Re: Conceptual doubt between an ASP and SGP

David,

David Laight wrote:                           (Fri, 14 Mar 2014 11:40:47)
> > 
> > Not confused: read Q.714/2.7.5.
> 
> Yes, but what has that to do with the colour of sliced bread?
> Section 2.7.5.1 is all about ensuring that the original opc
> is available when the calling party address is 'route on pc+ssn'.
> 
> > But you didn't answer my question: why would you want to mislabel it?
> 
> It would be mislabelled if the routing label contained anything other than
> the pointcode of the last SCCP node that processed the message.

Following are two frames from a simple TCAP query/response pair.

In the query, following Q.714/2.7.5, as the sender of the TCAP query
wants a response, it needs to set the routing indicator in the calling
party address to Route on SSN.  In this case, the originating SSP
places its OPC in the calling party address as well.  The message is
sent from the SSP 5-2-181 to the STP GTT alias point code 249-150-253.
This is not the point code of the STP.  It is an alias shared between
STP pairs.  The STP point codes are actually 249-40-0 and 249-41-0.

Frame 651: 91 bytes on wire (728 bits), 91 bytes captured (728 bits)
Message Transfer Part Level 2
Message Transfer Part Level 3
    Service information octet
        10.. .... = Network indicator: National network (0x02)
        ..01 .... = ANSI Priority: 1
        .... 0011 = Service indicator: SCCP (0x03)
    Routing label
        DPC: 249-150-253 (16357117) (0xf996fd)
            1111 1001 .... .... .... .... = DPC Network: 249
            .... .... 1001 0110 .... .... = DPC Cluster: 150
            .... .... .... .... 1111 1101 = DPC Member: 253
        OPC: 5-2-181 (328373) (0x502b5)
            0000 0101 .... .... .... .... = OPC Network: 5
            .... .... 0000 0010 .... .... = OPC Cluster: 2
            .... .... .... .... 1011 0101 = OPC Member: 181
        0000 1011 = Signalling Link Selector: 11
Signalling Connection Control Part
    Message Type: Unitdata (0x09)
    .... 0000 = Class: 0x00
    0000 .... = Message handling: No special options (0x00)
    Pointer to first Mandatory Variable parameter: 3
    Pointer to second Mandatory Variable parameter: 9
    Pointer to third Mandatory Variable parameter: 14
    Called Party address (6 bytes)
        Address Indicator
            1... .... = National Indicator: Address coded to National standard (0x01)
            .0.. .... = Routing Indicator: Route on GT (0x00)
            ..00 10.. = Global Title Indicator: Translation Type only (0x02)
            .... ..0. = Point Code Indicator: Point Code not present (0x00)
            .... ...1 = SubSystem Number Indicator: SSN present (0x01)
        SubSystem Number: SSN not known/not used (0)
        Global Title 0x2 (4 bytes)
            Translation Type: 0xfe
            Called Party Digits: 800572
                Called or Calling GT Digits: 800572
                Number of Called Party Digits: 6
    Calling Party address (5 bytes)
        Address Indicator
            1... .... = National Indicator: Address coded to National standard (0x01)
            .1.. .... = Routing Indicator: Route on SSN (0x01)
            ..00 00.. = Global Title Indicator: No Global Title (0x00)
            .... ..1. = Point Code Indicator: Point Code present (0x01)
            .... ...1 = SubSystem Number Indicator: SSN present (0x01)
        SubSystem Number: BSSAP/BSAP (254)
        PC: 5-2-181 (328373) (0x502b5)
            0000 0101 .... .... .... .... = PC Network: 5
            .... .... 0000 0010 .... .... = PC Cluster: 2
            .... .... .... .... 1011 0101 = PC Member: 181
ANSI Transaction Capabilities Application Part

The STP (and we can only tell which one by looking at the link upon which
the message was sent) performs GTT and sends the message on to SCP without
altering the OPC (in the Calling Party Address).  In this case the query
was forwarded to one of 4 SCPs in a pool: the SCP with point code 249-150-29.

In frame 654, the SSP receives the TCAP response directly from the SCP as
you can see from the OPC and DPC in the MTP label and thus utilizes the
transfer function of some STP in the network (again, only the incoming link
can identify which one).

Frame 654: 71 bytes on wire (568 bits), 71 bytes captured (568 bits)
Message Transfer Part Level 2
Message Transfer Part Level 3
    Service information octet
        10.. .... = Network indicator: National network (0x02)
        ..01 .... = ANSI Priority: 1
        .... 0011 = Service indicator: SCCP (0x03)
    Routing label
        DPC: 5-2-181 (328373) (0x502b5)
            0000 0101 .... .... .... .... = DPC Network: 5
            .... .... 0000 0010 .... .... = DPC Cluster: 2
            .... .... .... .... 1011 0101 = DPC Member: 181
        OPC: 249-150-29 (16356893) (0xf9961d)
            1111 1001 .... .... .... .... = OPC Network: 249
            .... .... 1001 0110 .... .... = OPC Cluster: 150
            .... .... .... .... 0001 1101 = OPC Member: 29
        0100 1000 = Signalling Link Selector: 72
Signalling Connection Control Part
    Message Type: Unitdata (0x09)
    .... 0000 = Class: 0x00
    0000 .... = Message handling: No special options (0x00)
    Pointer to first Mandatory Variable parameter: 3
    Pointer to second Mandatory Variable parameter: 5
    Pointer to third Mandatory Variable parameter: 7
    Called Party address (2 bytes)
        Address Indicator
            1... .... = National Indicator: Address coded to National standard (0x01)
            .1.. .... = Routing Indicator: Route on SSN (0x01)
            ..00 00.. = Global Title Indicator: No Global Title (0x00)
            .... ..0. = Point Code Indicator: Point Code not present (0x00)
            .... ...1 = SubSystem Number Indicator: SSN present (0x01)
        SubSystem Number: BSSAP/BSAP (254)
    Calling Party address (2 bytes)
        Address Indicator
            1... .... = National Indicator: Address coded to National standard (0x01)
            .1.. .... = Routing Indicator: Route on SSN (0x01)
            ..00 00.. = Global Title Indicator: No Global Title (0x00)
            .... ..0. = Point Code Indicator: Point Code not present (0x00)
            .... ...1 = SubSystem Number Indicator: SSN present (0x01)
        SubSystem Number: BSSAP/BSAP (254)
ANSI Transaction Capabilities Application Part

MSC/HLR location query/response pairs function the same.

So, you are incorrect: SCCP cannot function in even the simplest of
query/response pairs without using the transfer function capability
of an intermediate node in the network.

Nevertheless, I and a few others defined the point-to-point IPSP
behaviour for M3UA and it is not the definition you seem to want
to overlay over the standard, which sounds more like hop-to-hop.

--brian

-- 
Brian F. G. Bidulock
[email protected]
http://www.openss7.org/