LAN Concepts

1
LAN Concepts

• What is a LAN?
• High speed communication line for data processing
  equipment in a limited geographic area
• Configuration of transmission facilities to
  provide communication in a limited geographic
  area
• 2 or more micro computers communicating through a
  physical medium

2
Components of LAN

• Major components are
• Hardware
• Software
• Now, a much more detailed explanation of the above

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Hardware

• FILE SERVER - High speed, high capacity PC that
  serves same role as computer in a mainframe
  environment
• WORK STATIONS - IBM compatible, Macintosh type
  PCs, dumb terminal
• Purpose - Execution of application programs take
  place at workstations, which receive data from
  file server

4
Hardware contd

• CABLING - Connects the file server and the
  workstations
• NETWORK INTERFACE CARD (NIC) - Located in the PC
  and File Server.
• Connects PC an File Server
• HUB (CONCENTRATOR) - Needed to accommodate
  multiple PCs on a star topology
• Other equipment - specialized servers, repeaters

5
Software

• Network Operating System (NOS) - NOS resides on
  file server
• Manages access to data on hard disk
• Handles data security for file server's
• Workstation Operating System - Could be MSDOS.
  Loaded at workstation
• Network Shell (Requestor or Redirector) -
  Software created by NOS but loaded on the
  workstation.
• Determines if requests made by workstations are
  local processing or network processing

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Implementation of LAN

• Appropriate networking hardware and software
  added to every computer or shared peripheral
  device communicating with LAN
• Network hardware/software must be compatible with
  LAN components and OS
• Client/Server - idea is
• user are client
• slave is server

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Implementation of LAN contd

• Client server - refers to computing system that
  splits the workload between desktop PCs and one
  or more larger computers (servers) on a LAN
• Client licenses - purchased in groups (5 user,
  25 user, 100 user)

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Implementation of LAN contd

• Server licenses - purchased individually
• Compatibility NOS of server must be compatible
  with OS and hardware of client on which it is
  installed

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Why Install LAN

• Business needs are reflective of management
• LAN is needed to provide service to company
• LAN will help profit margin
• Increase efficiency

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Advantages of Local Area Networks

• Ability to share hardware and software
  resources.
• Individual workstation might survive network
  failure.
• Component and system evolution are possible.
• Support for heterogeneous forms of hardware and
  software.
• Access to other LANs and WANs (Next Figure).
• Private ownership.
• Secure transfers at high speeds with low error
  rates.

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Disadvantages of Local Area Networks

• Equipment and support can be costly.
• Level of maintenance continues to grow.
• Private ownership possible.
• Some types of hardware may not interoperate.
• Just because a LAN can support two different
  kinds of packages does not mean their data can
  interchange easily.
• LAN is only as strong as it weakest link, and
  there are many links.

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OSI MODEL

• Model of standard for network
• Model consists of a seven layers grouping
  functional requirements for communicating between
  two computing devices
• Can be used to organize protocols involved in
  communicating between two computing devices

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OSI MODEL contd

• Each layer in the OSI model relies on lower
  layers to perform more functions
• Each layer provides the transparent service to
  upper layers
• Protocol is a set of rules that govern
  communication between hardware and/or software
  components

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OSI MODEL contd

• OSI has seven layers
• Physical layer
• Data Link layer
• Media Access Control
• Logical Link Control
• Network layer

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OSI MODEL contd

• Transport layer
• Session layer
• Presentation layer
• Application layer

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OSI MODEL contd

• Each layer in the OSI model relies on lower
  layers to perform more functions
• Each layer provides the transparent service to
  upper layers
• Protocol is a set of rules that govern
  communication between hardware and/or software
  components

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Physical Layer

• Responsible for the establishment, maintenance,
  and termination of physical connections between
  communicating devices
• Transmits and receives a stream of bits
• Controlled by protocols that define electrical,
  mechanical, and procedural specifications for
  data transmission

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Data Link Layer

• Responsible for providing protocols that deliver
  reliability to upper layers for the
  point-to-point connections established by the
  physical layer protocol
• Layer which network architecture standards are
  defined
• Provides required reliability to the physical
  layer transmission organizing bit stream into
  frames
• Adds addressing and error checking information

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Data Link Layer contd

• Data-link layer frames built within the NIC card
  installed in a computer according to the
  predetermined frame layout particular to the
  network architecture of the installed NIC
• Physical and data link are hardware
• Remaining layers of the OSI model are installed
  as software protocols

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Data Link Layer contd

• Media Access Control (MAC) - sub layer interfaces
  with the physical layer
• MAC - represented by protocols that define how
  the shared local area network media is to be
  accessed by the many connected computers
• MAC - addresses assigned to NICs at the time of
  manufacture are referred to as MAC addresses

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Data Link Layer contd

• Upper sub layer of the data link layer interfaces
  to the network layer is logical link control
• Advantage to splitting the data link layer into
  two sub layers is that it offers transparency to
  the upper layer while the MAC sub layer protocol
  varies independently

