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The Electrical and Electronics Engineers (IEEE) 802.11 is standard that defines, develops, access to the medium and the properties of the physical layer for wireless LANs. IEEE 802.11 Medium Access Control (MAC) provides the access method and basic mechanisms. It offers various arguments and containment Free (CF), access control. The wireless stations can communicate in both modes (Bhandari, Kumar, Banjari, & Maskara, 2004). The network topology in the IEEE 802.11 standard for wireless LAN architecture seems very promising for achieving universal access to wireless Internet in the future (Loyola, Kumagai, Nagata, Otsuki, & Aikawa, 2005).
An IEEE 802.11 network is usually the Basic Service Set (BSS) which are connected by distributed systems (DS). The system can be deployed with or without metal counterpart. The area under the SRS is a Basic Service Area (BSA) announced. BSS stations access to the DS and other stations in BSSS through an access point (AP). The Palestinian Authority has deployed a set of two 1 and DS 802.1 MAC protocols. AP can communicate with stations on its own BSS and communication with other parts of the DS. BSSS connected set of the DS has been designated as an Extended Service Set (ESS).The IEEE 802.11 standard is also adopted, ad hoc WLAN network architecture. The ad-hoc wireless networks are characterized by: (1) the absence of PA, (2) not functional mobility and transfer (3) is only compatible with the data between the stations of the same wireless LAN (Bhandari, et al., 2004).
What is the MAC address
MAC is used to assign the unique number of the network card, depending on the number of shares for each NIC (Network Interface Card) for specific pieces for specific areas, the MAC address two key words, starting with a material handling and second is the physical address to identify an adapter on a LAN.
MAC address consists of 12 numbers and hexadecimal numbers, which is 48 bits long, is basically two ways to write (:) or (-) as follows:
Winner of the first 24 bits of the MAC address contains the card number is responsible for identifying the Internet standards body, the remaining 24 bits represent the serial number of the card by the manufacturer. To find the MAC address and sends to the network device in question, but any major network to offer these services to customers (Vuran & Akyildiz, 2007)
IEEE802.11 The IEEE 802.11 MAC uses raster Space (IFS) the hours of access control for the channel. Each station is allowed to communicate if they felt their sleep for at least one (DIFS Distributed IFS). Also, apply after waiting a DIFS before chance before trying d '. The time period between receipt of data and send a confirmation of IFS is short (FIS). Figure 1 shows the cycle of access mechanism as the basis for a successful transfer. After this cycle, all places of May for media access control (Ferre, Doufexi, Nix, & Bull, 2004).
Figher1. DCF Basic Access Mechanism
The massive deployment of IEEE 802.11 Wireless-based local area networks (WLAN) and sales growth in support for wireless mobile devices for research that urgently needed to enhance the effect of real-time applications, while the Wireless Users on the go. This requires a fundamental support for research on the current band wireless roaming capabilities (Yap, Qi, Sood, Bangolae, & Bell, 2005).
Wireless IEEE 802.11-based local area networks (WLANs) have increased markedly in recent years, and have access to privileged access to the Internet. With the proliferation of wireless LANs, jump to the next generation to support real-time applications like Voice over Internet Protocol (VoIP) over WLAN, looks promising. The most important is the voice roaming latency or forwarding during the transition from a client access point (AP) to another
2.1 Safety and quality of service by the original rule
In the original IEEE 802.11 standard defines two levels of security are: 1) open system, which is not essential, security, 2) shared key authentication with WEP keys that the AP and mobile station (STA) is divided. There are two phases to the use of WEP, the authentication phase and phase encoding. Each time a STA from one AP to another AP would require an authentication process.
More security with 802.11i
IEEE 802.11i, which was formulated to address problems with the original files, all of WEP encryption, new protocols for data confidentiality as TKIP (Temporal Key Integration Protocol) and AES-CCMP (Advanced Encryption Standard against Mode CBC-MAC Protocol). While being ratified 802.11i, Wi-Fi Protected Access or WPA, a subset of 802.11i is a provisional standard adopted by the Wi-Fi Alliance (WFA, to ensure secure encryption (with TKIP) and integrity data (with a new integrity algorithm known as Michael). WPA2/802.11i Both WPA and 802.1X support for authentication via port mode of action and technical management of the keys. 802.11 specified new standards for authentication, encryption and message integrity.
To resolve the security problems of the original 802.11b, IEEE 802.1x Port-Based Network Access Control mechanism has been introduced to authenticate mobile 802.11 stations (STA) for. In several full authentication, authorization and accounting superimposed with the help of common remote access Dial-In User Service (RADIUS) protocol has been used
802.11e quality of service
As wireless networks, voice over IP multimedia applications are beginning to have original 802.11 MAC service differentiation, transport of a bone of contention delay in the delivery of packages and sensitive. The IEEE Task Group E (802.11e) has identified some changes needed to support quality of service (QoS) in 802.11 MAC. The 802.11e standard provides a new hybrid coordinate function (HCF), which combines the functions of DCF and PCF mechanisms with a better quality of service and a special border style. HCF has two modes, namely) EDCA (Enhanced Distributed Coordination Access) and HCCA (controlled channel access). The channel access method EDCA defines four categories of access to new voice and video support, a story on traffic and best effort basis for prioritizing 802.1D standard for easy use. As WLANs have limited bandwidth and the range of right of access to the media was necessary for the implementation mechanism of control admission to regular traffic. compared to IEEE 802.11e roaming STA requests access to update the new specification roaming movement. With the current IEEE 802.11i IEEE 802.11e specification meeting, where appropriate, create an additional burden on the re-connection, a meeting of VoIP over WLAN (Boggia, Camarda, Grieco, & Mascolo, 2005).
IEEE 802.11e MAC
As in previous sections of IEEE 802.11 PCF has been designed to support time bounded services. However, there are problems that limit their use. One of them is a beacon period unpredictable due to unknown weather stations surveyed transferred. TBTT transferred when the team as a beacon to the next image, but cannot be transferred if the environment was considered to be inactive for at least PIFS. The environment cannot, by the day of downtime would be delayed. This delay data frames are automatically time that has been established that are sent by the FC mode. Another problem is the unknown duration of data frames transmitted by the stations studied. The Heads of State and Government in May, the duration is variable and may be sent to the various modes of transmission. This cannot be] controlled by the computer to support QoS, IEEE 802.11 Task Group E is currently developing an enhanced version of IEEE 802.11e MAC IEEE 802.11. This enhanced version as a hybrid role, coordination (FHC) is specified, use the best argument for the DCF access period. As in the legacy IEEE 802.11 MAC, a contention free period and a declaration of changing times (Ferre, et al., 2004).
Sequence IEEE 802.11 framework Exchange uptime
The general policy of the IEEE 802.11 frame details of change of the photo. 1. A matter of time they occupied not only deviate from the busy state of a beneficiary. During a break in the environment should also be significantly slower pause is interrupted. When an interval is interrupted in the DIF (Distributed Coordination Function Space frames), or EIFS (Extended Frame Space), is restarted when the medium became idle again. When an interval is interrupted at the BO (slow) field is reset at first, but the RB slot has already been made are not repeated. The BO time increases exponentially increases with the number of trials for the same frame. Interval B is for uncast frames over a certain threshold. RTS B can replace same query interval (- auto) when, if only IEEE 802.11g stations in IBSS (Independent Basic Service Set, BSS, an ad hoc group of nodes). C2, there are only Uncast frames. Some intervals are repeated, if the short and / or attempts to occur, or if there was fragmentation.
Figher.2 IEEE 802.11 Frame Exchange Sequence
With the popularity and wider adoption of IEEE 802.11 wireless networks are a growing number of applications. Wireless presents new challenges; there are protocols as the communication links unpredictable. To combat this problem, many research proposals for cross-layer design can be used. Often, the MAC layer provides link quality measures. Existing IEEE 802.11 radios and pilot of the detailed parameters of link quality, limited number of work between the layers, the simulation environment (Deziel & Lamont, 2005)
The authentication server and the mobile station would be in a series of pairs of master key (PMK). The PMK is distributed by the AP from the RADIUS messages. Both should use the STA and AP to KMP mutually authenticates each other and has a new pair of temporary keys (PTK) for encryption. With these new features, 802.11i is the next line of defence for access control and authentication for the mobile station. Unlike WEP, this new process of re-authentication process additional overhead between the STA and AP, and time for a new authentication method is clearly increased.
IEEE 802.11 family of standards that define the specifications for the physical (PHY) and Medium Access Control (MAC) to build a wireless network (Li & Battiti, 2007). While 802.11 defines the physical layer signalling and modulation characteristics of the protocol, the 802.11 MAC layer to control access to the shared wireless medium. , To achieve this objective, defined by the average access time of 802.11 MAC two functions: a mandatory Distributed Coordination Function (DCF) and an optional number Coordination Function (PCF). The role of BEB DFS for access to the central government, in this case, collisions of packets (Kanodia, Li, Sabharwal, Sadeghi, & Knightly, 2001).
The BEB algorithm is used by IEEE 802.11 wireless medium access control shared with stations in the race. This is done by adjusting the window size of the claim based on current income status. If the station has data, feels the channel to determine if in sleep mode. If support for a time interval equal to DIFS is idle, the station will be transferred. When used, the medium is limited to the transfer delayed until the current transmission. Meanwhile, a binary exponential back off slots procedure for each location corresponding to DIFS, and the number of slots is uniform chosen by a random value in 0, determines CW -1], where CW is the current size Window dispute. Finally, if the data packet is successfully received, the receiver sends an acknowledgment frame after a specified interval, called the Short Inter Frame Space (FIS), which is less than DIFS. If confirmation is received, the data in the context of its lost and a retransmission is scheduled. The value of CW cumin solid attempt at the first transmission and doubles with each transmission of CEMEX to predetermined value. Webcast to data frames can be made to a level determined retry limit, L-hour. Furthermore, the framework is (Nasir & Albalt, 2009).
Figure 3: IEEE 802.11 DCF operation.
IEEE 802.11 MAC has been presented. A detailed analysis of the flow of DCF / PCF access was made with the analysis of Markov chains necrotized impact on the number of users. The packages feature provides better performance than small packages and are preferable for broadband applications. But for many users, the system offers better performance than basic access, the system real-time strategy for the small package. CTS system for most of the packages that were in the RTS preference, ISE (11% increase for 10 users with a length of 1024 bytes per packet). The IEEE 802.11e standard was strengthened to assess the performance of EDCF service differentiation, the ACS introduced. The proposed priority for marketing differentiation involves a variety of services, improving river. No distinction guaranteed if the two stations will transmit two streams with the same priority. To resolve this problem, use the HCF the ballot in the economy. The use of TXOP BFC and improves performance and performance is more suitable for "time-limited applications