[PATCH 1/4] Each BTS can be configured for speech support (other than GSM full rate)

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Andreas Eversberg andreas at eversberg.eu
Thu Jan 9 10:13:11 UTC 2014


Holger Hans Peter Freyther wrote:
> Codec selection in a real network works a bit differently. It is applied
> in the BSC and the MSC. The MSC can/will look at the bearer capabilities
> and then ask the BSC to choose from a list of codecs.
>   
in oder to select a codec, the MSC must know.
 - what codecs it supports (or the other end, in case of TFO)
 - what codecs the MS supports (bearer capabilities)
 - what codecs the BTS supports

in my testing branch: the negotiation is done with LCR and even with
built-in MNCC support of osmo-nitb. in case of built-in MNCC, a commonly
supported codec (by both MS in a call) is used.

i do not know how the MSC (in a real network) knows about what codecs
are supported by the BTS in order to select a supported codec. in this
patch i simply remove unsupported codecs from bearer capabilities, so
all remaining codecs are supported by BTS and the MS. the MSC will only
receive a list of commonly supported codecs.

my question is: how does the MSC in a real network knows what codecs are
supported by BTS, so it can skip unsupported codecs when negotiating
with the other end?





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