Computer Networks

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Computer Networks Powered By Docstoc
					Who is Who in the Internet ?
   Internet Engineering Task Force (IETF): The IETF is
    the protocol engineering and development arm of the
    Internet. Subdivided into many working groups, which
    specify Request For Comments or RFCs. (www.ietf.org)
   IRTF (Internet Research Task Force): The Internet
    Research Task Force is a composed of a number of
    focused, long-term and small Research Groups.
     E.g., Anti-spam group, delay tolerant networking group,
       Network management group, Routing research group,
       Peer-to-peer research group (www.irtf.org)
   Internet Architecture Board (IAB)
   The Internet Engineering Steering Group (IESG)
Internet Standardization Process
   All standards of the Internet are published as RFC
    (Request for Comments).
   A typical way of standardization is:
       Internet Drafts
       RFC
       Proposed Standard
       Draft Standard (requires 2 working implementation)
       Internet Standard (declared by IAB)
   Consensus based standardization
At The Not So Very
Beginning
Necessity

   Proliferation of Computers in Public and Business
    Utilities
   Availability of Data Based Services (no pun
    intended)
   End User Growth
   Communication Technology Evolved
   Research and Commercial Motives
Sample Applications

   Remote Access to Resources
       E.g., Telnet
   Shared access to data/files
       FTP, NFS, AFS
   Remote Computer Aided Learning
       Online audio/video lectures, web casting, demos
   Remote Data Operations and Computation
       E.g., Airline reservation systems, inventory control systems
   Other applications like, e-mail, ftp, http, p2p, instant
    messaging, news groups etc
   Now: IP-* (Telephony, TV, Radio, Movies, Music etc)
Network Classification Parameters

   Latency
   Bandwidth
   Loss rate
   Number of end systems
   Service interface (how to invoke?)
   Other details
         Reliability
         Communication capability: unicast, multicast, broadcast
         Applicability: E.g., Real-time (e.g., postal service?)
         Switching technology: message vs. packet
Network Classification Parameters...

   Communication Medium: Electrons and photons
   Links: Optical fiber, copper, satellite, etc
   Switches: Electronic/optical, crossbar/Banyan
   Protocols: TCP/IP, ATM, MPLS, SONET,
    Ethernet, PPP, X.25, FrameRelay, AppleTalk,
    IPX, SNA
   Functionalities: Routing, error control,
    congestion control, Quality of Service (QoS)
   Applications: FTP, WEB, X windows, SSH
Types of Computer Networks

   Geographical distance
       Local Area Networks (LAN): Ethernet, Token ring, FDDI
       Metropolitan Area Networks (MAN): DQDB and later, SMDS
       Wide Area Networks (WAN): X.25, ATM, frame relay
   Information type
       Data networks vs. telecommunication networks
   Application type
       Special purpose networks: airline reservation network, banking
        network, credit card network, telephony
       General purpose network: Internet
Types of Computer Networks

   Right to use
       private: enterprise networks
       public: telephony network, Internet
   Ownership of protocols
       proprietary: SNA, DNA
       open: IP
   Technologies
       terrestrial vs. satellite
       wired vs. wireless
   Protocols
       IP, AppleTalk, SNA
Definition of Computer Network

   A computer network is an interconnected
    collection of autonomous computers.
     Two computer are interconnected if they are able to
      exchange information
     Two computer are autonomous if they are capable of

      operating independently, that is, neither is capable of
      forcibly starting, stopping, or controlling the other
     Network users (not necessarily application users) are

      aware of the network existence
    Autonomous
Just to be clear –What are not Computer
Networks
   Master/slave systems (ref. any centralized cluster)
   Single-host networks (E.g., UNIX)
   Multi-computers, such as the hypercube (ref. parallel computing)
   In terms of (operating) systems, there is some distinction between
    network systems and distributed systems
     Distributed system gives the view of a single computer to the user (user
        not aware of networking behind scenes)
     Failure of any node in the system might stop other nodes from operating
        correctly (non-autonomous)
     Focus is on software, distributed computation, that can do better
        resource sharing, concurrent processing etc
   Important problems: load balancing, fault-tolerance, mutual exclusion
Now That We are Clear

   How to build a computer network?
       Agree upon the communication technique (circuit
        switching or store-and-forward switching)
       Develop communication languages for hosts to interact
        (protocols)
       Implement appropriate functionality without affecting
        the computer’s performance (designing the protocol
        stack)
       Develop network-centric algorithms (routing,
        reliability, congestion control)
Types of Communication Networks
   Exchange mechanism
                                   Communication
                                     Network


          Switched                                          Broadcast
        Communication                                     Communication
          Network                                           Network



 Circuit-Switched       Packet-Switched
 Communication          Communication
     Network               Network


