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RFC 4006 Diameter Credit-Control Application August 2005
If independent credit-control of multiple services is used, the
validity-time and final-unit-indication SHOULD be present either in
the Multiple-Services-Credit-Control AVP(s) or at command level as
single AVPs. However, the Result-Code AVP MAY be present both on the
command level and within the Multiple-Services-Credit-Control AVP.
If the Result-Code on the command level indicates a value other than
SUCCESS, then the Result-Code on command level takes precedence over
any included in the Multiple-Services-Credit-Control AVP.
The credit-control client MUST indicate support for independent
credit-control of multiple services within a (sub-)session by
including the Multiple-Services-Indicator AVP in the first
interrogation. A credit-control server not supporting this feature
MUST treat the Multiple-Services-Indicator AVP and any received
Multiple-Services-Credit-Control AVPs as invalid AVPs.
If the client indicated support for independent credit-control of
multiple services, a credit-control server that wishes to use the
feature MUST return the granted units within the Multiple-Services-
Credit-Control AVP associated to the corresponding service-identifier
and/or rating-group.
To avoid a situation where several parallel (and typically also
small) credit reservations must be made on the same account (i.e.,
credit fragmentation), and also to avoid unnecessary load on the
credit-control server, it is possible to provide service units as a
pool that applies to multiple services or rating groups. This is
achieved by providing the service units in the form of a quota for a
particular service or rating group in the Multiple-Services-Credit-
Control AVP, and also by including a reference to a credit pool for
that unit type.
The reference includes a multiplier derived from the rating
parameter, which translates from service units of a specific type to
the abstract service units in the pool. For instance, if the rating
parameter for service 1 is $1/MB and the rating parameter for service
2 is $0.5/MB, the multipliers could be 10 and 5 for services 1 and 2,
respectively.
If S is the total service units within the pool, M1, M2, ..., Mn are
the multipliers provided for services 1, 2, ..., n, and C1, C2, ...,
Cn are the used resources within the session, then the pool credit is
exhausted and re-authorization MUST be sought when:
C1*M1 + C2*M2 + ... + Cn*Mn >= S
Hakala, et al. Standards Track [Page 19]
RFC 4006 Diameter Credit-Control Application August 2005
The total credit in the pool, S, is calculated from the quotas, which
are currently allocated to the pool as follows:
S = Q1*M1 + Q2*M2 + ... + Qn*Mn
If services or rating groups are added to or removed from the pool,
then the total credit is adjusted appropriately. Note that when the
total credit is adjusted because services or rating groups are
removed from the pool, the value that need to be removed is the
consumed one (i.e., Cx*Mx).
Re-authorizations for an individual service or rating group may be
sought at any time; for example, if a 'non-pooled' quota is used up
or the Validity-Time expires.
Where multiple G-S-U-Pool-Reference AVPs (section 8.30) with the same
G-S-U-Pool-Identifier are provided within a Multiple-Services-
Credit-Control AVP (section 8.16) along with the Granted-Service-Unit
AVP, then these MUST have different CC-Unit-Type values, and they all
draw from the credit pool separately. For instance, if one
multiplier for time (M1t) and one multiplier for volume (M1v) are
given, then the used resources from the pool is the sum C1t*M1t +
C1v*M1v, where C1t is the time unit and C1v is the volume unit.
Where service units are provided within a Multiple-Services-Credit-
Control AVP without a corresponding G-S-U-Pool-Reference AVP, then
these are handled independently from any credit pool and from any
other services or rating groups within the session.
The credit pool concept is an optimal tool to avoid the over-
reservation effect of the basic single quota tariff time change
mechanism (the mechanism described in section 5.1.1). Therefore,
Diameter credit-control clients and servers implementing the
independent credit-control of multiple services SHOULD leverage the
credit pool concept when supporting the tariff time change. The
Diameter credit-control server SHOULD include both the Tariff-Time-
Change and Tariff-Change-Usage AVPs in two quota allocations in the
answer message (i.e., two instances of the Multiple-Services-Credit-
Control AVP). One of the granted units is allocated to be used
before the potential tariff change, while the second granted units
are for use after a tariff change. Both granted unit quotas MUST
contain the same Service-Identifier and/or Rating-Group. This dual
quota mechanism ensures that the overall reported used units would
never exceed the credit reservation. The Diameter credit-control
client reports both the used units before and after the tariff change
in a single instance of the Multiple-Services-Credit-Control AVP.
Hakala, et al. Standards Track [Page 20]