XSR18xx / XSR3250 / SSA / N1 (2G4082-25) and DSCP46 without Policy

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Hi all,

I need some clarity on how the XSR and A/B/C-series switches handles packets marked with DCSP 46 (Expedited Forwarding).

The Scenario:
We have various makes of VoIP phones which are configured with vlan tagging with DSCP 46 enabled on them.
We do not use Policy on any equipment.
We mostly use XSR series routers via various communicatons mediums (T1/E1, Radio, Metro Ethernet).

With WireShark we can see that the DSCP46 is maintained all the way, so it is not stripped from the packet header.

So my question is how does the equipment (including the XSR routers handle packets marked with DSCP 46? Even if we don't have Policy configured on anything.
Do they still expedite the forwarding of those packets, or are they processed in sequence along with other packets entering the router?

We have been operating on the assumption that the EF tag will provide transmit priority for these packets before other (non-VoIP) traffic.
I just need confirmation (or refutation) that this is indeed the case.
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Eugene van Heerden

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Posted 3 years ago

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Paul Poyant, Employee

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All of the equipment cited here - A/B/C/N/S/XSR - behaves the same way under these conditions. In the absence of special configuration, they will pass along existing TOS/DSCP values but will not react to them. The assumption is thereby refuted.