Privately Owned Switches

In a corporate environment, where large numbers of staff need access to each other and the outside, individual telephone lines are not economically viable. A PBX is a smaller, privately owned version of the CO switches used by telephone companies, as illustrated in Figure 1-4.


Most businesses have a PBX telephone system, a key telephone system, or a Centrex service. Large offices with more than 50 telephones or handsets choose a PBX to connect users, both in-house and to the PSTN.

PBXs come in a variety of sizes, from 20 to 20,000 stations. The selection of a PBX is important to most companies, because a PBX has a typical life span of seven to ten years.

All PBXs offer a standard, basic set of calling features. Optional software provides additional capabilities.

A PBX connects to telephone handsets using line cards and to the local exchange using trunk cards.

A PBX has three major components:

• Terminal interface The terminal interface provides the connection between terminals and PBX features that reside in the control complex. Terminals can include telephone handsets, trunks, and lines. Common PBX features include dial tone and ringing.

• Switching network The switching network provides the transmission path between two or more terminals in a conversation. For example, two telephones within an office communicate over the switching network.

• Control complex The control complex provides the logic, memory, and processing for call setup, call supervision, and call disconnection.

PBX Installations

PBX switches are installed in large business campuses to relieve the public telephone company switches from having to switch local calls. When you call a coworker locally in your office campus, the PBX switches the call locally instead of having to rely on the public CO switch. The existence of PBX switches also limits the number of trunks needed to connect to the telephone company's CO switch. With a PBX installed, not every office desktop telephone needs its own trunk to the CO switch. Rather, the trunks are shared among all users.

Small organizations and branch offices often use a key telephone system, as shown in Figure 1-5, because a PBX offers functionality and extra features that they may not require. A key system offers small businesses distributed answering from any telephone, unlike the central answering position required for a PBX. Notice in Figure 1-5 that telephones interconnect to a key system via connector blocks, while trunks coming in from the local exchange interconnect to the key system via termination blocks.


Today, key telephone systems are either analog or digital and are microprocessor based. Key systems are typically used in offices with 30 to 40 users, but can be scaled to support over 100 users.

A key system has three major components:

• Key service unit A key service unit (KSU) holds the system switching components, power supply, intercom, line and station cards, and the system logic.

• System software System software provides the operating system and calling-feature software.

• Telephones (instruments or handsets) Telephones allow the user to choose a free line and dial out, usually by pressing a button on the telephone.

Larger companies use proprietary telephone networks with PBXs. In a key telephone system, each telephone has multiple lines that allow users to access outside lines to their CO. When a call comes into the company, a line or a key lights up on the telephone and indicates that a particular line is in use. Users can call another extension or let another person know where to pick up a call by using an intercom function, such as an overhead paging system or speakerphone.

Key telephone system functionality has evolved over time to include a class called hybrid telephone systems. The hybrid system adds many features that were previously available only in PBXs. There is no single definition of the functions and features that are classified as a hybrid system because all vendors provide a mix that they believe gives them a competitive advantage.

The main difference between a key telephone system and a hybrid telephone system is whether a single-line telephone can access a single CO local loop or trunk only (key telephone system) or whether the single-line telephone can access a pool of CO local loops or trunks (hybrid telephone system).

Introduction to Voice Technologies

Voice over IP (VoIP) is experiencing explosive growth. Many corporate environments have migrated, are actively migrating, or are researching the process of migrating to VoIP. Some long-distance providers are using VoIP to carry voice traffic, particularly on international calls. Companies, such as Vonage, offer VoIP service as a replacement for traditional telephony service in the home.

Migration is a process that involves gradually phasing out old components and replacing them with new ones. Many terms have been used to describe the technologies and applications for transporting voice in a converged packet network environment. When designing a converged network, it is necessary to clearly define all requirements and understand the various options that are available.

An important first step in designing a converged network is to understand the traditional telephony network and how it interfaces with voice components. You must know, from the start, how legacy voice equipment is connected and its possible migration paths.

The next step toward a good design is being knowledgeable about the components available for VoIP networks. You should be aware of the difference between voice and data flows within the network and the tools for controlling voice calls. Network requirements vary according to the size of the location. Knowing the difference between campus, enterprise, and service provider environments is crucial for choosing the right components and technologies.