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Network Layer

• Responsible for establishment, maintenance, and
  termination of end-to-end network links
• Network layer protocols are required when
  computers that are not physically connected to
  same LAN must communicate
• Network layer protocols are responsible for
  providing network layer addressing schemes and
  for enabling internetwork routing of network
  layer data

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Network Layer contd

• Packets - term is usually associated with network
  layer protocols
• Frames - term is usually associated with data
  link layers protocols
• Different NOS may use different network layer
  protocols
• Many NOS have ability to use more than one
  network layer protocol

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Transport Layer

• Transport layer protocols - responsible for
  providing reliability for end-to-end network
  layer connections
• Provide end-to-end recovery and flow control
• Provide mechanisms for sequentially organizing
  multiple network layer packets into coherent
  message

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Transport Layer contd

• NOS that supplies transport layer protocol are
  often linked with a particular network layer
  protocol
• Example, NetWare uses IPX/SPX in which IPX is the
  network layer protocol and SPX is the transport
  layer protocol
• Another transport/network protocol duo is TCP/IP
  in which TCP (Transmission Control Protocol) is
  transport layer protocol that provides
  reliability services for IP (Internet Protocol),
  the network layer protocol

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Transport Layer contd

• Another transport/network protocol is TCP/IP
• TCP (Transmission Control Protocol) is transport
  layer protocol that provides reliability services
  for IP (Internet Protocol), the network layer
  protocol

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Session Layer

• Responsible for establishing, maintaining, and
  terminating sessions between user application
  programs

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Presentation Layer

• Protocols that provide an interface between user
  applications and various presentation related
  services required by applications
• Data encryption/decryption protocols are
  considered presentation layer protocols
• Presentation layer protocols deal with network
  communications

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Application Layer

• Application layer protocols do not include end
  user application programs
• Application layer includes utilities that support
  end user application programs
• Examples of application layer protocols are the
• OSI protocols X.400 and X.500
• DNS (Domain Name Service), an Internet Protocol
  that resolves a computers domain name to a
  specific IP address

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OSI Model

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OSI Model - Architectural View
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Encapsulation/De-encapsulation

• Encapsulation - data message emerges from a
  client front-end program and proceeds down
  protocol stack of the network operating system
  installed in client PC
• Each layer of the OSI model adds a header
  according to the syntax of the protocol that
  occupies that layer
• In case of data link layer, both a header and
  trailer are added

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Encapsulation/De-encapsulation contd

• De-encapsulation - When full bit stream arrives
  at destination server, the reverse process of
  encapsulation takes place
• Each successive layer of OSI model removes
  headers and/or trailers and processes data that
  was passed to it from lower layer protocol on
  source client

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LAN Media

• Wire that is not twisted pair flat gray
• Unshielded twisted pair
• Shielded twisted pair
• Coaxial Cable
• Fiber Optic

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UTP Wire Category

• Cat 1 Not recommended for data
• Cat 2 Data transmission lt 1 Mbps
• Cat 3 Data transmission lt 16 Mbps. Used
  reliably for 4 Mbps token ring, and 10 Mbps
  Ethernet. Tested for attenuation and near end
  crosstalk up to 16 MHz.

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UTP Wire Category

• Cat 4 Tested for attenuation and near end
  crosstalk up to 20 MHz. Not widely used in favor
  of Cat 5
• Cat 5 Tested for attenuation ad near end
  crosstalk up to 100 MHz. Capability of
  transmitting up to 1,000 Mbps when strictly
  installed to EIA/TIA specifications. Most
  commonly installed category of UTP.

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Ethernet Wiring - Wiring Summary

• There are four main types of wiring systems for
  Ethernet
• Thick coaxial cable
• Thin coaxial cable
• Unshielded Twisted Pair (UTP)
• Fiber
• All may be used as one or intermixed on an
  Ethernet network.

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Ethernet Cable Names
Name
Fiber
Unshielded Twisted Pair
Thin coaxial
Thick coaxial
RG-8
Wire Type
22 - 26 AWG
62.5/125 micron
RG-58
10BASE5
10BASE2
10BASEF
10BASET
IEEE Name
N/A
Standard Number
IEEE 802.3
IEEE 802.3a
IEEE 802.3i
Other names
Thick net
Thin net
UTP
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Not Twisted Pair

• Telephone wire installed in homes
• Called flat gray wire
• Capable of carrying data only a short distance

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Unshielded Twisted Pair

• One or more pairs of insulated copper wire that
  are twisted at varying lengths, from 2 to 12
  twists per foot
• Reduces interference both between pairs and form
  outside sources such as electric motors and
  fluorescent lights
• Known as unshielded twisted pair (UTP)

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Unshielded Twisted Pair contd

• 2, 3, 4, and 25 pairs of twisted cooper wire are
  the most common numbers of pairs combined to form
  UTP cables
• Appeals of UTP is that it is often installed in
  modern building to carry voice conversations
  through voice PBX.
• EIA/TIA 568 specifies five different categories
  of UTP

