Local Area Networks _020607_

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					Local Area Networks
          Dr. Malloy
     MIS 340 Spring 2007
      February 6, 2007

• Describe and define the similarities and differences of
• Identify the network requirements for business
• Compare and contrast the use and function of network
• Define logical vs. physical connections in networks
• Understand how networks connection requirements
  relate to business
          Network Terminology

Telecommunications - the study of telephones and
the systems that transmit telephone signals
Computer network - an interconnection of computers
and computing equipment using either wires or radio
waves over small or large geographic distances
Data communications - the transfer of digital or
analog data using digital or analog signals
Voice network - a network that transmits telephone
Data network - a network that transmits computer data
      Convergence of Computing and
• Reliance of telecommunications on computers
• Role of telecommunications in computing
• New wired and wireless transmission
• New combinations of data and computing
            Network Terminology

• Local area network (LAN) - networks that are small in
  geographic size spanning a room, building, or campus
• Metropolitan area network (MAN) - networks that serve
  an area of 3 to 30 miles - approximately the area of a
  typical city
• Wide area network (WAN) - a large network that
  encompasses parts of states, multiple states, countries,
  and the world
• Network management - the design, installation, and
  support of a network and its hardware and software
Interconnected Networks
      Personal Area Network (PAN)
• PAN - computer network for communication among computer
  devices close to one person.
   – reach is typically a few meters
   – used for communication among the devices or for connecting to higher
     network or the Internet

• Types of PAN
   – Wired: USB and Firewire
   – Wireless: IrDA and Bluetooth
          Local Area Network (LAN)
• LAN - group of computers and associated devices that share a
  common communications line or wireless link and typically share the
  resources of a single processor or server within a small geographic
• Types of LANS
   – Ethernet
   – Token Ring
   – FDDI (Fiber Distributed Data Interface)
   Metropolitan Area Network (MAN)
• MAN - large computer networks usually spanning a campus or a
  city. They typically use optical fiber connections to link their sites.

• Types of MANs
    – POS
    – ATM
    – Gig
          Wide Area Network (WAN)
• WAN - computer network covering a wide geographical area,
  involving vast array of computers. The best example of a WAN is the

• Types of WANs:
   – Private
   – Public
            Storage Area Network (SAN)
• SAN - network of storage devices that are connected to each other
  and to a server, or cluster of servers, which act as an access point
  to the SAN.

• Types of SANs
    – Centralized
    – Decentralized
                       Server Farm
• Server Farm - collection of computer servers usually maintained by
  an enterprise to accomplish server needs far beyond the capability
  of one machine.
• Types of Servers:
   –   Email
   –   Web
   –   FTP
   –   image
          Value Added Network (VAN)
• VAN - computer network put in by a third party who also provides
  additional "value," i.e., they maintain the network, administer it,
  provide services not available from common network carriers, etc,
  usually for a fee.

• Types of VAN:
    –   Conferencing
    –   Voicemail
    –   Video
    –   Distance Education

Major benefits of LANs are:
  – Client/server communication
  – Shared resources
  – Peer-to-peer communication
  – Low cost is high priority
                LAN Architecture

• LAN architecture is the overall design of a LAN. It
   – LAN hardware
   – LAN software
   – LAN topology
   – Media access control (MAC) protocol

• The LAN’s network operating system is sometimes also
  considered to be part of LAN architecture
                   LAN Hardware

• LAN Hardware is composed of many devices,
   – workstations
  –   servers
  –   bridges
  –   routers
  –   hubs and switches
  –   nodes
• Servers enable network users to access shared
  computing and communication services. A variety of
  servers are found in LANs including:
   –   File servers
   –   Print servers
   –   Database servers
   –   Application servers
   –   Fax servers
   –   Remote access servers
   –   Communication servers
   –   Terminal servers
   –   Thin client servers
   –   Citrix™ servers
                   Layer 1 Hubs

• Alternative to bus topology
• Each station is connected to the hub by two lines
  (transmit and receive)
• When a single station transmits, the hub repeats the
  signal on the outgoing line to each station.
• Hubs can be cascaded in a hierarchical configuration.
Two-Level Hub Topology

