VIRTUAL PRIVATE NETWORKING- THE FLEXIBLE APPROACH
`
`Jon D. Brady
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`Introduction
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`Internal and external communication needs are a vital part of today’s business environment. The
`solution a business chooses tosatisfy these needs can be driven by many factors including financial,
`functional, and service considerations.
`The use of virtual services to satisfy these needs is growing, with Virtual Private Networks (VPN)
`and Centrex offering an alternative to more established solutions. This paper explains what these
`services are and what makes them attractive to customers. The FeatureNetservice, offered by BT,is
`used to illustrate implementationsof virtual services in the marketplace.
`
`Virtual Private Networks
`
`A VPNprovides a customer’s site with access to a “Cloud” that manages the inter-site and external
`traffic for the company (See figure 1). A dial plan is maintained for the customer’s sites that enables
`private numbering schemesto be implemented across the network.
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`Public Network
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`Figure 1. A Virtual Private Network
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`
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`Jon Bradyis the Market Strategy Manager for BT’s Advanced VoiceServices.
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`4/)
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`© 1997 Theinstitution of Electrical Engineers.
`Printed and published by the IEE, Savoy Place, London WC2R OBL, UK.
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`The service surround and connection options to the public network will vary across different service
`providers. Although adopting a VPN is not usually considered as outsourcing,
`the day to day
`management of the network is left to the service provider, leaving the customer free to focus their
`efforts on core business. The tariff for inter-site traffic will usually be designed to make the VPN
`moreattractive than the use of the public network for the target customers. As fluctuations in inter-
`site traffic levels occur, then the VPN can handle the variations without blocking or overflow to the
`public network, and therefore provide a cost effective and flexible solution.
`
`VPN’s provide a solution to a business need to connect more than one site together. This need can
`arise out of a business expanding out of a single site, or the desire to replace existing solutions.
`Existing solutions are usually the direct use of public network dialling between sites, or private
`circuits providing a companydial plan.
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`The use of the public. network (See figure 2) for all inter-site calls can be a sizeable part-of the
`communication spend for a business.If inter-site traffic is significant then a private network solution
`
`will usually provide a cost effective way of satisfying the business needs.
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`Figure 2. The public network for connectingsites
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`Private networks have been traditionally implemented using private circuits to build an interconnect
`network between the sites (See figure 3). This requires the customer to manage the ordering ofall
`the circuits, provide sizing information, and manage the fluctuations in traffic. The sizing of the
`routes requires the number of channels to be specified in and outof each site to all other sites. This
`information must be managed and any variation predicted. For a very stable companyinfrastructure
`this task can settle down but for a large proportion of businesses this task can quickly require a large
`amount of their resource. The greatly reduced level of management required for a VPN enables a
`company to re-focus this effort on core business and quite often the VPN “Cloud” can be more cost
`effective than under optimised or overflowing private circuits.
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`
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`Figure 3. A private circuit based private network
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`The use of Virtual Private Networks will usually appeal to customers who have one or more of the
`following characteristics :-
`
`1. Acompanythat has significant inter-site traffic and numeroussites
`2. A companythat is frequently changing its traffic patterns
`3. A company that wants to focus on core business
`4. A companythat is growing
`5. A companythatis looking for cost reduction opportunities
`6. A companythat wants to improve the managementofits private network
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`Implementing a VPN
`
`FeatureNet1000 is the VPN service currently offered by BT and it is targeted at the large multi-site
`companies. The VPN is supported by a network of 25 Nortel DMS100 switches which are located
`around the country (See figure 4). The sites get access lines to the VPN at the Point of Presence
`(POP) on.the network andthis is routed to the switch. The switches will manage the routing of any
`traffic between sites and generate usage based charging information for each inter-site call.
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`Public Network
`
`Figure 4. The BT FeatureNet VPN
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`Any calls to the public network get routed via the switch to a public access point. This access point
`can be the nearest switch to the public destination (Far-end breakout) so optimising usage of the
`VPN while reducing public network charges.
`The switches inter-connection network is managed by BT’s Network Management Centre and this
`ensures that capacity is always available between the switches. The routes between the switches are
`resilient, which can be an expensive additional cost for a private circuit based network. To size a
`network the customerhas only to specify how manyaccess lines they require from eachsite into the
`network and all inter-site dimensioning is handled automatically by the VPN. If traffic patterns
`change, the VPN has the capacily tu handle new traffic flows without the customer being involved.
`In a private circuit implementation the customer must anticipate and specify variations so that new
`capacity can be bought andalso potentially leaving under utilised routes.
`Feature transparency between the PBX’s is achieved by carrying DPNSS messages in the C7
`signalling between the switches. Customer data is partitioned on the switches so that the network is
`as secure as a private circuit implementation.
`FeatureNet offers the customer a reporting package that enables them to understand their use of the
`VPN. This along with an itemised bill, that can be broken down into cost centres, enables the
`customerto focus on cost managementrather than network management.
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`FeatureNet1000 also offers virtual circuits (See figure 5) that enable the customer to implement a
`route through the VPN analogous to a private circuit but with the advantages of the VPN
`infrastructure.
`Implementing the private network with virtual
`circuits
`requires
`inter-site
`dimensioning where the numberof channels in and outofasite to all the others must be specified
`and managed. Some customersfind this attractive because it has a fixed cost independent of usage
`providing they have specified excess capacity. These customers see predictability of costs as
`
`paramountto their business andput it before long term cost reduction.
