I'm not clear on the purpose of this type of adaptation (one type
encapsulated in the same type). Can you perhaps give a example?
Jerry brought this specific Ethernet example up, and I read through the standards to verify. The Q-in-Q double label is a single instance of the more generic 2..N label stacking supported by the standards. Jerry has the requirement to allow for an arbitrarily number of labels to be pushed and popped as the Ethernet packet transits the network. In this specific example, the packet arrives on one port in the domain, is a label is added, and it leaves another port in the domain with the same encoding. Somewhere else in the network the labels will be popped an equivalent number of times.
(slide 5)
What is the purpose of having different Service Domains in a Network
Topology? Because the STP in each services domain are of a different
type? Or to describe geographic subdivisions withing a Network Topology?
The definition of a Service Domain is that it contains STPs that can be connected without restriction. When STP are of different types then they must be in different service domains. In fact, if a network does not support label swapping then each STP with the same label value will be grouped in their own Service Domain.