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DCTE 740 Term Paper
Small Business Local Area Networks
Ellen J. Cramer
DCTE 740 Telecommunications and Computer Networks ~ Summer Institute 1997
Dr. Marlyn Littman
Nova Southeastern University
(Please excuse the boring presentation. I saved this from a Word 97 file format to HTML.)
Table of Contents
Small Business Local Area Networks
Any office with more than one computer could benefit from some form of networking, but every situation requires a thorough analysis of the unique needs and resources to prepare for the best scenario. The employment trend is moving towards more self-employed or consultant status positions (Small Business Administration, 1996). This presents a need for more small or home offices. The self-employed person lacks the large company resources, but gains the flexibility to be creative in using the available limited resources. A small local-area network (LAN) in combination with a connection to a wide-area network (WAN) provides a functional system that does not limit the self-employed individual's ability to be productive in today's business or education climate. This paper is an analysis of a small LAN for an office located in a renovated two-story residential building in a rural area in central New York State.
The physical layout
The physical layout includes three computer stations spread out over two floors in three different rooms. The three computers are an evolutionary representative of the last seven years in personal computer options:
The modems can connect on one of the two analog telephone lines. The Internet is currently accessed via a local independent service provider with multiple email accounts available. Each area has an analog telephone in place. One area has a printer and a fax machine installed.
Client productivity network needs
Station A and B are currently used for:
Station C is used for word-processing and Internet access for browsing and chat. The printer is located at station B and is used by all parties for production of documents. To use the printer, station A and C manually transfer files to station B via 3.5-inch floppy disks. All stations need telephone access for voice communication.
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With this in mind, this residential office would benefit from a LAN deployment to allow for shared access to the printer and shared access to the Internet. The next step is to decide on the number of devices that are needed to connect to the network and how they can be used efficiently. That includes all computers and other networkable devices like printers, modems, or servers (Microage, 1997).
Figure 1. Diagram of the local area network plan for this small business office.
Station A has the largest hard-drive so will be used as a file server allowing for shared text, and applications as well as file storage to compensate for station C's small hard-drive space. Having the fastest modem, Station A will also be the Internet gateway. Due to the physical size of the offices and location of the printer and fax machine, Station B will be the printer server for the LAN. Therefore, there are three computer stations and they will be sharing the printer, modem, and applications with each other (see Figure 1). In the future, there may be more stations added and/or the shared devices may need a port of their own. A minimum of eight ports should be installed to accommodate this future growth potential.
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LAN standards are established by the IEEE 802 committee and adopted by the American National Standards Institute (ANSI) and the International Standards Organization (ISO) (Stallings & Van Slyke, 1998). The standards are organized into a three-layer protocol hierarchy. The top layer is logical link control (LLC), the common link protocol for all the LANs. LLC specifies the mechanism for addressing stations across the medium and for controlling the exchange of data between two users (Stallings & Van Slyke, 1998). The second layer is medium access control (MAC) and the third deals with the physical layer. In deciding what network paradigm to use for this project, the LAN technology was examined from the perspective of the last two layers of the standards. Because the physical dynamics of the setting help to determine what MAC option to use, the physical layer is discussed first in this paper then the MAC options.
The physical layer
The physical layer is delineated by the network topologies and physical medium through which they travel. There are three common choices of network topology: bus, ring, and star. The bus or tree topology is flexible and able to handle many devices at moderate data-rate requirements. The ring works well for very high speed links over long distances, but the ring is vulnerable to being totally disabled by one link failure. The star topology is useful in short distances and for a small number of devices at very high rates (Stallings & Van Slyke, 1998). In this small network, the star topology will be used to avoid dependence on each link's performance and to keep the options open to high-speed devices.
Four forms of transmission media are available: twisted pair, coaxial cable, optical fiber, and wireless. Twisted pair can be either shielded or unshielded. The star topology requires point-to-point links between each device and node and commonly uses twisted pair, optical fiber, or wireless transmission at data rates of 10-100 Mbps. Twisted pair is by far the most common medium used because it is associated with the more popular star topology. It is inexpensive, and very easy to install, troubleshoot, and repair (3Com, 1997; Bay Networks, 1996). Of the two types of twisted pair cable, unshielded twisted pair (UTP) is more commonly used (Bay Networks, 1996). Of the three categories of UTP 3, 4, or 5; UTP 5 is highest grade and is used in both common and fast networks at $15 per 50 feet.
