HP-UX C SIP Stack Programmer's Guide (Novembery 2007)

Working with DNS 331

SIP Stack Implementation

Figure 15-1 A DNS/SRV Spanned Tree

DNS/ENUM RECORD RFC 3824 specifies the usage of ENUM NAPTR records for relating between

E.164 numbers and URIs. For more information on ENUM, see the Advanced

Features chapter.

SIP STACK

MPLEMENTATION

Before sending a request, the transaction obtains the destination host name from

the request message. If the SIP Stack is compiled without Enhanced DNS

features, it will try to resolve the host using a simple A/AAAA DNS, ENUM or

NAPTR queries. If the SIP Stack is compiled with Enhanced DNS support, the

SIP Stack will try to obtain the transport, port and IP of the host name as

specified in RFC 3263 and RFC 3824.

The answers from the DNS server are kept in a DNS List object. The DNS List

object holds the following sublists:

 SRV list—the result of the NAPTR query.

 Host list—the result of an SRV query applied on the first

element of the SRV list. After the DNS SRV query is made, the

first element in the SRV list is moved to the used SRV element

member of the DNS list.

SRV (SIP)

AAAAA

ROOT/NAPTR

SRV (SIP)

H3 H4 H5 H6 H7 H8