                    Datagram    Virtual Circuit Network
                    Network
Broadcast vs. Switched
Communication Networks
   Broadcast communication networks
       information transmitted by any node is received by every
        other node in the network in range
           E.g.,: usually in LANs (Ethernet, Wireless) , Radio
       Problem: coordinate the access of all nodes to the shared
        communication medium (Multiple Access Problem)
   Switched communication networks
       information is transmitted to a sub-set of designated nodes
           Examples: WANs (Telephony Network, Internet), ATM
       Problem: how to forward information to intended node(s)
           This is done by special nodes (E.g., bridges, routers,
            switches) running routing protocols
A Taxonomy of Communication
Networks
                                   Communication
                                     Network


          Switched                                          Broadcast
        Communication                                     Communication
          Network                                           Network



 Circuit-Switched       Packet-Switched
 Communication          Communication
     Network               Network


                    Datagram    Virtual Circuit Network
                    Network
Circuit Switching

   Three phases
    1.   circuit establishment
    2.   data transfer
    3.   circuit termination
   If circuit not available: “Busy signal”
   Examples
        Telephone networks
        ISDN (Integrated Services Digital Networks)
Timing in Circuit Switching
    Host 1                                               Host 2
                 Node 1          Node 2



                           processing delay at Node 1
                                                        propagation delay
                                                        between Host 1
Circuit                                                 and Node 1
 Establishment
                                                        propagation delay
                                                        between Host 2
                                                        and Node 1
Data
Transmission
                          DATA

Circuit
Termination
Circuit Switching

   A node (switch) in a circuit switching network
          incoming links   Node   outgoing links
Circuit Switching:
Multiplexing/Demultiplexing



     Time divided in frames and frames divided in slots
     Relative slot position inside a frame determines which
      conversation the data belongs to
     Needs synchronization between sender and receiver
     In case of non-permanent conversations
         Needs to dynamic bind a slot to a conservation
         How to do this?
A Taxonomy of Communication
Networks
                                   Communication
                                     Network


          Switched                                          Broadcast
        Communication                                     Communication
          Network                                           Network



 Circuit-Switched       Packet-Switched
 Communication          Communication
     Network               Network


                    Datagram    Virtual Circuit Network
                    Network
Packet Switching
   Data are sent as formatted bit-sequences, so-called packets.
   Packets have the following structure:


               Header                    Data                   Trailer


          Header and Trailer carry control information (e.g., destination
           address, check sum)
   Each packet is passed through the network from node to node along
    some path (Routing)
   At each node the entire packet is received, stored briefly, and then
    forwarded to the next node (Store-and-Forward Networks)
   Typically no capacity is allocated for packets
Packet Switching

   A node in a packet switching network
          incoming links   Node     outgoing links

                           Memory
Packet Switching:
Multiplexing/Demultiplexing




   Data from any conversation can be transmitted at
    any given time
   How to tell them apart?
       use meta-data (header) to describe data
A Taxonomy of Communication
Networks
                                   Communication
                                     Network


          Switched                                          Broadcast
        Communication                                     Communication
          Network                                           Network



 Circuit-Switched       Packet-Switched
 Communication          Communication
     Network               Network


                    Datagram    Virtual Circuit Network
                    Network
Datagram Packet Switching

   Each packet is independently switched
       Each packet header contains destination address
   No resources are pre-allocated (reserved) in
    advance
   Example: IP networks
 Timing of Datagram Packet Switching
      Host 1                                                               Host 2
                              Node 1               Node 2




                                       propagation
                                       delay between
transmission
                                       Host 1 and
time of Packet 1   Packet 1                                  processing
at Host 1
                                       Node 2
                                                             delay of
                   Packet 2
                                        Packet 1             Packet 1 at
                   Packet 3                                  Node 2
                                        Packet 2
                                                            Packet 1
                                        Packet 3
                                                            Packet 2

                                                            Packet 3
Datagram Packet Switching

                             Host C

  Host A                                                Host D

           Node 1   Node 2
                                               Node 3

                        Node 5




  Host B
                                      Node 7               Host E
                        Node 6
           Node 4
A Taxonomy of Communication
Networks
                                   Communication
                                     Network


          Switched                                          Broadcast
        Communication                                     Communication
          Network                                           Network



 Circuit-Switched       Packet-Switched
 Communication          Communication
     Network               Network


                    Datagram    Virtual Circuit Network
                    Network
Virtual-Circuit Packet Switching

   Hybrid of circuit switching and packet switching
       data is transmitted as packets
       all packets from one packet stream are sent along a pre-
        established path (=virtual circuit)
   Guarantees in-sequence delivery of packets
   However: Packets from different virtual circuits
    may be interleaved
   Example: ATM networks
Virtual-Circuit Packet Switching

   Communication with virtual circuits takes place
    in three phases
    1.   VC establishment
    2.   data transfer
    3.   VC disconnect
   On demand circuit setup, several packets may
    share same virtual link
Packet-Switching vs. Circuit-
Switching
   Most important advantage of packet-switching over
    circuit switching: Ability to exploit statistical
    multiplexing:
       efficient bandwidth usage; ratio between peek and average rate is
        3:1 for audio, and 15:1 for data traffic
   However, packet-switching needs to deal with
    congestion:
       more complex routers
       harder to provide good network services (e.g., delay and
        bandwidth guarantees)
   In practice they are combined:
       IP over SONET, IP over Frame Relay

				
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