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Tsunami MP.11 WORP Protocol by chenshu


									WAN Basics
Tsunami MP.11 - QB.11 – QuickBridge 60250

      Tsunami MP.11
      WORP Protocol

                                            April 2008
                                        Wireless Outdoor Router

 WORP is a polling algorithm designed for wireless outdoor networks
 WORP takes care of the performance degradation that happens when
  standards-based 802.11wireless LAN technology is used for outdoor building-
  to-building connectivity, incurred by the so-called “hidden-node” problem.
 WORP Benefits:
    More effective use of bandwidth
        Sustain more simultaneous users
    More concurrent subscribers (up to 250 depending on the Model)
        Reduces Infrastructure investment per subscriber
    Asymmetric Bandwidth Control and QoS
        Enables Service Provider to differentiate his service offering between i.e. business and
         residential customers

                                                                            Unwiring the Network
                                    WORP & The Hidden Node

 Hidden-node problem
    802.11 radios use CSMA/CA (Collision Avoidance) for transmission
    Requires radios to hear each other
    RTS/CTS (Request to send/Clear to send) mechanism should have solved this
    However, multiple radios can still send an RTS when another radio is transmitting,
     and this will corrupt all data being sent degrading overall performance
 WORP polling algorithm ensures that these collisions cannot occur
 WORP increases the performance of the overall network significantly
 WORP polling dynamically adapts to the number of satellites that are active
  on the network and how much data they have queued up to send

                                                                   Unwiring the Network
                                    WORP and IEEE 802.11 radios

 WORP uses IEEE 802.11 radios in a modified way
 IEEE802.11 radios require unicast frames to be responded by ACK frame
  within 10 microseconds after transmission of the frame
    This imposes a limit to the distance between stations, based on the speed of the
     transmission (speed of light = 2998 * 105 M/s)
    The theoretical limit on the distance between two radios would then be app. 1500
    Beyond that distance the ACK frames would not be in time
 WORP solves this issue by transmitting all information as multicast IEEE
  802.11 frames (even when sending to a single destination):
    Uses the unique MAC address of the destination radio with the multi-cast bit flipped

                                                                   Unwiring the Network
                                       WORP Protocol

 Network uses 2 strings for identification
    Network Name: same for entire “roaming area”
    Base Station Name: unique per BSU, so SU can be “locked”.
        avoids customers relocating without contacting you
        better bandwidth control.

 BSU to SU communication
    Registered Subscriber Unit gets port number assigned
        BSU‟s bridge learn table shows WORP Satellites as ports 2, 3…251.
    BSU is broadcasting the information listed above, but this broadcast stops when all
     configured SUs have registered and are active.
    Registration: MD-5 authentication uses “Network Secret” string
    De-registration: when BSU or SU has not seen its peer for 30 sec.
    Bandwidth control per interface (SU/BSU, wireless/Ethernet) or Radius.

                                                                       Unwiring the Network
                                WORP Functionality

 Announce identity of BSU
 Registration and authentication of SU
 De-registration of SU
 Polling SUs, request for service and dynamic scheduling
 No-Sleep mode
 SU Roaming
 Encryption of data
 Bandwidth control up/down
 Windowing, retransmit and timeout of data transfer
 Throughput, super-packeting and Fragmentation of data
 PtP and PtMP deployment

                                                            Unwiring the Network
                                    Announcing the presence of a

 BSU sends periodically ANNOUNCE (Broadcast) WORP message including
    Network name, Base Station name, Number and port-id of registered SUs
 ANNOUNCE message starts a Contention Period during which SUs can
  transmit without being polled.
    SU can initiate transmission only immediately after broadcast, before polling starts
     again, but needs to contend with other SUs
 ANNOUNCE message is the start of the registration process
 ANNOUNCE messages interrupts polling cycle every 150 ms (100 ms when
  roaming is enabled)
 No ANNOUNCE message when max configured # of SU have all registered
  and are being polled

                                                                    Unwiring the Network
                                  SU response to ANNOUNCE

 SUs operating on the same channel (or scanning the channels) will examine
  the ANNOUNCE message to match the network name to the one configured
  in the SU
 On receipt on an acceptable ANNOUNCE message (with matching network
  name) an SU can send
    a REQFORSERV message to start the registration process (when not yet
    a DATA message, in case the SU has not been polled for a certain amount of time
     (announcement time-out period)
    an ABORT message in case the SU goes into roaming mode and has not been
     polled for a certain amount of time (announcement time-out period)

                                                                Unwiring the Network
                                    Registration and

 The SU sends an REQFORSERV message to start the registration process
  (when not yet registered) on receipt of the ANNOUNCE message with
  matching network name
 The BSU will start the authentication process with a HELLO message
    Includes the logical port number assigned to the SU (used for bridging)
 The SU replies with a REGREQ message
    Starts the MD5 CHAP authentication by including the challenge string
    Starts the bandwidth negotiation by including the requested up- and down-stream
     requested bandwidth
 The BSU replies with a REGCONF message
    Including to the MD5 challenge (using the network secret)
    Including the granted up- and down-stream bandwidth
 The SU completes the sequence with a READY message
    Includes the reply to the MD5 challenge (using the network secret)

