CN102905337B - Routing method based on cross-layer design in self-organized network - Google Patents

Abstract

The invention aims to provide a routing method based on cross-layer design in a self-organized network. According to the invention, based on the cross-layer idea, an SR (smooth of retry count) is redefined in a routing protocol through two variables, namely, SSRC (station short retry count) and SLRC (station long retry count) to express retry counts during the frame transmission process, and PSAC (Probability of Successful Access to Channel) is determined on the basis, so as to achieve the aim of selecting the optimal channel. On the basis of multi-channel multi-interface AODV (Ad hoc on demand distance vector routing), by combining the SR and the current length of each buffering queue in each interface, the LTC (Link Transmitting Capacity) is determined to be taken as the routing probability. By comprehensively consideration of the PSAC and the routing probability, the purpose of obtaining high handling capacity and short delay by low route load is achieved in a multi-channel multi-interface AdHoc scene.

Description

Method for routing based on cross-layer design in self-organizing network

Technical field

The present invention is a Routing Protocol that is applicable to multi-signal-channel and multi-interface Ad Hoc network environment, belongs to communication technical field.

Background technology

AdHoc network is the acentric wireless multi-hop network of a kind of self-organizing, and it can not rely on any intrinsic radio infrastructure and can set up anywhere or anytime provisional network.It is a kind of equity network with special purpose, when the each node in network is being played the part of terminal role, is playing the part of again the role of router, realizes network service by internodal forwarding.Be summed up, compare common fixed network and mobile network, Ad Hoc network has following feature:

(1) without division center.The control centre that Ad Hoc network is not fixed, equal between all nodes, is a peer-to-peer network.Node in network can add and deviated from network at any time, and the fault of any node can not affect the operation of whole network, has very strong survivability.

(2) self-organizing.Network set up, launch not need to rely on any network facilities of setting up in advance.Between node, coordinate behavior separately by layered protocol and distributed algorithm, node just can rapidly, automatically form an independently network afterwards in start.

(3) multi-hop route.When node will with its wireless transmitter coverage outside node while communicating, need other intermediate node to carry out multi-hop forwarding.Different from the multi-hop of fixed network, the multi-hop route in Ad Hoc network is to be completed by common network node, instead of is completed by special routing device (as router).

(4) dynamic topology.Ad Hoc network is a dynamic network.Network node can move arbitrarily, startup and shutdown whenever and wherever possible, and these all can make topology of networks change at any time.These features make Ad hoc network all have obvious difference with common mobile communications network and fixed network at aspects such as network organization, architecture, Protocol Designs.

Along with the development of radio communication, Ad Hoc network comes into one's own in increasing field.Have benefited from independent networking, self-organizing, dynamic topology, without the good characteristic such as division center, multi-hop route, survivability be strong, Ad Hoc network has all occupied one seat in commercial communication and military communication field, as emergency disaster relief, ground observation, field rescue etc.

But we should see, as a kind of emerging network technology, it still has the problems to be solved such as many.Most critical be that it has the features such as the random mobile continuous variation that causes network topology of node, time-variant wireless channel environment, limited channel width, these have proposed challenge for Design and implementation Ad Hoc network, so must go to consider from the every aspect of network architecture carefully.The for example network layer of high spot reviews in this patent, needs design can adapt to that topology changes fast, stable routing mechanism, and the overheads such as route maintenance information can be controlled to a zone of reasonableness, to ensure the efficient utilization of Internet resources.

The research of Ad Hoc network routing protocol is very deep.By the drive pattern difference of finding route, class can be divided three classes: active (Proactive), response type (Reactive) and mixed type (Hybrid).Active Routing Protocol drives Routing Protocol also referred to as Proactive routing protocols or table, the each node of this protocol requirement needs to set up and safeguard the routing table of the recent route information that arrives all nodes, all routing iinformations are consistent, and Typical Representative is as DSDV, OLSR etc.; Response type Routing Protocol claims again on-demand routing protocol or source forcing Routing Protocol, and it is a kind of Routing Protocol of passive type, only in the time having business demand, just can trigger route discovery processes and find the route that arrives object, and Typical Representative is as DSR, AODV etc.; Hybrid Routing Protocol is to combine the active and corresponding advantage of response type, selects suitable route type of drive according to actual conditions, and Typical Representative is as ZRP agreement.

