The Building Blocks: Basic Components of Networks

Although the term "network" has many definitions, most people would agree that networks are collections of two or more connected computers. When their computers are joined in a network, people can share files and peripherals such as modems, printers, tape backup drives, or CD-ROM drives. When networks at multiple locations are connected using services available from phone companies, people can send e-mail, share links to the global Internet, or conduct videoconferences in real time with other remote users.

Every network includes:

• At least two computers
• A network interface on each computer (a device that lets the computer talk to the network), usually called a network interface card (NIC) or adapter.
• A connection medium, usually a wire or cable, although wireless communication between networked computers and peripherals is also possible.
• Network operating system software, such as Microsoft Windows 95 or Windows NT, Novell NetWare, Apple Share, or Artisoft LANtastic.

Most networks—even those with just two computers—also contain a hub or switch to act as a connection point between the computers.

Networking Technologies Overview

Local-Area Networks: Ethernet, Fast Ethernet, and Gigabit Ethernet

Ethernet has been around since the late 1970s and remains the leading network technology for LANs or networks contained in buildings or on a single site. Ethernet is based on a standard referred to as carrier sense multiple access with collision detection (CSMA/CD). (See Token Ring in the "Glossary" section to learn about another basic style of network communication.)

Simply put, an Ethernet workstation can send data packets only when no other packets are traveling on the network—when the network is "quiet." Otherwise, it waits to transmit, as a person might wait for another to speak during a conversation.

If multiple stations sense an opening and start sending at the same time, a "collision" occurs. Each station then waits a random amount of time and tries to send its packet again. After 16 consecutive failed attempts, the original application that sent it must start again. As more people try to use the network, the number of collisions, errors, and subsequent retransmits grows quickly, causing a snowball effect.

Collisions are normal occurrences, but too many can slow the network. When more than 50 percent of the total network bandwidth is used, collision rates begin to cause congestion. Files take longer to print, applications take longer to open, and users are forced to wait. At 60 percent or higher, the network can slow dramatically or even shut down.

As noted in the previous section, Ethernet bandwidth or data-carrying capacity (also called throughput) is 10 Mbps. Fast Ethernet and Gigabit Ethernet works the same way—through collision detection—but provide 10 times the bandwidth, at 100 Mbps, and 100 times the bandwidth, at 1000 Mbps, respectively.

Shared Ethernet is like a single-lane highway with a 10 Mbps speed limit. Shared Fast Ethernet is like a much wider highway with a 100 Mbps speed limit: there is more room for cars and they can travel at higher speeds. Switched Ethernet look likes a multilane highway with a speed limit of 10 Mbps in each lane. Switched Fast Ethernet also would be a multilane highway, but with a speed limit of 100 Mbps in each lane. Switched Gigabit Ethernet would have even more lanes, with a speed limit of 1000 Mbps in each lane.

10 Mbps Shared Ethernet

10 Mbps Switched Ethernet

100 Mbps Shared Fast Ethernet

100 Mbps Switched Fast Ethernet

1000 Mbps Switched Gigabit Ethernet

Remote Access and Wide-Area Networks

LANs accommodate local users—people within a building or on a campus. WANs connect users and LANs spread between various sites, whether in the same city, across the country, or even around the world. "Remote access" refers to a simple connection, usually dialed up over telephone lines as needed, between an individual user or very small branch office and a central network. Your business gains access to the Internet through some type of remote connection. A single user can dial up ISP via modem. Multiple users within a campus might choose to rely on a router to connect to the ISP, who then connects the campus to the Internet.

In general, LAN speeds are much greater than WAN and remote-access speeds. For example, a single shared Ethernet connection runs at 10 Mbps. Today's fastest analog modem runs at 56 kbps-less than one percent of the speed of an Ethernet link. Even the more expensive, dedicated WAN services such as T1 lines don't compare (with bandwidth of 1.5 Mbps, a T1 has only 15 percent of the capacity of a single Ethernet link). For this reason, proper network design aims to keep most traffic local—that is, contained within one site—rather than allowing that traffic to move across the WAN.

