Enhanced Distributed Coordination Function to IEEE AdHoc Networks

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1 Enhanced Distributed Coordination Function to IEEE 80. AdHoc Networks Tiago T. da ilva, Cláudia J.. Abbas University of rasilia (Un), Dept. Electrical Engineering Faculty of Technology 70900, rasilia, razil Arab Academy for E-usiness (ARAE) 0, Al anawbari treet, P.O. ox 8575, Aleppo, yria Abstract This paper presents a new Qo Medium Access procedure for IEEE 80. ad hoc networks, called DCFAH. It offers a fair mechanism to access the medium, and a minimum bandwidth to the stations that have requested Qo. Also it is concerned about delay and jitter Qo metrics. DCFAH makes use of the EDCA mechanism to differentiate the Qo service between the flows inside a station, so it can be considered a per flow Qo mechanism. The fairness of the DCFAH is provided through a distributed control of the slots during Qo period. DCFAH also provides E services to the applications that do not want Qo services. T Keywords IEEE 80., Medium Access Control, Qo. I. INTRODUCTION he actual development of the IEEE 80. wireless networks in corporations, homes and public hotspots has contributed to the implementation of Qo mechanisms through the use of IEEE 80.e standard [], that uses EDCF (Enhanced Distributed Coordination Function) mechanism [5] to access the medium based on contention period and HCF(Hybrid Contention Function) that has a hybrid behavior, a centralized access control and EDCF. The EDCF mechanism presents a solution to provide Qo differentiation to data flows using a medium access mechanism based on contention, but this mechanism does not provide a deterministic guaranteed access to the medium. The HCF mechanism depends on a central point coordination, what is not a good solution for ad hoc networks. The HCF also allows that the stations ask for TXOPs, that are opportunities to transmit, but does not guarantee that the station will have the medium free when the station has to transmit the data that asks the TXOPs. In this paper is presented a new mechanism called DCFAH (Distributed Coordination Function Ad Hoc) for ad hoc networks. It offers a fair medium access mechanism to all the stations that are participating in an I, guaranteeing a minimum number of slots to each station. Manuscript received April, 00. This work has been supported by Arab Academy for E-usiness, Aleppo, yria. II. RELATED WORK Nowadays there are a lot of works related to the IEEE 80.e standard [] and that provides mechanisms to offer Qo to IEEE 80. networks []. Most of these works, as [3], show that the IEEE 80.e standard presents access medium method based on contention period and centralized mode. [4, 5] show that the channel access method EDCF has advantages in the differentiation of flows. Also presents the necessity to the adaptation of the link layer to the physical layer, and it needs a Coordination Function to medium access and a strategy to MAC admission control and in layers above link layer [6]. A new distributed coordination function to ad hoc networks is presented in [7], but also does not present a fair and deterministic medium access method. III. DCFAH FUNCTIONAL PECIFICATION The Adhoc Distributed Coordination Function offers a delivery service of MDUs (MAC ervice Data Unit) with Qo (Quality of evice) for adhoc networks, this mean, without a coordination point. DCFAH uses slot reservation mechanism to transmit data of a specific flow that needs Qo. Also defines a minimum period of time for E (est Effort) flows of the QTAs (Quality of ervice tation). DCFAH uses a superframe structure divided by three periods: (i) reservation period, (ii) E period; (iii) Qo period. The reservation period is used to request slots reservation from QTAs to transmit data flows that need Qo. The Qo mechanism is distributed and should be executed in all QTAs that want to be the QTA superframe manager, sending beacon frames. The transmission of beacon frames during the superframe obeys the beacons frames transmission rules of IEEE 80. Adhoc networks. During the reservation period all QTAs should transmit reservation solicitation frames to the actual QTA manager. The transmission of these frames obeys the fundamental method to medium access of IEEE 80. DCF mode, CMA- CA. The reservation period is finalized by the QTA superframe manager and is indicated in the beacon frame. During Qo period, the QTA manager receives all solicitation frames from others QTAs and calculates the IN: IN:

