Subject: [Megaco] Gain in TDM package and in Annex C

From: Terry L Anderson <[email-masked]>
Date: Thu, 01 Aug 2002 12:24:10 -0400

There have been several issues raised over the last month or so about 
gain in the TDM package (Annex E.13) as well as in Annex C.  I will 
summarize the issues and propose changes to address them.

1. tdmc/gain is defined as integer which in 12.1.2 is clearly signed but 
the description and choice of value for "automatic" seem to have assumed 
that the value was unsigned.  [concensus was that gain should be signed, 
negative values have useful meaning and that the reserved value for 
automatic should be changed.  Note this last issue is definitely not 
backward compatible but no objections were raised.]

2. tdmc/gain does not specify if it applies to outbound signal level, 
inbound or both. [concensus was that it should be for outbound signal 
level.]

3. Nigel Williams suggested that the value in text encoding be 
restricted to decimal (non-hex) representation for easier parsing. 
[there was no discussion on this, but since the comment the in B.2 
specifies that either decimal and hexadecimal can be used for positive 
values of any integer property, I think we should NOT make this a 
special case.  Note that the specification does require decimal for 
negative values.]

4. There is also a Gain in C.1 (100C) for binary encoding.  It is not 
clear what it applies to and it is defined as unsigned integer and 
0..65535 (evidently 2 bytes). [Concensus was that this should be 
deprecated similar to what we did for echo control.]

I propose the following changes:

C.1
Gain, Property Tag 100C:  Remove the Type entry and change the Value 
entry to:
    Not used.  See H.248.1 Annex E.13 for an alternative gain property.

Annex E.13.1 Gain Control
Description:
Currently:
Gain control, or usage of of signal level adaptation and noise level 
reduction is used to adapt the level of the OUTBOUND signal. However, it 
is necessary, for example for modem calls, to turn off this function. 
[uppercase used only to indicate the addition.  It would be added as 
lowercase.]

Possible Values:

Currently:
    The gain control parameter may either be specified as "automatic" 
(0xffffffff), or as an explicit number of decibels of gain (any other 
integer value).  The default is provisioned in the MG.

Change to:
    The gain control parameter specifies the gain in decibels (positive 
or negative).  Values can range from - 2147483648 to 2147483646 
(0x7ffffffe) with the maximum positive value, 214748646 (0x7fffffff), 
reserved to represent "automatic".  The default value is provisioned in 
the MG.

[Note I am suggesting 0x7fffffff as the new reserved value, even though 
that makes the range more asymmetric, rather than 0x80000000 because 
that is a negative number and the note at the beginning of B.2 would 
require that it be represented in decimal, while I believe that some 
might prefer the easier to remember hex value for this.  I don't believe 
that the asymmetry is an issue, since the large values are useless in 
practice. Also this makes it differ in only one bit from the previous 
reserved value.]

-- 

------------------------------------------------------------
Terry L Anderson              mailto:[email-masked]
Tel:732.949.5628   Fax:732.949.7016
Lucent Technologies/INS/Voice Over IP Access Networks
Rm 2G-219A, 101 Crawfords Corner Rd, Holmdel, NJ 07733-3030
http://its.lucent.com/~tla (Lucent internal) http://www.gti.net/tla

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