Download (direct link):
• IP and Ethernet frames: This is done using the generic frame procedure (GFP). (See Section 2.7.)
• ATM cells: A constant bit rate ATM cell stream with a capacity identical to the OPU payload is mapped by aligning the ATM cell bytes to the OPU bytes. A cell can straddle two successive OPU payloads. Decoupling of the cell rate and cell delineation are described in Section 3.4.1.
• Test signals: User data is used to carry out stress tests, stimulus response tests, and mapping/demapping of client signals.
9.4 CONTROL PLANE ARCHITECTURES
The control plane consists of protocols that are used to support the data plane, which is concerned with the transmission of data. The control plane protocols are concerned with signaling, routing, and network management. Signaling is used to set up, maintain, and tear-down connections. The ATM protocols Q.2931 and PNNI (see Chapter 5) and the label distribution protocols for setting up LSPs (see Chapter 7) are examples of signaling protocols. Routing is an important part of the network operations. It is used to construct and maintain routes that the data has to follow in order to reach a destination. Finally, network management is concerned with controlling a network so as to maximize its efficiency and productivity. ISO’s model divides network management into five categories: fault management, accounting management, configuration management, security management and performance management.
There are basically two different control plane architectures. In the first one, the user is isolated from the network via a user network interface (UNI). The user is not aware of the network’s topology, its control plane and its data plane. The nodes inside the network interact with each other via a network-node interface (NNI). A good example of this control plane architecture is the ATM network. A user can only access the ATM network via an ATM UNI, and the ATM switches inside an ATM network interact with each other via an NNI, such as PNNI in the case of a private network (See Chapters 3 and 5).
In the second control plane architecture, the user is not isolated from the network through a UNI, and the nodes inside the network do not interact with each other via a
CONTROL PLANE ARCHITECTURES
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 SONET/SDH.
A large optical network will typically consist of interconnected smaller optical subnetworks, 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 external 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
Figure 9.15 Client networks interconnected via an optical networks.
Figure 9.16 The interfaces UNI, I-NNI, and E-NNI.
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.