[e2e] Admission Control and Policing in MPLS

Ping Pan pingpan at cs.columbia.edu
Sat Nov 6 06:37:37 PST 2004


Traffic provisioning at network edge seems to be largely depending on 
carriers. Some of the existing networks maintain traditional (ATM/frame) 
connections with almost static configuration. However, this is likely to 
change as they all move toward higher bandwidth (GigE) and offer more 

But if the bandwidth is high enough at access/edge, it becomes a simple 
over-provisioning model, thus no QoS/CAC needed....

Another observation, most deployed MPLS networks in metro area use LDP 
to setup LSP's. LDP does not have QoS awareness by design.

- Ping

Sudeep Goyal wrote:
> Hi Ping Pan,
>    Thanks for the information. But, you say that CAC would make sense at 
> the edge.  Would you please tell what are the mechanisms used in real 
> ISP networks to find out the explicit paths that meet certain QoS flow 
> requirement. Or are the paths are statically (manually) set without any 
> dynamic traffic engineering ?
>  I am presently working on algorithms on admission control on MPLS (and 
> MPLS over DiffServ network) and have worked out few algorithms in 
> theory. But, I donot yet know how and what actually ISPs are doing in 
> reality for admission control ? Does it make sense commercially to come 
> up with good TE techniques or algorithms that would help us find 
> explicit paths in MPLS network at the edge that would meet certain QoS 
> requirements. Or may be, given a LSP path, it makes more sense going for 
> a DiffServ admission control rather than finding explicit path.
> Thanks for anticipated help.
> warm regards,
> Sudeep
> On Thu, 4 Nov 2004, Ping Pan wrote:
>> First, in the (MPLS) backbone networks, most of the links are
>> over-provisioned, so not sure CAC and many QoS enforcement would make 
>> much
>> use there.
>> At the edge, CAC is relevant. In MPLS label, there is a 3-bit field, EXP,
>> that can be used to carry DiffServ class. The LSP's that carry such
>> information is called EXP-inferred LSP (E-LSP). The MPLS router can 
>> run the
>> standard DiffServ 2-color/1-color CAC, queuing, dropping etc. on all the
>> packets within the LSP. This function becomes more important during flow
>> aggregation.
>> There are a bunch of drafts from Cisco on this topic over the years.
>> - Ping
>>> -----Original Message-----
>>> From: end2end-interest-bounces at postel.org
>>> [mailto:end2end-interest-bounces at postel.org] On Behalf Of Fahad Dogar
>>> Sent: Wednesday, October 20, 2004 12:12 AM
>>> To: end2end-interest at postel.org
>>> Subject: [e2e] Admission Control and Policing in MPLS
>>> Hi,
>>> I would like to know the mechanism employed in MPLS networks
>>> for admission control and the process of subsequently
>>> policing the flow in order to ensure that it does not violate the SLA.
>>> Any help or pointers to any standardized requirements would
>>> be greatly appreciated.
>>> Thanks in advance,
>>> Fahad

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