Collision Avoidance and Resolution Multiple Access: First-Success Protocols

Transcription

1 Collision Avoidance and Resoltion Mltiple Access: First-Sccess Protocols Rodrigo Garcés and J.J. Garcia-Lna-Aceves askin Center for Compter Engineering and Information Sciences University of California at Santa Crz Santa Crz, CA 9564, USA Abstract Collision avoidance and resoltion mltiple access (CARMA) protocols establish a three-way handshake between sender and receiver to attempt to avoid collisions, and resolve those collisions that occr. This paper describes and analyzes CARMA protocols that resolve collisions p to the first sccess obtained by rnning a tree-splitting algorithm for collision resoltion. An pper bond is derived for the average costs of resolving collisions of floor reqests sing the tree-splitting algorithm is obtained and applied to the comptation of the average channel tilization in a flly connected network with a large nmber of stations. Or analysis indicates that, becase CARMA protocols garantee a sccessfl transmission for every bsy period of the channel, it achieves higher throghpt than other contention-based MAC protocols based on collision-avoidance handshakes. I. INTRODUCTION Several medim access control (MAC) protocols have been proposed over the past few years that are based on three- or for-way handshake procedres meant to redce the nmber of collisions among data packets, thereby providing better performance than the basic ALOHA or CSMA protocols [2], [3], [4], [5], [6], [9], [], [2]. The concept of floor acqisition was first introdced by Fllmer and Garcia-Lna-Aceves [5] for MAC protocols based on three- or for-way handshake procedres. In a single-channel network, floor acqisition entails allowing one and only one station at a time to send data packets withot collisions. Protocols that provide correct floor acqisition have been called floor acqisition mltiple access (FAMA) protocols. A FAMA protocol reqires a station who wishes to send one or more packets to acqire the right to se the channel exclsively (called the floor) before transmitting the data packets. In FAMA-NTR [5], before transmitting a data packet, a station senses the state of the channel to see if it is idle or not. If the channel is bsy, the station backs off and tries to acqire the channel at a later time; on the other hand, if the channel is sensed to be free, the station sends an. In short, stations follow a non-persistent CSMA strategy for the transmission of s. The sender listens to the channel for one maximm rond-trip time pls the time needed for the destination to send a CTS. If the CTS is not corrpted and is received within the time limit, the transmission of data packets from the sender proceeds. The CTS is sent by the destination station to let other stations in the system know that the floor of the channel has been acqired. Accordingly, when a station receives a correct CTS, it backs off ntil the channel is released by the sender. Althogh each station transmits an only when it determines that the channel is free, a collision with other transmissions may still occr de to propagation delays. s are vlnerable to collisions for time periods eqal to the propagation delays between senders of s. Dring these periods, mltiple stations may sense the channel free and also send s, ths casing collisions. FAMA protocols solve collisions by backing off and reschedling transmissions [5], [6]. As with CSMA protocols, this procedre yields good reslts if the traffic is low; however, the probability of collisions increases as the rate of transmissions increases, with a corresponding decrease of system throghpt. Eventally, as the This work was spported in part by DARPA nder Grants DAA7-95-C-D57 and DAAH transmission rate increases, the constant collisions case the channel to collapse, bringing the flow of data packets to a halt. To remedy this problem, we present CARMA (collision avoidance and resoltion mltiple access) protocols that resolve the collisions of s by allowing one to scceed in every rond of contention sing a tree-splitting algorithm. In high-speed wireless networks sing s mch smaller than data packets, these protocols improve over the performance of FAMA protocols, and other prior MAC protocols based on collision-avoidance handshakes, becase every new rond of sbmissions to the channel reslts in a sccessfl transmission of data packets, and the average time needed to obtain a sccess in a rond of contention is very small compared to the dration of data packets. Sections II and III describe a specific protocol, which we call CARMA-FS (for first sccess), and which ses non-persistent carrier sensing for the transmission of s and a tree-splitting algorithm to resolve collisions of s p to the first sccess. Section IV comptes an pper bond on the average costs of resolving collisions, i.e., the times associated with the evental sccessfl transmission of all data packets involved in a collision-resoltion tree; the importance of these bonds is that they are independent of the nmber of stations in the network. Section V ses them to compte a lower bond of average throghpt achieved by CARMA-FS when a very large poplation of nodes is assmed. We show that the throghpt achieved by CARMA-FS is always better than the throghpt of FAMA protocols. Section VI offers or conclding remarks. II. CARMA-FS CARMA-FS ses carrier sensing for the transmission of s and a tree-splitting algorithm to obtain the first sccess among a set of colliding s. more sophisticated collision-resoltion algorithms [] can be sed to obtain the first sccess in a rond of contention. Each station mst know the maximm nmber of stations allowed in the system and the maximm propagation delay in the network. For the slotted version of CARMA-FS, a time slot is assmed to last as long as the maximm propagation delay. Each station is assigned a niqe identifier, a stack and two variables ). is initially the lowest ID nmber that is ( and allowed to send an, while is the highest ID nmber that is allowed to send an. Together they constitte the allowable ID interval that can send s, i.e., attempt to acqire the floor. If the ID of a station is not within this interval, it cannot send its. As we describe sbseqently, the stack is simply a storage mechanism for ID intervals that are waiting to get permission to send an. A station can be in one of five different states in CARMA-FS, namely: PASSIVE: The station has no local packets pending and no transmissions are detected in the channel. : The station is trying to acqire the floor and has sent an. XMIT: The station has the floor and is sending data packets. REMOTE: The station is receiving transmissions from other stations, and started to detect channel activity before it had any local packet to send.

