Client Server and Peer-to-Peer Presence and IM
In keeping with the end-to-end control principle of the Internet, presence, and
IM services can also be implemented in the endpoints, without dependence on
intermediate elements in the network, as is the case with SIP. Figure 13.3 shows
a client-server (CS) based system (a) and a peer-to-peer (P2P) system (b).
Several operation modes are possible:
■■ Pure client-server, as in Figure 13.3a
■■ Pure peer-to-peer to peer without any server, using a P2P protocol (see
Chapter 20, “Peer-to-Peer SIP”
■■ Rendezvous for the SIP UAs using the SIP server, and then operating
presence and IM in a peer-to-peer mode, as indicated in Figure 13.3b
Both CS SIP and P2P SIP presence and IM have been implemented in well-
known commercial products, as seen in Figure 13.4a and in Figure 13.4b,
respectively.
The Microsoft Messenger 4.7 integrated with Microsoft Office 2003 shown
here is one of the first integration examples known to the authors for presence
with an application. Figure 13.4 a shows the e-mail in the Microsoft Outlook
client, as well as the presence icon for the author of the message. By clicking on
the author buddy icon of an Office 2003 document, an audio/video conversa-
tion can be invoked by the reader of the document to discuss it with the
author.Figure 13.3 (a) Client-server and (b) P2P presence and IM systemsServer Servera bUAUAUA UAUAUAUAUA228 Chapter 13