Subject: Proposed DLUR Signaling Information Formats

From: "Andrew S. Barclay" <[email-masked]>
Date: Thu, 16 Mar 95 17:43:49 EST

In response to a number of comments and suggestions concerning the DLC
signaling information for DLUR, I am proposing several changes and
additions for consideration by the AIW.  This contribution comprises the
following items:

A) Additions to the DLUR DLC Signaling Information TG Descriptor Subfield
formats are proposed for X.25 permanent virtual circuits (PVCs) and
switched virtual circuits (SVCs).  These extend the capability of DLUR
nodes to communicate to downstream PUs across an X.25 network.  Although
their selection may appear arbitrary, the subfield keys shown were chosen
to be compatible with current products.  In addition to the destination
address for SVCs, some formats for optional user facilities are included
to allow use of closed user groups and reverse charging.  Although there
are many other optional user facilities, they are not as important for
basic connectivity.  The formats for X.25 are based, to a great extent,
on the actual encoding of the call request packet.  Consequently, the
subfield contents for the optional user facilities can be placed directly
into the call request packet.

B) In order to maintain greater consistency in naming DLC Types, some
changes were made.  Frame-Relay PVC has been changed from "FR" to "FRPVC".
X.25 SVC has been changed from "X25" (as implemented in some products)
to "X25SVC",  X.25 PVC is named "X25PVC".

C) In response to concerns raised by Jim Cobban of BNR, the wording of
the Destination Dial Address and Calling Identification Number for
Physical Interface Type = V25 or V25BIS has been changed.

D) The use of subfield X'95' to convey SDLC station role was found to be
unnecessary, because the DLUR link station is always primary to its
downstream dependent-LU link stations.  Since no other use was found for
this subfield, it is being retired.

-------------------------------------------------------------------------

1. Under the heading "DLC Signaling Type (X'91') TG Descriptor Subfield"

A)

For DLC Type of Frame-Relay Permanent Virtual Circuit (PVC):

CHANGE:

2-3(=n)       DLC type (EBCDIC characters)

              FR (for frame-relay permanent virtual circuit)

              Note: For DLC Type = FR, ...
TO:

2-6(=n)       DLC type (EBCDIC characters)

              FRPVC (for frame-relay permanent virtual circuit) - or FR,
              now retired

              Note: For DLC Type = FRPVC, ...

--------------

B)

ADD:

For DLC Type of X.25 Permanent Virtual Circuit (PVC)

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

              X25PVC (for X.25 permanent virtual circuit)

              Note: For DLC Type = X25PVC, the following subfields
              (described following this subfield) may be included
              in the TG Descriptor (X'46') control vector following
              the DLC Signaling Type (X'91') subfield:

              X'92' Port Identifier (always present):  product-dependent
                    identifier

              X'93' Logical Channel Number (always present)

For DLC Type of X.25 Switched Virtual Circuit (SVC)

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

              X25SVC (for X.25 switched virtual circuit) - or X25, now retired

              Note: For DLC Type = X25SVC, the following subfields
              (described following this subfield) may be included
              in the TG Descriptor (X'46') control vector following
              the DLC Signaling Type (X'91') subfield:

              X'92' Port Identifier (always present):  product-dependent
                    identifier

              X'94' Protocol Identifier (optionally present)

              X'97' Closed User Group Selection Facility (optionally
                    present)

              X'9B' RC/ICRD/FS (Reverse Charging/ICRD Status Selection/
                    Fast Select) Facility (optionally present)

              X'A5' Called (destination) DTE address (always present)

--------------

C)

For DLC Type of SDLC Nonswitched:

CHANGE:       X'95' Station Role (present in signaling information; not
              present in a TG Descriptor control vector on a Locate)

TO:           X'95' Station Role (retired)

--------------

D)

For DLC Type of SDLC Switched:

CHANGE:       X'95' Station Role (present in signaling information; not
              present in a TG Descriptor control vector on a Locate)

TO:           X'95' Station Role (retired)

--------------

2. Under the heading "DLC Signaling Information ('92') TG Descriptor Subfield"

CHANGE: For DLC Type = TR, ETHERNET, FR, SDLCNS, or SDLCSW:

TO:     For DLC Type = TR, ETHERNET, FRPVC, X25PVC, X25SVC, SDLCNS or SDLCSW:

--------------

3. Under the heading "DLC Signaling Information ('93') TG Descriptor Subfield"

A)

CHANGE: For DLC Type = ETHERNET, or FR:

TO:   : For DLC Type = ETHERNET, or FRPVC:

--------------

B)

ADD:

For DLC Type = X25PVC

2-3(=n)   0-3   Reserved
          4-15  Logical channel number:  a binary number

--------------

C)

For DLC Type = SDLCNS or SDLCSW:

CHANGE:

2-3(=n)         Secondary station SDLC address

TO:

2-3(=n)         Secondary station SDLC address
                Note: The DLUR link station is always primary to its
                downstream dependent-LU link stations.

--------------

D)

For Physical Interface Type = V25 or V25BIS

CHANGE:

2-n           Destination dial address: E.160 circuit-switched network
              address (up to 12 digits) encoded in packed form, two hex
              digits to the octet.  If the dial address contains an odd
              number of digits, the low-order half-byte of the byte
              containing the last (low-order) digit contains X'C'.

TO:

2-n           Destination dial address: Circuit-switched network address
              (as defined in CCITT Recommendation E.163) of the
              destination, starting with the country code, encoded in
              packed form two decimal digits to the byte.  If the dial
              address contains an odd number of digits, the low-order
              half-byte of the byte containing the last (low-order)
              digit contains X'C'.  Lengths up to 18 digits are
              accommodated, thereby allowing for extension.