2 ' ' ACKOFF: The station has local packets pending and had to reschedle its reqest for the floor. When a passive station has one or mltiple packets to send, it first listens to the channel. If the channel is bsy (i.e., carrier is detected), the station backs off and reschedles its at some time into the ftre. Alternatively, if the channel is clear (i.e., no carrier is detected) for one maximm rond-trip time, the station transmits an. The sender then waits and listens to the channel for one maximm rond-trip time pls the time needed for the destination to send a CTS. When the originator receives the CTS from the destination, it acqires the floor and begins transmitting its data packet brst. The sender is limited to a maximm nmber of data packets, after which it mst release the channel and mst compete for the floor at a later time if it still has data packets to send. If the sender of an does not receive a CTS within a time limit, the sender as well as all other stations in the system know that a collision has occrred. As soon as the first collision takes place, every station divides the ID interval into two ID intervals. The! first ID interval, "$#%& which we will call the backoff ID interval, is (*),+, while the second ID interval, the allowed ID interval, is -&"$#% (.. Each station in the system pdates the stack by execting a PUSH stack command, the key being pshed is the backoff ID interval. After this is done, the station pdates and with the vales from the allowed ID interval. This procedre is repeated each time a collision is detected, ntil a sccessfl transmission is achieved. Only those stations that were in the state at the time the first collision occrred are allowed into the collision-resoltion phase of the protocol. All other stations will be in REMOTE state ntil the collisionresoltion phase ends. Collision resoltion evolves in terms of collisionresoltion intervals. In the first interval of the collision-resoltion phase all stations in the allowed ID interval that are in the state try to retransmit an. If none of the stations within this ID interval reqest the channel, the channel will be idle for a time period eqal to two times the maximm channel delay (/ ). At this point, a new pdate of the stack and of the variables and is de. Each station exectes a POP command in the stack. This new ID interval now becomes the new and. The second alternative is for mltiple stations to reqest the channel casing a collision. The stations in the allowed ID interval are once more split into two new ID intervals and the stack as well as the variables for each station are pdated. In this case, the dration of the collision-resoltion interval is eqal to the collision time pls the channel delay. The algorithm repeats these steps ntil the first sccessfl /CTS exchange is achieved. This is the case when only one station in the allowed ID interval is reqesting the channel; the originator receives the CTS from the destination and begins transmitting its data packet brst, after which the station releases the channel and transitions to the PASSIVE state. The total time for this sccessfl transmission is at most eqal to the dration of an, a CTS, the data packet brst, pls three channel delays. Notice that, as soon as the first sccess is achieved, all stations know that the collisions-resoltion phase has ended. Accordingly, once the treesplitting algorithm terminates, all stations are either in the PASSIVE state, or in the ACKOFF state if they have packets to send. A waiting period of two times the maximm channel delay dring which the channel is idle occrs pon termination of the tree-splitting algorithm. The next access to the channel is driven by the arrival of new packets to the stations and the transmission of s that have been backed off. To permit the transmission of packet brsts, CARMA-FS enforces waiting periods on receiving stations at strategic points in the operation of the protocol. A station that has received a data packet in the clear mst wait for one maximm propagation time after processing a data packet, this allows the sender to send more packets if desired. A station that has nderstood any control packet mst wait for twice the dration of the maximm propagation time; this allows correct /CTS exchanges to take place. On the other hand, if a