Understanding Delay in Packet Voice Networks

Publisher

Cisco Systems

URL

https://www.cisco.com/c/en/us/support/docs/voice/voice-quality/5125-delay-details.html

Published

2006-02-02

Updated

unknown

Accessed

2026-10-02

HTTP status

200

License

Cisco website terms of use; no-redistribution; short excerpts and locators only

Source notes citing this source

• Per Cisco, the de-jitter buffer's contribution to end-to-end delay is its initial play-out delay plus however long the first packet was itself buffered in the network. in context
• Cisco describes the de-jitter buffer as transforming variable network delay into a fixed delay by holding the first packet for an initial play-out delay. in context
• Cisco's technote states, citing G.131, that echo cancellers are required when one-way delay exceeds 25 ms, so added latency makes residual echo more noticeable. in context
• Cisco classifies coder (processing), packetization, serialization and the fixed part of network switching delay as fixed delay components in a voice delay budget. in context
• Cisco's packet-voice delay technote restates G.114 as classifying 0 to 150 ms one-way delay as acceptable for most user applications. in context
• The same Cisco technote states that 150 to 400 ms one-way delay is acceptable provided administrators are aware of the transmission time and its impact on quality. in context
• Cisco notes that the G.114 delay limits assume echo is adequately controlled, meaning echo cancellers are in use. in context
• Cisco's technote restates G.114 as treating one-way delay above 400 ms as unacceptable for general network planning purposes, while recognising exceptional cases. in context
• Cisco's technote lists G.729A coder delay as 2.5 ms best case and 10 ms worst case, versus 5 ms and 20 ms for G.723.1. in context
• Cisco cites satellite connections as a source of talker overlap, giving satellite delay as roughly 500 ms (250 ms up and 250 ms down). in context
• Cisco's worked single-hop delay budget example totals about 138 ms one-way. in context
• In Cisco's two-hop tandem example the voice must be decompressed and de-jittered, then recompressed and de-jittered a second time. in context
• Cisco classifies queuing and buffering delay as variable delay, which the receiving end absorbs with a de-jitter buffer. in context
• Each media hop that decodes and re-encodes audio (a transcoder or a B2BUA media processor) adds another coder, packetization and de-jitter stage to the one-way delay, so counting such hops is a first step when diagnosing talk-over. inferred in context

Cite this source record

APA

WarmTransfer. (2006, February 2). Understanding Delay in Packet Voice Networks. WarmTransfer. https://warmtransfer.net/knowledge/sources/cisco-technote-5125-voice-delay

BibTeX

@misc{warmtransfer-cisco-technote-5125-voice-delay,
  title  = {Understanding Delay in Packet Voice Networks},
  author = {{WarmTransfer}},
  year   = {2006},
  url    = {https://warmtransfer.net/knowledge/sources/cisco-technote-5125-voice-delay},
  note   = {Cisco Systems, accessed 2026-10-02}
}