The evolution of the telephone reveals one consistent evolving design principle: People do not want to be tied down to a particular location when using the phone. The first phones were attached to the wall, and people leaned down or stood on their toes to speak into the horn and listen to the response. Then the mouthpiece and listening device were combined into a single handset and connected to the phone by a chord; the phone still hung on the wall, but a person could rest the handset against his head and talk to the other person comfortably.
Finally, the phone was liberated from the wall. A cable attached to the phone itself allowed the caller to comfortably move the phone around the room. The caller was still restricted by the length of the phone cable, but at least she could lay on the couch while talking to a friend.
Then came wireless phones. Throw away the cable; the caller could be anywhere in the house, or even in the garden outside, and still comfortably speak with friends and family. This change was revolutionary in the independence it provided.
This principle of independence applies to wireless LANs. Notebook computers and personal digital assistants (PDAs) are commonplace in corporations; people take their computers with them to meetings, customer sites, airports, and hotels. Until recently, this mobility meant dragging a cable and being restricted to sitting somewhere near the wall where the cable plugged into the network.
With wireless networking, the computing user can easily access the network wherever he is as long as a wireless access point is nearby. Breaking the dependence on a cable and a wall jack is quite liberating.
Some benefits realized with the introduction of wireless networking include the following:
Computer users can access the corporate network and Internet anywhere on campus. This offers unprecedented convenience and flexibility.
Temporary networks are easier to set up when making moves, adds, and changes or when setting up war rooms or temporary workspaces.
It is easier to collaborate on the spot. Users can exchange files or handle requests for information when in meetings, for example.
Users can exchange data with servers directly rather than wait to download it from a wired connection. This flexibility is important in warehouse and manufacturing, for example.
Recently, with the addition of LEAP and other security and encryption-related protocols, wireless LANs are as secure as wired LANs. Before the development of these protocols, hackers could easily join a wireless network and access corporate or personal data.
Wireless LANs are meant to complement existing wired networks. Wireless access points (similar to a traditional Ethernet hub) provide access to devices that have wireless network interface cards. The access points connect to an Ethernet switch and are typically configured on their own VLAN. Wireless bridges can provide wireless connectivity as well. This setup allows for longer distance connectivity between buildings, for example. The current wireless standards include 802.1a, 802.1b, and 802.1g.
In general, wireless LANs cannot achieve speeds as fast as wired networks. The size of the antenna and the transmission power setting of the interface card determine the distance, speed, and area between the transmitter and receiver. If you must achieve greater distance must be achieved, you can reduce the data rate. Tradeoffs occur between greater distance and faster transmission speeds.
As a user moves from one part of a building to another, the network must be able to switch which access point is associated with the user. This roaming happens automatically, invisibly to the user.
Security is a significant concern with wireless networking. Anyone with a wireless card can walk by a company building and possibly gain access to the corporate network. For example, a teleworker might be running a virtual private network (VPN) from her house to the corporate network and running wireless. Someone could easily access the corporate network with a wireless card from outside that person’s house.
Wireless security consists of authentication and privacy. Authentication ensures that only authorized persons can access the wireless LAN. Privacy provides a means to securely encrypt the traffic on the wireless LAN so that it cannot be intercepted. These means are effective in preventing unauthorized access to the wireless network.
At-A-Glance—Wireless LANs
A wireless local-area network (WLAN) is a network of computers or terminals connected by radio frequencies. Unlike traditional LANs, WLAN users are free to move about while staying connected to the network.
Because of this mobility, WLANs offers business great flexibility when implementing a new network or when looking for new office space. You can implement a wireless LAN in a building not set up for traditional networking, saving the time and expense of making a new space business-ready.
WLANs typically connect users to a corporate network, but they can also connect physically separated buildings. This implementation is referred to as a building-to-building bridge system.
The following are the advantages of WLANs over traditional LANs:
With LANs, PCs must plug into Ethernet jacks. On WLANs, PCs can access the network from anywhere on the campus.
With LANs, temporary networks are difficult to set up. With WLANs, temporary networks are easy to set up.
Users on LANs typically share data files after work sessions due to a lack of connections. On WLANs, users can easily share data and files during work sessions.
Wireless LANs present network administrators with some new issues:
Unlike fixed Ethernet, WLANs must trade off between throughput and the power consumption of mobile devices on battery power.
One of the advantages of WLANs is mobility. Therefore, WLANs must employ schemes that allow users to remain connected as they move about a building or campus.
WLANs present new security issues such as access control and data privacy.
In-building WLANs give employees the flexibility to move about freely while staying connected to the network.
The number of access points (APs) required depends on the size of the building and the desired throughput. You must make trade-offs between power, battery life, and transmission throughput. Remember that in addition to receiving a signal, the PC must transmit a signal to the nearest AP.
</division>At-A-Glance—Wireless LANs and Roaming
Wireless transmissions cause a large power drain on a laptop battery.
This figure shows the trade-off between coverage and throughput.
Direct Sequence Spread Spectrum (DSS) is a wireless multiplexing scheme for combining multiple signals into the same block of frequencies.
<division> <title>WLAN Roaming</title>Because wireless APs are relatively inexpensive, and the desire for bandwidth is high, most companies opt for deploying multiple APs with a reduced transmission radius and increased throughput. This solution introduces the need for a WLAN roaming scheme. Roaming describes switching from the control of one AP to another. You should position APs so there are no “dead spots.” As a user moves away from one AP, the power and signal quality decrease. A good roaming plan ensures that as this happens, another AP signal is sufficiently strong enough to take control of the wireless connection. The network controls this “handoff” transparently to the user.
Wireless handoff can only occur on the same WLAN. If a user moves between two WLANs, connectivity is lost until the device authenticates on the new WLAN.
</division>At-A-Glance—Wireless Bridges and Security
Wireless bridges create a single LAN by linking remote networks together. For simple networks, the bridge connects to a hub or a switch on the LAN. If the network contains multiple subnetworks, the bridge is connected to a router. Wireless bridges are a convenient and cost-effective solution for rapidly growing companies or for users located in areas where a fixed connection is either expensive or impractical.
In some cases, building-to-building wireless bridges offer superior price and performance over the following competing technologies:
Direct cable connections:
– High installation costs
– Difficulty overcoming physical barriers such as lakes, highways, and other buildings
– Often require approval from local governments
– Inflexible after deployment
Telephone-line connections
– High monthly service fees
– High installation and equipment costs
Microwave connections
– Expensive
– Require licensing
– Difficult to install
Security is a major concern for WLANs. The two main security issues for WLANs are
Access control—. Because WLANs use radio waves for access, any WLAN client in the area is capable of accessing the network. Some hackers access networks while sitting in a car outside of a building. Businesses should protect their networks with centralized user-authentication schemes to protect against unauthorized access.
Privacy—. Privacy is also an issue with WLANs. Unlike fixed connections, which send information point to point, WLANs broadcast information everywhere. Hackers can “scoop” this information out of the air. Therefore, it is essential to encrypt the data packets that transmit through the air.