Network planning and design
is an iterative process, encompassing
topological design, network-synthesis, and network-realization, and is aimed at ensuring that a new network or service meets the needs of the subscriber and operator.
The process can be tailored according to each new network or service.
This process is performed before the establishment of a new telecommunication
Telecommunication is the transmission of information over significant distances to communicate. In earlier times, telecommunications involved the use of visual signals, such as beacons, smoke signals, semaphore telegraphs, signal flags, and optical heliographs, or audio messages via coded...
s network or service.
A network planning methodology
A traditional network planning methodology involves five layers of planning, namely:
- business planning
- long-term and medium-term network planning
- short-term network planning
- IT asset sourcing
- operations and maintenance.
Each of these layers incorporates plans for different time horizons, i.e. the business planning layer determines the planning that the operator must perform to ensure that the network will perform as required for its intended life-span. The Operations and Maintenance layer, however, examines how the network will run on a day-to-day basis.
The network planning process begins with the acquisition of external information. This includes:
- forecasts of how the new network/service will operate;
- the economic information concerning costs; and
- the technical details of the network’s capabilities.
Planning a new network/service involves implementing the new system across the first four layers of the OSI Reference Model
The Open Systems Interconnection model is a product of the Open Systems Interconnection effort at the International Organization for Standardization. It is a prescription of characterizing and standardizing the functions of a communications system in terms of abstraction layers. Similar...
. Choices must be made for the protocol
A communications protocol is a system of digital message formats and rules for exchanging those messages in or between computing systems and in telecommunications...
s and transmission technologies.
Network planning process involves three main steps:
- Topological design: This stage involves determining where to place the components and how to connect them. The (topological) optimisation methods that can be used in this stage come from an area of mathematics called Graph Theory
In mathematics and computer science, graph theory is the study of graphs, mathematical structures used to model pairwise relations between objects from a certain collection. A "graph" in this context refers to a collection of vertices or 'nodes' and a collection of edges that connect pairs of...
. These methods involve determining the costs of transmission and the cost of switching, and thereby determining the optimum connection matrix and location of switches and concentrators.
- Network-synthesis: This stage involves determining the size of the components used, subject to performance criteria such as the Grade of Service
In telecommunication engineering, and in particular teletraffic engineering, the quality of voice service is specified by two measures: the grade of service and the quality of service ....
(GoS). The method used is known as "Nonlinear Optimisation", and involves determining the topology, required GoS, cost of transmission, etc., and using this information to calculate a routing plan, and the size of the components.
- Network realization: This stage involves determining how to meet capacity requirements, and ensure reliability within the network. The method used is known as "Multicommodity Flow Optimisation", and involves determining all information relating to demand, costs and reliability, and then using this information to calculate an actual physical circuit plan.
These steps are performed iteratively in parallel with one another.
The role of forecasting
During the process of Network Planning and Design, estimates are made of the expected traffic intensity
In telecommunication networks, traffic intensity is a measure of the average occupancy of a server or resource during a specified period of time, normally a busy hour.It is measured in traffic units and defined as the ratio of the time during which a facility is cumulatively occupied to the time...
and traffic load that the network must support. If a network of a similar nature already exists, traffic measurements
Measurement of traffic within a network allows network managers and analysts to both make day-to-day decisions about operations and to plan for long-term developments...
of such a network can be used to calculate the exact traffic load . If there are no similar networks, then the network planner must use telecommunications forecasting
All telecommunications service providers perform forecasting calculations to assist them in planning their networks. Accurate forecasting helps operators to make key investment decisions relating to product development and introduction, advertising, pricing etc., well in advance of product launch,...
methods to estimate the expected traffic intensity.
The forecasting process involves several steps:
- Definition of problem;
- Data acquisition;
- Choice of forecasting method;
- Documentation and analysis of results.
Dimensioning a new network determines the minimum capacity requirements that will still allow the Teletraffic Grade of Service (GoS) requirements to be met. To do this, dimensioning involves planning for peak-hour traffic, i.e. that hour during the day during which traffic intensity is at its peak.
