<H1>statistical multiplexer, stat mux, dsu, remote access </H1>

Small Business Series: Connecting Remote Office LANs


This paper describes the general steps required to connect Local Area Networks (LANs) in two office locations. We discuss the technology available, telephone (or radio) circuit requirements, equipment needs, and general cost involved.

Many businesses now have a local area network (LAN) to connect personal computers or workstations at the headquarters location together. The next step in office automation is to install a similar LAN in remote offices. Once a LAN is installed in the first remote office, workers begin to see a need to connect the two LANs together into a wide area network (WAN). Business drivers for this effort include (1) the ability to share, between offices, documents such as spreadsheets or word processing documents, (2) electronic mail services between the offices, (3) access to the Internet for both offices without purchasing additional services, and (4) rapid software or document distribution.

Begin with an office having a server of some kind, local workstations, and possibly an Internet connection. There is a remote office having a similar setup... server and local workstations. We will assume that the LANs are using 10BaseT ethernet (by far the most common method). The PC brand, and server type are of little importance; however the way they talk on the network (called a network protocol) must be known to select the proper router. Figure one shows the beginning scene. We are not discussing connecting terminals (or PCs acting as terminals) in one office to a host computer in the other (although they could do that with telnet and this system) ... this discussion applies only to connecting LANs (and the PCs on them) in the two offices.

Lan Diagram one

There are many ways to connect the two offices. We can use a variety of telecommunications solutions including wireless radios for the basic data path. We need to determine communication equipment needs that include modems, terminal adapters, or DSU/CSUs and routers. Equipment configurations must be analyzed. The largest variable is the office applications in use. Before any technical decisions, we must examine the business purpose and applications software running at the two sites. There are rules of thumb to follow, but you should make sure all applicable options are considered.

In general, you need to add equipment to each office that consists of the following:

A router filters the data on your LAN and only forwards appropriate data to the remote site. The selection of a router is usually based upon performance, protocols, price, LAN type, and number of sites. Often, it does other things like security, and protocol spoofing, but we'll cover that later.

Communications Equipment
Some conversion hardware to convert between the electrical standards used in LAN environments and the electrical signals needed in a WAN environment. This could be a modem, DSU/CSU, or ISDN Terminal Adapter.

The first technical decision is which communications circuit technology to use. This choice is based upon your specific situation. Before listing the choices, let's describe the technologies involved. This technology choice is usually rated based upon a circuit's need of "bandwidth" (or speed) and whether it provides full-time or part-time connectivity. The "bandwidth" or speed of the circuit is rated in bits per second (bps), thousands of bits per second (Kbps), or millions of bits per second (Mbps). The higher the number, and thus the bandwidth or speed, the faster the data moves. The connection type is either full-time or dial-up. Full time circuits provide a connection 24 hours of every day; dial-up circuits must be dialed when there is data to send. This dialing is usually automatic, but it may take as much as a minute or two to establish the connection. Here are the most common technologies in use...

Dial-up Modems:
Modems are used when the connection is a "casual" connection, that is, it is used for very low volumes of information transfer and for just a few minutes at a time. If the offices are in the same city, the telephone costs are quite low... only purchase a plain telephone line at each office and let one automatically dial the other when needed. Usual speeds now are 9.6Kbps to 28.8Kbps. Some older modems operate as low as 300 bps.

Dedicated Leased Analog Line:
This technique uses similar modems as above, but a dedicated telephone line is leased between the two sites. This was the "high performance" method in the 70's and 80's. Now, it is the low to medium speed "full-time" connection available. Unfortunately, it is the only economical way to reach some sites in rural areas. Speeds are usually the same as dial-up, but the connection is always there. For long-distance circuits, other methods may be more cost effective, even when used at low speeds.

Dataphone Digital Service (DDS) Line:
This is the current work horse of data communications. A digital circuit between the two sites is leased from the telephone company. Instead of modems, devices called DSU/CSU (Data Service Unit/Channel Service Unit) terminate the line. Higher speeds than the modem method are available, usually at higher costs. Usually offered at 56Kbps through 1.544 Mbps.

Frame Relay Circuit:
This is a relatively new technology that many users are finding much more economical than DDS lines. To the user, it is similar to a DDS line between two sites in this application. It provides a full time connection between the sites. Since the frame relay technology offers some advantages to the phone company, they usually pass cost savings on to the customer. When the circuit is long distance, frame relay is quite cost effective as it isn't priced by the mile like other full time circuits. A frame relay circuit between two close cities is often the same cost as one between the two coasts. Frame relay speed is similar to DDS lines; faster than modems and leased lines. Frame relay is usually offered at 56 Kbps, 64 Kbps, or some multiple of these up to 1,544 Kbps (1.544Mbps).

