MIS 3523 Chapter 7

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MIS 3523 - Chapter 7

• LAN Topologies Media Access Control
• Dr. Segall - Fall 2001

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Review on LANs vs. WANs

• Ownership
• WANs can be either public or private
• LANs are usually privately owned
• Capacity
• LANs are usually higher capacity, to carry
  greater internal communications load

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LAN ApplicationsPC Networks

• Client/Server Communication
• Shared databases
• Shared hardware resources
• Shared Internet access
• Peer-to-Peer Communication
• Sharing work and information with colleagues
• Low cost is high priority
• Attachment costs in the hundreds of dollars

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LAN ApplicationsBackend Networks

• Computer room networks
• Interconnect large systems (mainframes,
  supercomputers, etc)
• Key requirement is high-speed bulk transfer
• Usually limited distance, few drops
• Speed more important than cost

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LAN ApplicationsHigh-Speed Office Networks

• Increased processing and transfer requirements in
  many applications now require significantly
  higher transfer rates
• Typical office LAN runs at 1-20mbps, insufficient
  for graphics-intensive applications
• Decreased cost of storage space leads to program
  and file bloat, increased need for transfer
  capacity

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LAN ApplicationsBackbone Local Networks

• Used instead of single-LAN strategy
• Better reliability
• Higher capacity
• Lower cost

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Tiered LANs

• Cost of attachment to a LAN tends to increase
  with data rate
• Alternative to connecting all devices is to have
  multiple tiers
• Bottom-up strategy individual departments create
  LANs independently, eventually a backbone brings
  them together
• Top-down strategy management develops an
  organization-wide networking plan

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IEEE Standards (pp. 190-194)

• Institute of Electrical and Electronics Engineers
• IEEE 802.1 - High-Level Interface
• 802.2 - Logic Link Control
• 802.3 - CSMA/CD bus
• 802.4 - Token Bus
• 802.5 - Token Ring
• 802.6 - MAN (see Figure 7-8 on pg.195)

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IEEE Standards (pp. 190-194) (Continued)

• 802.7 - broadband advisory
• 802.8 - fiber optic technical
• advisory
• 802.9 - integrated data and voice
• 802.10 - network security
• technical advisory
• 802.11 - wireless LANs
• 802.12- 100 VG-AnyLAN

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BASIC LAN Topologies (see Figure 7-1, p.185)

• Ring See also Figure 7-3 on page 187.
• IEEE 802.5
• token passing
• IBM
• FDDI/CDDI
• speeds

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Basic LAN Topologies

• Bus See also Figure 7-2 on page 186.
• IEEE 802.3
• CSMA/CD
• Ethernet
• token pasing - IEEE 802.4
• speeds
• ARCnet
• Carrier Sense with Multiple Access Collision
  Detection

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Basic LAN Topologies

• Star See also Figure 7-5 on page 190.
• StarLan
• ArcNet configuration NOT used much today.
• (Reference p.188)
• LANs with hubs
• See also Table 7-5 on page 206 for Protocol
  Summary for each LAN topology.

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LAN Topologies Bus

• Multipoint medium
• Stations attach to linear medium (bus) using tap
• Full-duplex between station and tap
• Transmission from any stations travels entire
  medium (both directions)
• Common transmission speeds are 1, 2,5, 5, 10, 100
  and 1000 Mbps.
• Termination required at ends of bus (See Figure
  7-2 for Spurs!)

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Bus LAN Diagram
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LAN Topologies Bus

• Generalization of Bus Topology Called Tree
• Branching cable with no closed loops
• Cable(s) begin at headend, travel to branches
  which may have branches of their own
• Each transmission propagates through network, can
  be received by any station

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Tree LAN Diagram
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Bus/Tree Topology Problems

• How do you identify who the transmission is
  intended for?
• Data transmitted in frames
• Each frame has header with addressing info
• How do you regulate access?
• Stations take turns sending, by monitoring
  control information in frames

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LAN Topologies Ring

• Repeaters are joined by unidirectional
  point-to-point links in a ring
• As a frame circulates past a receiver, the
  receiver checks its address, and copies those
  intended for it into a local buffer
• Frame circulates until it returns to source,
  which removes it from network
• Active vs. Inactive Nodes on page 187.