Analog Lines
Using analog lines to dial out to other networks or to the Internet—or to allow remote users to dial into your network—is a straightforward solution. Most ordinary phone lines are analog lines. Connect a modem to your computer and to a wall jack, and you're in business. You pay for a connection as you would pay for a phone call—by the minute, or at a set rate per local call (long-distance charges are the same as for a long-distance telephone call). At present, the fastest analog modems operate at 56 kbps for transferring data. With today's larger file sizes and graphically sophisticated Web sites on the Internet, you should choose modems that operate at a minimum of 33.6 kbps (also called V.34) and that have V.42 (error correction) and V.42bis (data compression) capabilities. Although modems offer a simple solution for dialout connections to other LANs and the Internet, they do not scale well as your network grows. Each modem can support only one remote "conversation" at a time, and each device that wants to connect with the outside world needs a modem. (Find more information in the "Small Business Networking Examples" section about overcoming this limitation by installing a router for wide-area communications and your Internet link.)

"Dial-on-demand" routing (DDR) is sometimes used as a compromise between the dialup method of connecting and full-fledged routing. With DDR, the router establishes (and is charged for) a connection only when the connection is in use. This solution uses a basic router paired with either a modem or an Integrated Services Digital Network (ISDN) line, makes the calls as requested by the router.

ISDN

ISDN operates at 128 kbps and is available from your phone company. Charges for ISDN connections usually resemble those for analog lines—you pay per call or per minute, usually depending on distance. ISDN charges also can be a flat rate, if they are linked to a local Centrex system.

Technically, ISDN comprises two 64 kbps channels that work separately. Load balancing or "bonding" of the two channels into a 128 kbps single channel is possible when you have compatible hardware on each end of a connection (for example, between two of your sites). What's more, as a digital service, ISDN is not subject to the "line noise" that slows most analog connections, and thus it offers actual throughput much closer to its promised maximum rate.

You can make ISDN connections with either an ISDN-ready router or an ISDN terminal adapter (also called an ISDN modem) connected to the serial port of your router. Again, modems are best for single users, because each device needs its own modem, and only one "conversation" with the outside world can happen at any one time. Your ISDN router, modem, or terminal adapter may come with analog ports, allowing you to connect a regular telephone, fax, modem, or other analog phone device. For example, an ISDN router with an analog phone jack would allow you to make phone calls and send faxes while staying connected via the other ISDN digital channel.

Leased Lines

Phone companies offer a variety of leased-line services, which are digital, permanent, point-to-point communication paths that are "open" 24 hours a day, seven days a week. Rather than paying a fee for each connection, you pay a set amount per month for unlimited use. Most appropriate leased lines for small- and medium-sized businesses range in speed from 56 kbps to 45 Mbps (a T3 service). Because they all work the same way, choosing the right line for you depends on the number of users and the amount of remote traffic the network will carry (and how much bandwidth you can afford). A common service for businesses with substantial WAN usage is a T1 line with 1.5 Mbps of bandwidth.

By "point-to-point," we mean that leased lines use a direct, physical connection from your business or branch office to the phone company's switch, and then to your other offices. Often, the phone or data services company may need to install new cabling.

Cable modems offer extremely fast and relatively inexpensive access to the Internet. A cable modem connects directly to the same line that provides cable TV service to a home or business, and then to an Ethernet NIC in a PC.

Whereas a traditional dialup modem provides access at speeds up to 56 kilobits per second (kbps), a cable modem can deliver transmission rates of up to 10 megabits per second (Mbps)—nearly 200 times as fast. And unlike dialup modems, cable modems have a connection to the Internet that is "always on." In other words, you won't face busy signals or delays while your computer connects to the Internet.

Likewise, because you are sharing the connection with multiple users on your cable system, your performance will depend on how many users are on line at once. Another caution: in today's cable modem systems, users on a single segment of cable are essentially connected to a single local-area network (LAN). To prevent neighbors from accessing files on a computer, the file sharing options of that computer should be turned off.

Ready to sign up? You might need to be patient. About 65 million locations in the United States alone have cable service. But only a small percentage of those links are cable modem-ready—the rest will require upgrades to handle the two-way traffic of Internet surfing.

