This is indicated by the framing bits,
which may not be preserved by N?—64 kbit/s basic service.
MEF 8 describes a generic method for extending the N?—64 kbit/s basic service by carrying
CE signaling (CAS or CCS) in separate signaling packets that are independent
of the TDM circuit type. This method may be used in situations where the individual
64 kbit/s channels are selected from multiple TDM circuits or picked off a TDM bus
rather than from a specific TDM circuit; it also saves SEN bandwidth.
Scalability
One of the major requirements of Carrier Ethernet is to scale to meet the needs of
Service Provider offerings. The limitations imposed by the QinQ (IEEE 802.1ad, stacked
VLANs) allow for only 4094 VLANs/service instances in a service area (based on the
12 bits used in the VLAN ID field for this purpose). However, this is inadequate to
support the kind of scale required by the MEF. Key standards developments are noted
in Table 2.3.
Provider Backbone Bridging Provider Backbone Bridging (PBB) or IEEE 802.1ah
addresses the service scaling limitations in native Ethernet networks by enabling
millions of service instances in a serving area through the creative use of the MAC
address.
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