Wireless Communication is the fastest growing and most vibrant technological areas in the communication field. Wireless Communication is a method of transmitting information from one point to other, without using any connection like wires, cables or any physical medium.
Generally, in a communication system, information is transmitted from transmitter to receiver that are placed over a limited distance. With the help of Wireless Communication, the transmitter and receiver can be placed anywhere between few meters (like a T.V. Remote Control) to few thousand kilometers (Satellite Communication).
We live in a World of communication and Wireless Communication, in particular, is a key part of our lives. Some of the commonly used Wireless Communication Systems in our day – to – day life are: Mobile Phones, GPS Receivers, Remote Controls, Bluetooth Audio and Wi-Fi etc.
What is Wireless Communication?Communication Systems can be Wired or Wireless and the medium used for communication can be Guided or Unguided. In Wired Communication, the medium is a physical path like Co-axial Cables, Twisted Pair Cables and Optical Fiber Links etc. which guides the signal to propagate from one point to other.
Such type of medium is called Guided Medium. On the other hand, Wireless Communication doesn’t require any physical medium but propagates the signal through space. Since, space only allows for signal transmission without any guidance, the medium used in Wireless Communication is called Unguided Medium.
If there is no physical medium, then how does wireless communication transmit signals? Even though there are no cables used in wireless communication, the transmission and reception of signals is accomplished with Antennas.
Antennas are electrical devices that transform the electrical signals to radio signals in the form of Electromagnetic (EM) Waves and vice versa. These Electromagnetic Waves propagates through space. Hence, both transmitter and receiver consists of an antenna.
What is Electromagnetic Wave?Electromagnetic Waves carry the electromagnetic energy of electromagnetic field through space. Electromagnetic Waves include Gamma Rays (γ – Rays), X – Rays, Ultraviolet Rays, Visible Light, Infrared Rays, Microwave Rays and Radio Waves. Electromagnetic Waves (usually Radio Waves) are used in wireless communication to carry the signals.
An Electromagnetic Wave consists of both electric and magnetic fields in the form of time varying sinusoidal waves. Both these fields are oscillating perpendicular to each other and the direction of propagation of the Electromagnetic Wave is again perpendicular to both these fields.
Mathematically, an Electromagnetic Wave can be described using Maxwell’s equations. Pictorial representation of an Electromagnetic Wave is shown below, where the Electric Field is acting in the Y – axis, magnetic field is acting in the Z – axis and the Electromagnetic Wave propagates in X – axis.
A Brief History of Wireless CommunicationSince the use of smoke signals, flags and flashing mirrors in the pre – historic period, Wireless communication has been a part of human life and it is continuously evolving. Modern Wireless Communication i.e., using electrical signals and radio waves for communication has been around us for more than 100 years.
In the year 1897, Guglielmo Marconi successfully demonstrated the Wireless Telegraphy by sending EM Waves for a short distance of 100 meters. This demonstration paved way for Radio Communication and the term Radio is derived from Radiant Energy.
By early 1900’s, Trans – Atlantic radio transmission had been established, where Marconi successfully transmitted messages in the form of Morse code. Since then, the technology related to wireless communication and wireless system has advanced rapidly and thus enabling transmissions over longer distances at low cost with cheaper devices.
Throughout the development of wireless communication, there are many wireless systems and methods that flourished and many got disappeared. The best example for this is Telephone Communication and Television Transmission. Initially, all telephone related communication was carried out (and still is) using wired network, which we call it as Landline Telephone.
But the rapid growth of Mobile Communication started to replace the complex wired telephone system. In this scenario, the wired technology became outdated and got replaced by wireless communication.
Another scenario where wireless communication got replaced by wired communication is Television broadcasting. In the early days, television signals were broadcasted using wireless radio transmitters. But this setup got replaced by cable television.
These two examples point out that with the development of technology, we always have to choose what’s best for the situation i.e., in some areas we have to use wired communication whereas in the other, going for wireless may be a better option.
Why Wireless Communication?When wired communication can do most of the tasks that a wireless communication can, why do we need Wireless Communication? The primary and important benefit of wireless communication is mobility.
Apart from mobility, wireless communication also offers flexibility and ease of use, which makes it increasingly popular day – by – day. Wireless Communication like mobile telephony can be made anywhere and anytime with a considerably high throughput performance.
Another important point is infrastructure. The setup and installation of infrastructure for wired communication systems is an expensive and time consuming job. The infrastructure for wireless communication can be installed easily and low cost.
In emergency situations and remote locations, where the setup of wired communication is difficult, wireless communication is a viable option.
Advantages of Wireless CommunicationThere are numerous advantage of Wireless Communication Technology, Wireless Networking and Wireless Systems over Wired Communication like Cost, Mobility, Ease of Installation, and Reliability etc.
CostThe cost of installing wires, cables and other infrastructure is eliminated in wireless communication and hence lowering the overall cost of the system compared to wired communication system. Installing wired network in building, digging up the Earth to lay the cables and running those wires across the streets is extremely difficult, costly and time consuming job.
In historical buildings, drilling holes for cables is not a best idea as it destroys the integrity and importance of the building. Also, in older buildings with no dedicated lines for communication, wireless communication like Wi-Fi or Wireless LAN is the only option.
