# Performance evaluation of pre-computation algorithms for inter-domain QoS routing

## Summary (2 min read)

### Introduction

- The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.
- The authors study different algorithms for QoS routing based on pre-computation.
- The ID-MEFPA heuristic has a lower complexity and provides a success rate always close to the exact algorithm.
- These applications require more and more extensive and varied quality of service (QoS) guarantees.

### II. THE INTER-DOMAIN QOS ROUTING PROBLEM

- Inter-domain QoS routing, also known as inter-domain multi-constraint routing, consists of computing a path subject to multiple QoS constraints between a source and a destination node of a multi-domain network.
- As the operators can be in competition, information about the internal topology or the available resources in the network is confidential.
- Many extensions for BGP are proposed to support QoS routing [7]-[8].
- When handling QoS requests with delay constraints, the first phase may precompute feasible paths for a wide range of possible delay constraints, while the second phase just needs to select a suitable path from the pre-computed set, i.e., one that satisfies the particular delay constraints of the request.
- Work in [2] proposes a precomputation based algorithm to solve the ID-MCP problem.

### III. PRE-COMPUTATION ALGORITHMS FOR INTER-DOMAIN QOS ROUTING

- The authors investigate different pre-computation algorithms for inter-domain QoS routing.
- Precisely, the authors detail the operations performed by the exact pre-computation algorithm pID-MCP [2]-[3], their algorithm ID-PPPA proposed in [1], and their novel pre-computation algorithm, named ID-MEFPA.
- Note that these pre-computation algorithms rely on a distributed architecture, such as the PCE architecture.
- These algorithms consist of two phases: an offline phase and an online phase.
- In the second phase, the algorithms attempt to compute an end-to-end path by combining the paths pre-computed in each domain.

### A. The offline phase

- This phase is executed in each domain separately.
- A low complexity of this phase enables to cope with a dynamic change in the network state information since it allows domains to rapidly pre-compute new valid paths.
- Therefore, ID-PPPA executes the Dijkstra algorithm m times per border node.
- This complexity is very high comparing with that of their proposed algorithms ID-MEFPA and ID-PPPA.

### B. The online phase

- This phase is triggered upon the reception of a QoS request.
- When receiving a QoS request, the service provider computes the best domain sequence that links the source and the destination domain according to the cooperation policy [9].
- Note that, without loss of generality, the authors rely on backward computation according to the PCE architecture.
- When receiving a VSPH, an intermediate domain combines the paths in the VSPH with the internally pre-computed paths.
- Hence, the complexity of combining the pre-computed paths with the received paths at the level of the entry border node n1 is in O(αkBk+1).

### IV. SIMULATION AND ANALYSIS

- The authors evaluate the performance of the precomputation algorithms ID-PPPA, pID-MCP, and their novel algorithm ID-MEFPA.
- The LatticeFM(25,3) and LatticeSL(25,3) topologies allow us to evaluate the effect of inter-domain connectivity on their algorithms.
- Figures 2, 3 and 4 illustrate the variation of the success rate according to the strictness of the QoS constraints in the LatticeSL(25,3), LatticeFM (25,3) and SYM-CORE topologies, respectively.
- Comparing these three figures illustrates the effect of inter-domain connectivity on the path quality for each algorithm.
- In LatticeSL(25,3) and SYM-CORE topologies the quality of paths computed by ID-MEFPA is slightly better than that of ID-PPPA.

### V. CONCLUSION

- The authors have investigated and evaluated performance of several pre-computation algorithms for interdomain QoS routing.
- These algorithms rely on a distributed architecture, such as the PCE architecture, which allows domain confidentiality to be preserved.
- The pID-MCP is an exact algorithm and has the best success rate.
- The complexity of this algorithm in its offline phase is very high.
- Besides, the complexity of the online phase of ID-PPPA and ID-MEFPA is lower than that of pID-MCP.

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##### References

1,769 citations

### "Performance evaluation of pre-compu..." refers background in this paper

...The ID-MCP problem is NP-hard [5] and may have zero, one, or multiple solutions....

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...As explained, the IDMCP problem is NP-hard, consequently, the performance of the on-demand routing algorithms in terms of response time are severely affected....

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968 citations

### "Performance evaluation of pre-compu..." refers background in this paper

...This topology consists of five interconnected areas and is taken from the work [14]....

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889 citations

### "Performance evaluation of pre-compu..." refers methods in this paper

...When receiving a QoS request, the service provider computes the best domain sequence that links the source and the destination domain according to the cooperation policy [ 9 ]....

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...Therefore, the research community has recently been exploring the use of distributed architectures to solve this problem, such as the PCE (Path Computation Element) architecture [ 9 ]....

[...]

278 citations

### "Performance evaluation of pre-compu..." refers methods in this paper

...In fact, the complexity of executing pID-MCP in each domain corresponds to the complexity of executing SAMCRA at each border node of the domain for each class of service....

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...ID-MCP [10] is a distributed algorithm which extends the exact algorithm SAMCRA [6] to an inter-domain level to solve the ID-MCP problem....

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...It pre-computes all feasible paths between each pair of nodes (n1, n2) by executing the SAMCRA algorithm at each entry border node n1 of Dk....

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...To speed up the computation, dominated paths can be discarded from the computation search space of the QoS routing algorithms without affecting their performance, according to [6]....

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166 citations