ࡱ > ~ [ R bjbj * ΐ ΐ 1 8 8 8 1F R E E E E E E E $ I %L X E E E E E E ? D J HD !#f A : lE F 0 1F B 2 }L H }L t HD }L HD $ E E : 1F }L 8 P : Wireless Multimedia System Quiz 4 (20 min) 2015 Professor Eric Hsiao-kuang Wu HYPERLINK mailto:hsiao@csie.ncu.edu.tw hsiao@csie.ncu.edu.tw Name: Student ID: (Needless Transmission Deferment) (A) IEEE802.11DCF employs RTS/CTS (Request To Send/Clear To Send) mechanism for mitigating effect of hidden terminals T h e R T S / C T S m e c h a n i s m s e t s t r a n s m i s s i o n d e f e r r a l t i m e r t o n e i g h b o r t e r m i n a l s b y e x c h a n g i n g R T S a n d C T S b e t w e e n t r a n s m i t t e r a n d r e c e i v e r T h e n i n t h e c a s e t h a t R T S / C T S e x c h a n g e s u c c e e d s e f f e c t o f h i d d e n t e r m i n a l s c o u l d b e s u p p r e s s e d o t h e r w i s e a n y n e i g h b o r w h i c h r e c e i v e d R T S a n d / o r C T S d e f e r s i t s n e w t r a n s m i s s i o n n e e d l e s s l y a l t h o u g h D A T A p a c k e t c o r r e s p o n d i n g t o t h e p r e v i o u s R T S / C T S e x c h a n g e w i l l n o t b e t r a n s m i t t e d ( A ) I n D C F , a t r a n s m i t t e r S s e n d s R T S t o a r e c e i v e r R i n o r d e r t o p r e v e n t t r a n s m i s s i o n s f r o m h i d den terminals. However, the RTS may collide with a packet from a hidden terminal at the R and R will not return CTS to the terminal S when the hidden terminal I transmits any packet in parallel with the RTS transmission of terminal S. Then, terminals Xs set needless NAV(RTS) although RTS/CTS handshake among the terminal S and the terminal R is missed. Can you offer a scenario which will cause needless transmission deferment due to RTS. (B) Do you have a solution to solve this needless transmission due to R ! # % ) * + - . / 0 : ? N O w x y ѳѨvrnfafafnZ hCk 5aJ h >*h h >*h hI~] hI~] hI\% 0J j hI\% UhI~] hI\% j hI\% Uhx hI\% hk[ hI\% h<5 5CJ aJ o( hk[ 5CJ aJ hLh hw 5CJ aJ hV 5CJ aJ hV 5CJ aJ o( hLr\ 5CJ aJ hLh h> 5CJ aJ hI\% 5CJ h> 5CJ 0 N d gdLr\ d 7$ 8$ 9D gdCk 1$7$ 8$ gdCk $1$7$ 8$ a$gdCk gd $a$gdw $a$ p r > @ H t x X Z ^ ` C E V X ķ|i %hJ hCk B*OJ QJ ^J aJ ph hCk B*OJ QJ ^J aJ ph /hJ hCk 6B*OJ PJ QJ ]^J aJ ph %hJ hCk B*OJ QJ ^J aJ ph hJ hCk PJ ^J aJ #hJ hCk OJ PJ QJ ^J aJ o(hJ hCk OJ QJ ]^J aJ hJ hCk aJ hCk aJ hK hCk 5aJ )X ʷ hI\% hH*e j hH*e UhJ* hJ* 5hCk CJ OJ QJ ^J hkva hCk CJ OJ QJ ^J %j hE hCk CJ OJ QJ U^J hCk B*CJ OJ QJ ^J ph UhCk B*OJ QJ ^J aJ ph %hJ hCk B*OJ QJ ^J aJ ph TS. (C) Offer a scenario which will cause needless transmission deferment due to CTS. (D) Can you offer a solution for this needless transmission deferment due to CTS. d 7$ 8$ 9D gdCk ( . A!"#$% S D y K h s i a o @ c s i e . n c u . e d u . t w y K: m a i l t o : h s i a o @ c s i e . n c u . e d u . t w m D d 0 0 # A b Gm 'ȪH/\% #m p nm 'ȪH/\%PNG IHDR = w V sRGB lIDATx^yUŵc~ߊZ% `(ӄ S@T@Aj(Q(&QG AD@qAދDWTr<;{{=WsvT:u±cǾKD@D@D@D { @-m" " " "ےNRD@D@D@bmhz?j$͓@bߖRTD@D@D@' -|*AD@D@D@ -!" " " >c " " " AE nJ nd@dX%@dAQ2D@D@D@D |gD@D@D@D ۂ(" " " ">m3V " " " "mAP (JO@v[UAcǎ!'-{?E@X~Tn6mׯ-[9rO<ˬTU^=QVieR( %}-a>jK/5lԈn;w^{1~g={\;om8t e˸SSSç]M}@L`Y[lYt$mc|mmͿ8:]αp7fĀm1h oνշc]5j{i 6_c庺u֠A>-(-zH@-m"fxV=Ԛ5kJjꤓNr_;vC/}J)" "I@vz!CM1lp?s_yϵ\ݦ> E wּ^7@li&v372ZI+X$ KPJ&I%|Ŋ,Pq幘s