1 week later Alice 'Is your offer still valid' 'I did not send you an offer' Figure 6.9 Example of non-repudiation Understanding Changing Telecommunications - Building a Successful Telecom Business An application sends thousands of e-mails to a specific user. Bugs in e-mail software can be utilized in a way that e-mails multiply themselves and overload the system/server. 6.4 NON-AVAILABILITY FOR NON-SECURITY REASONS This is a large area. All the traditional reasons for non-availability remain, but the suc- cessive reduction of physical volume decreases the number of elements, which is an advantage for reliability and availability. Other factors make the network more vulnerable, with the introduction of web services as one contributing factor. 6.5 CONNECTING SECURITY TERMS INTO TELECOMMUNICATION So far the vocabulary has mainly been security oriented. It has also been service oriented. What is needed is to apply or even translate the security requirements into the telecom- munication field. This could be done in various ways. One approach chosen for this book is to use the same tool as in Chapter 3: the fundamental technical plans (Figure 6.10). Another one is to use the 'stack'. The first measure is explained in Chapter 3: to integrate security within the fundamental plans. To make a parallel with QoS, it would have been logical to call the security area SoS, security of service (for the user), or security of system (for the actor). The next measure is to look at the nature of attacks in a broader way. What is really being attacked? Figure 6.10 can be developed into Figure 6.11. Let us use this FP figure to illustrate the attacks. Billing Telecom business Service Service, security Service Service layer management Numbering Dimensioning Charging Routing Signalling Control layer Dependability Mobility management Switching Frequency Transmission Traffic resources Synchronization in connectivity layer Organization M = Management system Traffic system = Network Figure 6.10 Security is in this book seen as a fundamenta