MobilityAs mentioned earlier, mobility is the main advantage of wireless communication system. It offers the freedom to move around while still connected to network.
Ease of InstallationThe setup and installation of wireless communication network’s equipment and infrastructure is very easy as we need not worry about the hassle of cables. Also, the time required to setup a wireless system like a Wi-Fi network for example, is very less when compared to setting up a full cabled network.
ReliabilitySince there are no cables and wires involved in wireless communication, there is no chance of communication failure due to damage of these cables, which may be caused by environmental conditions, cable splice and natural diminution of metallic conductors.
Disaster RecoveryIn case of accidents due to fire, floods or other disasters, the loss of communication infrastructure in wireless communication system can be minimal.
Disadvantages of Wireless CommunicationEven though wireless communication has a number of advantages over wired communication, there are a few disadvantages as well. The most concerning disadvantages are Interference, Security and Health.
InterferenceWireless Communication systems use open space as the medium for transmitting signals. As a result, there is a huge chance that radio signals from one wireless communication system or network might interfere with other signals.
The best example is Bluetooth and Wi-Fi (WLAN). Both these technologies use the 2.4GHz frequency for communication and when both of these devices are active at the same time, there is a chance of interference.
SecurityOne of the main concerns of wireless communication is Security of the data. Since the signals are transmitted in open space, it is possible that an intruder can intercept the signals and copy sensitive information.
Health ConcernsContinuous exposure to any type of radiation can be hazardous. Even though the levels of RF energy that can cause the damage are not accurately established, it is advised to avoid RF radiation to the maximum.
Basic Elements of a Wireless Communication SystemA typical Wireless Communication System can be divided into three elements: the Transmitter, the Channel and the Receiver. The following image shows the block diagram of wireless communication system.
The Transmission PathA typical transmission path of a Wireless Communication System consists of Encoder, Encryption, Modulation and Multiplexing. The signal from the source is passed through a Source Encoder, which converts the signal in to a suitable form for applying signal processing techniques.
The redundant information from signal is removed in this process in order to maximize the utilization of resources. This signal is then encrypted using an Encryption Standard so that the signal and the information is secured and doesn’t allow any unauthorized access.
Channel Encoding is a technique that is applied to the signal to reduce the impairments like noise, interference, etc. During this process, a small amount of redundancy is introduced to the signal so that it becomes robust against noise. Then the signal is modulated using a suitable Modulation Technique (like PSK, FSK and QPSK etc.) , so that the signal can be easily transmitted using antenna.
The modulated signal is then multiplexed with other signals using different Multiplexing Techniques like Time Division Multiplexing (TDM) or Frequency Division Multiplexing (FDM) to share the valuable bandwidth.
The ChannelThe channel in Wireless Communication indicates the medium of transmission of the signal i.e. open space. A wireless channel is unpredictable and also highly variable and random in nature. A channel maybe subject to interference, distortion, noise, scattering etc. and the result is that the received signal may be filled with errors.
The Reception PathThe job of the Receiver is to collect the signal from the channel and reproduce it as the source signal. The reception path of a Wireless Communication System comprises of Demultiplexing , Demodulation, Channel Decoding, Decryption and Source Decoding. From the components of the reception path it is clear that the task of the receiver is just the inverse to that of transmitter.
The signal from the channel is received by the Demultiplexer and is separated from other signals. The individual signals are demodulated using appropriate Demodulation Techniques and the original message signal is recovered. The redundant bits from the message are removed using the Channel Decoder.
Since the message is encrypted, Decryption of the signal removes the security and turns it into simple sequence of bits. Finally, this signal is given to the Source Decoder to get back the original transmitted message or signal.
Types of Wireless Communication SystemsToday, people need Mobile Phones for many things like talking, internet, multimedia etc. All these services must be made available to the user on the go i.e. while the user is mobile. With the help of these wireless communication services, we can transfer voice, data, videos, images etc.
Wireless Communication Systems also provide different services like video conferencing, cellular telephone, paging, TV, Radio etc. Due to the need for variety of communication services, different types of Wireless Communication Systems are developed. Some of the important Wireless Communication Systems available today are:
There are many other system with each being useful for different applications. Wireless Communication systems can be again classified as Simplex, Half Duplex and Full Duplex. Simplex communication is one way communication. An example is Radio broadcast system.
Half Duplex is two way communication but not simultaneous one. An example is walkie – talkie (civilian band radio). Full Duplex is also two way communication and it is a simultaneous one. Best example for full duplex is mobile phones.
The devices used for Wireless Communication may vary from one service to other and they may have different size, shape, data throughput and cost. The area covered by a Wireless Communication system is also an important factor. The wireless networks may be limited to a building, an office campus, a city, a small regional area (greater than a city) or might have global coverage.
We will see a brief note about some of the important Wireless Communication Systems.
Television and Radio BroadcastingRadio is considered to be the first wireless service to be broadcast. It is an example of a Simplex Communication System where the information is transmitted only in one direction and all the users receiving the same data.
Satellite Communication System is an important type of Wireless Communication. Satellite Communication Networks provide worldwide coverage independent to population density.
