Cisco Cisco WAE Planning White Paper

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White Paper

Best Practices in Core Network Capacity Planning

Architectural Principles of the MATE Portfolio of Products

What You Will Learn

Core network capacity planning is the process of ensuring that sufficient bandwidth is provisioned such that the

committed core network service-level agreements can be met. The best practices described in this paper -

collecting demand matrices, determining overprovisioning factors, and running simulations - are the basis of the

design principles for the Cisco

™

MATE

™

portfolio, especially (from a planning and engineering perspective) MATE

Design and MATE Collector.

Introduction

Capacity planning for the core network is the process of ensuring that sufficient bandwidth is provisioned such that

the committed core network service-level agreement (SLA) targets of delay, jitter, loss, and availability can be met.

In the core network, where link bandwidths are high and traffic is highly aggregated, the SLA requirements for a

traffic class can be translated into bandwidth requirements, and the problem of SLA assurance can effectively be

reduced to that of bandwidth provisioning. Hence, the ability to meet SLAs is dependent on ensuring that core

network bandwidth is adequately provisioned, which depends in turn on core capacity planning.

The simplest core capacity planning processes use passive measurements of core link utilization statistics and

apply rules of thumb, such as upgrading links when they reach 50 percent average utilization, or some other

general utilization target. The aim of such simple processes is to attempt to ensure that the core links are always

significantly overprovisioned relative to the offered average load, on the assumption that this will ensure that they

are also sufficiently overprovisioned relative to the peak load, that congestion will not occur, and hence that the

SLA requirements will be met.

There are, however, two significant consequences of such a simple approach. First, without a networkwide

understanding of the traffic demands, even an approach that upgrades links when they reach 50 percent average

utilization may not be enough to ensure that the links are still sufficiently provisioned to meet committed SLA

targets when network element (for example, link and node) failures occur. Second, and conversely, rule-of-thumb

approaches such as this may result in more capacity being provisioned than is actually needed.

Effective core capacity planning can overcome both of these issues. Effective core capacity planning requires a

way of measuring the current network load, as well as a way of determining how much bandwidth should be

provisioned relative to the measured load in order to achieve the committed SLAs. Hence, in this white paper we

present a holistic methodology for capacity planning of the core network that takes the core traffic demand matrix

and the network topology into account. This methodology determines how much capacity the network needs in

order to meet the committed SLA requirements, taking network element failures into account if necessary, while

minimizing the capacity and cost associated with overprovisioning.