Switching – Wireless concepts


Hello dear readers,

   This article will be focused in explaining the elements, roles and functionality of wireless connections. I always had problems with remembering all the encryption methods and algorithms, all the wireless technologies with all their names and numbers so this is why I will try to put them all together to enlighten anyone that is in the same situation. I hope you will enjoy this post, feel free to leave any comment or post any question that you have. I really appreciate when you are straight forward and say whatever is on your mind. I know that there are probably a lot of things to say about the wireless technology, this is why I encourage you to say whatever there is to say.
   Usually, businesses today use both physical and wireless connections. Wireless local area networks (WLANs) are more and more demanded in companies around the world. The main qualities of wireless networks are their flexibility, management and easy implementation. I will explain in this article how to configure, secure and implement a wireless network. Another aspect that you will need to consider is the area coverage of wireless networks. People moved slowly from physical workstations to wireless laptops, PDAs, mobile phones etc. Along with this migration, wireless networks became the crucial point in this transition. Everywhere from work places to home networks, people prefer the use of wireless network instead of physical connections. There are four main wireless technologies used today:
PAN (Personal Area Network)
LAN (Local Area Network)
MAN (Metropolitan Area Network)
WAN (Wide Area Network)
I will not talk much about these because they are not studied for the CCNA exam. You will have to know that they differ from each other in terms of area coverage, speed and applications. You can read more on this article from Wikipedia: http://en.wikipedia.org/wiki/Wireless_network.
WLAN connections use the RF(radio frequency) spectrum and are also known as 802.11 wireless LAN standard. RF uses the air medium to transmit signals from one point to another. These waves can be sent anywhere and through almost all materials. One big problem with wireless networks is the possibility of interference with other RF signals. Two devices that transmit RF signals between them must use the same transmission channel. Devices that use wireless connections must have a WNIC (Wireless Network Interface Card) hardware installed. Unlike Ethernet networks, wireless networks communicate using Access Points (AP) which are physical wireless devices. Another aspect of wireless technologies is the use of Collision Avoidance mechanism instead of Collision Detection. I don’t have a table with all the wireless standards, I will post a link from Wikipedia in which you can see all the available wireless standards used today: http://en.wikipedia.org/wiki/IEEE_802.11. What you will have to remember from here is that 802.11a and 802.11g have higher speeds (54 Mbps) than 802.11b (11 Mbps) and also they use a different modulation technology. 802.11b uses the DSSS (Direct Sequence Spread Spectrum) and 802.11a and 802.11g uses OFDM (Orthogonal Frequency Division Multiplexing). Remember that the area of coverage and the channels used are different from one technology to another. The 802.11n standard is a newer and much faster technology that uses a different band and modulation.
But what about the components needed in wireless communications? As I’ve written earlier, Wireless NICs are used as the main hardware component to transmit RF waves from one point to another. They encode data into RF signals by using the modulation mechanism. From mobile phones to laptops and even desktop computers, all use Wireless Network Interface Cards to communicate throughout the radio frequency spectrum. Usually, devices communicate with each other using Access Points (AP). These are physical devices, that convert Ethernet frames (802.3) into wireless frames (802.11), used in wireless communications. In wireless technologies, users must associate their devices with one AP in order to communicate with other wireless devices. Unlike Ethernet standard, wireless connections use the CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) technology. The mechanism of this technology is pretty simple, devices must first check the RF spectrum before transmitting frames. If a signal is detected then they must wait until the medium is free. Once frames are received by APs, ACK(acknowledgement) messages are exchanged between the two transmitting nodes. This technology has a problem, wireless signals are affected by attenuation. This means that the more distant wireless devices are from the AP, the more weaker the signal is. This issue has introduced the hidden node problem (from Wikipedia: “In wireless networking, the hidden node problem or hidden terminal problem occurs when a node is visible from a wireless access point (AP), but not from other nodes communicating with said AP” http://en.wikipedia.org/wiki/Hidden_node_problem). To connect one wireless network to another, you can use a classic network router or a wireless router. This is nothing more than a physical wireless device that acts like a gateway for devices that are behind it. When configuring a wireless Access Point, you will have to specify the SSID (Service Set Identifier) which is an element that identifies wireless connections. Also, always check to see if the mode (it can be mixed-mode to support multiple standards or single-mode to support only one) that the AP uses is the one that you need (802.11a,b,g or n) and that the channels are different from one AP to another in order to avoid interference. Check this Wikipedia link to see an image with the available channels: en.wikipedia.org/wiki/List_of_WLAN_channels.