Satellite Communication Systems offer telecommunication (Satellite Phones), positioning and navigation (GPS), broadcasting, internet, etc. Other wireless services like mobile, television broadcasting and other radio systems are dependent of Satellite Communication Systems.
Mobile Telephone Communication SystemPerhaps, the most commonly used wireless communication system is the Mobile Phone Technology. The development of mobile cellular device changed the World like no other technology. Today’s mobile phones are not limited to just making calls but are integrated with numerous other features like Bluetooth, Wi-Fi, GPS, and FM Radio.
The latest generation of Mobile Communication Technology is 5G (which is indeed successor to the widely adapted 4G). Apart from increased data transfer rates (technologists claim data rates in the order of Gbps), 5G Networks are also aimed at Internet of Things (IoT) related applications and future automobiles.
Global Positioning System (GPS)GPS is solely a subcategory of satellite communication. GPS provides different wireless services like navigation, positioning, location, speed etc. with the help of dedicated GPS receivers and satellites.
BluetoothBluetooth is another important low range wireless communication system. It provides data, voice and audio transmission with a transmission range of 10 meters. Almost all mobile phones, tablets and laptops are equipped with Bluetooth devices. They can be connected to wireless Bluetooth receivers, audio equipment, cameras etc.
PagingAlthough it is considered an obsolete technology, paging was a major success before the wide spread use of mobile phones. Paging provides information in the form of messages and it is a simplex system i.e. the user can only receive the messages.
Wireless Local Area Network (WLAN)Wireless Local Area Network or WLAN (Wi-Fi) is an internet related wireless service. Using WLAN, different devices like laptops and mobile phones can connect to an access point (like a Wi-Fi Router) and access internet.
Wi-Fi is one of the widely used wireless network, usually for internet access (but sometimes for data transfer within the Local Area Network). It is very difficult to imagine the modern World without Wi-Fi.
Infrared CommunicationInfrared Communication is another commonly used wireless communication in our daily lives. It uses the infrared waves of the Electromagnetic (EM) spectrum. Infrared (IR) Communication is used in remote controls of Televisions, cars, audio equipment etc.
ConclusionA brief overview on Wireless Communication, Advantages and Disadvantages, Different Types of Wireless Communication and also some important applications. If you feel we missed something or if you have a good point about wireless communication, please share so that other readers might find it useful.
What You Will Learn
After reading this chapter, you should be able to
Understand the components of a wireless network
Discover general wireless network architectural elements
Understand how information flows through a wireless network
Wireless networks utilize components similar to wired networks; however, wireless networks must convert information signals into a form suitable for transmission through the air medium. Even though wireless networks directly contribute only to a portion of the overall network infrastructure, attention to all network functions is necessary to counter impairments resulting from the wireless medium. This chapter discusses concepts common to all types of wireless networks, with emphasis on components and information signals.
A wireless network consists of several components that support communications using radio or light waves propagating through an air medium. Some of these elements overlap with those of wired networks, but special consideration is necessary for all of these components when deploying a wireless network. Figure 2-1 illustrates these primary components.
Figure 2-1 Wireless Networks Include Computer Devices, Base Stations, and a Wireless Infrastructure
A user can be anything that directly utilizes the wireless network. One of the most common types of user is a person. For example, a business traveler accessing the Internet from a public wireless LAN at an airport is a user. In some cases, however, the user might not be human. A robot, for example, might receive instructions over a wireless network from a central computer that controls a manu-facturing process. Because the wireless network exists to serve the user, the user is the component that receives the benefits of a wireless network. As a result, users are an important part of the wireless network.
The user initiates and terminates use of a wireless network, making the term end-user appropriate. Typically, a user operates a computer device, which often performs a variety of application-specific functions in addition to offering an interface to the wireless network.
Users of wireless networks tend to be mobile, constantly moving throughout a facility, campus, or city. Mobility is one of the most prominent benefits of deploying a wireless network. For example, a person walking through a convention center while sending and receiving e-mail from a PDA is exercising mobility. The PDA in this case must have continual or frequent connections to a wireless network infrastructure.
Some users might require only portability; whereby, they stay at a particular location while using the wireless network for a specific period of time. An example of this type of usage is someone operating a laptop wirelessly from a conference room. The user will turn on the laptop after sitting down in the conference room and shut off the laptop before leaving. As a result, the wireless network doesn't need to support continual movement.
Other users might actually be stationary, which means that they operate from one place for an indefinite period of time. An example of this type of user is someone working from a wireless computer in an office. The biggest difference between a stationary and portable user is that the stationary user will not require any form of roaming functions. Roaming functions are difficult to implement in some situations.
Many types of computer devices, sometimes referred to as clients, operate on a wireless network. Some computer devices might be specifically designed for users, whereas some computer devices are end systems. In generally, any computer device might communicate with any other computer device on the same wireless network. Figure 2-2 illustrates an assortment of computer devices for wireless networks.
Figure 2-2 Computer Devices for Wireless Networks Satisfy Different Applications
To support mobile applications, computer devices are often small, making them practical for people to carry with them at all times. These devices generally have small screens, limited keyboards, and small batteries. The devices are mobile, but they can support only certain applications.