This chapter provides an overview of the basic telephony functions and devices, including private branch exchanges (PBXs), switching functions, call signaling, and multiplexing techniques. It also reviews the basic components of the VoIP network and identifies the different requirements in campus, enterprise, and service provider environments. Together, these concepts and techniques provide a solid introduction to the VoIP arena.


Fundamentals of Telephony Networks

In traditional telephony networks, many components and processes are transparent to the customer. As you move from traditional telephony networks to converged voice and data networks, you must manage new components and processes to ensure seamless end-to-end call handling. To maintain acceptable service levels, you need to understand which devices you must now support and the processes that are necessary to ensure end-to-end call functionality.

Basic Components of Telephony Networks

A number of components must be in place for an end-to-end call to succeed. These components are listed here and shown in Figure 1-1:

• Edge devices

• Local loops

• Private or central office (CO) switches

• Trunks

Edge Devices

The two types of edge devices used in a telephony network include:

• Analog telephones Analog telephones are most common in home, small office/home office (SOHO), and small business environments. A direct connection to the public switched telephone network (PSTN) is usually made by using analog telephones. Proprietary analog telephones are occasionally used in conjunction with a PBX. These telephones provide additional functions such as speakerphone, volume control, PBX message-waiting indicator, call on hold, and personalized ringing.

• Digital telephones Digital telephones contain hardware to convert analog voice into a digitized stream. Larger corporate environments with PBXs generally use digital telephones. Digital telephones are typically proprietary, meaning that they work with the PBX or key system of that vendor only.

Local Loops

A local loop is the interface to the telephone company network. Typically, it is a single pair of wires that carry a single conversation. A home or small business may have multiple local loops.


Private or CO Switches

The CO switch terminates the local loop and handles signaling, digit collection, call routing, call setup, and call teardown.

A PBX switch is a privately owned switch located at the customer site. A PBX typically interfaces with other components to provide additional services, such as voice mail.


Trunks

The primary function of a trunk is to provide the path between two switches. There are several common trunk types, as shown in Figure 1-2, including the following:

• Tie trunk A dedicated circuit that connects PBXs directly

• CO trunk A direct connection between a local CO and a PBX

• Interoffice trunk A circuit that connects two local telephone company COs

The telephone installed in your home is considered an edge device because it terminates the service provided by your local telephone company. The local loop is the pair of wires that come to your house and provide residential telephone service. Trunks are the interconnections between telephone switches. They can be between private switches or telephone company switches.

CO Switches and Switching Systems

Figure 1-3 shows a typical CO switch environment. The CO switch terminates the local loop and makes the initial call-routing decision.


The call-routing function forwards the call to one of the following:

• Another end-user telephone, if it is connected to the same CO

• Another CO switch

• A tandem switch (that is, an intermediary switch between the source and destination switch)

The CO switch makes the telephone work with the following components:

• Battery The battery is the source of power to both the circuit and the telephone. It determines the status of the circuit. When the handset is lifted to let current flow, the telephone company provides the source that powers the circuit and the telephone. Because the telephone company powers the telephone from the CO, electrical power outages should not affect the basic telephone, also known as a POTS (plain old telephone service) phone.

• Current detector The current detector monitors the status of a circuit by detecting whether it is open or closed. Table 1-1 describes current flow in a typical telephone.

• Dial-tone generator When the digit register is ready, the dial-tone generator produces a dial tone to acknowledge the request for service.

• Dial register The digit register receives the dialed digits.

• Ring generator When the switch detects a call for a specific subscriber, the ring generator alerts the called party by sending a ring signal to that subscriber.

Some telephones on the market offer additional features that require a supplementary power source that the subscriber supplies; for example, cordless telephones. Some cordless telephones may lose functionality during a power outage.

When configuring a PBX connection to a CO switch, the signaling should match that of the CO switch. This configuration ensures that the switch and the PBX can detect on hook, off hook, and dialed digits coming from either direction.