The dimensioning process involves determining the network’s topology, routing plan, traffic matrix
In mathematics, a matrix is a rectangular array of numbers, symbols, or expressions. The individual items in a matrix are called its elements or entries. An example of a matrix with six elements isMatrices of the same size can be added or subtracted element by element...
, and GoS requirements, and using this information to determine the maximum call handling capacity of the switches, and the maximum number of channels required between the switches.. This process requires a complex model that simulates the behavior of the network equipment and routing protocols.
A dimensioning rule is that the planner must ensure that the traffic load should never approach a load of 100 percent. To calculate the correct dimensioning to comply with the above rule, the planner must take on-going measurements of the network’s traffic, and continuously maintain and upgrade resources to meet the changing requirements.. Another reason for "overprovisioning" is to make sure that traffic can be rerouted in case a failure occurs in the network.
Because of the complexity of network dimensioning, this is typically done using specialized software tools. Whereas researchers typically develop custom software to study a particular problem, network operators typically make use of commercial network planning software.
Comparing to network engineering, which adds resources such as links, routers and switches into the network, traffic engineering targets to change traffic paths on the existing network to alleviate traffic congestion or accommodate more traffic demand.
This technology is critical when the cost of network expansion is prohibitively high and network load is not optimally balanced. The first part provides financial motivation for traffic engineering while the second part grants the possibility of deploying this technology.
The available technologies for traffic engineering include MPLS
Multiprotocol Label Switching is a mechanism in high-performance telecommunications networks that directs data from one network node to the next based on short path labels rather than long network addresses, avoiding complex lookups in a routing table. The labels identify virtual links between...
Asynchronous Transfer Mode is a standard switching technique designed to unify telecommunication and computer networks. It uses asynchronous time-division multiplexing, and it encodes data into small, fixed-sized cells. This differs from approaches such as the Internet Protocol or Ethernet that...
for current Internet backbone. For example, MPLS allows carriers to provision LSPs with dynamic or explicit routes. The dynamic routes is controlled by CSPF while the explicit routes are optimized in an offline tool or through a path computation element
Routing is the process of finding a suitable route for conveying data between a source and one or a set of destination. Routing can be subject to a set of constraints, like QoS, policy, or price. Constraint-based path computation is a strategic component of traffic engineering in MPLS and GMPLS...
which is under study by IETF. Fast reroute
Fast reroute is a MPLS resiliency technology to provide fast traffic recovery upon link or router failures for mission critical services. Upon any single link or node failures, it could be able to recover impacted traffic flows in the level of 50 ms...
has been implemented by major vendors, such as Cisco
Cisco may refer to:Companies:*Cisco Systems, a computer networking company* Certis CISCO, corporatised entity of the former Commercial and Industrial Security Corporation in Singapore...
and Juniper Networks
Juniper Networks is an information technology and computer networking products multinational company, founded in 1996. It is head quartered in Sunnyvale, California, USA. The company designs and sells high-performance Internet Protocol network products and services...
, to provide localized resilient capability for MPLS networks. End-to-end protection is an alternative resilient approach. It provisions a backup route for each primary route. Pre-planning enough bandwidth for these backup routes is one of the active topic for survivable network design.
Provisioning a large number of LSPs also brought up a scalability problem. Various solutions have been proposed and it is still an active topic under study.
Network survivability enables the network to maintain maximum network connectivity and quality of service under failure conditions. It has been one of the critical requirements in network planning and design. It involves design requirements on topology, protocol, bandwidth allocation, etc.. Topology requirement can be maintaining a minimum two-connected network against any failure of a single link or node. Protocol requirements include using dynamic routing protocol to reroute traffic against network dynamics during the transition of network dimensioning or equipment failures. Bandwidth allocation requirements pro-actively allocate extra bandwidth to avoid traffic loss under failure conditions. This topic has been actively studied in conferences, such as the International Workshop on Design of Reliable Communication Networks DRCN