MPLS Experimental field renamed to Traffic Class field

I’ve just noticed on the IETF mailinglist that QoS on MPLS is no longer considered to be experimental. Therefore the EXP bits have been renamed to TC or Traffic Class bits.

So if you are referring to MPLS QoS, please use the term TC instead of EXP to smooth the renaming process. The new header looks like this.

The early Multiprotocol Label Switching (MPLS) documents defined the form of the MPLS label stack entry. This includes a three-bit field called the “EXP field”. The exact use of this field was not defined by these documents, except to state that it was to be “reserved for experimental use”.

Although the intended use of the EXP field was as a “Class of Service” (CoS) field, it was not named a CoS field by these early documents because the use of such a CoS field was not considered to be sufficiently defined. Today a number of standards documents define its usage as a CoS field.

To avoid misunderstanding about how this field may be used, it has become increasingly necessary to rename this field. This document changes the name of the field to the “Traffic Class field” (“TC field”). In doing so, it also updates documents that define the current use of the EXP field.

Source: RFC 5462