Switching systems provide three primary functions:

• Call setup, routing, and teardown

• Call supervision

• Customer ID and telephone numbers

CO switches switch calls between locally terminated telephones. If a call recipient is not locally connected, the CO switch decides where to send the call based on its own call routing information, which is stored in a call-routing table. The call then travels over a trunk to another CO or to an intermediate switch that may belong to an inter-exchange carrier (IXC). Although intermediate switches do not provide dial tone, they act as hubs to connect other switches and provide interswitch call routing.

PSTN calls are traditionally circuit-switched, which guarantees end-to-end path and resources. Therefore, as the PSTN sends a call from one switch to another, the same resource is associated with the call until the call is terminated.

CO switches provide local service to residential telephones. The CO switch provides dial tone, indicating that the switch is ready to receive digits. When you dial your phone, the CO switch receives the digits, then routes your call. The call routing may involve more than one switch as the call progresses through the network.

Cisco Wireless Router and Switch Services

While the preceding devices are the most common that organizations use in constructing and maintaining a WLAN, Cisco offers other devices that can help your organization provide a robust, feature-rich wireless solution.


Cisco 3200 Series Wireless and Mobile Routers

To connect mobile networks to a wireless network, Cisco offers its Cisco 3200 Series wireless and mobile routers, shown in Figure 1-19. Contained in rugged enclosures and offering 802.11g functionality, these small devices (they are about as wide and long as a pen) can fit in vehicles or in outdoor locales. They offer the capability to transfer voice, data, and video across mobile wireless networks.


These routers are targeted at public safety, homeland security, defense agencies, and transportation agencies that need a durable router in a compact design that can be installed in vehicles.


Cisco Catalyst 6500 Series Switches

The Cisco Catalyst 6500 Series switches are a popular line of Cisco switches. In addition to serving wired clients, these switches can also be upgraded with a WLAN Services Module (WLSM). The WLSM is a key component of the Cisco SWAN architecture and enables fast, secure WLAN roaming within and across IP subnets. It also enhances WLAN security and smoothes out WLAN deployment and subsequent management.


Cisco Wireless 7920 IP Phone

Convergence is bandied about in the world of technology. Think of convergence as a techie's Swiss Army knife. We have cellular telephones that can play video games and MP3s players that can take pictures. Who knows what else they will be able to do in the coming years. Cisco is no stranger to the world of convergence. In the realm of wireless networks, one of the more compelling and useful devices is the Cisco Wireless 7920 IP phone. This telephone, shown in Figure 1-20, looks like a cellular telephone; however, it connects via the WLAN infrastructure (through an Aironet AP, for instance) then to the organization's gateway to allow VoIP telephone calls.

The phone uses the 802.11b protocol and Cisco CallManager. The product is ideally suited for environments in which users need telephony, but are constantly on the move and cannot be pinned down to a hardwired telephone. For example, hospitals, warehouses, universities, and retailers are ideally suited for these telephones.


Cisco Compatible Extensions (CCX)

As wireless technology has exploded in popularity, Cisco has seen the necessity for providing a mechanism through which third-party vendors can ensure compatibility among products. As a result, Cisco developed the CCX program.

Through the CCX program, WLAN vendors licensefree of chargeWLAN technology from Cisco. After that technology is implemented into the vendor's product, it is tested at an independent, third-party lab. If the product passes the testing procedures, the vendor is allowed to add a Cisco-compatible logo with the product, indicating that it not only works with Cisco equipment, but also takes advantage of advanced features. Intel is an example of this program in action. The company earned Cisco-compatible status with its Centrino mobile technology. This has been integrated in a number of laptop computers, such as Dell, Hewlett Packard, and Toshiba, among others.

The CCX program has been rolled out in three iterations. The requirements of CCX Version 2 build on the requirements of Version 1. For example, Version 1 of CCX security demands:

• WEP
• IEEE 802.11 and 802.1X
• Wi-Fi compliance
• Windows Hardware Quality Labs (WHQL)

Version 2 also requires WPA compliance.

From connection for two wireless clients working in ad hoc mode to a hospital nurse connected via a wireless IP phone; from an enterprise connecting its clients and office buildings in a MAN to police cars equipped with wireless routers, Cisco has a number of devices that enable a plethora of wireless networking functionality.

Version 3 includes EAP-FAST, wireless multi-media, CCKM for EAP-FAST, and single sign on.