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Unshielded Twisted Pair contd

• Cat 1 (voice-grade) need only carry voice
  conversations with reasonably clarity
• Cat 3-5 (data grade) cable meets certain
  predefined electrical characteristics that ensure
  transmission quality and speed

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Sources of Signal Loss

• Attenuation decrease in power of signal over a
  distance in a particular type of wire or media.
•  Near-end (NExT) signal interference caused by
  a strong signal on one pair (transmitting)
  overpowering a weakness signal on an adjacent
  pair (receiving)
• Near-end crosstalk and attenuation are both
  measured in dB decibels

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Common Installation Mistakes

•   Untwisting UTP wire more than maximum 13 mm to
  secure the UTP to wall plates or punch down
  blocks.
•   Over-bending the wire can increase cross-talk
  between stretched pairs of wires.
• Bundling groups of UTP together too tightly with
  cable ties

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STP-Shielded Twisted Pair

• Data transmission can be improved by adding
  shielding around each individual wire and the
  entire group of twisted pairs
• Shielding shields the individual twisted pairs
  as well as the entire cable from either EMI
  (Electromagnetic Interference) or RFI (Radio
  frequency Interference)

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Coaxial Cable

• Coaxial cable (coax or cable TV cable) has
  specialized insulators and shielding separating
  two conductors, allowing reliable, high speed
  data transmission over relatively long distances

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Coaxial Cable contd
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Fiber Optic Cable

• Expensive media, price is going down
• High bandwidth in the range of several gigabytes
  per second over distances of several kilometers
• Most secure of all media relatively untappable,
  transmitting only pulses of light

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Fiber Optic Cable contd

• Fiber optic is a thin fiber of glass rather than
  copper
• Media is immune to electromagnetic interference
• Fiber optic contributes to high bandwidth and
  data transmission capabilities

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Fiber Optic Cable contd

• Multimode (one type) or multimode step index
  (second type) fiber optic cable - rays of light
  bounce off the cladding at different angles and
  continue down the core while others are absorbed
  in the cladding
• Multimode - capable of high bandwidth (200 Mbps)
  transmission, but usually over distances of less
  than 1 km

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Fiber Optic Cable contd

• Third type of fiber optic cable seeks to focus
  the rays of light even further so that only a
  single wavelength can pass through at a time is
  known as single mode
• Without numerous reflections of rays at multiple
  angles, distorting is eliminated and bandwidth is
  maximized

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Fiber Optic Cable contd

• Thickness of cables core and cladding is
  measured in microns (millionths of an inch)
• Wavelength of the light that is pulsed onto the
  fiber optic cable is measured in nanometers (nm),
  with the optimal light transmitting wavelengths
  coming in three distinct windows of 820 nm, 110
  nm, and 1500 nm

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Fiber Optic Cable Cross Section
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LAN Architecture Model

• To describe a given network architecture, one
  needs to know the following
• -  Access methodology
• -  Logical topology
• -  Physical topology

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LAN Architecture Model contd

•  Network architecture access topology Logical
  topology Physical topology
•  Network configuration network architecture
  network choice

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LAN Media Technology
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Access Methodologies

• CSMA
• CSMA/CD
• CSMA/CA
• Token Passing

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Contention

• CONTENTION - Nothing controls usage of the
  communication channels.
• Workstations share a common transmission channel.
  Messages broadcasts are overhead by all attached
  workstations.
• If problem transmitting, the sending workstation
  waits a random amount of time and then
  retransmits the packet.

60

Medium Access Control Protocols How does a
workstation get its data onto the LAN medium? A
medium access control protocol is the software
that allows workstations to take turns at
transmitting data. Three basic categories 1.
Contention-based protocols 2. Round robin
protocols 3. Reservation protocols

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Contention-Based Protocols Essentially first
come, first served. Most common example is
carrier sense multiple access with collision
detection (CSMA/CD). If no one is transmitting, a
workstation can transmit. If someone else is
transmitting, the workstation backs off and
waits.

62

Contention-Based Protocols If two workstations
transmit at the same time, a collision occurs.
When the two workstations hear the collision,
they stop transmitting immediately. Each
workstation backs off a random amount of time and
tries again. Hopefully, both workstations do not
try again at the exact same time. CSMA/CD is an
example of a non-deterministic protocol.

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Round Robin Protocols Each workstation takes a
turn transmitting and the turn is passed around
the network from workstation to workstation. Most
common example is token ring LAN in which a
software token is passed from workstation to
workstation. Token ring is an example of a
deterministic protocol. Token ring more complex
than CSMA/CD. What happens if token is lost?
Duplicated? Hogged? Token ring LANs are losing
the battle with CSMA/CD LANs.

