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Network Design – Theory _ Practice EIE507 – 2006 Fall Introduction by pengxiang


									Network Design – Theory & Practice
        EIE507 – 2006 Fall
                                Presented by:
                                SUNG, Sai Ping
  Part-time Visiting Lecturer   IP Support Manager
  HK PolyU                      REACH Networks Ltd
  Email:       Email :
                                Phone : 852-2983-3060
•   Introduction and network model
•   Switching Techniques
•   Network Standards
•   Industrial Trends and Developments
•   Basic Communication Models
•   Challenges of Network Design
•   Network Services by Telecom Industry
• The telecommunication (and computer
  communication) networks are undergoing
  rapid changes in network components
  (switches and transmission equipment),
  architecture (topology and control),
  protocols, and services.

Acknowledgement: the notes in this introduction part are based on Dr. C. K. Leung’s notes for the same subject offered previously.
                           Network Model
A generic model of network is as shown in the following:
          user                                           user


   user                           communication subnet
              Network Model
• According to the above model, users gain access
  to a communication subnet via an access network,
  and communicate with each other.
• The purpose of the access network is to grant
  users access to the subnetwork, it may be a simple
  dial-up line, terminal concentrator serving several
  terminals, a local area network with a router or a
  gateway, a mobile network, ...
           Network Model
• The network subsystems may consist of
  transmission systems, switching systems,
  and the signaling systems.
   Transmitter                                Transport                         Receiver
Customer Premise    Network                                                       Customer Premise
 Equipment (CPE)                                                Network           Equipment (CPE)
                     Access           PSTN
     Telephone                                                   Access               Telephone
     PBX                              PSDN                                            PBX
                    subscriber        private data networks
     FAX                                                        subscriber            FAX
     Multiplexers                                                   loops
     Modems                                                                           Modems

                              Host                node                   node


                                                           Communication subnet
          Purpose of Network
• Information is transmitted in the subnet
  from an origin site r via nodes of the subnet
  to a destination site t. The pair (r, t) will be
  termed the origin-destination (O-D) pair.
• Control information is generated at subnet
  nodes and sent to other subnet nodes as
          Error handling and
• covered in standard data communications
• handled by a suitable line protocol, or data
  link layer protocol
• to ensures “almost” error-free transmission
• the effect on network design:
1) Delay 2) Increased data flow
    The scope and extent of network
•   Routing                     •   Network topology
•   Congestion control          •   Network security
•   Flow control and policing   •   Reliability
•   Switching, transport and    •   Capacity
    transmission                •   Performance
• In a packet-switched network, routing deals
  with selecting a path to guide information
  within the subnet for an O-D pair.
• In a circuit-switched network, routing deals
  with selecting circuits to connect an O-D
• Offered load is the traffic input into a
• Throughput is the traffic that can get
  through a subnet successfully.
• A general relationship between offered load
  and throughput is:

                           Ideal case:
                           Throughput = Offered load
throughput (packets/sec)


                                   congestion begins

                                     offered load
•   At first, the offered load will be taken by the network and hence the
    throughput will be equal to the offered load.

•   As the offered load increases, the network cannot handle all the traffic,
    the increase in throughput is smaller than the increase in offered load,
    some of the offered load cannot be served and is lost.

•   Any further increase in offered load will tie up the network resources to
    such an extent that the throughput actual decrease, this is a situation of

•   The worst case of congestion is deadlock where some resources of the
    network are tied up permanently if no extra work (such as a reset of a
    node) is done.
              Flow Control
• Flow control can be interpreted as the
  regulation of flow between two entities. It
  may be between a terminal and a
  subnetwork node, or between two users
  connected across a subnetwork.
• E.g. Weighted Random Early Detection on
  TCP/IP packet flow
              Flow Control
• The purposes are
  – matching of different speeds between two
  – prevention of throughput and response time
    degradation due to increase in offered load
  – fair allocation of sources among competing
          Reactive vs Preventive
• Reactive: flow-control commences after congestion has
  developed within a subnetwork, popular for "old time"
  packet networks (i.e., not high speed network).

