1. Doc.: IEEE 802.11-01/319 Submission May 2001 Georg Dickmann, BridgeCo AG. AV Timing BridgeCo AG Georg Dickmann georg.dickmann@bridgeco.net

2. Doc.: IEEE 802.11-01/319 Submission May 2001 Georg Dickmann, BridgeCo AG. Principles Implicit Time Distribution –Lock on FIFO level associated with streams Explicit Time Distribution –Synchronize timers throughout AV network, timers are used to generate timestamps, recover clocks associated with each stream based on timestamp and local timer (IEC 61883)

3. Doc.: IEEE 802.11-01/319 Submission May 2001 Georg Dickmann, BridgeCo AG. Principles (2) Timing Master HC Wireless Node Wired Node

4. Doc.: IEEE 802.11-01/319 Submission May 2001 Georg Dickmann, BridgeCo AG. Timers Use wireless TSF timer for AV –Wireless timers need to be adjustable even in AP –Granularity/rate of 1  s is not appropriate Use independent timer –Any granularity/rate is feasible –Isochronous multicast/broadcast channel for clock distribution required –Timing master can be non-HC

5. Doc.: IEEE 802.11-01/319 Submission May 2001 Georg Dickmann, BridgeCo AG. Independent Timer Updates Sync. as in HL/2 sublayer for IEEE1394 1.Every (E)STA latches timer value upon reception of a beacon. 2.The timing master broadcasts its latched timer value within the BSS 3.Each timing slave adjusts its local timer by the difference between received time and latched time.

6. Doc.: IEEE 802.11-01/319 Submission May 2001 Georg Dickmann, BridgeCo AG. Independent Timer Update (2) Multicast channel from timing master to timing slaves required (the AP/HCF may be required to relay the timing channel) Define dynamic selection of timing master

7. Doc.: IEEE 802.11-01/319 Submission May 2001 Georg Dickmann, BridgeCo AG. Sources of clock error (Local oscillator deviation) x (Update Interval Length) Granularity of timer Beacon processing delay Signal propagation delay

8. Doc.: IEEE 802.11-01/319 Submission May 2001 Georg Dickmann, BridgeCo AG. Bounds on clock error IEC61883 requires jitter < 400ns AES11 requires any two digital audio signals to have a relative phase offset < 5% of sampling interval (approx. 1  s for 48 kHz sampling clock)

9. Doc.: IEEE 802.11-01/319 Submission May 2001 Georg Dickmann, BridgeCo AG. Implications on 802.11 Introduce tight bounds on both TSF timer jitter and phase offset between AV enabled AP/HC and (E)STAs Ensure efficient operation with beacon periods < 10 ms Provide multicast channel for time distribution