Service Request 

SrvRqst

1 

Issued by a UA to find services or by a UA or SA server during active DA discovery 

Service Reply 

SrvRply

2 

The DA or SA response to a service request 

Service Registration 

SrvReg

3 

Enables SAs to register new advertisements, to update existing advertisements with new and changed attributes, and to refresh URL lifetimes 

Service Deregistration 

SrvDereg

4 

Used by the SA to deregister its advertisements when the service they represent is no longer available 

Acknowledgment 

SrvAck

5 

The DA response to an SA's service request or service deregistration message 

Attribute Request 

AttrRqst

6 

Made either by URL or by service type to request a list of attributes 

Attribute Reply 

AttrRply

7 

Used to return the list of attributes 

DA Advertisement 

DAAdvert

8 

The DA response to multicast service requests 

Service Type Request 

SrvTypeRqst

9 

Used to inquire about registered service types that have a particular naming authority and are in a particular set of scopes 

Service Type Reply 

SrvTypeRply

10 

The message returned in response to the service type request 

SA Advertisement 

SAAdvert

11 

UAs employ the SAAdvert to discover SAs and their scopes in networks where no DAs are deployed