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									Komunikasi Data dan Jaringan
                   (Bagian 3)

         Dr. Tb. Maulana Kusuma

                 Magister Teknik Elektro       0
                 LAN Generation
 First
     Carrier Sense Multiple Access (CSMA) / Collision Detection (CD)
      and Token Ring
     Terminal to host and client server
     Moderate data rates
 Second
     Fiber Distributed Data Interface (FDDI)
     Backbone
     High performance workstations
 Third
     Asynchronous Transfer Mode (ATM)
     Aggregate throughput and real time support for multimedia
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       Third Generation LAN
Support for multiple guaranteed classes of
   Live video may need 2Mbps
   File transfer can use background class
Scalable throughput
   Both aggregate and per host
Facilitate LAN / WAN internetworking

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        LAN Applications (1)
Personal computer LANs
  Low cost

  Limited data rate

Back end networks and storage area networks
  Interconnecting large systems (mainframes and large

   storage devices)
      High data rate
      High speed interface
      Distributed access
      Limited distance
      Limited number of devices
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        LAN Applications (2)
High speed office networks
   Desktop image processing
   High capacity local storage
Backbone LANs
   Interconnect low speed local LANs
   Reliability
   Capacity
   Cost

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       LAN Architecture
Protocol architecture
Media Access Control (MAC)
Logical Link Control (LLC)

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     Protocol Architecture
Lower layers of OSI model
IEEE 802 reference model

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IEEE 802 v OSI

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          802 Layers -
Preamble generation/removal
Bit transmission/reception
Transmission medium and topology

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          802 Layers -
       Logical Link Control
Interface to higher levels
Flow and error control

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         802 Layers -
     Media Access Control
Assembly of data into frame with address and
error detection fields
Disassembly of frame
  Address recognition

  Error detection

Govern access to transmission medium
  Not found in traditional layer 2 data link

For the same LLC, several MAC options may be
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LAN Protocols in Context

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   Special case of tree
      One trunk, no branches

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LAN Topologies

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               Bus and Tree
Multipoint medium
Transmission propagates throughout medium
Heard by all stations
  Need to identify target station

       Each station has unique address
Full duplex connection between station and tap
  Allows for transmission and reception

Need to regulate transmission
  To avoid collisions

  To avoid hogging

       Data in small blocks - frames
Terminator absorbs frames at end of medium
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Frame Transmission - Bus LAN

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             Ring Topology
Repeaters joined by point to point links in closed loop
  Receive data on one link and retransmit on another

  Links unidirectional

  Stations attach to repeaters

Data in frames
  Circulate past all stations

  Destination recognizes address and copies frame

  Frame circulates back to source where it is removed

Media access control determines when station can insert

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Frame Transmission
    Ring LAN

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              Star Topology
Each station connected directly to central
   Usually via two point to point links
Central node can broadcast
   Physical star, logical bus
   Only one station can transmit at a time
Central node can act as frame switch

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        Media Access Control
  Central
      Greater control
      Simple access logic at station
      Avoids problems of co-ordination
      Single point of failure
      Potential bottleneck
  Distributed
  Synchronous
      Specific capacity dedicated to connection
  Asynchronous
      In response to demand
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     Asynchronous Systems
Round robin
  Good if many stations have data to transmit over extended

  Good for stream traffic

  Good for bursty traffic

  All stations contend for time

  Distributed

  Simple to implement

  Efficient under moderate load

  Tend to collapse under heavy load

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       Logical Link Control
Transmission of link level PDUs between two
Must support multiaccess, shared medium
Relieved of some link access details by MAC
Addressing involves specifying source and
destination LLC users
  Referred to as service access points (SAP)

