There are many other variations for IPv6 outside the scope of this book, but we
have covered the main formats used to identify interfaces used for various connections.
These are indeed the lowest form of addresses from the IMS sense (of course machine
addresses are the absolute lowest identities, but we will skip those). We are discussing
IPv6 addresses here, because they do appear in the SIP messaging used along with
higher-level SIP identities.
To further complicate addressing, the subscriber could move locations. Mobility is one
of the key factors that make VoIP such an attractive offering to many who travel or use
communications in a number of different locations. Our society has changed from one
that requires stability in a fixed number (with a fixed connection) to one that requires
mobility, even if the connection is not fixed.
Since IP addressing is dynamic, it is difficult to use IP addressing to reach subscribers
in any form of IP network. Certainly if your IP address were known, anyone could
reach you by your IP address. If your IP address is dynamically assigned, there is no
means of providing that information to anyone.
Not to mention that IP addressing is not user friendly, and even though we are a society
accustomed to memorizing numbers (i.e., telephone numbers) we frequently use,
1111 1111 Group ID Flags Scope
112 bits 4 bits 8 bits 4 bits
Figure 4.
Pages:
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211