We will look at the typical wired network architecture and how it relates to the architecture and components of a wireless network. Wireless network design is different than wired network design, so we will look at the issues of capacity and coverage when designing a wireless network.
We will then learn about some of the different environments where wireless networks are commonly deployed. At times some of the pros and cons of wireless in the different environments will be looked at along with some of the areas of concern.
Core, Distribution, and Access
If you have ever taken a networking class or read a book about network design, then you have probably heard the terms core , distribution , and access when referring to networking architecture. Proper network design is imperative no matter what type of network topology is used.
The core of the network is the high-speed backbone or the superhighway of the network. The goal of the core is to carry large amounts of information between key data centers or distribution areas, just as superhighways connect cities and metropolitan areas.
The core layer does not route traffic nor manipulate packets but rather performs high-speed switching. Redundant solutions are usually designed at the core layer to ensure the fast and reliable delivery of packets.
The distribution layer of the network routes or directs traffic toward the smaller clusters of nodes or neighborhoods of the network. The distribution layer routes traffic between VLANs and subnets.
The distribution layer is akin to the state and county roads which provide medium travel speeds and distributes the traffic within the city or metropolitan area. The access layer of the network is responsible for slower delivery of the traffic directly to the end user or end node.
The access layer mimics the local roads and neighborhood streets that are used to reach your final address. The access layer ensures the final delivery of packets to the end user.
Remember that speed is a relative concept. Due to traffic load and throughput demands, as data moves from the access layer to the core layer, the speed and throughput capabilities will increase. The additional speed and throughput tends to also mean higher cost.
Just as it is not practical to build a superhighway so that traffic can travel between your neighborhood and the local school, it would not be practical or efficient to build a two-lane road as the main thoroughfare to connect two large cities such as New York and Boston.
These same principles apply to network design. Each of the network layers—core, distribution, and access—are designed to provide a specific function and capability to the network. It is important to understand how wireless networking fits into this network design model.
As you know from previous article, wireless networking can be implemented as either point-to-point or point-to-multipoint solutions. Most wireless networking is used to provide network access to the individual client stations and are designed as point-to-multipoint networks.
This type of implementation is designed and installed on the access layer, providing connectivity to the end user. 802.11 wireless networking is most often implemented at the access layer.
Wireless bridge links are typically used to provide connectivity between buildings in the same way that county or state roads provide distribution of traffic between neighborhoods.
The purpose of wireless bridging is to connect two separate wired networks wirelessly. Routing data traffic between networks is usually associated with the distribution layer.
Wireless bridge links cannot typically meet the speed or distance requirements of the core layer, but they can be very effective at the distribution layer. An 802.11 bridge link is an example of wireless technology being implemented at the distribution layer.
Although wireless is not typically associated with the core layer, you must remember that speed and distance requirements vary greatly between large and small companies and that one person’s distribution layer could be another person’s core layer.
Very small companies may even implement wireless for all networking, forgoing any wired devices. Higher-bandwidth proprietary wireless bridges and some 802.11 mesh network deployments could be considered an implementation of wireless at the core layer.
Capacity vs. Coverage
When a wireless network is designed, two concepts that typically compete with each other are capacity and coverage. In the early days of wireless networks, it was very common to install an access point with the power set to the maximum level to provide the largest coverage area possible.
This was typically acceptable because there were very few wireless devices. Since the access points were also very expensive, companies tried to provide the most coverage while using the fewest access points. Figure below shows the outline of a building along with the coverage area that is provided by three APs.
If there are few wireless stations, this type of wireless design is quite acceptable. With the proliferation of wireless devices, network design has changed drastically from the early days.
Proper network design now entails providing necessary coverage while trying to limit the number of devices connected to any single access point at the same time. This is what is meant by capacity versus coverage.
As you know, all of the client stations that connect to a single access point share the throughput capabilities of that access point. Therefore it is important to design the network to try to limit the number of stations that are simultaneously connected to a single access point.
This is performed by first determining the maximum number of stations that you want connected to an access point at the same time (this will vary from company to company depending upon network usage).
