The peer-to-peer layer effectively replaces the registration,
location, and lookup steps of SIP. It handles three things:
ߜ Registering a phone or a user with the peer-to-peer
overlay network (when the phone or user joins the
network)
ߜ Looking up a phone or a user in the peer-to-peer overlay
network (when a call to the phone or user is made)
ߜ Dynamically sharing information when peers join and
leave, so that the load is balanced across peers, and
so that the sudden loss of one or more peers doesn’t
cause the peer-to-peer network to lose track of its cur-
rent registrants
Figure 6-1 shows how this process works.
Figure 6-1: The peer-to-peer SIP discovery process.
Internet
PSTN
PSTN Gateway
VoIP
Carrier
VP
VP
Teleworker
LAN
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