Cisco Client Adapters

As we move down the wireless food chain, we come to the devices connecting users with the wireless network. Wireless adapters can be fitted to a multitude of devices client PCs, personal digital assistants, network printers, and so forth. Cisco offers four client adapters for its Aironet line:

• Cisco Aironet 350
• Cisco Aironet 802.11a, 802.11b, and 802.11g CardBus Wireless Client LAN Adapter
• Cisco Aironet 802.11a, 802.11b, and 802.11g Peripheral Component Interconnect (PCI) Wireless Client LAN Adapter
• Cisco Aironet 5 GHz 802.11a Adapter

The type of client adapter you use depends on what type of computer you need to connect. Laptops and other devices with Personal Computer Memory Card International Association (PCMCIA) and CardBus combination slots use a CardBus device. Desktop and tower-style PCs use PCI adapters.


Cisco Aironet 350


The entry-level model of Cisco client adapters is its venerable Aironet 350 adapter, shown in Figure 1-15. These adapters are designed as PCMCIA or PCI devices, which allow them to work with both desktop and laptop PCs.

These adapters can be used in either ad hoc (meaning two or more computers connect among themselves) or infrastructure environments (meaning the clients connect to a WLAN) and use the 802.11b protocol, which allows them to work in the 2.4-GHz band with a range up to 800 feet at 11 Mbps. Although this product operates at just 11 Mbps, it is compatible with 802.11g APs (although speed is limited to the adapter's top speed of 11 Mbps).


Cisco Aironet 802.11a, 802.11b, and 802.11g CardBus and PCI Wireless Client LAN Adapters

The Aironet 802.11 a/b/g CardBus and PCI Wireless Client LAN Adapters allow for a variety of uses and applications. Although they provide the same functionality, the difference between the CardBus and PCI devices is their physical design and construction. The CardBus devices are suited for laptops and tablet PCs, but the PCI device is meant for desktop PCs.

The CardBus device (shown in Figure 1-16) plugs into an open CardBus or combo CardBus/PCMCIA slot and the end sticks out an inch or so, allowing its internal antenna to communicate with the WLAN. The PCI device (shown in Figure 1-17) is a card that plugs into an open PCI slot on the PC. The card is connected to a small antenna that can be adjusted for best connectivity to the WLAN.


In spite of their physical differences, the devices offer the same functionality and are the most feature-rich and functional. They both offer:

• 802.11a coverage
• 802.11b coverage
• 802.11g coverage
• Dual mode 802.11a and 802.11g coverage
• Trimode 802.11a, 802.11b, and 802.11g coverage

These devices support Wi-Fi Protected Access (WPA) and WPA2. They also support 802.1X authentication, which includes LEAP, EAP-TLS, PEAP-GTC, EAP-FAST, and PEAP-MSCHAP V2.


Cisco Aironet 5 GHz 802.11a Adapter

The Cisco Aironet 5 GHz 802.11a Adapter serves clients that need access to a WLAN using 802.11a technology, shown in Figure 1-18. This device uses a CardBus form and is designed for use with APs, such as the Cisco Aironet 1200 Series 802.11a AP or the Aironet 1130AG AP.

Because the device offers 802.11a functionality, it operates at speeds of up to 54 Mbps in the 5-GHz band. Data rates can be reduced to extend the device's range.

The adapter uses the Cisco Wireless Security Suite, which offers the EAP framework for user-based authentication. It also supports a number of 802.1X authentication modes that include Cisco LEAP, EAP-TLS, PEAP, and EAP-SIM.

Cisco Wireless Bridges

In the past, connecting buildings on a campus or constructing a metropolitan-area network (MAN) required copper, fiber optic cabling, or expensive microwave equipment. Thanks to Wi-Fi technology, it is possible to unite geographically dispersed networks wirelessly. Cisco provides several options for wireless network connectivity.

The ranges for these devices depend on a number of factors, especially the antenna. Antennas are explained in greater detail in Chapter 2.