Upsides

• Transmission rates for downloading Web pages and files are extremely fast (uploading to the Internet—mostly mouse clicks and e-mail—occurs at a slower but still quick speed of up to about 2 Mbps).
• Inexpensive service—Service costs about $50 per month today, or close to the cost of basic cable TV.
• Minimal requirements—All you need to make the connection is a relatively new PC, a cable modem (often leased from the cable company), an Ethernet card in the PC, and a connection point from your cable service provider.

Downsides

• Limited availability—At this writing, only about 10 percent of the United States has access to the upgraded cable systems needed to support cable modems. The experts say it will be about five years before the technology is widespread.
• Extra installation steps—Gaining Internet access today can be as simple as installing a modem and browser software and calling your Internet service provider's (ISP's) access number. With a cable modem, the cable company most likely will need to send out a technician to check your wiring quality and install the device. You also will need to have an Ethernet card installed in the PC, if it doesn't already have one.

Example:

• Cisco 900 series

Digital Subscriber Line Service

Digital subscriber line (DSL) technology is a high-speed service that operates over ordinary twisted-pair copper wires supplying phone service to businesses and homes in most areas. DSL is often less expensive than ISDN in markets where it is offered today.

Using dedicated equipment in the phone company's switching office, DSL offers faster data transmission than either analog modems or ISDN service, plus—in most cases—simultaneous voice communications over the same lines. This means you don't need to add lines to supercharge your data access speeds. And because DSL devotes a separate channel to voice service, phone calls are unaffected by data transmissions.

There are several types of DSL including asynchronous DSL (ADSL), synchronous DSL (SDSL), high-bit-rate DSL (HDSL), ISDN DSL (IDSL), and very-high-bit-rate DSL (VDSL). ADSL delivers asymmetrical data rates (for example, data moves faster on the way to your network than it does on the way out to the Internet). Other DSL technologies deliver symmetrical data (same speeds going in and out of your network).The different types are dependent on "upstream" and "downstream" speeds. With ADSL, the most common DSL today, traffic moves upstream at 1 Mbps and downstream at 8 Mbps. SDSL is the next most popular DSL technology. With SDSL, traffic moves at the same speed in both directions. Speeds reach up to 1.54 Mbps.

Additionally, DSL comes in residential and business services. Residential DSL services include high-speed and affordable Internet access. Business DSL offers the same high-speed, affordable access with enhanced business functionality which can include differentiated classes of service (CoSs) offered by service providers for guaranteed service levels, integrated toll-quality voice service, and business-class security. The type of service (ToS) available to you will depend on the carriers operating in your area. Because DSL works over the existing telephone infrastructure, it should be easy to deploy over a wide area in relatively little time. As a result, the pursuit of market share and new customers is spawning competition between traditional phone companies and a new breed of firms called competitive local exchange carriers (CLECs). If you choose DSL service for connecting your business to the Internet or for giving remote sites and users high-speed access to your central network, your carrier will help you install the appropriate hardware and software.

Example:

• Cisco 600 series
• Cisco 800 series                                               Back to menu

Virtual Private Networks: A Cost-effective Alternative to Building Your Own WAN

As businesses grow, they need to connect a rising number of remote offices and individuals to their central network to share information and resources electronically. Traditionally, this has been accomplished by building a private WAN, using leased lines to connect offices, and dial-access servers to support mobile users and telecommuters.

For a small or medium-sized business, a traditional private WAN can be costly to build and manage. The leased lines, telecommunications services, and equipment needed to interconnect offices can be expensive, and each added location requires a new leased line. Individuals or small branches dialing into a central site via the public telephone network incur long-distance charges, and managing dial-access servers at the central site can be resource intensive and complex.

Now, businesses have an alternative for connecting remote sites and users to the main company network—virtual private networks (VPNs). A VPN offers the security and full data access of a private WAN, but because it runs over the Internet, it is more affordable and flexible.