  Typically higher level protocol

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                 Bus LAN
Signal balancing
  Signal must be strong enough to meet receiver’s

   minimum signal strength requirements
  Give adequate signal to noise ration

  Not so strong that it overloads transmitter

  Must satisfy these for all combinations of sending

   and receiving station on bus
  Usual to divide network into small segments

  Link segments with amplifies or repeaters

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          Transmission Media
Twisted pair
  Not practical in shared bus at higher data rates
Baseband coaxial cable
  Used by Ethernet
Broadband coaxial cable
  Included in 802.3 specification but no longer made
Optical fiber
  Expensive
  Difficulty with availability
  Not used
Few new installations
  Replaced by star based twisted pair and optical fiber

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   Baseband Coaxial Cable
Uses digital signaling
Manchester or Differential Manchester encoding
Entire frequency spectrum of cable used
Single channel on cable
Few kilometer range
Ethernet (basis for 802.3) at 10Mbps
50 ohm cable

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Ethernet and 802.3 originally used 0.4 inch
diameter cable at 10Mbps
Max cable length 500m
Distance between taps a multiple of 2.5m
   Ensures that reflections from taps do not add
    in phase
Max 100 taps
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0.25 inch cable
   More flexible
   Easier to bring to workstation
   Cheaper electronics
   Greater attenuation
   Lower noise resistance
   Fewer taps (30)
   Shorter distance (185m)
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Transmits in both directions
Joins two segments of cable
No buffering
No logical isolation of segments
If two stations on different segments send
at the same time, packets will collide
Only one path of segments and repeaters
between any two stations
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Baseband Configuration

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                 Ring LAN
Each repeater connects to two others via
unidirectional transmission links
Single closed path
Data transferred bit by bit from one repeater to the
Repeater regenerates and retransmits each bit
Repeater performs data insertion, data reception, data
Repeater acts as attachment point
Packet removed by transmitter after one trip round ring

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Ring Repeater States

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       Listen State Functions
Scan passing bit stream for patterns
   Address of attached station
   Token permission to transmit
Copy incoming bit and send to attached
   Whilst forwarding each bit
Modify bit as it passes
   e.g. to indicate a packet has been copied
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     Transmit State Functions
Station has data
Repeater has permission
May receive incoming bits
   If ring bit length shorter than packet
      Pass back to station for checking (ACK)
   May be more than one packet on ring
      Buffer for retransmission later

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            Bypass State
Signals propagate past repeater with no
delay (other than propagation delay)
Partial solution to reliability problem (see
Improved performance

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                      Star LAN
Use unshielded twisted pair wire (telephone)
  Minimal installation cost

       May already be an installed base
       All locations in building covered by existing installation
Attach to a central active hub
Two links
  Transmit and receive

Hub repeats incoming signal on all outgoing lines
Link lengths limited to about 100m
  Fiber optic - up to 500m

Logical bus - with collisions

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         Hubs and Switches
Shared medium hub
  Central hub

  Hub retransmits incoming signal to all outgoing lines

  Only one station can transmit at a time

  With a 10Mbps LAN, total capacity is 10Mbps

Switched LAN hub
  Hub acts as switch

  Incoming frame switches to appropriate outgoing line

  Unused lines can also be used to switch other traffic

  With two pairs of lines in use, overall capacity is now

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             Switched Hubs
No change to software or hardware of devices
Each device has dedicated capacity
Scales well
Store and forward switch
  Accept input, buffer it briefly, then output

Cut through switch
  Take advantage of the destination address being at

   the start of the frame
  Begin repeating incoming frame onto output line as

   soon as address recognized
  May propagate some bad frames

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Hubs and Switches

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           Wireless LAN
Wireless LANs are growing in popularity
because they eliminate cabling and
facilitate network access from a variety of
The most common wireless networking
standard is IEEE 802.11, often called
Wireless Ethernet or Wireless LAN.
Broadband wireless (IEEE 802.16) is now
growing in popularity

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    Wireless Communications
In wireless communications signals travel
through space instead of through a
physical cable.
Two general types of wireless
communications are:
   Radio transmission
   Infrared transmission

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      Why Wireless LAN?
Hard to wire areas
Reduced cost of wireless systems
Improved performance of wireless

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   Types of Wireless LANs
IEEE 802.11a
IEEE 802.11b
IEEE 802.11g

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              IEEE 802.11b
Two forms of the IEEE 802.11b standard currently exist:

  Direct Sequence Spread Spectrum (DSSS)
  systems transmit signals through a wide range of
  frequencies simultaneously. The signal is divided into
  many different parts and sent on different frequencies
  simultaneously. Data rate: ~ 11Mbps.
  Frequency Hopping Spread Spectrum (FHSS)
  divides the frequency band into a series of channels
  and then use each frequency in turn. FHSS changes
  its frequency channel about every half a second,
  using a pseudorandom sequence.

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FHSS is more secure, but is only capable of data
rates of 1 or 2 Mbps.
IEEE 802.11a is another Wireless LAN standard
developed around the same time as 802.11b. It
operates in the 5 GHz band and is capable of data
rates of up to 54 Mbps.
IEEE 802.11g combines the best of both 802.11a
and 802.11b. 802.11g supports bandwidth up to 54
Mbps, and it uses the 2.4 Ghz frequency for greater
range. 802.11g is backwards compatible with
802.11b, meaning that 802.11g access points will
work with 802.11b wireless network adapters and
vice versa.
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IEEE 802.11a vs 802.11b vs
802.11a is the most expensive. It fits
predominately in the business market, whereas
802.11b better serves the home market.
802.11a supports bandwidth up to 54 Mbps and
signals in a regulated 5 GHz range. Compared
to 802.11b, this higher frequency limits the
range of 802.11a. The higher frequency also
means 802.11a signals have more difficulty
penetrating walls and other obstructions.

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Although slower than 802.11a, the range of 802.11b
is about 7 times greater than that of 802.11a.
Because 802.11a and 802.11b utilize different
frequencies, the two technologies are incompatible
with each other.
Some vendors offer hybrid 802.11a/b network gear,
but these products simply implement the two
standards side by side.
802.11g offers the best of both worlds and allow for
greater flexibility.

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                    Pros                                  Cons

 802.11a     fastest maximum speed;    highest cost;
             supports more             shorter range signal that is
           simultaneous users;        more easily obstructed
             less signal interference
           from other devices

 802.11b     lowest cost;                          slowest maximum speed;
             signal range is best and              supports fewer
           is not easily obstructed              simultaneous users;
                                                   appliances may interfere
                                                 on the unregulated
                                                 frequency band

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                  Pros                                 Cons

 802.11g     fastest maximum                     costs more than
           speed;                              802.11b;
             supports more                       appliances may
           simultaneous users;                 interfere on the
             signal range is best              unregulated signal
           and is not easily                   frequency

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  Wireless LAN Applications
LAN Extension
Cross building interconnection
Nomadic access
Ad hoc networks

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            LAN Extension
Buildings with large open areas
   Manufacturing plants
   Warehouses
Historical buildings
Small offices
May be mixed with fixed wiring system

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Single Cell Wireless LAN

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Multi Cell Wireless LAN

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Cross Building Interconnection
Point to point wireless link between
Typically connecting bridges or routers
Used where cable connection not possible
   e.g. across a street

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           Nomadic Access
Mobile data terminal
   e.g. laptop
Transfer of data from laptop to server
Campus or cluster of buildings

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      Ad Hoc Networking
Peer to peer
e.g. conference

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Wireless LAN Configurations

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 Wireless LAN Requirements
Number of nodes
Connection to backbone
Service area
Battery power consumption
Transmission robustness and security
Collocated network operation
License free operation
Hand-off / roaming
Dynamic configuration

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  Wireless LAN Technology
Infrared (IR) LANs
Spread spectrum LANs
Narrow band microwave

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     Wireless LAN standard –
           IEEE 802.11
The IEEE 802.11 standard for wireless
LANs was finalized in 1997.
The standard defines three different
physical layer specifications - 2 are radio
frequency-based and one is infrared-
   Direct Sequence Spread Spectrum
   Frequency-hopping spectrum
   Infrared

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   Wireless LAN Components

The smallest building block of a wireless LAN
is called the Basic Service Set (BSS).
BSS is a number of stations executing the
same MAC protocol and using the same
shared medium.
A BSS may be isolated or connected to a
backbone distribution system via an access
The distribution system is usually a wired
backbone LAN.

