CN101801021A - Method for estimating peer-to-peer bandwidth and delay of MAC layer in wireless Ad hoc network - Google Patents

Abstract

The invention discloses a method for estimating the peer-to-peer bandwidth and delay of an MAC layer in a wireless Ad hoc network. In the method, two fields are expanded from a data frame header of the MAC layer to store bandwidth and delay information; the bandwidth and delay of each hop are estimated hop by hop; the bandwidth of the hop with the smallest bandwidth is taken as the available bandwidth of a path; and the summation of the delay of each hop is taken as the transmission delay of a packet on the path. The method is characterized in that: the delay caused by the retransmission of a data frame is added into the total delay when the delay of each hop is calculated. The method has the advantage of simply and directly measuring the MAC layer so as to accurately estimate the bandwidth and delay in the wireless Ad hoc network.

Description

In the wireless Ad hoc network in the method for MAC layer estimating peer-to-peer bandwidth and delay

Technical field

The present invention relates in a kind of wireless Ad hoc network method in MAC layer estimating peer-to-peer bandwidth and delay.

Background technology

Wireless Ad hoc network has characteristics such as no center, self-organizing, multi-hop route, dynamic topology, and these characteristics make Ad hoc network all have different significantly with common network at aspects such as architecture, network organization, design of protocol.How how the limited bandwidth of better utilization finds effective route in the topological structure of dynamic change, how to improve the TCP performance in the Ad hoc network, and these all are to need the problem that solves.And the basis that addresses these problems is exactly the estimation of rapid and precise realization to the Ad hoc network bandwidth and delay.

Early stage certain methods is estimated current available bandwidth in transport layer, wherein a kind of relatively typical method is to judge current network condition by the arrival rate of ACK, but, ACK delay and the reason of losing also might be that the higher bit error rate and the node high mobility of network causes, and this just makes that results estimated is inaccurate.Simultaneously, the characteristics of Ad hoc network show mainly on MAC layer and the physical layer that only the detection by the upper strata comes estimated bandwidth and delay to be difficult to obtain scheme preferably.The current method that also exists some to estimate MAC layer bandwidth delay in the wireless Ad hoc network preferably, as the MAC layer available bandwidth of current transmission path is estimated, but a tangible leak is exactly, these class methods do not take into account the re-transmission of Frame, this will make the estimated value of bandwidth too high, causes the inaccurate of final result.

Summary of the invention

The present invention is intended to overcome the above-mentioned deficiency of prior art, and a kind of method that can fast, accurately estimate end-to-end bandwidth and delay in the wireless Ad hoc network is provided.

In order to achieve the above object, the present invention adopts following technical scheme:

In the method for MAC layer estimating peer-to-peer bandwidth and delay, this method is in a kind of wireless Ad hoc network:

(1) header extension at MAC layer data frame goes out two field store bandwidth information and forward transmitted deferred message;

(2) before transmitting terminal MAC layer sends Frame, the bandwidth field is made as maximum, forward transmitted postpones field clear 0;

(3) generate a chained list at each node place, store the bandwidth and the forward transmitted deferred message of each Frame, when the ACK that receives corresponding to this frame, the information of this frame is deleted from chained list;

(4) receive the node of this Frame for each, if this node is not a receiving terminal, and the information of this frame not in the chained list, calculate one-hop delay and single-hop bandwidth, the forward transmitted that one-hop delay is added to Frame postpones on the field, and the single-hop bandwidth compared with the bandwidth field value of Frame, with the bandwidth field that wherein minimum value assignment is given Frame, send after storing data frame header into.

(5) if had the information of this Frame in the chained list, will send the re-transmission time and one-hop delay addition till now last time after, be added to again on the delay field of Frame, send after storing data frame header into.

(6) when Frame arrives receiving terminal, take out the bandwidth and the forward transmitted deferred message of data frame header, when the network layer of receiving terminal is sent ACK, deposit this two parts information in the TCP head as bandwidth information and reverse transfer deferred message respectively, make bandwidth and reverse transfer deferred message to return transmitting terminal with ACK.