• More affordable—Remote users can connect with central network resources through a local link to an ISP, at the price of a local call. This is a much more cost-effective method than making a long-distance call to the central site.
• More flexible—New sites can be added easily, without need for extensive new equipment or an additional, dedicated private line. VPNs also simplify the task of creating an extranet, giving customers or suppliers password-protected access to a portion of a private network—for example, to order products, check status of shipments, or submit invoices.
• More reliable—VPNs take advantage of the equipment and full-time expertise of the vast public network infrastructure and the companies that oversee it.

How VPNs Keep an Internal Network Safe

Offering access to your internal network through the Internet might seem like a recipe for data disaster, but VPNs use tunneling and encryption to protect your private traffic. Tunneling creates a temporary, point-to-point connection between the remote and central sites, blocking access to anyone outside. Encryption scrambles the data on the sending end and reassembles it on the receiving end, so it cannot be read or changed while in transit.

What You Need to Build a VPN

You can build and maintain your own VPN, but most small and medium-sized businesses will find it easier to rely on a SP. In this case, you simply connect to the SP using routers (for sites with multiple users or heavy-duty usage) or modems (for individuals or branch offices with light usage)—just as you might connect your central site and remote users to the Internet.

Note that there are two types of VPNs: dial VPNs and dedicated VPNs. This means VPNs can take advantage of the low cost of ordinary dialup services, or, where a high-speed, high-capacity remote link is needed, they can operate over Frame Relay services or leased lines. When you implement a VPN, the offices in your network will need a firewall to act as a "sentry" to protect your network from unauthorized users. This firewall can be a standalone device, but for small networks, firewalls can be integrated into a server or router, simplifying management and lowering capital cost.

Keep in mind that using a VPN means relinquishing some control over your network. Be sure to find a SP who can provide a strong service-level guarantee (99-percent uptime or better) and support the protocols you are using (most likely, IP, or Internet Protocol) with minimal latency or traffic delay. If you have sites in multiple countries, you also may want to look for a SP that already has—or is planning to have—local points or presence in the nations where you operate. This keeps your costs down by minimizing long-distance charges; your sites connect using local calls.

Example:

• Cisco 1700 series with VPN module

Making the Right Connection: Network How-Tos

How to Connect to the Internet

The Internet is a global network of thousands of computers, growing by leaps and bounds each year. It allows a global community comprising tens of millions of people to communicate over any distance, access information from anywhere in the world, and publish text and images instantly. The Internet is a link to the information resources of businesses, universities, and governments, simplifying information gathering and providing a medium for an increasing amount of electronic trade in both goods and services.

A large number of businesses still lack Internet connections. If your business is among them, you will be pleased to hear that connecting to the Internet is easier than ever.

Whereas connections once required costly special services, you now have a range of options. Commercial online services such as America Online and the Microsoft network offer dialup Internet access for $20 or less per month. ISPs offer dialup and shared-access connections for a range of prices, based on a range of line speeds up to T3 (45 Mbps) for environments with heavy demand or a large number of users.

On the hardware side, you can make a dialup connection with a modem attached to one computer, or a router attached your local-area network, allowing multiple users to access the Internet.

Modem connections are inexpensive and easy to acquire, so they can be a good idea if you're just starting out, or if your business has only a few users or computers. But only one person can use a modem at any given time, leading to heavy competition for Internet access. A single router can provide a shared-access solution, accommodating multiple users and multiple simultaneous connections to the Internet. It connects you directly to a router at your ISP's location.

However you choose to connect, your window on the Internet is a browser such as Netscape Navigator or Microsoft Internet Explorer, easy-to-use programs that link you to any active site on the Internet.

Networking Basics Checklist

The following checklists provide a general idea of the components you will need to install your network. These are meant to be approximate guidelines only; your own installation will vary based on your needs.

• Clients with NICs installed
• Server
• Hub
• Cabling
• Network operating system software (for example, Windows NT, Windows 95, Novell NetWare, LANtastic, and AppleShare)
• Modem for dialup Internet access (optional)

Wireless Networking for Small LAN

• Clients with wireless NICs installed
• Correctly deployed access points

• Clients with NICs installed
• Servers
• Hubs
• Switch
• Cabling
• Network operating system software (for example, Windows NT, Windows 95, Novell NetWare, LANtastic, and AppleShare)
• Router for shared Internet access (optional)

Wireless Networking for Connecting Offices and Departments

• Clients with wireless NICs installed
• Correctly deployed access points

Connecting Dispersed Office Sites

• Clients with NICs installed
• Servers
• Hubs
• Switches
• Routers at each location for WAN connections, shared Internet access
• Access Server for dialup access for remote users
• Cabling
• WAN Service (ISDN, Frame Relay, or leased line service from phone company)
• Network Operating System software (e.g., Windows NT, Windows 95, Novell NetWare, LANtastic, and AppleShare.)

