Below is an example of the Association failures are commonly caused by either a client misconfiguration or an incompatibility between the client and access point. Sometimes when a device roams between APs quickly it will not be able to fully associate to an AP before going out of range, which can contribute to low overall Success Rates without actually indicating an issue in the network.
For more information about the Authentication issues are one of the most common types of connection failures. If Authentication issues appear to be limited to specific clients ensure that those clients are connecting to the correct SSID and have the correct user credentials. One of the most common reasons for low success rates in a network is a client with incorrect credentials that is attempting to automatically re-connect to an SSID and failing repeatedly.
If Authentication issues appear to be located around a certain AP then depending on the type of Authentication configured that could indicate a potential issue with the upstream switchport configuration or a configuration error on an Authentication server, such as a RADIUS server. If Authentication issues appear to be centered on a specific SSID, ensure that the SSID is configured as expected and that any additional configuration, such as required for The new access point communicates with the old access point over the wired link to verify that the wireless client was previously associated.
If the wireless client was previously associated, the new access point issues a reassociation response frame to the wireless client; otherwise, it issues a disassociation frame. After sending the reassociation response, the new access point contacts the old access point over the wired link to complete the reassociation process. Any buffered frames at the old access point are transferred to the new access point. After completing the reassociation process, the new access point begins processing frames from the wireless client.
As previously stated, there are two Home users who need to join their enterprise networks using access points that are not configured for Another frame type related to authentication frames is the deauthentication frame. When a deauthentication frame is received by a wireless LAN client, the client is disconnected from the access point.
This might cause a wireless LAN client to go through the entire probe request process again or cause the client to restart the authentication association process again. Deauthentication frames can be sent to the broadcast MAC address.
Security should be considered a network design component that needs to be integrated and not something that is added later. Enterprise security discussions consistently indicate that the wireless LAN's RF signals typically travel beyond the deployed building's perimeter.
This allows the network to be monitored and attacked from beyond the property line. However, the range for this type of attack is very limited.
To make any attack feasible an attacker with the appropriate skills needs to be in physical proximity to a wireless LAN. This requires the attacker to roam extensive areas looking for a suitable wireless LAN. The location of an enterprise, and the type of business operated by that enterprise, will determine any recommended augmentation of the native wireless LAN security.
Hostile activities are equally applicable to all networks and can be broadly broken down into:. The choice of EAP type used in authentication and the configuration of the supplicant can determine whether username information is exposed during authentication.
This is generally addressed in two ways:. This type of security needs to be assessed with a understanding of the end node's mobility. This attack typically uses The two core standards introduced in secure wireless LAN deployment are the The IEEE owns the The original These amendments have added different physical layer implementations, provided greater bit rates The IEEE also owns the The advantage of EAP is that it decouples the authentication protocol from its transport mechanism.
EAP can be carried in See the "EAP" section. In wired networks it is common for devices to be from the same vendor where integration is part of product testing. When different vendor devices are combined into the same network, interoperability and integration must be managed and controlled by a group of network specialists who understand the devices and their interaction. In wireless networks that include devices from many vendors, the wireless standards allowed different interpretations and optional features to be developed.
A group of industry companies and organizations formed the Wi-Fi Alliance www. The WPA standard was developed to address the weakness in the WEP encryption process prior to the ratification of the One of the key development goals was to make it backward compatible with WEP hardware. This allowed the continued support of the base RC4 encryption used in WEP, but added keying enhancements and message integrity check improvements that addressed the weaknesses in WEP encryption.
WPA2 is based upon the ratified This encryption requires new client and access point hardware. They are one of several or many people accessing information through the same conduit - someone speaking. Access Points Master. Most wireless networks are made using Access Points - devices that host and control the wireless connection for laptops, tablets, or smart phones.
If you use Wi-Fi in your home or office, it is most likely through an Access Point. An AP is sometimes a stand-alone device that bridges between a wireless and wired Ethernet network, or is part of a router.
APs can cover a range of areas with a wireless signal, depending on the power of the device and the type of antenna. There are also some APs that are weatherproof, designed to be mounted outdoors.
An Access Point is similar to a person on stage, addressing an audience or crowd - they are providing the information for everyone else. Those audience members can ask questions of the person on the stage, and receive a response. Ad-Hoc Node Mesh. Some wireless devices laptops, smart phones, or wireless routers support a mode called Ad-Hoc. This allows those devices to connect together directly, without an Access Point in-between controlling the connection.