transmitting station is in the state, the protocol enforces a waiting period of two maximm propagation times after sending its. This allows the destination to receive the and transmit the corresponding CTS. A sending station mst also wait one maximm propagation time after the last data packet of its packet train. III. EXAMPLE We illstrate CARMA-FS sing a simple example. Each station has a distinct position in the leaves of a binary tree based on its ID. If is the total nmber of stations in the system, the binary tree has /32 + nodes. The root of the tree is labeled as %4 and its right and left child as 5 and 76, respectively. For each of the other nodes, the labels are composed of the parent label, pls a 8 if it is the left child or a + if it is a right child. As an example, take a system with for stations labeled 6$6, 6 5,!5 6, and!5$5. The binary tree has a total of seven nodes with the for stations as its leaves. The root of the tree has the label %4. The left child of the root node is 5 while its right child is 76. Station 76 is the parent node of 76 5 and 76$6. Similarly, station 5 6 is the right child of node 5, while station!5$5 is its left child. We define the sbtree 9%:<;&=?>$: as the sbtree at node %:<;&=@>$:. In or example, the sbtree for node 6 5 is Assme that, at time A ", we are at node 4 and we are allowed to listen simltaneosly at all the stations of its sbtree 9%4 for a time period of seconds. Only one of the following three things can occr: Case Idle: There are no s in any of the leaves (stations) in sbtree 9%4 ; therefore, the channel is idle. This lasts an idle transmission period 9. Case 2 Sccess: There is only one in the sbtree 9 4 ; therefore, there is no collision and a station acqires the floor terminating the collision-resoltion phase. This lasts one sccessfl transmission period 9!C. Case 3 Collision: There are two or more stations (leaves) in the sbtree 9 4 sending an ; therefore, a collision occrs. This lasts one failed transmission period 9!D. Assme that, at time AE6, Case 3 occrs with station 76$6 and 76 5 each sending an in the same slot, while station 5 6 and station 5$5 do not reqest the channel. Fig. illstrates this. The first collision occrs at time A 6 ; all stations in the system notice the beginning of the resoltion F algorithm and pdate their stacks and their as well as their vales. Stations 6$6 and 6 5 are members of the backoff ID interval; therefore, they wait ntil the collisions in the allowed ID interval are resolved. They both are exclded from sending s. After a time period 9 D, Stations!5 6 and!5$5 are allowed to reqest for the channel. Since stations 5 6 and 5$5 in tree 9 5 do not wish the channel, the first case applies here. After 9 HG /I seconds, all stations notice that the channel is idle, which means that there were no collisions in tree 9!5. All the stations in the system mst pdate their intervals and the stack. They execte a POP-stack command and the new allowable interval is?j6$ ; therefore, 9 6 can proceed to solve its collisions. oth stations 6$6 and 6 5 transmit an control packet and Case 3 occrs again. Since a collision occrred, the interval is split, i.e.,, the sbtree 9 6 is split in two halves, 976$6 and Station 76 5 is within the allowable interval while the 76$6 station mst wait, its interval is the top of the stack. Since has only one station reqesting the channel, that station acqires the floor and transmits its data package. At this point, all the stations know that the collision-resoltion phase has terminated, becase a sccessfl /CTS exchanged was sensed by all stations. The stations empty their stacks and pdate the allowable ID interval allowing all stations to contend in the next rond of contention. Fig. illstrates the transmission for each of the GLK stations in the system, as well as in channel for the nslotted version of CARMA-FS. ICC 97 2 Rodrigo Garcés and J.J. Garcia-Lna-Aceves

