Information Technology Reference
In-Depth Information
Delay
d
We determine the smallest
such that the mean packet delay
is smaller than
ij
ij
the given requirement
Delay
. The following is an example. Let the mean packet arrival rate
(in terms of number of packets per second) be given by
*
⎡
6
6
6
⎤
0
1.0
×
10
1.5
×
10
2.0
×
10
⎢
⎥
×
6
×
6
×
6
1.5
10
0
2.0
10
3.0
10
(3)
⎢
⎥
[]
α
=
⎢
ij
N
×
N
⎥
1.5
×
10
6
2.0
×
10
6
0
3.0
×
10
6
⎢
⎥
6
6
6
3.0
×
10
3.5
×
10
4.0
×
10
0
⎣
⎦
and the mean packet transmission time be 1 μs. If the mean packet delay cannot be larger than
*
Delay
=
1.5
μ
, then the channel requirement matrix can be found to be:
0233
3035
3305
5560
⎡
⎤
⎢
⎥
(4)
⎢
⎥
D
=
⎢
⎥
⎢
⎥
⎣
⎦
If the mean packet delay requirement is relaxed to
*
, then the channel
Delay
=
5.0
μ
requirement matrix becomes:
⎡
0223
2034
2304
4450
⎤
⎢
⎥
(5)
⎢
⎥
D
=
⎢
⎥
⎢
⎥
⎣
⎦
In other words, when the mean packet delay requirement is looser, fewer channels are
needed.
4.
C
HANNEL
A
SSIGNMENT
After determining the number of channels
d
required from node
i
to node
j
, it is
ij
necessary to assign
i
d
wavelength channels to this node pair. In this assignment, if two or
more channels at the same wavelength are connected to the same passive combiner within the
multi-passive-combiner hub, then there is
wavelength conflict
and the signals transmitted in
these channels interfere with each other. Therefore, it is important to avoid
wavelength
conflict
such that only the channels at distinct wavelengths are connected to each passive
combiner. For example, wavelength conflict is avoided in the multi-passive-combiner hub
shown in Figure 7. In this section, we define the channel assignment problem for the multi-
passive-combiner hubs and propose an efficient algorithm for channel assignment.
