John Vollbrecht wrote:
So what exactly is an adaptation.
See also my mail yesterday. Loosly, adaptation is the encapsulation of one data layer into another data layer. A de-adaptation is the extraction of data from that lower layer (which also terminates the lower layer path). Formally (G.800):
The adaptation source function is a labelling and encoding entity that takes one or more client communications passing through its client facing input port(s), and combines them into instances of adapted information. The adaptation source function also adds sufficient labelling in order to distinguish each client communication from all others within the scope of the access point to which the adaptation source is bound. The instances of adapted information are passed through the server facing port.
For example, and OTN port might convert things to SONET, Ethernet, and other line protocols. Is this adaptation?
Yes, if "things" is a higher layer than SONET or Ethernet.
Also, what is it that keeps there to be only two adaptations?
There is at most one adaptation per data source: that data is adapted into one or more server layer channels using ONE adaptation function. However, our ports are bidirectional, and thus have two sources and two sinks. Therefore, a port can have at most two adaptations. The same applies for links and cross connects: since there are two sources and two sinks per port, there can be two links and/or two cross connects at most. (Typically, one link and one cross connect, but I know of situations with two links) It is still open for discussion if this is the best approach. Thinking of it now, I am almost inclined to define unidirectional ports, though I think that is too verbose for most topology descriptions.
Another point that I was thinking about: what is the cardinality of the implementedBy relation? I think it might be *-*, but I'm not sure.
I'd say 1:*, since one (virtual) node is -I think- typically implemented by a physical node. The converse, a set of nodes behaving like a virtual node is handled by the topology concept (formerly known as Graph, formerly know as Network) Regards, Freek