Wireless LAN Technologies Overview
In modern networks, the use of Wireless LAN technologies is becoming more common. This article will provide an overview of the available wireless LAN technologies, and then discuss the Cisco wireless solution.
Wireless LAN Overview
There are a number of different wireless LAN technologies available; these different technologies require the wireless implementation engineer to understand an alphabet soup of standards. All of the modern technologies are amendments of the original IEEE 802.11 standard. The most commonly known of these standards is the 802.11a, b, g and n amendments. As can be followed by the order in which the amendments are in the alphabet, the 802.11a and 802.11b standard were implemented widely first, followed by 802.11g and then 802.11n most recently. Each evolution of the standard added different range and speed advantages over the previous options. Table 1 shows a summary of the different 802.11 standards, their frequencies, bandwidth, and channel options.
As anyone who has implemented a wireless network has found out, there can be a number of different devices which overlap and operate in the same frequency ranges as used by the wireless LAN. On top of this, the 2.4 GHz band has a number of available channels which overlap into their neighboring channels. At this time, the 2.4 GHz band has more devices which contend for, or interfere with those devices trying to use the band. This is compounded by the fact that most of the initial wireless LAN devices used the 802.11b (then 802.11g) standard that operates in the 2.4 GHz band and thus can cause additional overlapping/interference problems. Figure 1 shows this 2.4 GHz band crowding problem in a standard apartment complex. As shown, within the range of a standard wireless router (or AP) there are a number of separate wireless networks which utilize the same channels within the 2.4 GHz band.
Figure 1 – 2.4 GHz channels
The 5 GHz band, while less cluttered then the 2.4 GHz band, had issues with initial implementation as the devices that were available in this frequency range (802.11a) were considerably more expensive than competing devices (802.11b) and were brought out much later. This difference in usage is slowly being remedied by the newer 802.11n devices that can support both the 2.4 and 5 GHz bands (not all devices do however). Figure 2 shows the utilization of channels in the 5 GHz band; each of these networks is using 40 MHz channel bandwidth which uses two available channels.
Figure 2 – 5 GHz channels
As shown in Table 1, there are a number of different channels which are available within the 2.4 and 5 GHz Wi-Fi bands. For devices using the 802.11b, 802.11g and 802.11n standards, the 2.4 GHz band is available with 14 total channels, 3 (or 4 in Japan) of which are non-overlapping with each other, these non-overlapping channels include channels 1, 6 and 11 (and 14 in Japan). For devices using 802.11a and 802.11n standards, the 5 GHz band is available with 23 (to 24) total channels, all which are non-overlapping. The number of channels that are permitted to be used in each specific locality changes as well; for example, in the U.S. only 11 of the 14 channels are available in the 2.4 GHz band.
As shown briefly in Figure 2, the 802.11n standard allows for both 20 MHz and 40 MHz channels; this is accomplished by combining the frequency ranges of two adjacent channels. While this may not cause an issue in the 5 GHz band, it could have issues with the already tight 2.4 GHz band. Some proprietary systems also use this method for providing double the bandwidth using the 802.11a and 802.11g standards (i.e. 108 Mbps).
Cisco LAN Technologies
Cisco offers a number of different wireless products, including products that support all of the available 802.11 standards reviewed above. There are two ways to implement Cisco Access Points (APs); each AP is configured as standalone (Autonomous) or by having lightweight APs that are configured and managed by a Wireless LAN Controller (WLC). The lightweight option gives the administrators the ability to centralize the management of the AP infrastructure, which can be easier to maintain than many individual standalone APs.
Lightweight Access Point Protocol (LWAPP)
In order to configure and manage the lightweight APs, Cisco’s wireless products use LWAPP. An important concept to understand about LWAPP is the use of Split MAC architecture. What this does is functionally split the duties of a standalone AP into two groups. The first group of duties is completed by the lightweight AP and the second group of duties is handled by the WLC. The following list shows the common duties which are completed by the lightweight APs and the WLC.
Lightweight AP duties:
- Frame exchange handshake between the wireless client and the AP
- Transmission of beacon frames
- Buffering and transmission of frames for clients in power save mode
- Response to probe request frame from clients; the probe requests are also sent to the WLC for processing
- Forwarding notification of received prove requests to the WLC
- Provision of real-time signal quality information to the switch with every received frame
- Monitoring each of the radio channels for noise, interference and other WLANs
- Monitoring for the presence of other APs
- Encryption and decryption of 802.11 frames
- 802.11 authentication
- o802.11 association and reassociation
- 802.11 frame translation and bridging
- 802.1x/EAP/RADIUS processing
- Termination of 802.11 traffic on a wired interface
The WLC tunnels the traffic from the lightweight APs using either layer 2 (via Ethernet) or layer 3 (via UDP).
The implementation of the available wireless LAN options provides mobility options, which allow for free movement within an organization. There are a number of different ways of utilizing these technologies, and how this is done is completely up to the organization implementing them. Cisco offers a number of different products, from support for small offices up to options for very large wide scale campus implementations.
Cisco Wireless Certifications
As with most of their certification tracks, Cisco has a Wireless track as well. This track includes the CCNA Wireless, CCNP Wireless and CCIE Wireless certifications.
Hopefully the information contained within this article will give a basic understanding of the wireless LAN technologies offered, and an overview of Cisco’s wireless implementation possibilities.
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