How to properly use services in a layered iOS app architecture?

Question

iOS

I read an excellent article from robots about the layered architecture of an iOS application: habrahabr.ru/company/redmadrobot/blog/246551
There was a question regarding this item:

Services must be as autonomous as possible, which does not prevent you from building logical dependencies between them. For example, it is quite logical that the application has a service responsible for authorizing and maintaining a session with the server, and other services depend on it - they use the token provided by it to generate requests.

How can one service access another service? Through the ServiceLayer or by creating a new instance of the desired service?
And the same question regarding parsers - how should they handle arrays of nested objects? Initialize the parser for these objects yourself, or do it through their service?