Wednesday, December 11, 2013

Silent TCP Connection Closure for Cellular Networks

Presenter: Feng Qian
Authors: Feng Qian (AT&T Labs - Research), Subhabrata Sen (AT&T Labs - Research), Oliver Spatscheck (AT&T Labs - Research)

Often application layer have unexpected conseguences on radio.
For example, a connection close at the transport layer can cause an energy waste due to the state machine of UMTS.
There is a tail of energy waste due to this state machine.
The power consumption has been measured with a power meter in different conditions.
TCP connection is studied and a great power waste is observed due to the tradeoff between early closure and the need to reuse TCP connections.
The author propose STC, silent connection closure. Both sides exchange the closure timer info when the connection is setup, negotiate on that, and they can close the connection without exchanging any packets! In this way the long tail of energy waste is avoided!
Of course, this scheme requires TCP change and API for upper layers. It can be incrementally deployed using proxies that are compatible.
A trace driven evaluation is presented, achieving 11.3% radio energy saving and 6% of signalling load reduction.
A real Android implementation is work in progress.

Q: What about HTTP 1.0?
A: If use HTTP 1.0 there is no need for our proposal

Q: How the proxy know the timeout on the server?
A: It can notify it

Q: What are the implication using SPDY?
A: STC is applicable to SPDY as well

Q: What about fast dormancy?
A: It was disabled for performance issues.

Q: The protection period could cause packet loss?
A: No, is is specifically designed to avoid that, and we do not expect losses

Q: Why google is forcing the connection to stay alive for 5s?
A: To reuse the TCP connection and carry multiple objects, reducing latency

Q: Security?
A: I do not see any security problem of our solution