2 reservation during the E period. After this, the QTA manager mounts the lots Distribution Map, that indicates the transmission sequence that should be used by QTAs to transmit MPDUs with Qo. During the Qo period of DCFAH is used the lotted Arbitrary Interframe pace (AIF) period to guarantee the periodicity of the slots access of a QTA. DCFAH does not take in consideration the backoff period used in the access functions based on CMA-CA (DCF, EDCA and HCCA). All QTAs that are mapped on lot Distribution Map should wait AIF times after the medium is free. The AIF of each QTA is calculated as: AIF i lottime NumberOfl ots i AIF i : AIFs period of QTA i. i: Index of QTA in lot Distribution Map with Qo. lottime: lot time duration. NumberOflots i : number of reserved slots of QTA i. The network should be synchronized for each QTA know exactly when begins its slots. The synchronization information is transported in beacons frames in the timestamp field. All QTA should also know the lots Distribution Map and the number of QTAs that are using the slots of the Qo period. IV. UPERFRAME TRUCTURE Figure shows the superframe structure divided in three periods along with the delay that could occur at the beginning of each period caused by the medium is occupied. The beginning of each period is marked by a beacon frame that signals all the operation of the next period. () At the beginning of the protocol, all QTAs will have the same quantity of slots. The QTAs just have to confirm the reservation during the reservation period. When a QTA needs more slots should ask the actual manager of the uperframe. If a QTA have confirmed some slots but will not use all of them, for example in case of that it have used the non Qo period to transmit its data frames, should indicate that will not transmit more data frames, sending to the actual manager of the uperframe a Null frame. The transmission of a null frame should only occur if the remaining slots are sufficient to transmit the null frame. V. PERIOD ETWEEN FRAME The DCFAH defines a period called AIF (lotted Arbitrary Interframe pace) between the periods defined by the IEEE 80. standard. Figure presents the AIF that pertains to the QTA that is the owner of the first slot during the period with Qo. Immediate access when medium is free >= DIF/AIF[i] DIF/AIF usy Medium PIF IF Defer Access DIF AIF AIF[i] AIF[j] Contention Window lot Time ackoff Window elect lot and Decrement ackoff as long as medium is idle Next Frame Fig.. Periods between IEEE 80. frames with AIF period added by DCFAH Period E Period Qo Period Interval E Interval Transmission lots usy Medium of lots est Effort Others lots n- n F Fig.. uperframe with reservation, E and Qo periods. Qo Period After the transmission of the beacon frame at the beginning of the superframe, QTAs should begin the reservation of slot for the next period of Qo. The reservations should obey a network policy, that at the beginning of the protocol divides equally the slots among all QTAs. This division should obey the equation (): Immediate access when medium is free >= DIF/AIF[i] DIF/ AIF usy Medium DIF eacon AIF AIFn AIFi AIF lots of QTA lots of QTA R R = number of slots reserved for each QTA; s = total number of slots in uperframe; n = total number of QTAs in I. s n () Fig. 3. AIF periods during the Qo period inside a superframe. In figure 3 we have the AIF period in the Qo period of a superframe, where AIF is related to the total period, after a beacon frame, sent by the QTA that is the owner of the first slot, and so on. IN: IN:

3 VI. NETWORK MANAGEMENT The network management task is distributed and for each superframe a new QTA becomes the manager of the actual superframe, being responsible to send all beacons frames of the superframe. Also is responsible to receive the reservations, process them and transmit the Qo lots Distribution Map. The period of the generation of beacons frames is included in the eacon and Probe Response Frames, and the QTAs should accept the beacon period specified when it enters into an I. All of the I QTAs should participate in the generation of beacons frames. Each QTA should maintain its TF timer, that is used by the aeaconperiod object. The beacon interval inside an I is established