diff --git a/xep-0156.xml b/xep-0156.xml index 7713c8a5..39b18b65 100644 --- a/xep-0156.xml +++ b/xep-0156.xml @@ -65,9 +65,9 @@
Specify a &w3wsdl; definition (or other XML file format) and a canonical URL for that definition at a domain that offers XMPP services. Unfortunately, this approach requires access to the HTTP server for the domain (and quite possibly to the root directory thereof), which may be difficult for XMPP server administrators to arrange. In addition, it requires a client to retrieve the relevant file via HTTP before performing DNS lookups and XMPP connection; it would be more efficient to use recognized DNS methods since DNS lookups are already required by RFC 3920.
Specify a way to define the required service discovery information as part of the existing DNS SRV records (see &rfc2782;) for a domain that offers XMPP services. While this approach sounds promising, it is not feasible since the DNS SRV Target field can be used only to specify domain names and cannot be used to specify full URIs (such as the URL for an HTTP connection manager).
Specify a way to define the required service discovery using the "straightforward NAPTR" (S-NAPTR) profile of the Dynamic Delegation Discovery System (see &rfc3958; and &rfc3401;). Unfortunately, S-NAPTR also does not allow inclusion of full URIs, and thus does meet the requirements for discovery of XMPP connection methods.
Specify a way to define the required service discovery using the "straightforward NAPTR" (S-NAPTR) profile of the Dynamic Delegation Discovery System (see &rfc3958; and &rfc3401;). Unfortunately, S-NAPTR also does not allow inclusion of full URIs, and thus does not meet the requirements for discovery of XMPP connection methods.
Specify a way to define the required service discovery using a new profile of the Dynamic Delegation Discovery System, which would be nearly identical to S-NAPTR except that it would specify only one app-service (most likely "xmpp") and allow inclusion of the DDDS "U" flag (see &rfc3404;), so that the output of a DDDS rule could be a URI. While this is a valid approach that is worth pursuing, the authors are concerned about the deployability of such an approach, especially for client-side applications (the main focus of this specification).
Specify a way to define the required service discovery information via properly-formatted DNS TXT records (see &rfc1464;). While this approach requires an update to the DNS records for the server domain, that is usually necessary in order to establish XMPP services in the first place. Furthermore, although there are some perils to be avoided in the use of DNS TXT records (e.g., wildcards), the technology is well understood and widely deployed (e.g., it is used by the SPF and SenderID systems).
Specify a way to define the required service discovery information via properly-formatted DNS TXT records (see &rfc1464;). While this approach requires an update to the DNS records for the server domain, that is usually necessary in order to establish XMPP services in the first place. Furthermore, although there are some perils to be avoided in the use of DNS TXT records (e.g., wildcards), the technology is well understood and widely deployed (e.g., it is used by the Sender Policy Framework and SenderID email server verification technologies).
Therefore this document defines a way to encapsulate information about XMPP connection methods in DNS TXT resource records.