In terms of wireless topology, there are three main topologies used today:
Ad hoc – wireless networks that do not use APs. Devices communicate directly with each other (low coverage or BSA-Basic Service Area)
BSS (Basic Service Set) – a wireless network that uses an AP to provide the wireless communication channel between devices.
ESS (Extended Service Sets) – multiple BSSs connected between each other to provide an extended are of wireless coverage (multiple APs are connected to form a larger wireless network).
The association between a wireless device and an AP is made by using the following steps:
APs send beacons which are wireless messages that contain the SSID, speed rates and the authentication method. The beacons are received by wireless devices which will try to establish a connection with the AP. If wireless hosts are already configured for one wireless network, they will send probe messages to establish a wireless connection with an already known SSID. After this step is complete, the authentication is made between the client and the AP using the configured method. We will talk in a moment about authentication methods. If the authentication is successful then the two devices establish an association.
Probably the most important aspect that you need to consider when implementing wireless networks is the security. Because RF signals are transmitted in the air, these signals can be intercepted by malicious users. There are different security methods and technologies used today this is why you’ll have to ensure that you choose the best one for your desires. Attacks like man-in-the-middle, Dos or DDoS (Denial of Service or Distributed Denial of Service) are a real threat to wireless networks. In the first implementations of wireless networks, two security protocols where introduced, open and WEP (Wired Equivalent Privacy). Open meant that there is no security involved, a device would simply ask an AP to authenticate and the AP would simply grant access to the network. The WEP authentication method uses a shared key between an AP and a client. The client sends an authentication request to the AP. The AP receives the request and then sends a challenge text to the client. The client encrypts the text using the shared key and then the encrypted message is sent back to the AP. The AP decrypts the message using its own key and if the text is the same with the one that has been sent, the client is authenticated. Even if this mechanism introduced a certain level of security, it could be easily cracked because the shared key could be intercepted by a hacker. With the shared key in hands, the hacker could easily authenticate with the AP and gain control to the network resources. A new encryption algorithm was invented to provide better security to the WPA protocol, TKIP or Temporal Key Integrity Protocol (read more about this protocol on this article from Wikipedia: http://en.wikipedia.org/wiki/Temporal_Key_Integrity_Protocol). The Wi-Fi Protected Access (WPA) protocol was introduced as a better solution for the WPA protocol. This protocol uses a preshared key (PSK) and the TKIP protocol for encryption.
The most used standard in today’s enterprise networks is the 802.11i/WPA2 standard. This uses the AES encryption with a dynamic key management and a feature to authenticate clients using a Remote Authentication Dial In User Service (RADIUS) database. Enterprise networks, beside the normal authentication mechanism, often use a login mechanism using an authentication server. The following link from Cisco’s website will show you how EAP authentication works: http://www.cisco.com/en/US/i/000001-100000/65001-70000/65001-66000/65583.jpg . Other known security mechanisms are MAC address filtering and SSID broadcasting disabled. These methods are not so used because they can be easily cracked.
As a conclusion, remember always to take the necessary steps from installing the AP, configuring SSID, band, mode and channels, to implementing wireless network security using the WPA or WPA2 standards (authentication and encryption). Ensure that the APs will not suffer from interferences by placing them in the right locations and by selecting the appropriate channel. Ensure that you choose the best hardware devices to set up your wireless network and design a wireless map.
I think that’s it for this article folks, I hope I’ve covered all the elements of wireless networks, please share it to others and rate it. Have a wonderful day and stay tuned because more will come.
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