  Metropolitan Area Network.
• Normally, in a MAN, the inter-node distance
  does not exceed ten kilometers. This, however, is
  not a hard-and-fast rule.
 (c) Dr. Rahul Banerjee, BITS,
                                  29
 Pilani, India
                                 WANs
• The term WAN stands for Wide Area Network.
• A computer network that is not usually owned by a
  single organization / entity and that is spread over an
  area larger than that of any city of operation is called a
  Wide Area Network .
• A WAN may be spread over several cities / towns, a
  state, a country or even a continent.
• In many a cases, when people say WAN, they actually
  mean Wide Area Internetwork (WAI), however!

 (c) Dr. Rahul Banerjee, BITS,
                                  30
 Pilani, India
                                PANs
• The term PAN stands for Personal Area
  Network.
• Typically these networks are small in size,
  belong to a single person and are limited to
  his / her environment within a small area like
  his room, body or garden etc.
• PANS mostly use short-range wireless
  technologies for interconnecting various
  nodes that comprise them.
(c) Dr. Rahul Banerjee, BITS,
                                 31
Pilani, India
                     Local Area Internetwork
• Traditionally, a Campus Internetwork is a campus-wide internetwork
  of individual LANs which may be geographically spread over the part
  or whole of a single campus. This sometimes called campus intranet.
• In common practice, the entire campus internetwork including its
  communication subnet is wholly owned by a single organization or
  institution.
• Usually, the campus internetworks use LAN technology; however, it
  is possible to use WAN technology, when so desirable. The latter
  may be desirable in some cases when the campus is very large and
  comprises of a vast set of buildings spread over it. Protocols used in
  both of these cases at the lower layers, are, generally, different.



 (c) Dr. Rahul Banerjee, BITS,
                                   32
 Pilani, India
                                Physical Layer
   • Physical Layer deals with transmission of raw
      digital data using analog or digital signal.
   • This layer is concerned with the logic type
     (negative or positive), amplitude of the
     signal, signal representation, bit-length,
     direction of transmission etc.
   • It deals with connection-establishment and
     termination.


(c) Dr. Rahul Banerjee, BITS,
                                      33
Pilani, India
                                More on Physical Layer

   • This layer is, in a nutshell, a layer that deals with
     various electrical and mechanical characteristics
     of every physical component of a computer
     network.
   • Exact electrical, mechanical and procedural
     Interface Definition is therefore its responsibility.
   • Choice and use of the physical medium are the
     Physical Layer Design Issues.


(c) Dr. Rahul Banerjee, BITS,
                                          34
Pilani, India
                       On the Transfer of Data ...
   • Any information can be transmitted over a
     medium only by making use of its physical
     characteristics.
   • By the way of varying one or more physical
     properties like frequency, phase, voltage, current
     etc. we can transmit over a medium: guided or
     unguided.
   • A common unit of representing Rate of Data
     Transfer is Baud which is defined as the number
     of changes in some property of the signal per
     second.

(c) Dr. Rahul Banerjee, BITS,
                                    35
Pilani, India
                       On the Transfer of Data ...
• Maximum rate of data transfer of a noiseless
  channel is governed by the Nyquist’s Theorem
  that states:
      DTR(Max) = 2Hlog2 (V) bps
  where V is the number of discrete levels of the
  signal and H is bandwidth in Hz.
• For a channel with linear noise, the Max. DTR is
  governed by Shannon’s Law which states:
       DTR(Max) = Hlog2(1 + S/N) bps
  where S/N is Signal to Noise Ratio and H is
  bandwidth in Hz.
(c) Dr. Rahul Banerjee, BITS,
                                    36
Pilani, India
          On the Transmission Media ...
   Classification of Transmission Media:
           – There exist many schemes of classification of
             transmission media.
           – The most common of these is based on the
             capability of the physical medium to guide a
             signal propagating through it.
           – Given this basis, media can be classified into:
                   • Guided Media &
                   • Unguided Media



(c) Dr. Rahul Banerjee, BITS,
                                      37
Pilani, India
        On the Transmission Media ...
Types of Guided Media:
• Unshielded Twisted Pair Cable (e.g. CAT-5, CAT-6
  (requires RJ-45 connector))
• Shielded Twisted Pair Cable
• Baseband Coaxial Cable (50-Ohm Coax (requires BNC
  connector))
• Broadband Coaxial Cable (75-Ohm Coax)
• Optical Fibre Cable (Multi-mode and Single-mode
  Fibres)
where CAT=> Category, RJ=> Recommended Jack, BNC=>
  British Naval Connector
(c) Dr. Rahul Banerjee, BITS,
                                38
Pilani, India
                           About the UTP/STP Cabling
• In its simplest form, it comprises of two insulated Copper wires of approximately 1
  mm. Diameter.
• These two wires are twisted in helical fashion with each-other for the purpose of
  reducing the effect of Electrical Interference by the signals traveling through other
  wires in the vicinity.
     – This is because of the fact that twisting eliminates the Antenna-like behaviour which,
       otherwise, would have been demonstrated by these wires, had they been used in
       parallel fashion.
•   A Twisted-Pair cable may have up to four such pairs of wire. In other words, an
    eight-core/wire TP cable has four TPs.
•   Such cables (UTP/STP) may be used for Analog as well as Digital Transmissions.
•   They provide an acceptably good performance at a low-cost.
•   CAT-6 and CAT-5 provide more twists per unit length than the CAT-3.
•   CAT-6 and CAT-5 provide less Cross-Talk and improved signal quality than the
    CAT-3.
•   CAT-5 supports a maximum data transfer rate of 1 Gbps for short distances.
•   CAT-6 is still under evolution in terms of standardisation and is expected to
    support higher data transfer rates for shorter distances (10 Gbps).

