Introduction
In continents and markets where the same SS7 variant is deployed in different countries,
or by different network providers within the same country, it is highly probable
that there will be point code overlap between countries and providers.
The overlap of point codes between networks makes inter-operation between networks
very difficult; it is impossible for two network elements with the same point code
to co exist in an integrated network. These conditions are a common source of difficulty
for MVNEs (Mobile Virtual Network Enablers) that offer their services across multiple
countries or multiple carriers within a country.
Challenges
Regardless of the number of networks to be interworked, the traditional approach
to the interworking of homogeneous SS7 variants is to use an International Gateway,
which has an appearance in every network to be interworked. International Gateways
are an expensive cost-of-entry whose scale applies to larger interworking configurations.
Furthermore, interworking is performed at the ISUP or TCAP user level in the gateway.
With this form of solution, the general case of interworking non homogeneous networks,
ANSI to ITU for example, is provided and is also sufficient for interworking of
similar network variants. Solutions of this form are limited in capacity since the
SS7 messages must traverse the full protocol stack of each network being interworked.
MTP network management across all the networks is a complex proposition for which
the International Gateway provider must deliver a solution. Such solutions have
to be managed above the MTP layer so the plurality of point codes appears transparent
to the MTP layer in each separate network.
Solution
The problem space can be divided in two; interworking of four or less networks,
and interworking of five or more networks. In ITU and ANSI SS7 variants, the MTP3
address contains a sub field known as the Network Indicator (NI). The NI field is
used to differentiate between four instances (similar to subnet) of the same variant
of SS7. Using the NI field as part of the SS7 address, any point code value can
exist in all four networks: PC1 in NI 0, PC1 in NI 1, PC1 in NI 2 and PC1 in NI
3.
For applications involving the interworking of four or less of the same SS7 variant,
an interworking function that conceals the redundancy of point codes can be implemented
at the MTP3 layer. In this solution, an SS7 STP with an appearance in up to four
networks performs the interworking.
In applications involving the interworking of five or more of the same SS7 variant,
the International Gateway would apply.
Ulticom nSignia eSTP
When Ulticom's nSignia® eSTP is used to interconnect up to four networks, there
is one PC in each network. When each PC is created, a different Network Indicator
(NI) value must be specified.
An nSignia eSTP that is located between two networks, and has a Point Code defined
in each network, can translate PCs from one network to another with the Point Code
Translation feature. This enables a network element with Point Code X in one network
(Network 1, NI=0) to be addressed as another Virtual Point Code X' (X prime) in
a different network (Network 2, NI=1).
MTP network management (STP functionality) works transparently across the multiple
networks. Consider the example shown in Figure 2, where Point Code Translation has
been configured and provisioned on STP1. STP1 has one PC defined in Network 1, and
one PC defined in Network 2. Availability for SP1 (PC=101) in Network 1 is reported
as availabile for the virtual SP1 V(PC=204) in Network 2, if a Point Code Translation
exists between the two point codes. SP1 V does not have a physical connection to
STP2, but it appears as though it is available in network 2 because of Point Code
Translation.
Key Business Benefits
- A cost-effective solution
- A solution that integrates into the customer's existing network addressing plan
- Interworking at the STP level of performance
- Provides a solution that creates no network operations disruption
- Delivers a single network management solution