Internet Communications Using SIP : Delivering VoIP and Multimedia Services With Session Initiation Protocol {2Nd Ed.}

Figure 4.3 DNS and NAPTR service examples

The regular expression in the NAPTR response is a powerful technology to

control the search process used in ENUM. It allows you, for example, to search

not only for a single phone numbers but also for blocks of phone numbers. For

example:

^123(.*)567$

will search for all numbers starting with 123 and ending with 567. The fol-

lowing apply:

■■ “^”—Start of the string

■■ “.*”—Wildcard

■■ “$”—End of the string

DNS Resolver DNS Server

DNS QUERY (NAPTR)

4.3.2.1.5.5.5.2.7.9.1.e164.arpa.

SIP

Proxy

or UA

DNS

System

DNS RESPONSE (NAPTR)

IN NAPTR 100 10 “u” “E2U+SIP” “!^.*$!sip:[email protected]!”

DNS QUERY (NAPTR)

example.com.

DNS RESPONSE (NAPTR)

0 10 “S” “SIP+d2u” “” _sip._udp.example.com.

DNS QUERY (SRV)

_sip._udp.example.com.

DNS RESPONSE (SRV)

10 0 5060 sip04.example.com.

DNS QUERY (A)

sip04.example.com.

DNS RESPONSE (A)

105.48.228.150

66 Chapter 4