Mesh Optical Networks PROTECTION SCHEMES

THE ITU-T G.709 STANDARD – THE DIGITAL WRAPPER 217 Carrier B Carrier A Carrier A User B User A Over several carriers Per carrier basis End-to-end Figure 9.13 An example of networking monitoring. network operator to monitor the error performance of a connection that originates and terminates within its own network, but traverses different operators. An example of such a connection is shown in Figure 9.13. FAS and OTU overhead The frame alignment signal FAS fields are located in columns 1 to 7 of the first row, as shown in Figure 9.14. FAS is carried in the first six bytes and is used by the receiving equipment to identify the beginning of the OTU frame. The FAS value is the same as in SONETSDH i.e., F6F6F6282828, and is transmitted unscrambled. Some of the overheads are transmitted over successive OTU frames. For instance, as we saw above, the payload structure identifier byte of the OPU overhead located on row 4 and column 15 is used to transport a 256-byte message. In view of this, groups of successive ODU frames are organized logically into multi-frames. The position of an ODU frame within a multi-frame is indicated by the multi-frame alignment signal MFAS byte located in row 1 column 7. The value of the MFAS byte is incremented each frame, thereby providing a multi-frame consisting of 256 frames. It is transmitted scrambled along with the remainder of the OTU frame. Row 1 ODU OH Client payload 2 3 4 1 7 8 14 15 16 17 3824 3825. . .4080 FAS OTU OH O P U FEC FAS MFAS SM GCC RES 1 13 12 11 10 9 8 7 6 5 4 3 2 14 Figure 9.14 The FAS and OTU overheads. 218 WAVELENGTH ROUTING OPTICAL NETWORKS In Figure 9.14, the OTU overhead fields are located in columns 8 to 14 of the first row. These fields provide supervisory functions for section monitoring and condition the signal for transport between retiming, reshaping, and regeneration 3R points in the optical network. The following fields have been defined: section monitoring SM and general communication channel GCC. Finally, the forward error correction is carried in columns 3825 to 4080 of all four rows. The Reed-Solomon code RS 255239 is used. Client signals As mentioned earlier on, the following types of traffic can be mapped onto the OPU payload: • SONETSDH : STS-48, STS-192, and STS-768 data streams are mapped onto an OPU payload using a locally generated clock or a clock derived from the SONETSDH signal. • 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 mappingdemapping 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 sig- naling 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 cat- egories: 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