3 s Stack before first collision Allowable Interval Station n Station n Station n Station Channel T QQQ QQQ QQQ QQQ QQQ QQQ QQQ QQQ QQQ QQQ RRR RRR RRR RRR RRR RRR RRR RRR RRR SSS SSS SSS SSS SSS SSS SSS SSS SSS TTT TTT TTT TTT TTT TTT TTT TTT nr MN MN O OP OP CTS DATA CTS DATA n n n n Idle Idle first collision Allowable Interval Idle n τ τ T second collision n n n n n n n first sccess Allowable Interval Allowable Interval Allowable Interval LowID HiID LowID HiID HiID HiID HiID LowID LowID LowID (n,n) Fig.. Transmission period and tree strctre to solve the collisions for a system with UWVX stations ot of which Y,V[Z are reqesting the floor. \^]-X_?Z&` VaZ, b ]XI_cZ&` Ved and f ]XI_?Z&`^Vgd. IV. AVERAGE COLLISION RESOLUTION COSTS For the prpose of or analysis, we assme that (a) the channel introdces no errors, so packet collisions are the only sorce of errors, and stations detect sch collisions perfectly, (b) two or more transmissions that overlap in time in the channel mst all be re-transmitted, and (c) a packet propagates to all stations in exactly seconds []. The average size of a data packet is h seconds, and and CTS packets are of size i seconds. oth h i and are assmed to be mltiples of in order to accommodate the comparison with the slotted version of the protocol. There are only three possible cases to consider for the resoltion of collisions: idle, sccess, or collision. For each of these cases, we obtained [8] three distinct average-cost recrsive eqations: jk? &ln for the idle case, op? (n) for the sccess case, and q!? τ time for the collision case. These three costs depend on the total nmber of stations in the system and the nmber l of stations with one. They represent an average nmber over all the possible permtations of l s in total stations ntil the first sccessfl /CTS exchange. In [8] we se mathematical indction to prove the pper bonds for the average idle cost j*? rl and for the average collision cost q!? rl lts. For all + and +, we find that jk?. ' 5 and q!? rl3wvxiy l 2 +. op? contribtes positively to the overall throghpt of the system. Every rond of contention is garanteed to allow one sccessfl /CTS exchange, therefore, oz? {l G +. V. THROUGHPUT ANALYSIS The analysis in this section makes the same assmptions introdced in the previos section and ses the same traffic model sed for the FAMA- NTR protocol [5]. Given that the pper bonds on average collisionresoltion costs are independent of the nmber of stations, we approximate the traffic into the channel with an infinite nmber of stations, each having at most one to send at any time, and forming a Poisson sorce sending s with an aggregate mean generation rate of s per nit time. With this model, the average nmber of arrivals in a time interval of length 9 is }9 l, i.e., G }9. All data blocks have a dration of h seconds. The average channel throghpt is given by ~z H ƒ () is the average tilization time of the channel, dring which the channel is being sed to transmit data packets; is the expected dration of a bsy period, dring which the channel is bsy with sccessfl or nsccessfl transmissions; and is the average idle period, i.e., the average interval between two consective bsy periods. A. A sccessfl transmission consists of an with one propagation delay to the intended recipient, a CTS with a propagation delay to the sender, and a data packet followed by a propagation delay. Therefore, the average dration period for a sccessfl transmission is I %Hˆ?! zš{ J zœ (2) For an to be sccessfl, it mst be the only packet in the channel dring its transmission. Its probability of sccess eqals the probability that no arrivals occr in seconds, becase there is a delay across the channel of seconds before all the other stations in the network detect the carrier signal. After this vlnerability period of seconds, all stations defer their transmissions. Therefore, given that arrivals of s to the channel are Poisson with parameter, we obtain I %H 7Ž No arrivals in seconds H $ (3) The nmber of stations that participate in the collision-resoltion phase is l G 7. Within the tree, the three cases of the collision resoltion discssed in the previos sections are present. Each one of them has an average pper bond cost that is independent of the nmber of stations ( ), bt is a fnction of the nmber of stations reqesting the channel ( l ). In the case of a colliding transmission ( l s + ), the time period consists of one package followed by one or more s transmitted by other stations within time, 8, pls one propagation delay. Accordingly, the average dration of a failed transmission period is l bonded by 9 D i 2 / [5]. In the case of an idle transmission ( G 8 ), the time period has a dration