ZyXEL Communications MSC1024G Series User Manual page 46

Chapter 1 Getting to Know Your MSC
Figure 3 IMA Application
Remote
CO Site
Site
TDM
ADM
ADM IMA-2
IMA-1
xDSL
CPE
one E1 line
Remote Site Traffic Flow Scenario
In remote sites, traffic coming from subscribers through a DSL line card is sent to the MSC
management card and then forwarded to the specified IMA card in your configuration. One
DSL line card can only map to one IMA card. One IMA card can handle traffic sent from
multiple DSL line cards.
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.
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MSC1000G/1024G/1224G Series User's Guide