As you read through the product descriptions for APs and bridges (and later when client adapters are introduced), you might wonder why it is important to have an AP or bridge with a range of several thousand feet, or even a few miles, especially when client adapters can reach only a few hundred feet. It is important to understand that bridges and APs serve different functions. Although the job of an AP is to provide a point of connection to wireless clients, a bridge's main function is to connect with other bridges, and it serves as a link between two or more networks. APs, on the other hand, can also be added to enhance the range of a WLAN. Extending the network by adding APs can provide access to clients that are too far away from the WLAN to connect. As such, the greater ranges that APs and bridges afford are useful when bridges have to communicate with each other and when APs are placed to increase overall range.


Cisco Aironet 1300 Series as a Bridge

As noted in the previous section, the Cisco Aironet 1300 can be used as an outdoor AP or it can be used to connect several LANs in a MAN or campus environmentor even mobile networks. For optimal results in this capacity, the AP must be configured with the proper antenna.

The Aironet 1300 can serve as either a point-to-point or point-to-multipoint bridge. This is illustrated in Figure 1-12.


The Aironet 1300 bridge can also perform double duty. While connecting with bridges at other sites, the Aironet 1300 can simultaneously perform the functions of a wireless AP, accepting wireless clients.

If operating as a workgroup bridge, the Aironet 1300 connects wired Ethernet-enabled devices (laptops, network printers, and so on) to your WLAN. When the bridge is connected to an Ethernet switch, up to 255 devices can be added. Figure 1-13 illustrates this.

The Aironet 1300 comes with either integrated antennas or it can be purchased with connectors for external antennas.

As noted in the AP section, the Aironet 1300 bridge is capable of 802.11g. It offers a range up to 9 miles (in the United States) at 11 Mbps. For vehicle deployments, vehicles traveling over 60 mph (100 kph) with data rates at 12 Mbps and 24 Mbps and 128-byte packets experience a 1 percent packet error rate.


Cisco Aironet 1400 Series

Like the Aironet 1300, the 1400 seriesshown in Figure 1-14comes with either an integrated antenna or connectors for optional external antennas.

Using the 802.11a protocol, the Aironet 1400 with a built-in antenna allows 54-Mbps data rates up to 8.5 miles for point-to-point links and up to 2.75 miles for point-to-multipoint links. Adding an upgradeable antenna, speeds of 9 Mbps can be achieved at a distance of 23 miles.

The Aironet 1400 can be deployed in several ways, depending on your network's need. For example, it can be configured to be the singular connection between two geographically disparate networks. Alternately, it can be used as either the primary or the backup connection, in tandem with a second type of connection, such as a T1 line.

The Cisco Wireless Security Suite manages security on both the Aironet 1300 and 1400 series. Centralized management is employed through a Remote Authentication Dial-In User Service (RADIUS) server.

Cisco Aironet APs

APs are the devices that connect to the LAN, providing wireless access to the network. Wireless clients communicate with APs to access LANs or WLANs, as shown in Figure 1-1.


APs serve either as the core of an all-wireless network or as a point of connection between the wired and wireless networks. In addition, APs can be located throughout an organization to ensure access at remote locations in a facility.

Cisco features several models of APs. The model that fits best for your organization depends on a number of factors, which include:

• The number of wireless devices accessing the WLAN.
• The desired range.
• The desired speed.
• Your budget.

The following sections examine the Cisco Aironet APs, with specific details of each model.


Cisco Aironet 1100 Series
The Aironet 1100 AP (shown in Figure 1-2) includes a single radio and supports the 802.11g protocol. 802.11g is backward compatible to support the earlier 802.11b protocol. The most important distinction between 802.11b and 802.11g is the data rate802.11b provides 11 Mbps, whereas 802.11g allows up to 54 Mbps.


The 802.11b device can be upgraded to 802.11g capability. The 802.11g version allows wireless networks to leverage their investment on existing 802.11b equipment. It is also capable of 54-Mbps speeds with any new equipment. The Aironet 1100 AP allows the use of up to 16 virtual LANs (VLANs) and quality of service (QoS) functions. The AP also features hot standby and load balancing, which allow an organization to deploy intelligent network services and ensure network reliability and availability.

VLANs allow an organization to segment its users into their own discrete LANs. Thus, individual LAN policies, services, security levels, and QoS levels can be established for different groups of users.