Buses, hubs, and switches
A typical star layout has either a shared medium bus, a shared medium hub, or a switched hub. In the shared bus, all the stations share the total capacity of the bus. In a shared hub, only one station can transmit at a time to avoid collision. The switched hub increases the total capacity of the LAN by dedicating capacity to each station (Stallings & Van Slyke, 1998). The term hub is generally associated with Ethernet networks, while the term multistation access unit (MAU) is used to refer to the token ring wiring concentrator. They both function as network wiring concentrators. Stand-alone hubs are usually the least expensive type of hub and are often not managed. Stand-alone hubs are best suited for small, independent workgroups, departments, or offices typically with fewer than 12 users per LAN (Bay Networks, 1996).
Network interface cards (NICs)
NICs work with software to send and receive messages on the network. Every desktop or notebook computer on your network needs a NIC. Ethernet network interface cards are available in 10 Mbps, 10/100 Mbps, and 100 Mbps configurations. Dual function 10/100 Mbps network interface cards let you keep your options open if you're planning an upgrade to Fast Ethernet in the future (3Com, 1997).
The MAC layer
The function of the MAC layer is to control access to the transmission medium in an orderly and efficient manner (Stallings & Van Slyke, 1998). In the past, CSMA/CD (carrier-sense multiple access with collision detection) and Token Ring have been the two most commonly used options for the star topology in the second layer (MAC) of the IEEE 802 standards. There are also MAC layer standards for wireless and very fast LANs (FDDI, 100 Mbps Ethernet, and ATM).
Common slower LANs
CSMA/CD (IEEE 802.3) grew out of the commercial product called Ethernet. The specification for running Ethernet on UTP is called 10BASE-T. This stands for 10 Mbps, baseband signaling, over twisted pair cable (Bay Networks, 1996). IEEE 802.3 is a MAC standard, which controls access by having stations sense if the medium is busy and only transmits data if it is idle and ceases transmission if it detects a collision. After a collision, the station waits a random amount of time and attempts to transmit again (Stallings & Van Slyke, 1998).
The Token Ring (IEEE 802.5) standard was developed from IBM's commercial Token Ring LAN product. It specifies the use of shielded twisted pair wiring with data rates of 4 and 16 Mbps and unshielded rates at 4 Mbps. This is a flexible MAC where a token circulates around the ring to regulate access to provide for priority and guaranteed bandwidth services. Unfortunately, the Token Ring requires loss or duplicate token maintenance (Stallings & Van Slyke, 1998). Token Rings are more commonly used for larger industrial networks and due to higher maintenance needs, this technology option was eliminated.
Wireless standards are determined by another MAC called CSMA (IEEE 802.11). The IEEE 802.11 uses a contention mechanism to allow stations to share a wireless channel, based on CSMA (carrier-sense multiple access), like 802.3 but without the CD (collision detection) (WLANA, 1997). Wireless LANs use radio frequency or infrared to transmit data. Wireless can be used in combination with cabled LANs, where the machines that require mobility will be connected wirelessly and the stations that are permanent can be connected with cable (Wood, 1995).
Wireless can be useful at university settings, for warehouse inventory collection, or in hospitals to deliver patient information. It can be advantageous for difficult to wire buildings and for backup to wired networks (IBM, 1997). Peer-to-peer wireless LANs are self-defining since they permit direct communication between devices without going through a base station. The downside of this, is that security and network management concerns are not easily addressed and the range of communications is limited.
High speed LANs work well in a work place that needs to support multimedia applications including video-on-demand or videoconferencing. This is not necessary at this moment for this LAN, but the future may hold more need for large amounts of data transfer, like conferencing or a CD server. Scalability is a factor in deciding what technology to use.
The purpose of fast (100 Mbps) Ethernet is to take advantage of pre-existing, widespread use of the Ethernet principle at faster speeds. Two types of Fast Ethernet are available: 100base-TX, which runs over Category 5 UTP; and 100base-FX, which operates over multimode fiber optic cabling (Bay Networks, 1996). 100base-FX allows for the use of most multimedia applications, especially if there is only one station or server per segment (Fluckiger, 1995).
