Study on WindowBased Reliable Multicast Protocols for Wireless
Study on Window-Based Reliable Multicast Protocols for Wireless LANs Huei-Wen Ferng, Ph. D. Assistant Professor Department of Computer Science and Information Engineering (CSIE) Nation Taiwan University of Science and Technology (NTUST) Wireless Communications and Networking Engineering (WCANE) Lab E-mail: hwferng@mail. ntust. edu. tw 9/6/2004 PIMRC 2004 NTUST/WCANE Lab
Outline Introduction l Description of the proposed protocols l Performance study and numerical examples l Conclusions l 9/6/2004 PIMRC 2004 NTUST/WCANE Lab 2
Introduction (1/2) l l l Unicast vs. Multicast Wired vs. Wireless Unreliable vs. Reliable We deal with the issue of incorporating the reliability into the multicast of wireless LANs. Two major problems: ACK/NAK implosion and media access 9/6/2004 PIMRC 2004 NTUST/WCANE Lab 3
Introduction (2/2) l Existing approaches (Kuri and Kasera [6]): ¡ ¡ ¡ l Based on LBP, we further propose ¡ ¡ l Delay feedback-based protocol (DBP) Probabilistic feedback-based protocol (PBP) Leader-based protocol (LBP) LBP with a sliding window (LBPW) LBP with a sliding window and n-fold acknowledgement reduction (LBPR(n)) To achieve reliability, automatic repeat request (ARQ) is applied in this paper. 9/6/2004 PIMRC 2004 NTUST/WCANE Lab 4
Outline Introduction l Description of the proposed protocols l Performance study and numerical examples l Conclusions l 9/6/2004 PIMRC 2004 NTUST/WCANE Lab 5
Scenario Basic network architecture: AP and several mobile hosts l We split the communication link into l ¡ ¡ l Merits of such an arrangement ¡ ¡ l Sender to APs An AP to group members (GMs) Scalability Local error recovery LBPW and LBPR(n) are designed for the basic network architecture. 9/6/2004 PIMRC 2004 NTUST/WCANE Lab 6
LBPW Phase of RTS/CTS exchange ØEvent PCW 1 - AP to GMs (starting in slot k): u Send an RTS to all GMs ØEvent PCW 2 - Leader/GMs to AP (in slot k+1): u Leader Send a CTS if it is ready to receive data frames; otherwise, do nothing. u Other GMs Send an NCTS if it is not ready to receive data frames; otherwise, do nothing. 9/6/2004 PIMRC 2004 NTUST/WCANE Lab 7
LBPW Phase of data frames transfer ØEvent PTW 1 - AP to GMs (in slot k+2): u If a CTS was received by the AP in slot k + 1, start to transmit contiguously available na (<= WS) data frames with labels, say, 1, 2, . . . , na; otherwise, go back to event PCW 1. ØEvent PTW 2 - Leader/GMs to AP (during slot k + 2 + �(fl * ttr * na + tpc + tpp)/tst� and slot k + 1 + �(fl * ttr * na + tpc + tpp)/tst � + na) : u Leader If the leader received the ith frame correctly, it sends an ACK in slot k+1+ �(fl * ttr * na + tpc + tpp)/tst � +i; otherwise, it sends a NAK. 9/6/2004 PIMRC 2004 NTUST/WCANE Lab 8
u Other GMs If the ith frame was received with error bits by any GM, it sends a NAK in slot k + 1 + �(fl * ttr * na + tpc + tpp)/tst � + i; otherwise, it does nothing. 9/6/2004 PIMRC 2004 NTUST/WCANE Lab 9
LBPW l Based on feedbacks from GMs, AP should make a decision. l Three cases AP faces: ¡ An ACK is received ¡ Nothing is received ¡ A collision occurs l Case I: frame is correctly received. l Other cases: retransmission is required. 9/6/2004 PIMRC 2004 NTUST/WCANE Lab 10
LBPR(n) Phase of RTS/CTS exchange ØEvent PCW 1 - AP to GMs (starting in slot k): u Send an RTS to all GMs ØEvent PCW 2 - Leader/GMs to AP (in slot k+1): u Leader Send a CTS if it is ready to receive data frames; otherwise, do nothing. u Other GMs Send an NCTS if it is not ready to receive data frames; otherwise, do nothing. 9/6/2004 PIMRC 2004 NTUST/WCANE Lab 11
LBPR(n) Phase of data frames transfer ØEvent PTR 1 - AP to GMs (in slot k+2): u If a CTS was received by the AP in slot k + 1, start to transmit contiguously available na (<= WS) data frames with labels, say, 1, 2, . . . , na; otherwise, go back to event PCW 1. ØEvent PTR 2 - Leader/GMs to AP (during slot k + 2 + �(fl * ttr * na + tpc + tpp)/tst� and slot k + 1 + �(fl * ttr * na + tpc + tpp)/tst � + � na/n �) : u Leader Send an acknowledgement in a bit map, including the receiving status for at most n frames at a time. Hence � na/n � times of ACKs are 9/6/2004 PIMRC 2004 NTUST/WCANE Lab 12
