Session Chair: Dina Katabi, Massachusetts
Institute of Technology
Softspeak: Making VoIP Play Well in Existing 802.11
Deployments
Patrick Verkaik, Yuvraj Agarwal, Rajesh Gupta, and
Alex C. Snoeren, University of California, San Diego
——————-
We have many VoIP users over 802.11
- However, 802.11 is designed for data traffic.
- What is the call quality for them?
- What is its impact on users who only transfer data?
There are problems which lead to degradation of call quality.
- Exponential back-off when contention happens
- Framing overhead per packet
Possible Solutions:
- Decrease the packet rate
- Use higher speed networks like 802.11g
- It would not help, the degradation problem still exist
- Use 802.11e which prioritize VoIP traffic
- It would increase contention
Our solution:
- For uplink: prioritized TDMA
- Stablish an schedule for sending packets
- Sync clock between nodes
- Compete with non-TDMA traffics
- use several level of prioritization
- For downlink: use an aggregator
- Send the aggregated traffic towards only one station
- The other stations must overhear that
Evaluation:
- On 801.11b and 802.11g
- The improvement on 802.11g is less
Q: Your evaluation did not cover the case for multiple TCP traffics
A: We had experiments with Web traffic which is the case of multiple
TCP traffics
Q: How does it work in practice? In practice, we have collisions and
also assigning slides between multiple hops is a big challenge!
A: -
Q: What is the delay performance?
A: -
Q: Why not just give higher priority to short packets?
A: -
Q: Why not use a separate single channel for all VoIP traffics?
A: Yes, why not?
Block-switched Networks: A New Paradigm for
Wireless Transport
Ming Li, Devesh Agrawal, Deepak Ganesan, and Arun Venkataramani, University
of Massachusetts Amherst
—————————
TCP performs bad over wireless.
1) It is because end-to-end rate control mechanism is too conservative
- It leads to redundant retransmissions
2) It uses packets as unit of control
3) It has complex cross-layer interaction
Re-design:
1) End-to-end -> hop by hop
2) Packets -> Blocks
3) Complexity -> minimalism
Techniques:
- virtual retransmission
- use data in cache for retransmission
- Back pressure
- limit # of outstanding blocks per flow at forwarder node
- ACK withholding
Q: What about connections to wired networks?
A: Future work
Q: What about responsiveness? For SSH traffics, the responsiveness
is very important.
A: In the evaluation, we have results related to small files.
Q: Your solution does not cover the case that two routers are
feeding a downstream router.
A: We treat them similarly.
This entry was posted on
Wednesday, April 29th, 2009 at 1:02 pm and is filed under NSDI 2009. You
can follow any responses to this entry through the RSS 2.0 feed. You
can leave a response,
or trackback from your own site.