In early stage Ad Hoc network, due to the restriction of hardware technology, equipment price and avoid the needs of mutually coordinating between node, most of terminal is all single channel list interface type, and the network performance of composition is very limited thus.Along with the raising of system to throughput demand, in a terminal, equipping multiple transceivers has been a trend of Ad Hoc network terminal development in the future, and the development of hardware technology and the reduction of equipment cost have aggravated this trend especially.IEEE 802.11 has defined multiple nonoverlapping channels in 2.4GHz and 5GHz frequency range, in the time that multiple wireless channels are available, in terminal, equip more than one R-T unit, can make adjacent different nodes communicate on different channels simultaneously, can greatly reduce thus the phase mutual interference between adjacent node, reduce time delay, improve the throughput of system.Can say, multi-signal-channel and multi-interface is a main trend of following Ad Hoc network Development.And how to distribute and to make good use of these channels, and corresponding route metric is proposed on this basis, become the study hotspot of current Ad Hoc network routing protocol.

Summary of the invention

Technical problem: the object of the invention is to provide the method for routing based on cross-layer design in a self-organizing network, i.e. multi-signal-channel and multi-interface Ad Hoc method for routing.The method that the method designs by cross-layer, calculates channel allocation tolerance and route metric, can realize with lower routing cost and obtain higher bag arrival rate, throughput of system, reduces the average delay of system simultaneously.

Technical scheme: the present invention has provided the method for routing based on cross-layer design in a self-organizing network.The method is carried out channel allocation according to successfully accessing channel probability, determines route metric based on link transmission ability simultaneously, and the method can obtain higher bag arrival rate and throughput of system with lower routing cost, and reduces the average delay of system simultaneously.

Cross-layer technology is to improve a kind of effective means of mobile Ad Hoc network resource utilization.So-called cross-layer is exactly to break to a certain extent or change original restriction of communication between layers, change original protocol layer interface, by using between layers mutual, make the at all levels of protocol stack can share local information, to eliminate the redundant interaction between each layer of wireless network, greatly reduce communication overhead, the overall performance of optimization system.For the Ad Hoc network becoming when, limited bandwidth large for time delay, channel, the impact that the benefit that cross-layer design is brought is brought much larger than mutual between layers complexity.Therefore, it is necessary in Ad Hoc network, adopting the thought of cross-layer design design with combined optimization, and it can improve the overall performance of wireless network.Existing cross-layer design can roughly be divided into following a few class: physical layer and the design of MAC layer cross-layer; Physical layer and the design of network layer cross-layer; Physical layer and the design of transport layer cross-layer; MAC layer and the design of network layer cross-layer; MAC layer and the design of transport layer cross-layer; Network layer and the design of transport layer cross-layer.

The method comprises following content:

A. determine the channel allocation tolerance of broadcast packet: the neighbours that establish node A concentrate N neighbor node, in node A, the channel of the broadcast packet of channel j success access probability PSAC is wherein FC _j(n) be illustrated in the bag quantity that one-period interior nodes A transmits to its neighbor node n by channel j, be illustrated in i the re-transmission index SR value of wrapping that one-period interior nodes A sends to neighbor node n by channel j, SR _maxre-transmission index during for bust this, the best broadcast channel of node A selects tolerance to be:

$\mathrm{BestChannelForBroadcast}\left(A\right)=\left\{j\right|\underset{j\∈[0,K-1]}{\max }\left\{{\mathrm{PSAC}}_j^{\mathrm{Broadcast}}\left(A\right)\right\}\},$ Wherein K represents all available numbers of channel of node A;

B. determine the channel allocation tolerance of non-broadcast packet: non-broadcast packet channel allocation tolerance only considers to transmit the average re-transmission index SR value of bag to down hop, suppose that node A works as front jumping, and Node B is down hop, in node A, channel j for the channel success access probability PSAC of non-broadcast packet is:

wherein FC _j(B) be illustrated in the bag quantity that one-period interior nodes A transmits to Node B by channel j, be illustrated in i the re-transmission index SR value of wrapping that one-period interior nodes A sends to Node B by channel j, calculate the PSAC value of all K channel, the maximum channel of PSAC value is as optimum channel;

