RE: IETF NCS Sig MIB Gain (loss) plan and tone Levels

 
After looking at the "pktcNcsEndPntConfigTxGain" and
"pktcNcsEndPntConfigRxGain" MIB objects more closely, here are some concerns
with these objects resurrected in draft-08 since being obsolete in draft-02.
 
The concerns are two-fold:
 
1. The real value in having this solution for future proofing:
As Rich pointed out, we are trying to future proof the unknown requirements.
If this becomes important in the future then we can figure it out then, it is
impossible to solve everything up front without understanding all the
problems and consequences. The draft-02 has obsolete these two objects after
the extensive discussions. Are the problems these two MIB objects are
presumably solving important enough to consider the draft change given the
current late stage.
 
2. Implementation problems associated with the functionality introduced by
these two objects
We understand the benefits of having configurability to meet different
country specifications. However, the gain/loss plan is only one component in
trying to adapt to different country deployments. The MIB doesn't address
other items such as complex impedance, ring voltage, etc. By trying to
address the gain/loss in isolation we are actually creating implementation
difficulties. This is already solved by MTA manufactures through more
intelligent and coordinated methods using both H/W and S/W
 
Providing the ability to dynamically adjust gains means that you are
inherently limiting the dynamic range of the DSP to try and address all
corner case scenarios. This is a huge implementation problem. Often the per
country matching of complex impedances and gains is done in H/W or within the
analog interface components like the SLIC. These interfaces are configured
for a given country specifications independent of signaling MIBs. This
creates a problem when you want to have the gain setting larger than the
natural country default. The only solution to meet the desired MIB value is
to generate a loud signal (likely clipping within the DSP) in order to adjust
for the analog hardware gain.
 
Eugene Nechamkin,
 
Broadcom Corp.

________________________________

From: [email protected] [mailto:[email protected]] On Behalf Of
Woundy, Richard
Sent: Tuesday, February 15, 2005 4:48 PM
To: 'Freyman Phillip-FPF300'
Cc: '[email protected]'
Subject: RE: [ipcdn] IETF NCS Sig MIB Gain (loss) plan and tone Levels


>While it is recognized that current standard connection establishment
protocols (NCS, SIP) do not support dynamic gain (loss) plan negotiation or
assignment at this time, it should be recognized that by establishing the MIB
now will enable future protocol updates to improve the end user experience.
 
Or sometimes, they interfere with future protocol updates. :^(
 
For example, do your proposed read-write MIB object value override the
NCS/SIP negotiated value? Or vice versa?
 
-- Rich, ordinary cable guy, Comcast

	-----Original Message-----
	From: [email protected] [mailto:[email protected]] On
Behalf Of Freyman Phillip-FPF300
	Sent: Tuesday, February 15, 2005 2:07 PM
	To: '[email protected]'; '[email protected]'
	Subject: [ipcdn] IETF NCS Sig MIB Gain (loss) plan and tone Levels
	
	
	Colleagues,

	 

	This is a proposal to establish the Transmit and Receive gain (loss)
plan parameters in the SigMIB to provide a solution to the setting of
supervisory tone levels at the a-b termination points and it also provides an
intelligent approach to future migration of a dynamic gain (loss) plan based
on the connection requirements.

	 

	The first point to consider in this proposal is when the MTA passes
in band signaling tones.  Per CableLabs and ETSI these tones are passed to
the POTS a-b (T/R) termination points through signal paths that apply a known
loss.  This is usually implemented in the POTS SLIC circuitry either with
fixed loss devices or provisioned by the vendor/operators. 

	 

	However, when directed by the Call Agent the MTA may generate the
supervisory tones locally.  The same loss plan specifications per CableLabs
and ETSI for in band signaling are assumed to still be active when the tones
are locally generated.  Therefore it is necessary for the internal
supervisory tone generator to compensate for the analog gain (loss) in the
MTA (Typically in the POTS SLIC circuitry) to achieve the desired level at
the a-b (T/R) termination point.  While this gain (loss) may be known to a
vendor during manufacture, the second consideration in this proposal suggests
that this gain (loss) may be required to be changed based on far end (analog
loop) connection characteristics that change depending on the actual far end
connection point.

	 

	While CableLabs PKT-SP-EMTS-PRIMARY-I01-001128 Clause 8.4.4 and
Telcodia GR-909-CORE R5-17 guildance suggest a 2 dB loss plan default
setting, there is also guildance in GR-909-CORE R4-134 referencing ANSI
T1.401-1988 Figure 24 that DTMF levels may be as high as +4 dBm under low
loop current conditions.  Per Telcordia GR-506-CORE Clause 15.1.5, the DTMF
receiver acceptance levels must be greater than -25 dBm and less than 0 dBm.
Considering a + 4dBm DTMF level applied to a 2 dB loss plan would resulting a
DTMF PCM coding level greater than the GR-506-CORE guidance of 0 dBm maximum
for the DTMF detector.  The setting of the default value to -4 dB gain,
ensures proper DTMF signal quality for proper detection and is also
consistent with Telcordia GR-909-CORE which references TR-NWT-000057 for
parameter settings and where 6.1.8 DLC System Loss O-11 suggests a DLC
transmission path loss in each direction o the RT line unit should be 4 dB
+/-2 dB (- 4 dB gain).  

