ndard RFC is issued, it's accompanied by a new Internet draft. All changes and additions required for the proposed standard RFC to reach the draft standard level are executed on this new draft, which in final form becomes the draft standard RFC. The basic specification of the SIP protocol [RFC 2543] is currently a proposed standard, having reached this maturity level in February 1999. Since then, an Internet draft displaying all the mod- ifications made to the specification since March 1999 has been posted. This Internet draft [draft-ietf-sip-rfc2543bis] will be the future SIP draft stan- dard RFC. Figure 2-16 shows the life cycle of an IETF specifiction-from the first Internet draft until the specification is issued as an Internet standard. Sev- eral Internet drafts with different version numbers are released until the spec reaches a particular maturity level. At that point, the specification published as an RFC, and a new Internet draft is issued to gather feedback in order to reach the next maturity level. It is worthwhile mentioning that some specifications, after having reached the proposed standard maturity level and having gathered feed- back in a new Internet draft, are re-issued as a new proposed standard RFC rather than as a draft standard RFC. This happens when the specification has changed substantially from the last RFC that was issued so a new RFC is needed but the new RFC cannot have draft standard status since the specification is not mature enough. Naming Internet Drafts As described previously, the charter of a working group contains a limited set of deliverables that the working group agrees to work on. With these deliverables in mind, the group defines a set of work- ing group items. When the working group releases a draft about a particu- lar item, it is named according to the following format: draft-ietf- followed by the name of the working group followed by version number. Packet Switching, IP, and the IETF Standard Figure 2-16 RFCxxxx = STDxxx (New RFC and STD numbers) Life cycle of an Int