by the QTA that created the I. The zero is defined as the first TTT. For each TTT the QTA should:. top the decreasing the backoff timer to any frame that is not a beacon or an ATIM frame;. Calculate a random delay uniformly distributed between zero and two times of the product of acwin per alottime; 3. Wait for a random delay time, decreasing the timer of the random delay using the same backoff algorithm; 4. Cancel the remaining random delay and transmit a beacon frame if the beacon arrives before the random delay timer has expired. The backoff timer ATIM should be decreased; 5. end a beacon frame if the random delay expired and non beacon frame has been received during the delay period. The DCFAH changes the functionality showed before, determining that the TTT has to be used only to transmit the beacons frames at the beginning of the superframes, that means, the QTAs competes to the transmission of the beacon frames to the next superframe period. The network policy should be analyzed inside each QTA, where the mapping of the different data flows should be done before the transmission of the reservation solicitation frames. Always that a QTA sends a reservation solicitation frame should inform the type of data that will be transmitted in the slots requested. If there is more than one type of data frame, it should inform the quantity of slots that will be sent for each type. To avoid jitter of a flow inside a QTA, the actual superframe manager should follow the sequence of slots used on the last superframe. s that are not confirmed for three superframes periods, should be put available. In the lot lot Map there is a field that counts the number of timeouts of each reservation. When the QTA wants to finish the reservation should transmit a lot Cancel Frame. VII. REERVATION MECHANIM The reservation mechanism should be executed in all QTAs, but only the QTA manager does the reservation control, transmitting the beacon frame with the Qo lot Distribution Map element at the beginning of Qo period. Figure 3 shows the reservation mechanism diagram, where () reservations solicitations done by superior layers that are submitted to the Admission Control Module (). The module (3) verifies the policies applied to the network. If the reservation surpasses the policy rules to accept the traffic, the admission control module authorizes the QTA to send the reservation solicitation frame to the actual superframe manager (5). The QTA superframe manager ends the reservation slots period sending a beacon frame at the beginning of the E period. During the E period the superframe manager processes the reservation solicitations and mounts the Qo lot Map, that is included in the beacon frame transmitted at the beginning of the reservation period. When a QTA receives the beacon frame at the beginning of the Qo period it should update the Database (7), that is used to determine the IAF of the QTA during the Qo period. When a QTA does not receive the Qo lot Distribution Map it does not have to transmit any frame during the Qo period. 8 Input of Data Request Mapping datas for Qo slots or E Admission Control 4 Reserve 3 Reserve 5 6 Control 9 Policies Fig. 4. Mechanism Diagram. Database VIII. FRAME FORMAT E 0 Qo 7 ignalling of the s (roadcast) Output of Data The DCFAH defines two new frames to the IEEE 80. standard: (i) lot olicitation Frame; (ii) lot Cancel Frame. All DCFAH frames should obey the general format of the IEEE 80. frames, adding only values to the Type and ubtype fields, that are in the header of Control Frames (table ). Table. Values added to the fields Type and ubtype of the Control Frame. Type Type Description ubtype Value 0 Control 0 0 Control 00 ubtype Description Request Cancel Also should be added values, showed in table, to the Qo control field of the data frames with Qo, during the Qo period. Each field has 6 bits and is included in all Data frames, where the Qo subfield has the value. Another change is on the 7 th bit, where is included a value to indicate that the frame pertains to the DCFAH protocol. IN: IN:

