Traffic units many used in traffic engineer analysis are offered traffic (A), grade of service (B), and device capacity (N). This third unit is connect very tight, so that when two unit already known, then third unit countable. Usually B value is determined, so that if A is fluctuates then N will follow that change.
Generally companies make device with N standard, so that when A is big and b is certain, then will emerge how if N that need is bigger than N standard? (N > Nstd ?)
Example:
Figure 5.1 Example system divide in to several group.
Like showed in figure 5.1, for example showed a switching system that has line out (selector or server) is bigger than N standard and used to serve 1000 customers. To handle that condition, so system is divided in to 5 sub-system with each serve 200 customers and line capacity n1, n2, ……, n5, each £ total line out (server) standard.
In next example, see figure 5.2, showed complete calculation so that seen change A and N value for appointed B value.
In example is showed switching system that used to process traffic as big as 6,71 Erlang with desirable grade of service 0,2 %. Based on calculation, for the mentioned is need 15 line out (server). The bundle is perfect bundle.
When obvious there is no N standard that have 15 line out, so the solution with divide to be 2 sub group as follows:
Sub group I : A = 6,71 / 2 = 3,355 Erlang
B = 0,2 %
® needed n1 = 10 line
Sub group II : A = 6,71 / 2 = 3,355 Erlang
B = 0,2 %
® needed n2 = 10 line
The result from that technique showed in figure 5.2 (B), where seen:
- A is total and B is constant
- Each sub group is perfect bundle
- Need 2 x 10 = 20 line out (server)
- In its entirety not perfect bundle again
Figure 5.2 Solving example for N > N standard.
Conclusion:
Perfect bundle gives:
Total line out is minimum
Efficiency per line out optimum
By becoming imperfect bundle then efficiency is decreased. To increase the efficiency, can be done by multiplication process with interconnection, grading, or increasing switching level. Example configuration that simplified from multiplication is showed in figure 5.3 and 5.4.
Interconnection :
Figure 5.3 Multiplication configurations with interconnection.
Increasing Switching Level:
Figure 5.4 multiplication configurations with increasing switching level.
Interconnection example:
- Selector system that used has line connection k = 5
- N = 8 line out (server)
- Found 2 groups that will interconnected
K = 5 ü before interconnection, total line out (server) = 10
ý
2 group þ After interconnection N = 8 line
Interconnection can be done with several ways, usually done with cascade interconnection (grading). Example from cascade interconnection form, showed in figure 5.5, with:
k = 10
total group = 4
N = 23
Figure 5.5 Example cascade interconnection (grading) configuration.
Before interconnection: Total line out (server) : N = 4 x 10 = 40 line
After interconnection: N = 23 line (12 individual, 8 pair, 3 four).
In this case explanation from interconnection = grading.