This forms a different type of network - in Ad-Hoc mode, all devices are responsible for sending and receiving messages to the other devices - without anything else in between. In an Ad-Hoc network, every device must be in this role, and using the same configuration to participate. An Ad-Hoc or Mesh node is similar to an individual in a group or roundtable discussion. They can take equal part in the conversation, raising their hand when they want to speak so the others will listen.
If someone at the end of the table cannot hear, one of the individuals in-between can repeat the original message for the listener.
Quick Activity: Describe the differences in the two example networks below. What are the roles and relationships between the different colored nodes in the networks? Are there places or times in a social situation where you are in an Access Point or Client situation?
Are there places or times when you are in an Ad-Hoc situation? From the roles above, you can see that Clients always need to connect to an Access Point, and Mesh nodes all connect to each other.
It should also be noted that due to how Wi-Fi is designed, this also prevents different roles from connecting to each other as well. Treat the three types of roles above - Clients, Access Points, and Ad-Hoc nodes - as the building blocks for large networks.
Below are several examples that demonstrate how devices configured for different roles can be used. Wireless networks used in your home or office are generally a combination of a router and a wireless Access Point AP.
In many home networks, or small office networks, the router and AP may be combined into a single device. This is usually just called a wireless router. In large office scenarios, there may be several AP devices spread throughout the building to provide more even wireless coverage, connected back to the router through long Ethernet cables. Wireless networks can be used to connect distant buildings or areas. It usually requires very focused antennas - such as a dish antenna - that can send a narrow beam in a specific direction.
This is discussed in Learn Wireless Basics - so go there for more details on how that works. The name describes the concept: two points are connected together, and nothing else. This requires two wireless devices: one configured as an Access Point; the other configured as a Client.
In the example below, two wireless devices are configured to create a point-to-point link. Here we have another example of a point-to-point link, but where the routers have dish antennas for greater link distance. This could look like the network below, where an AP mounted on a tower is able to connect with a Client device in a home very far away, since the dishes are facing one another. In both of these examples, there are just two wireless devices linked together - and the antennas determine the range at which they can connect.
Some phones may also contain the capability to edit the picture directly on the phone using a built-in picture editor. Formatted text. In addition to plain text, EMS makes it possible to format text. This may include changing font sizes; using text attributes such as boldfacing, italics, or underscoring; and changing text alignment. This feature will help to make news items and information updates more attractive. Concatenated messages. To help overcome the message size limitations, EMS allows for message concatenation.
This can be accomplished directly on the mobile phone for both sending and receiving messages. This is very important for messages containing rich content, since EMS is still limited by message size as defined in SMS.
There is some doubt on whether EMS will truly succeed as a messaging standard. Ericsson is promoting it heavily, but other vendors, including Nokia, are not embracing EMS as warmly—for obvious reasons: Nokia has a competing messaging format called Nokia Smart Messaging, which the company is promoting until carriers and devices support MMS.
The bottom line is that it looks as though SMS will continue to dominate for text messaging, and MMS will be the leader for multimedia content, leaving EMS with little hope for widespread adoption. In addition to the capability for pictures, formatted text, and sound introduced in EMS, MMS also provides support for voice, audio and video clips, and presentation information. This is accomplished in a manner very similar to SMS: providing automatic immediate delivery for custom content, as well as store-and-forward capabilities when the recipient is unable to receive the message.
MMS also adds support for email addressing, so messages can be sent to an email address from the MMS client. OMA's MMS specification defines the message encapsulation and application protocols, while the 3GPP specification defines the network architecture and general functions. This also makes it possible to use WAP Push features to deliver the message from the server to the recipient.
To enable true multimedia content, the SMS message size limitation and the transport mechanism had to be discarded. And to avoid the problems encountered with SMS, and to enable future interoperability, no maximum size has been specified for MMS messages.
This leaves the message size open to the implementation of each operator. That said, the message size will still be defined, but by the bandwidth and mobile device storage capabilities. The obvious drawback to this message size is that many of today's wireless networks do not provide the bandwidth to support it.
For this reason, MMS is a technology that requires 2. Once the receiving phone has been located, the message is immediately forwarded to the intended recipient and deleted from the MMSC.
If the MMS message originates at an enterprise server rather than another mobile phone, the application developer will be responsible for integrating with the MMSC API to send the message. The first generation of MMS messages are laid out as slide shows. Each slide show will contain at least one slide, divided into two sections, one for text and the other for multimedia.
The slides simply define the layout, while the actual content, such as video, audio, and text, are separate pieces sent along with the slides. Within the SMIL specification is a set of tags that can be used for defining images, text areas, and layouts. If you are interested in learning more about SMIL, visit www.
