ZyXEL Communications MSC1000G User Manual page 45

Chapter 1 Getting to Know Your MSC
Figure 4 IMA Application in Remote Sites
Normally, traffic coming from subscribers is untagged or has one VLAN tag. The receiving xDSL line
card adds an inner VLAN tag (C-tag) or add both inner (C-tag) and outer VLAN tag (S-tag) into
untagged frames. The MSC receives the frames, then forwards the frames to the specified IMA
card. The IMA card converts the frames into ATM cells and assigns them to a corresponding channel
(PVC) based on their VLAN tags.
The return traffic is handled in a similar way. The IMA converts ATM cells into Ethernet frames and
adds VLAN tags according to your DTPVC or PVC settings. The MSC forwards the frames to the
corresponding xDSL line cards. The xDSL removes the VLAN tag and forwards the frames to
subscribers.
Figure 5 Remote Site Traffic Flow Scenario
Central Office Site Traffic Flow Scenario
Unlike the remote site, in the central office, traffic from each IMA line card of the IES is directly
forwarded to the MSC and the connected Ethernet (IP) network. The following figure shows an
example.
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Management Switch Card User's Guide