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Reservation Protocols Workstation places a
reservation with central server. Workstation
cannot transmit until reservation comes up. Under
light loads, this acts similar to CSMA/CD. Under
heavy loads, this acts similar to token
ring. Powerful access method but again losing out
to CSMA/CD. Most common example of reservation
protocol is demand priority protocol.

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Medium Access Control Sublayer To better support
local area networks, the data link layer of the
OSI model was broken into two sublayers 1.
Logical link control sublayer 2. Medium access
control sublayer Medium access control sublayer
defines the frame layout and is more closely tied
to a specific medium at the physical layer. Thus,
when people refer to LANs they often refer to its
MAC sublayer name, such as 10BaseT.

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CSMA

• CARRIER SENSE MULTIPLE ACCESS (CSMA) - before
  information is sent, the workstation listens -
  usually on a secondary frequency - to sense
  whether any Workstation is using the primary
  transmission channel (the carrier).
• Only when the line is clear will the workstation
  transmit.

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CSMA contd

• If a workstation becomes ready to retransmit
  while another workstation is active, it detects
  the signal passing on the cable and does not send
  its message until the current transmission is
  complete.
• In addition to transmitting its message on the
  main channel, the active workstation broadcasts a
  carrier sense signal on the secondary channel to
  inform other workstations that the line is busy.

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CSMA/CD contd

• In CSMA/CD, workstations monitor the link during
  a transmission.
• When a collision is detected, transmission is
  halted.
• Because of the ability to listen before and
  during transmission, the number of collisions is
  relatively low.
• Less delay occurs.

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CSMA/CD contd

• If two user PCs should both sense a free line and
  access the media at the same instant, a collision
  occurs and collision detection lets the user PCs
  know that their data was not delivered and
  controls retransmission in such a way as to avoid
  further data collisions.
• Another possibility factor leading to data
  collision is the propagation delay, which is the
  time it takes to signal from a source PC to reach
  a destination PC. 

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CSMA/CD contd

• In event of a collision, station that first
  detects a collision sends special jamming signal
  to all attached workstations.
• Each workstation is preset to wait a random
  amount of time before retransmitting, thus
  reducing likelihood of reoccurring collisions.

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CSMA/CA

• Station with a message to transmit monitors the
  medium and waits for the line to be available.
• When the channel is clear, the workstation
  signals its intention to broadcast.
• If multiple workstations are waiting, the order
  of precedence is determined by a pre-established
  table.

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IEEE 802 Frame Formats The IEEE 802 suite of
protocols defines the frame formats for CSMA/CD
(IEEE 802.3) and token ring (IEEE 802.5). Each
frame format describes how the data package is
formed. Note how the two frames are different.
If a CSMA/CD network connects to a token ring
network, the frames have to be converted from one
to another.

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Local Area Network Systems Ethernet or
CSMA/CD Most common form of LAN today. Star-wired
bus is most common topology but bus topology also
available. Ethernet comes in many forms depending
upon medium used and transmission speed and
technology.

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Ethernet Originally, CSMA/CD was 10 Mbps. Then
100 Mbps was introduced. Most NICs sold today
are 10/100 Mbps. Then 1000 Mbps (1 Gbps) was
introduced. 10 Gbps is now beginning to appear.

80

Ethernet 1000 Mbps introduces a few interesting
wrinkles Transmission is full duplex (separate
transmit and receive), thus no collisions. Priorit
ization is possible using 802.1p
protocol. Topology can be star or mesh (for
trunks).

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Ethernet A few more interesting wrinkles Cabling
can be either UTP or optical (but 10 Gbps
Ethernet may not work over UTP due to radio
frequency interference). Where 10 Mbps Ethernet
has less than 30 utilization due to collisions,
1000 Mbps is limited only by traffic
queueing. Distance with 10 Mbps is limited by
CSMA/CD propagation time, whereas 1000 Mbps is
limited only by media.

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Local Area Network Systems IBM Token
Ring Deterministic LAN offered at speeds of 4, 16
and 100 Mbps. Very good throughput under heavy
loads. More expensive components than
CSMA/CD. Losing ground quickly to CSMA/CD. May
be extinct soon.

84

Local Area Network Systems FDDI (Fiber
Distributed Data Interface) Based on the token
ring design using 100 Mbps fiber
connections. Allows for two concentric rings -
inner ring can support data travel in opposite
direction or work as backup. Token is attached to
the outgoing packet, rather than waiting for the
outgoing packet to circle the entire ring.

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Polling

• POLLING - involves the central control of all
  workstations in a network.
• The central workstation acts like a teacher going
  down the rows of the classroom asking each
  student for homework. When one student has
  answered, the next is given a chance to respond.
• Each time a workstation is polled, the primary
  workstation must wait for a response to be
  returned.

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Polling contd

• After a workstation responds, the next station is
  polled.
• The primary workstation has access to the network
  at any one time.
• Communication between workstations is possible
  only under the direction of the polling computer.

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Token Passing

• Token passing ensures that each PC user has 100
  of the network channel
• No PC accesses the network without first
  possessing a specific packet (24 bits) of data
  known as a token.
• Token is generated by a designated PC known as
  the active monitor.

