Basic Concepts

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					Ethernet and Wireless
Local Area Networks
History of Ethernet Standards

   Ethernet
       The dominant wired LAN technology today
       Only “competitor” is wireless LANs (which actually are

   The IEEE 802 Committee
       LAN standards development is done primarily by the
        Institute for Electrical and Electronics Engineers (IEEE)
       IEEE created the 802 LAN/MAN Standards Committee
        for LAN standards (the 802 Committee)

History of Ethernet Standards

    The 802 Committee creates working groups for
     specific types of standards
        802.1 for general standards
        802.3 for Ethernet standards
           The terms 802.3 and Ethernet are interchangeable

        802.11 for wireless LAN standards
        802.16 for WiMax wireless metropolitan area network

Ethernet Physical Layer Standards

 UTP Physical               Maximum              Medium
    Layer         Speed       Run                Required
  Standards                  Length
 10BASE-T        10 Mbps    100 meters 4-pair Category 3 or higher

 100BASE-TX     100 Mbps    100 meters 4-pair Category 5 or higher

 1000BASE-T     1,000 Mbps 100 meters 4-pair Category 5 or higher

              100BASE-TX dominates access links today.
       Although 1000BASE-T is growing in access links today

Ethernet Physical Layer Standards

  Fiber Physical   Speed Maximum           Medium
      Layer                Run    850 nm light (inexpensive)
    Standards             Length       Multimode fiber
  1000BASE-SX      1 Gbps   220 m     62.5          160
                                    microns        MHz-km
  1000BASE-SX      1 Gbps      275 m       62.5           200

  1000BASE-SX      1 Gbps      500 m        50            400

  1000BASE-SX      1 Gbps      550 m        50            500

      The 1000BASE-SX standard dominates trunk links today.
     Carriers use 1310 and 1550 nm light and single-mode fiber.
Gigabit Ethernet

   10 Gbps Ethernet usage is small but growing
   Several 10 Gbps 10GBASE-x fiber standards are
    defined, but none is dominant
   Copper is cheaper than fiber but cannot go as far
   100 Gbps has been selected as the next Ethernet
       Chosen over 40 Gbps

   100 Gbps Ethernet standards development is just
    getting underway
Data Link Using Multiple Switches

 Original Received Regenerated Signal            Received
 Signal    Signal                     Regenerated Signal

         UTP               62.5/125                  UTP
                        Multimode Fiber

     100BASE-TX           1000BASE-SX          100BASE-TX
   (100 m maximum)      (220 m maximum)      (100 m maximum)
     Physical Link         Physical Link       Physical Link

          Each trunk line along the way has a distance limit

Multi-Switch Ethernet LAN Architecture

         Switch 2 (root switch)

                                                  Port 7 on Switch 2
            Port 5 on Switch 1                   to Port 4 on Switch 3
           to Port 3 on Switch 2
    Switch 1                                                 Switch 3

                         Switch 2, Port 5

                          Switch 1, Port 7

A1-44-D5-1F-AA-4C                  D4-55-C4-B6-9F     E5-BB-47-21-D3-56
  Switch 1, Port 2                 Switch 3, Port 2    Switch 3, Port 6
Single Point of Failure in a Switch Hierarchy

                         Switch Fails

                                 Switch 2
       No Communication           No Communication

        Switch 1                               Switch 3

           B2-CD-13-5B-E4-65    D4-47-55-C4-B6-9F
   A1-44-D5-1F-AA-4C                    E5-BB-47-21-D3-56
Hierarchy Implications

     Single possible path between stations.
     Makes switching tables very simple because there is only one
      possible row for each address. Find the row, send the frame out
      the indicated port. Very fast, so minimizes switching cost.

       Port Station
         2 A1-44-D5-1F-AA-4C
         7 B2-CD-13-5B-E4-65
         5 E5-BB-47-21-D3-56

     Creates the potential for single points of failure.
     Low cost is responsible for Ethernet’s LAN dominance.