With portable and stationary applications, however, the computer devices are much larger. These devices generally have larger displays and keyboards, making them more suitable to use when browsing the Internet and other applications requiring relatively high performance. The problem, however, is that these devices weigh more and are difficult to carry from one place to another.
Computer devices within a wireless network also include end systems such as servers, databases, and websites. For example, the http://www.cnn.com website includes news that someone can view from a public wireless LAN connection from a hotel room. Similarly, a clerk can wirelessly interface with a warehouse management system, which acts as an end-system computer device.
Users can adapt many existing computer devices to operate on a wireless network. A user, for example, can purchase and install a wireless network interface card (NIC) within his laptop to enable operation on a particular type of wireless network. Some devices, such as a wireless bar code scanner, operate only on a wireless network.
A computer device also has an operating system, such as Windows XP, LINUX, or MAC OS. The operating system runs software needed to realize the wireless network application. In some cases, the operating system has built-in features that enhance wireless networks. For example, Windows XP has the ability to automatically identify and associate with wireless LANs.
The network interface card provides the interface between the computer device and the wireless network infrastructure. The NIC fits inside the computer device, but external network adaptors are available that plug in and remain outside the computer device. Figure 2-3 shows examples of several types of wireless NICs.
Figure 2-3 Wireless NICs Have Various Types of Form Factors
Wireless network standards define how a wireless NIC operates. For example, a wireless LAN NIC might implement the IEEE 802.11b standard. In this case, the wireless NIC will only be able to interface with a wireless network infrastructure that complies with the 802.11b standard. As a result, users must be careful to ensure that the wireless NIC they choose matches the type of wireless network infrastructure they want to access.
Wireless NICs also comply with a specific form factor, which defines the physical and electrical bus interface that enables the card to communicate with the computer device. Again, the user must consider this to ensure that the chosen wireless NIC will fit within their computer device. The following is a summary of the different internal form factors available for wireless networks:
Industry-Standard Architecture (ISA)—ISA has been around since the early 1980s. Because of this, the proliferation of the ISA bus has been significant. Despite its limited performance, nearly all PCs manufactured up until recently had at least one ISA bus. The ISA bus has failed, however, to advance at the pace of the rest of the computer world, and other higher-speed alternatives are now available. ISA doesn't impose too much of a performance impact on 802.11b wireless LANs. It's not advisable, however, to purchase new ISA cards because of the possibility of them becoming obsolete.
Peripheral Component Interconnect (PCI)—The PCI bus is the most popular interface for PCs today and boasts high performance. Intel originally developed and released PCI in 1993, and it satisfies the needs of the recent generations of PCs for multimedia and graphics. PCI cards were the first to popularize "plug-and-play" technology, which makes it easy to install the NIC. PCI circuitry can recognize compatible PCI cards and work with the computer's operating system to set the configurations for each card. This saves time and prevents installation headaches for nontechnical users.
PC Card—The PC Card was developed in the early 1990s by the Personal Computer Memory Card International Association (PCMCIA). The PC Card is a credit-card-sized device that provides extended memory, modems, connectivity to external devices, as well as wireless LAN capabilities to small computer devices such as laptops and PDAs. In fact, they are the most widely available NICs available. They are more popular than ISA or PCI cards because of use in a growing number of laptops and PDAs.
It's possible to share a PC Card with a desktop PC by using an adaptor that converts a PC Card into a PCI card. This allows purchasing one NIC for use in both types of computers. You can take the PC Card with you on a business trip— or home from work— and utilize the same card when back in the office using a PC. Some PDAs require a sled device that accommodates the PC Card and mounts underneath the PDA. This is the only way to add wireless network capability to some older PDAs. The combination of the sled, PC Card and PDA, however, adds a lot of bulk and weight that depletes the usability.
Mini-PCI—A Mini-PCI card is a smaller version of a standard desktop PCI card and fits well within small, mobile computer devices. It has all the same features and functionality of a normal PCI card, but is about one quarter the size. Mini-PCI cards are integrated within laptops as an option to buyers. A strong advantage of this form of radio NIC is that it frees up the PC Card slot for other devices, such as memory extenders and graphics accelerators. In addition, manufacturers can provide Mini-PCI–based wireless NICs at lower costs. The Mini-PCI card is not without disadvantages, however. The replacement of a Mini-PCI card typically requires the disassembly of the laptop, which might void the manufacturer's warranty. Mini-PCI cards might also lead to lower performance because they require the computer to do some, if not all, of the processing. Despite these drawbacks, the Mini-PCI card is becoming a solid technology in the wireless laptop world.
CompactFlash—SanDisk Corporation first introduced CompactFlash (CF) in 1994, but wireless NICs were not available in CF form factors until recently. A CF card is small, weighing half an ounce, and is less than half the thickness of a PC Card. It also holds only one quarter the volume of PC Card radio card. The CF cards draw little power, which enables the batteries to last longer than devices using PC Cards. Some PDAs come with direct CF interfaces, which results in a lightweight and compact wireless PDA. If the computer device doesn't have a CF slot, you can purchase an adapter so that the CF card will fit into a standard PC Card slot. A CF radio card is definitely the way to go, especially for compact computing devices.