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Token Passing contd

• Token passed among PCs until one PC would like to
  access the network
• Successful delivery of the data frame is
  confirmed by the destination workstation setting
  frame status flags The sending PC resets the
  token status from busy to free and releases it.

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Token-Passing Access Methodology
91
CSMA/CD vs. Token Passing

• CSMA/CD requires less overhead more efficient
  than token passing at low traffic levels
• At higher traffic levels, the inherent
  collisions and retransmissions make token passing
  more efficient
• CSMA/CD provides nearly perfect efficiency until
  the number of collisions and retransmits start to
  erode the performance overhead on CSMA/CD

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CSMA/CD vs. Token Passing contd

• This phenomenon starts to seriously affect
  performance around 60 bandwidth demand and
  increases until performance actually deteriorates
  with additional bandwidth demand.
• Overhead associated with token passing makes it
  less efficient than CSMA/CD at lower levels of
  demand.

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CSMA/CD vs. Token Passing
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Logical topology

• Sequential Data is passed from one PC to
  another. Each node examines the destination
  address to determine if packet is meant for it.
  Messages are passed until correct destination is
  achieved.
• Broadcast Data is sent simultaneously to all
  nodes. Messages not meant for node are ignored.
  Non recipient workstation ignore messages.

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Physical Topologies

• Physical layout is known as network
  architectures physical topology
• Types of Physical topology
• Bus
• Ring
• Star
• Tree

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LAN Physical Topology Choices
97

Bus/Tree Topology Baseband signals are
bidirectional and more outward in both directions
from the workstation transmitting. Broadband
signals are usually uni-directional and transmit
in only one direction. Because of this, special
wiring considerations are necessary. Buses can be
split and joined, creating trees.

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Star-wired Bus Topology Logically operates as a
bus, but physically looks like a star. Star
design is based on hub. All workstations attach
to hub. Unshielded twisted pair usually used to
connect workstation to hub. Hub takes incoming
signal and immediately broadcasts it out all
connected links. Hubs can be interconnected to
extend size of network.

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Star-wired Bus Topology Modular connectors and
twisted pair make installation and maintenance of
star-wired bus better than standard bus. Hubs can
be interconnected with twisted pair, coaxial
cable, or fiber optic cable. Biggest
disadvantage when one station talks, everyone
hears it. This is called a shared network. All
devices are sharing the network medium.

105

Star-wired Ring Topology Logically operates as a
ring but physically appears as a star. Star-wired
ring topology is based on MAU (multi-station
access unit) which functions similarly to a
hub. Where a hub immediately broadcasts all
incoming signals onto all connected links, the
MAU passes the signal around in a ring
fashion. Like hubs, MAUs can be interconnected to
increase network size.

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Wireless LANs Not really a specific topology
since a workstation in a wireless LAN can be
anywhere as long as it is within transmitting
distance to an access point. Newer IEEE 802.11
and 802.11b standard defines various forms of
wireless LAN connections. Speeds up to 11 Mbps
with 802.11b standard. Workstations reside within
a basic service set, while multiple basic service
sets create an extended service set.

111

Wireless LANs Two basic components necessary the
client radio, usually a PC card with an
integrated antenna, and the access point (AP),
which is an Ethernet port plus a transceiver. The
AP acts as a bridge between the wired and
wireless networks and can perform basic routing
functions. Workstations with client radio cards
reside within a basic service set, while multiple
basic service sets create an extended service set.

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Wireless LANs With directional antennae designed
for point-to-point transmission (rare), 802.11b
can work for more than 10 miles. With an
omni-directional antenna on a typical AP, range
may drop to as little as 100 feet. Distance is
inversely proportional to transmission speed - as
speed goes up, distance goes down.

116

Wireless LANs In actual tests, 11 Mbps 802.11b
devices managed 5.5 Mbps (from a July 2000 test
by Network Computing). To provide security, most
systems use Wired Equivalent Privacy (WEP), which
provides either 40- or 128-bit key
protection. What will Bluetooths impact be on
802.11b?

117

• Other Wireless Standards
• IEEE 802.11 (older 2 Mbps)
• IEEE 802.11b (11 Mbps, 2.4 GHz)
• IEEE 802.11a (54 Mbps, 5 GHz, in 2002)
• IEEE 802.11g (54 Mbps, 2.4 GHz, in 2002)
• HiperLAN/2 (European standard, 54 Mbps in 5
  GHz band)

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Peer-to-Peer LANs Not as common as server-based
LANs Less, if any reliance on servers Most
peer-to-peer LANs still use one or more
servers Interesting collaborative-type
applications (world-wide law firm)

120
Network Architecture

• Types
• Ethernet
• Token ring
• FDDI

121
Ethernet

• Functionality
•  Access methodology CSMA/CD
•  Logical topology Broadcast
•  Physical topologically Traditionally, bus
  currently, most often star.
•  Ethernet frames in next figure
• Length varies from 64 to 1518 octets

