Dialogic SS7G2X - Manual (Page 143)

143
Dialogic ® SS7G2x Signaling Server SGW Mode User Manual Issue 4
7.6.2 Dual Resilient Operation
Two Signaling Gateways have the ability to work in conjunction with one another to realize a single SS7
signaling point where the operation of the Message Transfer Part (MTP) is distributed. Failure (or planned
maintenance) of one or other of the Signaling Gateways operating in “Dual Mode” therefore does not result
in a loss of SS7 signaling capability.
The use of the dual functionality does introduce some restrictions that are described below. The user is
responsible for ensuring that these restrictions are acceptable, otherwise the dual mode of operation may
not be applicable.
7.6.2.1 Overview of Dual Resilience
The dual Signaling Gateway solution assumes that each Signaling Gateway has one (or more) signaling links
facing the network.
The ability for each of the Signaling Gateways to communicate with each other is addressed by adding an
additional link set (containing one or two links, for example LS2 in
Figure 11, “Dual Resilient Operation” on
page 144 ) between the two platforms. This link set is used to convey network status and management
messages between the two halves of the system and to pass signaling traffic as necessary.
On each Signaling Gateway, there is (a minimum of) two link sets, one connected to the adjacent signaling
point and the other connected to the other half of the dual pair. Each MTP route is configured so that the
primary link set is the link set connected to the adjacent signaling point and the secondary link set is the link
set connected to the partner Signaling Gateway. Load sharing across these link sets is disabled.
The link set between the two halves of the dual Signaling Gateway is configured so that the originating and
destination point codes are identical.
Under normal circumstances, messages that have been determined for the SS7 network are routed directly
over the link set that connects to the adjacent signaling point. Under failure conditions, when the link to the
adjacent signaling point is not available, the traffic messages are sent instead on the secondary link set to
the partner Signaling Gateway. On receipt of these messages, the partner Signaling Gateway recognizes that
the message is not destined for itself and transfers the message to its network-facing link set.
The signaling that takes place between each half of the dual Signaling Gateway system makes use of two
reserved Network Indicator values in the Sub-Service Field, these values designated “National - Reserved”
and “International - Reserved” must therefore not be used for signaling either to or from the network.
The link set between the two halves of the dual pair now becomes a key element in the system and to avoid
a single point of failure, this link set should contain at least two signaling links. Where possible, these links
should be located on different signaling boards.
7.6.2.2 Configuration
Each half of the dual configuration needs to be configured separately using existing configuration techniques
and noting the following.
The additional link set between the two Signaling Gateways should have the local point code and the
adjacent point code set to the same value.
Each route to a destination signaling point should be configured to use the network link set as the primary
link set and the inter Signaling Gateway link set as the secondary link set. Load sharing must be disabled.
When connecting to a pair of adjacent STPs, each STP must have a route declared on each Signaling
Gateway and in all cases the inter-Signaling Gateway link set must be specified as the secondary link set.
A route must be configured to the other half of the dual Signaling Gateway system, this must use the inter-
Signaling Gateway link set as the only link set.
In addition, the link set between the two halves of the dual Signaling Gateway system must be designated as
a “special” link set. The method of achieving this depends on the equipment and configuration tools in use as
follows: