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EDA 1200 System Overview

3.1.2.2 PVC Based Traffic Mapping

The PVC based traffic mapping is the original ATM based mapping. However,

there are two special variants: PVC bundling and Ethertype mapping. In the

PVC bundling, the same Service VLAN is used for multiple traffic Flows that

require different class of service. Therefore, different PVCs are used, to enable

different QoS through the ADSL line. However, the two traffic Flows must have

the same Access Method, and the C tag (see Section 3.1.2.3 on page 26)

must either be used in both, or not used in either. In order to be able to map

the traffic in the downstream direction, the same p-bit must not be used in two

different downstream flows (see EDA 1200 QoS Features description.)

3.1.2.3 DSL VLAN Based Traffic Mapping

VLAN based traffic mapping maps traffic from a VLAN at the local loop to a

Service VLAN in the Access Domain. The traffic mapping is based on a single

VLAN tag in the local loop (Q tag) and one or two VLAN tags in the Access

Domain. The VLAN tags in the Access Domain are referred to as S and C tags

to distinguish the outer (S) and inner (C) tags.

Note: In the switched Ethernet, aggregation switches do not care about the

inner tag. Therefore, all traffic with the same outer VLAN tag will be in

the same broadcast domain.

The Ethertype used for S and C tags are configurable. Typically, the S-tag

Ethertype corresponds to the S-tag of IEEE802.1ad Provider Bridges (using

the Ethertype value 0x88A8), but it may also for example use the standard

IEEE802.1Q tag (Ethertype 0x8100) or the VMAN tag (Ethertype 0x9100). The

C-tag, in other words, the inner tag, typically uses the standard IEEE802.1Q

tag (Ethertype 0x8100).

Figure 20 VLAN Tags used in VLAN Based Traffic Mapping

The VLAN ID of the Q tag, set by the End-user device, is mapped to an S

tag and an optional C tag in the Access Domain, and the other way around.

The identification of the service and thereby also the desired properties of the

transport are based on either the Q tag (Uplink) or the S and C tags (downlink).

The CoS indication in the VLAN tags (P-bit) is not used for traffic mapping,

only for QoS purposes.

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APC IP DSLAM User's Guide Page 30