                                                                   Unwiring the Network

 When BSU or SU have not seen their peer for 30 seconds then they consider
  the SU deregistered and it needs to re-register as soon as it sees the BSU
  again (waiting for an ANNOUNCE message)
 BSU can send a REGREJ message to de-register an SU
    This message will contain the reason for termination
 An SU can initiate de-registration by sending the ABORT message
    SU entering a roaming process
    SU shutting down

                                                            Unwiring the Network
                                   (Contention Free Period)

 BSU will poll each satellite regularly sending the POLLDATA message
 At minimum every 4 seconds (sleep mode)
 The POLLDATA message contains:
    Signal and noise levels recorded at the BSU (recorded on traffic coming from the
     polled SU)
    Acknowledgement information related to data transmitted from the polled SU to the
    Data frames transmitted by the BSU to the SU (if available)
    Control information to allow burst mode transmissions

                                                                 Unwiring the Network
                                   (Contention Free Period)

 An SU that is polled will reply with a DATA message
    Signal and noise levels recorded at the SU (recorded on traffic coming from the
    Acknowledgement information related to data transmitted from the BSU to the SU
    Data frames transmitted by the SU to the BSU (if available)
    Control information to allow burst mode transmissions
 If a SU has new data it will request to be polled immediately as soon as it
  sees the BSU ANNOUNCE message and was not polled since last
 For PtP mode you need BSU-SU pair and configure it for 1 SU, so it stops
  sending the ANNOUNCE.

                                                                 Unwiring the Network
                                  SU Roaming

 Allows SUs to „roam‟ from BSU to BSU, allowing mobility and/or redundancy
 Roaming includes
      Scanning channels for new BSU‟s (listening to ANNOUNCE messages)
      Select the new BSU from the list of found new BSUs
      Terminating the relationship with the current BSU
      Re-registering at the new (selected) BSU
 See PCBA MP.11 Roaming Chapter for more details

                                                              Unwiring the Network
                                 Bandwidth Control

 Configurable Per SU – BSU link
    Local static config in each SU
    Central config statically in the BSU
    Central config via Radius Asymmetric up/down
 Polling guarantees fair sharing of available bandwidth over SUs
 See PCBA MP.11 Quality of Service chapter for more details

                                                            Unwiring the Network
                                    Windowing, Retransmit and

 Data is sent between SU and BSU with
                                                                     TX data
  incrementing sequence number and ack.
 New data is sent immediate if “window” of
  sequence numbers is not yet filled                  TX Queue
 Bottom of the window is the last
                                                      discard on
  acknowledged sequence number
 Selective retransmit after several frames
                                                                     Transmit data
  when no ACK is received.
 Timeout and discard happens when:
                                                         Re-TX                 Acknowledge
    data too long in TX queue: 1.5 sec (max 512         Queue
                                                                          Retransmit data
    data too long in retransmit queue (16 entries)
     dependent on baudrate and # of satellites
                                                                       discard on timeout
                                                                       or acknowledge

                                                                   Unwiring the Network
                                 Super-packeting and

 Packets are sent over the air in 802.11    100%
  frames, max size                            80%
  2304 bytes                                  70%
 Ethernet frames only have 1514 data         40%
  bytes.                                      30%

    60% of IP packets are below 100 data     10%
     bytes.                                          <100   128   256   512   1024   1514

 WORP minimizes overhead via:
                                            Mbps 5
    Super-packeting
    Fragmentation                            20 4
                                              15 3
                                              10 2
                                                      64    128   256   512   1024   1514

                                                                  Unwiring the Network

  More than one Ethernet packet become “payload” of a WORP frame

                                             BSU                             SU

                                          Ethernet port                      Ethernet port
                                          receiving/transmitting             receiving/transmitting
                                          standard Ethernet frames           standard Ethernet frames

    5        4        3       2       1                                              5          3       2
Color indicates destination MAC domain

                  5       3       2                                  5   3   2

               WORP Frame

                                                                                         Unwiring the Network

 Splits one packet over 2 frames when the packet does not fit in the
  space remaining at the end of the first frame.

                 6              5        4         2       3            1

           Ethernet Packets: Color indicates destination MAC “domain”

                                    6         6            5       2           3

          WORP Frame 2                                 WORP Frame 1

                                                                            Unwiring the Network
                                Packet Format - summary

 Packet header
      Dest Source     Len   SNAP Ver      MsgType    Port    Payload     FCS

     Payload (either one of):
      Announce          Nr of SU   System name      Network name

      ReqForServ        SNR System name

      Hello             SNR
      Wait              SNR

      RegReq            SNR ACB BWdown           BWup

      RegConf           SNR ARB ACS BWdown              BWup

      Ready             SNR ARS

      PollData          SNR Seq     Ack    Qlen Flags Data

                                                            Unwiring the Network

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