Then you need to determine how big the cell size needs to be to provide this capacity, and then you need to adjust the power level of the access point in order to create a cell of the desired size.
Figure below shows the outline of the same building, but since there are many more wireless stations, the cell sizes have been decreased while the number of cells has been increased. Another way of providing wireless support for a large capacity of users is by access point co-location.
Co-location refers to placing multiple access points near each other, where the RF signal from one AP could potentially affect the signal from another AP. 802.11b and 802.11g APs are only capable of having three access points in the same area without causing interference.
The three APs would need at least a five-channel separation to prevent RF interference. By co-locating three APs, theoretically the potential cumulative speed is three times the speed of a single AP (assuming the three APs are equal).
For example, three co-located 802.11g APs would provide a cumulative maximum speed of 162 Mbps (remember that actual throughput will be significantly less).
Access point co-location is recommended only when the concentration of users is so dense that even when the cell size is at its smallest, there are still more stations per cell than desired.
It is important to note that while the channels may be separate, it is crucial that the antennas have enough separation so they will not drown out the other signals.
This often will occur in large meeting halls or university lecture halls. When co-located, end users can be load-balanced and segmented by MAC filters or by separate SSIDs.
Co-location is a method of meeting capacity needs; however, cell-sizing is almost always the preferable method. Currently there are no standards for load balancing, so any load balancing technologies that exist are proprietary.
Corporate Data Access and End User Mobility
As corporations decide whether to install wireless networking, they typically look toward the wireless network to provide two capabilities to their existing network. The first is the ability to easily add network access in areas where installation of wired connections is difficult or expensive.
The second is to provide easy mobility for the wireless user within the corporate building or campus environment. The installation of wired network jacks is very expensive, often costing as much as or even more than $200 (in U.S. dollars) per jack.
As companies reorganize workers and departments, network infrastructure typically needs to be changed as well. Other areas such as warehouses, conference rooms, manufacturing lines, research labs, and cafeterias are often difficult places to effectively install wired network connections.
In these and other environments, the installation of wireless networks can save the company money and provide consistent network access to all users.
Another key reason for companies to install wireless networking is to provide continuous access and availability throughout the facility. With computer access and data becoming critical components of many people’s jobs, it is important for them to be continuously available and to be able to get up-to-the moment information.
By installing a wireless network throughout the building or campus, the company makes it easier for employees to meet and discuss or brainstorm while maintaining access to corporate data, email, and the Internet from their laptops, no matter where they are in the building or on the campus.
Whatever the reason for installing wireless networking, companies must remember its benefits and its flaws. Wireless networking is typically slower than wired networking and therefore cannot always provide a direct replacement to wired networking.
Wireless provides mobility, accessibility, and convenience, but can lack in performance and throughput. Wireless is an access technology, providing connectivity to end user stations.
Wireless should rarely be considered for distribution or core roles, except for building-to-building bridging. Even in these scenarios, make sure that the wireless bridge will be capable of handling the traffic load and throughput needs.
Network Extension to Remote Areas
If you think about it carefully, network extension to remote areas was one of the driving forces of home wireless networking, which also helped to drive the demands for wireless in the corporate environment.
As households connected to the Internet and as more households purchased additional computers, there was a need to connect all of the computers in the house to the Internet.
Although many people installed Ethernet cabling to connect the computers, this was typically too costly, impractical due to accessibility, or beyond the capabilities of the average homeowner.
Around this time 802.11b wireless devices were becoming more affordable. The same reasons for installing wireless networking in a home are also valid reasons for installing wireless in offices, warehouses, and just about any other environment.
The cost of installing network cabling for each computer is expensive, and in many environments running cable or fiber is difficult due to building design or aesthetic restrictions.
When wireless networking equipment is installed, far fewer cables are required, and equipment placement can often be performed without affecting the aesthetics of a building.
Bridging—Building-to-Building Connectivity
To provide network connectivity between two buildings, you can install an underground cable or fiber between the two buildings, you can pay for a high-speed leased telephone connection, or you can use a building-to-building wireless bridge.
