[e2e] Traffic Engineering: OSPF-TE and RSVP-TE

[Sireen Habib Malik]

Hi,

No clue about the RFCs but here is the basic idea....

OSPF-TE mantains the state of the network. The algorithm, Constrained 
Shortest Path First (CSPF) used for TE is actually SPF (Dijkstra's) with 
a little pre-conditioning. Suppose your demand is 10Mbps. In CSPF, all 
those links which do not have 10Mbps of residual capacity would be first 
pruned out. Then SPF is run. The route you would get will support 
10Mbps. This is your constrained based route. You can use other 
constraints but the idea remains the same. RSVP-TE, a signalling 
protocol, establishes the LSP.

I am not very sure about your question about state propagation but i 
think OSPF would learn of the new network state on its own, on a slower 
time granularity.

--
SM





Fahad Dogar wrote:

>I am currently implementing a restoration routing module for MPLS
>Traffic Engineering. I've few questions related to the various
>protocols that are required for traffic engineering. Any help or
>pointers to relevant RFC's/drafts would be highly appreciated.
>
>1) There are extensions proposed to OSPF v2 which specifies the
>additional information required to be propagated for Traffic
>Engineering [RFC 3630:TE extensions to OSPF v2]. However, this RFC
>does not provide details of the constraint based routing that can be
>done using this additional information. RFC 2676: "QoS routing
>Mechanisms and OSPF extensions" specifies the constraint based routing
>algorithms but the OSPF extensions proposed in this document are
>different from RFC 3630.  Can any one point out the mechanisms that
>could be used for constraint based routing using the additional
>information proposed in RFC 3630.
>
>2) There have been proposed extensions to RSVP to support Traffic
>Engineering [RFC 3209]. However, these extensions do not provide
>details of the interfacing between RSVP-TE and OSPF-TE. Just to
>elaborate, RSVP-TE would need to find a path that could satisfy the
>QoS constraint specified by the request. How would it use OSPF to find
>a constraint based route? Moreover, once approprate reservations are
>made, how is it ensured that the new link state is correctly
>propagated through OSPF-TE extensions?  The answers to the above
>questions relate to the interfacing issues pertaining to RSVP-TE and
>OSPF.
>
>Thanks in advance,
>Fahad
>  
>


-- 

Sireen Malik, M.Sc.
PhD. Candidate,

Communication Networks
Hamburg University of  Technology,
FSP 4-06 (room 3008)
Denickestr. 17
21073 Hamburg, Deutschland

Tel: +49 (40) 42-878-3387
Fax: +49 (40) 42-878-2941
E-Mail: s.malik at tuhh.de

--Everything should be as simple as possible, but no simpler (Albert Einstein)