The newest popular service is Integrated Services, Digital Network (ISDN). This is a digital dial-up service... similar to your plain telephone dial service, only digital in nature. It is a dial-up service, but it dials quickly (2-4 seconds for a connection instead of a minute or two for modems). The speeds of ISDN are typically two or more times as fast as normal modem dial-up or leased lines. Pricing for ISDN varies from city to city. There is often a per-minute usage charge, and it is not usually available over long distances. You must have a site within about four miles of a telephone company central office for it to work. A variation on this service, Centrex ISDN, doesn't have the per-minute charge; but is usually available only where there are multiple sites to connect. ISDN is most often sold at the speeds known as BRI or Basic Rate Interface. This is either 64 Kbps (known as one B channel) or 128 Kbps (known as 2B or "bonded channels"). Faster than that, you have to get ISDN at 1.544 Mbps known as the Primary Rate Interface (PRI).
A comparison...

Technology Full-Time Cost Speed
Modem Dial-up NO Low Low
Modem Leased YES Medium Low
DDS YES Medium to High Medium to High
Frame Relay YES Medium Medium to High
ISDN NO Low to Medium Medium
One other option should be mentioned. Wireless, radio links are available for distances up to about 10 miles. These have some great applications and compete favorably with telephone lines in many cases. However, the telephone company is still the most popular way to connect the sites.

What it all means....

The connection is either full time or dial-up (part-time). If you need more than an hour per day of connection, it us usually better to install a full-time circuit. Full-time circuits are much easier to maintain and their performance is generally better. When using a dial-up system, you typically get a different set of telephone company equipment (lines internal to the telephone company) each time you dial. This makes the circuit less stable, and harder to troubleshoot. If there are per-minute useage charges, dial-up costs can quickly exceed the cost of a private line. We recommend full-time connections for most customers.

The speed of the circuit should match your application needs. Circuit speed is referred to as "bandwidth". The higher the bandwidth (speed), the faster information is transferred. Few modern applications can survive with the slower speeds of dial-up modems. Common speeds in the real world are...

  1. Under 56 Kbps. Modems on dial-up and leased circuits typical run between 9.6 Kbps and 28.8 Kbps. This is adequate for a terminal to host computer connection, or in some cases for a workstation to host LAN-type connection. It is often used for workstation to Internet connections. It is normally too slow for LAN-to-LAN connections that are used for anything other than email transfers or system management.

  2. 56 Kbps. Here we move to ISDN, leased DDS lines, and Frame Relay. This is the journeyman speed for most of today's cost effective LAN-to-LAN connections. You typically need a file server or host computer on each end of the circuit since this is too slow to load programs across the line, but it is fast enough for most client-server applications and transferring data. This is the minimum bandwidth required for any "real" multi-media applications such as graphic web browsing, or digital sound transfers. Some applications software must be written specifically for remote operations (known as client-server) for it to be used with the data stored on the far end of the line.

  3. 128 Kbps to 1.544 Mbps: Serious work here! These speeds are necessary to connect multiple locations that use client-server software, "wordy" network systems (usually known as Netware), electronic commerce, and multi-media applications. Trade journals seem to indicate that all corporate data moves at these speeds; but in reality, the most common speed we run into is 56 Kbps. At these speeds, you can also share some of the bandwidth with voice circuits to cut down on long distance voice charges. The technology is almost always Frame Relay or DDS. The 1.544 Mbps circuit is known as a "T-1" circuit. T-1 bandwidth can be divided into 24 channels of 56 (or 64) Kbps each. "Fractional T-1", is a subset of a full T-1 circuit. For example, you may buy 112 Kbps (or two channels at 56) as one circuit. You can buy what you need, but the economics change at around 4 channels... it's often just more economical to buy a full T-1 at that speed.

How much bandwidth is needed?

An analysis of your specific application is required to answer accurately. Most often, when connecting two LAN-based offices, a 56 Kbps circuit is adequate so long as you are not transferring programs, multi-media, or heavy graphics over the line. Connecting two normal, small business offices such as insurance agents, retail stores, common white collar or clerical work locations is most often done with the 56 Kbps circuit. Where ISDN is priced aggressively, the number is 64 Kbps. Same bandwidth class, slightly different technology. Slower, dial-up circuits are sometimes practical but always more trouble-prone.

Full-time connectivity or part time?

We seldom recommend dial-up because it causes so many problems over the long term and has such low bandwidth. The main exception to this is ISDN. Connection times are quick enough that you don't notice the dialing, and since the circuit is digital all the way, the quality of transmission circuits is high. Look at your application. Is it long distance? How many hours per month will it be used? Is it "mission critical" to your profitability?

