1. doc.: IEEE 802.11-12/0110r8 SubmissionLiwen Chu Etc.Slide 1 Frame Header Compression Date: 2012-05-14 Authors: Date: May, 2012

2. doc.: IEEE 802.11-12/0110r8 Submission MAC Frame Header The typical frame payload of Smart Grid is tens/hundreds bytes. –100 bytes payload frame with 3 MAC addresses has about 30/100=30% MAC header overhead! –300 bytes payload frame with 3 MAC addresses has about 30/300=10% MAC header overhead! The following parts of the MAC header can be compressed : –Some MAC address fields can be removed from the MAC header, Before transmission, the removed MAC address should be negotiated and recorded in the transmitter and the receiver as defined in Backup slides. –Do we need 2 bytes Sequence Control in a low rate Smart Grid BSS? –Do we need Duration/ID since 2-bit ACK Indication is added to PHY SIG? –Do we need 2 bytes QoS Control field? –Do we need 4 byte FCS? Frame Control Duration/ ID Address 1Address 2Address 3Sequence Control Address 4QoS Control HT ControlFrame BodyFCS Octets: 2 26662 6 24Variable4 Frame Header Slide 2 Date: May, 2012

3. doc.: IEEE 802.11-12/0110r8 Submission Frame Header Compression MPDU type (Normal or compressed) should be identified by either the PHY or MAC header. –One bit in PHY PLCP SIG. –One bit in MAC header, e.g. Bit15 of the AID/CH identifier field is set to 1 in a data/management frame, the data/management frame is a frame with frame header compression. –Indication in Frame Control such as New MPDU type/subtype, new protocol version to indicate compressed frame format. Slide 3 Frame Control AID/CH Identifier BSSIDSequence Control QoS Control Frame Body FCS Octets: 2 2611Variable2 Frame Control Duration/ ID Address 1Address 2Address 3Sequence Control Address 4QoS Control HT ControlFrame BodyFCS Bit15 of Duration/Id is always 0 in data/management frame. Bit15 of AID/CH Identifier is 1 in compressed data/management frame. Date: May, 2012

4. doc.: IEEE 802.11-12/0110r8 Submission Frame Header Compression (cont’d) BSSID and one AID are used to identify the transmitter and the receiver of the data and management frames. –BSSID field is used to identify whether the frame is in the same BSS. –When “From DS” is 1 and “To DS” is 0, BSSID is the transmitter identifier and AID is the receiver identifier. When “From DS” is 0 and “To DS” is 1, BSSID is the receiver identifier and AID is the transmitter identifier. –When both “From DS” is 1 and “To DS” is 1, compressed MPDU header is not used. –TDLS is not allowed, because two AIDs would be needed. Slide 4 Date: Jan, 2012 Frame Control AID/CH Identifier BSSIDSequence Control QoS Control Frame Body FCS Octets: 2 2611Variable2

5. doc.: IEEE 802.11-12/0110r8 Submission Frame Header Compression (cont’d) AID/CH Identifier field are used for indicating AID and DA/SA. –Bit15~Bit13 is the CH Identifier: If Bit115 is set to 1, the compressed header is in the frame. Bit 14—13 are used to identify DASA MAC address and other fields negotiated by management frames. –Bit12 ~ Bit0 are used to identify the RA/TA’s AID. Slide 5 AIDCH Identifier Bit0 Bit12Bit13 Bit15 AID/CH Identifier Date: May, 2012

6. doc.: IEEE 802.11-12/0110r8 Submission Frame Header Compression (cont’d) Duration field can be removed since 2-bit ACK Indication is added to PHY SIG. RA is the MAC address of the receiver One octet Sequence Control is used. One octet QoS control is used: 4 bits in QoS Control field are used to indicate TID of the frame. 2 bits are used to indicate ACK policy. Other bits are reserved. Single Address frames are not allowed to use compressed frame format. CRC-16-CCITT can detect 1, 2, 3 bit-errors when the frame size is smaller than 128 bytes. So 2-byte FCS is ok to frames with frame header compression. Slide 6 Date: May, 2012

7. doc.: IEEE 802.11-12/0110r8 Submission Conclusion Frame header compression can decrease short frame overhead through: –AID replaces RA/TA MAC address in MAC header, –CH identifier indentifies SA/DA MAC address, –Single octet QoS Control field, –Single octet Sequence Control field, –Duration field is removed. Totally 14 bytes is removed from the MAC header of 3-address frame. –With 2-byte FCS, 16 bytes MAC overhead can be removed. With further frame header compression, 20 bytes can be removed from MAC header and FCS of 3-address frame. Slide 7 Date: May, 2012

8. doc.: IEEE 802.11-12/0110r8 Submission Backup Slides Slide 8 Date: May, 2012

9. doc.: IEEE 802.11-12/0110r8 Submission CH Identification Management Before compression frames are transmitted, the transmitter and the receiver negotiate the fields that CH Identifier indicates. –A non-AP STA sends CH Identification Request frame to the AP to indicate the mapping between CH Identifier and DASA MAC Address. –The AP sends CH Identification Response frame to acknowledge the mapping between CH Identifier and DASA MAC Address. –Other MAC information may be indicated by CH Identifier. But the layers that is upper layers of MAC layer shouldn’t be indicated by such negotiation. The transmitter and the receiver record the CH Identifier and DA/SA MAC address matching, and use the matching to create the compress frame and decode the compress frame. CategoryAction Value Dialog Token CH Identifier DASA MAC Address ……CH Identifier DASA MAC Address Octets: 1 111121 IdentifierReserved Bit0 Bit2Bit3 Bit7 CH Identification Request frame CH Identifier field CategoryAction ValueDialog TokenStatus Code Octets: 1 112 CH Identification Response frame Slide 9 CH Identification Request CH Identification Response Compressed frame ACK Compressed frame ACK Compressed frame ACK Date: May, 2012

10. doc.: IEEE 802.11-12/0110r8 Submission Other Possible Variant of Compress Frame BSSID is included in compress frame. AID/CH Identifier is used to identify the TA or RA per From DS and To DS values. Further Compression can be done: –Each AP selects a 2-octet Compressed BSSID (BSSID[47--32], randomly, by IT manager etc.) to itself and notifies the Compressed BSSID to its associated STAs. Compressed BSSID conflict detection and avoidance: –An AP selects BSSID[47--32] as its Compressed BSSID if BSSID[47--35] does not conflict with its OBSS. –If an STA receives an Beacon with the same Compressed BSSID with its associated AP from another AP, it notifies its associated AP. –If an AP receives a Beacon with the same Compressed BSSID with it or receives a Compressed BSSID conflict from its associated STAs, it shall randomly select another Compressed BSSID and notify the new Compressed BSSID to its associated STAs. Slide 10 Date: May, 2012