No concensus for ASN.1 extension support (was: Re: APC-1265)

Paul Long plong at SMITHMICRO.COM
Wed Sep 3 20:26:44 EDT 1997

Paul Long wrote:

> What is the difference between DTMF and MF tones? I've never heard of

MF (multifrequency) tones are, as far as I can tell, used only for
in-band trunk signalling, such as on international circuits (Signalling
System No. 5) and between PBXes and COs. They use a combination of two
tones from the set of 700, 900, 1100, 1300, 1500, and 1700 Hz. See
Recommendation Q.151 for how they're used in SS5 to encode digits and
control signals. I've not identified a need for MF signals to be carried
over H.32x terminals, but maybe Dale or someone else has.

>> 1. It shall be mandatory for all H.323 V2 terminals to promote
>> interoperability.
>Please, Mr. Nilsson or Mr. Toga, correct me if I'm wrong, but I don't
>believe it can be made mandatory at this time. A newer version of a
>Recommendation can augment and clarify but cannot constrain previous

But a new version of a recommendation CAN add new mandatory requirements
on terminals claiming compliance to that new version. For example, if
"X" was optional in Version 1, version 2 could make "X" mandatory for
terminals claiming compliance to version 2. Or, if "X" was mandatory in
version 1, and version 2 specifies an improved technique "XX", version 2
could require that two version 2 terminals communicating with each other
use "XX" instead of "X" even though both implement "X" for backward
compatibility with version 1. A new version should always require
backward compatibility by continuing to mandate fallback to mechanisms
required in previous versions.

        -- Toby
Toby Nixon, Program Manager - NetMeeting
Microsoft Corporation, Applications and Internet Client Group, Redmond
+1 (425) 936-2792     Fax: +1 (425) 936-7329
mailto:tnixon at

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