Wireless Networking for Connecting Dispersed Office Sites

• Building-to-building bridges                                                                                              Back to menu

Glossary

ADSL—Asymmetric DSL. A DSL technology providing asymmetrical bandwidth over a single wire pair. The downstream bandwidth going from the network to the subscriber is typically greater than the upstream bandwidth going from the subscriber to the network.

ATM—Asynchronous Transfer Mode.Under ATM, multiple traffic types (such as voice, video, or data) are conveyed in fixed-length cells (rather than the random-length "packets" moved by technologies such as Ethernet and Fiber Distributed Data Interface [FDDI]). This enables very high speeds, making ATM popular for demanding network backbones. With networking equipment that has recently become available, ATM will also support WAN transmissions. This feature makes ATM valuable for large, dispersed organizations.

Backbone—The part of a network that acts as the primary path for traffic moving between, rather than within, networks.

Bandwidth—The "data-carrying" capacity of a network connection, used as an indication of speed. For example, an Ethernet link is capable of moving 10 million bits of data per second. A Fast Ethernet link can move 100 million bits of data per second—10 times more bandwidth.

Bridge—A device that passes packets between multiple network segments using the same communications protocol. If a packet is destined for a user within the sender's own network segment, the bridge keeps the packet local. If the packet is bound for another segment, the bridge passes the packet onto the network backbone.

Client—A networked PC or terminal that shares "services" with other PCs. These services are stored on or administered by a server.

DSL—digital subscriber line. A public network technology that delivers high bandwidth over conventional copper wiring at limited distances. There are four types of DSL: ADSL, HDSL, SDSL, and VDSL. All are provisioned via modem pairs, with one modem located at a central office and the other at the customer site. Because most DSL technologies do not use the whole bandwidth of the twisted pair, there is room remaining for a voice channel.

Ethernet—A popular LAN technology that uses CSMA/CD (collision detection) to move packets between workstations and runs over a variety of cable types at 10 Mbps. Also called 10BASE-T.

Extranet—A network that provides external users (such as suppliers, independent sales agents, and dealers) access to company documents such as price lists, inventory reports, shipping schedules, and more.

Fast Ethernet—Uses the same transmission method as 10-Mbps Ethernet (collision detection) but operates at 100 Mbps- 10 times faster. Fast Ethernet provides a smooth upgrade path for increasing performance in congested Ethernet networks, because it uses the same cabling, applications, and network management tools. Variations include 100BASE-FX, 100BASE-T4, and 100BASE-TX.

FDDI—Fiber Distributed Data Interface, a LAN technology based on a 100- Mbps token-passing network running over fiber-optic cable. Usually reserved for network backbones in larger organizations.

Frame Relay—Wide-area network service that provides switched ("on-and-off") connections between distant locations.

FTP—File Transfer Protocol, a part of the chief Internet protocol "stack" or group (TCP/IP), used for transferring files from Internet servers to your computer.

Gigabit Ethernet—The latest version of Ethernet. It offers 1000-Mbps (1-gigabit per second [Gbps]) raw bandwidth, that is 100 times faster than the original Ethernet, yet is compatible with existing Ethernets, because it uses the same CSMA/ CD and Media Access Control (MAC) protocols. Gigabit Ethernet competes most directly with ATM and is forcing out FDDI and Token Ring.

HTML—Hypertext Markup Language, a simple document formatting language used for preparing documents to be viewed by a tool such as a worldwide Web browser.

HTTP—Hypertext Transfer Protocol, a protocol that governs transmission of formatted documents over the Internet.