Multimedia messaging on wireless devices is definitely of interest to many consumers and corporate users alike. Trials are underway in other regions in Asia and Europe, but the lack of devices and suitable wireless networks is delaying its availability. In North America, adoption is even further off.
There, SMS is just starting to catch on, and few users are willing to pay to download pictures and videos wirelessly when they can download them for free at home. Instant messaging IM is well positioned to be the next killer application for the wireless industry.
With the monumental growth rate of SMS, and more than million desktop instant messaging users, the potential for wireless instant messaging is incredible. It provides similar capabilities to other two-way messaging technologies, such as paging, SMS, and email, with the addition of one significant feature: presence!
Presence lets users know the current status of the people with whom they are conversing. This introduces a new way of communication. Presence information can include device availability, device capabilities, user status, location information, as well as personal information such as the user's mood.
When a user wants to send a message to another party, he or she can first check the status of the intended recipient to make sure that person is available. Based on the presence information, the user may decide to send a message, try another means of communication, or simply wait until later. This is an important concept because instant messaging does not have store-and-forward capabilities.
When a message is sent, it goes directly to the intended recipient. If that person is not able to receive the message, it is lost; it is not sent at a later time. Instant messaging has been available for fixed Internet users for some time and is very popular.
Adding the mobile aspect to these services will enable users everywhere to communicate with one another, regardless of their type of connectivity. Interoperability between IM services will be a key ingredient to its success. Messenger, and ICQ, do not allow for cross-service communication. Users can only communicate with others using the same vendor's product, resulting in many users having multiple IM clients on their PCs.
In the mobile market, having multiple clients will not be an option, and in some cases, users will be required to use the IM service that comes preinstalled on their device. Several mobile instant messaging clients are already available, including those from Microsoft, AOL, and Openwave, and the list is sure to grow. To promote interoperability, and in turn drive IM adoption, Nokia, Motorola, and Ericsson are involved in a joint effort called Wireless Village which is now a component of the Open Mobile Alliance.
Their goal is to create a set of standard specifications for handset makers and carriers to follow. This will enable all users to communicate with each other using instant messaging regardless of the device or carrier they are using.
If successful, a user at his or her desktop will be able to send a message to a wireless user across the country with little effort, even if the recipient is using a different IM service. The potential for mobile instant messaging is tremendous. As devices with always-on capabilities penetrate the market, the opportunity for IM will become even stronger. Some believe that IM will be the answer to the slow uptake of SMS services in North America, which would be a welcome relief for wireless carriers who are looking to capitalize on the growing messaging market.
HDML notifications were the first form of push messaging available to mobile Internet users. They allow for asynchronous communication, allowing the server to send relevant information to clients in a timely fashion—similar to SMS text message functionality.
They are different from SMS in that they interact with the device's microbrowser. This interaction can take on many forms, including:. A text message sent to the browser that will beep or display a visual signal to notify the user that new information is available. The alert will often contain a URL, which, if selected will load the URL's deck or page and display the content on the device's microbrowser.
These notifications are often referred to as actionable alerts. Cache operation. This is done to prevent obsolete content from being viewed and enacted upon before the specified time to live TTL is reached. This type of operation can occur behind the scenes, without the user's involvement. HDML decks, images, and digests. These can all be preloaded into the microbrowser's cache to make interaction with the application more efficient.
To send one of these notifications, you are required to know the subscriber ID of the target device. Once you know the ID of the device to which the message is being sent, you then need to interact with the carrier's HDML gateway. Methods of accomplishing this are covered in the "Mobile Message-Oriented Middleware" section later in this chapter.
There are two delivery channels for HDML notifications: the push channel and the pull channel. On packet-switched networks, all data transmissions are treated the same, allowing for push delivery of information, regardless of the size. In all cases, the push channel is meant for delivering time sensitive material, using only alert or cache operations. The pull channel is better suited for data that is not critical, and for preloading content into the microbrowser.
Once an alert is sent to the HDML gateway, it is queued for delivery. The length of time it spends in the gateway's queue depends on the following information:. For all push notifications and for pull notifications on packet-switched networks, the gateway will attempt to deliver the message immediately. If the destination phone is unavailable, the gateway will keep the message in its queue and reattempt to deliver it periodically. If the message TTL is exceeded, it will be removed from the queue.
For pull notifications on circuit-switched networks, the message will remain in the queue until the destination phone opens up a circuit. At this time, the message will be sent to the user for viewing. Any notification that is in the gateway's queue but has not been delivered is referred to as a pending notification.
The sender of the notification can request to delete or get the status of any pending notification.
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