, into a larger VC, its phase offset in bytes can be identified relative to some reference point in this larger VC (see Figure 10.6). Furthermore, there is also a mechanism for allowing the value of this pointer to change if, for some reason, there is a loss of synchronization and the smaller-capacity VC is running either slightly slower or slightly faster than the larger VC. In fact, each of the smaller-capacity VCs has its own pointer, which can change independently of any of the others. Although the use of these pointers still entails some input buffers, these are much smaller than would be required if there were no mechanism for changing the phase of small-capacity VC within a larger one; hence the problem of excessive delays can be con- tained. We can now picture an SDH network where the majority of VCs, both large and small, are well synchronized to each other, but, at the same time, there are a few that are not SO well synchronized, and every SO often the increasing strain of their asynchronism has to be relieved by a byte-sized slip relative to the majority of the other VCs in the network. Large VC Large VC Path Overhead Payload Path Overhead Small Small Small Small Small Small Small VC-1: Because of its phase relative to the Payload large VC POH, it is split between one large VC and the following one Fig. 10.6 Pointers allow a small VC to have arbitrary phase with respect to a large VC. Chapter 10 Synchronous Optical Networks and Synchronous Digital Hierarchy The crucial point is that we retain our ability to locate the management and control informa- tion in the VC's POH bytes because the pointer value associated with the VC is recalculated whenever a slip occurs. The pointer mechanism previously described is at the very heart of the SDH standard. It is this mechanism that enables us to construct networks that are nearly, but not com- pletely, synchronous, and yet still allows us to easily locate each traffic channel (VC) together with its associated management and control information (i.e., POH), but w