CCITT SIGNALING SYSTEM NO. 7
Message Routing Message routing is the process of selecting the signaling link to
be used for each signaling message. Message routing is based on analysis of the rout-
ing label of the message in combination with predetermined routing data at a particular
Message Distribution Message distribution is the process that determines to which user
part a message is to be delivered. The choice is made by analysis of the service indicator.
Message Discrimination Message discrimination is the process that determines, on
receipt of a message at a signaling point, whether or not the point is the destination point
of that message. This decision is based on analysis of the destination code of the routing
label in the message. If the signaling point is the destination, the message is delivered to
the message destination function. If not, the message is delivered to the routing function
for further transfer on a signaling link.
Signaling Network Management
Three signaling network management functional blocks are shown in Figure 14.3.
These are signaling traffic management, signaling link management, and signaling route
Signaling Traffic Management
. The signaling traffic management func-
1. To control message routing. This includes modification of message routing to pre-
serve, when required, accessibility of all destination points concerned or to restore
2. In conjunction with modifications of message routing, to control the resulting trans-
fer of signaling traffic in a manner that avoids irregularities in message flow.
3. Flow control.
Control of message routing is based on analysis of predetermined information about all
allowed potential routing possibilities in combination with information, supplied by the
signaling link management and signaling route management functions, about the status
of the signaling network (i.e., current availability of signaling links and routes).
Changes in the status of the signaling network typically result in modification of cur-
rent message routing and thus in the transfer of certain portions of the signaling traffic
from one link to another. The transfer of signaling traffic is performed in accordance
with specific procedures. These procedures are changeover, changeback, forced rerouting,
and controlled rerouting. The procedures are designed to avoid, as far as circumstances
permit, such irregularities in message transfer as loss, missequencing, or multiple delivery
The changeover and changeback procedures involve communication with other signal-
ing point(s). For example, in the case of changeover from a failing signaling link, the
two ends of the failing link exchange information (via an alternative path) that normally
enables retrieval of messages that otherwise would have been lost on the failing link.
A signaling network has to have a signaling traffic capacity that is higher than the
normal traffic offered. However, in overload conditions (e.g., due to network failures
or extremely high traffic peaks) the signaling traffic management function takes flow
control actions to minimize the problem. An example is the provision of an indication