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					Komunikasi Data dan Jaringan
        Komputer
                   (Bagian 3)


         Dr. Tb. Maulana Kusuma
        mkusuma@staff.gunadarma.ac.id
    http://staffsite.gunadarma.ac.id/mkusuma



                 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
      applications
                           Magister Teknik Elektro                  1
       Third Generation LAN
Support for multiple guaranteed classes of
service
   Live video may need 2Mbps
   File transfer can use background class
Scalable throughput
   Both aggregate and per host
Facilitate LAN / WAN internetworking


                   Magister Teknik Elektro   2
        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
                     Magister Teknik Elektro             3
        LAN Applications (2)
High speed office networks
   Desktop image processing
   High capacity local storage
Backbone LANs
   Interconnect low speed local LANs
   Reliability
   Capacity
   Cost

                   Magister Teknik Elektro   4
       LAN Architecture
Protocol architecture
Topologies
Media Access Control (MAC)
Logical Link Control (LLC)




              Magister Teknik Elektro   5
     Protocol Architecture
Lower layers of OSI model
IEEE 802 reference model
Physical
LLC
MAC




               Magister Teknik Elektro   6
IEEE 802 v OSI




    Magister Teknik Elektro   7
          802 Layers -
            Physical
Encoding/decoding
Preamble generation/removal
Bit transmission/reception
Transmission medium and topology




              Magister Teknik Elektro   8
          802 Layers -
       Logical Link Control
Interface to higher levels
Flow and error control




                 Magister Teknik Elektro   9
         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

   control
For the same LLC, several MAC options may be
available
                 Magister Teknik Elektro    10
LAN Protocols in Context




        Magister Teknik Elektro   11
                Topologies
Tree
Bus
   Special case of tree
      One trunk, no branches
Ring
Star



                    Magister Teknik Elektro   12
LAN Topologies




    Magister Teknik Elektro   13
               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
                      Magister Teknik Elektro    14
Frame Transmission - Bus LAN




           Magister Teknik Elektro   15
             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
frame

                    Magister Teknik Elektro           16
Frame Transmission
    Ring LAN




      Magister Teknik Elektro   17
              Star Topology
Each station connected directly to central
node
   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


                    Magister Teknik Elektro   18
        Media Access Control
Where
  Central
      Greater control
      Simple access logic at station
      Avoids problems of co-ordination
      Single point of failure
      Potential bottleneck
  Distributed
How
  Synchronous
      Specific capacity dedicated to connection
  Asynchronous
      In response to demand
                        Magister Teknik Elektro   19
     Asynchronous Systems
Round robin
  Good if many stations have data to transmit over extended

   period
Reservation
  Good for stream traffic

Contention
  Good for bursty traffic

  All stations contend for time

  Distributed

  Simple to implement

  Efficient under moderate load

  Tend to collapse under heavy load

                      Magister Teknik Elektro              20
       Logical Link Control
Transmission of link level PDUs between two
stations
Must support multiaccess, shared medium
Relieved of some link access details by MAC
layer
Addressing involves specifying source and
destination LLC users
  Referred to as service access points (SAP)

  Typically higher level protocol



                  Magister Teknik Elektro       21
                 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




                    Magister Teknik Elektro         22
          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

                         Magister Teknik Elektro           23
   Baseband Coaxial Cable
Uses digital signaling
Manchester or Differential Manchester encoding
Entire frequency spectrum of cable used
Single channel on cable
Bi-directional
Few kilometer range
Ethernet (basis for 802.3) at 10Mbps
50 ohm cable

                 Magister Teknik Elektro     24
                 10Base5
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
10Base5
                   Magister Teknik Elektro          25
                  10Base2
Cheaper
0.25 inch cable
   More flexible
   Easier to bring to workstation
   Cheaper electronics
   Greater attenuation
   Lower noise resistance
   Fewer taps (30)
   Shorter distance (185m)
                    Magister Teknik Elektro   26
             Repeaters
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
                Magister Teknik Elektro      27
Baseband Configuration




        Magister Teknik Elektro   28
                 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
next
Repeater regenerates and retransmits each bit
Repeater performs data insertion, data reception, data
removal
Repeater acts as attachment point
Packet removed by transmitter after one trip round ring

                    Magister Teknik Elektro          29
Ring Repeater States




       Magister Teknik Elektro   30
       Listen State Functions
Scan passing bit stream for patterns
   Address of attached station
   Token permission to transmit
Copy incoming bit and send to attached
station
   Whilst forwarding each bit
Modify bit as it passes
   e.g. to indicate a packet has been copied
    (ACK)
                   Magister Teknik Elektro      31
     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



                      Magister Teknik Elektro   32
            Bypass State
Signals propagate past repeater with no
delay (other than propagation delay)
Partial solution to reliability problem (see
later)
Improved performance




                 Magister Teknik Elektro       33
                      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

                         Magister Teknik Elektro                    34
         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

   20Mbps
                      Magister Teknik Elektro            35
             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

                    Magister Teknik Elektro             36
Hubs and Switches




     Magister Teknik Elektro   37
           Wireless LAN
Wireless LANs are growing in popularity
because they eliminate cabling and
facilitate network access from a variety of
locations.
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

                Magister Teknik Elektro       38
    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



                   Magister Teknik Elektro   39
      Why Wireless LAN?
Mobility
Flexibility
Hard to wire areas
Reduced cost of wireless systems
Improved performance of wireless
systems



               Magister Teknik Elektro   40
   Types of Wireless LANs
IEEE 802.11a
IEEE 802.11b
IEEE 802.11g
Infrared
Bluetooth




               Magister Teknik Elektro   41
              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.

