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Multicast Transmission in WLAN

Multicast Transmission in WLAN. Authors:. Date: 2008-05-13. Abstract. Participation in Multicast Session signalling and request for Reliable Multicast Transmission Message flow for reliable multicast setup and operation Synchronization of sequence numbers.

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Multicast Transmission in WLAN

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  1. Multicast Transmission in WLAN Authors: Date: 2008-05-13 Naveen K. Kakani, Nokia Inc

  2. Abstract • Participation in Multicast Session signalling and request for Reliable Multicast Transmission • Message flow for reliable multicast setup and operation • Synchronization of sequence numbers Naveen K. Kakani, Nokia Inc

  3. Need for Signaling to indicate participation in Multicast Group • Multicast recipient needs reliable Multicast Transmission • Poor link condition • Multicast stream needs reliability to ensure QoS • Allow power save • If the STA is a PSMP capable STA, AP can schedule Multicast and Unicast transmissions to the STA in the same PSMP sequence Naveen K. Kakani, Nokia Inc

  4. Determining Unicast entities that are part of Multicast Group Explicit signaling : • AP indicates support for reliable Multicast Broadcast (RMB) in the capability field : B7 in Wireless Network Management Capabilities • STAs can transmit Reliable MB Request Frame to signal participation in a Multicast Group and request for setting up a reliable Multicast Transmission Naveen K. Kakani, Nokia Inc

  5. MAC Header Frame Body FCS Action = 3 1 bytes Category(3) 1 byte Dialong Token 1 byte Trigger Code 1 byte Multicast Address 6 bytes RMB Reserved TID Valid TID BA Bits 1 1 1 4 1 Reliable MB Request frame • Unicast frame transmitted by MB Recipient to the MB transmitter • Interpretation of the fields in next slide Naveen K. Kakani, Nokia Inc

  6. Interpretation of the fields Naveen K. Kakani, Nokia Inc

  7. Reliable MB Response frame MAC Header Frame Body FCS RMB field is copied from the Request Frame Multicast Address 6 bytes Action = 4 1 bytes Category(3) 1 byte Dialong Token 1 byte Trigger Code 1 byte RMB BA Retransmit TID Valid TID Bits 1 1 1 1 4 • Unicast frame transmitted by MB Transmitter and destined to a specific recipient • Interpretation of the fields in next slide Naveen K. Kakani, Nokia Inc

  8. Interpretation of the fields Naveen K. Kakani, Nokia Inc

  9. Retransmission Address • Assign locally administered “Multicast Address” • Retransmitted data needs to be encrypted (new value in Address 1 field) • Nothing needs to be specified in the standard • Flip one bit in the prefix that would be appended to the IP multicast address to create the “Multicast Address” • If the retransmitted data is not encrypted then in the standard it needs to be specified that the recipient should flip the AAD field of the received retransmitted data • If the retransmitted data is encrypted again (with new value in Address 1 field) nothing needs to be specified in the standard Naveen K. Kakani, Nokia Inc

  10. MSG 1 Reliable MB Request Frame Reliable MB Response Frame MSG 2 Multicast/Broadcast Data Transmitter ADDBA Request Frame MSG 3 MSG 4 ADDBA Response Frame Multicast/Broadcast Data Receiver Multicast Data Transmission Explicit BAR Frame / Implicit Signalling during PSMP Repeat for recepients who requested Reliable Multicast Broadcast BA Frame Retransmit Multicast Data with signalled MAC address for retransmission Proposed Algorithm Messages marked in blue color are present if the Multicast Recipient requests for reliable multicast session (RMB bit = 1 in Reliable MB Request frame) and the transmitter signals that it is going to set up a new BA session Naveen K. Kakani, Nokia Inc

  11. Mapping of Multicast/Broadcast (MB) Stream for each STA • STAs that require/support reliability in receiving MB streams should have a TID assigned for each MB stream for which they need reliability • TIDs are assigned dynamically (QoS type TID’s) and the STA has prior knowledge of the current BA sessions established between the AP and the STA Naveen K. Kakani, Nokia Inc

  12. Multicast Data frame • QoS Multicast Data frame • ACK Policy bit setting • When transmitting Multicast data with in a PSMP sequence the rules of ACK Policy setting follow the rules as described in PSMP • When transmitting Multicast data outside PSMP sequence • the ACK policy shall be set to “No Ack” • STAs that need reliable Multicast map the received “Multicast Address” to a the corresponding TID • STAs transmit BA in response to explicit BAR only • Non QoS Multicast Data • STAs that need reliable Multicast map the received “Multicast Address” to a specific TID and the STA transmits a BA/MTBA in response to explicit BAR/MTBAR Naveen K. Kakani, Nokia Inc

  13. Synchronizing Sequence numbers after BA Setup • RX side • The starting sequence number is set to the sequence number of data frame received after setting up the BA • TX side • The starting sequence number is set to the starting sequence number of the first frame transmitted after setting up the BA Naveen K. Kakani, Nokia Inc

  14. Reserved (B3-B11) TID (B12-15) ACK Policy B0 MT BA/BAR B1 Multicast/Broadcast MB (B2) Rules at TX • BA is requested explicitly outside PSMP • Explicit request: BAR/MTBAR frame has Bit 3 in BA control field to indicate that the request is for MB stream, TID corresponds to the TID of the MB stream at the RX STA • Window updates are done as per the rules of regular BA • Decision to retransmit the data (either using multicast address or unicast address) is at the discretion of the transmitter Naveen K. Kakani, Nokia Inc

  15. MTBA/BAR (B1) ACK Policy (B0) Multicast/Broadcast MB (B2) Reserved (B3-B11) TID (B12-B15) Rules at RX • BA/MTBA frames that carry the bitmap of MB stream shall set Bit 3 in BA control field, and the TID value corresponds to the MB stream that was signaled for this STA for the specific MB stream • Window updates are done as per the rules of regular BA if data is received addressed to the multicast address or if data for the TID is transmitted as a unicast frame • When the window is full and there is new data received the starting sequence number of the Bit Map is shift to accommodate the new data Naveen K. Kakani, Nokia Inc

  16. FBMS Based Streams • If the AP supports FBMS then STAs that are participating in reliable Multicast/Broadcast can negotiate a specific DTIM period for the retransmission data (using retransmission MAC address) • Nothing new required for the baseline FBMS mechanism to setup the DTIM period for the retransmission data Naveen K. Kakani, Nokia Inc

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