UIT - Secteur de la normalisation des télécommunications
ITU - Telecommunication Standardization Sector
UIT - Sector de Normalización de las Telecomunicaciones
Study Period 1997-2000
Commission d' études 
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Study Group
 16
Comisión de Estudio 
Contributi on tardive 
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Delayed Contributi on  D.xxx
Contribuci ón tardía 
Geneva, 13-17 November 2000
Texte disponible seulement en 

Text available only in
 E
Texto disponible solamente en 
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Question(s): Q8/16
SOURCE*:
3Com Corporation
TITLE:
Changes that are required in V.42 as a result of approval of Recommendation V.44
___________________
ABSTRACT
This contribution points out the need to investigate changes to V.42 resulting from the approval of
Recommendation V.44.
1. Introduction:
With the approval of new ITU-T Recommendation V.44 there is a need to include references to that new
Recommendation in Recommendation V.42. In addition, V.44 has made use of the manufacturer specific
User Data Fields in the XID frame of V.42. This presents problems for some modems that already utilise
the User Data Sub-field. Since this field was defined to be manufacturer-specific, any variation from the
specific manufacturer's ID is to be ignored. Thus, manufacturers who are already using the User Data Field
cannot support both V.44 and manufacturer-specific features simultaneously, without some other way of
knowing which type of modem is calling.
2. Proposal:
3Com proposes that a modified ADP (Answerer Detection Pattern) may be sent in V.42 Detection Phase to
indicate extended User Data Field capability. Below is the proposed text, with revision marks relative to the
current ITU-T V.42 recommendation.
* Contact:
Michael Nicholas
Tel:
+1 847 342 6772
Fax:
+1 847 342 6785
E-mail: Michael_Nicholas@3com.com
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7.2.1.3
Answerer actions
Upon indication of successful establishment of a connection between the signal converters, the
control function of the answerer shall transmit 1-bits (mark) until termination of the detection
phase, receipt of the ODP, or detection of the start of the protocol phase (the start of the protocol
phase is indicated by receipt of continuous flags, or of an LAPM or alternative procedure protocol
frame).
The answerer shall examine the incoming bit stream from the signal converter for the presence of
the ODP, which is defined in 7.2.1.2. Correct receipt of at least four DC1s of alternating parity shall
be required for the answerer to determine that the ODP is being observed.
If, after establishment of the physical connection, the ODP is not observed within the period of
T400 (see 9.1.1) and the start of the protocol establishment phase is not observed within the same
period, then the answerer shall decide that the originator is not capable of V.42 error-correcting
operation and shall fall back to non-error-correcting operation.
If the ODP is observed, the answerer interprets this as an indication from the originator that the
originator is capable of error-correcting operation and desires to continue into the protocol
establishment phase. The answerer shall immediately send one of the answerer detection patterns
(ADPs) defined in Table 3 at least ten times.
The answerer may indicate both the capability of accepting an extended V.42 User Data Subfield
and V.42 support by sending the Extended User Data Subfield (EP) ADP 16 times, followed by the
V.42 supported ADP (EC) at least ten times.
All transmissions are sent using the scrambling function of the signal converter and in
synchronization with the derived carrier clock signal.
Table 3/V.42
Answerer detection patterns
Type
Meaning
0 1010 0010 1 11. . .11 0 1100 0010 1 11. . .11
(E) and © separated by 8 to 16 one's
V.42 supported
0 1010 0010 1 11. . .11 0 0000 0000 1 11. . .11
(E) and (Null) separated by 8 to 16 one's
No error correcting protocol desired
0 1010 0010 1 11. . .11 0 0000 1010 1 11. . .11
(E) and (P) separated by 8 to 16 one’s
V.42 supported with Extended User Data
Subfield
0 1010 0010 1 11. . .11 0 0000 XXXX 1 11. . .11
The remaining 14 code points are reserved for
future study and assignment
NOTE - The above bit patterns are listed left to right in order of transmission (i.e. low-order bit
transmitted first).
12.2.1.3
User data subfield
A GI has been defined to specify a user data subfield used in conjunction with the “general
purpose” FI. This subfield follows, which follows all data link layer subfields as Figure 10 shows,
does not contain a GL. The subsequent information is bounded by the frame’s FCS field.
For the purposes of this Recommendation, this subfield is also divided into sets of PIs, PLs, and
PVs.
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12.2.2 Encoding for negotiation/indication of parameter values and optional procedures
The information field shall be encoded as specified below. Fields that are not recognized are
ignored.
Format identifier subfield
For negotiation/indication of parameter values and optional procedures, the FI subfield shall be
encoded as “10000010” to indicate the ISO-standardized “general purpose” FI.
Data link layer subfields
Only two of the data link layer subfields specified in ISO 8885 shall be used in conjunction with this
Recommendation. These are:
a) the “parameter negotiation” subfield (this subfield has a GI value of “10000000”); and
b) the “private parameter negotiation” subfield (this subfield has a GI value of
“11110000”).
The length of these subfields (GL) is dependent on the actual information to be transmitted.
Each item to be negotiated and/or indicated is identified by a PI. Table 11 shows each item, its PI
value, and with which data link layer subfield it is associated.
User data subfield
The user data subfield may be present independently of whether negotiation and/or indication is
performed. This subfield has a GI value of “11111111”.
The only parameters within this subfield defined in this Recommendation at this time are V.44 and
a “manufacturer ID”. The V.44 Parameter Identifiers are defined in Table A.1/V.44.
The manufacturer ID parameter shall be identified by a PI value of “11111111”. The V.44
parameters are all in PI, PL, PV formatting. All V.44 parameters shall precede the manufacturer
ID if both are present. The encoding of the associated PV subfield is manufacturer-specific. The
high-order bit of the first octet of the PV field is used as follows:
–
bit = 0: Manufacturer IDs not assigned by CCITT;
–
bit = 1: CCITT-assigned manufacturer IDs (the assignment of these identifiers is for
further study).
When receiving a manufacturer ID that is not recognized, the manufacturer ID field is ignored.