Aironet 1130AG Series AP
The 1130AG AP builds on the functionality and utility of the Aironet 1100 Series AP. This AP uses two built-in radios (802.11a and 802.11g) for optimal coverage and usability.

Shown in Figure 1-4, the 1130AG AP employs two internal antennas for omnidirectional coverage. The ring on the front of the device changes color, depending on its current state. For example, when nothing is associated, the ring glows a pale green. When one or more devices have associated, it glows blue. If an error occurs, it glows red.


Because the AP employs both 802.11a and 802.11g radios, it affords a capacity of up to 108 Mbps. In addition, because both radios are used, it can handle 15, nonoverlapping channels (12 from the 802.11a radio and 3 from the 802.11g radio). In a future firmware upgrade, this capacity will increase to 22 channels. This will ensure less interference with neighboring WLANs and fewer transmission errors.


Cisco Aironet 1200 Series
The big brother to the Aironet 1100 is the Cisco Aironet 1200. The 1200 series (shown in Figure 1-5) incorporates single or dual radios, and it allows connectivity in both the 2.4-GHz (802.11g) or 5-GHz (802.11a) bands. The device can be configured for optimal flexibility (as shown in Figure 1-6), and it can be set up to operate solely in the 802.11a, 802.11b, or 802.11g mode. Alternately, it can be set in dual mode, which allows connectivity for clients operating in two different protocols. Ultimately, it can be set in trimode, to offer simultaneous service for all three protocols. This functionality provides great flexibility and return on investment because devices using any of the popular protocols can be used.


Like the Aironet 1100 series, the Aironet 1200 offers up to 16 VLANs, QoS capabilities, and Cisco Wireless Security Suite manages its security set.

The Aironet 1200 series is an important component in the Cisco Structured Wireless-Aware Network (SWAN). SWAN is a framework for deploying, operating, and managing thousands of Aironet APs when using a Cisco infrastructure.

For 802.11a networks, the Aironet 1200 series offers a variety of antennas including one that can be configured omnidirectionally (in a circle surrounding the AP) or as a patch antenna that directs a hemispherical signal from the wall and across the room.


Aironet 1230AG Series AP
The Aironet 1230AG Series AP provides many of the same features as its younger brother, the 1130AGchiefly dual 802.11a and 802.11g radios. However, the Aironet 1230AG is designed for environments in which omnidirectional antennas would be lacking. The 1130AG AP employs only internal antennas, but the 1230AG AP features connectors for external antennas.

This is ideal in environments such as factories, warehouses, or large retail facilities that require specialized antennas for proper functionality. Figure 1-7 shows this device.


Like other AP offerings from Cisco, the Aironet 1230AG AP is a component of the Cisco SWAN framework that delivers an integrated wired and wireless network.

Because the device uses both 802.11a and 802.11g radios, up to 15 nonoverlapping channels are available. This number will increase to 22 channels in a future firmware release.

The Aironet 1230AG AP is rugged enough to withstand high levels of heat.


Cisco Aironet 1300 Series
For outdoor wireless applications, Cisco offers its Aironet 1300 Series of APs, shown in Figure 1-8. These APs are encased in a tough, durable exterior, which makes them well suited for operation in the elements. In addition to its work as an AP, this device is also used as a network bridge.

The Aironet 1300 supports the 802.11g standards, providing data transfer rates of up to 54 Mbps.

These APs are not just for employees to take their laptops outside during lunch breaks. A number of organizations that benefit from an outdoor AP include the following:

• Campus networks For multibuilding organizations (schools, apartment buildings, hospitals, and so on), Wi-Fi makes interbuilding networks easy and inexpensive.
  

• Nomadic users Networks and users are not just tethered to their desks, offices, or even buildings. Many users work in trucks, vans, cars, or ambulances and require connectivity to the network. To resolve this problem, outdoor, Wi-Fi networks come in handy.
  

• Outdoor public access Wi-Fi hotspots pop up at many places, such as coffee shops, libraries, hotels, and now truck stops. As hotspots grow, devices such as the Cisco Aironet 1300 can be employed to provide Wi-Fi access to large outdoor areas.
  

• Temporary access The Aironet 1300 is a good solution when a temporary wireless network is needed. For example, aid workers caring for victims of a natural disaster can employ this sort of device to provide easy, reliable connectivity among its users and devices.

