The MPLS-OPS Archive

[Yakov Rekhter <yakov@juniper.net>]

Danny,

> There's NOTHING you can do with MPLS-based VPNs that couldn't 
> be done with IP-based VPNs (likely in a more scalable manner), 
> it's just that marketing hype and a bunch of glue has pushed 
> the former of the two into the spotlight.  
> 
> As well, MPLS doesn't give you QoS any more than IP does, it's
> a big bunch of marketing hype.
> 
> MPLS gives you TE capabilities and a few subsets of interesting 
> features (e.g., FRR).  In large part, I agree with Henry here.

There is a long standing view that there is no relationship between
QoS and routing. And if you subscribe to this view, then you may
say that "MPLS doesn't give you QoS any more than IP does".

However, one may observe that depending on the exact semantics of
QoS, supporting QoS may mean more than just selective queueing
and/or selective discard - it may also mean finding a path in a
network that has sufficient resources to accommodate the required
QoS. One may observe that the latter, finding the path, is
*fundamentally* a routing, and not a queueing problem. And from
this one may conclude that for certain QoS semantics selecting
queueing and discard is necessary, but not sufficient - one also
needs support from the routing system. That is where MPLS, or more
precisely, MPLS constraint-based routing comed into the picture,
as MPLS constraint-based routing provides a mechanism to find a
path in a network that has sufficient resources to accommodate the
required QoS.

Of course, one may say that one could just use traditional IP
routing, and run the network at sufficiently low utilization, as
to assure that any path has sufficient amount of resources to
accommodate the required QoS. But that approach has its own cost
as well.

Yakov.

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