name. ENUM defines a new service named E.164 to URI, termed 'E2U'. Before all, it is necessary to define and record the type of application in the DNS server. The following shows some example NAPTR records with the E2U service: $ORIGIN 2.2.7.3.5.3.8.9.6.1.2.e164.arpa. IN NAPTR 10 10 "u" "sip+E2U" !^.*$!sip:handoura@sip.tn". IN NAPTR 10 10 "u" "mailto+E2U" *$!mailto:handoura@enig.tn". IN NAPTR 10 10 "u" "http+E2U" *!http://hand.enig.tn". IN NAPTR 10 10 "u" "tel+E2U" 1.*$!tel:+216-98-353722" IN NAPTR 10 10 "u" "ldap+E2U" "!^+216(.*)$!Idap://ldap.tn/cn=01!" © 2009 by Taylor & Francis Group, LLC SIP Handbook: Services, Technologies, and Security And this shows specific SRV records added to your DNS for SIP: IN A @IP or IN SRV 0 1 5060 server.example.com The sources of location information in the network (SIP client, phone, PSTN, IP) are: SIP REGISTER or SIP NOTIFY for client SIP registration. TRIP for location gateway or server. DNS A, SRV, NAPTR records for SIP server or ENUM services regis- tration. LDAP or TRIB for local data bases. Figure 21.6 shows our proposal allowing interconnection between PSTN, IN and IP. Intelligent service gateway (ISG) is a gateway presenting the processor real- izing the different transitions between the SIP state machine O, T and the O,T BCSM model. It is the SIN, presented in the preceding paragraph. SIP client network server SIP server? Intelligent network O-SIP network server Intelligent service gateway Gateway Phone T-SIP network server SIP client LS Location server SIP server network TRIP : Telephony routing over IP FIGURE 21.6 Interconnection PSTN-IN-IP and Services (in gray) invocation by a SIP client. C 2009 by Taylor & Francis Group, LLC Secure Intelligent SIP Services SIP Client SIP Server SIN-O SIN-T SIP Server SIP Client INVITE INVITE Trying Calling Initial DP3 Connect To Resource req Connect To Resource conf Initial DP24 INVITE INVITE Trying Trying Trying FIGURE 21.7 Diagram of to access IN services by SIP. Figure 21.7 illustrates the following functions: Communication bet