• Preventive: flow-control is effective to police the traffic
  generated by a source, to make it conform to the traffic
  contract made between the subnetwork and the source
  when admission to the subnetwork is granted; this is more
  popular in high-speed network such as ATM
  (asynchronous transfer mode) networks.
      Network Classifications
• Geographical extent based:
  – local area networks (LAN) - restricted to
    several km, a single office or a factory floor
  – metropolitan area networks (MAN) – 10’s of
    km, a campus
  – wide area networks (WAN) - 100 or 1000 of
    km, international
  – terrestrial radio networks - wireless
  – satellite networks – international
         Network Classifications
• centralized vs. distributed   • mesh (fully-connected),
  (control regime)                bus, ring, star, tree
• private vs. public              topologies
  (ownership)                   • broadcast networks
• voice, data and video         • switched networks
  (information type)               – signals have to be "routed"
• analog, digital, radio,            through intermediate
                                     network points (network
  satellite (transmission            nodes, or switches) to their
  technique)                         desired destination
          Switching Techniques
• According to the switching technique, for the
  packet-switched network, routing can be further
  divided into virtual-circuit or datagram operation
   – In virtual-circuit mode routing, a virtual circuit, which
     is a sequence of subnetwork nodes, is set up for an O-D
     pair and then packets are guided over the same virtual
   – In datagram mode routing, each packet is routed from
     O to D independently. If a network problem occurs, the
     packets may be routed so as not be affected by the
     network problem (e.g. bypassing a failed link).
An illustration of different modes of switching:
                                 A       B                 C         D

     Call Request Signal


            Call Accept


     A    B       C          D       A       B       C      D    A       B       C        D
         Circuit switching                   Message switching             Packet switching
           Circuit Switching
• Establish dedicated circuit between nodes
  and terminals before the users communicate
• Each user has sole access to a circuit during
  network use
• E.g. Public Telephone Switching Network
       Message Switching
• A continuous path is not established.
• Message is sent from one node to the next node,
  stored, and then sent to the further next node
  until the destination is reached.
• also known as “store-and-forward networks”
• Some nodes may experience message queuing
  and congestion.
            Packet Switching
• A "message" is divided into a series of “packets"
  of limited lengths.
• These packets traverse the network until they
  reach the desired node, where they are
  reassembled into the corresponding message.
• Many packets of the same message may be
  transmitted within the network simultaneously,
  thus reducing delay.
   Difference between Circuit &
         Packet Switching
Circuit Switching           Packet Switching
• guaranteed bandwidth      • Best effort based
• Establish a path before   • No specific pre-
  sending data                defined path
• Sequential data flow      • Re-order packet
                              sequence is allowed
• Dedicated data path       • Diversified data paths
Example – Internet traffic packet
         switching (I)
• Step 1:
   – An application generates a message in which the data is
• Step 2:
   – Transmission Control Protocol (TCP) or User
     Datagram Protocol (UDP) breaks the data into units
     called segments (in TCP) or datagrams (in UDP). A
     header is appended to the front of the packet that helps
     with processing at the destination site.
Example – Internet traffic packet
        switching (II)
• Step 3:
  – Internet Protocol (IP) adds a source and
    destination IP address as part of the the
    digitized packet.
• Step 4:
  – The packet is transmitted from a host computer
    through a series of routers until it arrives at its
    final destination and is directed to the proper
    host computer there.
Example – Internet traffic packet
        switching (III)
• Step 5:
  – After a packet is received at the destination end,
    the digital packet and all headers are discarded.
    The data inside can be recombined with the
    data from other packets that make up a
    complete piece of information
• All works of directing and forwarding
  traffic on the internet was handled by
       Packet Switching Illustration
              Packet forwarding path

