Information Technology Reference
The existing passive-star-coupler hub and the AWG hub cannot fulfill the above
requirements. In particular, the passive-star-coupler hub can only provide W channels which
may not be enough for the ever-increasing traffic load, and the AWG hub provides uniform
channel allocation (specifically, one channel to every input-output pair) and hence it cannot
efficiently transport non-uniform traffic.
In our recent studies [1-2], we propose a new design of metro hubs called multi-passive-
combiner hubs . This new design can provide the same communication functions as the
existing hubs while it can also fulfill the above two requirements (i.e., the multi-passive-
combiner hub can efficiently transport non-uniform traffic and it can easily be scaled up to
provide more channels to fulfill the ever-increasing bandwidth demand).
In this chapter, we summarize our research work on multi-passive-combiner hubs [1-2].
In Section 2, we describe the multi-passive-combiner hubs. In Section 3, we determine the
channel requirements for the input-output pairs based on the traffic load and patterns. In
Section 4, we assign wavelength channels to the input-output pairs to fulfill the channel
requirements while avoiding wavelength conflict. In Section 5, we present numerical results
to demonstrate the effectiveness of the multi-passive-combiner hubs. In Section 6, we
conclude this chapter.
2. D ESIGN OF M ULTI -P ASSIVE -C OMBINER H UBS
We consider the network model shown in Figure 1. The metro network has N nodes. In
each local region, a node serves the end terminals in this region and grooms their traffic into
one or more wavelength channels. The nodes are connected to the metro hub through optical
fibers. The multi-passive-combiner hub is shown in Figure 4. Within the hub, each incoming
fiber is connected to a demultiplexer, the demultiplexers are connected to the passive
combiners based on a channel assignment (to be determined in Section 4), and each passive
combiner is connected to an outgoing fiber. This hub only involves passive components
(namely, demultiplexers and passive combiners) and hence it has low cost and high
reliability. In the following, we explain how the multi-passive-combiner hub can provide the
same communication functions as the AWG hub (which is a well-regarded design in the
literature) as well as other desirable functions.
The multi-passive-combiner hub can provide the same communication as the AWG hub
as follows. Let the inputs/outputs of the hub be numbered from 1. An AWG hub connects
wavelength channel λ i from input j to output (
+ − + (e.g., see Figure 3). A
multi-passive-combiner hub can provide the same communication function as follows: it uses
W demultiplexers and W passive combiners, connects wavelength channel λ i from input j to
passive combiner (
+− + , and connects passive combiner j to output j .
Figure 4 shows a multi-passive-combiner hub which provides the same communication
function as the AWG hub shown in Figure 3.
The multi-passive-combiner hub can efficiently transport non-uniform metro traffic as
follows. It can allocate different number of channels to different input-output pairs based on
their traffic requirements (the details are given in Section 3). In other words, it can realize
non-uniform channel allocation within the hub to best fit the non-uniform traffic. On the other
hand, the AWG hub provides one wavelength channel to each input-output pair (e.g., see