Dynamics of Contention Free Period Reservation in IEEE 1901 Networks - - PowerPoint PPT Presentation

Dynamics of Contention Free Period Reservation in IEEE 1901 Networks

Brad Zarikoff and David Malone Hamilton Institute, NUI Maynooth and Latitude Technologies. 29 March 2012

Overview

• IEEE 1901, broadband, in-home.
• Options for contention-based and contention-free access.
• Contention part looks like WiFi.
• Contention free arises from previous work12
• Good for traffic with QoS requirements?
• 1H. Hrasnica and R. Lehnert, Reservation Domains in MAC Protocols for

Broadband PLC Networks, ISPLC 2005.

2Y.-J. Lin, H. A. Latchman, J. C. L. Liu, and R. Newman, Periodic

Contention-Free Multiple Access for Broadband Multimedia Powerline Communication Networks, ISPLC 2005.

Contention Free Access

B CFP CAP B CFP For each flow wanting to use CFP:

• Station must make request to BSS manager in CAP.
• BSS manager must update CFP schedule.
• Schedule is announced by BSS manager in beacons.
• Station begins use of CFP, until reservation is canceled.

Schedules are transmitted with a lifetime; to expire a schedule you must wait for the lifetime CSCD (= M frames) and transmit a preview of the new schedule.

Sources Reservation of Delay

• Contending for access (backoff, collisions, ACKs, etc.).
• Waiting for preview schedule to become current.
• Waiting for modification to current schedule.

Has to be repeated if reservation is canceled.

• BSS manager can cancel the reservation.
• The station can request the cancellation.
• There is an inactivity limit (Til).

Setup

• Focus on reservation delay.
• Simulate with discrete event simulator.
• N stations making reservations.
• Run with beacon interval of 40ms for 80s (2000 intervals).
• Start with defaults of TCAP = 4ms and M = 3.

0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 0.2 0.4 0.6 0.8 1

Time (ms) Signals Success Success Success Failure Back-off Slots

Saturated Traffic

10 20 30 40 50 80 160 200 320 400 600 800 1000 1200 1400 M = 7 M = 3 M = 1

N E[d] (ms)

How big should CAP be?

1 2 3 4 5 6 7 8 9 10 0.4 0.8 1.2 1.6 2.0 N = 50 N = 10 N = 5

TCAP (ms) E[d] (s)

How about voice?

• Saturated traffic won’t time out, delay is one off.
• Saturated traffic usually not too delay sensitive.
• How about voice?
• Simple model, 64kbps, on-off exponential mean 1.5 with talk

clamped below at 240ms3.

• Note, delay budget on the order of a few frames.
• 3A. P. Markopoulou, F. A. Tobagi, and M. J. Karam, Assessing the quality
• f voice communications over internet backbones, IEEE/ACM ToN, vol. 11, no.

5, 2003.

Saturated vs. Voice with long timeout

10 20 30 40 50 80 160 200 320 400 600 800 1000 1200 1400 M = 7 M = 3 M = 1

TCAP (ms) E[d] (s)

10 20 30 40 50 80 160 200 320 400 600 800 1000 1200 1400 M = 7 M = 3 M = 1

TCAP (ms) E[d] (s)

Saturated Voice Really measuring setup. How about with more realistic timeouts?

How big should Til be?

160 320 480 160 168 176 184 192 200 208 216 N = 50 N = 2 Til (ms) E[d] (ms) 160 320 480 2e3 4e3 6e3 8e3 10e3 12e3 14e3 16e3 18e3 Til (ms) E[E]

Delay Timeouts M = 3, TCAP = 40 ms

Mixed Saturated and Voice

Saturated would usually live in contention period.

2 4 6 8 10 160 240 320 400 480 160 240 320 400 480 N = 50 N = 20 N = 8 N = 2

Nbg E[d] (ms)

10 20 30 40 50 3.7 3.8 3.9 4 4.1 4.2 4.3 4.4 4.5

N MOS Nbg = 0 Nbg = 2 Nbg = 4 Nbg = 6 Nbg = 8 Nbg = 10

Delay E-Model MOS

MOS: 4.34 Very satisfied; 4.03 Satisfied; 3.60 Some users dissatisfied.

Conclusion

• Contention-free access looks useful.
• Reservation delays can be significant.
• Use small M if possible.
• Use long Til if possible.
• Careful use of prioritisation may help.
• Matching application may help.