122
Ethernet II Frame

• Preamble alert and synchronize NIC to incoming
  data
• Destination and source address Known a MAC
  layer address. Permanently burned into NIC
• Type field identifies which network protocols
  are embedded within data field

123
Ethernet II Frame, contd

• Data unit field contains all encapsulated upper
  layer protocols. Length is 46 to 1500 bytes.
• Frame check sequence error detection mechanism
  generated by NIC.Error bursts of up to 31 bits
  can be detected with 100 accuracy with 32 CRCs

124
Ethernet and IEEE 802.3 Standards
125
Media Related Ethernet Standards

• UTP is known as 10BaseT 10 Mbps baseband T
  for twisted pair
• 10Base5 Thick coaxial cable in bus physical
  topology. Length is limited to 500 Meters. Max of
  100 workstations. Can have 5 segments.
• 10Base2 called Thinnet. Length of 185 meters.
  30 workstations per segment. Max of 5 segments.

126
Thick Coaxial Makeup
Thick braid for EMI
Foil
Thin braid for EMI
Thin foil bonded to insulation
Center conductor of tin plated solid copper
conductor
Jacket of PVC or Teflon
Teflon is used for fire code regulations
127
Token Ring Technology Summary

• Access method by which network attachments gain
  access to the cable plant by acquiring acquiring
  a special frame called the token.
• Token is a special 24-bit pattern that
  continuously circulates the ring.
• Token Ring is a broadcast medium.
• To receive data, a destination station performs
  an address match.

128
Token Ring Technology Summary Contd

• Destination station merely copies the frame as it
  repeats it back to the ring.
• When frame arrives back to source station, it
  strips frame from ring and then
• releases the token (4 megabit operation only)
• token is allowed to be released prior to frame
  reception on 16-megabit rings

129
Token Ring Technology Summary Contd

• Token Ring originally ran at 4 Mbps.
• Upgraded in 1989 to 16 Mbps
• Maximum frame size for 4 Mbps is 4472.
• This is based only on the fact a station cannot
  hold the token longer than 0.010 milliseconds.
• Maximum frame size for 16 Mbps is 17,800.

130
Token Ring Frame Field Definitions
no preset size
Routing Information Fields
IEEE 802.2
SD
AC
DA
Data
FCS
ED
FS
FC
SA
4 bytes
1 byte
1 byte
1 byte
1 byte
1 byte
6 bytes
6 bytes
lt 18 bytes

• SD - Starting Delimiter
• AC - Access Control
• FC - Frame Control
• DA - Destination Address
• SA - Source Address
• FCS - Frame Control Sequence
• ED - Ending Delimiter
• FS - Frame Status

DSAP
SSAP
Control
Legend
1 or 2 bytes
1 byte
1 byte
131
Claim Token Process

• A ring cannot operate without a token circulating
  on the ring.
• Only one token per ring.
• Token-claiming process allows one station to
  insert token onto ring.
• This station will be elected as the AM.
• It will purge the ring (ability to transmit a
  frame to itself).
• After purging ring, it will insert a new token on
  ring.

132
Claim Token Process contd

• Token-Claim process can be started when AM
• detects a loss of signal,
• a timer expires and it has not yet received its
  AM frame back, or the AM
• cannot receive enough of its own Purge Ring MAC
  frames.
• It can be started when the SM
• detects loss of signal or
• detects expiration of its timer for receiving SM
  frames.

133
Details of Claim Token Process

• If there is no token on ring, all activity will
  cease on ring.
• Active Monitor should be able to recover by
  purging ring and issuing new Token.
• If Active Monitor cannot recover, token-claim
  process will begin.

134
Details of the Claim Token Process contd

• Any station will insert its master clock, a
  24-bit delay, and start to transmit Token-Claim
  frames.
• These frames are received by all stations on the
  ring.
• The station will follow these frames with idle
  (clock) signals.
• After transmitting the Token Claim frames, the
  station starts a timer.
• If it does not receive its frames or someone
  elses claim frames, it will beacon the ring.

135
Details of Claim Token Process, contd

• Once the process is started other stations may
  participate.
• Stations bid for the right to become the AM.
• The station with the highest priority (MAC
  address) wins.
• That station becomes the AM.
• It will purge the ring and insert a new token.

136
Active Token Monitor

•  Removes frames from ring that heave not been
  removed by their sending workstations.
•  Regenerates lost or damaged tokens.
•  Provides a special 24 bit buffer if physical
  ring is so small that it does not have enough
  delay or latency to hold the 24 bit token.
•  Controls the master clock.
• Makes sure that there is only one designated
  active monitor on this ring.

