The IMS: IP Multimedia Concepts And Services, Second Edition

23.1. SigComp architecture

SigComp's architecture can be broken down into five entities (see Figure 23.1). The entities are described as follows:

• Compressor dispatcher – this is the interface between the application and the SigComp system. It invokes a compressor, indicated by the application using a compartment identifier. The compressor dispatcher forwards the returned compressed message to its destination.

• Decompressor dispatcher – this is the interface between the SigComp system and the application. It invokes a UDVM that decompresses the message. The decompressor dispatcher then passes the decompressed message to the application. If the application wishes the decompressor to retain the state of the message, it returns what is called a "compartment identifier".

• Compressors – this entity compresses the application message. It uses a compartment that is identified using the compartment identifier. The compressed message is passed to the compressor dispatcher. DEFLATE is an example of a compression algorithm.

• UDVM – This entity decompresses a compressed message. A new instance is invoked for every new SigComp message. UDVM uses the state handler to create a state for a new message or make use of an existing state.

• State handler – this holds information that is stored between SigComp messages (referred to as the "state of the messages"). It can store and recover the state.

Figure 23.1. SigComp architecture.