Subject: Network Appearance.

From: Normand Glaude <[email-masked]>
Date: Fri, 30 Mar 2001 18:23:42 -0500

Folks, I circulated a message on the list in January about the
definition of the Network Appearance. This was discussed in Minneapolis,
and I thought I'd produce a bit more info, so that we all agreed on
basic definitions.

There are 2 definitions circulating in the drafts today for Network
Appearance

1) In M3UA, it means the appearance OF a network. Essentially, all point
codes in the same network belong network appearance.

2) In SUA, it means the appearance IN a network. Essentially, a single
point code in any given network is a network appearance, in a one-to-one
relationship.

There are issues with (1), in that all network management messages
(DUNA, DAVA, etc.) use the network appearance as the context, and that
creates ambiguities in cases where multiple point codes are represented
by a single signaling gateway in a network.

There are duplication issues with (2), as a single event in the SS7
network may generate multiple events on the M3UA side.

I propose we use definition (2), since duplication is less of an issue
than ambiguity.

The following is what I circulated in January, and it covers the same
issue for different reasons, and the SUA definition has changed since.

Greg/John, I'll produce some text for the drafts to clearly indicate
this, unless this becomes a hot debate on the mailing list, like it did
the last time :-)

Norm.

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

Background -

In the various SS7 SCCP specifications, it is assumed that MTP is
aware of the local point code of its users, i.e. SCCP.  In an
end-node configuration, there is only one point code, therefore
the local point code is implicit. In an STP configuration, there
could be many point codes, but traditionally, there is an
SCCP user only for the alias point code which is used for the
Global Title Translation function. Also, in the proposed sigtran scheme,
it is also possible for a SG to have multiple End-node point codes in
the same network

Issue -

In SUA, although there is support for STP-like configuration, where
multiple point codes within the same SS7 network are hosted, there
is no way to distinguish which SCCP-user, or more importantly, to
which network element (point code within a network) when an ASP sends
a message to a SG. Essentially it is not possible to properly support
STP configurations at the SG in the current SUA draft.

Proposed solutions:

1) Change the definition of Network Appearance, and make the parameter
optional for all messages:

In the current definition, for a single SCTP association, the network
appearance is the set of all point codes within the same network,
"hosted" or "represented" by the same signaling gateway.

If the definition was changed so that a network appearance was
constricted to a single point code, or network element, and the
parameter was made optional for all messages, then the conditions
would be satisfied.  In fact, such a concept already exists in M3UA
and SUA, as it is implied in the definition of the Signalling Point
Management Cluster (SPMC).

A definition could go something like this:

   Network Appearance - The Network Appearance identifies an SS7
   signaling node (a unique point code in a single SS7 network) for
   the purpose of logically separating the signaling traffic between
   the SG and the ASP over a common SCTP Association.  This partitioning
   is necessary where an SG is logically partitioned to appear as an
   end-node elements in multiple separate national SS7 networks, in
   which case there is a separate network appearance for each SS7
network.
   It is also necessary when an SG is configured as an STP and hosts
   multiple point codes within the same network, in which case each
point
   code is a separate network appearance.

One I need to clear in my mind is what does "Network Appearance" really
means - is it:
  (a) the appearance **OF** an SS7 network to an element or
  (b) the appearance of an element **IN** an SS7 network?

In any case, I think that the definition of network appearance needs
clarification.

2) Introduce the MTP routing label in some of the SUA messages.

That method is a bit less appealing to the SS7 purists, since in changes
the nature of the SCCP-user primitives, by forcing the SCCP user to know
about MTP-L3 information. - But - it has been done before, and in some
ways, it is simpler to add.

3) Remove STP configurations altogether.

A bit more drastic. I don't endorse this one myself, but I'm trying to
be more complete with the alternatives.

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