Comparison of wireless network technology

Wireless network technology has come into our lives, in the face of various network technology, how should we compare it? Here is a detailed introduction for us.





Wireless access technology is different from the cable access is one of the characteristics of the standard is not uniform, different standards have various applications. Because of this, the wireless access technology has emerged in a situation of contention. Among the many wireless access standards, the wireless LAN standard has become the focus of people's attention.





IEEE 802.11 protocol family





the current well-known wireless LAN products support this standard, it is already the wireless LAN is the de facto main standard.





in wireless LANs, 802.11 refers to the protocol families proposed by IEEE, which are 802.11,802.11a and 802.11b. IEEE802.11 Wireless network standards were promulgated in 1997, at that time, some such as the media access control layer function, roaming function, automatic rate selection function, power consumption management function, confidentiality function, and 1999 wireless Network International standard update and improve, Further standardizing the development and application of products with different frequency points and higher network rate products, in addition to the content of original IEEE802.11, the Management Information Base (MIB) based on SNMP (Simple Network Management Protocol) protocol is added to replace the management information base of the original OSI protocol. In addition, high-speed network content has been added. IEEE802.11 points ieee802.11a and ieee802.11b.




The frequency point of
ieee802.11a is 5GHz, and the orthogonal Frequency Division multiplexing (OFDM) technique is used to modulate the data flow. The biggest advantage of OFDM technology is its unmatched multi-channel echo reflection, so it is especially suitable for indoor and mobile environments. The transmission speed is: 1 to 2Mbps.





ieee802.11b is working at 2.4GHz frequency, and the compensation code is used to control CCK modulation technique. When the distance between workstations is too long or interference is too large, the signal to noise ratio is lower than a certain threshold value, the transfer rate can be reduced from 11mb/s to 5.5mb/s, or to 2mb/s and 1mb/s rate of direct sequence spread spectrum technology. However, the 802.11B standard has a maximum rate of 20Mbps, which remains backward compatible with 802.11.





All of these protocols are CSMA/CD for media sharing policy, if the source needs to send data, it must check whether the transmission media is being used by others, if the media is not used by others, send packets; Conversely, the source host must wait for a period of time, wait until the media is idle before it can send. The source can be sent after the destination host returns to the CTS (which can send) packages by continuously emitting a RTS (ready to send) package to check for media usage.


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ieee802.11e and ieee802.11g are the next-generation wireless LAN standards. An extended standard known as the Wireless LAN standard Way IEEE802.11. The extended standard of the so-called IEEE802.11 is to append the QoS function and the security function standard to the existing 802.11b and 802.11a mac layer. The standard work is done by the Operation department named "802.11e" and "802.11f". Additional QoS features improve the ability to transmit voice data and data flow data. In addition, the operating department "802.11G" was also established, by which to explore the extended physical layer standard ieee802.11b, so that the highest data transmission speed from the current 11mb/s to 20mb/s above. The band used is the same as in the past, still 2.4GHz band. However, with regard to modulation, it has not been decided whether to use the spectrum (Spectrum) diffusion technology which has been used in direct diffusion mode.





now, our common, technical mature is ieee802.11b.




Bluetooth

Technology




In fact, the concept of Bluetooth system and wireless personal area network (WPAN) is complementary, it is already a prototype of wireless personal LAN. In its December 1999 launch of the Bluetooth 1.0 version of the standard, has defined the use of WAP protocol to connect the Internet, a variety of software applications. It enables cellular phone systems, cordless communication systems, wireless LAN and the Internet and other existing networks to add new features, so that all types of computers, fax machines, printer equipment to add wireless transmission and networking functions, in the home and office automation, home Entertainment, E-commerce, wireless portfolio applications, all kinds of digital electronic equipment, industrial control, Intelligent building and other occasions to open up a wide range of applications. With the development of wireless personal LAN, a working group of IEEE 802.15 is developing a wireless personal LAN standard with speeds up to 20mb/s, which is also based on the Bluetooth specification. Therefore, wireless personal LAN and Bluetooth will tend to convergence, by the SIG participating in the Bluetooth program and the IEEE 802.15 Working Group work together to create tomorrow's wireless personal LAN.





Bluetooth technology from the application point of view, and the recently widely used in microwave communications, a point of multiple access technology is very similar, so it is very easy to penetrate obstacles to achieve a full range of data transmission. As early as the year before the Bluetooth standard was set up, the IEEE Working Group had already started the wireless personal area network preparation work. At first, the IEEE Executive Committee considered that since this was a wireless communication technology within the LAN, the task was given to the "802.11 working group", which had made a prominent contribution to the wireless LAN, when the main task was to realize the seamless connection between WLAN and wireless personal LAN. After a year of hard work, the team concludes that the existing IEEE 802.11 infrastructure, as defined in the Mac (Medium access control, media access controls) that supports three physical media tiers, does not apply to wireless personal LANs.





802.15 The Working Group began drafting a standard based on the Bluetooth 1.0 version in the fall of 1999 and was presented to the IEEE Standards Committee for discussion in November 2000. The reason why this is so rapid is that the IEEE 802.11 workgroup has lagged behind the market in developing wireless LAN standards, which in turn has led to a repeat of the Wireless LAN standard "ATM (asynchronous Transfer mode, asynchronous transmission mode)". Although IEEE 802.11 is an internationally recognized technical standard, but the market share is not large, Bluetooth decided to use the wireless LAN use of the 2.4GHz band (due to the frequency of the conflict, it is likely to cause the existing wireless LAN performance degradation). Bluetooth supporters have even boldly predicted that with the continuous development of Bluetooth technology, the adoption of IEEE 802.11 standard Wireless LAN will no longer exist, so that the two sides of the competition will be solved.





if the equipment belongs to that kind of activity wide range, request can and a variety of equipment quickly interconnected, such as notebook computer, digital cordless phone, personal digital assistant, mobile phone, etc., using Bluetooth or wireless personal LAN is very ideal.





IrDA





Infrared Data Standards Association IrDA (Infrared Data Association), founded in 1993, is a non-profit organization dedicated to establishing international standards for wireless communication connections, with 160 members worldwide, including computer and communications hardware, Software and telecommunications companies and so on. In a nutshell, IrDA is a technique of point-to-point communication using infrared ray, and its corresponding software and hardware technology are more mature. Its main technical advantages are:





1, there is no need to specifically apply for a specific frequency license, which is very important in the context of the current frequency resource shortage and the increase in channel usage costs.





2, with mobile communication equipment necessary for small size, low power characteristics. HP (HP) company has now introduced a combination of module applications from 2.5x8.0x2.9 (mm) to 5.3x13.0x3.8 (mm) of special devices, compared with the same technology, the power consumption is also the lowest.





3, the transmission rate is suitable for home and office use of the Pico Network (piconet) is the highest, because the use of point-to-point connection, data transmission is less interference, the rate can reach 16mb/s.





In addition to technology has its own technical characteristics, IrDA market advantage is also very obvious. Currently, 50 million devices worldwide use IrDA technology and are still growing at a rate of 50% a year. 95% of laptops have an IrDA interface installed. In the cost, infra-red LED and receiver components are far more inexpensive than the general RF components, IrDA port costs within 5 U.S. dollars, if the speed requirements are not high, or even low to 1.5 U.S. dollars, the equivalent of a few days before the Bluetooth product One-tenth.





face the challenges of other technologies, IrDA has not stalled. In addition to the transmission rate from the original FIR (Fast infrared) 4mb/s to the latest Vfir 16mb/s standard, the reception angle from the traditional 30 degrees to 120 degrees. In this way, the use of low power, small volume, mobile redundancy with a large keyboard with IrDA interface, the mouse, there is a basic technical support. At the same time, due to the rapid development of the Internet and the increasing number of graphics files, IrDA high speed transmission advantage in scanners and digital cameras and other graphics processing equipment can be more.





for the requirements of high transmission rate, less use, moving a small range, the price is lower than the equipment, such as printers, scanners, digital imaging machines, IrDA technology is preferred.


