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

Working with Resolvers 343
16
WORKING WITH RESOLVERS
INTRODUCTION The SIP Stack uses resolvers to produce data that is related to DNS. A resolver
object (resolver) is responsible for retrieving a piece of DNS information. In
some cases this information can be obtained by a single DNS query (such as
NAPTR resolution), in other cases several queries are required (such as host
resolution when the network type, <IPv4 or IPv6>, is unknown).
The SIP Resolver is used mainly by the transmitter to implement RFC 3263:
Session Initiation Protocol (SIP): Locating SIP Servers. This RFC describes the
ways to retrieve the transport of the destination, IP address and port. The
destination details can be obtained separately or in a single query by calling the
Resolvers API functions. The Resolver layer, which is exposed to the
application, can be used for connection reuse and mutual TLS, when DNS
operations are needed.
RESOLVER
E
NTITIES
The resolver layer has two entities:
 Resolver (resolver)
 Resolver Manager (ResolverMgr)
RESOLVER A resolver is responsible for obtaining one data element according to the
RFC 3263 algorithm. The answers from the DNS are stored in the a DNS list
object. For more information, see the Working with DNS chapter.
The DNS data element types correspond to the following RvSipResolverMode
enumeration components: