5. RSVP Extension for Diff-Serv Support

The MPLS architecture does not assume a single label distribution protocol. [RSVP_MPLS_TE] defines the extension to RSVP for establishing LSPs in MPLS networks. This section specifies the extensions to RSVP, beyond those defined in [RSVP_MPLS_TE], to establish LSPs supporting Differentiated Services in MPLS networks.

One new RSVP Object is defined in this document: the DIFFSERV Object. Detailed description of this Object is provided below. This new Object is applicable to Path messages. This specification only defines the use of the DIFFSERV Object in Path messages used to establish LSP Tunnels in accordance with [RSVP_MPLS_TE] and thus containing a Session Object with a C-Type equal to LSP_TUNNEL_IPv4 and containing a LABEL_REQUEST object.

Restrictions defined in [RSVP_MPLS_TE] for support of the establishment of LSP Tunnels via RSVP are also applicable to the establishment of LSP Tunnels supporting Diff-Serv: for instance, only unicast LSPs are supported and Multicast LSPs are for further study.

This new DIFFSERV object is optional with respect to RSVP so that general RSVP implementations not concerned with MPLS LSP set up do not have to support this object.

The DIFFSERV Object is optional for support of LSP Tunnels as defined in [RSVP_MPLS_TE]. A Diff-Serv capable LSR supporting E-LSPs using the preconfigured EXP<-->PHB mapping' in compliance with this specification MAY support the DIFFSERV Object. A Diff-Serv capable LSR supporting E-LSPs using a signaled EXP<-->PHB mapping' in compliance with this specification MUST support the DIFFSERV Object. A Diff-Serv capable LSR supporting L-LSPs in compliance with this specification MUST support the DIFFSERV Object.

5.1.1. Path Message Format

The format of the Path message is as follows:

         <Path Message> ::=       <Common Header> [ <INTEGRITY> ]
                                  <SESSION> <RSVP_HOP>
                                  <TIME_VALUES>
                                  [ <EXPLICIT_ROUTE> ]
                                  <LABEL_REQUEST>
                                  [ <SESSION_ATTRIBUTE> ]
                                  [ <DIFFSERV> ]
                                  [ <POLICY_DATA> ... ]
                                  [ <sender descriptor> ]

         <sender descriptor> ::=  <SENDER_TEMPLATE> <SENDER_TSPEC>
                                  [ <ADSPEC> ]
                                  [ <RECORD_ROUTE> ]

5.2. DIFFSERV Object

The DIFFSERV object formats are shown below. Currently there are two possible C_Types. Type 1 is a DIFFSERV object for an E-LSP. Type 2 is a DIFFSERV object for an L-LSP.

5.2.1. DIFFSERV object for an E-LSP:

class = 65, C_Type = 1

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |        Reserved                                       | MAPnb |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                            MAP (1)                            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      //                               ...                            //
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                            MAP (MAPnb)                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Reserved (28 bits): This field is reserved. It must be set to zero on transmission and must be ignored on receipt.
MAPnb (4 bits): Indicates the number of MAP entries included in the DIFFSERV Object. This can be set to any value from 0 to 8.
MAP (32 bits): Each MAP entry defines the mapping between one EXP field value and one PHB. The MAP entry has the following format:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |            Reserved     | EXP |             PHBID             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Reserved (13 bits): This field is reserved. It must be set to zero on transmission and must be ignored on receipt.
EXP (3 bits): This field contains the value of the EXP field for the `EXP<-->PHB mapping' defined in this MAP entry.
PHBID (16 bits): This field contains the PHBID of the PHB for the `EXP<-->PHB mapping' defined in this MAP entry. The PHBID is encoded as specified in [PHBID].

5.2.2. DIFFSERV object for an L-LSP:

class = 65, C_Type = 2

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |        Reserved               |             PSC               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Reserved (16 bits): This field is reserved. It must be set to zero on transmission and must be ignored on receipt.
PSC (16 bits): The PSC indicates a PHB Scheduling Class to be supported by the LSP. The PSC is encoded as specified in [PHBID].

5.3. Handling DIFFSERV Object

To establish an LSP tunnel with RSVP, the sender creates a Path message with a session type of LSP_Tunnel_IPv4 and with a LABEL_REQUEST object as per [RSVP_MPLS_TE].

To establish an E-LSP tunnel with RSVP, which uses the Preconfigured `EXP<-->PHB mapping', the sender creates a Path message:

with a session type of LSP_Tunnel_IPv4,
with the LABEL_REQUEST object, and
without the DIFFSERV object.

To establish an E-LSP tunnel with RSVP, which uses the Preconfigured `EXP<-->PHB mapping', the sender MAY alternatively create a Path message:

with a session type of LSP_Tunnel_IPv4,
with the LABEL_REQUEST object, and
with the DIFFSERV object for an E-LSP containing no MAP entries.

To establish an E-LSP tunnel with RSVP, which uses a signaled `EXP<-->PHB mapping', the sender creates a Path message:

with a session type of LSP_Tunnel_IPv4,
with the LABEL_REQUEST object,
with the DIFFSERV object for an E-LSP containing one MAP entry for each EXP value to be supported on this E-LSP.

To establish with RSVP an L-LSP tunnel, the sender creates a Path message:

with a session type of LSP_Tunnel_IPv4,
with the LABEL_REQUEST object,
with the DIFFSERV object for an L-LSP containing the PHB Scheduling Class (PSC) supported on this L-LSP.

If a path message contains multiple DIFFSERV objects, only the first one is meaningful; subsequent DIFFSERV object(s) must be ignored and not forwarded.

Each LSR along the path records the DIFFSERV object, when present, in its path state block.

If a DIFFSERV object is not present in the Path message, the LSR SHOULD interpret this as a request for an E-LSP using the Preconfigured `EXP<-->PHB mapping'. However, for backward compatibility purposes, with other non-Diff-Serv Quality of Service options allowed by [RSVP_MPLS_TE] such as Integrated Services Controlled Load or Guaranteed Services, the LSR MAY support a configurable "override option". When this "override option" is configured, the LSR interprets a path message without a Diff-Serv object as a request for an LSP with such non-Diff-Serv Quality of Service.

If a DIFFSERV object for an E-LSP containing no MAP entry is present in the Path message, the LSR MUST interpret this as a request for an E-LSP using the Preconfigured EXP<-->PHB mapping'. In particular, this allows an LSR with the "override option" configured to support E-LSPs with Preconfigured EXP<-->PHB mapping', simultaneously with LSPs with non-Diff-Serv Quality of Service.

If a DIFFSERV object for an E-LSP containing at least one MAP entry is present in the Path message, the LSR MUST interpret this as a request for an E-LSP with signaled `EXP<-->PHB mapping'.

If a DIFFSERV object for an L-LSP is present in the Path message, the LSR MUST interpret this as a request for an L-LSP.

The destination LSR of an E-LSP or L-LSP responds to the Path message containing the LABEL_REQUEST object by sending a Resv message:

with the LABEL object
without a DIFFSERV object.

Assuming the label request is accepted and a label is allocated, the Diff-Serv LSRs (sender, destination, intermediate nodes) must:

update the Diff-Serv Context associated with the established LSPs in their ILM/FTN as specified in previous sections (incoming and outgoing label),
install the required Diff-Serv forwarding treatment (scheduling and dropping behavior) for this NHLFE (outgoing label).

An LSR that recognizes the DIFFSERV object and that receives a path message which contains the DIFFSERV object but which does not contain a LABEL_REQUEST object or which does not have a session type of LSP_Tunnel_IPv4, sends a PathErr towards the sender with the error code Diff-Serv Error' and an error value of Unexpected DIFFSERV object'. Those are defined below in section 5.5.

An LSR receiving a Path message with the DIFFSERV object for E-LSP, which recognizes the DIFFSERV object but does not support the particular PHB encoded in one, or more, of the MAP entries, sends a PathErr towards the sender with the error code Diff-Serv Error' and an error value of Unsupported PHB'. Those are defined below in section 5.5.

