Exam essay: WANs
January 4, 2009
In this essay, I will define WANs and describe why they are important to enterprises.
Exam essay: WANs
Wide area networks (WANs) are a vital part of many enterprises. Discuss common WAN solutions, and enterprise concerns.
In this essay, I will define WANs, describe why they are important to enterprises, discuss common solutions and detail some aspects of WAN design that enterprises will want to be aware of.
WANs are the long haul component of a corporate/organizational network that connect LANs at several different sites. WANs are what allow organizations to be geographically distributed while still being able to exchange data (voice, data, image, video) easily among their disparate sites. Also, WANs can allow multiple organizations to internetwork.
There are a number of options available to organizations when considering WAN implementation. They can be classified as public options, private options, circuit switched, packet switched and direct. What we are talking about here are last mile options for the sites, not necessarily intermediate network options. By “intermediate network options,” I mean how the carrier may choose to deal with the organization’s data after they accept it via whatever connection scheme they have in place for the organization.
Most simply, an organization may buy a leased line to connect two sites. Although it may be implemented in a public or private circuit switched network, this is a non-switched connection. The problems with leased lines become apparent when we have many sites to connect – we need a line between any two sites in the set, and the number of lines increases dramatically with each additional site.
Next, an organization can opt to connect to a private switched network – either a circuit or packet switched one. The org either builds one itself via constructing its own switching nodes and connecting them via leased lines, or contracts with a third party who has such a network and connects to it via leased line.
There are also public circuit and packet switched networks. The public telephone system is one such example of a public circuit switched network, while telco providers may offer packet switched networks (such as X.25, ATM and frame relay) networking to the organization’s doorstep.
Alternatively, an organization can connect to the most famous public packet switched network: the Internet. They may do this via a mechanism as simple as via using a modem to connect over the public circuit switched network to their internet service provider (ISP), to leasing a line to their provider, to leasing a line to an internet exchange point (IXP), a single site (typically a single building or a few sites in a building) to which many organizations connect via leased line and in which two stub networks connect to each other directly, or connect to larger transit networks. A transit network is one which connects to many other networks, and thus an organization’s traffic will transit that network on its way to its destination. A stub network is the opposite of a transit network – it’s an end point for data.
The factors that organizations should consider when deciding upon WAN options concern the characteristics of an organization’s data, data security and control of network design, availability, and day-to-day operations. If the organization’s data is bursty, it would be better off with a packet switched network than a circuit switched network. Control of network design, availability and day-to-day operations all have to do with a compromise between the cost of running, provisioning, and troubleshooting one’s own network with and hiring one’s own staff vs. the lack of control over performance characteristics, downtime and troubleshooting and fixing issues that comes with contracting with a third party for networking services. In terms of security, this is another “lack of control” issue, but also has to do with the increased vulnerability of placing organizational data onto a public network vs. using a private one.
All the considerations that come with forging outsourcing agreements apply to forming agreements with WAN providers: one should look at financial stability, past performance with other customers, availability statistics, facilities, etc.. One should build contracts that include performance and availability requirements and provider penalties for failing to meet them. The relationship with the WAN provider should be maintained carefully and continuously.
My self-critique:
In enterprise considerations, I forgot growth capacity. I note that I just say what orgs should consider, but don’t give guidelines (aside from packet vs. circuit) for how to resolve those considerations. A private circuit switched network is multiple PBXs connected by leased lines. PBXs are privately owned circuit switching nodes.
In terms of day-to-day operation, what we’re concerned about is reliability and peak traffic flow. Stallings says that packet switched networks are inherently more reliable (because we can route around issues), so choose them if that is your concern. For growth (traffic and reach), packet switched nodes are again easier to build out.