77 Chapter 7 Making WAN Connections 78 Networking: A Beginner’s Guide M any companies have multiple locations that need to share network resources. For example, maybe the company’s accounting system runs at the headquarters building where the accounting and MIS staff are located, but the warehouse across town still needs access to the accounting system for inventory picking tickets, data entry, and other order fulfillment and inventory tasks. Or, perhaps the company uses a groupware system such as Lotus Notes that requires regular updates of information and messages from one site to another. In the real world, the situation can become even more complex. Some companies have offices all around the globe, and each office has different requirements both to access and update data in other locations. All of these are situations in which a wide area network (WAN) can be useful. Certainly, in a pinch, multiple offices can exchange data by using Federal Express and identical tape machines, CD-R discs, external USB hard disks, or other media. Sure, it’s possible to simply send the data back and forth like this (assuming the application supports exchanging data in this fashion), but such an arrangement has some drawbacks—the biggest one being that it is pretty slow. There are many ways to connect local area networks (LANs) in one location to LANs in another location, and making such connections is the subject of this chapter. But before looking into the different WAN technologies, you should assess your networking requirements. Because of the cost and the time required to implement and maintain a WAN, you usually do not want to install one unless it’s the only way to meet your needs. Determining WAN Needs WAN links are almost always fairly expensive to maintain. Bandwidth needs increase over time; and these upgrades are costly. Also, WAN links are generally much more prone to trouble than LANs, because many additional possible points of failure exist. For these reasons, it’s important to assess the need for a WAN carefully, and then study the different options available, their costs, and the trade-offs involved. Costs can vary wildly between different technologies, speeds, and other factors (including your location), so you need to rely heavily on cost and availability data from local providers for your own WAN analysis. Plus, prices and availability change almost every week, so make sure to get current data from your local providers before committing to a particular WAN technology. TIP Often, the need for a WAN can be satisfied using a technology called virtual private networks (VPNs). A VPN is a private network created through a public network, typically the Internet. A VPN is called “private” because all of the packets between two points are encrypted, so even though the packets are transmitted over a public network, their information remains secure. And because VPNs use the Internet, they’re usually much cheaper than dedicated WAN links, and they often can make use of existing Internet connections for two (or more) locations. VPNs are discussed in detail in Chapter 10. 79 Chapter 7: Making WAN Connections Analyzing Requirements A company’s first WAN is usually driven by a particular application, such as an accounting system. Then once the WAN is operational, the company begins to use the WAN for other applications. If you fail to take into account all the uses that the company might have for the WAN, you could find that you’ve invested a lot of money in a solution that doesn’t meet all of your needs. Here are some questions to help you determine the requirements for your company’s WAN: N What are the locations that will participate in the WAN and what kind of WAN services are available to them? A sales office in Tahiti, for instance, is unlikely to be able to purchase the latest xDSL line. N How much data needs to be transferred from each site to each other site, and in what time frame? N How quickly does the data need to be transferred? N Does the data transfer need to be synchronous or can it be asynchronous? For example, a warehouse clerk who is entering records directly into an accounting system located at another site requires a synchronous (real-time) connection, while a restaurant that needs to upload sales data to its headquarters at some time each night needs only an asynchronous connection. N When do the data transfers need to be accomplished? Do they need to occur 24 hours a day, 7 days a week? Or do they need to occur once every 30 minutes, or follow some other schedule? N What are the budget constraints, and what are the costs of the different available alternatives? Once you have the answers to these questions, you can determine whether you need a switched or dedicated link, and if it should be public or private. These issues are discussed in the following sections. Switched or Dedicated? A switched WAN link is one that is not active all the time. For instance, a dial-up modem connection or an ISDN connection from one location to another is a switched connection. These are connections that are formed only when you need them, and you usually pay for the time the connection is open, rather than the amount of data you’re able to transmit over the connection. Figure 7-1 is an example of a switched WAN link. Switched links can be either connection-based or packet-based. A connection-based switched link forms a connection as needed and makes a fixed amount of bandwidth available over that link. A packet-based switched link sends data packets into a network cloud in which they can follow a number of paths to their destination, and then emerge from the cloud. Packet-switched networks can be more reliable because the data can take many different paths, but you are not guaranteed that each packet will arrive in 80 Networking: A Beginner’s Guide a certain amount of time. A connection-based switched link just gives you one “pipe” from your source to your destination, but you can control what goes into the pipe and how long it will take to get to its destination. A dedicated WAN link is one that is always up and running. Examples of dedicated WAN connections are DS1 (T-1) lines, xDSL lines, and leased telephone lines. You use a dedicated connection when you need the connection to be up all the time or when the overall economics show that such a connection is cheaper than a switched link. Figure 7-2 illustrates a dedicated WAN link. Figure 7-1. A switched WAN link LAN Switched dial-up connection Modem Modem LAN Figure 7-2. A dedicated WAN link 81 Chapter 7: Making WAN Connections Private or Public? A private network is one that is exclusive to a particular company. No other company’s data is sent over the private network. The advantages are that the data is secure, you can control how the network is used, and you can predict how much bandwidth you have available. A public network (or external network), such as the Internet, is a network through which many companies’ data passes. Public networks are less secure than private networks, but the advantages are that public networks are less expensive to use and you don’t need to maintain the external network yourself. Use a public network under the following conditions: N You don’t care if data occasionally takes longer to reach its destination or if the delay between sites is relatively unpredictable. N You want the lowest cost network connection possible. N The data does not need to be secure or you have the ability to make it secure over the public network. (Technologies such as virtual private networks or some types of data encryption can provide such security.) Use a private network under these conditions: N Data security is of utmost concern. N You have a large, experienced staff to set up and maintain the public network. N Cost is unimportant relative to the benefits that the network brings. N You need full, reliable control over the network’s bandwidth use. Comparing WAN Connection Types Now that you understand some basics of WAN links, the remainder of this chapter provides an overview of the available WAN technologies, ranging from telephone connections to very high-speed, high-bandwidth connections. Plain Old Telephone Service (POTS) Plain old telephone service (POTS) is the telephone service everyone knows. While it does not technically qualify as a WAN connection (at least as most people think of WANs), POTS can still serve to link two or more sites together for certain low- bandwidth needs. Although it is among the slowest methods of establishing a network connection, POTS is ubiquitous and easily used throughout the world. POTS is carried over one set of twisted-pair wires (in other words, just two wires). In some cases, two sets of twisted-pair wires are used, but only the two main wires carry the telephone signal and ring signals. The other two wires are used for other features, such as backlighting a keypad on a phone or providing a message-waiting light with some PBX systems. POTS connections currently use RJ-11 telephone jacks, which simply snap into place. . connection-based or packet-based. A connection-based switched link forms a connection as needed and makes a fixed amount of bandwidth available over that link. A packet-based switched link sends data packets. 7: Making WAN Connections Analyzing Requirements A company’s first WAN is usually driven by a particular application, such as an accounting system. Then once the WAN is operational, the company. into an accounting system located at another site requires a synchronous (real-time) connection, while a restaurant that needs to upload sales data to its headquarters at some time each night