	 

	Guidance in TIA/EIA TSB122-A and ETSI ES 202 020 further offers the
need to adjust the gain (loss) plan based on if a given MTA is attempting a
connection to one of several analog POTS termination points.  In reviewing
these documents if one considers the MTA as the referenced ONU unit, various
connection cases can be made (ONU to OPS, DGS, WAN, DAL, FXO, FXD, or ATT or
these terminations back to the ONU) where the recommended gain (loss) plan
per connection vary between 0 dB and 9 dB in loss or in some cases 3 dB of
gain.

	 

	While it is recognized that current standard connection establishment
protocols (NCS, SIP) do not support dynamic gain (loss) plan negotiation or
assignment at this time, it should be recognized that by establishing the MIB
now will enable future protocol updates to improve the end user experience.

	 

	Finally, a text enhancement is proposed to clarify the
pktcSigDevToneDbLevel tone level setting measurement with respect to complex
tones (tones sometimes consisting of more than one frequency).

	 

	Respectfully,

	 

	Phillip Freyman

	Distinguished Member of the Technical Staff

	Motorola Connected Home Solutions (formally BCS)

	
	 
	
=============================================================================
=============================================

	
	

	   pktcNcsEndPntConfigTxGain                  Integer32,  

	       pktcNcsEndPntConfigRxGain                  Integer32  

	 

	   pktcNcsEndPntConfigTxGain    OBJECT-TYPE  

	       SYNTAX       Integer32 

	       UNITS        "dB"  

	       MAX-ACCESS   read-write

	       STATUS       current  

	       DESCRIPTION  

	           "The per line transmitter (A/D) gain.  A positive number
reflects a signal gain, a negative number reflects a signal loss.  This
Object may provision the gain or it may be used to document a
non-provisionable gain between the telco (POTS) a-b (T/R) terminals and the
analog codec maximum PCM coding limit (PCM maximum coding limit).  

	 

	Based on the default G.711 Vocoder maximum of 3.14 or 3.17 dBm the -4
dB gain default provides Vocoder coding protection against TE maximum signals
while also providing an initial loss to minimize analog signal echo.  

	       DEFVAL { -4 }  

	       ::= { pktcNcsEndPntConfigEntry 42 }  

	    

	 

	


	 

	   pktcNcsEndPntConfigRxGain    OBJECT-TYPE  

	       SYNTAX       Integer32 

	       UNITS        "dB"  

	       MAX-ACCESS   read-write  

	       STATUS       current  

	       DESCRIPTION  

	           "The per line receiver (D/A) gain. A positive number
reflects a signal gain, a negative number reflects a signal loss.  This
object may provision the gain or it may be used to document a
non-provisionable gain for use with the pktcSigDevToneDbLevel Object to set
the desired level at the a-b (T/R) terminals.  

	 

	Based on the default G.711 Vocoder maximum of 3.14 or 3.17 dBm the -4
dB gain default provides a maximum analog signal level at the a-b (T/R)
termination point. It should be noted that ETSI TS 101 909-4 provides
guidance of 11 dB loss (-11 dB gain) and based on this reference a DEFVAL {
-11 } in international markets may be considered.  

	       DEFVAL { -4 }  

	       ::= { pktcNcsEndPntConfigEntry 43 }  

	    

	


	pktcSigDevToneDbLevel    OBJECT-TYPE 

	       SYNTAX       TenthdBm (-250..-30) 

	       UNITS        "dBm"  

	       MAX-ACCESS   read-write  

	       STATUS       current  

	       DESCRIPTION  

	           "This is the decibel level for each analog signal (tone)
that is locally generated (verses in band supervisory tones) and sourced to
the a-b terminals (TE connection point).  Per the PktcSigDevToneEntry this
DbLevel represents the level required for each tone where each tone may
consist of multiple frequencies which may be summed or amplitude modulated.
This Object must reflect the desired level at the Telco (POTS) a-b (T/R)
terminals including the affect of the pktcNcsEndPntConfigRxGain setting on
the delivered tone.  The wide range of levels for this Object is required to
provide signal generator levels across the wide range of gains but does not
imply the entire range is to be achievable given the range of negative values
of gain (positive loss).     This Object must be set for each tone so as to
generate the combined frequency level at the a-b (T/R) terminals." 

	       DEFVAL { -40 }  

	       ::={pktcSigDevToneEntry 2 }

_______________________________________________
IPCDN mailing list
[email protected]
https://www1.ietf.org/mailman/listinfo/ipcdn