WiSP

1
WiSP Wireless Sidelink Protocol

• Wim Diepstraten
• Gerrit Hiddink
• Agere Systems

2
WARP functionality

• The WARP protocol is a new mechanism in the draft
  standard.
• Its intent is to allow the Stations in
  Infrastructure mode an option to send frames to
  stations within the same BSS directly.
• Saving bandwidth by not going via the AP
• Dealing with remote stations in Power Save mode.

3
Existing WARP

• Consist of
• The Direct Communication Setup procedure
• Registration procedure
• Location discovery procedure
• Direct negotiation procedure
• The Status change notification procedure
• The Wake notify procedure
• With 12 WARP Action Codes
• And various fields and elements
• This is considered much more complex than needed.

4
WiSP Alternative

• The Wireless Sidelink Protocol (WiSP) is a much
  simpler alternative
• It uses a Wakeup Action request and response
  frame in the Wakeup procedure.
• With 4 possible status codes
• And uses existing directed Probe request and
  response frames in the location Discovery
  procedure.

5
WiSP Wakeup Action phase

• QSTA-1 send Wakeup Action request frame to
  QSTA-2
• AP will forward the request to QSTA-2 when it is
  in the same BSS.
• If QSTA-2 is in Power Save mode, then this will
  be done in the appropriate way by buffering the
  frame, and announce the pending traffic in the
  TIM, so that QSTA-2 can retrieve it as desired.
• Else If QSTA-2 not in the BSS, then AP returns
  Wakeup Action response with status code Not
  present
• Else If STA-2 is a legacy station, then AP
  returns Wakeup Action response with status code
  incapable.
• QSTA-2 upon the request will respond with a
  Wakeup Action response destined to QSTA-1, with
  a status Succesfull if it wants to engage in
  side traffic, and will stay awake for a minimum
  timeout period.
• If it does not want to engage in side traffic,
  then QSTA-2 will respond with status code
  Denied.
• The AP will forward this Wakeup Action response
  frame to QSTA-1 as appropriate.

6
WiSP Location discovery phase

• After QSTA-1 receives a response indicating
  Succesfull
• It can enter the Location Discovery phase, to
  find out whether the remote station is indeed in
  direct communication range.
• QSTA-1 will send a directed Probe Request frame
  to QSTA-2 at a rate determined by QSTA-1.
• QSTA-2 will respond with a directed Probe
  Response frame to QSTA-1 at the same rate at
  which it received the Probe Request.
• The Probe request and response frames do contain
  all the information needed by each station to
  understand each others capabilities.
• This allows the stations to decide whether it
  wants to continue using the side channel, and can
  determine the appropriate rate.
• QSTA-2 will if it was in Power Save mode, stay
  awake for a no-activity timeout period after
  every reception.
• QSTA-1 can assume that QSTA-2 is awake within
  such a timeout period, and send all data to
  QSTA-2 via the side channel.
• QSTA-1 can judge from the Pwr Mgt bit in the
  Frame Control word whether QSTA-2 is indeed in
  power save mode, and will return to sleep after
  the timeout period.
• Both sides can assume that both sides are awake
  during the timeout period.
• Stations maintain a cache with the side channel
  capabilities on a per destination basis.

7
WiSP contd

• After the timeout period has elapsed, stations
  can use the Wakeup Action procedure to wakeup
  the remote station again.
• And can send data without having to go through
  the Location discovery procedure.
• The Location discovery procedure is in itself
  optional, as stations can directly start with
  sending data.
• The no-activity timeout period can be a MIB
  parameter, with a defined default.

8
Evaluation

• The proposed procedure is simple and adequate,
  and uses a minimum of new frames.
• It is envisioned that the WiSP will only be
  used for high bandwidth bulk traffic.
• So Power Save sensitive applications may not want
  to use it.
• We believe that the described provisions are
  sufficient for side channel operation.
• Stations engaged in side link traffic, have to
  deal with changes in the link, that require rate
  changes, and they can even go out of range (while
  it is still in the same BSS).
• So those stations that do not receive an Ack on
  multiple retries, should conclude that the remote
  station is gone, so that it should direct all
  traffic destined to that station via the AP
  again.
• Stations roaming away to another BSS is an other
  possible situation, that can be dealt with using
  a similar algorithm.
• No additional status change mechanisms are felt
  needed, but can easily be included.

9
Possible enhancements

• APs can monitor the Wakeup Action response
  frames, and register that QSTA-1 and 2 are
  Sidelink capable
• It can send unsolicited Wakeup Action responses
  with status Not Present when it discovers that
  one of the stations has roamed away.
• Remote stations that do want to go back into
  sleep mode, can send a directed Data-null frame
  to the remote station to signal that the station
  goes back into sleep mode.
• Instead of the Wake-up timeout, the stations
  can use the More bit to keep the remote station
  awake during the desired time.
• This timeout period could however also be an
  extra field in the Wakeup Action
  request/response frames.
• While a zero could identify No Power Save mode.

10
WiSP Conclusion

• WiSP is a simple yet adequate solution to allow
  stations to use Side channel in an infrastructure
  environment.
• And uses only one additional Action
  request/Response pair.
• With status codes Succesfull,Not Present,
  Denied
• It is much simpler than WARP.
• WiSP should be adopted to replace WARP.

11
Issues

• What enhancements are needed for security
  purposes?
• Some protocol may be needed to aid in the key
  distribution.
• Can we use the option to do sidelink traffic
  using the common BC/MC key?
• Do we need to add something in the Wakeup Action
  frame to signal this?

12
Straw-Polls

• In order to start drafting normative text for
  WiSP
• StrawPoll Question
• Who wants WiSP to replace WARP?
• Should WiSP be enhanced in any way?

13
How to merge?