Presentation on theme: "A Bandwidth Allocation/Sharing/Extension Protocol for Multimedia Over IEEE 802.11 Ad Hoc Wireless LANs Shiann-Tsong Sheu and Tzu-fang Sheu IEEE JOURNAL."— Presentation transcript:
A Bandwidth Allocation/Sharing/Extension Protocol for Multimedia Over IEEE 802.11 Ad Hoc Wireless LANs Shiann-Tsong Sheu and Tzu-fang Sheu IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, VOL 19. NO. 10. OCT. 2001 Presented: Nov. 1 2001
3 Idea concepts The bandwidth allocation/sharing/extension protocol (DBASE) approach is proposed to support multimedia traffic over ad hoc networks. The basic concept is that each time real time station transmits packet it will also declare and reserve the needed bandwidth at the next contention free period (CFP). Every rt-station collects this information and then calculates its actual bandwidth at the next cycle.
4 Introduction As the speed and capacity of wireless LAN increases, so dose the demand for improving quality of service for real-time multimedia applications. The MAC is one of the most important issue to efficiently use wireless channel.
5 Assumptions The wireless channel is error-free. The propagation delay and state transition time are ignored. There are no hidden terminals and all stations in a WLAN can hear each other.
6 DBASE protocol For non-rt-stations, access method is the same with the conventional DCF. For rt-stations, access method contains all of the following procedures: - Reservation - Allocation - Sharing - Extension
7 Skeleton diagram RBT: Real time Backoff time DBT: Data Backoff time
8 Access approaches nrt-session D max Abbreviations - ReSerVation Table (RSVT) - Sequence ID (SID) and Active counter (AC) - D max interval - Reservation Frame (RF) - Contention Free Period Generator(CFPG) RF frame all rt-sessions MAC address Packet length Traffic type
9 Reservation procedure Every rt-session needs build and maintain a RSVT. RF must be sent in the time stamp t+D max if there is any session recorded in the RSVT.
11 Reservation procedure(cont d) Collision resolution for rt-stations: - P-persistent The rt-backoff time is defined as: If collision occurs, rt-station will retransmit the RTS in next slot with probability P, and in next backoff range in probability 1-P. The next backoff time is defined as:
12 Reservation procedure(cont d) Normal transmission c d P 1 - P After collision c+1 d
13 Allocation procedure Each station can only reserve the bandwidth less than average bandwidth requirement (ABR). Retransmission approach. Next Degree Extension Flag (used in extension procedure) Raise Degree (used in extension procedure)
14 Sharing procedure This procedure is to reallocate residual bandwidth for the overloaded rt-stations.
15 Extension procedure This procedure to solve the circumstance that the burst traffic arrives just after a rt-station has issued the ND for the next cycle. Extension Flag (EF) and Raise Degree (RD) are used here! Reschedule the SID in the beginning of the CFP.
16 Extension procedure(cont d) Next Current Raise
27 Conclusions The DBASE approach is proposed to support multimedia traffic over ad hoc networks. The RF frame would be a heavy overhead when lots of rt-stations recorded on it. The circumstance that the information in PF may influence to the neighbor BSS. The DBASE approach really likes the PCF!!