eqals to two propagation delays. Accordingly, the average dration of an idle transmission period is 9 G /I. A bsy period is composed of both the sccessfl and the tree transmission periods. A waiting period of /I seconds is reqired for both transmission periods. The dration of an average bsy period eqals the sm of the percentage of sccessfl transmission periods times their dration, 9!C, pls the percentage of the tree periods times their dration. The tree periods are composed of three parts, corresponding to sccess, idle, and collision periods, each with a distinct cost and dration. According to the pper bonds derived in [8], the average bsy period can be bonded as follows: š œ Ÿž? ž- I ˆ?ª ž žž ˆ$ $ &? ž c Š{ c { ž! zˆ$ $ &? ž c I zš?! z«{ J pœ (4) The channel carries ser data for h seconds dring each transmission period; therefore, G h. The average idle period is eqal to the average interarrival time pls the average waiting period enforced. ƒ zˆ{ zˆ{ ž zˆ{ (5) Sbstitting the vales for, and obtained above into Eq. (), we obtain the following lower bond for the average throghpt of CARMA- FS: ~ Œ z (6) ICC 97 3 Rodrigo Garcés and J.J. Garcia-Lna-Aceves

4 ž pˆ c ž $ zš ž zˆ c? ž $ Š z Œ size of s and CTSs is /Ã8 bytes. We normalize the throghpt reslt by setting G + and defining the following variables Ä Œ (normalized data packets) ÅÆ (normalized control packets) Ç (normalized offered load) (). In this section, we se the same assmptions sed for nslotted CARMA-FS. The channel is slotted and each slot lasts a maximm propagation delay. With slotting, stations are restricted to start transmissions only on slot bondaries. As it was the case in nslotted CARMA-FS, the average dration period for a sccessfl transmission is given by Eq. (2). The probability that an is sccessfl is H 7Ž$± ² arrival in a slot³ some arrivals in a slot (7) ĺ s In the case of a colliding transmission ( + ), the time period consists of one followed by a propagation delay. All colliding s are sent at the beginning of the same slot; accordingly, we have 9 D G i 23. As it was done for nslotted CARMA-FS, can be bonded according to Eq (4). Sbstitting the vales for µ C, 9 D, 9!C, 9 l and, we obtain I I 7 ž<? ž- ¹ ˆ º ª ž I c ž< c ž c zš@! z»$ 7 zœ ž Ÿ ž F ˆ? ž c ž ž< ˆ ˆ Š@»$ Œ$ ž- The average idle period is ƒ zˆ{ I ^ zˆ{ ž I $ zˆ{ (9) The average tilization is simply h. Sbstitting this vale and Eqs. (8) and (9) into Eq. (), we obtain the following lower bond on the average throghpt of slotted CARMA-FS: ~z Œ ž Ÿ Ÿ z () ž! c ^ ˆ m? ž $ p % zˆ ˆ pš?! z¼{ J zœ ž< c ž $ Š? z Œ C. Nmerical Reslts We compare CARMA-FS with FAMA-NTR for the cases of a lowspeed network (½I¾8I8 b/s) and high-speed network ( + Mb/s) in which either small data packets ( À bytes) or large data packets (K 88 bytes) are transmitted. We assme the distance between stations to be the same and define the diameter of the network to be + mile. Assming these parameters, the propagation delay of the channel is Á K s. In order to accommodate the se of IP addresses for destination and sorce, the minimm (8) Sbstitting the new normalized variables from Eq. () into Eq. (6), we obtain ~ Ä 7È Ç z (2) È ž Å zˆ@ m? ž<ç^ I zå zš È ž Å zˆ@ &? ž<ç7 Š@Å F 7 Ä for nslotted CARMA-FS. The throghpt of nslotted FAMA-NTR in [5] normalize with the variables in Eq. () is For slotted CARMA-FS we obtain ~ Ä Ä Ä Ä zå ž<ˆ Ç Ç z Ç ž<é zåe (3) ~ Ä ž Ç È Ç z È (4) È ž<å zå Ç H Ç7 ž Ç7 ž<å ÇH zˆ@çf pš?å Ä z¼? È ž Å} ž Ç7 ž<š?å Ä while the throghpt of slotted FAMA-NTR in [5] normalize with the variables in Eq. () is ~ Ä Ä Ä Ç^ Ç ž Ä zå Ç Ç ž Š} zå Êž- Ç (5) Table I smmarizes the protocol parameters sed in or comparison. Network Speed Packet Size Œ Ä Œ Å7 96 bps 424 bits Ë s bps 32 bits Ë s Mbps 424 bits 424 Ë s Mbps 32 bits 32 Ë s TALE I PROTOCOL VARIALES FOR LOW-SPEED NETWORKS (ÌrÍ&Î&Î PS) AND HIGH-SPEED NETWORKS ( d MPS) WITH TWO TYPES OF DATA PACKETS, SMALL (XZ X ITS) OR LARGE (ÏZ&ÎrÎ ITS). THE CHANNEL DELAY ÐzVÑÃÒ XÓ S, WHILE THE CONTROL PACKETS ARE dmí&î ITS LONG. Figs. 2 and 3 show the average throghpt (S) verss the offered load (G) for CARMA-FS and FAMA-NTR. It is clear that slotting does not provide mch performance improvement in CARMA-FS, and that to achieve high throghpt the size of the control packets need to be small compared to the length of the data packets or packet trains. CARMA-FS behaves like FAMA-NTR when the offered load is small. As the offered Ç ICC 97 4 Rodrigo Garcés and J.J. Garcia-Lna-Aceves