Header Data

           Cell Switching
• Closely resemble packet switching
• Fixed-size packet
• Offer, in principle, bounded delay
• E.g. Asynchronous Transfer Mode (ATM)
• International Telecommunications Union (ITU)
  under the United Nations, further divided into:
   – ITU Telecommunications Sector (ITU-T), formerly the
     Comite Consultatif Telegraphique et Telephonique
     (CCITT), and
   – ITU Radiocommunications Sector (ITU-R),
     formerly the Comite Consultatif International des
     Radiocommunications (CCIR)
   – International Standards Organization (ISO)
   – European Telecommunications Standards Institute (ETSI)
– National standards bodies such as American National
  Standards Institute (ANSI), British Standards
  Institute(BSI), Deutsches Institut fur Normung (DIN)
– large learned societies and professional bodies such as
  Institute of Electrical and Electronic Engineers (IEEE)
– prominent groups and associations from industry, such
  as Electronics Industry Association (EIA), ATM
– large companies such as: Bell Companies Research and
  Engineering organization (Bellcore), IBM, DEC
Transmission Signaling
                  Digital Hierarchy
• An example: American system

     1                    1                  1
            T1                 T2                 T3
     2      MUX
                          2    MUX
                                             2    MUX
                                                        44.736 Mbps

    24                    4                  7
   64kbps          1.544Mbps         6.312 Mbps
                   T1                DS2
Synchronized Digital Hierarchy
 (SDH) Multiplexing Scheme
 Synchronous Optical Network
(SONET) Multiplexing Scheme
       Pulse Code Modulation
• Pulse Coded Modulation (PCM) is a system to
  transmit speech signals in digital format.
• A block diagram:
                  LPF       Sample      A/D
                              &      Conversion   M
                             Hold                 U
                        .                         P
                        .                         E
                        .                         I

                  LPF       Sample      A/D
                              &      Conversion
  Analysis in switched networks
• Packet switching: delay
• Circuit switching: blocking probability

       An example of fully
       connected terminals

 For N fully connected terminals, it requires N(N-1)/2 lines and N(N-1)
 switches so that every user can connect to any other, provided it is not
 engaged, this an example of non-blocking switch.
• Blocking: when A wants to connect to B and B is available,
  but the connection cannot be set-up due to the problem of
  the switch, the call is blocked.
                             subscriber’s      exchange

• In general, there will be M inlets and N outlets and the
  total number of cross-points needed is MN, the number of
  simultaneous connections that can be made is either the
  smaller of M and N.


                    a     b       c

           A                                          N
                                      M      N

           C                                      M

 Industrial Trends & Developments

• Analogue communication to Digital
• Voice Network – mainly circuit switched
• Data Network – mainly packet switched
  Network Development - Voice
• Telegraph (in 1838 with the introduction of
  Morse code in 1844)
• Telephone (in 1876)
• Wireless Radio Transmission (in 1901)
• Satellite Transmission (in 1965 Intelsat 1
  with 240 phone circuits)
• Optical Cable Transmission
  Network Development - Data
• Wide Area Network (WAN)
  – Developed in 1970’s
  – Limited to long-distance networks
• Local Area Network (LAN)
  – Developed in 1980’s
  – Ethernet standard
• WAN & LAN Integration
  – Started in 1990’s
  Basic Communication Models
• Centralized Network
     • All nodes are connected directly and ONLY to a
       centralized hub or switch
• Decentralized Network
     • Several small centralized networks join together
• Distributed Network
     • Each node would be connected to several of its
       neighboring nodes in a sort of lattice-like
Communication Models

   Source: Baran, Rand Memorandum 3420-PR, CH.1
 Basic Communication Model –
Open System Interconnection (OSI)
 •   Developed by the International Organization for Standardization (ISO)
 •   As a guideline for developing standards to enable the interconnection
     of dissimilar computing devices
 •   Seven layers : physical, data link, network, transport, session,
     presentation, and application layers
                 OSI Model
• Physical
    – Defines the electrical, mechanical, procedural, and functional
      specifications – transmission of (raw) signals (bits)
• Data link
    – Provides a reliable transit of data across a physical link,
      concerned with physical addressing, network topology, line
      discipline, error notification, the ordered delivery of frames, and
      flow control.
• Network layer
    – Provides connectivity and path selection between two end
      systems. Routing occurs at this layer
                  OSI Model
• Transport layer
    – Provides error recovery and flow control between two end points
      of the network connection
• Session layer
    – Establishes and manages end users connections and manages the
      interaction between end system
• Presentation layer
    – Performs data transformation to provide a common interface for
      user applications. E.g. data compression/encryption
• Application layer
    – Delivers service directly to user applications
OSI Model Illustration:
The applications, the OS,
and the hardware
implement the seven
functions described in the
OSI model are working