An LSR receiving a Path message with the DIFFSERV object for E-LSP, which recognizes the DIFFSERV object but determines that the signaled EXP<-->PHB mapping' is invalid, sends a PathErr towards the sender with the error code Diff-Serv Error' and an error value of Invalid EXP<-->PHB mapping'. Those are defined below in section 5.5. The EXP<-->PHB mapping' signaled in the DIFFSERV Object for an E-LSP is invalid when:

the MAPnb field is not within the range 0 to 8 or
a given EXP value appears in more than one MAP entry, or
the PHBID encoding is invalid.

An LSR receiving a Path message with the DIFFSERV object for L-LSP, which recognizes the DIFFSERV object but does not support the particular PSC encoded in the PSC field, sends a PathErr towards the sender with the error code Diff-Serv Error' and an error value of Unsupported PSC'. Those are defined below in section 5.5.

An LSR receiving a Path message with the DIFFSERV object, which recognizes the DIFFSERV object but that is unable to allocate the required per-LSP Diff-Serv context sends a PathErr with the error code "Diff-Serv Error" and the error value "Per-LSP context allocation failure". Those are defined below in section 5.5.

A Diff-Serv LSR MUST handle the situations where the label request can not be accepted for reasons other than those already discussed in this section, in accordance with [RSVP_MPLS_TE] (e.g., reservation rejected by admission control, a label can not be associated).

5.4. Non-support of the DIFFSERV Object

An LSR that does not recognize the DIFFSERV object Class-Num MUST behave in accordance with the procedures specified in [RSVP] for an unknown Class-Num whose format is 0bbbbbbb i.e., it must send a PathErr with the error code `Unknown object class' toward the sender.

An LSR that recognize the DIFFSERV object Class-Num but does not recognize the DIFFSERV object C-Type, must behave in accordance with the procedures specified in [RSVP] for an unknown C-type i.e., it must send a PathErr with the error code `Unknown object C-Type' toward the sender.

In both situations, this causes the path set-up to fail. The sender should notify management that a L-LSP cannot be established and should possibly take action to retry LSP establishment without the DIFFSERV object (e.g., attempt to use E-LSPs with Preconfigured `EXP<-->PHB mapping' as a fall-back strategy).

5.5. Error Codes For Diff-Serv

In the procedures described above, certain errors must be reported as a Diff-Serv Error'. The value of the Diff-Serv Error' error code is 27.

The following defines error values for the Diff-Serv Error:

      Value    Error

       1       Unexpected DIFFSERV object
       2       Unsupported PHB
       3       Invalid `EXP<-->PHB mapping'
       4       Unsupported PSC
       5       Per-LSP context allocation failure

5.6. Intserv Service Type

Both E-LSPs and L-LSPs can be established with or without bandwidth reservation.

As specified in [RSVP_MPLS_TE], to establish an E-LSP or an L-LSP with bandwidth reservation, Int-Serv's Controlled Load service (or possibly Guaranteed Service) is used and the bandwidth is signaled in the SENDER_TSPEC (respectively FLOWSPEC) of the path (respectively Resv) message.

As specified in [RSVP_MPLS_TE],to establish an E-LSP or an L-LSP without bandwidth reservation, the Null Service specified in [NULL] is used.

Note that this specification defines usage of E-LSPs and L-LSPs for support of the Diff-Serv service only. Regardless of the Intserv service (Controlled Load, Null Service, Guaranteed Service,...) and regardless of whether the reservation is with or without bandwidth reservation, E-LSPs and L-LSPs are defined here for support of Diff-Serv services. Support of Int-Serv services over an MPLS Diff-Serv backbone is outside the scope of this specification.

Note also that this specification does not concern itself with the DCLASS object defined in [DCLASS], since this object conveys information on DSCP values, which are not relevant inside the MPLS network.

5.1. Diff-Serv related RSVP Messages Format​

5.1.1. Path Message Format​

5.2. DIFFSERV Object​

5.2.1. DIFFSERV object for an E-LSP:​

5.2.2. DIFFSERV object for an L-LSP:​

5.3. Handling DIFFSERV Object​

5.4. Non-support of the DIFFSERV Object​

5.5. Error Codes For Diff-Serv​

5.6. Intserv Service Type​

5.1. Diff-Serv related RSVP Messages Format