137
FDDI

•  Access methodology Modified token passing
•  Logical topology Sequential
• Physical Topology Dual counter rotating rings

138
FDDI Supplies

• FDDI supplies good deal deal of bandwidth
• High degree of security
• Not associated with or promoted by any particular
  vendor
• High degree of reliability through the design of
  the physical topology

139
FDDI Supplies

• FDDIs physical topology comprised of separate
  rings around which data moves simultaneously in
  opposite directions
• One ring is primary data ring
• Other is a secondary/backup data ring
• Up to 500 nodes at 2 km apart can be linked to an
  FDDI network
• Reduce FDDI cost by using one ring

140
FDDI Network Architecture and Technology
141
FDDIs Self-Healing Ability
142
FDDI Standard

• FDDI uses modified token ring passing methodology
• Different from 802.5 token ring in two ways
• Physically removes token from the ring and
  transmits a full data frame. Upon completion of
  transmission, it immediately releases new token.
• Single PC may send numerous messages before
  relinquishing the token

143
FDDI Token and Data Frame Layouts
144
Application of FDDI

• Bandwidth demanders
• - Network architecture trends
• - Network application trends

145
FDDI Network Architecture

• Campus backbone - connect LANs located throughout
  closely situated buildings
• High Bandwidth Workgroups - connect PCs or
  workstations that require high bandwidth
  communication
• High bandwidth Sub workgroup Connections
  Increasing demand for high-speed server-to-server
  data transfer

146
Alternative Applications of the FDDI Network
Architecture
147
High Speed Network Architecture

• 100BaseT represents a family of Fast Ethernet
  standards offering 100 Mbps
• Three media specific physical layer standards of
  100BaseT are 
• - 100BaseTX Specifies 100 Mbps performance over
  two pair of Cat 5 UTP or to pair of Type 1 STP
• - 100BaseT4 Physical layer standard for 100
  Mbps transmission over four pair of Cat 3, 4, or
  5 UTP
• 100Base FX Physical layer standard for 100 Mbps
  transmission over duplex multimode fiber optic
  cable

148
100BaseT Network Architecture

• 100BaseT standards transmit at 10 times faster
  than 10BaseT. Trade-off comes in the maximum
  network diameter
• 10BaseTs maximum network diameter is 2500 m with
  up to four repeaters/hubs.
• 100BaseTs maximum network diameter is 210 m with
  up to only two repeaters/hubs

149
100BaseT Network Architecture, contd

• Collisions on any CSMA/CD network architecture.
• Slot time - Time required for a workstation to
  detect a collision. Measured in bits.
• The collision notification and retransmission
  must occur before the slot time has expired. The
  slot time for both 10BaseT and 100BaseT is 512
  bits.

150
100BaseT Network Architecture, contd

• To insure collision notifications are received by
  100BaseT network workstations before slot time
  expires, maximum network diameter was reduced
  proportionately to the increase in network in
  network speed.
• Maximum network diameter shrinks from 2500 m to
  210 m.

151
100BaseT Network Architecture Implementation
152
HPNA Implementation
153
FDDI Ring Operation

• FDDI allows stations to communicate over a dual
  ring topology by guaranteeing access to the cable
  plant at timed intervals using a Token to control
  access.
• Network stations must wait for Token before
  transmitting.

154
FDDI Ring Operation, contd

• A network station will capture the Token and
  transmits a series of symbols (data) to the ring.
• Station may transmit as many frames as it can
  until a timer expires.
• Downstream neighbors of the transmitting station
  will receive and retransmit the symbols.

155
FDDI Ring Operation, contd

• Destination as indicated in the FDDI frame copies
  the frame and repeats it to the ring.
• Originating station strips the frame from ring
  when it returns.

156
FDDI Timers

• Proper ring operation requires connection
  establishment, ring initialization, steady-state
  operation, and ring maintenance.
• A series of timers play a very important part for
  proper ring operation.

157
FDDI Timers, contd

• These timers are
• Token Rotational Timer (TRT) - used to time the
  duration of operations in a station.
• Token Holding Timer (THT) - determines the amount
  of time a station may hold the token.
• Valid Transmission Timer (TVX) - detects
  excessive ring noise, loss of a token and other
  faults.

158
FDDI Timers, contd

• Another parameter that is not a timer but is a
  parameter used by the timers is the
• Target Token Rotational Timer (TTRT) - a ring
  latency parameter which sets the latency for the
  ring.

159
FDDI Frames
FDDI frame
up to 4472 bytes
Source Service Access Point (SSAP)
Destination Service Access Point (DSAP)
Control fields
Ending Delimiter
Frame Status
Frame Control
Destination address
Source address
Starting Delimiter
Preamble
FCS
Data
Optional IEEE 802.2 fields
A R E
C L F F Z Z Z Z
A Address recognized C Frame copied bit E -
Error bit
Token frame
Starting Delimiter
Frame Control
Ending Delimiter
Preamble
160
FDDI Addressing and Bit Order
FDDI frame
up to 4472 bytes
Source Service Access Point (SSAP)
Destination Service Access Point (DSAP)
Control field
Ending delimiter
Frame status
Frame Control
Destination address
Source address
Starting Delimiter
Preamble
FCS
Data
Optional IEEE 802.2 fields
Destination address
Source address
46 bit remainder of the address
RII
46 bit remainder of the address
Bit 0
Bit 48
Bit 0
Bit 48
Transmitted first
Transmitted first
161
Synchronous and Asynchronous

• There are two types of transmission on FDDI
• synchronous and asynchronous.
• Synchronous traffic is reserved bandwidth that is
  guaranteed to a network station that holds the
  token.
• It is is used for voice and video applications.

