Time Alignment Using RTCP Feedback

Document Type Expired Internet-Draft (individual)
Author Tom Taylor 
Last updated 2006-06-16
Stream (None)
Expired & archived
plain text pdf htmlized bibtex
Stream Stream state (No stream defined)
Consensus Boilerplate Unknown
RFC Editor Note (None)
IESG IESG state Expired
Telechat date
Responsible AD (None)
Send notices to (None)

This Internet-Draft is no longer active. A copy of the expired Internet-Draft can be found at


This memo describes the use of RTCP-based feedback to reduce end-to- end delay through the use of time alignment between the source and receiver. Time alignment is useful, for example, in certain gateway-to-gateway scenarios and certain gateway-to-VoIP-terminal scenarios. It is the ability for a receiver to request that the sender shift the time reference for packetization by a specified amount. When a receiver with strict packet timing limitations, e.g., due to a 3G UMTS Iu interface, is connected to an sender at a peer endpoint capable of responding to time alignment requests, e.g., with an AMR encoder associated with a PCM interface to the PSTN, this allows the endpoints to reduce delay in the speech path by as much as the 20 ms frame-block duration, depending on the degree of misalignment in the time reference.


Tom Taylor (tom.taylor.stds@gmail.com)

(Note: The e-mail addresses provided for the authors of this Internet-Draft may no longer be valid.)