4. Under the heading "DLC Signaling Information ('94') TG Descriptor Subfield"

A)

CHANGE: For DLC Type = FR:

TO:     For DLC Type = FRPVC:

--------------

B)

ADD:

For DLC Type = X25SVC

2(=n)         Protocol Identifier:

              X'C2'   PSH  - Physical Services Header
              X'C3'   QLLC - Qualified Logical Link Control
              X'C6'   ELLC - Extended Logical Link Control
              X'CB'   QLLC - Qualified Logical Link Control with SNA-specific
                             diagnostic codes
              X'CE'   ELLC - Extended Logical Link Control with SNA-specific
                             diagnostic codes

--------------

C)

For Physical Interface Type = V25 or V25BIS

CHANGE:

2-n           Calling Identification Number: E.160 circuit-switched
              network address of the calling data station starting with
              the country code encoded in packed form, two hex digits to
              the octet.  If the calling identification number contains
              an odd number of digits, the low-order half-byte of the
              byte containing the last (low-order) digit contains X'C'.

TO:

2-n           Calling Identification Number: Circuit-switched network
              address (as defined in CCITT Recommendation E.163) of the
              calling data station, starting with the country code,
              encoded in packed form two decimal digits to the byte.
              If the calling identification number contains an odd
              number of digits, the low-order half-byte of the byte
              containing the last (low-order) digit contains X'C'.
              Lengths up to 18 digits are accommodated, thereby
              allowing for extension.

--------------

5. Under the heading "DLC Signaling Information ('95') TG Descriptor Subfield"

A)

CHANGE: For DLC Type = ETHERNET or FR:

TO:   : For DLC Type = ETHERNET or FRPVC:

--------------

B)

DELETE: For DLC Type = SDLCNS or SDLCSW:

        (and everything that follows concerning station role)

--------------

6. Under a new heading "DLC Signaling Information ('97') TG Descriptor Subfield"

ADD:

--------------------------------------------------------------------------------
Byte    Bit   Content
--------------------------------------------------------------------------------

0-1           Subfield Header; Key=X'97'

2-n           Subfield Data

For DLC Type = X25SVC:

2-n             Closed User Group Selection Facility

2               Closed user group facility code:
                X'03'  basic closed user group
                X'47'  extended closed user group

3               For basic for extended format index (binary coded decimal)
          0-3   First digit of closed user group index
          4-7   Second digit of closed user group index

4               For extended format index (binary coded decimal)
          0-3   Third digit of closed user group index
          4-7   Fourth digit of closed user group index

--------------

7. Under a new heading "DLC Signaling Information ('9B') TG Descriptor Subfield"

ADD:

--------------------------------------------------------------------------------
Byte    Bit   Content
--------------------------------------------------------------------------------

0-1           Subfield Header; Key=X'9B'

2-n           Subfield Data

For DLC Type = X25SVC:

2-3(=n)         X.25 RC/ICRD/FS (Reverse Charging/ICRD Status Selection/
                Fast-Select Facility

2               Facility code:
                X'01'  RC/ICRD/FS facility

3               RC/ICRD/FS parameter field
          0-1   Fast select parameter:
                00  fast-select not requested
                01  fast-select not requested
                10  fast-select requested with no restriction
                11  fast-select requested with restriction
          2-3   ICRD parameter:
                00  ICRD status not selected
                01  ICRD allowance requested
                10  ICRD prevention requested
                11  reserved
          4-6   Reserved
          7     Reverse charging parameter:
                0   reverse charging not requested
                1   reverse charging requested

                Note: Only the reverse charging parameter is expected
                to be used with APPN.

--------------

8. Under a new heading "DLC Signaling Information ('A5') TG Descriptor Subfield"

ADD:

--------------------------------------------------------------------------------
Byte    Bit   Content
--------------------------------------------------------------------------------

0-1           Subfield Header; Key=X'A5'

2-n           Subfield Data

For DLC Type = X25SVC:

2-n           X.25 Called (destination) DTE Address
              (based on CCITT Recommendation X.25 1992)

2        0    Address Format Type Indicator (X.25 A bit):
              0    non-TOA/NPI (type of address/numbering plan identification)
                   Address
              1    TOA/NPI Address
         1-7  Reserved

3-n           Address Information For Address Format Type Indicator = 0

3        0-3  Reserved
         4-7  Length, in binary, of Called DTE Address in half-bytes
              (number of BCD digits - maximum of 15)

4-n           Called DTE Address: Packet-switched network address (as
              defined in CCITT Recommendation X.25 1992), starting with
              the country code, encoded in packed form two decimal digits
              to the byte.  If the DTE address contains an odd number of
              digits, the low-order half-byte of the byte containing the
              last (low order) digit contains X'0'.

3-n           Address Information For Address Format Type Indicator = 1

3             Length, in binary, of called DTE address in half-bytes
              (number of BCD digits - maximum of 17 for X.121 address)

4             TOA/NPI Indicators

         0-3  Type of Address:
              0000      Network-dependent number
              0001      International number
              0010      National number
              0101      Alternative address

         4-7  Numbering plan identification:
              0001      Address as defined in CCITT Recommendation E.164
              0011      Address as defined in CCITT Recommendation X.121

5-n           Called DTE Address: Packet-switched network address
              encoded in packed form, two decimal digits to the byte.
              If the DTE address contains an odd number of digits,
              the low-order half-byte of the byte containing the
              last (low order) digit contains X'0')

--------------

The reason for using X'0' to pad out the X.25 address to a byte boundary
is that this is the type of padding required in the call request packet
when the concatenation of the calling DTE address and called DTE address
does not result in byte alignment.

Andy Barclay