Airespace

Cisco completed its acquisition of a company called Airespace in early 2005. Now, the new Cisco 1000 Series Lightweight AP and WLAN controllers are included in its Wi-Fi catalog. These components work in tandem to deliver easy setup and configuration and a robust radio frequency (RF) environment.

Cisco 1000 Series Lightweight AP
This device has its benefits. It can be installed and connected to the network, with no configuration or setup needed on the AP, because configuration data is downloaded to the thin AP from a WLAN controller. This device is shown in Figure 1-9.

Although its easy installation and setup are big selling points for this device, it does much more. Because the AP's functioning is somewhat centralized to the WLAN controller, the AP can feed information about the RF environment back to the WLAN controller and the Cisco Wireless Control System. This allows these applications to make real-time decisions.

The data is forwarded and the RF environment monitored, which eliminates the need for additional nodes dedicated to those management functions. In turn, the overall network design is much simpler and more cost efficient. Within the 1000 series are three models:

• 1010 Offers two internal, sectorized antennas, used in places such as classrooms or office spaces.
  

• 1020 Offers two internal, sectorized antennas and connectors for external antennas, used in places such as factories or for outdoor applications.
  

• 1030 Offers two internal, sectorized antennas and connectors for external antennas. Also known as a Remote-Edge AP, this device is designed for use at branch offices to communicate with centrally located WLAN controllers using WAN technologies. This allows IT staff to centrally control service set identifiers (SSID), security settings, and configuration for a cohesive wireless environment.

The 1000 series allows power over Ethernet connections and over the air QoS.

The 1000 series also operates using 802.11a and 802.11g radios, affording compatibility with both standards and operation on up to 15 nonoverlapping channels.

Cisco WLAN Controllers

Earlier, we discussed the lines of the Cisco Lightweight APs. The APs and wireless control system are two legs of a three-legged stool; WLAN controllers comprise the other.

WLAN controllers are the hub of systemwide WLAN operation. They are the devices on which information is stored and disseminated to thin APs. In return, environmental data is sent back to the WLAN controller for analysis and action. The information stored on the WLAN controllers includes:

• Voice and data service
• Security policies
• Intrusion prevention
• RF management
• QoS
• Mobility
• Thin AP configuration

WLAN controllers communicate with the thin APs over Layer 2 or Layer 3 infrastructure using the Lightweight Access Point Protocol (LWAPP). This protocol ensures that communication between WLAN controllers and thin APs is secure.

Cisco offers three series of WLAN controllers: the 2000 Series, the 4100 Series, and the 4400 Series.

The Cisco 2000 Series WLAN controller is targeted at small- to medium-sized enterprise applications. Its 2006 model is capable of controlling up to 6 thin APs. The 2000 is shown in Figure 1-10.


The Cisco 4100 Series WLAN controller is targeted at medium- to large-sized enterprise applications. Its three modelsthe 4112, 4124, and 4136offer support to 12, 24, or 26 thin APs, respectively. This series features dual Gigabit Ethernet uplinks for LAN connectivity. The 4100 Series is shown in Figure 1-11.


These WLAN controllers can detect and adapt to changes in the RF environment. This level of management affords the following functionality:

• Channels are dynamically assigned to optimize network coverage and lessen interference.
• The system detects interference and makes changes to the network to remedy the interference.
• Load balancing prevents a large number of users from overburdening a specific thin AP.
• The power outpoint of the thin APs is adjusted to detect and correct coverage holes.
• Power is automatically adjusted across the network to specific APs, based on changing network conditions.

WLAN controllers use up-to-date security features that include WPA2, WPA, WEP, multiple EAP types, and a VPN termination module for IPSec and Layer 2 Tunneling Protocol.

Other security features include:

• The capability to detect and avoid unwanted RF propagation.
• Intrusion prevention and location to ensure that rogue APs are not only found, but located.
• Network admission control that manages client access based on policies.

Because the WLAN controller operates at both Layer 2 and 3 levels, users can roam among APs, switches, and routed subnets without interruption in service. In addition, security and QoS information follows them, so the operation environment is consistent.