2.2.1.8 P-Preferred-Registrar Header Field Syntax

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This protocol defines a new P-Preferred-Registrar header field.<10> The ABNF syntax, as defined in [RFC5234], for the P-Preferred-Registrar header field is as follows:

 p-preferred-registrar = "p-preferred-registrar" HCOLON preferred-registrar-value
 preferred-registrar-value = addr-spec

The ABNF for addr-spec is specified in [RFC3261] section 25.1.

The SIP registrar SHOULD add, at most, one P-Preferred-Registrar header field in the NOTIFY to the UAC.<11>