 attributes and the acknowl- edgment can contain the far-end identity attributes. The service capability information can be also contained in the acknowledgment message. In the unacknowledged mode both ends send their identity attributes. Recommendation G.7714 discusses the following two discovery methods: 1. Trace identifier method 2. Test signal method In the trace identifier method, the discovery is carried out by using the trail identifiers that are included in all the overheads of the transport ITU-T standards (both in SONET/SDH and in OTN, see Chapter 2). In particular, the trail termination points are first identified and then links connections are inferred. Just to give an example, let us imagine to have an ASON-managed next gen- eration SONET network and to consider path layer discovery. A trace identifier discovery protocol will reside into the CC and will detect in all the network entities if the JO field of the SONET path layer header is terminated and regenerated (the JO field is the trail identi- fier in this case). Once all the points in which the JO is terminated and recreated are detected, the path layer logical topology is inferred by connecting the point where a value of JO is created with the point where such a value is terminated with a virtual link (that is, links at the path layer). It is to be observed that, under a layering point of view, the trail reports an information that is typical of the service layer, thus the trace identifier method performs discovery in layer one by exploiting also information relative to the client layer. In the test signal method, test signals are used to directly find associations between subnetwork termination points (see network layering, Chapter 3) without discovering any service layer trails. While the use of overhead elements identifying a trail allows discov- ery to be carried out during normal network working, the use of data field to send test messages implies that the client data transmission is suspended. Thus the first discov- ery method is a type o