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`Figure 5. Implementing virtual circuits through a VPN
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`Centrex
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`A Centrex service provides internal switching capability to a site which satisfies the needs
`commonly met by a PBX (See figure 6). The extension lines are terminated in the service. providers
`network and PBX type features can be associated with them. Short code dialling is used between
`extensions on the site along with inter-extension features like call diversion,
`
` ienent
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`Customer Site
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`Figure 6. A Centrex site
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`Wide Area Centrex (WAC)provides centrex working across multiple sites (See figure 7). Customers
`can have a dial plan and use private numbers between their sites. Network based features can
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`provide centralised call handling functionality that can operate across all the sites.
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`Customer Site C
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`Figure 7. A Wide Area Centrex network
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`Centrex provides a solution for a business need for intra-site calling with call handling features.
`Traditionally companies have used PBX’s to meet
`this need but
`they require large capital
`expenditure. Centrex is usually a rental service so allowing companies to avoid tying up capital in
`infrastructure and allowing them to utilise it in the core business. Centrex provides a flexible way to
`grow avoiding capital purchases that becometoo small to handle increasing numbersof extensions.
`The managementof a network of PBX’s can also require a lot of a companies resource but with the
`adoption of WAC this management is done by the service provider. Also the adoption of WAC
`ensuresconsistent featuresat each site and avoidsloss of functionality through PBX incompatibility.
`As the service provider enhances the features offered, then they are usually available at all sites
`rather than waiting for upgrade or replacement cycles with each PBX.It is often more cost effective
`upgrading your Centrex service than a PBX becauseofthe rental nature of Centrex andthe ability to
`order a feature on a line by line basis as required.
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`The use of Centrex will usually appeal to customers who have one or more of the following
`characteristics :-
`
`1. A company that wants to focus capital on core business
`2. A companythatis growing _
`3. A company that wants to reduce the load of managing their communications
`4. A company that wants consistency of features at all sites
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`Implementing Centrex
`
`FeatureNet5000 is one of the Centrex services currently offered by BT and it is targeted at the large
`multi-site companies. The service is supported by the same network of DMS100’s providing the
`FeatureNet1000 service (See figure 8)
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`PatAs
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` a
`Customer Site B
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`Figure 8. The BT FeatureNet Centrex
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`The customer’s extension is connected to the switch either directly or via a concentrator called a
`Small Remote Unit (SRU) supplied by Nortel. The SRU can be located on the premises for large
`sites or just used as a line extender within the BT network. An SRU can be located hundreds of.
`miles away from the switch so enabling a national service coverage.
`The extension can have the features expected from a modern PBX and these include extensive group
`workingfacilities. Sophisticated handsets are available that enable a very high functionality desktop
`environment to be created. Extensions can be easily made into call centre positions by using
`Automatic Call Distribution (ACD) lines and these come with an on-line management information
`system. Feature interwoking is clearly defined, as it is not dependent on any PBX compatibility
`betweensites.
`The service is rental based and all calls internal to the site are not charged. Anyinter-site or public
`traffic can be billed on a usage basis allowing cost effective connection. Extensive reporting and
`itemised billing are available allowing analysis of the use of the service. The customer has the
`option of having their own terminal
`to manage the re-configuration of their service as their
`organisation changes.
`To order the service the customer has to specify how many extensions they want on a site and what
`features they want on each extension. For PBX solutions growth must either be built into the initial
`purchase so increasing the capital expenditure or there is a risk that the equipment will be overtaken
`by demand. A FeatureNet customer can start off with the optimum numberof extensions and order
`more as they require them therefore not only saving capital expenditure but optimising cashflow.
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`Hybrid working
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`Hybrid working is a term used for customers who want to use both VPN/PBXsolutions and Centrex
`solutions to meet their business needs (See figure 9). This is quite a common migratory step to
`Centrex working where a business has a wide range of PBX ages and can only write off the oldest
`for financial considerations. This avoids new capital purchases but enables full value to be extracted
`from modern equipment. The level of interworking between the Centrex and VPN environment is
`key to the success of hybrid working and the support of a common dial plan across them is usually
`considered essential.
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` Customer Site
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`Figure 9. Hybrid working between PBX and Centrex solutions
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`Implementing hybrid working
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`The FeatureNet service offered by BT was intentionally based on one platform for both the VPN
`and Centrex implementations because of the importance of hybrid working to the market place. The
`Nortel’s DMS100 platform provides a high functionality hybrid environment and it’s available
`across the whole network (See figure 10).
`
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`Custo
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`Customer Site C
`mer Site A
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`Figure 10. The BT FeatureNet hybrid solution
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`Customers can maintain a dial plan across all their FeatureNet sites, whether they are VPN or
`Centrex supported. The switch treats the Centrex site as a pseuda PBX and provides DPNSS
`interworking with the PBX’s.
`The FeatureNet service provides one set of managementreports and itemised billing for the hybrid
`solution allowing the customer to manageits usage in a coherent way.
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`Conclusion
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`VPN’s provide a cost effective solution to managing inter-site traffic for many companies. They
`provide easier management,
`flexible support of traffic variations, and often cost
`reduction
`opportunities.
`Centrex provides a non-capital way of realising a sites imternal communication needs. It gives
`flexibility for a company to grow and to enhance the functionality of its infrastructure. Wide Area
`Centrex enables companiesto have a consistent feature set acrossallit’s sites.
`Hybrid working is a practical way for a company to adopt a virtual services strategy while
`maintaining a coherent dial plan across the whole network. It enables modern PBX’s to be fully
`utilised in a VPN environment and for obsolete PBX’s to be replaced with Centrex.
`Virtual services are unlikely to completely replace traditional solutions to business communication
`needs. However in a business environment that is changing more rapidly daily, the flexibility
`offered by these services will become valued by an increasing customer base as time gocs on. As
`companies try to focus their resource and capital on core business, the adoption of virtual services
`will increasingly be seen as a vital factor in their success.
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