intelligence. The functionality required by the
control plane is based on IP models. Thus the
functionality carried out by the control plane
here includes service invocation via the UNI,
neighbour discovery, status updating, as well as
routing of optical channels, wavelength alloca-
tion and path establishment. These can be based
on GMPLS as presented in the previous section.
Indeed, both effective development when adapt-
ing existing well-proven protocols, and easier
migration scenarios towards future solutions,
justify this choice.
The control plane comprises local Optical Con-
nection Controllers (OCC) at each node that
exchanges information with the optical network
via the Connection Controller Interface (CCI).
The OCC instructs the local optical switch to
reconfigure via the CCI, which also carries
topology updates from the node. Communication
between OCCs is done via the Network Network
Interface (NNI). This can be an internal network
interface (I-NNI) when it carries routing/signal-
ling messages within a single ASON administra-
tive domain (e.g. a single operator), or an exter-
nal network interface (E-NNI) when it connects
two separate administrative domains. The main
difference between the two is that no topology
information is carried through the E-NNI; nei-
ther is resource control possible through this
interface. Finally, the control plane communi-
cates with the network management system via
the NNI-A and NNI-T interfaces.
Signalling information within the control plane
can be embedded information but is best con-
veyed using a separate signalling channel. This
signalling channel can be out-of-fibre, i.e. going
through an altogether separate network, or in-
fibre. In the latter case the signalling channel can
be in-band, i.e. within the range of the (standard-
ised) optical channels that are used for the trans-
mission of traffic, or out-of-band. The signalling
channel requires a dedicated resilience strategy.
GMPLS-based signalling protocols are envis-
aged used in ASON as well as through the UNI
and a lot of development work is being carried
out in this area.Classes of Service
ASON can provide service differentiation as
based upon a set of parameters such as priority,
resilience, delay, jitter, etc., following IP
resource handling models [12]. Figure 5 shows
an example of an ASON providing end-to-end
connections arranged by client. Optical channels
are then allocated separately to each client,
according to a set of classes of service (CoS) as
shown in Figure 6. This would place trafficSDHGbEthIPENENEN ENOCh ServicesEdge
NodeGbEth
ATMATMNMS SLASDHIPFigure 5 Multi-client end-to-
end wavelength services
offered by ASON – here an
example with wavelength
allocation performed
separately for each clientCoS IICoS IIICoS IVCoS Ikcba • • • • • • •λ 1
λ 2
λ 3λ 5
λ 6λ 4λiService description CoS
mappingOCh
allocationService
parameterClient 2Client nClient 1Figure 6 Service requirements
are mapped in Classes of
Services, followed by route
computation (not shown) and
wavelength allocation