In addition to the internal NICs, a variety of external network interfaces connect to the computer device through parallel, serial, and USB ports. These might be suitable for stationary computers, but they certainly hinder mobility in most wireless applications.
As Chapter 3, "Radio Frequency and Light Signal Fundamentals: The Invisible Medium," discusses in detail, a wireless NIC includes an antenna that converts electrical signals to radio or light waves for propagation through the air medium. Antennae employ many structures, and they can be external, internal, permanent, or detachable. The antenna for a PC Card, for example, generally attaches to the end of the card and protrudes out the side of the laptop.
Mini-PCI cards, however, might have an antenna that resides inside the outer edge of a laptop monitor. Some NICs have antennaes that are permanent, which have one particular propagation pattern. Other NICs allow the replacement of the antenna, which increases flexibility in choosing an antenna that best satisfies requirements.
Air serves many purposes, such as providing a basis for speech, enabling air travel, and sustaining life. Air also provides a medium for the propagation of wireless communications signals, which is the heart of wireless networking. Air is the conduit by which information flows between computer devices and the wireless infrastructure. Think of communication through a wireless network as similar to talking to someone. As you move farther apart, it's more difficult to hear each other, especially when a loud noise is present.
Wireless information signals also travel through the air, but they have special properties that enable propagation over relatively long distances. Wireless information signals cannot be heard by humans, so it's possible to amplify the signals to a higher level without disturbing human ears. The quality of transmission, however, depends on obstructions in the air that either lessen or scatter the strength and range of the signals.
Rain, snow, smog, and smoke are examples of elements that impair propagation of wireless communications signals. In fact, a heavy downpour of rain can limit signal range by 50 percent while the rain is occurring. Other obstacles, such as trees and buildings, can impact the propagation and performance of the wireless network. These issues become most important when planning the installation of a wireless MAN or WAN.
With wireless networks, the air medium supports the propagation of radio and light waves that travel from one point to another. These types of signals have been in use for more than 100 years, but they are still somewhat mysterious and not well understood by most computer professionals. Chapter 3 provides details on signal characteristics and impairments that relate to the air medium.
The infrastructure of a wireless network interconnects wireless users and end systems. The infrastructure might consist of base stations, access controllers, application connectivity software, and a distribution system. These components enhance wireless communications and fulfill important functions necessary for specific applications.
The base station is a common infrastructure component that interfaces the wireless communications signals traveling through the air medium to a wired network—often referred to as a distribution system. Therefore, a base station enables users to access a wide range of network services, such as web browsing, e-mail access, and database applications. A base station often contains a wireless NIC that implements the same technology in operation by the user's wireless NIC.
Base stations go by different names, depending on their purpose. An access point, for instance, represents a generic base station for a wireless LAN. A collection of access points within a wireless LAN, for example, supports roaming throughout a facility. The NIC within a user's computer device connects with the nearest access point, which provides an interface with systems within the infrastructure and users associated with other access points. As the user moves to a part of the facility that's closer to another access point, the NIC automatically reconnects with the closest access point to maintain reliable communications.
Residential gateways and routers are more advanced forms of base stations that enable additional network functions. The gateway might have functions, such as access control and application connectivity, that better serve distributed, public networks. On the other hand, a router would enable operation of multiple computers on a single broadband connection.
As show in Figure 2-4, a base station might support point-to-point or point-to-multipoint communications. Point-to-point systems enable communications signals to flow from one particular base station or computer device directly to another one. This is a common infrastructure for supporting long-range wireless communications links. For example, a wireless Internet service provider (WISP) can use this system to transport communications signals from a base station at a remote site— such as a home or office— to a base station near a communications facility.
Figure 2-4 Base Stations Support Different Configurations
As the name implies, point-to-multipoint functionality enables a base station to communicate with more than one wireless computer device or base station. An access point within a wireless LAN implements this form of communications. The access point represents a single point whereby many computer devices connect to and communicate with each other and systems within the wireless infrastructure.
In the absence of adequate security, quality of service (QoS), and roaming mechanisms in wireless network standards, companies offer access-control solutions to strengthen wireless systems. The key component to these solutions is an access controller, which is typically hardware that resides on the wired portion of the network between the access points and the protected side of the network. Access controllers provide centralized intelligence behind the access points to regulate traffic between the open wireless network and important resources. In some cases, the access point contains the access control function.
Access controllers apply to a wide range of applications. In a public wireless LAN, for example, an access controller regulates access to the Internet by authenticating and authorizing users based on a subscription plan. Similarly, a corporation can implement an access controller to help a hacker sitting in the company's parking lot from getting entry to sensitive data and applications.
The use of an access controller reduces the need for smart access points, which are relatively expensive and include many non-802.11 features. Generally, vendors refer to these smarter access points as being enterprise-grade components. Proponents of access controllers, however, argue that 802.11 access points should focus on RF excellence and low cost. Proponents also argue that access points should centralize access control functions in an access controller that serves all access points. These thin access points primarily implement the basic wireless network standard (such as IEEE 802.11), and not much more.