                     Magister Teknik Elektro               42
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.
                   Magister Teknik Elektro            43
IEEE 802.11a vs 802.11b vs
         802.11g
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.


                 Magister Teknik Elektro        44
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.



                   Magister Teknik Elektro             45
IEEE LAN
Standard
                    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


                       Magister Teknik Elektro                           46
IEEE Lan
Standard
                  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
           obstructed

                     Magister Teknik Elektro                        47
  Wireless LAN Applications
LAN Extension
Cross building interconnection
Nomadic access
Ad hoc networks




               Magister Teknik Elektro   48
            LAN Extension
Buildings with large open areas
   Manufacturing plants
   Warehouses
Historical buildings
Small offices
May be mixed with fixed wiring system



                   Magister Teknik Elektro   49
Single Cell Wireless LAN




        Magister Teknik Elektro   50
Multi Cell Wireless LAN




        Magister Teknik Elektro   51
Cross Building Interconnection
Point to point wireless link between
buildings
Typically connecting bridges or routers
Used where cable connection not possible
   e.g. across a street




                    Magister Teknik Elektro   52
           Nomadic Access
Mobile data terminal
   e.g. laptop
Transfer of data from laptop to server
Campus or cluster of buildings




                  Magister Teknik Elektro   53
      Ad Hoc Networking
Peer to peer
Temporary
e.g. conference




                  Magister Teknik Elektro   54
Wireless LAN Configurations




          Magister Teknik Elektro   55
 Wireless LAN Requirements
Throughput
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

                    Magister Teknik Elektro   56
  Wireless LAN Technology
Infrared (IR) LANs
Spread spectrum LANs
Narrow band microwave




             Magister Teknik Elektro   57
     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-
based:
   Direct Sequence Spread Spectrum
   Frequency-hopping spectrum
   Infrared

                  Magister Teknik Elektro     58
   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
point.
The distribution system is usually a wired
backbone LAN.

                Magister Teknik Elektro         59
Wireless LAN Components (cont’d)




            Magister Teknik Elektro   60
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
 LANs.
                  Magister Teknik Elektro          61
     Medium Access Control

The MAC protocol used in 802.11 LANs is
called Distributed Foundation Wireless MAC
(DFWMAC).
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
CSMA/CD.

                Magister Teknik Elektro        62
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.



                 Magister Teknik Elektro         63
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.

             Magister Teknik Elektro    64
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
 Ethernet.
 Two different WLAN MAC techniques are now
 in use: the Physical Carrier Sense Method
 and the Virtual Carrier Sense Method.
                   Magister Teknik Elektro            65
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.
                   Magister Teknik Elektro            66
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.
                Magister Teknik Elektro        67
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.




                   Magister Teknik Elektro        68
       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
wiring.
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.


                     Magister Teknik Elektro                69
Infrared Wireless LAN (cont’d)




           Magister Teknik Elektro   70
                Bluetooth

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.
                   Magister Teknik Elektro             71
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.


                  Magister Teknik Elektro            72
       Ethernet (CSMA/CD)
 Carriers Sense Multiple Access with
  Collision Detection
 Xerox - Ethernet
 IEEE 802.3




                 Magister Teknik Elektro   73
      IEEE802.3 Medium Access
              Control
 Random Access
     Stations access medium randomly
 Contention
     Stations content for time on medium




                     Magister Teknik Elektro   74
                        CSMA
 Propagation time is much less than transmission time
 All stations know that a transmission has started almost
  immediately
 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
      utilization
                        Magister Teknik Elektro             75
                  If Busy?
 If medium is idle, transmit
 If busy, listen for idle then transmit
  immediately
 If two stations are waiting, collision




                   Magister Teknik Elektro   76
                 CSMA/CD
 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
  transmission
 After jam, wait random time then start again
    Binary exponential back off


                    Magister Teknik Elektro      77
CSMA/CD
Operation




 Magister Teknik Elektro   78
           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
  (10Base2)
 For twisted pair (star-topology) activity on more
  than one port is collision
 Special collision presence signal

                     Magister Teknik Elektro          79
Gigabit Ethernet Configuration




           Magister Teknik Elektro   80
 Gigabit Ethernet - Differences
 Carrier extension
 At least 4096 bit-times long (512 for
  10/100)
 Frame bursting




                  Magister Teknik Elektro   81
      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
                     Magister Teknik Elektro        82
            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
   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

                        Magister Teknik Elektro              83
Token Ring Operation




       Magister Teknik Elektro   84
Priority Scheme




    Magister Teknik Elektro   85
         Dedicated Token Ring
   Central hub
   Acts as switch
   Full duplex point to point link
   Concentrator acts as frame level repeater
   No token passing




                   Magister Teknik Elektro      86
                 FDDI
 100Mbps
 LAN and MAN applications
 Token Ring




                Magister Teknik Elektro   87
FDDI Operation




    Magister Teknik Elektro   88
               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

   switches
Workgroup ATM
  End systems connected directly to ATM switch

Mixed system
                  Magister Teknik Elektro         89
Example ATM LAN




     Magister Teknik Elektro   90
ATM LAN HUB




   Magister Teknik Elektro   91
          Compatibility
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



               Magister Teknik Elektro   92

				
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