Merge branch 'master' into john-comments

draft-ietf-core-groupcomm-bis.md

@@ -110,7 +110,7 @@ informative:
 
 --- abstract
 
-This document specifies the use of the Constrained Application Protocol (CoAP) for group communication, including the use of UDP/IP multicast as the default underlying data transport. Both unsecured and secured CoAP group communication are specified. Security is achieved by use of the Group Object Security for Constrained RESTful Environments (Group OSCORE) protocol. The target application area of this specification is any group communication use cases that involve resource-constrained devices or networks that support CoAP. This document replaces RFC 7390, while it updates RFC 7252 and RFC 7641.
+This document specifies the use of the Constrained Application Protocol (CoAP) for group communication, including the use of UDP/IP multicast as the default underlying data transport. Both unsecured and secured CoAP group communication are specified. Security is achieved by use of the Group Object Security for Constrained RESTful Environments (Group OSCORE) protocol. The target application area of this specification is any group communication use cases that involve resource-constrained devices or networks that support CoAP. This document replaces and obsoletes RFC 7390, while it updates RFC 7252 and RFC 7641.
 
 --- middle
 
@@ -287,9 +287,13 @@ Different types of groups are named as specified below, separately for CoAP grou
 
 #### CoAP Groups ### {#sec-groupnaming-coap}
 
-A CoAP group is identified and named by the authority component in the group URI (see {{sec-groupdef-coapgroup}}), which includes the host subcomponent (possibly an IP multicast address literal) and an optional UDP port number.
+A CoAP group is always defined by the two properties of IP multicast address and UDP port number (see {{sec-groupdef-coapgroup}}).
 
-It follows that the same CoAP group might have multiple names, which are possible to simultaneously and interchangeably use. For example, if the two hostnames group1.example and group1.alias.example both resolve to the IP multicast address \[ff15::1234\], then the following authority components are all names for the same CoAP group.
+However, a CoAP group is for practical purposes identified and named by the authority component in the group URI. This component includes the host subcomponent and an optional UDP port number.
+The host subcomponent directly defines the IP multicast address of the CoAP group, in case the host consists of an IP literal. 
+The host subcomponent indirectly defines the IP multicast address of the CoAP group, in case the host consists of a hostname: resolving the hostname to an IP address in this case produces the IP multicast address.
+
+It follows that the same CoAP group might have multiple names, which can be simultaneously and interchangeably used. For example, if the two hostnames group1.com and group1.alias.com both resolve to the IP multicast address \[ff15::1234\], then the following authority components are all names for the same CoAP group.
 
 * group1.example:7700
 * group1.alias.example:7700