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Wireless LAN Components (cont’d)

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Wireless LAN Components (cont’d)

 Signals from wireless computers are
 transmitted via built-in antennas on the NIC to
 the nearest access point, which serves as a
 wireless repeater.
 Because of the ease of access, security is a
 potential problem.
 The IEEE 802.11 has specified a data link
 security protocol called Wired Equivalent
 Privacy (WEP), which is designed to make
 the security of WLAN as good as that of wired
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     Medium Access Control

The MAC protocol used in 802.11 LANs is
called Distributed Foundation Wireless MAC
This protocol provides a distributed access
control mechanism with an optional
centralized control built in.
A distributed access mechanism distributes
the decision to transmit over all the nodes,
using a carrier sense mechanism, like

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Medium Access Control (cont’d)

A centralized access mechanism involve
regulation of transmission by a centralized
manager. It is particularly useful for time-
sensitive or high priority data.
The MAC layer is divided into 2 sub-layers:
The lower layer is called the Distributed
Coordination Function (DCF), operates
similar to CSMA/CD. Used for ordinary traffic.

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Medium Access Control (cont’d)

The upper layer is called the Point
Coordination Function (PCF). PCF is a
centralized MAC algorithm used for
contention-free service.
All implementations must support DCF,
but PCF is optional.
When DCF is employed, 802.11 uses a
protocol called CSMA/CD to regulate
access to the medium.

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Carrier Sense Multiple Access with
 Collision Avoidance (CSMA/CA )
 Wireless LANs use CSMA/CA .
 Like CSMA/CD, stations listen before they
 transmit and if the line is free, they transmit.
 Detecting collisions is more difficult in wireless
 networks, so wireless LANs try to avoid
 collisions to a greater extent than traditional
 Two different WLAN MAC techniques are now
 in use: the Physical Carrier Sense Method
 and the Virtual Carrier Sense Method.
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Physical Carrier Sense Method
 In the physical carrier sense method, a node
 that wants to send first listens to make sure that
 the transmitting node has finished, then waits a
 period of time longer.
 Each frame is sent using the Stop and Wait ARQ,
 so by waiting, the listening node can detect that
 the sending node has finished and can then
 begin sending its transmission.
 With Wireless LAN, ACK / NAK signals are sent
 a short time after a frame is received, while
 stations wishing to send a frame wait a
 somewhat longer time, ensuring that no collision
 will occur.
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Virtual Carrier Sense Method

When a computer on a Wireless LAN is near
the transmission limits of the AP at one end
and another computer is near the
transmission limits at the other end of the
AP’s range, both computers may be able to
transmit to the AP, but can not detect each
other’s signals.
This is known as the hidden node problem.
When it occurs, the physical carrier sense
method will not work.
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Virtual Carrier Sense Method (cont’d)

 The virtual carrier sense method solves this
 problem by having a transmitting station first
 send a request to send (RTS) signal to the AP.
 If the AP responds with a clear to send (CTS)
 signal, the computer wishing to send a frame
 can then begin transmitting.

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       Infrared Wireless LAN
Infrared WLAN is less flexible than IEEE 802.11
WLANs because, as with TV remote controls that are
also infrared based, they require line of sight to work.
Infrared Hubs and NICs are usually mounted in fixed
positions to ensure they will hit their targets.
The main advantage of infrared WLAN is reduced
A new version, called diffuse infrared, operates
without a direct line of sight by bouncing the infrared
signal off of walls, but is only able to operate within a
single room and at distances of only about 50-75 feet.

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Infrared Wireless LAN (cont’d)

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Bluetooth is a 1 Mbps wireless standard developed
for piconets, small personal or home networks.
It may soon be standardized as IEEE 802.15.
Bluetooth is designed to facilitate networking of
different hand-held and mobile devices. For example:
  linking a wireless mouse to a computer, a

    telephone headset to a base unit, or a Palm
    handheld computer to your car to lock or unlock
    the door.
  3-in-1 phone concept

  automatic synchronizer : automatically

    synchronizes a user’s desktop PC, mobile PC and
    mobile phone.
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Bluetooth was designed to operate within a very
small area (up to 30 feet). May be extended.
Devices are small and cheap.
A Bluetooth network consists of no more than
eight devices, but can be linked to other piconets
to from larger networks.
Although Bluetooth uses the same 2.4 GHz band
as Wireless LANs, it is not compatible with the
IEEE 802.11 standard and so cannot be used in
locations that use the Wireless LANs.

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       Ethernet (CSMA/CD)
 Carriers Sense Multiple Access with
  Collision Detection
 Xerox - Ethernet
 IEEE 802.3

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      IEEE802.3 Medium Access
 Random Access
     Stations access medium randomly
 Contention
     Stations content for time on medium

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 Propagation time is much less than transmission time
 All stations know that a transmission has started almost
 First listen for clear medium (carrier sense)
 If medium idle, transmit
 If two stations start at the same instant, collision
 Wait reasonable time (round trip plus ACK contention)
 No ACK then retransmit
 Max utilization depends on propagation time (medium length)
  and frame length
     Longer frame and shorter propagation gives better
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                  If Busy?
 If medium is idle, transmit
 If busy, listen for idle then transmit
 If two stations are waiting, collision

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 With CSMA, collision occupies medium for
  duration of transmission
 Stations listen whilst transmitting

 If medium idle, transmit
 If busy, listen for idle, then transmit
 If collision detected, jam then cease
 After jam, wait random time then start again
    Binary exponential back off

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           Collision Detection
 On baseband bus, collision produces much
  higher signal voltage than signal
 Collision detected if cable signal greater than
  single station signal
 Signal attenuated over distance
 Limit distance to 500m (10Base5) or 200m
 For twisted pair (star-topology) activity on more
  than one port is collision
 Special collision presence signal

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Gigabit Ethernet Configuration

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 Gigabit Ethernet - Differences
 Carrier extension
 At least 4096 bit-times long (512 for
 Frame bursting

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      Gigabit Ethernet - Physical
 1000Base-SX
     Short wavelength, multimode fiber
 1000Base-LX
     Long wavelength, Multi or single mode fiber
 1000Base-CX
     Copper jumpers <25m, shielded twisted pair
 1000Base-T
     4 pairs, cat 5 UTP
 Signaling - 8B/10B
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            Token Ring (802.5)
 MAC protocol
   Small frame (token) circulates when idle
   Station waits for token
   Changes one bit in token to make it SOF for data frame
   Append rest of data frame
   Frame makes round trip and is absorbed by transmitting
   Station then inserts new token when transmission has
    finished and leading edge of returning frame arrives
   Under light loads, some inefficiency
   Under heavy loads, round robin

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Token Ring Operation

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Priority Scheme

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         Dedicated Token Ring
   Central hub
   Acts as switch
   Full duplex point to point link
   Concentrator acts as frame level repeater
   No token passing

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 100Mbps
 LAN and MAN applications
 Token Ring

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FDDI Operation

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               ATM LANs
Asynchronous Transfer Mode
Virtual paths and virtual channels
Preconfigured or switched
Gateway to ATM WAN
Backbone ATM switch
  Single ATM switch or local network of ATM

Workgroup ATM
  End systems connected directly to ATM switch

Mixed system
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Example ATM LAN

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Interaction between end system on ATM
and end system on legacy LAN
Interaction between stations on legacy
LANs of same type
Interaction between stations on legacy
LANs of different types

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