3. They may be semiautomatic, fully automatic, or manual in nature. They can also vary in type from
analog to digital and range in size from 12 to 600 lines. The SES connects to only one node while the
LBS will connect to more than one node. All switches dump into and receive traffic from the major
switches. When calculating the size of the trunk group cluster (TGC) between nodes, the traffic the SES
and LES have to offer must be determined first. Before calculating the size of a TGC, a switch's traffic
profile must be determined. A switch's traffic profile is obtained by metering reports that the automatic
switches produce on a reoccurring basis.
4. Before we continue, clarification must be made. The SEN and LEN we normally hear when
speaking about MSE are not the same as the LES and SES we are referring to throughout these lessons.
In MSE, we do not need to determine the TGC, since flood search is automatic and done without regard
to paths assigned.
PART A - DEFINITIONS
Before we continue, you must understand the items listed below.
a. Trunk is defined as a single circuit between two points, both of which are switching centers
and/or individual distribution points.
b. Trunk groups are trunks with identical characteristics (designation, signaling, and traffic route)
with the same destination.
c. Trunk group cluster is a set of trunks with different characteristics (including analog and digital
types) with the same destination.
d. Grade of service (GOS) is the number of calls completed divided by the number of calls
e. SES is a switchboard that has only one possible path in or out for all traffic.
f. LES is a switchboard that has more than one possible path in or out for all traffic. This
switchboard may or may not provide tandem service. An LES will also have extensive local traffic.
g. A node has numerous paths in and out and extensive tandem service provided. There is
minimum local traffic and that traffic is normally reserved for signal personnel's command and control
of the network.
h. Erlang is the international unit of measurement for traffic intensity. One Erlang is the intensity
in a traffic path continuously occupied. An Erlang can measure the intensity in one or more traffic paths
for one call-hour per hour period. Each trunk has a maximum capacity of 36 call completed second
(CCS) per hour. A CCS is the number of calls multiplied by the average holding time for the calls. The
CCS cannot exceed 3,600 call-second.