162
Synchronous and Asynchronous, contd

• Asynchronous traffic is a service class in which
  unreserved bandwidth is available to the station
  that has captured the token
• This is the most common mode of FDDI operation.
• There are two modes of asynchronous traffic
• Restricted and non restricted.

163
Synchronous and Asynchronous, contd

• The two service classes should not be confused
  with the serial transmission standard used in
  terminal to computer communications.

164
FDDI Station Management (SMT)

• FDDI provides for a standardized mechanism for
  managing FDDI rings
• SMT provides management in four areas
• Connection Management (CMT)
• Operates at the physical link level
• Physical Connection Management (PCM)
• Configuration Management (CFM)
• Link Error Monitoring (LEM)

165
FDDI Topologies

• Like any LAN, FDDI topologies play a large role
  in planning an efficient network.
• The recommended topologies for FDDI are
• Standalone concentrator
• Dual Ring
• Tree of Concentrators
• Dual Ring of Trees
• Dual Homing

166
FDDI Topologies, contd

• Network attachment level
• Configuration Management (CFM)
• Entity Coordination Management (ECM)
• Ring level management
• Ring Management (RMT)
• Frame Based Management
• Consists of a series of frames that allow
  management of the ring stations over the ring.

167
Standalone Concentrator
Dual ring
Dual Attachment Station
Single ring
Single Attachment Stations
168
Dual Ring
Dual Attachment Station
Dual Attachment Station
Dual Attachment Station
Dual Attachment Station
169
Dual Ring of Trees
DAC
DAC
Dual ring
SAC
SAC
SAS
SAS
SAS
170
Tree of Concentrators
Root Concentrator
Concentrator
Concentrator
SAS
SAS
171
Ethernet, Token Ring, and FDDI
FDDI IEEE 802.3 IEEE 802.5 Bandwidth 10
0 Mbps 10 Mbps 4 or 16 Mbps Number of
stations 500 1024 250 Maximum distance between
stations 2 km (1.2 mi) 2.8 km (1.7 mi) 300 m
(984 ft) station to with MMF wiring closet (4
Mbps) 20 km (12.4 mi) recommended
standard with SMF is 100 m (330 ft) for 16/4
Mbps Maximum network extent 100 km (62
miles) 2.8 km 300 / 100 m Logical topology Dual
ring, dual ring Bus Single ring of
trees Physical topology Ring, Star, Star,
bus Ring, star Hierarchical star Hierarchical
star Hierarchical star Media Optical
fiber Optical fiber Shielded or unshielded
twisted pair Unshielded twisted pair Optical
fiber Coaxial Cable Access method Timed
token passing CSMA/CD Token passing Token
acquisition Captures the token N/A Sets a bit
converting token into a frame Token
Release After transmit N/A After stripping (4)
or after transmit (16) Frames on a
LAN Multiple Single 1 (4) or multiple(16) Frame
s transmitted Multiple Single Single per
access Maximum frame size 4500 bytes 1518
bytes 4,500 bytes (4) or 17,800 (16)
MMF Multimode fiber, SMF Single Mode Fiber
172
Data Link Encapsulation Types
DataLink Encapsulation Types
6 bytes
2 bytes
Up to 1500 bytes
4 bytes
6 bytes
Destination address
Source address
Type field
Ethernet V2.0
Data field
CRC
Up to 1496 bytes
6 bytes
6 bytes
4 bytes
Destination address
Source address
Length field
Data field
CRC
IEEE 802.3
Destination address
Source address
Length field
IEEE 802.3 with IEEE 802.2
DSAP
SSAP
CTRL
Data field
CRC
4 bytes
IEEE 802.3 SNAP
Destination address
Source address
Length field
DSAP
SSAP
CTRL
Data field
CRC
OUI
EtherType
SNAP header
Novell proprietary
Destination address
Source address
Length field
FFFF
Data field
CRC
Token Ring
4 bytes
6 bytes
6 bytes
1 byte
1 byte
4472 (4 Mbps or 17800 (16 Mbps) bytes
Destination address
Source address
RIF
FS
SD
AC
FC
DSAP
SSAP
CTRL
Data field
CRC
6 bytes
6 bytes
2 bytes
1 byte
1 byte
4 bytes
4472 bytes
1 byte
1 byte
Destination address
Source address
Length field
DSAP
SSAP
CTRL
Data field
Preamble
SD
FC
FCS
FS
ED
FDDI