5 FAMA-NTR verss CARMA-FS: Low Speed, Small Packets FAMA-NTR verss CARMA-FS: Low Speed, Large Packets e Fig. 2. Throghpt of FAMA-NTR and CARMA-FS for low-speed network..8 FAMA-NTR verss CARMA-FS: High Speed, Small Packets.8 FAMA-NTR verss CARMA-FS: High Speed, Large Packets Simlation CARMA-FS e Fig. 3. Throghpt of FAMA-NTR and CARMA-FS for high-speed network. load increases, the throghpt of FAMA-NTR decreases rapidly, while CARMA-FS decreases logarithmically at a mch slower rate. To verify that the vale of Ô approximated sing an infinite poplation and the pper bonds on average costs for collision resoltion times provides a good lower bond for any traffic load, we simlated slotted CARMA-FS sing 65 stations that generate s according to a Poisson probability distribtion l fnction. The simlations were done ten times for each given G vale to insre convergence. The reslts of the simlation are shown in Fig. 3 only for the case of long data packets in a high-speed network, and indicate that or analysis provides a very good approximation of the average throghpt. VI. CONCLUSIONS CARMA-FS implements a three-way handshake based on small control packets between sender and receiver, pls a limited collision resoltion algorithm ensring that there is always a sccessfl dring each bsy period. Or analysis shows that this limited collision resoltion improves the performance of FAMA protocols considerably; or simlation validates the simplifying assmptions made to obtain a lower bond of average throghpt as a fnction of channel load. The importance of exploring limited collision resoltion lies on its potential application to wireless networks with dynamic topologies, in which the nodes engaged in collision resoltion may move, therefore changing the constitency of the tree. A protocol aimed at resolving the first sccess is attractive in a dynamic setting, becase resolving the first sccess can be done faster than resolving an entire tree [7]. Or work contines to explore the performance of limited resoltion algorithms when the members of the tree have inconsistent information abot the allowable ID interval. REFERENCES [] D. ertsekas and R. Gallager, Data Networks, Second Edition, Prentice-Hall, 992. [2] V. harghavan, A. Demers, S. Shenker, and L. Zhang, MACAW: A Media Access Protocol for Wireless LAN s, in Proc. of ACM SIGCOMM 94, pp , ACM, 994. [3] K. iba, A Hybrid Wireless MAC Protocol Spporting Asynchronos and Synchronos MSDU Delivery Services, Tech. Rep. Paper 82./9-92, IEEE 82. Working Grop, 992. [4] R. L. rewster and A. M. Glass, Throghpt Analysis of Non-Persistent and Slotted Non-Persistent CSMA/CA Protocols, in Proc. 4th International Conference on Land Mobile Radio, pp. 23 6, Instittion of Electronic and Radio Engineers, 987. [5] C. Fllmer and J.J. Garcia-Lna-Aceves, Flooracqisition mltiple access forpacket-radionetworks, Proc. ACM SIGCOMM 95, Cambridge, MA, Agst 3-September, 995. [6] C. Fllmer and J.J. Garcia-Lna-Aceves, FAMA-PJ: A Channel Access Protocol for Wireless LANs, Proc. ACM Mobile Compting and Networking 95, erkeley, CA, Nov. 4-5, 995. [7] R. Garcés and J.J. Garcia-Lna-Aceves, Floor Acqisition Mltiple Access with Collision Resoltion, Proc. ACM Mobile Compting and Networking 96, Rye, NY, Nov. -2, 996. [8] R. Garcés and J.J. Garcia-Lna-Aceves, Collision avoidanceand resoltion mltiple access with transmission grops, Proc. IEEE INFOCOM 97, Kobe, Japan, April 7-, 997. [9] P. Karn, MACA - a new channel access method for packet radio, in ARRL/CRRL Amater Radio 9th Compter Networking Conference, pp. 34 4, ARRL, 99. [] L. Kleinrock and F. A. Tobagi, Packet switching in radio channels: Part I - carrier sense mltipleaccess modes and their throghpt-delay characteristics, IEEE Trans. Commn., vol. COM-23, no. 2, pp. 4 46, 975. [] W. F. Lo and H. T. Moftah, Carrier Sense Mltiple Access with Collision Detection for Radio Channels, in IEEE 3th International Commnications and Energy Conference, pp , IEEE, 984. [2] G. S. Sidh, R. F. Andrews, and A.. Oppenheimer, Inside AppleTalk, Second Edition. Addison-Wesley Pblishing Company, Inc., 99. ICC 97 5 Rodrigo Garcés and J.J. Garcia-Lna-Aceves