(7) return in the process of transmitting terminal at ACK,, still need calculate one-hop delay T, and it is added to the TCP head according to the same procedure in the step (4) (5) for each jumping.

(8) when the MAC of transmitting terminal layer is received the Frame that contains ACK, at first from MAC layer data frame header and TCP head taking-up bandwidth information and deferred message separately, and the total delay and the bandwidth of calculating transmission path, total delay is that forward transmitted postpones and reverse transfer postpones sum, and the bandwidth of transmission path is the bandwidth information of the head storage of tcp data bag.

As preferred implementation, in (4), one-hop delay is queueing delay, obtains required time and the transmission delay three sum of medium access that the single-hop bandwidth is the Frame length of MAC layer transmission and the merchant of one-hop delay; When calculating queueing delay, need the record data frame to enter the moment of link layer formation, earlier deposited in MAC layer data frame header this time, when taking out this frame from the MAC layer queue, it is poor that the time of this frame header and current time are done, and can calculate queuing time; The computing formula of transmission delay Tr is following three formulas, and in the formula, PIFS and DIFS represent priority frame period and dispersion frame period respectively, and PLCP is the encapsulation of physical layer to Frame, and Preamble and header are respectively its prefix and heads; MAC is the encapsulation of link layer to Frame, and header is its head; Basic.Rate is the transmission rate of PLCP head; Data.Rate is the transmission rate in general data territory; FCS is the cyclic check code of 4 bytes:

Tr＝Tdata+SIFS+Tack+DIFS

$\mathrm{Tdata}=\frac{\mathrm{PLCP}.\mathrm{Preamble}+\mathrm{PLCP}.\mathrm{Header}}{\mathrm{Basic}.\mathrm{Rate}}+\frac{\mathrm{MAC}.\mathrm{Header}+\mathrm{FCS}+\mathrm{Data}}{\mathrm{Data}.\mathrm{Rate}}$

$\mathrm{Tack}=\frac{\mathrm{PLCP}.\mathrm{Preamble}+\mathrm{PLCP}.\mathrm{Header}}{\mathrm{Basic}.\mathrm{Rate}}+\frac{\mathrm{ACK}.\mathrm{Header}+\mathrm{FCS}}{\mathrm{Data}.\mathrm{Rate}}.$

Method provided by the invention is directly measured carry out simple of MAC layer, and has been considered the re-transmission of Frame, can rapid and precise realization to the estimation of the Ad hoc network bandwidth and delay.

Description of drawings

Fig. 1 is the MAC layer data frame header after the expansion.

Fig. 2 is the TCP head after the expansion.

Fig. 3 is that bandwidth--delay is estimated flow chart.

Embodiment

Technical scheme of the present invention is:

(1) expands two fields in MAC layer data frame header, respectively memory bandwidth and deferred message.Be defined as follows:

BWE unsigned?short?int 16bits

Delay unsigned?short?int 16bits

Also need in addition to go out two fields, make ACK can store the bandwidth and the deferred message of forward in the header extension of TCP.

(2) before transmitting terminal MAC layer sends Frame, BWE is initially maximum, Delay clear 0.

(3) for each jumping, when calculating one-hop delay T, need to calculate queueing delay Tq, obtain medium and insert required time T c, and transmission delay Tr, afterwards three's summation can be obtained T.

Need the record data frame to enter the moment of link layer formation when calculating Tq, earlier deposited in MAC layer data frame header this time, when the MAC layer took out this frame from formation, it is poor that the time of this frame header and current time are done, and can calculate queuing time.

Wherein the computing formula of transmission delay Tr is suc as formula shown in (1) (2) (3).

Tr＝Tdata+SIFS+Tack+DIFS (1)

$\mathrm{Tdata}=\frac{\mathrm{PLCP}.\mathrm{Preamble}+\mathrm{PLCP}.\mathrm{Header}}{\mathrm{Basic}.\mathrm{Rate}}+\frac{\mathrm{MAC}.\mathrm{Header}+\mathrm{FCS}+\mathrm{Data}}{\mathrm{Data}.\mathrm{Rate}}---\left(2\right)$

$\mathrm{Tack}=\frac{\mathrm{PLCP}.\mathrm{Preamble}+\mathrm{PLCP}.\mathrm{Header}}{\mathrm{Basic}.\mathrm{Rate}}+\frac{\mathrm{ACK}.\mathrm{Header}+\mathrm{FCS}}{\mathrm{Data}.\mathrm{Rate}}---\left(3\right)$

PIFS in the formula (1) and DIFS represent the priority frame period respectively and disperse frame period.

PLCP in formula (2) and the formula (3) is the encapsulation of physical layer to Frame, and Preamble and header are respectively its prefix and heads; MAC is the Frame that forms behind the link layer packaging packet; Basic.Rate is the transmission rate of PLCP head; Data.Rate is the transmission rate in general data territory; FCS is the cyclic check code of 4 bytes.

Tc is meant when the MAC layer queue takes out and begin to handle this Frame, until the time that RTS/CTS finishes access control.Consider the repeatedly re-transmission of MAC layer, the MAC layer need define a timer, divides two parts to calculate the time of Tc: 1) Frame is fetched into the acquisition channel right to use and is ready for sending data during this period of time from formation; 2) after data sent, timer restarted timing, when the ACK that successfully receives this Frame confirms, and the time of from this timer, taking out.Having carried out n secondary channel competition altogether if transmit this Frame, so the 2nd) part-time is exactly the time that retransmits the competitive channel needs for n-1 time.Before sending to data on the media each time, the value that all need take out this timer is added to it on channel competition time T c, till receiving MAC layer ACK affirmation or surpassing the number of retransmissions restriction.

(4) length of establishing the Frame of transmission is Packet_len, and the required time T of this Frame of single-hop transmission records in step (3), then can calculate the available bandwidth bandwidth=Packet_len/T of single-hop.

(5) obtain the bandwidth of single-hop and postpone after, before the Frame that sends, the bandwidth value that records and original BWE value compared get smaller value, will postpone T and be added to Delay, at last with bandwidth that obtains and the corresponding region that postpones to deposit in again MAC layer data frame header.

When (6) running into the situation of re-transmission,, therefore, there have been bandwidth and deferred message in the packet that needs to retransmit when not receiving ACK because the MAC layer can not deleted data packet frame information from chained list.In addition, when sending a packet, we start timer and pick up counting, and therefore only need before transmission the time in the timer be taken out, and can obtain retransmitting the needed time.

(7) return in the process of transmitting terminal at ACK,, still need calculate one-hop delay T, and it is added to the MAC layer data frame header of ACK according to the same procedure in the step (3) for each jumping.

(8) when the MAC of transmitting terminal layer is received the Frame that contains ACK, at first the ACK head from MAC layer data frame header and TCP takes out bandwidth--delay information, and computing relay Delay and bandwidth BW E, and computational process is:

Delay＝th.tcp_delay+mh.mac_delay；

BWE＝th.tcp_bandwidth；

Wherein, th.tcp_delay is that the forward transmitted of the head storage of tcp data bag postpones, and th.tcp_bandwidth is the bandwidth information of the head storage of tcp data bag, and mh.mac_delay contains the reverse transfer of storing in the data frame header of ACK to postpone.

The bandwidth and the deferred message of whole piece link have so just been obtained.

