1. doc.: IEEE 802.11-08/1265r0 Submission November 2008 Liwen Chu, et al.Slide 1 STA Communication Inside a BSS and Outside the Context of a BSS Date: 2008-11-04 Authors:

2. doc.: IEEE 802.11-08/1265r0 Submission November 2008 Liwen Chu, et al.Slide 2 802.11p allows 3 Types of transmissions (1) Baseline 802.11 BSS transmissions (2) 802.11p “outside the context of a BSS” transmissions, which allow for two additional types of transmission: –(2a) 802.11p “outside the context of a BSS” broadcast safety transmissions on the 1609 control channel –(2b) 802.11p “outside the context of a BSS” broadcast & unicast transmissions between STAs and RSUs on 1609 service channels

3. doc.: IEEE 802.11-08/1265r0 Submission November 2008 Liwen Chu, et al.Slide 3 Case 2: STA Communicating Outside the Context of a BSS An 802.11p STA communicating outside the context of a BSS may transmit and receive frames without scanning or without MAC sublayer authentication or association procedures. An 802.11p STA may be a member of a BSS (Case 1) and/or communicate outside the context of a BSS (Cases 2a and 2b). –This implies that 802.11p may require multiple EDCA parameter sets--one for inside BSS communication (only one is allowed by the baseline in Case 1) and one or more for outside BSS communications (i.e. safety may use the default parameters in Case 2a, and multiple RSUs in Case 2b may have different EDCA parameter sets, as well). –It is not clear in subclause 11.18 of [3] whether these transmission types are active simultaneously. This ambiguity needs to be removed. –The intended use of 1609 is to use one transmission type at a time.

4. doc.: IEEE 802.11-08/1265r0 Submission November 2008 Liwen Chu, et al.Slide 4 Problems: Multiple Active EDCA Parameter Sets in a STA (1) Multiple active EDCA parameter sets in a STA violate basic 802.11 architecture assumptions. –In the 802.11 baseline standard [1], a product can have multiple STAs in it: dot11StationConfigTable includes multiple dot11StationConfigEntry (c.f. Annex D page 987), each dot11StationConfigEntry has its unique MAC address, EDCA parameter set… (c.f. Annex D page 1018-9) –A STA only has one MAC/PHY pair [2]. Note: If a product has both an 11a/b/g STA and a WAVE STA, the issues that arise when both a/b/g STA and WAVE STA are active simultaneously or when one STA is active are beyond the scope of our discussion and 11P standard. –MAC state information for transmissions within a BSS would have to be maintained during “outside the context of a BSS” communication (e.g. Block ACK).

5. doc.: IEEE 802.11-08/1265r0 Submission November 2008 Liwen Chu, et al.Slide 5 Problems: Multiple Active EDCA Parameter Sets in a STA (Cont’d) (2) A STA with multiple active EDCA parameter sets would have more chances to access the medium than a STA with one active EDCA parameter set. This is a fairness issue. –A STA with 2 active EDCA parameter sets will have 8 counters to count down to 0 to access medium. –A STA with 1 active EDCA parameter set will have 4 counters to count down to 0 to access medium. (3) A STA with multiple active EDCA parameter sets would need to scale its MAC state to communicate with an indefinite number of RSUs. This is an extensibility with hardware complexity implications. –A STA with 1 active EDCA parameter set needs 4 transmission queues. –A STA communicating on the control channel and with N RSUs, would need N+1 active EDCA parameter sets which implies 4×(N+1) transmission queues.

6. doc.: IEEE 802.11-08/1265r0 Submission November 2008 Liwen Chu, et al.Slide 6 One Active EDCA Parameter Sets in a STA 802.11p allows for the EDCA parameter set to be updated when a STA changes from control channel to a service channel or conversely. Both cases are communication outside a BSS, but the latter case has a 1609 application-layer association to the RSU. –In a STA, only one EDCA parameter set is active at any time. –Changing channels (and EDCA parameter sets) is decided by the SME (IEEE 1609 specifies this using a time division method). After the MLME receives the appropriate MIB variable set primitive(s), the MLME: (a) operates either within a BSS or outside the context of a BSS; (b) changes channel; and/or (c) updates its EDCA parameters. Control Channel Service Channel1 Service Channel2 SME sends 11P channel switch primitive to indicate the switched channel and EDCA parameters

7. doc.: IEEE 802.11-08/1265r0 Submission November 2008 Liwen Chu, et al.Slide 7 References [1] IEEE STD 802.11 TM 2007, “IEEE Standard for Information technology – Telecommunications and information exchange between systems – Local and metropolitan area networks – Specific requirements – Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications”. [2] Jon Rosdahl, 11-08/0930r0, “3 Responses to Interpretations for July 2008”. [3] IEEE STD 802.11p TM /4.02, “Draft Standard for Information Technology – Telecommunications and information exchange between systems – Local and metropolitan are networks – Specific requirements – Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications – Amendment 7: Wireless Access in Vehicular Environments”.