Subject: TG Descriptor CV subfield X'91' for X.25

From: "jim (j.) cobban" <[email-masked]>
Date: Tue, 5 Jul 1994 16:09:00 -0400

The DLUR specification currently does not discuss the contents of the DLC
Signalling Type (X'91') TG descriptor subfield for X.25 virtual circuits.  I
would propose the following:

For DLC Type of X.25 Permanent Virtual Circuit:

2-7(=n)     DLC type (EBCDIC characters):

	    X25PVC

	    Note: For DLC Type = X25PVC the following subfields (described
	    following this subfield) may be included in TG Descriptor (X'46')
	    Control Vector following the DLC Signaling Type (X'91') Subfield.

	    X'92'  Port Identifier (optionally present product dependent
	           identifier if for Signaling use; not present in LOCATE TG
		   vector)
	    X'93'  Logical Channel Number (always present)
	    X'94'  Protocol Identifier

For DLC Type of X.25 Switched Virtual Circuit:

2-7(=n)     DLC type (EBCDIC characters):

	    X25SVC

	    Note: For DLC Type = X25SVC the following subfields (described
	    following this subfield) may be included in TG Descriptor (X'46')
	    Control Vector following the DLC Signaling Type (X'91') Subfield.

	    X'92'  Port Identifier (optionally present product dependent
	           identifier if for Signaling use; not present in LOCATE TG
		   vector)
	    X'93'  Logical Channel Number (optionally present)
	    X'94'  Protocol Identifier
	    X'95'  Destination address expressed in X.25 (1988) extended
		   address block format.

For DLC Type of FR Switched Virtual Circuit:

2-7(=n)     DLC type (EBCDIC characters):

	    FRSVC

	    Note: For DLC Type = FRSVC the following subfields (described
	    following this subfield) may be included in TG Descriptor (X'46')
	    Control Vector following the DLC Signaling Type (X'91') Subfield.

	    X'92'  Port Identifier (optionally present product dependent
	           identifier if for Signaling use; not present in LOCATE TG
		   vector)
	    X'93'  Destination Service Access Point Address (DSAP)
	    X'94'  Data Link Connection Identifier (DLCI) (optionally
	           present)
	    X'95'  Source Service Access Point Address (SSAP)
	    X'96'  Destination address expressed in Q.931 format

The appropriate text is added to subfield X'92'.

For subfield X'93':

Change the line "For DLC Type = FR" to "For DLC Type = FR or FR SVC".

For DLC Type = X25PVC or X25SVC:

2-3     0-3     reserved
	4-15    Logical Channel Number

I have a concern about the specification of the Destination Dial Address for
V25 and V25BIS DLC Types.  Why is this restricted to 12 digits when E.163
permits 15 and E.164 permits 17 digits, both excluding escape digits (such as
the 1 to select long distance in North America).

For Subfield X'94':

For DLC Type = X25PVC or X25SVC:

2               Protocol Identifier
		X'C2' - PSH
		X'C3' - QLLC BNN
		X'C6' - ELLC
		X'CB' - QLLC BNN with extended clear cause and diagnostic

For Subfield X'95':

For DLC Type = X25SVC:

2              Destination address type and format.

	0-3    type of address
	       0000 - unknown
               0001 - international, the address begins with the
                      country code
               0010 - national, the address excludes the country
                      code
               0011 - network specific, for example operator
                      information number
               0100 - subscriber number
               0110 - abbreviated number
               0111 - extension

        4-7    numbering plan
               0000 - unknown 
               0001 - PSPDN X.121                 
               0011 - ISDN E.164 (E.163)
               0100 - Telex F.69
               1000 - national standard
               1001 - private numbering plan
               1111 - extension
 
3-n            Destination address digits encoded in packed form, two digits
               to the octet.  If the dial address contains an odd number of
               digits, then the low order half-byte of the byte containing
               the last (low-order) digit contains X'C'.
	       address block format.

For Subfield X'96':

For DLC Type = FRSVC:

2              Destination address type and format.

	0-3    type of address
	       0000 - unknown
               0001 - international, the address begins with the
                      country code
               0010 - national, the address excludes the country
                      code
               0011 - network specific, for example operator
                      information number
               0100 - subscriber number
               0110 - abbreviated number
               0111 - extension

        4-7    numbering plan
               0000 - unknown 
               0001 - ISDN E.164 (E.163)
               0011 - PSPDN X.121                 
               0100 - Telex F.69
               1000 - national standard
               1001 - private numbering plan
               1111 - extension
 
3-n            Destination address digits encoded in IA5 characters
               according to the Q.931 specification.