HomeRF





HomeRF a shared Wireless Connection protocol (SWAP) as a technical metric for future home networking, Using IEEE802.11 wireless Ethernet as the data transfer standard, the communication frequency band is also the 2.4ghz,homerf workgroup, like the original ATM, proposed a complete system for home networking, including connections between peripherals and home hosts, connections between peripherals, Host and HomeRF central control of the connection, access network, Psin and so on. August 31, 2000, the U.S. Federal Communications Commission approved the Intel, Microsoft, Motorola and Proxim and other HomeRF organizations members of the request to allow the HomeRF transmission rate of the original 2mb/s based on the increase of four times times, to achieve 8m~11mb/ s transfer rate; and, like Bluetooth, HomeRF can interconnect multiple (up to 5) devices. But the FCC's decision has drawn opposition from members of the internal and Bluetooth groups, mainly on the basis of frequency conflicts and large power consumption. At the same time, some members of the HomeRF Working Group suggested that the original launch bandwidth from 1MHz to 5MHz, so that the rate can be increased more, but opponents believe that the message was in the narrow signal channel beat, now if the narrow channel widened, it will be like a truck in several lanes rampage, Thus causing mutual interference between swap devices. Therefore, many people in the industry are not optimistic about this technology.





However, HomeRF technology is convenient for small companies or family-like homes, because both environments have a larger range of activities than Bluetooth and W, and are generally less than the radius of a wireless LAN. But this is not to say that HomeRF's position is safe and easy. Because the uniqueness of a technology is essential if it is to become an internationally recognised standard. HomeRF's advantage in transmission distance is likely to be defeated by Bluetooth.





Broadband Wireless Standard IEEE 802.16





In recent years, wireless network technology as a user access technology has become a traditional copper wire local loop technology is an alternative technology, and more and more people pay attention to. People's interest in wireless network technology is mainly focused on the wireless local loop wll (Wireless) or fixed wireless access. To provide a standard for local wireless loop WLL, the IEEE 802 committee set up 802.16 working groups in 1999 to specialize in the development of broadband wireless standards.





IEEE 802.16, which is responsible for setting standards for wireless interfaces and their associated functions of the wireless local loop, consists of three small workgroups, each of which is responsible for different aspects: IEEE 802.16.1 is responsible for setting wireless interface standards at frequencies of 10G to 60G Hz; IEEE 802.16.2 is responsible for developing standards for the coexistence of broadband wireless access systems; The IEEE 802.16.3 is responsible for setting the wireless interface standard for applications that have a frequency range between 2G to 10G Hertz. We can see that 802.16.1 is responsible for very high frequencies, and its work is at the forefront of these three groups. Because of its unique bandwidth, 802.16.1 is most likely to attract industry interest in the future.




The role of the
802.16 wireless service is to establish a communication path between the user site and the core network, which can be a public telephone network or an Internet. The IEEE 802.16 standard is concerned with the wireless interface between the user's transceiver and the base station transceiver. The protocol specifically deals with the problem of wireless transmission of large chunks of data in the network, and the protocol standards are organized according to the three-tier architecture.




The bottom layer of the
three-layer structure is the physical layer, the protocol of which is mainly about frequency bandwidth, modulation mode, error correction technology, synchronization between transmitter and receiver, data transmission rate and time division multiplexing structure. For communications from the user to the base station, the standard uses the on-demand multiplexing-TDMA DAMA-TDMA technology. On-Demand Multicast Dama technology is a technology that dynamically allocates channel capacity according to the capacity requirements of multiple sites. TDMA is a time division technique, which divides a channel into a series of frames, each of which contains a lot of small time units called slots. Time Division multiplexing technology can be used for each site to allocate a certain number of slots in each frame to form the logical channel of each site. Through DAMA-TDMA technology, the time slot allocation of each channel can be changed dynamically.





Above the physical layer is the data link layer, on which IEEE 802.16 provides primarily the functionality required to provide the service to the user. These features are included in the media access control MAC layer, which is primarily responsible for transferring data into frame format and controlling how users are connected to shared wireless media. The MAC protocol provides a way for the base station or user to initialize the channel when it is used. Because some layers on the MAC layer, such as ATM, need to provide QoS service, the MAC protocol must be able to allocate wireless channel capacity. A series of slots in multiple TDMA frames form a logical channel for the user, and Mac frames are transmitted through this logical channel. IEEE 802.16.1 stipulates that the data transfer rate range for each individual channel is from 2M bits/sec to 155M bits per second.





is a convergent layer on top of the MAC layer, which provides different functions according to the different service offerings. For IEEE 802.16.1, the services available include digital audio/video broadcasting, digital telephony, asynchronous transfer mode ATM, Internet access, wireless relaying and frame relay in the telephone network.