4 The TID field in the Qo Control field of the IEEE 80. standard is not used in DCFAH to simplify the reservation mechanism. The field ACK Policy is the same defined in IEEE 80.. The field queue length has 6 bits and always has an integer value that indicate the number of frames that pertains to the QTA. Table. Value added to Qo Field Frame. ubtype of Frames Data frames sent during Qo period its 0-3 Not used it 4 0 its 5-6 Política de Ack it 7 its 8-5 Tamanho da Fila 6 its 4 its 4 its... 4 its s Information QTA QTA... QTAn Fig. 6. Qo lot Distribution Map. Arbitrary Length The Information contains 6 bits and has two subfields: (i) Number of s; (ii) Number of QTAs (figure 7). The field Number of s indicates the number of reservations inside a Qo lot Distribution Map. The field Number of QTAs indicates the quantity of QTAs that has reservations and also indicates the length of Qo lots Distribution Map as can be seen on equation (3). IX. EACON FRAME 0 5 DCFAH adds in the beacons frame of the IEEE 80. the information showed in table 3. Number of s Num QTAs Table 3. Information added to the beacon frame. equence Information Notes 4 Qo Ad hoc Inside all beacons frames of the Capacity DCFAH 5 Qo lot Distribution Map ent in beacon during the Qo Period The Qo Ad hoc Capacity element has a length of 3 octets and has information about the I capacity related to the DCFAH as showed in figure 5. The field Number of QTAs indicates the quantity of QTAs that takes part in the I. The field lot Length indicates the length of the slots in microseconds. The field Next Period has bits and indicates which period is after the beacon frame, as is showed in table 4. The field Period Length has 0 bits and indicates the duration time of the next period in milliseconds. 0 Num QTAs 3 4 Fig. 5. Qo Adhoc Capacity. Table 4. Values of the field Next Period of Qo Adhoc Capacity Element. Values 3 lot Length 3 4 Next Period Next Period 0 0 Period 0 E Period 0 Qo Period Not Used Period Length The length of the Qo lots Distribution Map is arbitrary and depends on the quantity of stations with reservations. Figure 6 shows the Qo lot Distribution Map with its s Information, QTA, where index,, n represents the sequence of the QTAs reservations. 4 Fig. 7. Information Element. T MRQo NoQTA T MRQo : Qo lots Map. NoQTA: Number of QTA with reservations. The value is the octets used by the Information. The QTA i element (where i is the index of QTA in the slots reservation queue) is shown in figure AID - QTA Fig. 8. QTAs Element. Number of lots Time Out (3) Reser. The field AID-QTA has 6 bits and contains the number of Association ID of the QTA that identify which QTA is the owner of the next slots, the field Number of lots has 4 bits and indicates the number of reserved slots and the field TimeOut has bits and indicates the quantity of timeouts that the reservation can have before to be excluded. The bits and 3 are reserved. The field Timeout is increased on each superframe if the owner of the reservations does not send the reservation solicitation frame to confirm the reservations that the QTA already is the owner. X. REERVATION FRAME The Control frame with subtype olicitation just can be transmitted by QTAs that are associated to the same I and during the Period. Those frames should be transmitted by the actual QTA superframe manager. The olicitation Frame, showed in figure 9, contains the field AID QTA that has 6 bits and indicates the Association ID of the QTA that is doing the reservation. The field Number of lots has 4 bits and indicates the number of slots that are being solicited. The last 4 bits do not have any function. IN: IN:

5 Number of AID - QTA Reserved lots Fig. 8. lot olicitation Frame. The Cancel Frame has the same structure of the olicitation Frame. The only difference is the field Number of lots that indicates that the QTA wants to cancel the reservation. XI. CHANNEL ACCE PROCEDURE The DCFAH define two mechanisms to access the channel. One during the reservation period and E period and the other one to the Qo period. The procedure of channel access during reservation and E periods is the same of the IEEE 80. standard. The medium access procedure during the Qo period follows the EDCA rules just to solve problems of collisions between flows inside a QTA. The data medium access during Qo period is done using the position of the QTA inside the Qo lots Distribution Map. At the beginning of the reservation period all QTAs that has some reservation should compute its AIF times using the equation () showed before and should adjust its NAVs (Network Available Vector) period with the AIF value. After the adjustment of the NAVs the QTAs should begin