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Ring LAN Diagram
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LAN Topologies Star

• Each station connected directly to central node,
  usually with two unidirectional links
• Central node can broadcast info, or can switch
  frames among stations
• Star-wired LAN similar to ARCnet configuration
  in Figure 7-6.

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Star LAN Diagram (nodes should emanate in both
directions from central hub.)
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Choosing a Topology

• Factors to consider include reliability,
  flexibility/expandability, and performance
• Bus/tree is most flexible
• Tree topology easy to lay out
• Ring provides high throughput, but reliability
  problems.
• Star can be high speed for short distances, but
  has limited expandability

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Transmission Media Options

• Twisted pair--digital signaling
• Optical fiber--analog signaling
• Baseband coax--digital signaling
• Broadband coax--analog signaling
• Uses FDM to carry multiple channels
• Can be used over longer distances
• Inherently unidirectional, due to amplifier
  limitations

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Selecting Transmission Media

• Capacity Can it support expected network
  traffic?
• Reliability Can it meet requirements for
  availability?
• Types of data supported Is it well-suited to the
  applications involved?
• Environmental scope Can it provide service in
  the environments required?

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Medium and Topology

• Choices are related, but not on a one-to-one
  level
• Broadband not realistic in ring topology
• Until recently, fiber not realistic for bus
• Bidirectional baseband not best for tree

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Structured Cabling System

• Cabling scheme for wiring within a building
• Includes cabling for all applications, including
  LANs, voice, video, etc
• Vendor and equipment independent
• Designed to encompass entire building, so that
  equipment can be easily relocated
• Provides guidance for pre-installation in new
  buildings and renovations

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Wiring Layouts

• Wiring layout is different from topology
• Linear layout minimizes amount of cable
• Star layout uses individual cable from
  concentration point to subscribers
• Can be used for bus and ring as well as star
• Concentration point can be wiring closet or hub
  (an active node that accepts frames and
  regenerates signals for transmission)

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LAN Standards (802.x)

• Advantages of standards
• Assure sufficient volume to keep costs down
• Enable equipment from various sources to
  interconnect
• IEEE 802 committee developed, revises, and
  extends standards
• Use a three-layer protocol hierarchy physical,
  medium access control (MAC), and logical link
  control (LLC)

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Logical Link Control (LLC)

• Specifies method of addressing and controls
  exchange of data
• Independent of topology, medium, and medium
  access control
• Unacknowledged connectionless service (higher
  layers handle error/flow control, or simple apps)
• Connection-mode service (devices without
  higher-level software)
• Acknowledged connectionless service (no prior
  connection necessary)

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OSI Reference Model Layers (p.192, Fig 7-7)

• Application Layer
• Presentation Layer
• Session Layer
• Transport Layer
• Network Layer
• Data Link Layer
• Physical Layer
• See Benjamin Cummings Module Section 1,Program
  1 OSI Reference Model
• See Benjamin Cummings Module Section 2, Program
  4 SNA Session Flows

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Ethernet and CSMA/CD (IEEE 802.3)

• Carrier sense multiple access with collision
  detection
• Four step procedure
• 1. If medium is idle, transmit
• 2. If medium is busy, listen until idle and then
  transmit
• 3. If collision is detected, cease transmitting
• 4. After a collision, wait a random amount of
  time before retransmitting
• See Benjamin Cummings Module Section 2, Program
  2 Media Access
• See Table 7-2 on pg. 201 for CSMA/CD Protocol

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802.3 Medium Notation

• Notation formatltdata rate in Mbpsgtltsignaling
  methodgtltmaximum segment length in hundreds of
  metersgt
• e.g 10Base5 provides 10Mbps baseband, up to 500
  meters
• T and F are used in place of segment length for
  twisted pair and fiber

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IEEE 802.3 Alternatives

• See Table 7-1 on page 193.
• 10 BASE5
• 10 BASE2
• 10 BASE T
• 10 Broad 36
• 10 BASE F

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10BASE5 (Thick Ethernet)