Fiber Distributed Data Interface (FDDI) provides data transport at 100 Mbps. It is not an IEEE 802 standard, but it was developed to conform to the IEEE 802 reference model (Stallings & Van Slyke, 1998). Originally, FDDI networks required fiber optic cable, but today they can be run on UTP as well. Fiber is still preferred in many FDDI networks because it can be used over much greater distances than UTP cable. Like Token Ring, FDDI uses a token passing media access method. It is also usually configured in a physical star topology. FDDI is used primarily as a backbone, a segment of network that links several individual workgroup or department LANs together in a single building. It is also used to link several building LANs together in a campus (Bay Networks, 1996).
ATM is a connection-oriented (virtual connection) service that allows multiple logical connections to be multiplexed over a single physical layer. The data is organized into fixed-sized "cells" that follow a single "virtual path" and are switched together (Stallings & Van Slyke, 1998). It can be used as a wide-spread transport technology, a connection from long distance services to user premises, or within sites as a LAN (IBM, 1997). ATM may run over optical fibers or twisted pairs. Multimedia is not a focus for this particular LAN, but if ATM becomes the commonly used technology, using the LAN ATM would be uniform with the long-haul ATM networks (Fluckiger, 1995).
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For most small networks, there is no need to buy new software to connect if most of the computers are using Windows 95 as their operating system. Windows 95 has built-in networking functions which allow computers to connect together and form a peer-to-peer network easily and inexpensively (3Com, 1997; MicroAge, 1997).
A peer to peer network with a hub is a recommended option with less than five computers (3Com, 1997; MicroAge, 1997). Each computer is an equal or "peer" of the others, and can share files and peripherals connected to the network. The biggest part of managing a network is knowing what is there. A small network is much easier to manage than a large one.
While a peer-to-peer network is a low-cost, easy-to-install solution, it is not as efficient for sharing large and complex files, such as databases or graphics. Since this network is not focused on databases or graphics at this time, a peer-to-peer setup will be used. This decision does not affect scalability for the future. If the needs of the network change, the hardware needs would remain the same if client/server software were added. i.Share is software available to allow the set up of multiple user access on one Internet account.
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In deciding what technology to use in a LAN, an important variable is cost. Determining a budget in terms of personal computer networks, the cost of the network should be far less than the cost of the same services without the network. The cost of this network needs to be less than buying another printer, two more telephone lines, and two more ISP accounts, which comes out to about $1380 for the first year (Table 1). The financial benefits of having the computer stations interconnected and communicating is not as easily measured, but increased productivity does mean increased financial worth.
Costs of having the same services for one year without a network.
Two telephone lines
Two ISP accounts
As the data rates increase, so does the cost for a network (Stallings & Van Slyke, 1998). The table below shows current market prices for the potential technologies and the speed at which each transfers data (CDW, 1997; Dell Computer, 1997; IBM, 1997; PC Connection, 1997; & PC Zone, 1997):
The cost and speed of three network interface cards (NICs) and a hub.
In looking at what the network needs are at this time, the future needs of the network, and the current cost of the technology, a decision was made to use Ethernet with UTP-5 wiring, a 10 base-T NIC and an 8-port-hub.
Windows 95 can be easily used as a network operating system (NOS). Two of the three computers have Windows 95 as their operating system. The computer that does not have Windows 95 can be upgraded for $95 (Microsoft, 1997). Other network operating systems, like Windows NT and Novell cost anywhere from $370-$740 for a five user license. This would be an unnecessary cost at this time. The software, i.Share, is advertised for around $70 for three users (CDW, 1997; PC Connection, 1997; PC Zone, 1997).
The overall cost of the proposed network (Table 3) at $480 easily meets the financial criteria of a total cost less than $1380 for the same services without creating a network. Any of the fast or wireless networks would be too expensive to justify at this time. There are some companies marketing "Networks in a Box" which include a package with three NICs, an 8-port hub, and three 50 foot wires at $270-$330. All things being equal, if the "Network in a Box" package meets the network's needs, the wiring is basically supplied for free (3Com, 1997; Rigney, 1997).
|10 base-T NICs and 8-port hub||
|i.Share and Windows 95 upgrade||
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A 10 base-T Ethernet will send data at a rate of 10 Mbps. That allows 100 nanoseconds per bit. Light and electricity travel about one foot in a nanosecond. Two stations can begin to send data at the same time, and their signals will "collide" nanoseconds later. When such a collision occurs, the two stations stop transmitting and try again later after a randomly chosen delay period (Gilbert, 1995).
A block of data transmitted on the Ethernet is called a "frame." The first 12 bytes of every frame contain the 6-byte destination address (the recipient) and a 6-byte source address (the sender). Each Ethernet adapter card comes with a unique factory-installed address. This hardware address guarantees a unique identity to each card. In normal operation, an Ethernet adapter will receive only frames with a destination address that matches its unique address, or destination addresses that represent a multicast message (Gilbert, 1995).
Ethernet is a fault-tolerant network. Since each station has its own wire connecting it to the hub, it is far less likely that any station can cause the entire network to fail. The hub also has a "partitioning" function built into it which allows it to detect a problem on any of its ports and if a problem is found, the node is disconnected from the rest of the network (Mazza, 1997). This isolates the problem until the faulty node can be diagnosed and repaired.
Because of this partitioning function built into the hubs and the star-wired topology, Mazza (1997) feels it is usually easy to troubleshoot a 10 Base-T network. One way of diagnosing problems is to rule out the problem by simply disconnecting stations from the hub one at a time until the network recovers. Usually, the hub will give an indication as to which node is causing a problem. Another advantage is that modifications to the Ethernet are not disruptive to the network. Disconnecting a node from the network has no effect on the rest of the network. Therefore, moving an attached device is simply a matter of unplugging it from the hub and reconnecting it somewhere else.
One disadvantage of an Ethernet is the limitation on distance. 10 base-T only allows distances from the hub to the node of 330 feet and 10 base-T is more sensitive to electrical noise than coaxial cable (Mazza, 1997). In some installations, this can be a major problem, but in this situation, the farthest wire will only travel 50 feet and there is not a large amount of electrical noise in this environment.
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The hardware and software have been ordered. When they arrive, time must set aside to implement the network. It should only take 1-2 days to run the wire and set the boxes in the wall. The workload timing needs to be analyzed to determine when the computers can be shut down to place the NICs into the processing units. The network manager needs to configure the software and hardware drivers for all the computers. Baring any major problems, this should only take one day. Each computer station user needs to be shown how to share their files and devices through Network Neighborhood, then shown how to access the other computers' files and devises. A written log of problems will be kept and assistance will be available to the users during business hours from the network manager. One of the reasons the Ethernet technology in a peer-to-peer network is favorable is because of its simplicity in management.
In this basic peer-to-peer environment, everybody is equal; there is no strong security control (Chernicoff, 1997). But each user can determine which resources they want to share with the other people on the network. Resources to share include programs, documents and other files, modems, and printers. Sharing resources makes them available for other network users to connect to and use. There are two ways to control access to shared resources (Windows 95 Networking Help, 1997):
Net Watcher is a built-in monitor program in Windows 95. It observes who is currently using the resources on your computer. It also allows you to add shared folders and disconnect users from your computer or from specific files (Windows 95 Networking Help, 1997).
The i. Share software (http://www.artisoft.com/ishare/index.html) which allows multiple users to access the Internet provides some security from Internet invasion. It acts as a firewall by preventing unauthorized intruders from accessing the LAN because TCP/IP packets never get beyond the single IP address. The product also offers built-in administration features that let you block access to selected Web sites and track Internet usage with two levels of password security (Kawamoto, 1997).
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Hopefully, the wires will make it through the walls, the connectors will be tight, the NICs will function with the software, and the whole thing will not crash. In the event the hardware and software function the way they are intended, the network users will be able to print without physically transferring the files via disks and will be able to access the Internet through the 56 Kps modem. Since this is a small office setting, it should be easy to tell if the users are able to perform their duties or if the network is getting in the way.
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