Concepts for Wireless Ad Hoc

Transcription

1 Bandwdth and Avalable Bandwdth oncepts for Wreless Ad Hoc Networks Marco A. Alzate Unversdad Dstrtal, Bogotá Néstor M. Peña Unversdad de los Andes, Bogotá Mguel A. abrador Unversty of South Florda, Tampa

2 Schedule Introducton : Bandwdth (BW) and Avalable Bandwdth (ABW) concepts n wred pont-to-pont p networks The Spatal hannel nk and path bandwdth nk and path avalable bandwdth An example: IEEE 8.b onclusons Page

3 Basc Bandwdth and Avalable Bandwdth oncepts BandWdth h(bw) : What sthe Maxmum Transmsson rate I can acheve when nobody competes wth me for usng the network resources? Avalable BandWdth (BW) : What s the Maxmum Transmsson rate I can acheve gven the current load wthn the network? Page 3

4 Bandwdth of a wred pont-topont path 3 h BW = mn =... h "Narrow nk" = arg mn =... h Page 4

5 Avalable Bandwdth n a pont-topont wred lnk λ(t) ABW(t) = - λ(t) t t λ() s ds t ABW ( t τ, t) = ( λ( s) ) ds τ t τ - t t ( λ () ) - s ds Page 5

6 Avalable Bandwdth n a pont-topont wred mult-hop ppath 3 h ABW = mn =... h ABW "Tght nk" = arg mn ABW =... h Page 6

7 Why s t mportant to know BW and ABW? Source transmsson rate adustment At whch h rate should I transmt n order to take the maxmum advantage of network resources, wthout degradng the servce receved by current sessons? Admsson ontrol Is the current ABW on the selected route greater than the requred bandwdth announced n the admsson request? Optmal routng Whch one, among the possble routes, has the requred bandwdth and mnmze the routng metrc? Traffc Engneerng How to dstrbute the traffc among dfferent alternate routes n order to optmally balance the load over the lnks? QoS verfcaton Is the servce provder delverng the BW we agreed? PP servce dscovery Wth whch of the possble pars do I have a greater avalable bandwdth to mnmze the fle transfer tme? Page 7

8 BW and ABW Estmaton RTT P[oss] (, (λ,γ), ) n (,, ) OWD {θ } BW = BW θ θ + ε ABW = ABW θ θ + δ n Page 8

9 Two Basc Prncples R out ross Traffc ABW R n D n t Probe Traffc D out t + D n (, ) (,, ) ABW t t + D = f D D + ε n n out Page 9

10 Some tools Pathhar Pathrate probe Pathoad IGI/PTR Pathhrp Delph Spruce approbe Netperf etc Many tools based on the same concept! u(s) ( ) Tx Rx NAV t-τ Ut ( τ, t) usds ( ) = ABW ( t τ, t ) = U ( t τ, t ) ABW = mn =... h t t τ t s ( ) ABW Page

11 What s a lnk n an Ad Hoc network? Tx Rx Tx Rx Error Rate Frame bytes Dstance (meters) th Fracton of ava alable bandwdt Fracton of avala able bandwdth d = 4 bytes, = Mbps, wth no RTS/TS. Sender Sender Dstance between senders, d (m) = 4 bytes, = Mbps, wth RTS/TS. Sender Sender Dstance between senders, d (m) Page

12 The ontenton Graph and the Spatal hannel ontenton graph: The vertces are the lnks wthn the network and the edges represent the mpossblty of smultaneous use Spatal hannel: A maxmal clque (a completely nterconnected subgraph not contaned wthn another completely nterconnected subgraph The Resource Unt s not the nk, but the Spatal p hannel Page

13 apacty of a nk, a Spatal hannel and a Path 3 Transmsson tme of a sngle bt = / Physcal transmsson rate = = n Transmsson tme of a sngle bt Physcal transmsson rate = n = The end-to-end capacty of a mult-hop path that traverses H spatal channels, where the th spatal channel s composed by n lnks wth capactes {,,=..H, =..n }, s defned as = mn = mn =.. H =.. H n =, = Page 3

