The Optical Channel Och Frame
CONTROL PLANE ARCHITECTURES 219
separate NNI. Rather, all users and nodes run the same set of protocols. A good example of this architecture is the IP network.
Both control plane architectures have been used to devise different control planes for wavelength routing networks. The Optical Internetworking Forum OIF, following the
first control plane architecture, has proposed a user-network interface. It is also working on a network-node interface. IETF has proposed three different control plane models for
the transmission of IP traffic over an optical network, which are based on the above two control plane architectures.
An optical network provides interconnectivity to client networks see Figure 9.15. These client networks could be packet-switching networks, such as IP, ATM, and frame
relay networks, and circuit-switching networks, such as SONETSDH. A large optical network will typically consist of interconnected smaller optical sub-
networks, each representing a separate control domain. Each of these smaller networks could be a different administrative system. Also, the equipment within a smaller network
could all be of the same vendor, with their own administrative and control procedures. Within the first control plane architecture, the following three interfaces have been
defined: user-network interface UNI, internal network-node interface I-NNI, and exter- nal network node interface E-NNI.
See Figure 9.16. As mentioned above, OIF has specified a UNI which provides signaling procedures
for clients to automatically create a connection, delete a connection, and query the status connection over an optical wavelength routing network. The UNI is based on the label
distribution protocols LDP and RSVP-TE see Section 9.6. IETF has defined three different control plane models: the peer model, the overlay
model , and the augmented model. In the discussion below and in Figure 9.15, we assume
that the client networks are IP networks. The data plane for the networks is shown as
Optical network Client network
Client network
Figure 9.15 Client networks interconnected via an optical networks.
UNI E-NNI
Optical subnetwork
I-NNI UNI
I-NNI
Optical subnetwork
Client network Client network
Optical network
Figure 9.16 The interfaces UNI, I-NNI, and E-NNI.
220 WAVELENGTH ROUTING OPTICAL NETWORKS
a mixture of packet-switching and circuit-switching. Packet switching is used within the IP networks; circuit-switching is used within the optical network, where a circuit is a
lightpath or subrate channel if traffic grooming is used. The peer model uses the second control plane architecture described above. That is,
the client networks and the optical network are treated as a single network from the point of view of the control plane. The generalized MPLS GMPLS architecture is used in the
control plane. GMPLS is an extension of MPLS for MPLS, see Chapter 6; for GMPLS, see Section 9.5. The IP and the optical networks run the same IP routing protocol – OSPF
with suitable optical extensions. Consequently, all of the optical nodes and IP routers maintain the same topology and link state information. An IP router computes an LSP
end-to-end, which is then established using the label distribution protocols CR-LDP or RSVP-TE see Chapter 7, appropriately extended for GMPLS.
In the overlay model, the optical network uses the first control plane architecture described above see also Figure 9.16. An IP client network is connected to the optical
network via an edge IP router which has an optical interface to its ingress optical node, i.e. the optical node to which it is directly attached. Before an edge IP router can transmit
over the optical network, it has to request a connection from its ingress optical node. This is done by using a signaling protocol defined over a UNI. A connection over the optical
network can be a lightpath permanent or switched or a subchannel. The edge router is not aware of the topology of the optical network; nor is it aware of its control and data
planes. The control plane of the optical network can be based on GMPLS. However, UNI maintains a strict separation of the client networks and the optical network.
Finally, in the augmented model, the IP client networks and the optical network use separate control planes. However, routing information from one network is passed to the
other. For instance, IP addresses from one IP client network can be carried by the optical network to another IP client network to allow reachability. Routing within the IP and
optical networks is separate, but both networks use the same routing protocol. The inter- domain IP routing protocol BGP can be adapted for exchanging information between IP
and optical domains.