to decrease the NAVs periods until reaches the value zero, that determines that the QTA should begin the medium access. The QTA should verify the medium until it is free. After that waits a PIF times and begin to transmit the data frames in its slots. The QTAs that do not have reservations should adjust its NAVs with the value of the field Period Length that is inside the Qo Ad Hoc Parameters of the beacon frames, that indicates the begin of the Qo period. When a QTA begins the medium access procedure it should update the slots counter value with the number of slots reserved. For each slot used the QTA should decrease the slot counter value. When the slot counter reaches the value zero, the QTA should stop its transmissions and waits the final of the superframe to transmit new frames. The QTA owner of the actual slot can negotiate with the receiver QTA the acknowledgment mechanism that fits its necessities. For example the IEEE 80. defines three: (i) lock Acknowledgment; (ii) No Acknowledgment; (iii) Normal Acknowledgment. When a QTA receives a data frame that need to be recognized, it should ignores its NAV and waits PIF times after the final of the data frame that ask for acknowledgment and should send a ACK frame. The QTAs that are not the owner of the actual slot only can access the medium if it receives a frame of the owner of the actual slot asking for an acknowledgment or a frame to establish the block acknowledgment mechanism. The frames RT and CT do not have to be used during the Qo period because QTAs only can transmit in two situations: (i) During its slots period; (ii) An answer frame of another frame transmitted by the QTA owner of the actual slot. All subtypes data frames allowed by the IEEE 80. standard to ad hoc networks can be transmitted during the Qo period. It also permits the fragmentation of frames and the transmission of multiple frames in sequence with any of the acknowledgment mechanism offered by the IEEE 80. standard. XII. CONCLUION This paper presents a new DCFAH (Distributed Coordination Function AdHoc) mechanism that guarantees the fair access to the medium to all stations that are associated to a specified I. The DCFAH uses a structure of superframe divided in three periods called Period, E Period and Qo Period. All QTAs competes to the transmission of beacon frame that begins the superframe. The QTA that transmit this frame becomes the manager of the superframe and is responsible to the reception of reservation frames from others QTAs during the reservation period. The QTA manager is responsible to transmit all beacon frames during superframe period. The QTA manager transmits a beacon frame to indicate the final of the reservation period and to begin the E period. This frame contains the Qo lots Map that defines the sequence of the transmission that the QTAs should follow during the Qo period. During the Qo period stations only can transmit during its slots or when they have to send a frame that is a response to another frame transmitted by the station owner of the actual slot. ADCF offers an excellent method to medium access in adhoc IEEE 80. networks. The mechanism, all the time, guarantees a fair use of the medium and a minimum access to each station that needs Qo. REFERENCE [] IEEE 80. WG, Part : Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) pecification. Agu. 999 (Reaffirmed June 003). [] IEEE 80. WG, Draft upplement to Part : Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) pecification. Amendment: Medium Access Control (MAC) Quality of ervice Enhancements. IEEE td 80.e/D3.0, January 005; draft supp. To IEEE td 80., 999 Edition (Reaffirmed June 003). [3] Y. XIAO, IEEE 80.e: Qo Provisioning at the Mac Layer, IEEE Communications, June 004, pp [4] DAQUINQ GU and JINYUM ZHANG, Qo Enhancement in IEEE 80. Wireless Local Area Networ, IEEE Communications Magazine, June 003, pp 0-4. [5] K. XU, Q. WANG, H. HAANEIN, Performance Analysis of Differentiated Qo upported by IEEE 80.e Enhanced Distributed Coordination Function (EDCF) in WLAN, Globecom, 003, pp [6] H. ZHU, M. LI, I. CHLAMTAC,. PRAHAKARAN, A urvey of Quality of ervice in IEEE 80 Networks, IEEE Wireless Communications, August 004, pp 6-4. [7] H. ZHU, G. CAO, A YENER, A. D. MATHIA, EDCF-DM: A Novel Enhanced Distributed Coordination Function for Wireless Ad Hoc Networks, IEEE Communications ociety, 004, pp IN: IN: