Introduction to Wi-Fi

Wireless Fidelity – popularly known as Wi-Fi, developed on IEEE 802.11 standards, is the recent technology advancement in wireless communication. As the name indicates, WI-FI provides wireless access to applications and data across a radio network. WI-FI sets up numerous ways to build up a connection between the transmitter and the receiver such as DSSS, FHSS, IR – Infrared and OFDM. The development on WI-FI technology began in 1997 when the Institute of Electrical and Electronic Engineers (IEEE) introduced the 802.11 technology that carried higher capacities of data across the network. This greatly interested some of major brands across the globe such as the world famous Cisco Systems or 3COM. Initially, the price of Wi-Fi was very high but around in 2002, the IT market witnessed the arrival of a break through product that worked under the new 802.11 g standards. In 2003, IEEE sanctioned the standard and the world saw the creation of affordable Wi-Fi for the masses.

Wi-Fi provides its users with the liberty of connecting to the Internet from any place such as their home, office or a public place without the hassles of plugging in the wires. Wi-Fi is quicker than the conventional modem for accessing information over a large network. With the help of different amplifiers, the users can easily change their location without disruption in their network access. Wi-Fi devices are compliant with each other to grant efficient access of information to the user. Wi-Fi location where the users can connect to the wireless network is called a Wi-Fi hotspot. Through the Wi-Fi hotspot, the users can even enhance their home business as accessing information through Wi-Fi is simple. Accessing a wireless network through a hotspot in some cases is cost-free while in some it may carry additional charges. Many standard Wi-Fi devices such as PCI, miniPCI, USB, Cardbus and PC card, ExpressCard make the Wi-Fi experience convenient and pleasurable for the users. Distance from a wireless network can lessen the signal strength to quite an extent; some devices such as Ermanno Pietrosemoli and EsLaRed of Venezuela Distance are used for amplifying the signal strength of the network. These devices create an embedded system that corresponds with any other node on the Internet.

The market is flooded with various Wi-Fi software tools. Each of these tools is specifically designed for different types of networks, operating systems and usage type. For accessing multiple network platforms, Aircrack-ng is by far the best amongst its counterparts. The preferred Wi-Fi software tools list for Windows users is: KNSGEM II, NetStumbler, OmniPeek, Stumbverter, WiFi Hopper, APTools. Unix users should pick any of the following: Aircrack, Aircrack-ptw, AirSnort, CoWPAtty,Karma . Whereas, Mac users are presented with these options: MacStumble, KisMAC, Kismet. It is imperative for users to pick out a Wi-Fi software tool that is compatible with their computer and its dynamics.

Wi-Fi uses radio networks to transmit data between its users. Such networks are made up of cells that provide coverage across the network. The more the number of cells, the greater and stronger is the coverage on the radio network. The radio technology is a complete package deal as it offers a safe and consistent connectivity. Radio bands such as 2.4GHz and 5GHz depend on wireless hardware such Ethernet protocol and CSMA. Initially, Phase Shift Keying (PSK), a modulation method for conveying data was used, however now it has been replaced with CCK. Wi-Fi uses many spectrums such as FHSS and DSSS. The most popular Wi-Fi technology such as 802.11b operates on the range of 2.40 GHz up to 2.4835 GHz band. This provides a comprehensive platform for operating Bluetooth strategy, cellular phones, and other scientific equipments. While 802.11a technology has the range of 5.725 GHz to 5.850 GHz and provides up to 54 Mbps in speed. 802.11g technology is even better as it covers three non-overlapping channels and allows PBCC. 802.11e technology takes a fair lead by providing excellent streaming quality of video, audio, voice channels etc.

Wireless Standards:

The official name for the specification is IEEE 802.11, and it is comprised of more than 20 different standards, each of which is denoted by a letter appended to the end of the name. The most familiar standards are 802.11b and 802.11g (Wireless B and G) which are used in the majority of commercial Wi-Fi devices. Both of these standards operate in the 2.4 GHz band, and the only major difference between the two is the transfer rate.

Some consumer electronics, however, use a different standard—Wireless A. These devices operate within the 5 GHz range and have transfer rates equivalent to 802.11g. However, since they operate on different frequencies, devices using the 802.11a standard cannot communicate with B and G-enabled devices. For this reason, it is important to check the compatibility of components with your wireless network prior to purchasing them.

