on explicit routing (which requires a large
number of tunnels), but that mixed routing
strategies based on IGP routing and MPLS
tunnels can produce very interesting routing
patterns in terms of performance. We give an
algorithm minimising the number of MPLS
tunnels that need to be added to reproduce a
given single-path routing pattern;Based on those results, an off-line Traffic Engi-
neeringmethodology is proposed. It is based on
an optimisation of the IGP routing (by a wise
choice of the administrative metrics) enhanced
by the use of a limited number of explicitly
routed MPLS tunnels. Advantages of such a
Traffic Engineering system would be to benefit
from the highly proven robustness of the IGP
routing while improving the performance and
reactivity of the routing control in terms of
resource utilisation with a limited added opera-
tional complexity.
B) ECMP-based Traffic Engineering
Methodology
We assume that routers are able to split the traf-
fic towards one destination on multiple paths
according to some administratively defined
load balancing parameters. It is then possible to
reproduce the same (optimal) link loads in the
network as those resulting from any given (opti-
mal) multi-path routing pattern. This does not
require any MPLS tunnels.
However, MPLS can integrate various types of
routing constraints allowing to implement spe-
cific routing strategies and QoS policies.
Acknowledgement
We wish to thank Jérome Geffard for providing
his single path optimization software.
9 References
[Awduche_1] Awduche, D et al. A framework
for Internet Traffic Engineering.(draft-ietf-
tewg-framework-05.txt), June 2001.
[Awduche_2] Awduche, D. 1999. MPLS and
Traffic Engineering in IP Networks. IEEE Com-
munications Magazine,37 (12), 42–47.
[Ben-Ameur&al] Ben Ameur, W et al. 2000.
Designing Internet networks. In: Proc. DRCN
2000, Reliable Networks for the Information
Age,56–61, Munich, Herbert Utz Verlag.
[Ben-Ameur&Gourdin_1] Ben Ameur, W,
Gourdin, E. Internet routing and related topology
issues. Submitted to SIAM journal of discrete
mathematics(2000).
[Ben-Ameur&Gourdin_2] Ben-Ameur, W, Gour-
din, E. An exact method to optimize IP networks.
- (FT R&D, Internal Technical Report.)
[Ben-Ameur&Liau] Ben-Ameur, W, Liau, B.- Computing Internet routing metrics. Annals
of telecommunications,56 (3-4), 150–168.
[Ben-Ameur] Ben-Ameur, W. Multi-hour design
of survivable Internet networks. Submitted to
Telecommunications Systems,2000.[Geffard] Geffard, J. 2001. A 0-1 model for
singly routed traffic in telecommunication net-
works. Annals of Telecommunications,56 (3-4),
140–149.[Kompella] Kompella, K, Rekhter, Y, Berger, L.
Link bundling in MPLS Traffic Engineering.
(draft-kompella-mpls-bundle-04.txt), May 2000.[Kompella_2] Kompella, K, Rekhter, Y. LSP
hierarchy with MPLS TE.(draft-kompella-lsp-
hierarchy-00.txt), December 2000.[Li] Li, T. 1999. MPLS and the Evolving Inter-
net Architecture. IEEE Communications Maga-
zine, 37 (12), 38–41.[MATE] Widjaja, I, Elwalid, A. MATE : MPLS
Adaptive Traffic Engineering.(draft-widjaja-
mpls-mate-01.txt), October 1999.[Michel&al] Ben-Ameur, W et al. Optimizing
administrative weights for efficient single-path
routing. In: Networks 2000.[Mo&Walrand] Mo, J, Walrand, J. 2000. Fair
End-to-End Window-Based Congestion Control.
IEEE/ACM Transactions on Networking,8 (5),
556–567.[OSPF-OMP] Villamizar, C. OSPF Optimized
Multipath (OSPF-OMP).(draft-ietf-ospf-omp-
00.txt), March 1998.[Pioro&al] Pioro, M et al. 2000. Solving an OSPF
Routing Problem with Simulated Allocation. In:
Proceedings of the First Polish German Teletraf-
fic Symposium, PGTS 2000. Ude Verlag, 177–184.[Smit] Shen, N, Smit, H. Calculating IGP routes
over Traffic Engineering tunnels.(draft-hsmit-
mpls-igp-spf-00.txt), June 1999.[Thorup&al] Fortz, B, Thorup, M. 2000. Internet
Traffic Engineering by Optimizing OSPF
Weights. In: Proceedings of INFOCOMM 2000.
Piscataway, NJ, IEEE, 519–528.[Villamizar_1] Villamizar, C (UUNET). MPLS
Optimized Multipath.draft-villamizar-mpls-
omp-01.txt, February 1999.[Villamizar_2] Villamizar, C. (November 12,
2001) [online] – URL: http://www.fictitious.org/
omp/simulations.html.