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NETWORKING TECHNOLOGIES OVERVIEW:
Understanding networking technologies helps you build a network design ranging from basic LAN access to more robust, open network solutions that meet growing demands for bandwidth-intensive applications. This guide allows you to review which technology approach is best for your network today and which will work best for you as your business needs grow.
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 accesses with collision detection.
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 resembles 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.
Basic Network Design:
Good Network Design: the 80/20 Rule
The key to good network design is how you place clients in relation to servers. Ideally, client computers should be placed on the same "logical" network as the servers they access most often. (By contrast, a "physical" network connection would mean that a client and server were attached to the same hub. A logical connection can be defined in your network software so that users in one area of a building can be in the same logical network segment as a server located at the opposite end of that building.) This simple task minimizes the load on the network backbone, which carries traffic between segments.
A good general rule: In a properly designed small to medium-sized network environment, 80 percent of the traffic on a given network segment should be local (destined for a target in the same workgroup), and not more than 20 percent of the network traffic could be moved across a backbone (the spine that connects various segments or "subnetworks"). Backbone congestion can indicate that traffic patterns are not meeting the 80/20 rule. In this case, rather than adding switches or upgrading hubs, it may be easier to improve network performance by doing one of the following:
Move resources (applications, software programs, and files from one server to another) to contain traffic locally within a workgroup.
Move users (logically, if not physically) so that the workgroups more closely reflect the actual traffic patterns
Add servers so that users can access them locally without having to cross the backbone. After you have ensured proper network design and resource location, the next step is to determine the optimal technology to meet your growing needs
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 Modem/Router
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.
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.
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 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.
Which Service Is Right for You?
The best service depends first of all on what is available in your area and then on what your usage will be and how much the services cost.
Analog services are least expensive, widely available, and easy to use. ISDN and DSL cost somewhat more, but both improve performance over even the fastest analog offerings at present. ISDN is more widely available than DSL and cable, making it more viable. Cable modems are faster still and inexpensive for Internet access, but they are available only in a small percentage of locations at present. Leased lines are the costliest of these options, but leased lines offer dedicated, digital service for more demanding situations. Which option is best? Answer the following questions:
Will employees use the Internet frequently?
Will you use the Internet for conducting business (for example, inventory management, online catalog selling or account information, bidding on new jobs)?
Do you anticipate a large volume of traffic between branch offices of your business?
Do you plan to use videoconferencing or video training among your locations?
Who will use your main-office connection to the Internet-individual employees at the central office, telecommuting workers dialing in from home, mobile workers dialing in from the road? The more times you answered "yes," the more likely it is that you need to move up the scale of connectivity choices-away from analog lines toward ISDN, DSL, or even leased lines.
It is also possible to mix and match services. For example, small branch offices or individual employees dialing in from home might connect to your central office using ISDN or DSL, while the main connection from the central office to the Internet would be a T1.
Which service you select also depends on what your ISP is using. It is important to understand that as the bandwidth increases, so do the charges, both from the ISP and the phone company. Keep in mind that rates for different kinds of connections vary from location to location. See the next chapter for illustrations of how various "wide-area" connections might work.
Also consider that a VPN can allow you to extend full private-network and Internet access to remote offices and individuals, at a significant savings compared to using leased lines or long-distance calls for remote connectivity. Ask yourself these additional questions:
Are you adding remote sites or remote users at a rapid pace?
Are your current remote-access line costs rising rapidly?
Would you rather focus on your core business than on building a WAN?
Do you plan to create an extranet, and offer password-protected access to suppliers, customers, or other trading partners?
Small Business Networking Examples
A Local-Area Network for a Small Office
This LAN starts simply shared Ethernet, with a pair of servers and analog modems connecting employees to the Internet. Employees can share documents, presentations, spreadsheets, and customer reports between computers; they can dial up the Internet for occasional research; they can communicate via e-mail; and the business can save money by sharing printers, modems, and hard-drive storage between users.
Because of the bandwidth demands that high-performance applications place on the network, traditional shared 10 Mbps Ethernet networks will not provide an adequate foundation for very long. In recent years, the price of 10/100 Mbps LAN switches has dropped significantly. Migrating from 10-Mbps shared Ethernet hubs to 100 Mbps Fast Ethernet switches, then, has become quite affordable, and customers can realize exponential network performance boosts at a very attractive price. In addition, they can gain these benefits with minimal disruption to their networks because Fast Ethernet is based on the same protocol as traditional Ethernet, and the expertise required is virtually the same.
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.
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