Comparison of standards:

The table below provides a brief overview of the three most popular current 802.11 standards, as well as information about the next version of Wi-Fi — 802.11n.

Advantages of Wi-Fi
Now that we've covered the basics of the technology, let's check out some of the advantages Wi-Fi has over its wireless (and wired) competition.

Unparalleled mobility and flexibility:
If you've ever installed a multi-room stereo and had to run wires through a wall, you know the amount of time and effort it requires, not to mention the permanence of your installation. If you want to move the receiver to another room, the wiring has to be completely redone, and the holes patched.
Thanks to Wi-Fi, users are no longer confined by the cords that link their devices, enabling new levels of connectivity without sacrificing function or design options. Many new products, called music streamers, are being introduced that utilize Wi-Fi technology to wirelessly broadcast your music to speakers located throughout your house. Some systems are different than others, but typically you can listen to the same, or different music in each room, play music from the server or any computer attached to the network, and even listen to internet radio.

Quick, easy setup

Setting up a wireless network may sound like a daunting task, but it's actually a pretty straightforward process. Wi-Fi networks don't require professional installation, and, best of all, there are no holes to drill or wires to run through walls. Many new routers are "plug-and-play," meaning you just connect them to a power outlet, plug in an Ethernet cord, your network has been created. Unfortunately, wireless security doesn't automatically configure itself, so it's important to remember to enable it via a personal computer once a connection to the wireless network has been established.

Fast data transfer rates:

With transfer speeds up to 54 megabits (Mb) per second (6.75 megabytes), 802.11g is currently the fastest commercially available Wi-Fi protocol on the market. It is important to note that this is the maximum theoretical transfer rate, not that which one should expect on a daily basis. Nonetheless, typical 802.11g networks are more than capable of handling the demands of streaming standard-definition TV signals, as well as CD-quality audio.

Limitations of Wi-Fi:

Security and interference are the main issues with current Wi-Fi standards, as well as its inability to reliably stream high definition audio and video.

Security concerns:
Though typically very easy to set up, securing your Wi-Fi network requires more effort. Wi-Fi access points do not come with encryption straight out of the box; you have to do it from your computer once the network is up and running. An unsecured wireless network is susceptible to attacks from hackers, potentially giving them access to all of the information stored by the devices on your network. In addition, "friendly," yet unauthorized computers will also be able to connect to your network, occupying the bandwidth and hindering overall network performance.

Interference from other devices:

Wi-Fi transmissions take place primarily within the 2.4 GHz spectrum, making them susceptible to interference from Bluetooth® wireless enabled devices, cordless telephones, microwave ovens, baby monitors, and other household devices. The farther your Wi-Fi devices are located from these known interferers—and the closer they are to one another—the more robust your signal will be, so keep that in mind during setup.

If you live in an apartment complex or in close proximity to your neighbors, their wireless network can also be a source of interference. However, many newer routers automatically select the channel with the least amount of interference, ensuring that you get the best possible connection.

Lack of support for high-quality media streaming:

Even the fastest current Wi-Fi standards are pushed beyond their limit when trying to handle some of today's high-end media. High-definition audio and video files are bandwidth and timely-delivery-intensive, and typical wireless networks have neither the transfer speeds nor the consistency to transfer them flawlessly. This problem is further compounded if there are multiple devices connected to the same access point because the bandwidth must be divided between all of the equipment.

Securing your Wi-Fi network

The best choice for wireless network encryption is currently Wi-Fi Protected Access (WPA2). Most newer access points support WPA2 encryption, and it can be configured once your network has been set up. For more security tips, check out our article on creating a home network.

Bluetooth® wireless technology, on the other hand, has security built in, and it automatically requires devices to enter a passkey in order to connect to the network.

Wi-Fi's Future: 802.11n

When completed (currently scheduled for late 2009), wireless specification 802.11n should open the door to a vast assortment of new applications. Though the final specifications have not been determined, transfer speeds are reportedly 10 times faster than current standards (540 Mbps as opposed to 802.11g's 54 Mbps). That's more than enough bandwidth to support even the most demanding transfers, enabling users to stream high-definition audio and video, play games, and surf the internet with no delays or quality loss.

Pre-N products
Unable to wait for the 802.11n standard to be finalized, some manufacturers have released "pre-N" routers and wireless cards. With 600% speed increases over 802.11g, they are capable of handling streaming HDTV signals and audiophile-grade audio. In addition, pre-N routers reportedly offer an 800% increase in wireless network coverage, adding both range and stability. For home theater enthusiasts who have to have the newest technology, pre-N routers offer a glimpse of the future, and they're pretty reasonably priced, with both routers and wireless cards in the $100 neighborhood.

Interoperability remains a question mark for pre-N products, since no official standard has been approved, but manufacturers claim their products not only have no problems communicating with devices using other standards, they actually increase their performance as well. Whether or not the pre-N devices will be compliant with the 802.11n standard when it is released is still unknown, and we probably won't know for sure until the first 802.11n products begin rolling off the shelves in late 2009.

High-quality media streaming finally a reality
The main advantage of 802.11n is the interconnectedness it creates between components on the same network. Internet speeds are restricted by numerous factors (including the speed of the access point, the quality of the internet connection, and the memory on your computer). While the step from G to N will not typically lead to drastic improvement in internet download speeds, internal data transfer rates are not restricted by the same factors, allowing the full potential of the technology to be realized. Since 802.11n devices are ten times faster than current standards, devices will be able to transfer ten times the information in the same amount of time. If the standard is approved, and transfer rates remain at their speculated levels, reliable, high-definition streaming media may finally become a reality.

The ability to transfer data internally, between the devices on your personal network, is where 802.11n differentiates itself from previous standards. It will be interesting to see the creative new products that are made possible by the certification of the new standard.

WiMax -> What is WiMax (Part-I)?

WiMAX is a wireless industry coalition whose members organized to advance IEEE 802.16 standards for broadband wireless access (BWA) networks. WiMAX 802.16 technology is expected to enable multimedia applications with wireless connection and, with a range of up to 30 miles, enable networks to have a wireless last mile solution.

WiMAX was formed in April 2001, in preparation for the original 802.16 specification published in December of that year. According to the WiMAX forum, the group's aim is to promote and certify compatibility and interoperability of devices based on the 802.16 specification, and to develop such devices for the marketplace. Members of the organization include Airspan, Alvarion, Analog Devices, Aperto Networks, Ensemble Communications, Fujitsu, Intel, Nokia, OFDM Forum, Proxim, and Wi-LAN.

WiMax -> Why WiMax

The hot network technology is WiMax, an informal term that covers two emerging broadband wireless standards for metropolitan-area networking. WiMax promises alternate routes to land lines for disaster recovery and relief from the price and service tyranny of the incumbent local-exchange carriers. It also has a compelling high-speed mobile component.

WiMax has the potential for what Carlton O'Neal, vice president of marketing at Tel Aviv-based broadband wireless manufacturer Alvarion Ltd., describes as "high-quality broadband everywhere that mirrors your connectivity experience in the office."

To the casual observer, WiMax backhaul services might not seem substantially different from today's broadband wireless access (BWA) services, though speed and coverage range are expected to improve. However, having standards for non-line-of-sight (NLOS) BWA products will create economies of scale and vendor interoperability, which should help WiMax-based services proliferate beyond the niches where BWA services can currently be found. This means that the benefits of BWA as a land-line alternative should theoretically become available to more sites and users.

"Fixed" access services and products will emerge in early 2006, followed by the mobile flavor a year or so later. There are two corresponding WiMax standards:

• IEEE 802.16-2004 for fixed point-to-point and point-to-multipoint wireless access. It's akin to a faster, airborne version of Digital Subscriber Line (DSL) or cable-modem services and became the industry's first NLOS BWA standard last June.
• IEEE 802.16e, for mobile wireless access from laptops and handhelds. It's analogous to a faster version of third-generation telecommunications technology. WiMax proponent Intel Corp. has promised 802.16e-enabled laptops by early 2007.
  

Intel is also involved in the 802.16-2004 standard effort. The vendor says it's providing silicon to Alvarion, Proxim Corp. and Redline Communications Inc., which are manufacturing last-mile fixed products for the carrier market.

The technologies based on the two standards operate in licensed and unlicensed frequency bands below 11 GHz. The standards are being overseen from a market-acceleration standpoint by a 230-company consortium called the WiMax Forum.

Enterprise Impact

WiMax is being deployed from the top down as a carrier technology first, which means that schedules for service availability are dependent on widespread testing and buy-in. WiMax product standards certification and interoperability testing, overseen by the WiMax Forum and to be conducted by independent test lab Cetecom Spain in Malaga, is slated to begin in July.

Once services become available, growing business sites should gain inexpensive broadband access with speeds between T1 and T3 line capabilities. And because they're airborne, these services can be quickly deployed—often in a day's time—and bypass lengthy ILEC lead times.

"Every enterprise struggles with the cost of [local] access, which is often 40%" of a telecommunications bill, says David Willis, an analyst at research firm Meta Group Inc. "The natural monopolies have starved out local competition. But WiMax doesn't require dealing with lobbyists or tariffs."

Adds Alan Menezes, vice president of marketing at Aperto Networks Inc., a maker of BWA products in Milpitas, Calif., "Enterprises gain alternatives to the [regional Bell operating companies] and backups to terrestrial T1 and fiber links that can be cut at the same time." In addition, WiMax comes ready-made with provisions for quality of service, so many prestandard services already support voice over IP, unlike many DSL and cable-modem options.

And standards-based technology should drive down customer premises equipment (CPE) costs for fixed connections, from about $800 today to $300 to $400 in 2006 or 2007, says Bob Egan, president of Mobile Competency Inc., a consultancy in Providence, R.I. Meta Group is even more bullish: Willis says he expects WiMax CPE to drop to $70 by 2007.

Finally, businesses can buy WiMax-certified products to install in their campus-area networks as alternatives to private fiber connections and more-complex wireless bridging options.

GSM -> GSM Vs CDMA

One of the most contentious battles being waged in the wireless infrastructure industry is the debate over the efficient use and allocation of finite airwaves. For several years, the world's two main methods -- Code-Division Multiple Access (CDMA) and Global System for Mobile communications (GSM) -- have divided the wireless world into opposing camps. Ultimately, the emergence of a victorious technology may owe more to historical forces than the latest wireless innovation, or the merits of one standard over the other.

CDMA'War II Foundationss World

CDMA, put into an historical context, is a recently patented technology that only became commercially available in the mid-1990s, but had its roots in pre-World War II America.In 1940, hollywood actress turned inventor, Hedy Lamarr, and co-inventor George Antheil, with World War II looming, co-patented a way for torpedoes to be controlled by sending signals over multiple radio frequencies using random patterns. Despite arduous efforts by the inventors to advance the technology from experiment to implementation, the U.S. Navy discarded their work as architecturally unfeasible. The idea, which was known as frequency-hopping, and later as frequency-hopping spread-spectrum technology (FHSS), remained dormant until 1957 when engineers at the Sylvania Electronic Systems Division, in Buffalo, New York took up the idea, and after the Lamarr-Antheil patent expired, used it to secure communications for the U.S. during the 1962 Cuban Missile Crisis. After becoming an integral part of government security technology, the U.S. military, in the mid-80s, declassified what has now become CDMA technology, a technique based on spread-spectrum technology.

What interested the military soon caught the eye of a nascent wireless industry. CDMA, incorporating spread-spectrum, works by digitizing multiple conversations, attaching a code known only to the sender and receiver, and then dicing the signals into bits and reassembling them. The military loved CDMA because coded signals with trillions of possible combinations resulted in extremely secure transmissions.

Qualcomm, which patented CDMA, and other telecommunications companies, were attracted to the technology because it enabled many simultaneous conversations, rather than the limited stop-and-go transmissions of analog and the previous digital option.

CDMA was not field tested for commercial use until 1991, and was launched commercially in Hong Kong in 1995. CDMA technology is currently used by major cellular carriers in the United States and is the backbone of Sprint's Personal Communications System (PCS). Along with Sprint, major users of CDMA technology are Verizon and GTE.

Advantages of CDMA include:

• Increased cellular communications security.
• Simultaneous conversations.
• Increased efficiency, meaning that the carrier can serve more subscribers.
• Smaller phones.
• Low power requirements and little cell-to-cell coordination needed by operators.
• Extended reach - beneficial to rural users situated far from cells.
  

Disadvantages of CDMA include:

• Due to its proprietary nature, all of CDMA's flaws are not known to the engineering community.
• CDMA is relatively new, and the network is not as mature as GSM.
• CDMA cannot offer international roaming, a large GSM advantage.

