Network Capacity Planning IACT 418 IACT 918 Corporate Network Planning

The Importance of Planning Network capacity planning lies at the heart of all network management functions The design of networks to route data from one location to another with the least cost is of great concern to network designers

The Importance of Planning The objective of network designers is to minimise the cost of installing and maintaining the network These problems are complicated by the need to consider many factors such as Cable capacity End-to-end blocking probabilities Delay and reliability requirements

The Importance of Planning The process of designing a network requires that many variables are determined simultaneously In designing and upgrading a network, it is necessary to simultaneously select Node location Links connecting backbone nodes Links between end users

The Importance of Planning Mathematically we can say that The objective of designing and maintaining a network is to:  Minimise the cost of installation and maintenance  Whilst meeting some given performance criteria

The Importance of Planning Or more specifically: Given  Node locations  Edge locations  Traffic requirements between node pairs  Cost of transmission capacity  Cost of node installation Minimise  Total network costs Determine  Network topology  Edge capacities  Routing policy Subject to  Performance constraints  Capacity constraints  Reliability constraints

Working It Out These models generally end up being combinatorially explosive or NP complete To simplify the problem of solving these models several assumptions are used Packet (data) arrival is independent of other traffic (Poissonian arrival) Packet size is independent of other traffic (exponential packet size)

Working It Out Modern network based applications don’t follow these assumptions Most applications have a real time component These types of applications tend to create a traffic stream that creates packets:  At fixed time intervals (deterministic)  Have a fixed size (deterministic)

Working It Out This means that all the simplifying assumptions are no longer valid Also potential savings can be achieved by installing excess capacity to meet future requirements

Developing the Network Capacity Plan We start with a knowledge of the present network and its traffic loads etc, and our prediction of the future demands of the organisation We will develop the network capacity plan in three steps, 1. facilities, 2. equipment and 3. evaluation

Facilities "A facility is a transmission path between two or more locations, not including terminating or signalling equipment. The addition of terminating equipment would produce either a channel, a central office line, or a trunk." (Terplan P 556)

Facilities A facility has a theoretical maximum capacity which is given by the bandwidth In practice it is found to be impossible to use all the bandwidth because of: Overheads Downtime Utilisation ceiling (depends on burstiness)

Facilities For practical purposes, we can estimate the effective capacity as about 60-70% of the bandwidth (See Terplan P ) As the traffic approaches this maximum, the performance drops. Response time and packet loss increase This effective capacity is the upper limit available to the network, and we can use our estimates of future traffic to predict when we will run out of capacity

Facilities Terplan shows a graph as follows: We will run out of capacity when we reach the usable limit. Then we are in trouble on this facility

Equipment Equipment is everything not included in the facility Equipment capacity can be computed in the same way as facility capacity, using overhead, downtime and utilisation ceiling.

Evaluation When major upgrades are considered, there is always a choice among several alternatives The different possibilities must be developed and evaluated Development requires thinking of the alternatives, discussion among those involved and may include brainstorming

Evaluation Evaluation requires computer modelling or simulation It can be done on a spreadsheet or a simulation package designed for the purpose (eg Arena, nm) The value of any of these exercises depends on the accuracy of the original information on present and future loads