• Hubs are used to provide device interconnection
   – A hub is a central interconnection point for workstations,
     servers, and other network equipment that is used in
     numerous LAN implementations to provide node-to-node
   – Because a hub does not process the frames transmitted by
     network-attached computers, it is often considered to be
     physical layer devices

• Hubs vary in terms of:
   –   LAN architecture (e.g. Ethernet vs. token ring)
   –   number of ports
   –   stand-alone vs. stackable
   –   unmanaged vs. managed
                Layer 2 Switches

• Has replaced hub in popularity, particularly for high-
  speed LANs
• Provides greater performance than a hub
• Incoming frame from a particular station is switched to
  the appropriate output line to be delivered to the
  intended destination
• At the same time, other unused lines can be used for
  switching other traffic

• Switches physically resemble hubs and vary in terms of:
   –   LAN architecture (e.g. Ethernet vs. token ring)
   –   number of ports
   –   stand-alone vs. stackable
   –   unmanaged vs. managed

• Switches read and process transmitted frames in order
  to provide a switched connection between network-
  attached devices
   – Switches are considered data link layer (or higher) devices

• Some switches support virtual LANs (VLANs).
   – A VLAN is a logical group of workstations interconnected by one
     or more LAN switches that function as a self-contained LAN or
                 Types of Switches
• Store and forward switch
   – Accepts a frame on input line
   – Buffers it briefly
   – Routes it to appropriate output line

• Cut-through switch
   – Begins repeating the frame as soon as it recognizes the
     destination MAC address
   – Higher throughput, increased chance of error
   Advantages of Layer 2 Switches

• No modifications needed to workstations when replacing
  shared-medium hub
• Each device has a dedicated capacity equivalent to
  entire LAN
• Easy to attach additional devices to the network
 Disadvantages of Layer 2 Switches

• Broadcast overload
• Lack of multiple links
• Can be solved with subnetworks connected by routers
• However, high-speed LANs layer 2 switches process
  millions of packets per second whereas a software-
  based router may only be able to handle well under a
  million packets per second
                  Layer 3 Switches

• Implement the packet-forwarding logic of the router in
• Packet-by-packet switch operates like a traditional router
   – Forwarding logic is in hardware
   – Achieves an order of magnitude increase in performance
     compared to software-based routers

• Flow-based switch identifies flows of IP packets that
  have the same source and destination
   – Once flow is identified, a predefined route can be established to
     speed up the forwarding process
   – Again, huge performance increases over a pure software-based
     router are achieved
• Allow connections between LANs and to WANs
• Used between networks using identical physical and link
  layer protocols
• Makes no modification to content or format of frames it
  receives; simply copies from one LAN and repeats with
  exactly the same bit pattern as the other LAN.
• Should contain enough buffer space to meet peak
• Must contain addressing and routing intelligence.
• Provide a number of advantages
   –   Reliability: Creates self-contained units
   –   Performance: Less contention
   –   Security: Not all data broadcast to all users
   –   Geography: Allows long-distance links
               Bridge Functions

• Read all frames from each network
• Accept frames from sender on one network that are
  addressed to a receiver on the other network
• Retransmit frames from sender using MAC protocol for
• Must have some routing information stored in order to
  know which frames to pass
Bridge Operation
          Switches versus Bridges

• Bridge frame handling is done in software. A layer 2
  switch performs the address recognition and frame
  forwarding functions in hardware.
• Bridges typically only analyze and forward one frame at
  a time; a layer 2 switch can handle multiple frames at a
• Bridges uses store-and-forward operation; layer 2
  switches use cut-through instead of store-and-forward
• New installations typically include layer 2 switches with
  bridge functionality rather than bridges.

• Routers are the most powerful networking device used
  today to interconnect LANs

• Routers use network address (network layer) to make
  routing decisions regarding forwarding data packets
   – Routers are configured to know how to route packets entering and
     exiting the LAN.
• Routers are used to interconnect:
   –   LANs in a campus network
   –   LANs that use the same or different protocols and hardware
   –   LANs around the country and the world
   –   Many different networking protocols

• Routers have multiple ports connections for connecting
  LANs and by definition must have a minimum of three
• Routers are bidirectional
   – Data can enter and exit through the same router port