The users of access controllers realize the following benefits when deployed with thin access points:
Lower Costs—Access points with limited functionality cost less, which generally results in lower overall system costs. This is especially true for networks requiring a larger number of access points, such as an enterprise system. The use of thin access points results in cost savings of approximately $400 per access point. In larger networks, this savings far outweighs the additional cost of an access controller, which costs $5000 on the average.
Open Connectivity—Smart access points offer enhancements related to security and performance to the basic wireless connectivity that wireless network standards offer. The problem in many cases is that these enhancements are only possible if the user devices implement a wireless NIC made by the same vendor as the access point. This significantly reduces the openness of the system and limits the selection of vendors. On the other hand, thin access points can easily communicate using the basic wireless network protocol with wireless NICs made by multiple vendors, while the access controller transparently provides enhancements.
Centralized Support—An advantage of placing the smarts of the network in an access controller is that the system is easier to support, primarily because fewer touch points are in the network. If all of the intelligence of the network is within the access points, support personnel must interface with many points when configuring, monitoring, and troubleshooting the network. An access controller enables the access points to have fewer functions, reducing the need to interface with the access points when performing support tasks.
Access controllers often provide port-based access control, allowing administrators to configure access to specific applications on a per-user basis. The port, which is actually a number (such as 80 for http), corresponds to a specific type of application. For example, an access controller can block access to port 80, which forces a user to log in before being able to browse web pages. After users enter their username and password, the access controller will validate their identity through an authentication server. The network application could, as an alternative, use digital certificates for authentication purposes. This function regulates the user access to the protected network.
Access controllers generally employ the following features:
Authentication—Most access controllers have a built-in database for authenticating users; however, some offer external interfaces to authentication servers such as Remote Authentication Dial-In User Service (RADIUS) and Lightweight Directory Access Protocol (LDAP). For smaller, private networks, an internal database might suffice. For enterprise solutions, however, external and centralized authentication servers provide better results.
Encryption—Some access controllers provide encryption of data from the client to the server and back, using such common methods such as IPSec. This provides added protection beyond what the native wireless network standard provides. Some of these features, however, are also part of web browsers.
Subnet Roaming—In order to support roaming from one network to another, access controllers provide roaming across subnets without needing to re-authenticate with the system. As a result, users can continue utilizing their network applications without interruption as they roam about a facility. This feature is especially useful for larger installations where access to the network for specific users will span multiple subnets.
Bandwidth Management—Because users share bandwidth in a wireless network, it's important to have a mechanism to ensure specific users don't hog the bandwidth. Access controllers provide this form of bandwidth management through the assignment of user profiles based on required QoS levels. A profile specifies the types of services, such as web browsing, e-mail, and video streaming, as well as performance limits. For example, an unsubscribed visitor attempting to utilize a public wireless LAN could classify as fitting a "visitor" profile, which might only allow access to information related to the local hotspot. A subscriber, however, could have a different role that allows him to have a broadband Internet connection.
Web surfing and e-mail generally perform well over wireless networks. All it takes is a browser and e-mail software on the client device. Users might lose a wireless connection from time to time, but the protocols in use for these relatively simple applications are resilient under most conditions.
Beyond these simple applications, however, special application connectivity software is necessary as an interface between a user's computer device and the end system hosting the application's software or database. Applications could be warehouse management software running on an IBM AS/400, a modeling application located on a UNIX box, or a time-management system residing on an old mainframe system. The databases are part of a client/server system where part, or all of the application software, resides on the client device and interfaces with a database such as Oracle or Sybase. In these cases, application connectivity software is important in addition to access points and controllers to enable communications between the user's computer device and the application software or databases located on a centralized server.
The following are various types of application connectivity software:
Terminal Emulation—Terminal emulation software runs on a computer device, making the device operate as a terminal that provides a relatively simple user interface to application software running on another computer. The terminal merely presents screens to the user and accepts input rendered by the applications software. For example, VT220 terminal emulation communicates with applications running on a UNIX host, 5250 terminal emulation works with IBM AS/400-based systems, and 3270 terminal emulation interfaces with IBM mainframes.
The advantage of using terminal emulation is its low initial cost and changes made to the application automatically take affect when the user logs in. Wireless systems using terminal emulation, however, might not be able to maintain continuous connections with legacy applications, which have timeouts set for more reliable wired networks. Timeouts will automatically disconnect a session if they don't sense activity within a given time period. As a result, IT groups might spend a lot of time responding to end-user complaints of dropped connections and incomplete data transactions. Therefore, implementing terminal emulation can have a disastrous effect on long-term support costs.
Direct Database Connectivity—Direct database connectivity, sometimes referred to as client/server, encompasses application software running on the user's computer device. With this configuration, the software on the end-user device provides all application functionality and generally interfaces to a database located on a central server. This enables flexibility when developing applications because the programmer has complete control over what functions are implemented—and is not constrained by a legacy application located on a central computer. Direct database connections are often the best approach when needing flexibility in writing the application software. A problem, however, is that the direct database approach depends on the use of Transmission Control Protocol/Internet Protocol (TCP/IP), which is not well-suited for communications across a wireless network.