Switch Operation in Ethernet

   Today, Switches Dominate in Ethernet
       A frame comes in one port
       The switch looks up the frame’s destination MAC
        address in the switching
       The switch sends the frame
        out a single port
       Only two ports are tied up
       Other conversations can
        take place on other port
        pairs simultaneously
Ethernet 802.3 10Base2

    Ethernet 10Base2

         To Next

               T-Connector to Link NIC to next segments
Ethernet 802.3 10Base2

     Ethernet 10Base2
                                       To next
                         T-connector   station

 BNC connector

Virtual LAN with Ethernet Switches

                  Server broadcasting without VLANS
Frame is Broadcast
Goes to all other stations
Creates congestion


                               Client C

                  Client B
Client A                                    Server D   Server E

Virtual LAN with Ethernet Switches

                     Server multicasting with VLANS
     With VLANs,                                      Multicasting
 broadcasts go to a                                   (some), not
    server’s VLAN                                     Broadcasting (all)
 clients; less latency

                         NO                    NO

                                Client C
                               on VLAN1
                   Client B
 Client A         on VLAN2                    Server D       Server E
 on VLAN1                                    on VLAN2       on VLAN115
Handling Momentary Traffic Peaks with
Overprovisioning and Priority
                        Momentary traffic peak:
                        Congestion and latency

                                            Momentary traffic peak:
                                            Congestion and latency
    Network capacity

  Momentary traffic peaks usually last fraction of a second;
    They occasionally exceed the network’s capacity.            Time
   When they do, frames will be delayed, even dropped.

Handling Momentary Traffic Peaks with
Overprovisioning and Priority

              Overprovisioned traffic capacity in Ethernet

   Overprovisioned network capacity           Momentary peak:
                                              No congestion

    Build high capacity than will rarely if ever be exceeded.   Time
     This wastes capacity. But cheaper than using priority.

Handling Momentary Traffic Peaks with
Overprovisioning and Priority

                           Priority in Ethernet

                             Momentary        High-priority traffic goes
                             peak             Low-priority waits
    Network capacity

     Priority: During momentary peaks, give priority to             Time
       traffic that is intolerant of delay, such as voice.
   No need to overprovision, but expensive to implement.
         Ongoing management is very expensive.
Routed LAN with Ethernet Subnets

If a routed LAN links multiple Ethernet switched
networks, the switched networks are called subnets
Wireless LANs
Local Wireless Technologies

   802.11 Wireless LANs (Wi-Fi)
       Today, mostly speeds of tens of megabits per second
        with distances of 30 to 100 meters or more
          Can serve many users in a home or office

       Increasingly,100 Mbps to 600 Mbps with 802.11n

       Organizations can provide coverage throughout a
        building or a university campus by installing many
        access points

802.11 Wireless LANs (WLANs)

                Wireless hosts connect
               by radio to access points

Transmission speed: up to 300 Mbps but usually 10 Mbps to 100 Mbps.
   Distances between station and access point: 300 to 100 meters. 22
Wireless Access Points and NICs

Typical 802.11 Wireless LAN Operation with
Wireless Access Points

                          802.11 uses a different
                         frame format than 802.3

                       The access point translates
                      between the two frame formats

                     However, the packet goes all the
                       way between the two hosts

Hosts and Access Points Transmit
in a Single Channel

    The access point and all the hosts it servers
           transmit in a single channel

       If two devices transmit at the same time,
  their signals will collide, becoming unreasonable

        Media access control (MAC) methods
         govern when a device may transmit;
      It only lets one device transmit at a time
Media Access Control (MAC)

    MAC methods govern when devices transmit so
     that only one station or the access point can
     transmit at a time
    To control access (transmission), two methods
     can be used
        CSMA/CA+ACK (mandatory)
        RTS/CTS (optional unless 802.11b and g stations
         share an 802.11g access point)

CSMA/CA+ACK in 802.11 Wireless LANs

   CSMA/CA (Carrier Sense Multiple Access with
    Collision Avoidance)
       Sender listens for traffic
          1. If there is traffic, waits

          2. If there is no traffic:

              2a. If there has been no traffic for less than the critical

                 time value, waits a random amount of time, then returns
                 to Step 1.
              2b, If there has been no traffic for more than the critical

                 value for time, sends without waiting
              This avoids collision that would result if hosts could
                 transmit as soon as one host finishes transmitting

CSMA/CA + ACK in 802.11 Wireless LANs

    ACK (Acknowledgement)
        Receiver immediately sends back an
         acknowledgement; no waiting because ACKs have
         highest priority.
        If sender does not receive the acknowledgement,
         retransmits the frame using CSMA/CA.
        802.11 with CSMA/CA+ACK is a reliable protocol!