• Original 802.3 medium specification
• 50-O coax and Manchester signaling
• Segment length can be extended past 500m with
  repeaters
• transparent at the MAC level
• maximum of 4 allowed
• No looping allowed--one path between any two
  stations

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10BASE2 (Thin Ethernet)

• Intended to provide lower-cost system for PC LANs
• Commonly called Thinnet or Cheapnet.
• Uses thinner cable and supports fewer taps than
  10BASE5
• Can combine 10BASE2 and 10BASE5 segments in the
  same network (but backbone must then be 10BASE5)

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10BASE-T

• Uses UTP, often prewired in buildings
• Star-shaped topology is well-suited to existing
  wires terminating in a closet
• Stations attach to central multi-port repeater
  (hub)
• Hubs can be cascaded
• Physical star, but logical bus (all transmissions
  are repeated)

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10BROAD36

• Only 802.3 broadband spec
• Uses 75 -O CATV coax
• Maximum length of individual segment is 1800m
• Broadband is by nature analog, so analog encoding
  must be used (DPSK)

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10BASE-F

• Standard includes 3 specifications (not in
  Chapter 7!)
• 10-BASE-FP Passive star topology, up to 1km per
  segment
• 10-BASE-FL Point-to-point link connecting
  stations or repeaters up to 2km
• 10-BASE-FB Point-to-point backbone link
  connecting repeaters at up to 2km
• Chapter 7 only talks about 100 Base-FX in Table
  7-1 on pg. 193.
• All specs use two fibers, one for transmission in
  each direction

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ANSI FDDI Standards (See pg. 194)

• Fiber Distributed Data Interface
• High speed LAN using fiber-optic cables
• Can be used as a backbone network as shown in
  Figure 7-10 on pg. 196.
• FDDI specifications call for a token-ring LAN
  operating at 100 Mbps.
• Maximum cable segment allowed without repeaters
  is 2 km.
• Token passing ring used for message passage.

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ANSI CDDI Standards

• Copper Distributed Data Interface
• Uses twisted-pair wires
• Used for shorter distances for wire lengths of
  100 m or less.

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Data Link Protocols

• Important aspects of the message exchange
  process
• delineation of data
• See Fig 7-12 on pg. 198 for Ethernet Message
  Formats
• error control
• addressing
• transparency
• code independence
• media access

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Data Link Protocols

• Transparency
• the ability to send any bit string as data in a
  message.
• the data bits are not interpreted as control
  characters.
• See Figure 7-13 on page 200 for start-of-text
  and end-of-text framing characters which
  provide transparency of data.

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MAC Protocols

• Media Access
• the way in which a device gains access to the
  medium
• i.e. the protocol by which a device gains the
  right to transmit data on the medium
• Contention
• when devices compete for control of the line
  either by transmitting directly on an idle line
  or by issuing a request for line control.
• See Table 7-2 on pg. 201 for CSMA/CD Media
  Access Control Protocol whixh is sometimes
  called Listen-before-Talk Protocol.

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MAC Protocols

• Token Passing
• lost tokens
• inserting new stations in token buses
• See Table 7-3 on page 202 for Token-Passing
  Media Access Control Protocol.

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Medium Access Control (MAC) (pp.196-202)

• Provide a means of controlling access to a shared
  medium
• Two techniques to consider CSMA/CD and token
  passing
• See Table 7-4 on page 205 for comparison of these
  two Media Access Control Protocols.
• See Figure 7-11 on page 197 for Token Passing in
  a FDDI LAN.
• See Benjamin Cummings Module Section 2, Program
  2 Media Access.

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Medium Access Control (MAC) (pp.196-202)

• LLC frames data, passes it to MAC which frames it
  again
• MAC control (e.g. priority level)
• Destination physical address
• Source physical address
• See Figure 7-12 on pg. 198 for Ethernet Message
  Formats.

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Making the Decisions

• Token Passing and CSMA/CD Compared
• See Table 7-4 on page 202.
• Notice that the only same item is the first
  listed of Access is equal for all nodes.
• All of the remaining items listed in this table
  are the opposite of each other.
• Topology and Protocol Tradeoffs
• See Table 7-5 on page 206.

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Chapter 7 LAN Topologies Media Access Control

• THE END!!!