                          SOURCE: http:/
    Centralized network design
• Example : Deploy in Voice over IP application

    Distribution network design
• Example : For geographically dispersed remote sites

    Challenges of Network Design
•   Scalability
•   Security
•   Availability
•   Manageability
• Dramatic increase in size of network that
  imposes chances of instability and change
  – i.e. failures, bursty traffic
• Solutions :
  – Hardware redundancy
  – Transmission path redundancy
• Capability of future network expansion due
  to natural/ad-hoc growth
• Solutions:
  – Design dynamic logical architecture
  – Deploy state-of-the-art hardware
• Denial of Service Attacks (DoS Attack)
• Spoofing : host disguising as another
• Solutions:
  –   Firewall protection
  –   Intrusion detection device
  –   Active network traffic inspection
  –   Network profiling
• Device Management
• Logical routing management
• Solutions:
  – Proactive network monitoring tools
  – Centralized management server
  – Dedicated & out-of-band management segment
  Network Services by Telecom
• Voice Service
   – Fixed Line
   – Wireless
   – Voice Over IP (VoIP)
• Satellite Service
   –   TV Broadcast
   –   Satellite Private Lease Line
   –   Digital Video Broadcast-IP Satellite Internet Access
   –   Teleport Service
  Network Services by Telecom
• Data Service
  – Private Lease Line (International and domestic)
  – Frame Relay, ATM
  – Internet Protocol Services
     •   International and Local Internet Exchange
     •   Dedicated Internet Access
     •   Multi Protocol Labe Switching – Virtual Private Network
     •   Layer 2 Virtual Private Network
     •   Internet Data Center
     •   Internet Version 6 Connectivity
              Data Service
• Frame Relay (FR) and Asynchronous
  Transfer Mode (ATM) Internet Access
  – Flexible in bandwidth expansion
  – Perform statistical multiplexing in service
    provider network
  – Need to understand the amount of aggregation
    performed by the FR or ATM network to avoid
    performance degradation
Example of Internet Connectivity
Internet     Provider’s

                                                                    e.g. Router

                                                    Local Tail
  Provider                                                                        Customer
                                Cable     Cable
                                Station   Station

                   Management Domain of
                     Service Provider

                                                Backbone Router             CSU/DSU
                                                Edge Router                 Local Tail

                                                Customer Premises           International Circuit
Basic Network Elements in

                ISP Service
• Dedicated Internet Access
  – Used when bandwidth utilization is predictable
    and the frequency of network access is high
    enough to justify a line’s being up 24 hours a
  – Involved termination of the physical circuit on
    the Customer Premises Equipment (CPE)
                  ISP Service
• Dial-up Services
   – Traditional modem access, Integrated Service Digital
     Network (ISDN), Basic Rate Interface (BRI) of up to
     128kbps, Primary Rate Interface (PRI) with speeds up
     to 1.5Mbps
   – Digital Subscriber Line (DSL) service that utilizes
     existing twisted-pair coppers loops in Plain Old
     Telephone System (POTS)
   – Cable Modem that utilizes existing fiber and coaxial
     cable TV infrastructure.
                ISP Service
• Dedicated Hosting Services
  – Provides co-location facilities for content
• Higher-layer services
  –   Web-hosting
  –   Email
  –   News group
  –   Domain Name Service
• P. Oppenheimer, Top-Down Network Design,
  Cisco Press, 1999.
• ANSI T1.105.xx Telecommunications,
  Synchronous Optical Network (SONET)
• ITU-T Recommendation G.707 (1996), Network
  node interface for the synchronous digital
  hierarchy (SDH)

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