Request to Send/Clear to Send

Specific 802.11 Wireless LAN Standards

 Characteristic 802.11 802.11a 802.11b 802.11g 802.11g 802.11n
 Rated Speed      2      54      11      54      Not   100 Mbps
                Mbps Mbps       Mbps    Mbps    Speci-       to
                                                 fied  300 Mbps
 Actual           1      25    6 Mbps    25       12   Closer to
 Throughput,    Mbps Mbps               Mbps    Mbps      rated
 3m                                                      speed
 Actual           ?      12    6 Mbps    20       11    High at
 Throughput,            Mbps            Mbps    Mbps     longer
 30 m                                                  distances
Specific 802.11 Wireless LAN Standards

Characteristic 802.11 802.11a 802.11b   802.11g   802.11g   802.11n
Unlicensed    2.4      5       2.4      2.4 GHz     2.4  2.4 GHz
Band          GHz     GHz      GHz                 GHz      and
                                                          5 GHz
Remarks       Dead     Little Bloomed Today’s Get rid of Greater
               and   market    briefly dominant   old     speed
              gone   accep-             802.11  802.11b     and
                      tance            standard  equip.  distance

Specific 802.11 Wireless LAN Standards

   802.11g
       Most popular 802.11 standard today
       54 Mbps rated speed with much slower throughput
       Generally sufficient for Web browsing
       Inexpensive
       All access points support it


    Under development
        Rated speeds of 100 Mbps to 600 Mbps

        Will operate in both the 2.4 GHz and 5 GHz bands

        May use twice current bandwidth per channel (~20
         MHz) to roughly double speed

        Currently a draft standard

        A bit of overkill for most users

Bluetooth Personal Area Networks (PANs)

     Bluetooth is standardized by a consortium
     Connect devices on or near a single user’s
         PC, Printer, PDA, Laptop, Cellphone
     Connect devices on or near a single user’s
         Laptop, Printer, PDA, Cellphone

     The goal is cable elimination

Bluetooth PANs

     There may be multiple PANs in an area
         May overlap
         PANs are called piconets

Bluetooth PAN Operation

        master             File synchronization

                                                          Client PC
                Printing                                    slave
                                        Printer slave

                                                        Note: Printer
Piconet 1                     Call through company        is in both
                                  phone System            piconets;
            Cellphone                                    Slave has
             master                                     two masters.
                                   Telephone slave

             Piconet 2
802.11 versus Bluetooth PANs

                          802.11                   Bluetooth

     Focus             Large WLANs            Personal Area Network
                                               722 kbps with back
                   11 Mbps to 54 Mbps
     Speed                                     channel of 56 kbps.
                    In both directions
                                                 May increase.
                  100 meters for 802.11b
                                                   10 meters.
    Distance       (but shorter in reality)
                                                  May increase
                  Even shorter of 802.11a
                                                Only 10 piconets,
                  Limited in practice only         each with
  of devices in
                  by bandwidth and traffic         8 devices
     an area

802.11 versus Bluetooth PANs

                               802.11                   Bluetooth
                       Good through having
    Scalability                                        (but may get
                       multiple access points
                                                      access points)

        Cost               Probably higher           Probably Lower

   Battery Drain                Higher                    Lower

      Profiles                   No                         Yes

   Profiles allow specific products to work together. Different profiles
   for printing, cordless telephones, headsets, etc. Must be
   implemented on both master and slave.

Bluetooth PANS

   Trends
       Bluetooth Alliance is enhancing Bluetooth

       The next version of Bluetooth is likely to grow to use
        ultrawideband transmission
            This should raise speed to 100 Mbps (or more)
            Transmission distance will remain limited to 10
            Good for distributing television within a house

Emerging Local Wireless Technologies

     In mesh wireless networks, the access points do all routing
                There is no need for a wired network
   The 802.11s standard for mesh networking is under development
         This P2P networking needs high density of devices

Emerging Local Wireless Technologies

     Can be focused electronically to give better reception

Emerging Local Wireless Technologies

   Ultrawideband (UWB)
       Uses channels that are several gigahertz wide
            Each UWB channel spans multiple frequency bands

       Low power per hertz to avoid interference with other

       Wide bandwidth gives very high speeds

       But limited to short distance and ideal for video networking
        at home

       Wireless USB provides 480 Mbps up to 3 meters, 110
        Mbps up to 10 meters
Emerging Local Wireless Technologies

   ZigBee for almost-always-off sensor networks
       Very low speeds (250 kbps maximum)
       Very long battery life (months or years)
       At the other end of the performance spectrum from

Emerging Local Wireless Technologies

   RFID (Radio Frequency Identification) Tags
       Like UPC tags but readable remotely

       In most cases, the radio signal from the reader provides power
        for the RFID tag

       The RFID tag uses this power to send information about itself

       Battery-operated RFID tags can send farther and send more
       30-500 KHz, short distances, for supermarket scanning and
        inventory control
       850-950 MHz, large distances, higher speed, for automated toll
Emerging Local Wireless Technologies

   Software-Defined Radio
       Can implement multiple wireless protocols
       No need to have separate radio circuits for each
       Reduces the cost of multi-protocol devices