Wireless Middleware—Wireless middleware software provides intermediate communications between user computer devices and the application software or database located on a server. (See Figure 2-5.) The middleware—which runs on a dedicated computer (middleware gateway) attached to the wired network—processes the packets that pass between the user computer devices and the servers. The middleware software primarily offers efficient and reliable communications over the wireless network while maintaining appropriate connections to application software and databases on the server through the more reliable wired network. Sometimes this is referred to as session persistence.
Figure 2-5 Wireless Middleware Efficiently Interconnects Computer Device Applications to Hosts and Servers
Look for the following features in middleware products:
Optimization techniques—Many middleware products include data compression to help reduce the number of packets sent over the wireless link. Some implementations of middleware use proprietary communications protocols, which have little overhead as compared to traditional protocols, such as TCP/IP.
Intelligent restarts—With wireless networks, a transmission can be unexpectedly cut at midstream. Intelligent restart is a recovery mechanism that detects the premature end of a transmission. When the connection is reestablished, the middleware resumes transmission from the break point instead of at the beginning. This avoids errors from occurring in applications that utilize databases.
Data bundling—Some middleware is capable of combining smaller data packets into a single large packet for transmission over the wireless network, which can help lower transmission service costs of WANs. Since some wireless data services charge users by the packet, data bundling results in a lower aggregate cost.
Screen scraping and reshaping—The development environment of some middleware products allows developers to use visual tools to shape and reshape portions of existing application screens to more effectively fit data on the smaller display of some non-PC wireless devices, such as PDAs and bar code scanners.
End system support—Wireless middleware interfaces with a variety of end system applications and databases. If clients need access to tomultiple types of applications and databases, wireless middleware acts as a concentrator. For example, a user can use the middleware connection to interface with applications on an AS/400 and UNIX box simultaneously without needing to be concerned about running the correct terminal emulation software.
A wireless network is seldom entirely free of wires. The distribution system, which often includes wiring, is generally necessary to tie together the access points, access controllers, and servers. In most cases, the common Ethernet comprises the distribution system.
The IEEE 802.3 standard is the basis for Ethernet and specifies the use of the carrier sense multiple access (CSMA) protocol to provide access to a shared medium, such as twisted-pair wiring, coaxial cable, and optical fiber. CSMA is the predominant medium access standard in use today by both wired and wireless networks.
CSMA enables sharing of a common medium by allowing only one NIC to transmit information at any particular time. This is similar to a meeting environment where people (like NICs) speak only when no one else is talking. This gives each person responsibility in a way that distributes speaking decisions to each person. If more than one person talks at the same time, a collision occurs, and each person needs to take turns repeating what he said.
All computer devices on the network must take turns using the medium with Ethernet hubs. An Ethernet switch, however, enables multiple collision domains that can allow simultaneous transmission among users to improve performance. For larger networks beyond the size of a home or small office application, be sure to use switches for optimum performance.
Ethernet employs twisted-pair wiring, coaxial cable, and optical fiber for interconnecting network devices, such as access points and other distribution equipment. The use of coaxial cables in older wired LANs was common 10 years ago, but today most companies use twisted-pair wiring and optical fiber. The Electronic Industries Association (EIA) and Telecommunications Industry Association (TIA) specifies Category 5 (referred to as Cat 5) twisted-pair wiring, the most popular of all twisted-pair cables in use today with Ethernet.
Cat 5 consists of four unshielded twisted pairs of 24-gauge wires that support Ethernet signals over 100 meters (m)— about 300 feet— of cabling. Ethernet repeaters increase this range if necessary, which is one method of reaching a wireless network base station that's beyond 100 m from a communications closet.
There are also other variations of twisted-pair wiring. Enhanced Cat 5 (referred to as Cat5e) makes use of all four pairs of wires to support short-range Gigabit Ethernet (1000 Mbps) connectivity. It is also backward compatible with regular Cat 5. Cat 6 and Cat 7 cable are now available, bringing more bandwidth and range to copper-based Gigabit Ethernet networks. Cat 7 cable features individually shielded twisted pairs (STP) of wires, making it ideal for installation in locations where there is a high potential for electromagnetic interference.
The following are specific types of twisted-pair options for Ethernet common to wireless LAN distribution systems:
10BASE-T—10BASE-T is one of the 802.3 physical layers and specifies data rates of 10 Mbps. A typical 10BASE-T cable uses two of the four pairs within a Cat 5 cable for sending and receiving data. Each end of the cable includes RJ-45 connectors that are a little larger than the common RJ-11 telephone connector used within North America.
The advantage of having extra pairs of wires open is support for other uses, such as Power-over-Ethernet (PoE). This is a mechanism in which a module injects DC current into the Cat 5 cable, enabling you to supply power to the access point from the communications closet. PoE often eliminates the need for having an electrician install new electrical outlets at every access point. For larger networks, definitely consider the use of PoE.
100BASE-T—Another 802.3 physical layer, 100BASE-T supports data rates of 100 Mbps. Similar to 10BASE-T Ethernet, 100-Base-T uses twisted-pair wiring, with the following options:
100BASE-TX uses two pairs of Cat 5 twisted-pair wires.
100BASE-T4 uses four pairs of older, lower-quality (Cat 3) twisted-pair wires.
