GSM [03.50] specifies a maximum round trip delay of 143.9mS in the terminal but no upper limit has been specified by ETSI for TETRA.
However delay is an important factor to consider when using a system and every attempt should be taken to minimise the round trip delays for speech. The same applies for PTT delays in non-duplex calls.
Because of this no requirement for a round trip delay shall be specified other than keeping the delay as small as possible. A basic procedure for measuring the audio delays can be found in [GSM 03.50, Annex C.10]. The system delays shall be measured and noted.
A suggested limit for the one way delays within the system is 250mS in any direction.
Copyright ©2002 Andy Fletcher andy@x31.com