Hub—A device that interconnects clients and servers, repeating (or amplifying) the signals between them. Hubs act as wiring "concentrators" in networks based on star topologies (rather than bus topologies, in which computers are daisy- chained together).

IDSL—ISDN digital subscriber line, a DSL technology that is basically a naming convention for an ISDN Basic Rate Interface (BRI), both B channels and the D channels permanently bonded for 144 kbps over a single wire pair. ISDN digital subscriber line (IDSL) uses 2B1Q line coding.

Internet—A massive global network, interconnecting tens of thousands of computers and networks worldwide and accessible from any computer with a modem or router connection and the appropriate software.

Intranet—An internal network that takes advantage of some of the same tools popularized on the Internet (browsers for viewing material, HTML for preparing company directories or announcements, and so on).

IP telephony—IP telephony combines different types of communications-such as data, voice, and video-over a single packet cell-based infrastructure. IP telephony extends the value of the network with these nontraditional applications. By combining different types of traffic on a single network connection, small and medium-sized businesses and small branch offices can dramatically reduce the costs of their voice and data networks.

ISDN—Integrated Services Digital Network, a communication protocol offered by telephone companies that permits high—speed connections between computers and the network in dispersed locations.

LAN—Local Area Network, typically, a network or group of network segments confined to one building or a campus. Compare to WAN.

Modem—Device that enables a computer to connect to other computers and networks using ordinary phone lines. Modems "modulate" the digital signals of the computer into analog signals for transmission, and then "demodulate" those analog signals back into digital language that the computer on the other end can understand.

Packet—A block of data with a "header" attached that can indicate what the packet contains and where it is headed. Think of a packet as a "data envelope," with the header acting as an address.

Remote-access server—Device that handles multiple incoming calls from remote users who need access to central network resources. A remote-access server can allow users to dial into a network using a single phone number. The server then finds an open channel and makes a connection without returning a busy signal.

Router—Device that moves data between different network segments and can look into a packet header to determine the best path for the packet to travel. Routers can connect network segments that use different protocols. They also allow all users in a network to share a single connection to the Internet or a WAN.

Server—A computer or even a software program that provides services to clients-such as file storage (file server), programs (application server), printer sharing (print server), fax (fax server) or modem sharing (modem server). See also client.

Switch—A device that improves network performance by segmenting the network and reducing competition for bandwidth. When a switch port receives data packets, it forwards those packets only to the appropriate port for the intended recipient. This further reduces competition for bandwidth between the clients, servers, or workgroups connected to each switch port.

Token Ring—LAN technology in which packets are conveyed between network end stations by a token moving continuously around a closed ring between all the stations. Runs at 4 or 16 Mbps.

VPN—Virtual private network, enables IP traffic to travel securely over a public TCP/IP network by encrypting all traffic from one network to another. A VPN uses "tunneling" to encrypt all information at the IP level.

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Small Business Networking Examples

This section highlights common examples of network designs for growing businesses. Examples include:

• A LAN for a small office
• As the office network grows
• A WAN for multiple small sites
• A small-scale VPN

Small Business Networking Examples

As the Office Network Grows

Unfortunately, this network cannot accommodate the growing demands of the business. Too many users are competing for the 10 Mbps Ethernet network pathway. Only one user can connect to the Internet at one time from a modem. And as employees begin incorporating more graphics in their files and sending these files back and forth between their clients and the server, network performance stumbles.

The solution is to segment the network using Ethernet switches and add a router for Internet connections. This setup provides more bandwidth for all employees and permits multiple simultaneous links to the Internet through one line. The business can give product designers using bandwidth-hungry computer-aided design (CAD) programs the performance they need and dedicated 10 Mbps Ethernet channels to their individual workstations. And the network upgrade saves money by incorporating existing equipment and wiring.

A Wireless LAN
If the business wants to add mobility or flexibility to its network, it may choose to add a wireless network segment as a complement to or substitute for portions of its wired LAN. Properly deployed, wireless LAN components can allow employees to remain connected regardless of where they are on campus. This setup offers scalability to the small business that may have to host differing numbers of mobile workers, such as sales people. Wireless networking can also be used in situations where pulling cable for wired network is not possible, or doesn't make good fiscal sense; for example, in older or historic buildings, or leased office space.