Claims (4)

1. In the wireless Ad hoc network in the method for MAC layer estimating peer-to-peer bandwidth and delay, this method is:

   (1) header extension at MAC layer data frame goes out two field store bandwidth information and forward transmitted deferred message;

   (2) before transmitting terminal MAC layer sends Frame, the bandwidth field is made as maximum, forward transmitted postpones field clear 0;

   (3) generate a chained list at each node place, store the bandwidth and the forward transmitted deferred message of each Frame, when the ACK that receives corresponding to this frame, the information of this frame is deleted from chained list;

   (4) receive the node of this Frame for each, if this node is not a receiving terminal, and the information of this frame not in the chained list, calculate one-hop delay and single-hop bandwidth, the forward transmitted that one-hop delay is added to Frame postpones on the field, and the single-hop bandwidth compared with the bandwidth field value of Frame, with the bandwidth field that wherein minimum value assignment is given Frame, send after storing data frame header into.

   (5) if had the information of this Frame in the chained list, will send the re-transmission time and one-hop delay addition till now last time after, be added to again on the delay field of Frame, send after storing data frame header into.

   (6) when Frame arrives receiving terminal, take out the bandwidth and the forward transmitted deferred message of data frame header, when the network layer of receiving terminal is sent ACK, deposit this two parts information in the TCP head as bandwidth information and reverse transfer deferred message respectively, make bandwidth and reverse transfer deferred message to return transmitting terminal with ACK.

   (7) return in the process of transmitting terminal at ACK,, still need calculate one-hop delay T, and it is added to the TCP head according to the same procedure in the step (4) (5) for each jumping.

   (8) when the MAC of transmitting terminal layer is received the Frame that contains ACK, at first from MAC layer data frame header and TCP head taking-up bandwidth information and deferred message separately, and the total delay and the bandwidth of calculating transmission path, total delay is that forward transmitted postpones and reverse transfer postpones sum, and the bandwidth of transmission path is the bandwidth information of the head storage of tcp data bag.
2. 2. in the wireless Ad hoc network according to claim 1 in the method for MAC layer estimating peer-to-peer bandwidth and delay, it is characterized in that, (4) in, one-hop delay is queueing delay, obtains required time and the transmission delay three sum of medium access that the single-hop bandwidth is the Frame length of MAC layer transmission and the merchant of one-hop delay.
3. 3. in the wireless Ad hoc network according to claim 1 and 2 in the method for MAC layer estimating peer-to-peer bandwidth and delay, it is characterized in that, when calculating queueing delay, need the record data frame to enter the moment of link layer formation, earlier deposited in MAC layer data frame header this time, when taking out this frame from the MAC layer queue, it is poor that the time of this frame header and current time are done, and can calculate queuing time.
4. 4. in the wireless Ad hoc network according to claim 1 and 2 in the method for MAC layer estimating peer-to-peer bandwidth and delay, it is characterized in that, the computing formula of transmission delay Tr is following three formulas, in the formula, PIFS and DIFS represent the priority frame period respectively and disperse frame period, PLCP is the encapsulation of physical layer to Frame, and Preamble and header are respectively its prefix and heads; MAC is the encapsulation of link layer to Frame, and header is its head; Basic.Rate is the transmission rate of PLCP head; Data.Rate is the transmission rate in general data territory; FCS is the cyclic check code of 4 bytes:

   Tr＝Tdata+SIFS+Tack+DIFS

   $\mathrm{Tdata}=\frac{\mathrm{PLCP}.\mathrm{Preamble}+\mathrm{PLCP}.\mathrm{Header}}{\mathrm{Basic}.\mathrm{Rate}}+\frac{\mathrm{MAC}.\mathrm{Header}+\mathrm{FCS}+\mathrm{Data}}{\mathrm{Data}.\mathrm{Rate}}$

   $\mathrm{Tack}=\frac{\mathrm{PLCP}.\mathrm{Preamble}+\mathrm{PLCP}.\mathrm{Header}}{\mathrm{Basic}.\mathrm{Rate}}+\frac{\mathrm{ACK}.\mathrm{Header}+\mathrm{FCS}}{\mathrm{Data}.\mathrm{Rate}}.$

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