The Euro-Asian Alternative: GSM

Analysts consider Qualcomm's major competitive disadvantage to be its lack of access to the European market now controlled by Global System for Mobile communications (GSM). The wireless world is now divided into GSM (much of Western Europe) and CDMA (North America and parts of Asia).

Bad timing may have prevented the evolution of one, single global wireless standard. Just two years before CDMA's 1995 introduction in Hong Kong, European carriers and manufacturers chose to support the first available digital technology - Time Division Multiple Access (TDMA). GSM uses TDMA as its core technology. Therefore, since the majority of wireless users are in Europe and Asia, GSM has taken the worldwide lead as the technology of choice.

Mobile Handset manufacturers ultimately split into two camps, as Motorola, Lucent, and Nextel chose CDMA, and Nokia and Ericsson eventually pushed these companies out and became the dominant GSM players.

Advantages of GSM:

• GSM is already used worldwide with over 450 million subscribers.
• International roaming permits subscribers to use one phone throughout Western Europe.
• CDMA will work in Asia, but not France, Germany, the U.K. and other popular European destinations.
• GSM is mature, having started in the mid-80s. This maturity means a more stable network with robust features. CDMA is still building its network.
• GSM's maturity means engineers cut their teeth on the technology, creating an unconscious preference.
• The availability of Subscriber Identity Modules, which are smart cards that provide secure data encryption give GSM m-commerce advantages.

In brief, GSM is a "more elegant way to upgrade to 3G," says Strategis Group senior wireless analyst Adam Guy.

Disadvantages of GSM:

• Lack of access to burgeoning American market.

Conclusion

Today, the battle between CDMA and GSM is muddled. Where at one point Europe clearly favored GSM and North America, CDMA, the distinct advantage of one over the other has blurred as major carriers like AT&T Wireless begin to support GSM, and recent trials even showed compatibility between the two technologies.

GSM still holds the upper hand however. There's the numerical advantage for one thing: 456 million GSM users versus CDMA's 82 million.

GSM Network Aspects

SIM Information System (PTA) (Please click to view your information)

1. Handover
2. Location updating and call
3. Authentication and security

Ensuring the transmission of voice or data of a given quality over the radio link is only half the problem in a cellular mobile network. The fact that the geographical area covered by the network is divided into cells necessitates the implementation of a handover mechanism. Also, the fact that the mobile can roam nationally and internationally in GSM requires that registration, authentication, call routing and location updating functions exist in the GSM network.
The signalling protocol in GSM is structured in three layers , shown in Figure 3. Layer 1 is the physical layer, which uses the channel structures discussed above. Layer 2 is the data link layer. Across the Um interface, the data link layer uses a slight modification of the LAPD protocol used in ISDN, called LAPDm. Across the A interface, the lower parts of Signalling System Number 7 are used. Layer 3 is subdivided into 3 sublayers.

Radio Resources Management
controls the setup, maintenance, and termination of radio channels
Mobility Management
manages the location updating, handovers, and registration procedures, discussed below
Connection Management
handles general call control, similar to CCITT Recommendation Q.931, and provides supplementary services.

Signalling between the different entities in the network, such as between the HLR and VLR, is accomplished throught the Mobile Application Part (MAP). Application parts are the top layer of Signalling System Number 7. The specification of the MAP is complex. It is one of the longest documents in the GSM recommendations, said to be over 600 pages in length . Described below are the main functions of the Mobility Management sublayer.

1. Handover

Handover, or handoff as it is called in North America, is the switching of an on­going call to a different channel or cell. There are four different types of handover in the GSM system, which involve transferring a call between

• channels (time slots) in the same cell,
• cells (Base Transceiver Stations) under the control of the same Base Station Controller (BSC),
• cells under the control of different BSCs, but belonging to the same Mobile services Switching Center (MSC)
• cells under the control of different MSCs.
  

The first two types of handover, called internal handovers, involve only one Base Station Controller (BSC). To save signalling bandwidth, they are managed by the BSC without involving the Mobile service Switching Center (MSC), except to notify it at the completion of the handover. The last two types of handover, called external handovers, are handled by the MSCs involved. Note that call control, such as provision of supplementary services and requests for further handoffs, is handled by the original MSC.

Handovers can be initiated by either the mobile or the MSC (as a means of traffic load balancing). During its idle time slots, the mobile scans the Broadcast Control Channel of up to 16 neighboring cells, and forms a list of the six best candidates for possible handover, based on the received signal strength. This information is passed to the BSC and MSC, and is used by the handover algorithm.