All three are very capable solutions, each with its benefits and downfalls. Although a copper or fiber connection between two buildings will provide you with the highest throughput, installing copper or fiber between two buildings can be very expensive.
If the buildings are separated by a long distance or by someone else’s property, this may not even be an option. Once its installed, there are no monthly service fees since you own the cable.
Leasing a high-speed telephone connection can provide flexibility and convenience, but since you do not own the connection, you will pay monthly service fees. Depending upon the type of service that you are paying for, you may or may not be able to easily increase the speed of the link.
A wireless building-to-building bridge requires that the two buildings have a clear RF line of sight between them. Once this has been determined or created, a point-to-point or point-to-multipoint transceiver and antenna can be installed.
The installation is typically easy to perform by trained professionals, and once it’s installed, there are no monthly service fees since you own the equipment.
In addition to connecting two buildings using a point-to-point bridge, three or more buildings can be networked together using a point-to-multipoint solution.
In a point-to-multipoint installation, the building that is most centrally located will be the central communication point, with the other devices communicating directly to the central building.
This is known as a “hub and spoke” or star configuration. A potential problem with the point-to-multipoint solution is that the central communication point becomes a single point of failure for all of the buildings.
To prevent a single point of failure and to provide higher data throughput, it is not uncommon to install multiple point-to-point bridges.
Wireless ISP (WISP)
The term last-mile is often used by the telephone and cable companies to refer to the last segment of their service that connects the home subscriber to their network.
The last-mile of service can often be the most difficult and costly to run since at this point, a cable must be run individually to every subscriber. This is particularly true in rural areas where there are very few subscribers and they are separated by large distances.
In many instances, even if a subscriber is connected, since services such as xDSL have a maximum distance limitation of 18,000 feet (5.7 km) from the central office, the subscriber may not be able to receive some services such as highspeed Internet.
Wireless Internet service providers (WISPs) deliver Internet services via wireless networking. Instead of directly cabling each subscriber, a WISP can provide services via RF communications from central transmitters.
WISPs often use wireless technology other than 802.11, allowing them to provide wireless coverage to much greater areas. Service from WISPs is not without its own problems.
As with any RF technology, the signal can be degraded or corrupted by obstacles such as roofs, mountains, trees, and other buildings. Proper designs and professional installations can ensure a properly working system.
Small Office, Home Office (SOHO)
One common theme of a small or home office is that your job description includes everything from janitor to IT staff and everything in between. Small business owners and home office employees are typically required to be very self-sufficient since there are usually few if any other people around to help them.
Wireless networking has helped to make it easier for a small or home office employee to connect the office computers and peripheral devices together and also to the Internet.
The main purpose of a SOHO 802.11 network is typically to provide wireless access to an Internet gateway. Most small office, home office (SOHO) wireless routers provide fairly easy-to-follow installation instructions and offer performance and security near what their corporate counterparts provide.
They are generally not as flexible or feature rich as comparable corporate products, but most SOHO environments do not need all of the additional capabilities.
What the small or home office person gets is a capable device at a quarter of the price their corporate counterparts pay. Dozens of devices are available to provide the SOHO worker with the ability to install and configure their own secure Internet-connected network without spending a fortune.
Mobile Office Networking
Mobile home offices are used for many different purposes: as construction site offices, as temporary offices during construction or after a disaster, or as temporary classrooms to accommodate unplanned changes in student population.
Mobile offices are simply an extension of the office environment. These structures are usually buildings on wheels that can be easily deployed for short- or long-term use on an as-needed basis.
Since these structures are not permanent, it is usually easier to extend the corporate or school network to these offices by using wireless networking. A wireless bridge can be used to distribute wireless networking to the mobile office.
If needed, an AP can then be used to provide wireless network access to multiple occupants of the office. By providing networking via wireless communications, you can alleviate the cost of running wired cables and installing jacks.
Additional users can connect and disconnect from the network without having to make any changes to the networking infrastructure. When the mobile office is no longer needed, the wireless equipment can simply be unplugged and removed.
Moveable wireless networks are used in many environments, including military maneuvers, disaster relief, concerts, flea markets, and construction sites. Due to the ease of installation and removal, mobile wireless networking can be an ideal networking solution.
