Hi Amit
To be precise the various QoS levels like basic/silver/gold/platinum are define by the SP with respect to the class of service they offer in their network.
Platinum usually being used for Voice latency/jitter sensitive and the service levels are maintained accordingly.
In the SP backbone you will have the respective MPLS Exp bits being allocated for catering platinum service.
Also the QoS should start from the CE itself to avoid uniform behavior and end to end control..
Other levels are basically mapped to the respective MPLS Exp bits in the SP network to offer respective levels of service.
Gold may be used for video traffic which is burstable & bandwidth greedy in nature.
Silver level can be used for mission critical applications being used on the end clients and the basic level of service supports ur mailing and the traffic which requires best effort level of service...
regds