u required to send during slot k+2+ �(fl * ttr * na + tpc + tpp)/tst � and slot k+1+ �(fl * ttr * na + tpc + tpp)/tst � + � na/n �. Other GMs Break the na frames into � na/n � subsegments (each including exactly n frames except the last one). If one of frames for subsegment i was received with error bits by any GM, it sends a NAK directly in slot k + 1 + �(fl * ttr * na + tpc + tpp)/tst � + i; otherwise, it does nothing. 9/6/2004 PIMRC 2004 NTUST/WCANE Lab 13
LBPR(n) l Based on feedbacks from GMs, AP should make a decision. l Two cases AP faces: ¡ An ACK in a bit map is received ¡ A collision occurs l Case I: erroneous frames are retransmitted. l Case II: all frames are retransmitted. 9/6/2004 PIMRC 2004 NTUST/WCANE Lab 14
Outline GSM/GPRS system l Description of the proposed protocols l Performance study and numerical examples l Conclusions l 9/6/2004 PIMRC 2004 NTUST/WCANE Lab 15
Assumptions A minimal wireless LAN is considered. MAC is neglected. Perfect time synchronization is assumed. One multicast group is considered. Each GM is assumed to be always ready to receive data frames. l Data frames may be corrupted but not lost. l Control frames are always correctly received. l Frames are generated according to Batch Poisson. l l l 9/6/2004 PIMRC 2004 NTUST/WCANE Lab 16
Performance Metrics l Cost the average time lasting since the AP contends the channel until the AP ascertains that all group members correctly receive the frame. l Exposure ratio of the number of mobile hosts actually receiving the frame and the number of mobile hosts who do need the frame. l Average queueing delay/queue length, Number of ACKs or NAKs. 9/6/2004 PIMRC 2004 NTUST/WCANE Lab 17
LBPW vs. LBP (1/2) • These results evidently show that LBPW with a large window size, say 10, performs much better than LBP. • The reductions when WS = 2 and WS = 10 compared to LBP are 4. 3% and 7. 0%, when fl = 20 and n. GM = 10 7. 3% and 13. 3%, when fl = 10 and n. GM = 10 • The increase of the window size WS causes a lower cost, i. e. , higher throughput. 9/6/2004 PIMRC 2004 NTUST/WCANE Lab 18
LBPW vs. LBP (2/2) ØWe see that the queueing delay goes down as the window size increases or the number of group members decreases. ØExposure is not affected by the increase of the window size but it increases as the group grows up. 9/6/2004 PIMRC 2004 NTUST/WCANE Lab 19
LBPR(n) vs. LBPW (LBP) (1/3) LBPR(n) achieves ACKs/NAKs reduction approximately by a factor of n compared to LBP or LBPW. 9/6/2004 PIMRC 2004 NTUST/WCANE Lab 20
LBPR(n) vs. LBPW (LBP) (2/3) 9/6/2004 PIMRC 2004 NTUST/WCANE Lab 21
LBPR(n) vs. LBPW (LBP) (3/3) • LBPR(n) performs better than LBPW due to the saving of ACKs/NAKs. • The cost reduction is more obviously when FEP is high. 9/6/2004 PIMRC 2004 NTUST/WCANE Lab 22
Outline GSM/GPRS system l Description of the proposed protocols l Performance study and numerical examples l Conclusions l 9/6/2004 PIMRC 2004 NTUST/WCANE Lab 23
Conclusions l l l The cost of LBPR(n) is lower than that of LBPW which is subsequently lower than LBP. The attainable cost reduction of LBPW compared to LBP can be over 10%. Both LBPW and LBPR(n) perform better than LBP in terms of queueing delay. LBPW mostly performs better than LBPR(n) for n ≥ 3, while LBPR(2) performs better than LBPW when the frame loss probability is low. As for the exposure metric, LBPW is the same as LBP and smaller than LBPR(n). For larger n, the exposure of LBPR(n) becomes higher. So, we suggest LBPW and LBPR(2) to be used. 9/6/2004 PIMRC 2004 NTUST/WCANE Lab 24
Thank You! 9/6/2004 PIMRC 2004 NTUST/WCANE Lab 25
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