Most implementations today use 100BASE-TX cabling. As with 10BASE-T, PoE can make use of unused pairs of wires. 100-Base-T4 was popular when needing to support 100-Mbps data rates over the older Cat 3 cabling, which was prominent during the early 1990s.
Optical Fiber—Optical fiber is more expensive than twisted pair, but fiber can be cost effective because it supports gigabit speeds and has a range of up to two kilometers. Instead of using the traditional electrical-signal-over-copper-wire approach, optical fiber cable uses pulses of light over tiny strips of glass or plastic. This makes optical fiber cable resistant to electromagnetic interference, making it valuable in situations where electronic emissions are a concern. In addition, it's nearly impossible to passively monitor the transmission of data through optical fiber cable, making it more secure than twisted-pair wiring.
With wireless LANs, optical fiber is a possible solution for reaching an access point located beyond a 100 m from a communications closet. This requires the use of an expensive pair of transceivers, however, which transforms electrical signals into light (and vice versa). One issue when dealing with optical fiber cable is the difficulties in splicing cables. You must work with glass or plastic materials that require precise alignment. You need special tools and training to make effective optical fiber cables. You should purchase precut fiber cables to avoid problems that are difficult to troubleshoot.
As with other types of networks, enterprise wireless networks require effective management that ensures user needs are met over the life of the network. A network management system, which involves both people and software tools, satisfies this need. The following are functions that management systems should provide.
The security element involves mechanisms that avoid the compromise or damage of network resources, such as databases and e-mail messages. This includes enforcing security policies for the configuration of the wireless network in a way that counters issues related to the propagation of wireless signals. For example, policies could specify the use of a particular type of encryption to ensure a mischievous person can't receive and decode e-mail messages being sent between a user and an access point.
For more details on wireless network security methods, refer to Chapter 8, "Wireless Network Security: Protecting Information Resources."
The help desk provides the first level of support for users. A user having difficulties with a wireless connection should know how to reach the help desk. Users often have problems with association or experience erratic performance.
Help desk personnel are capable of solving simple connection problems, such as assisting the user configure a radio card and operating system to comply with specific wireless network policies. The help desk should have a communications interface with more advanced support functions, such as maintenance and engineering, to solve more complex problems that arise from contact with users.
Configuration management consists of controlling changes made to the wireless network architecture and installed system. Changes might consist of installing or moving access points, changing access point parameters, and updating firmware. Because of the dynamic nature of wireless networks, changes are more common than with wired networks.
An enterprise should review all wireless network modification proposals that impact the performance or security of the network. This review enables a company to take into account relevant implications that involve additional costs and use of resources. The company should implement an independent design review process that evaluates each proposed wireless network solution and verifies conformance to a common architecture and support elements. The verification should, for example, include reviewing access point placement, radio frequency channel assignments, and security settings.
Network monitoring includes continuously measuring various attributes of the wireless network, including access point utilization and user traffic routes through the distribution system. This plays a key role in proactively managing the wireless network to support a growth of users and solve issues before they hamper the performance and security of the network.
An enterprise should continually measure the usage of base stations to properly scale the wireless network as user traffic changes. Base stations act as a gauge to indicate when additional base stations, access controllers, and Internet bandwidth are necessary. A problem with wireless networks is that network managers might not notice that a base station is inoperative for quite some time.
In most cases, coverage from base stations overlaps, and users will likely associate with another base station at lower performance if the primary access point is not available. Network monitoring tools, however, will notice the outage immediately and alert the appropriate support person. If possible, a company should integrate the wireless network monitoring function with tools already in use in the existing corporate network. This simplifies operational support.
The reporting element offers information regarding various aspects of the wireless network, including usage statistics, security alarm notifications, and performance. These reports are necessary for managers to effectively gauge the operation of the network and make decisions on changes. This reporting should, at a minimum, indicate potential breaches of security, inoperable access points, and utilization. This type of information should be available to all operational support functions, such as the help desk, maintenance, and engineering.
The engineering element provides advanced technical support for reengineering the wireless network to include newer technologies and solve problems to ensure effective performance and security. Ordinarily, the company or group that designs the initial wireless network will perform the engineering functions. The engineering function should review and verify compliance of designs with the common architectural design. In addition, the engineering group should continually monitor the evolution of wireless network technologies and products to ensure effective migration in a manner that meets growing network utilization.
The maintenance element repairs and configures the wireless network, including replacing broken antennae, setting channels on access points, and re-evaluating radio wave propagation. Some maintenance tasks might result from the engineering support function. For example, engineers might find the need to install an additional access point in an area where new coverage is necessary. In this case, maintenance personnel would install the access point at a location that the engineer identifies.
An important task for maintaining the wireless network is to periodically upgrade the firmware in access points. This ensures that the access point operates with the latest features and freedom from defects, which maximizes performance and security. As a result, a company should institute regular upgrades to firmware as new versions become available.
The maintenance group should also periodically perform coverage tests to ensure that the access points are properly covering the facilities at applicable levels of performance. This is necessary as the company modifies the structure of the facilities, which changes the radio wave propagation characteristics. If discrepancies are found, the maintenance group should report findings to the engineering group for resolution.