WLAN Protocol

2.2.5 WLAN Protocol

With the rapid development of the Internet, communication network has evolved from traditional network to wireless network. WLAN (Wireless Local Area Network) which is becoming the public wireless local network and the Internet gateway.

WLAN is a kind of locally built networks based on wireless communication technologies, the combination of computer network and wireless communication technology. Because wireless multi-channel is regarded as transmission media, it provides the functions of traditional local area network and enables the users to have Internet access at any location and any time.

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Since WLAN is based on computer networks and wireless communication technologies, LLC (logic link control) has the same or different requirements for physical layer as the upper application layer does. Thus, WLAN standard primarily focuses on the physical layer and media access control (MAC) layer. It is related to technical standards such as wireless frequency range and air interface communication protocol. The technical standard of WLAN is illustrated in Fig. 2.7.

Figure 2.7 WLAN technical standards

1. IEEE 802.11X

(1) IEEE 802.11 In 1990 the IEEE802 standardization committee has established the IEEE 802.11

WLAN standard panel. IEEE802.11 (also name as Wi-Fi (Wireless Fidelity)) is a standard passed in June 1997, which defines the physical layer and MAC regulation. The physical layer defines the data transmission feature and modulation, as well as two RF transmission methods and an infrared transmission method. The RF transmission standard is frequency-hopping spread spectrum (FHSS) and direct sequence spread spectrum (DSSS), working at the frequency band of 2.4000 2.4835GHz. FHSS uses 2 data transmission at the rate of 1 Mbps, with 22 sets of frequency-hopping patterns in total and 79 channels included. DSSS uses BPSK and DQPSK modulation technologies and supports data transmission at the rate of 1 Mbps and 2 Mbps. Infrared transmission method works at the frequency band of 850 2W peak power, and supports data transmission at the rate of 1 Mbps and 2 Mbps.

IEEE 802.11 is the initial standard published for wireless LAN, primarily used for office LAN and wireless access in campus networks. The highest transmission speed just reaches 2 Mbps. Because the speed and transmission distance did not satisfy the need, IEEE 802.11 standard was quickly replaced by IEEE 802.11b.

(2) IEEE 802.11b In September 1999, IEEE 802.11b was formally approved. This standard

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prescribes that the working frequency interval of WLAN is between 2.4 GHz, the data transmission rate reaches 11 Mbps, and the transmission distance is

50 Code Keying (CCK), with p2p and basic modes, so it can accomplish automatic speed switch among 11 Mbps, 5.5 Mbps, 2 Mbps and 1 Mbps. It has changed the design status of WLAN, and extends the application area of WLAN.

IEEE 802.11b has become the mainstream WLAN standard, and has been adopted by most of the manufacturers. Now the products have widely been used. However, new standards like IEEE 802.11a and IEEE 802.11g are receiving more attention.

(3) IEEE 802.11a In 1999, IEEE 802.11a was published. This new standard prescribes that the

working frequency interval of WLAN lies between 5.15 transmission rate is 54 Mbps/72 Mbps (Turbo), and the transmission distance is

10 Orthogonal Frequency Division Multiplexing (OFDM) and QFSK modulation. It can provide wireless ATM interface of 25 Mbps and wireless frame interface of 10Mbps for Ethernet. And it supports multiple operations such as voice, data and images. Within one sector, it allows access from multiple users, who each may use more than one terminal.

IEEE 802.11a is a subsequent standard of IEEE 802.11b, and its design aims to replace the 802.11b standard; however, working under 2.4 GHz does not require license, because this frequency interval is reserved for industry, education and medicine. On the other hand, working in the frequency interval 5.15 GHz needs to be approved. And since IEEE 802.11a works at 5.15 which may cause interference to domestic apparatus such as microwave oven and cordless telephone, some companies have not demonstrated support for 802.11a while others think better of a new mixed standard, 802.11g.

(4) IEEE 802.11g Now IEEE has published the latest IEEE 802.11g standard, which declares to

have the transmission rate of IEEE 802.11a, with better security than IEEE 802.11b. In order to be compatible with 802.11a and 802.11b, it uses two kinds of modulations.

Although 802.11a is more suitable for enterprises, the operators of WLAN are more likely to choose 802.11g for the compatibility with 802.11b. For the manufacturers of WLAN, there is no unique choice of the standards in their R&D. They have to consider all of the existing standards.

(5) IEEE 802.11i IEEE 802.11i combines the user port verification and device verification of

IEEE 802.11x, modifies the MAC layer of WLAN, and defines strict encryption format and authentication to improve the security of WLAN. The newly revised standard of IEEE 802.11i primarily includes two points: “Wi-Fi Protected Access”

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and “Robust Security Network”. The principal task of “Wi-Fi Protected Access” is to insert security holes into old devices, usually accomplished by updating of hardware or drivers, which employs the TKIP (Temporal Key Integrity Protocol) to improve the security of the WEP (Wired Equivalent Privacy) key. TKIP is based on RC4 like WEP, but the method of creating key is different. It can update the key quickly, which solves the weakness of WEP. “Robust security network” is based on 802.1X protocol and extensible authentication protocol (EAP). With the use of Advanced Encryption Standard (AES), it has become more powerful in encryption and wholeness of information. The Wi-Fi league planned to use the 802.11i as the second version of WPA, and put it into effect from the beginning of 2004.

The IEEE 802.11i standard is quite important in the construction of WLAN, and the data security is the principal issue of the WLAN manufacturers and ISPs. Only when the security of user data is guaranteed do the WLAN products have a promising future.

(6) IEEE 802.11e/f/h The IEEE 802.11e standard improves the WLAN MAC protocols to support

multimedia transmission.

IEEE 802.11f defines the communication between nodes, supporting the IAPP of IEEE 802.11. IEEE 802.11h is applied to spectrum management technology of 802.11a.

2. HIPERLAN

The BRAN panel of the European Telecommunication Standardization Institution (ETSI) is setting about establishing the Hiper (High Performance Radio) standard, which has already been preceded by HiperLAN1 and HiperLAN2. When HiperLAN1 was just published, the data transmission rate is low. In 2000 when HiperLAN2 was published, the transmission rate can reach 54Mbps. The HIPERLAN2 standard defines the testing function and signal switching of WLAN to support wireless network, dynamic frequency selection (DFS), wireless signal transformation, link adaptation, multi-bean antenna and power control. This standard also gave some definitions on WLAN performance, security, and quality of service (QOS).

HiperLAN1 corresponds to 1EEE802.11b, while HiperLAN2 and IEEE082.11a have the same physical layer, which has the same unit. Moreover, HiperLAN2 emphasizes the integration with 3G. HiperLAN2 is also a rather sound protocol of WLAN. Now the manufacturers that support HiperLAN2 primarily cluster in the European areas.

3. HomeRF

The HomeRF working group is established in 1997, the aim of which is primarily to establish the interactive voice and data communication network for homes. In Aug. 2001 HomeRF2.0 was published, which integrated voice and data transmission

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technology. And its working frequency is 10GHz and its data transmission rate is 10Mbps. It pays more attention to access control and encryption technologies in WLAN security.

HomeRF is the integration and improvement of existing wireless communication standards. When data transmission is going on, TCP/IP protocol is being used; when voice communication is going on, DECT (Digital Enhanced Cordless Telecommunication) is being used.

Besides the IEEE 802.11 committee and European Telecommunications Standards Institute (ETSI), the WLANA (Wireless LAN Association) has also done much work in the technical support and execution. The WLANA is a non-profitable organization established by WLAN manufacturers, including 3Com, Aironet, Cisco, Intersil, Lucent, Nokia and Symbol, whose primary work is to authenticate the compatibility of the products from different manufacturers, and give trainings to WLAN users.

4. WLAN standards in China

The Ministry of Information Industry of PRC is also trying to publish an industrial WLAN standard, which is concerned with the IEEE 802.11X series (including IEEE 802.11, 802.11a, IEEE 802.11b, IEEE 802.11g, IEEE 802.11h, IEEE 802.11i) and HiperLAN2. The WLAN devices will be evaluated comprehensively in terms of performance, compatibility, security and reliability.

Besides the standards mentioned above, WLAN will have some other standards concerning WLAN applications, among which are two national standards formulated by China Broadband Wireless IP Standards Working Group. These two standards are based on ISO/IEC 8802.11 and ISO/IEC 8802.11b and will standardize the application of WLAN in China.

The WLAN standard is the foundation of promoting the development of WLAN. So many standards in WLAN and their swift changes reveal that WLAN is deeply favored by WLAN equipment manufacturers, ISPs and users. Since WLAN rids itself of complex wires, it is easy to install, manage, maintain. It will play an important role in the future network construction.