A Wireless Bridge for Multiple Small Sites
Many businesses choose to link multiple sites by building a WAN, using some type of direct connection such as a T1 line. Wireless networking offers another option in the form of building-to-building bridges. These bridges allow the business to expand its LAN. This option can be worthwhile if a business needs to go through the time and expense of physically connecting the buildings, and if the buildings have a line-of-sight access within 25 miles of each other.

A Wide-Area Network for Multiple Small Sites

To improve communications between a pair of small remote offices and a central office, a business decides to install a WAN. The upgrade also will allow the business to economize on Internet connectivity by offering all offices a link through a central high-speed line.

A High-Performance WAN
A growing business sees rising network traffic at its three locations in different cities. It wants to install future-ready local networks to support rapidly rising traffic volumes. It also wants to provide high-speed WAN links to allow employees at the Chicago and Omaha offices to take advantage of video training, which originates at the Minneapolis office. In addition, because several sales employees work from home, the business wants to allow them to dial up their local servers from home.

Small Business Networking Examples

A Small-Scale VPN

A small business is adding remote sites and users at a hectic pace. Connecting them all via leased lines and dialup access would require the business to devote more time to administering its wide-area network and would mean dramatically higher line charges and long-distance phone bills each month. Instead, the company chooses to implement a VPN, with help from its SP. The SP has access points to its network across the nation, so the remote users can connect with their company's central network using inexpensive local calls. At the central site, a Cisco 1720 access router with the added VPN module provides an all-in-one solution for connecting to the SP (and the public Internet). It integrates a router, firewall, encryption and tunneling services, password protection, and a high-speed link to the central site LAN.

   

Basic Network Design: Issues & Answer

A Problem Solver's Guide to Relieving Congestion

Congestion is the networking term for too much traffic clogging network pathways. Common causes of congestion in today's networks include:

• Too many users on a single network segment or collision domain
• High demand from networked applications, such as groupware (for scheduling and appointments) and e-mail with large attached files
• High demand from bandwidth-intensive applications, such as desktop publishing and multimedia
• A rapidly growing number of users accessing the Internet
• The increased power of new PCs and servers

How to Spot Network Congestion
Some common indicators of network congestion include:

Increased Network Delay
All networks have a limited data-carrying capacity. When the load is light, the average time from when a host submits a packet for transmission until it is actually sent on the LAN is relatively short. When many users are vying for connections and communicating, the average delay increases. This delay has the effect of making the network appear "slower," because it takes longer to send the same amount of data under congested conditions than it does when the load is light.

In extreme circumstances, an application can fail completely under a heavy network load. Sessions may timeout and disconnect, and applications or operating systems may actually crash, requiring a system restart. But remember that many factors contribute to application performance (for example, CPU speed, memory, and disk performance). The LAN is only one of several possible bottlenecks.

Higher Network Utilization
One important measure of congestion is "channel utilization," which is the percentage of time that a channel is busy carrying data. It is directly related to the traffic load. Although many network management software programs offer visual displays of this information, special network monitoring equipment, such as protocol analyzers or Remote Monitoring (RMON) devices, may be required.

Many variables should be considered when trying to determine what constitutes acceptable utilization, including the number of stations on the LAN, software or application behavior, and network traffic patterns. In other words, is most traffic between users and a local server, or are users reaching out of their own segments across the network and creating congestion? For most small and medium-sized business environments, any of the following utilization levels can be used as general rules for determining when an Ethernet LAN is approaching excessive load:

• Twenty percent of full capacity, averaged over an eight-hour work day
• Thirty percent averaged over the worst hour of the day
• Fifty percent averaged over the worst 15 minutes of the day

Dissatisfied Users
Network speeds are partly subjective: the ultimate measure of LAN congestion is whether users can get their work done efficiently. If users are dissatisfied with network performance, there's a problem—regardless of statistics indicating the network is doing just fine. Note that user dissatisfaction with performance may not indicate a network congestion problem. The slowdown may be due to applications, computer CPU speeds, hard-disk performance, servers, and WAN access devices (slow modems or WAN connections).