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2.5
 
Evaluation criteria 
For the evaluation of the different end-to-end services we have designed several quality 
attribute utility trees [13], which define some criteria we need to take in consideration. 
Each criterion has one or many scenarios which the evaluation of our services are based 
on.
2.5.1
 
Security 
Figure 2-21 Security evaluation scenarios 

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2.5 Background information: : Evaluation criteria 
Page 20 of 93 
2.5.2
 
Usability 
Figure 2-22 Usability evaluation scenarios 
2.5.3
 
Modifiability 
Figure 2-23 Modifiability evaluation scenarios 
2.5.4
 
Interoperability 
Figure 2-24 Interoperability evaluation scenario 

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2.6 Background information: : Session Initiation Protocol 
Page 21 of 93 
2.5.5
 
Reliability 
Figure 2-25 Reliability evaluation scenarios 
2.5.6
 
Billability 
Figure 2-26 Billability evaluation scenarios 
2.6
 
Session Initiation Protocol 
SIP[14] is an emerging application layer protocol specified by the Internet Engineering 
Task Force (IETF). SIP is designed to establish and manage multimedia sessions over 
Packet Switched (PS) networks. It provides basic functionality for establishing, 
modifying, and tearing down sessions, as well as capabilities to implement a host of more 
advanced services.
SIP supports five facets of establishing and terminating multimedia communication, 
these are: 
ƒ
User location 
ƒ
User availability 
ƒ
User capacities 
ƒ
Session setup 
ƒ
Session management