Re: Some questions about dissecting EVS protocol

[Nan Xiao <xiaonan830818 () gmail com>]

Hi Community,

Please ignore my second question in previous email:

(2) From A.2.2.1.2 ToC byte section:
> F (1 bit): If set to 1, indicates that the corresponding frame is
followed by another speech frame in this payload, implying that another ToC
byte follows this entry; if set to 0, indicates that this frame is the last
frame in this payload and no further header entry follows this entry.

I know there can be multiple TOCs followed by "speech data '', and use "F
bit" in ToC byte to indicate whether this is the last TOC byte. I am just
wondering if there is a possibility that the first byte of speech data can
also have the "F bit" set to 1, so it is misunderstood as Toc byte?

I just realised I made a silly mistake, and very sorry for causing
inconvenience!

Best Regards
Nan Xiao


On Fri, Oct 15, 2021 at 5:30 PM Nan Xiao <xiaonan830818 () gmail com> wrote:

> Hi Community,
>
> Greetings from me!
>
> Now I am reading EVS dissection code, and have two questions:
>
> (1) There is evs_132_bwctrf_idx_vals variable (
> https://gitlab.com/wireshark/wireshark/-/blob/master/epan/dissectors/packet-evs.c#L352)
> which helps to decode BW, CT and RF parameters. But from spec (
> https://www.etsi.org/deliver/etsi_ts/126400_126499/126445/12.01.00_60/ts_126445v120100p.pdf), 7.1.2
> Bit allocation at 13.2 kbps section, I can only find following words:
>
> > Note that the BW, CT, and RF parameters are combined together to form a
> single index. ......
>
> But the spec doesn't say how to decode the "single index", so I just want
> to know where to find the definition of this index.
>
> (2) From A.2.2.1.2 ToC byte section:
> > F (1 bit): If set to 1, indicates that the corresponding frame is
> followed by another speech frame in this payload, implying that another ToC
> byte follows this entry; if set to 0, indicates that this frame is the last
> frame in this payload and no further header entry follows this entry.
>
> I know there can be multiple TOCs followed by "speech data '', and use "F
> bit" in ToC byte to indicate whether this is the last TOC byte. I am just
> wondering if there is a possibility that the first byte of speech data can
> also have the "F bit" set to 1, so it is misunderstood as Toc byte?
>
> Hope someone can give me some advice! Thanks very much in advance!
>
> Best Regards
> Nan Xiao
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