doc.: IEEE /0110r6 SubmissionLiwen Chu Etc.Slide 1 Frame Header Compression Date: Authors: Date: March, 2012

doc.: IEEE /0110r6 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, –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: Variable4 Frame Header Slide 2 Date: March, 2012

doc.: IEEE /0110r6 Submission Frame Header Compression 1 MPDU type (Normal or compressed) should be identified by either the PHY or MAC header. –One bit in PHY PLCP SIG. –Other methods. When both “From DS” is 1 and “To DS” is 1, compressed MPDU header is not used. TDLS is not allowed, because there is almost no intra-BSS traffic in smart grid BSS. Duration field can be removed since 2-bit ACK Indication is added to PHY SIG. BSSID are used to identify the transmitter or the receiver of the 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. When “From DS” is 0 and “To DS” is 1, BSSID is the receiver identifier. Frame Control BSSIDSequence Control QoS Control AID/DASA Identifier Frame Body FCS Octets: Variable2 Slide 3 Date: March, 2012

doc.: IEEE /0110r6 Submission Frame Header Compression 1 AID/DASA Identifier field are used for indicating AID and DA/SA. –Bit15~Bit13 is the DA Identifier (when “From DS” is 0 and “To DS” is 1) and SA (when “From DS” is 1 and “To DS” is 0). DASA Identification Request/Response action frames are used to match DASA identifier to DASA MAC address. –Bit12 ~ Bit0 are used to identify AID When “From DS” is 1 and “To DS” is 0, AID is the receiver identifier. When “From DS” is 0 and “To DS” is 1, AID is the transmitter identifier. AIDDASA Identifier Bit0 Bit12Bit13 Bit15 AID/DA RA Identifier 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. 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. Single Address frames are not allowed to use compressed frame format. Slide 4 Date: March, 2012

doc.: IEEE /0110r6 Submission Frame Header Compression 2 MPDU type (Normal or compressed) should be identified by either the PHY or MAC header. –One bit in PHY PLCP SIG. –Other methods. When both “From DS” is 1 and “To DS” is 1, compressed MPDU header is not used. TDLS is not allowed, because there is almost no intra-BSS traffic in smart grid BSS. Duration field can be removed since 2-bit ACK Indication is added to PHY SIG. RA is the MAC address of the transmitter. Slide 5 Frame Control RAAID/DASA Identifier Sequence Control QoS Control Frame Body FCS Octets: Variable2 Date: March, 2012

doc.: IEEE /0110r6 Submission Frame Header Compression 2 AID/DASA Identifier field are used for indicating AID and DA/SA. –Bit15~Bit13 is the DA Identifier (when “From DS” is 0 and “To DS” is 1) and SA (when “From DS” is 1 and “To DS” is 0). DASA Identification Request/Response action frames are used to match DASA identifier to DASA MAC address. –Bit12 ~ Bit0 are used to identify the TA’s AID. AIDDASA Identifier Bit0 Bit12Bit13 Bit15 AID/DA RA Identifier 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. Another possibility is that the receiver is identified by its AID and the transmitter is identified by its MAC address. Slide 6 Date: March, 2012

doc.: IEEE /0110r6 Submission Conclusion Frame header compression can decrease short frame overhead through: –AID replaces RA/TA MAC address in MAC header, –SA/DA 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: March, 2012

doc.: IEEE /0110r6 Submission Backup Slides Slide 8 Date: March, 2012

doc.: IEEE /0110r6 Submission DASA Identification Management A non-AP STA sends DASA Identification Request frame to the AP to indicate the mapping between DASA Identifier and DASA MAC Address. The AP sends DASA Identification Response frame to acknowledge the mapping between DASA Identifier and DASA MAC Address. CategoryAction Value Dialog Token DASA Identifier DASA MAC Address ……DASA Identifier DASA MAC Address Octets: At most 16 DASA Identifier and DASA MAC Address pairs IdentifierReservedDASA Indication Bit0 Bit2Bit3 Bit6Bit7 DASA Identification Request frame DASA Identifier field CategoryAction ValueDialog TokenStatus Code Octets: DASA Identification Response frame Slide 9 Date: March, 2012

doc.: IEEE /0110r6 Submission Further Frame Header Compression 1 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 is used to identify the RA or TA –When “From DS” is 1 and “To DS” is 0, Compressed BSSID is the transmitter identifier. When “From DS” is 0 and “To DS” is 1, Compressed BSSID is the receiver identifier. 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. 20 Bytes MAC overhead can be removed. Frame Control Compressed BSSID Sequence Control QoS Control AID/DASA Identifier Frame Body FCS Octets: Variable2 Slide 10 Date: March, 2012

doc.: IEEE /0110r6 Submission Further Frame Header Compression 2 Each AP selects a 13-bit Compressed BSSID (BSSID[47--35], 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--35] 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. 20 Bytes MAC overhead can be removed. Slide 11 Frame Control RA IDTA ID /DASA Identifier Sequence Control QoS Control Frame BodyFCS Octets: Variable2 Date: March, 2012