     (c) Dr. Rahul Banerjee, BITS,
                                               39
     Pilani, India
                   About the Co-axial Cabling
• There exist two types of coaxial cables:
    – Baseband Coax & Broadband Coax
• A Co-axial cable comprises of a solid copper wire as its core. This
  core is insulated by a thick layer of insulating material.
• Often, this insulation layer is further surrounded by a thin braided
  Copper mesh that takes care of external noises.
• This braided mesh is further encapsulated by a protective sheath.
• A major difference between the Baseband and the Broadband Co-
  axial Cables is the area of coverage, that can be larger in the latter
  case than in that of the former.
• Broadband Networking:
    – Dual Cable & Head-end scheme & Single-cable scheme.


  (c) Dr. Rahul Banerjee, BITS,
                                     40
  Pilani, India
   Bandwidth of a Transmission Link

      • The maximum Rate of Data Transfer that a given
        transmission link may support, is often called its
        Maximum Bandwidth.
      • However, in an internetwork, it is often the
        slowest intermediate link between two networks
        that influences the maximum data transfer rate
        actually achievable.



(c) Dr. Rahul Banerjee, BITS,
                                41
Pilani, India
      Bandwidth of a Transmission Link ...
   The Effective Link-bandwidth actually depends
     on several physical factors like:
   • the transmission quality supported by a guided or
     unguided medium
   • the effect of proximity of adjacent signal
     frequencies
   • the type of physical terminators and /or connectors
     intended to be used along with the link
   • effect of noise(s) and external interference(s)


(c) Dr. Rahul Banerjee, BITS,
                                42
Pilani, India
  Bandwidths Supported by various
      Communication Schemes
   •     FDDI: 100 Mbps
   •     Ethernet: 10 / 100 Mbps / 1 Gbps / 10 Gbps
   •     POTS (Analog):57.6 Kbps
   •     VSAT: (1.2 Kbps / 9.6 Kbps / 64 Kbps / 128 Kbps / 512 Kbps)
   •     Frame Relay: 1.54 Mbps
   •     Basic Rate ISDN: 128 / 144 Kbps (2B+1D)
   •     Primary Rate ISDN: 23B+1D / 30B+1D
   •     Broadband ISDN: 1200 Mbps

   Here, A=4KHz, B=64Kbps, C=8/19 Kbps, D=16Kbps, E=64Kbps, H=384 /
      1536 / 1920 Kbps
   FDDI=> Fibre Distributed Data Interface, POTS=> Plain Old Telephone
      System, VSAT=> Very Small Aperture Terminal, ISDN=> Integrated
      Services Digital Network.
(c) Dr. Rahul Banerjee, BITS,
                                         43
Pilani, India
                           Bandwidths Supported ...
•   T1: 1.54 Mbps
•   T2: 6.312 Mbps
•   T3: 46 Mbps
•   T4: 273 Mbps
•   E1: 2.048 Mbps
•   E2: 8.448 Mbps
•   E3: 34.368 Mbps
•   E4: 139.264 Mbps
•   Token Ring: 16 Mbps
•   X.25: 56Kbps
•   SMDS: 34 Mbps
•   SONET: 4976 Mbps
    Where, rates shown indicate maximum rates of data transfer at the current
    state of technology. Please note that under laboratory conditions, it may be
    possible to obtain substantially high DTR for many of these systems /
    schemes. Similarly, some of these schemes / systems are scalable.
SMDS=>Switched Muli-megabit Data Service, SONET=> Synchronized Optical NETwork.



