1-PREQ : n-Targets versus n-PREQ : 1-Target January 2009 doc.: IEEE 802.11-yy/xxxxr0 January 2009 1-PREQ : n-Targets versus n-PREQ : 1-Target Date: 2009-01-22 Authors: Michael Bahr, Siemens AG Michael Bahr, Siemens AG

January 2009 doc.: IEEE 802.11-yy/xxxxr0 January 2009 Abstract This presentation list several reasons for having multiple targets in a single PREQ. Furthermore, it shows that the concept of having multiple PREQs with a single target in the same Mesh Path Selection frame has the potential of erroneous processing. The presentation recommends to keep the currently specified mechanism of having multiple targets in a single PREQ. Michael Bahr, Siemens AG Michael Bahr, Siemens AG

PREQ with multiple Targets (I) 1:n-PREQ January 2009 PREQ with multiple Targets (I) 1:n-PREQ used in Path Maintenance path maintenance necessary due to changing link qualities path maintenance updates path metric and finds better paths than the existing ones keeps paths current used for simultaneous discovery of multiple destinations Low number of octets 28 + N*11 minimum is 39 all destinations have same HWMP SN and PREQ ID order of targets is not important all targets are processed for the same HWMP SN (same point in time) Michael Bahr, Siemens AG

PREQ with multiple Targets (II) 1:n-PREQ January 2009 PREQ with multiple Targets (II) 1:n-PREQ simple generation processing the freshness of all targets is defined by the same condition, that is, the freshness or improvement of the reverse path to the originator the path to the originator is updated only once processing of targets is a for-loop from 1 to n over all targets processing of all targets happens in a single “IE processing function”, that is, the IE processing routine is entered only once completely described in draft more complex description but complete and implementable and “processable” Michael Bahr, Siemens AG

Multiple PREQ with single Target (I) n:1-PREQ January 2009 Multiple PREQ with single Target (I) n:1-PREQ simultaneous discovery of multiple destinations has to be done with multiple PREQs with a single target in the same Mesh Path Selection frame Increased number of octets N * 38, minimum is 38 Michael Bahr, Siemens AG

Multiple PREQ with single Target (II) n:1-PREQ January 2009 Multiple PREQ with single Target (II) n:1-PREQ all destinations have different HWMP SN and PREQ ID order of PREQs is important! PREQs have to be ordered with ascending HWMP SN all targets are processed for different HWMP SN (different points in time) increased overhead and complexity for the compilation of the mesh path selection frame Problem with HWMP SN number ordering if a PREQ IE of higher order in the mesh path selection frame has a lower HWMP SN than a PREQ IE of lower order, it will not be processed, that is, no generation of PREP and no propagation. if the same HWMP SN is used for all PREQs, the problem is simply pushed to the PREQ ID Michael Bahr, Siemens AG

Multiple PREQ with single Target (III) n:1-PREQ January 2009 Multiple PREQ with single Target (III) n:1-PREQ complex generation due to necessary ordering based on HWMP SN processing the freshness of all targets, that is, the freshness or improvement of the reverse path to the originator is defined by the different conditions due to the sequential processing of independent PREQs the path to the originator is updated multiple times processing of targets is the same as for 1:n-PREQ except for the repeated processing of the targets processing of all targets happens in multiple (n) “IE processing function” calls, that is, the IE processing routine is entered multiple (n) times simpler description Michael Bahr, Siemens AG

Byte Overhead January 2009 January 2009 doc.: IEEE 802.11-yy/xxxxr0 1:n PREQ n:1 PREQ Overhead 1 39 38 -1 2 50 76 26 3 61 114 53 4 72 152 80 5 83 190 107 6 94 228 134 7 105 266 161 8 116 304 188 9 127 342 215 10 138 380 242 11 149 418 269 12 160 456 296 13 171 494 323 14 182 532 350 15 193 570 377 Michael Bahr, Siemens AG Michael Bahr, Siemens AG

1:n-PREQ vs. n:1-PREQ Smaller overhead Larger overhead January 2009 1:n-PREQ vs. n:1-PREQ Smaller overhead Larger overhead Simple generation Complex generation Single call of IE processing routine with repeated processing of targets (for loop)  passes interfaces only once Multiple calls of IE processing routine, code is almost same amount, for-loop is realized by repeated IE processing passes interfaces multiple times (2*n) Correct validation of freshness due to single HWMP SN Correct validation of freshness depends on external things, error-prone No target will be lost Some targets might be lost Michael Bahr, Siemens AG

January 2009 Summary path maintenance is necessary in wireless mesh network with radio-aware link metrics need efficient mechanism (overhead, processing, correctness) PREQs with multiple targets have less overhead, can be implemented and processed effiently provide no potential pitfalls for erroneous processing multiple PREQs with single target increase byte overhead require a more complex generation (ordering of PREQ IEs based on HWMP SN) result in processing errors if order of HWMP SN is not correct have as major advantage an easier specification only recommendation: keep the multiple targets in the PREQ Michael Bahr, Siemens AG

References IEEE 802.11s Draft 2.06 January 2009 References IEEE 802.11s Draft 2.06 11-09/0149r1 „Action frames and addressing“ Michael Bahr, Siemens AG