Now, back to the main issues. Someone has looked over your system and determined the bandwidth requirements and preferred connectivity option. Based upon that choice, you can select the correct line termination equipment (either a dial-up modem, leased line modem, ISDN Terminal Adapter, or DSU/CSU). You can order the proper circuit from the telephone company after comparing rates between long distance carriers. The other equipment to specify is the router for each end.

Router Selection

Router selection is a relatively straightforward decision process. First, from the above analysis, you know the bandwidth requirement and WAN technology, so you can specify the WAN port(s). Since you should know the ethernet media type, you can specify that for the LAN port (10BaseT, 10Base2, 100BaseTx, etc.). We also need to specify the protocols in use. If you are using Novell Netware, you need to specify IPX as a routed protocol. For Windows NT, Windows for Work Groups, Windows 95, or Unix, you'll probably specify TCP/IP. Appletalk networks will need Appletalk, and some DEC installations need to be concerned about DECNET. (In general, if you don't know what those other protocols are, IPX or TCP/IP will be the choices). Where the network is Novell Netware, but you are also connecting to the Internet, you need to specify both IPX and TCP/IP protocols. Although some protocols require other features (like spoofing), that's about it. Security "firewall routing" is seldom used in these small applications. However, it is a MUST for Internet connections.

The Results...

Let's look at the results for a typical installation. This example has a central office and one remote sales office. At the central office are 25 users on a Novell Netware system. The sales office has a small Novell server and 5 users. They want to transfer electronic mail, spreadsheet documents, and sales reports. After comparing rates from several telephone providers, they selected a 56 Kbps frame relay connection. This circuit cost about $380.00 per month.
Lan Diagram two
Equipment shown on figure two consists of ...

No magic is involved. The steps are straight-forward. Use the attached checklist to make sure you didn't forget anything. Call 1-800-4-DCBNET and get our assistance when you are ready!

Office Interconnection Checksheet

A. Preplanning

  1. Create a project goal. What are you trying to accomplish? List everything that can be construed as definable targets. Examples would be "to send electronic mail between offices" or "allow remote salesmen update their pricing spreadsheets". Make sure these goals will be met before the project is closed.

  2. Inventory the LAN at each site. Include servers, wiring, hubs, bridges, and other equipment, including the PC's and workstations. Get a list of model and serial numbers for all hardware. Don't forget the ethernet cable and wiring hardware. Make sure all software is listed, including the operating system and all applications version numbers. The software list should include configuration details such as protocol.ini file and startup.ncf file examples.

  3. Decide who is the project manager or champion. You must have someone with the enthusiasm to push the project to completion. Buy a book on networking or contact a vendor or two for information.

  4. Make the determination... Do we need a consultant or is this simply a run-of-the-mill installation that we are just unfamiliar with.

B. Design

  1. Analyze the goals along with your applications software and network software to determine bandwidth requirements and circuit criteria. Pay special attention to those goals and software version numbers. Get outside opinions from several sources.

  2. Analyze the network system protocol requirements so you can specify router features.

  3. Obtain quotes from competitive telephone providers. Select the best technology and


  4. Select line termination equipment (modems, DSU/CSU, or ISDN TA).

  5. Schedule the project. You don't want to have the installation hit on payday and end of month accounting close out.

C. Installation

  1. Order the telephone line. Make sure you already specified the termination equipment so they can install the proper jack for your equipment. You need to put an "X" on the wall where the phone jack will be. Get their projected install and "turn-up" dates.

  2. Order the Routers and termination equipment. Don't forget any additional cables you may need.

  3. Install your new equipment and begin configuration of the servers and workstations.

  4. When the telephone company says they are ready, turn the system on and verify that the communications equipment talks together. The vendor and telephone company will assist here.

  5. Verify that all applications work together as required. Update the spreadsheet, send the email, etc. You did make a backup of all software before it was changed... didn't you? Do it again now with the new configurations.

D. Completion

  1. Update your inventory listings. You bought new hardware, probably new software, and new telephone circuits that should be on your inventory lists. Configurations probably changed too.

  2. Write procedures for troubleshooting the system. Include screen prints and listings for normal operation of all equipment. You don't want to guess "was that LED normally yellow or red" when you're troubleshooting. Include telephone numbers of your vendors, equipment models and serial numbers, and circuit numbers. Establish the warranties and maintenance contracts for all new equipment.

  3. Set up a maintenance program. Since you will (hopefully) outgrow the system you just installed, learn how to monitor it and look for signs of upcoming stress. Measure how long it takes to update your spreadsheet or receive an email from the other site. Record these numbers to compare against later.

  4. Have lunch with your datacom vendor and thank them for helping you. You will want their help again as your company grows.

Data Comm for Business Inc.

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