QoS (EXP)
There are necessary conditions for QoS: guaranteed bandwidth, class related scheduling and packet discarding treatment.
The MPLS-TP label has a 3-bit EXP field. These bits define the QoS treatment, e.g. the class of service and dropping priority (Per-Hop-Behavior or PHB) that an MPLS-TP node should give to a packet. For example, a high priority, delay sensitive packet should not be held up in queue by low priority traffic during periods of congestion.
At the Initiator
The mapped EXP value is determined by FOX61x as follows:
− In case of tagged incoming user traffic, the received PCP (Priority Code Point) value of the VLAN tag is automatically mapped to EXP value.
− In case of untagged incoming user traffic, the classification of the outgoing traffic is done using a fixed port priority of the PWAC port (=0).
The outgoing EXP value is then determined via ENP Service Creation wizard by:
− selecting the mapped EXP value (Trust mapped priority),
or
− specifying the outgoing EXP value.
The method of specifying the outgoing EXP value applied for the operator to have better control of the EXP bits modification. For example, the operator can specify outgoing EXP value as zero on all packets coming from an interface (PWAC) connected to a non-QoS paying customer.
At the Transit nodes and Terminator node
The incoming LSP label’s EXP value is mapped to Per Hop Behaviour (PHB), which consists of scheduling class, drop precedence and traffic class.