March 2001 Sid Schrum, et al., Texas InstrumentsSlide 1 doc.: IEEE 802.11-01/163 Submission p-DCF Proposal Summary Sid Schrum, Jin-Meng Ho, Khaled Turki Donald P. Shaver and Matthew B. Shoemake Texas Instruments Incorporated 3000 Aerial Center, Suite 160 Morrisville, NC 27560 (919) 463-1043 (Schrum) firstname.lastname@example.org
March 2001 Sid Schrum, et al., Texas InstrumentsSlide 2 doc.: IEEE 802.11-01/163 Submission 1.Calculate TCPP sum from TCPP 0, TCPP 1 … (Note – this step needs to be done only when TCPP sum is subject to change) 2.Repeatedly generate random numbers (X) and compare to TCPP sum, until either: a) X TCPP sum or b) number of random numbers generated is 256. Increment backoff timer by one slot time each time a new random number is generated. With each random number generated, an additional slot time is available for determining backoff value! 3.Select and queue next frame to transmit under contention access based upon rule: (TCPP 0, …, k – 1 ) < X sum (TCPP 0, …, k ). 4.When back-off timer expires, transmit frame previously queued Example Access Control Algorithm
March 2001 Sid Schrum, et al., Texas InstrumentsSlide 3 doc.: IEEE 802.11-01/163 Submission Single back-off counter vs. multiple backoff counters – no requirement to resolve internal collisions No non-decrementing offset vs. decrementing offset –IFS rules same as legacy DCF, compatible with HCF Multiple straightforward implementation options with hardware / software function partitioning Time-critical transmit access control functions similar to current DCF SIMPLE implementation Facilitates reuse of legacy DCF functions Implementation Complexity, Cont.
March 2001 Sid Schrum, et al., Texas InstrumentsSlide 4 doc.: IEEE 802.11-01/163 Submission Summary, Cont. P-DCF transmit access behavior –Back-off delay DOES NOT equate to Access Delay –What matters is performance under moderate to heavy load implies multiple collisions for worst-case frames. –Binary Exponential Back-off results in long delays when frames experience multiple collisions, even for priority traffic P-DCF –Improved aggregate throughput (fewer collisions) –Fair access with bandwidth available to all traffic classes –lower delay –robust differentiation between traffic classes –Compatible with legacy DCF: P-DCF lowest priority ~ legacy DCF
March 2001 Sid Schrum, et al., Texas InstrumentsSlide 5 doc.: IEEE 802.11-01/163 Submission