• Brouter is a device that contains both a router and a
                  LAN Topologies
• There are two types of LAN Topologies: physical and logical
• Physical LAN topology refers to the physical layout of the
   – The way in which the communication is configured and how
     nodes attach to the network
   – Because the focus is on physical connections among hardware
     component, physical topologies correspond to the physical layer
     of the OSI reference model

• Logical topology is concerned with how messages are passed
  from node to node within the network
Physical Topologies
               Physical Topologies

• LAN’s have three basic physical topologies:
   – bus: all nodes attach to a common communication pathway or
   – ring: the medium forms a loop to which all nodes are attached
   – star: uses a central station (hub or switch) to which all other
     nodes have point-to-point connections; all communication
     among nodes occurs through this central station

• Physical star topologies are most common in today’s
                   Bus Topology

• In a classic bus topology, the medium consists of a
  single wire or cable to which other nodes are attached
  via connectors or transceivers:
   – Variations include a primary bus with spurs

   – Disadvantages include the potential for loose connections
     or breaks in the bus to disrupt the entire network
                   Ring Topology
• In a physical ring topology, the communication medium
  forms a closed loop (ring) and all stations are connected
  to the loop
   – Data is transmitted node-to-node in one direction on the
   – Similar to a linear bus, the entire network could be
     disrupted if one of the connectors or links in the ring
     should fail

• Token ring and Fiber Distributed Data Interface (FDDI)
  LANs have physical ring topologies
                   Star Topology

• In a star topology, all nodes are connected to some kind
  of wiring center such as a hub or switch
   – Most LAN implementations physically resemble star
   – Each node is isolated on its own network segment in a
     physical star topology which minimizes the possibility of
     total network disruption by a malfunctioning connector,
     NIC, or link
   – The network is vulnerable to wiring center failure
Choosing Among LAN Architectures

• Important factors to consider include:
  – Immediate and recurring LAN costs Total Cost of
    ownership (TCO)
  – Number of concurrent users that can be supported
  – Transmission speed and data throughput
  – Vendor support
  – Manageability
  – Scalability/expandability
  – Security
  – Adherence to widely accepted standards
 IEEE LAN Standards & Committees

• 802.1 High-Level          • 802.7 Broadband
  Interface                   Technical Advisory Group
• 802.2 Logical Link        • 802.8 Fiber Optic
  Control                     Technical Advisory Group
• 802.3 CSMA/CD             • 802.9 Integrated Data
                              and Voice Networks
• 802.4 Token Bus
                            • 802.10 LAN Security
• 802.5 Token Ring
                            • 802.11 Wireless LANs
• 802.6 Metropolitan Area
  Networks (MANs)           • 802.12 Demand Priority
                              Access Method
     Basic Network Configurations
• Computer terminal to mainframe computer
• Microcomputer to mainframe computer
• Microcomputer to local area network
• Microcomputer to Internet
• Local area network to local area network
• Local area network to wide area network
• Sensor to local area network
• Satellite and microwave
• Wireless telephone
Computer terminal to mainframe computer

• Used in many types of businesses for data entry and
  data retrieval.
• Usually involves a low-speed connection.
 Microcomputer to mainframe computer

• Very common throughout business and academic
• Typically a medium- to high-speed connection.
        Microcomputer to Internet

• Very popular with home users.
• Typically a modem is used to connect user’s
  microcomputer to an Internet Service Provider
• Newer technologies such as DSL and cable modems are
  replacing modems.
                    LAN to LAN

• Found in businesses and schools that have two or more
  LANs and a need for them to intercommunicate
• The bridge is a typical device used to interconnect LANs
Local area network to wide area network

• One of the best ways to interconnect a user on a
  workstation to the Internet (a wide area network).
• A router is the typical device that performs LAN to WAN
      Sensor to local area network

• Often found in industrial environments.
• Assembly lines and robotic controls depend heavily on
  sensor-based local area networks.
          Satellite and microwave

• Many types of applications including long distance
  telephone, television, radio, long-haul data transfers, and
  wireless data services.
• Typically expensive services but many companies offer
  competitive services and rates.
        Wireless/mobile telephone

• Quickly expanding market across the U.S. and world.
• First generation analog services and second generation
  PCS services available in most areas and under many
  types of plans.
• Third generation services beginning to appear in Europe
  and Asia.

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