Educational/Classroom Use
Wireless networking can be used to provide a safe and easy way of connecting students to the school network. Since the layout of most classrooms is flexible (with no permanently installed furniture), it is not possible to install a wired network jack for each student.
Because students would be constantly connecting and disconnecting to the network at the beginning and end of class, the jacks would not last long even if they were installed.
Prior to wireless networking, in classrooms that were wired with Ethernet, usually all of the computers were placed on tables along the classroom walls, with the students typically facing away from the instructor.
Wireless networking allows any classroom seating arrangement to be used, without the safety risk of networking cables being strung across the floor.
A wireless network also allows students to connect to the network and work on schoolwork anywhere in the building without having to worry whether a wired network jack is nearby or whether someone else is already using it.
The use of wireless bridging is also very prevalent in campus environments. Many universities and colleges use many types of wireless bridge links, including 802.11, to connect buildings campuswide.
Industrial—Warehousing and Manufacturing
Warehouses and manufacturing facilities are two environments in which wireless networking has been used for years, even before the 802.11 standard was created.
Due to the vast space and the mobile nature of the employees in these environments, companies saw the need to provide mobile network access to their employees so they could more effectively perform their jobs.
Warehouse and manufacturing environments often deploy wireless handheld devices such as bar code scanners, which are often used for inventory control. Most 802.11 networks deployed in either a warehouse or manufacturing environment are designed for coverage rather than capacity.
Handheld devices typically do not require much bandwidth, but large coverage areas are needed to provide true mobility. Most early deployments of 802.11 frequency hopping technology was in manufacturing and warehouse environments.
Some legacy 802.11 FHSS deployments still exist today. Wireless networks are able to provide the coverage and mobility required in a warehouse environment and provide it cost effectively.
Healthcare—Hospitals and Offices
Although healthcare facilities such as hospitals, clinics, and doctors offices may seem very different than other businesses, they essentially have the same networking needs as other companies: corporate data access and end-user mobility.
Healthcare providers need quick, secure, and accurate access to their data so they can react and make decisions. Wireless networks can provide mobility, giving healthcare providers faster access to important data by delivering the data directly to a handheld device that the doctor or nurse carries with them.
Hospitals rely upon many forms of proprietary and industry-standard wireless communications that may have the potential of causing RF interference with 802.11 wireless networks. Medical carts used to monitor patient information often have wireless connections back to the nursing station.
VoWiFi is another common use of 802.11 technology in a medical environment. Many hospitals have designated a person or department to keep track of the frequencies and biomedical equipment that are used within the hospital to help avoid conflicts.
Public Network Access
The term hotspot typically refers to a free or pay-for-use wireless network that is provided as a service by a business. When people think of hotspots, they typically associate them with cafes, bookstores, or a hospitality-type business such as a hotel or convention center.
Hotspots can be used effectively by businesses to attract customers. Business travelers often frequent restaurants or cafes that are known to provide free Internet access.
Many of these establishments benefit from the increased business generated by offering a hotspot. Free hotspots have drawn much attention for the 802.11 wireless industry, helping to make more people aware of the benefits of the technology.
Other hotspot providers have had difficulty convincing people to pay upwards of $40 per month for a subscription. Many airports and hotel chains have installed pay-for-use hotspots; however, there are many different providers, each one offering a separate subscription from the other, which is often not practical for the consumer.
Most hotspot providers perform network authentication using a special type of web page known as a captive portal. When a user connects to the hotspot, the user must open up a web browser. No matter what web page the user attempts to go to, a logon web page will be displayed instead.
This is the captive portal page. If the hotspot provider is a paid service, then the user must enter either their subscription information, if they are a subscriber to the service, or credit card information, if they are paying for hourly or daily usage.
Many free hotspots also use captive portals as a method for requiring users to agree to a usage policy before they are allowed access to the Internet.
If the user agrees to the terms of the policy, they are required to either enter some basic information or click a button, validating their agreement with the usage policy. Many corporations also use captive portals to authenticate guest users onto their corporate networks.