(c) Dr. Rahul Banerjee, BITS,
                                                 44
Pilani, India
                                The VSAT WANs
• VSAT=> Very Small Aperture Terminal
• Terminal=> Earth Station
• Types of VSATs:
   – One-way / Non-Interactive VSATs
   – Two-way / Interactive VSATs
   – TSATs (T-1 rate based VSATs)
• VSATs, as their name suggests, employ very small
  aperture and therefore use low-cost dish-antenna
  of lesser than 2.4 m. diameter.
• TSATs use larger dishes (Dia.: 2.4 m. - 3.5 m.)
(c) Dr. Rahul Banerjee, BITS,
                                     45
Pilani, India
                                The VSAT WANs ...
   • Although, VSATs are available in various
     flavours and capacities, in many cases 56 /
     64 Kbps systems are used because of low
     cost.
   • Most of the VSAT networks around the
     world use Geostationary / Geosynchronous
     Satellites.
   • Geostationary satellites are the satellites
     orbiting in the Equatorial Plane of the Earth
     at about 35786 Kms. Above the surface.
(c) Dr. Rahul Banerjee, BITS,
                                       46
Pilani, India
                                The VSAT WANs ...
 • Approximate propagation delay for a signal to
   reach such satellites is 250 ms.
 • Such a large distance also causes signal
   attenuation of the order of about 200 dB.
 • Such satellites are often used as relay stations as
   they can always be treated as being fixed with
   respect to their footprints on the Earth.
 • VSATs are not always served by such satellites
   alone. In fact, in a few cases non-geostationary
   satellites have been used for limited periods
   successfully.
(c) Dr. Rahul Banerjee, BITS,
                                       47
Pilani, India
                                The VSAT WANs ...
   • VSATs offer small (typically tens of Watts) radio
       frequency power for transmission.
   • Their small size also provides lesser sensitivity of
       reception.
   It is for these two primary reasons because of which
       direct VSAT-to-VSAT Links do not provide
       acceptable performance.
   A larger co-ordinating Earth Station of improved
       capacity and quality called ‘Hub’
      is therefore employed in practice.
   A typical Hub may have a dish antenna of diameter
       of (4 m. - 11 m.).
(c) Dr. Rahul Banerjee, BITS,
                                       48
Pilani, India
            Another Classification of the VSAT
                      based WANs
   Types of VSAT Networks:
   • Meshed VSAT Networks
   • One-Way Star VSAT Network
   • Two-way Star VSAT Networks




(c) Dr. Rahul Banerjee, BITS,
                                49
Pilani, India
            Bandwidth of a Transmission Link:

     • The maximum Rate of Data Transfer that a
       given transmission link may support, is often
       called its Maximum Bandwidth.
     • However, in an internetwork, it is often the
       slowest intermediate link between two
       networks that influences the maximum data
       transfer rate actually achievable.




(c) Dr. Rahul Banerjee, BITS,
                                50
Pilani, India
      Bandwidth of a Transmission Link ...
   The Effective Link-bandwidth depends on
    several physical factors:
   • the transmission quality supported by a
     guided or unguided medium
   • the effect of proximity of adjacent signal
     frequencies
   • the type of physical terminators and /or
     connectors intended to be used along with
     the link
   • effect of noise(s) and external interference(s)
(c) Dr. Rahul Banerjee, BITS,
                                51
Pilani, India
       Data Encoding over the Physical Link
• Data encoding typically involves, in most cases,
  encoding the binary data to be sent / transmitted by
  the sending node into a signal that could be carried
  by the physical links.
• In practice, this is one of the several physical layer
  functions carried out by the NICs or Network
  Adopters.
• Types of encoding include NRZ, NRZI, Manchester
  encoding, Differential Manchester Encoding, 4B/5B
  encoding etc.

(c) Dr. Rahul Banerjee, BITS,
                                52
Pilani, India
                       Data Encoding Samples
 0 1 0 1 0 1 1 0 0 0 1




(c) Dr. Rahul Banerjee, BITS,
                                 53
Pilani, India
            Multiplexing: TDM, FDM etc.
• Multiplexing:
     – Purpose: Capacity sharing for cost-effective delivery
     – Mechanism: Division / partitioning of the resource /
       capacity based on one or more parameters of
       physical medium or representation scheme or
       statistical / probabilistic estimate of usage
     – Examples: Time Division Multiplexing, Statistical
       Time Division Multiplexing, Frequency Division
       Multiplexing and many more …


(c) Dr. Rahul Banerjee, BITS,
                                54
Pilani, India
Switching Fabric, Network Processors and
       the Semantic Gap <recap>
• Switching Fabric
       – High-speed Physical mechanism that allows the backplanes to execute
         low-latency switching
• Channels
       – Process-to-Process abstraction / view
       – Request-Response abstraction / view
       – Message-Stream abstraction / view
• Network Processors
       – Specialized network nodes optimized for functions like switching /
         routing / forwarding / provisioning etc.
• Semantic Gap
       – Gap between services / functionalities / features expected by
         applications and the capabilities of the networking technology

(c) Dr. Rahul Banerjee, BITS,
                                        55
Pilani, India
                             Any questions?



                              Thank you!




Wednesday 27 February 2008    (c) Dr. Rahul Banerjee, BITS-Pilani, INDIA   56