WME 802 11 ABC s Layer a b

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WME

802. 11 ABC’s Layer a b c Description PHY 54 Mb/s in 5 GHz bands PHY 11 Mb/s direct sequence in 2. 4 GHz band MAC Bridging operation PHY International domains MAC Quality of service (Qo. S) (late ’ 04) both Access point interoperability PHY 54 Mb/s at 2. 4 GHz (802. 11 b compatible) h both Coordination with European Hiper. LAN 2 standards i MAC Security (mid ’ 04) d e f g

Technology Roadmap IEEE Standardization 802. 11 i 2004 2003 2005 WPA 802. 11 i/WPA 2 Qo. S/WME Wi-Fi Certifications 802. 11 e Qo. S/WSM

Qo. S Considerations for Voice n. Admission Control is required Streaming applications need priority service n Bandwidth management required to maximize capacity and minimize contention n n. Battery life must be maximized Traffic is predictable n Schedule periods of “sleep” are possible n

IEEE 802. 11 e n New medium access mechanism– Hybrid coordination function (HCF) n Priority classes n n Polled access n n Enhanced Distributed Coordination Access (EDCA) HCF Coordinated Channel Access (HCCA) Automatic Power Save Delivery (APSD) n n APSD requires the Access Point to maintain a schedule for the intervals it will send packets This allows device to predict when traffic will arrive and schedule periods of ‘sleep’

Wi-Fi Alliance Qo. S Activities Defined by the Wi-Fi Alliance, optional for Wi-Fi certification Two profiles n Wi-Fi [Wireless] Multimedia Extensions (WME) n Based on EDCA priority service n Wi-Fi [Wireless] Scheduled Multimedia (WSM) n Based on HCCA polled access, includes EDCA

WME vs. WSM WME WSM Based on 802. 11 e, includes WME Based on EDCA (Enhanced Distributed Coordination Access) Based on HCCA (HCF Coordinated Channel Access) EDCA provides priority classes of service HCCA ‘reserves’ bandwidth based on traffic specifications from client devices Best suited for one way audio applications Best suited for two way streaming media (voice, video) Triggered APSD Optional Uses Scheduled APSD- suitable for power save

A Hybrid Approach

Enhanced distributed channel access (EDCA) n n n Enhancement for 802. 11 Distributed Coordination Function EDCA supports 8 priority values (traffic classes) Priority values (0 to 7) identical to the IEEE 802. 1 D priorities It does not guarantee that low priority frames will always wait until all higher priority frames are transmitted Provides statistical traffic class differentiation Background Spare Best Effort Excellent Effort Controlled Load Video Voice Network Control Mapping between 802. 1 D priorities and EDCA access categories.

HCF Controlled Channel Access (HCCA) n n Qo. S-aware centralized coordinator (Hybrid Coordinator HC) ▪ Has higher priority than EDCA ▪ Polls terminals ▪ Provides o Negotiated connections between an access point and terminals o Specifically assigned transmit times for every frame Close to strict Qo. S guarantees => Support for Voice over wireless LAN

WME 802. 11 access point

Summary Wireless LAN (WLAN) and Voice over IP (Vo. IP) are no longer considered emerging technologies. n All we have to do is reference the WLAN phones that offer voice services to understand that wireless IP phones are now as real as wired IP phones. n

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