SIP Basics

SIP is a layered protocol. Thus we start with describing all the layers:

• Message Layer,

• Transport Layer,

• Transaction Layer,

• Transaction User,

• UAC Core,

• UAS Core,

• Proxy Core.

The various cores use additional building blocks to implement actual functionality:

• Dialogs,

• Sessions,

• Registrations,

• Event Notification.

Some additional building blocks are used:

• Authentication,

• Digest Authentication.