The algorithm for when a handover decision should be taken is not specified in the GSM recommendations. There are two basic algorithms used, both closely tied in with power control. This is because the BSC usually does not know whether the poor signal quality is due to multipath fading or to the mobile having moved to another cell. This is especially true in small urban cells.

The algorithm for when a handover decision should be taken is not specified in the GSM recommendations. There are two basic algorithms used, both closely tied in with power control. This is because the BSC usually does not know whether the poor signal quality is due to multipath fading or to the mobile having moved to another cell. This is especially true in small urban cells.

The 'power budget' method uses handover to try to maintain or improve a certain level of signal quality at the same or lower power level. It thus gives precedence to handover over power control. It avoids the 'smeared' cell boundary problem and reduces co­channel interference, but it is quite complicated.

2. Location updating and call routing

The MSC provides the interface between the GSM mobile network and the public fixed network. From the fixed network's point of view, the MSC is just another switching node. However, switching is a little more complicated in a mobile network since the MSC has to know where the mobile is currently roaming - and in GSM it could even be roaming in another country. The way GSM accomplishes location updating and call routing to the mobile is by using two location registers: the Home Location Register (HLR) and the Visitor Location Register (VLR).

Location updating is initiated by the mobile when, by monitoring the Broadcast Control Channel, it notices that the location­area broadcast is not the same as the one previously stored in the mobile's memory. An update request and the IMSI or previous TMSI is sent to the new VLR via the new MSC. A Mobile Station Roaming Number (MSRN) is allocated and sent to the mobile's HLR (which always keeps the most current location) by the new VLR. The MSRN is a regular telephone number that routes the call to the new VLR and is subsequently translated to the TMSI of the mobile. The HLR sends back the necessary call­control parameters, and also sends a cancel message to the old VLR, so that the previous MSRN can be reallocated. Finally, a new TMSI is allocated and sent to the mobile, to identify it in future paging or call initiation requests.

With the above location­updating procedure, call routing to a roaming mobile is easily performed. The most general case is shown in Figure 4, where a call from a fixed network (Public Switched Telecommunications Network or Integrated Services Digital Network) is placed to a mobile subscriber. Using the Mobile Subscriber's telephone number (MSISDN, the ISDN numbering plan specified in the ITU­T E.164 recommendation), the call is routed through the fixed land network to a gateway MSC for the GSM network (an MSC that interfaces with the fixed land network, thus requiring an echo canceller). The gateway MSC uses the MSISDN to query the Home Location Register, which returns the current roaming number (MSRN). The MSRN is used by the gateway MSC to route the call to the current MSC (which is usually coupled with the VLR). The VLR then converts the roaming number to the mobile's TMSI, and a paging call is broadcast by the cells under the control of the current BSC to inform the mobile.

2. Authentication and security

Since the radio medium can be accessed by anyone, authentication of users to prove that they are who they claim to be, is a very important element of a mobile network. Authentication involves two functional entities, the SIM card in the mobile, and the Authentication Center (AC). Each subscriber is given a secret key, one copy of which is stored in the SIM card and the other in the Authentication Center. During authentication, the AC generates a random number that it sends to the mobile. Both the mobile and the AC then use the random number, in conjuction with the subscriber's secret key and a ciphering algorithm called A3, to generate a number that is sent back to the AC. If the number sent by the mobile is the same as the one calculated by the AC, the subscriber is authenticated.

The above calculated number is also used, together with a TDMA frame number and another ciphering algorithm called A5, to encipher the data sent over the radio link, preventing others from listening in. Enciphering is an option for the very paranoid, since the signal is already coded, interleaved, and transmitted in a TDMA manner, thus providing protection from all but the most persistent and dedicated eavesdroppers.

Another level of security is performed on the mobile equipment, as opposed to the mobile subscriber. As mentioned earlier, each GSM terminal is identified by a unique International Mobile Equipment Identity (IMEI) number. A list of IMEIs in the network is stored in the Equipment Identity Register (EIR).

EIR is one of the following:

white­listed
The terminal is allowed to connect to the network
grey­listed
Under observation from the network, possible problems
black­listed
The terminal has either been reported as stolen, or it is not type approved (the correct type of terminal for a GSM network). The terminal is not allowed to connect to the network.