The Potential of SIP Presence, Events, and IM
Presence has been predicted to be the dial tone of the twenty-first century.
Here are some of the new communication capabilities enabled by presence:
■■ Replace the dialing of phone numbers or the typing of URIs with a sin-
gle click on the icon of the buddy (a frequently called party).
■■ The icon can replace numerous phone numbers and URIs for all the
devices and network services the called party may have, since the
Address of Record (AOR) in the SIP registrar can resolve the AOR to
many Contact addresses.
■■ Using the presence icon, we can determine if the desired party is avail-
able on line, is in a good mood, is busy, is in a place where he or she
must be quiet (in a meeting), and so on.
■■ Presence enables polite and sensitive communications.
■■ Presence avoids futile calls that may terminate in voice mail and
require the called party to listen to sometimes long, ranting voice
messages, and then try to call back only to get voice mail in turn.
■■ SIP events enable the integration of communications and applications,
as we will discuss here.
IM is also an often preferred communication mode because of the following:
■■ IM works in emergencies when there may be network congestion.
■■ IM works in quiet places: People often exchange IM during a confer-
ence call with other parties (for example, to get key information or to
evade boredom while in conference).
■■ IM enables the quick redirection to valuable information by typing a
web URI.
■■ IM can bridge language difficulties, since the written words may be eas-
ier to understand.
■■ Agents in customer contact centers or in financial institutions can multi-
plex communications with several parties at the same time, in contrast
to phone calls that can be conducted with only one party at a time.
Enhanced agent productivity may be a significant reason to invest in
and to use IM. IM log files can serve as legal proof for important finan-
cial transactions.
These capabilities of presence and IM have made the voice-only PBX or IP
PBX obsolete for enterprise communications.224 Chapter 13