Microsoft Word Master master doc

2.6.3
 
Back-to-back User Agent 
In [14]], a UA is defined as an entity that represents an end-system. The UA involves a 
UAC which sends requests to a UAS via a number of proxy servers. The UAS sends 
responses back to the UAC forwarded by the proxy servers. This leads us to the 
definition of a Back-to-back User Agent (B2BUA. A B2BUA is a logical entity that 
receives a request and processes it as a UAS. In order to determine how a request should 
be answered, it acts like a UAC and generates requests. It maintains dialog state and must 
participate in all requests sent on the dialogs it has established. 
2.6.4
 
Security 
Fundamental security services required for the SIP protocol are preserving the 
confidentiality and integrity of messaging, preventing replay attacks or message spoofing, 
providing for the authentication and privacy of the participants in a session, and 
preventing denial-of-service attacks. Bodies within the SIP messages separately require 
the security services of confidentiality, integrity, and authentication. Instead of defining 
new security mechanisms, SIP uses existing security models derived from HTTP and 
SNMP when possible. 
In addition to SIP URIs, SIP also provides a secure URI called SIPS URI. The use of 
these SIPS URIs guarantees secure encrypted transport of SIP messages.
Example of a SIPS URI is: 
sips:[e-mail] 
2.7
 
Streaming Protocols 
As mentioned in 2.4.2.7 our TMMS Clients have the opportunity to use streaming to get 
some of the media in the TMMS. Here follow an introduction to the streaming protocols 
used in our services. This background material is based on [10]. 
2.7.1
 
Real-Time Streaming Protocol 
Real-Time Streaming protocol (RTSP) is a protocol that allows users to control the 
transmission of a media stream. It is an out-of-band protocol which means that the 
RTSP messages are sent using different port numbers than the media stream.

---

2.7 Background information: : Streaming Protocols 
Page 26 of 93