802.1X | Wi-Fi Radio Types

802.1X, also known as EAPOL, for EAP over LAN, is a basic protocol supported by enterprise-grade Wi-Fi networks, as well as modern wired Ethernet switches and other network technologies. The idea behind 802.1X is to allow the user's device to connect to the network as if the RADIUS server and advanced authentication systems did not exist, but to then block the network link for the device for all other protocols except 802. IX, until authentication is complete. The network's only requirements are twofold: prevent all data traffic from or to the client except for EAPOL (using Ethernet protocol 0×888E) from passing; and taking the EAPOL frames, removing the EAP messages embedded within, and tunneling those over the RADIUS protocol to the AAA server.

The job of the network, then, is rather simple. However, the sheer number of protocols can make the process seem complex. We'll go through the details slowly. The important thing to keep in mind is that 802.1X is purely a way of opening what acts like a direct link between the AAA server and the client device, to allow the user to be authenticated by whatever means the AAA server and client deem necessary. The protocols are all layered, allowing the highest-level security protocols to ride on increasingly more specific frames that each act as blank envelopes for its contents.

Once the AAA server and the client have successfully authenticated, the AAA server will use its RADIUS link to inform the network that the client can pass. The network will tear down its EAPOL-only firewall, allowing generic data traffic to pass. In the same message that the AAA server tells the network to allow the client (an EAP Success), it also passes the PMK—the master key that the client also has and will be used for encryption—to the network, which can then drop into the four-way handshake to derive the PTK and start the encrypted channel. This PMK exchange goes in an encrypted portion of the EAP response from the RADIUS server, and is removed when the EAP Success is forwarded over the air. The encryption is rather simple, and is based on the shared password that the RADIUS server and controller or access point have. Along with the PMK comes a session lifetime. The RADIUS server tells the controller or access point how long the authentication, and subsequent use of the keys derived from it, is valid. Once that time expires, both the access point and the client are required to erase any knowledge of the key, and the client must reauthenticate using EAP to get a new one and continue using the network.

For network administrators, it is important to keep in mind that the EAP traffic in EAPOL is not encrypted. Because the AAA server and the client have not agreed on the keys yet, all of the traffic between the client and the RADIUS server can be seen by passive observers. This necessarily limits the EAP methods—the specific types of authentication—that can be used. For example, in the early days of 802.1X, an EAP method known as EAP-MD5 was used, where the user typed a password (or the client used the user's computer account password), which was then hashed with the MD5 one-way cryptographic hash algorithm, and then sent across the network. Now, MD5 is flawed, but is still secure enough that an attacker would have a very hard time reverse-engineering the password from the hash of it. However, the attacker wouldn't need to do this, as he could just replay the same MD5 hashed version himself, as if he were the original user, and gain access to the network. For this reason, no modern wireless device supports EAP-MD5 for wireless authentication.

Types of Phones | Voice Communications

Although different types of phones require the same basic system components to allow a standard level of operation with the cellular network, significant differences between mobile, transportable, and handheld units can most often create the major decision points as to which is right for any specific application.

Mobile units

Mobile units are permanently installed in a vehicle, usually by the provider of the equipment, and typically consist of "bolted-in" components. This type of installation generally involves installing the equipment and routing the cables so that they will not be damaged as part of the normal use of the vehicle. Cables and equipment are placed and secured so that cargo and people cannot easily displace them. Since the system is subject to continuous vibration and the rough jolts caused by road hazards, potholes, and other everyday occurrences, the installation should typify equipment that might be factory installed, and some manufacturers have in fact offered this as an option. Since space in the driver's area is at a premium, the handset is typically mounted to be accessible to the driver, and the other components can be installed elsewhere in the car.

As noted, mobile units utilize the vehicle's 12-V DC battery as a power source. Mobile phone transmitters generally operate at a full 3-W level, the maximum for cellular units. This provides the best available overall performance in terms of signal quality and physical range of use. The transmitter output power level is very dependent upon a strong input power source.

Transportable units

Transportable phones comprise the same components as the mobile telephones but are packaged as a single unit. The transportables are generally used in vehicles by plugging them into the cigarette lighter outlet to obtain a reliable power source, and also by connecting to either a temporary magnet-mount antenna on the car roof or to a permanently installed antenna. The unit is not bolted to the vehicle but is commonly placed on the seat. Performance of these transportable units can rival a mobile unit, especially since the critical power source and antenna system components are virtually identical. By disconnecting the power and the antenna, the unit can be carried from the vehicle to be used in another car or to be used as a self-contained system through use of an integral rechargeable battery and a small antenna. The units ordinarily weigh about five pounds, but the battery capabilities and battery weight increase in a directly proportional manner. In this portable configuration outside a car, the system becomes subject to limitations of the battery.

All phones—mobile, portable, and handheld—draw increased levels of power while in use, and lower levels when in standby mode (on-hook). The battery must be either replaced or recharged after a few hours of continuous talk time, or following a somewhat greater number of hours of combined talk and standby time. Although portables are available that offer full 3-W transmit power, use of reduced power levels of less than 3-Wcan enable some of these phones to operate over an extended period of time, given the same battery capability. The antenna, which now has no metal vehicle underneath to act as a performance-enhancing ground plane, performs adequately but certainly not with the range of a car-mounted antenna. These units are especially suited to field use where, even though the phone might remain in a fixed location, no conventional telephone service exists. In such applications, auxiliary power might be available to augment the battery in a configuration similar to that of a mobile installation.

Handheld units

Handheld units range from those that weigh approximately a pound to tiny pocket phones that can weigh less than 4 ounces. These most closely resemble handheld two-way radios with extendible or flexible rubber antennas and small batteries contained within the handset. The smallest of these, the microminiature pocket phones, represent the ultimate in portability, but at the expense of battery life and transmit power levels. Talk time from a single battery can be as little as an hour or two, with standby time of 8 to 36 hours. Some units can operate with disposable alkaline batteries as well as, or instead of, the rechargeable nickel-cadmium or nickel-metal hydride battery packs in order to improve the phone's weight-to-performance ratio and to free the user from the constraint of maintaining a supply of recharged battery packs. Handheld units generally operate at transmit power levels of approximately a half-watt. This certainly limits their range and capabilities as compared to a three-watt mobile or transportable unit, but they do perform well as long as they are used in reasonable proximity to the main coverage areas of most cellular networks.

Wearable units

The ultimate communications device for mobile professionals is the cellular phone that can be worn as an accessory on clothing. Motorola's StarTAC phone, for example, may be worn easily and unobtrusively by both men and women on the go. Such units weigh in at 3.1 ounces. When opened to its full size, the StarTAC phone forms to the face to maintain the familiar ear-to-mouth ratio. When folded, the StarTAC phone can be worn fashionably as an accessory.

Despite their light weight and compact design, such phones are capable of advanced features. Motorola's StarTAC 8600 Series of VoiceNote Cellular Phones, for example, feature an answering machine/voice recorder with up to 4 minutes of record time. Other phone features available with the StarTAC phone are: a "Smart" Button, which allows for simplified one-handed use of the phone; silent vibration alert for incoming calls; and a headset jack for hands free conversations. A 1.9-MHz GSM (Global Systems for Mobile communication) version of the phone—the StarTAC Select Series—weighs slightly more at 3.5 ounces, but incorporates a full-size SIM (Subscriber Identity Module) card.

Many value-added services will be aided by a unique feature of GSM's SIM card. This removable "smart card" uses a microchip to store the owner's billing data, special features, speed dial numbers, and other vital information, and can be used in any compatible handset. The SIM card allows for over-the-air activation, contributes to secure network access, and facilitates roaming among international locations.

Types of Services & Standard Billing Process | Introduction to Billing

The control of a billing system is usually under the finance department. Billing systems are often viewed as accounts receivable as the billing system assists in the collection (receipt) of money from customers. Billing systems are also is part of accounts payable (for inter-carrier settlements) as customers often use services from other companies such as long distance and call completion through other networks. The network operator is usually financially responsible for services provided to their customers by other networks regardless if the customer pays for the service or not.

Types of Services

There types of services that a customer may use in a network include system access (basic information transfer), information processing (such as email), and content delivery (current traffic information for example). When the communication service involves system access through different networks, the call is normally routed through a toll center and a toll charge may apply. A toll is any message telecommunications charge for services provided beyond a local calling area.

Examples of system access services include plain old telephone service (POTS), integrated services digital network (ISDN), digital subscriber line (DSL), and other data connectivity services that transfer information between points. Information processing services include phone card (Telecard), voice mail, fax store and forward, and other services that involve the processing of information that is passed between two or more points. Content delivery involves linking customers to sources of information content and transferring the content to the end customer. Examples of content delivery include weather advisory services, stock quotes, and the delivery of other sources of information that the customer requests.

Standard Billing Process

The typical billing process involves collecting usage information from network equipment (such as switches), formatting the usage information into records that a billing system can understand, transferring these records to the billing system, assigning charge fees to each record, receiving and recording payments from the customers, and creating invoices.

Figure 1 shows a standard billing process. In this diagram, the customer calls customer care or works with an activation agent to establish a new wireless account. The agent (customer care) enters the customer’s service preferences into the system, checks for credit worthiness, and provides the customer with a phone number so that the customer may make and receive calls through the telephone network. As the customer makes calls, the connections made by the network (such as switches) create records of their activities. These records include the identification of the customer and other relevant information that are passed onto the billing system. The billing system also receives records from other carriers (such as a long distance service provider, or a roaming partner). The billing system now guides and updates these call detail records (CDRs) to their correct customer and rating information. As information about the customer is discovered (e.g. rate plan), the updated billing records are placed in a billing pool so that they may be combined into a single invoice that is sent to the customer. The customer then sends his payment to the telecom service provider. Payments are recorded in the billing system. History files are then updated for the use of customer service representatives (CSRs) and auditing managers.

Figure 1: Standard Billing Process. Source: The Billing College