14 Bandwdth of a nk T : Tme to acqure and release the medum : Packet length : Physcal data transmsson rate lnk BW ( ) = = T + T tx lnk E BW ( ) + E T [ ] The tme t takes an -bt long packet to be sent s = + T T tx f lnk ( b) = f BW ( ) T b b Page 4

15 Bandwdth of an h-channel mult-hop Path hannel hannel hannel h path E BW ( ) = mn =... h n + E T, = h = Number of, spatal channels n the path n = Number of lnks n the th spatal channel, = apacty of the th lnk of the th spatal channel T, = tme t takes a packet to get and release the medum n order to be transmtted at the th lnk of the th spatal channel Page 5

16 Avalable Bandwdth of a nk T occ =Occupaton tme of channel durng an nterval of length τ occ E ( ) k T = τ λ, k + ET τ k= =Set of lnks n chanel τ λ,k = Number of k-bt long packets sent through lnk durng τ T = Tme to acqure and release the chanel at lnk = Physcal transmsson rate of source node of lnk Page 6

17 Avalable Bandwdth of a nk nk x wthn wants to transmt τ λ more -bt long packets durng (t-τ, t] k λ + E[ Tx] + λ, k + ET x k= lnk k x E ABW = channel ( ) λ + ET k, [ ] E k= T + x x Page 7

18 Avalable Bandwdth of a nk lnk k x E ABW ( ) = maxλk, + ET Vx k= + E [ T ] x x V x = Set of spatal channels lnk x belongs to Page 8

19 Avalable Bandwdth of a Path, ( ) mn mn [ ] [ ] x Path k x X V k k ABW E T ET λ = = + [ ] X ET + X = Set of lnks wthn the path Page 9 X Set of lnks wthn the path

20 IEEE 8.b example DIFS RTS SIFS Hdr Pkt Backoff SIFS TS SIFS AK RTS TS Hdr AK ttx = DIFS + + t p + SIFS + + t p + SIFS t p + SIFS + + t p + nσ T = DIFS + 3 SIFS + 4 t p = RTS + TS+ Hdr + AK X = nσ, n ~ U (, W ) f BW ( b) t Tx T X = b f b = f T + + b b = ( ) BW X σ W b, + + ( T + σ W ) + + T Otherwse ( ) ( ) Page

21 IEEE 8.b example.8 x -5.6 Pro obablty de ensty funct ton.4. = =8 =4 =56 =5 = Bandwdth (bps) x 6 Page

22 IEEE 8.b example Tme to acqure and release the channel n the n hops of channel : Bandwdth of channel : n n T = T + + σ BO =, = BW ch ( ) = + T If we assume the sum of BOs s a normal random varable, f BW ch b / m ( b) = exp ( ) π s s / b b m + W = + + σ m n T s = nσ ( W ) Page

23 IEEE 8.b example (b) pdf f BW f f BW3 (b) pdf x -6 One Hop, 4 bytes x -5 Two Hops, 4 bytes bandwdth, b (bps) x 6 x -5 Three Hops, 4 bytes pdf f (b) BW f f BW4 (b) pdf Smulaton Theory Gaussan approx bandwdth, b (bps) x x -5 Four Hops, 4 bytes bandwdth, b (bps) x 5 bandwdth, b (bps) x 5 ch E BW ( ) = + W + n T + σ ( W ) n σ V ch BW ( ) = 3 + W + n T + +σ Page 3

24 IEEE 8.b example () (λ 3, 3 ) (3) (5) (4) ABW()/BW() ross-traffc packet length n bytes 8 7 BW() BW()? ABW()? () λ 3 E [ T ] ( + E [ T] ) Packet length n bytes ross-traffc data rate n kbps 5 5 P k t l th b t Page 4 Bandwdth n kbps

25 onclusons We have proposed new defntons for capacty, bandwdth, and avalable bandwdth, whch consder the multple nterdependences n a moble ad hoc network by replacng the concept of lnk by that of spatal channel. These defntons generalze the wdely accepted defntons, n the sense that, f each spatal channel becomes a sngle pont-to-pont lnk, the orgnal defntons are recovered. We verfed the new concepts n an IEEE 8.b ad hoc network context. We hope these defntons put on sold grounds the search for approprate estmators, whch consttute the future work. Page 5