C. determine the route metric based on link transmission ability LTC: establish set PATHS={P ₁, P ₂... ..P _mcomprise all m paths from source node S to destination node D, gather represent path P _tin point sequence, altogether l jumps, path P _tq jump be from node h _q-1to node h _q, node h _q-1to node h _qlink transmission ability LTC is:

$\mathrm{LTC}(h_{q-1},h_q)=\mathrm{\β}\×{\mathrm{PSAC}}_j^{\mathrm{Data}}(h_{q-1},h_q)+(1-\mathrm{\β})(1-\frac{C_j}{C_{\max }}),$ Wherein β is weight factor, β ∈ (0,1), C _jrepresent the current buffer queue length of the interface that channel j is corresponding, C _maxrepresent the maximum of egress buffer queue, routing metric is rM (P _t) react path P _tthe bottleneck value of the link that passes through, in the time that source node finds that there is mulitpath, selects the maximum path of RM value as optimal path;

D. within certain cycle, in the time that node is received the HELLO bag of certain neighbor node for the first time, no matter by which channel receive when this bag, all will be immediately reply an ACK information by each interface to this neighbor node is each, the time in cycle is identical with the broadcast cycle that HELLO wraps;

E. optimal path discovery procedure is as follows:

Step 1: if there is not the route of destination node in source node routing table, carry out route discovery by inundation routing request packet, in the time that intermediate node is received routing request packet, first it set up reverse route in routing table, if it is less than the LTC value of storing in routing request packet to the LTC value of previous dive, upgrade the LTC value in routing request packet by this value, the route weight of reverse link is characterized by the LTC value in routing request packet;

Step 2: whether node inspection oneself is destination node, if not, directly forward this routing request packet, if so, go to step 3;

Step 3: reply routing reply bag along reverse link, the LTC value update mechanism in routing reply bag is the same with routing request packet, the routing metric RM value of forward link can be determined by the LTC value in routing reply handbag;

Step 4: source node is received after the routing reply bag in all paths, selects the maximum path of routing metric RM value as optimal path.

Beneficial effect: the routing algorithm based on cross-layer design in the Ad Hoc scene that the present invention has provided at multi-signal-channel and multi-interface, the load that this algorithm synthesis the has been considered link transmission capacity of channel carries out the selection of route, can obtain higher bag arrival rate and throughput of system with lower routing cost, and reduce the average delay of system simultaneously.

Brief description of the drawings

Fig. 1 is the Routing Protocol model of layer Network Based and the design of MAC layer cross-layer, in the Routing Protocol of layer Network Based and the design of MAC layer cross-layer, the Routing Protocol of network layer determines Route Selection and channel selection by receiving from the feedback information of MAC layer, and will select accordingly to feed back to MAC layer, determine transceiver and channel that transmission information is used.

Embodiment

The given cross-layer routing protocol of the present invention designs by MAC layer and network layer cross-layer, concrete model as shown in Figure 1, in the Routing Protocol of layer Network Based and the design of MAC layer cross-layer, the Routing Protocol of network layer determines Route Selection and channel selection by receiving from the feedback information of MAC layer, and will select accordingly to feed back to MAC layer, determine transceiver and channel that transmission information is used.In the present invention, the number of channel of each terminal and number of ports are assumed to be equal, as being made as K.In the transport process of bag, bag of every transmission, transmits the channel that this bag uses and retransmits index and all recorded by meeting.Be that MAC layer can constantly be delivered to retransmission information in network layer.Routing Protocol in network layer is the calculating through certain algorithm by the re-transmission index of collecting, and draws the transmittability of each channel, then the destination of comprehensive suite, determines to transmit bag channel and path used.

Concrete agreement is achieved as follows: two variablees in the management information bank maintenance in IEEE 802.11 MAC agreements, the short frame number of retransmissions of SSRC() and the long frame number of retransmissions of SLRC().Based on the thought of cross-layer, by these two variablees in Routing Protocol, define retransmit index SR (smooth of retry count) characterize transmit in frame process number of retransmissions, and define on this basis channel and select tolerance channel success access probability obability of Successful Access to Channel), reach with this target of selecting preferred channels.On the basis of multi-signal-channel and multi-interface AODV, in conjunction with the current length of buffer queue in SR and each interface, determine route metric link transmission ability LTC (Link Transmitting Capacity).Measure the Routing Protocol CL-IAOR realizing in multi-signal-channel and multi-interface Ad Hoc scene for comprehensive above-mentioned two, obtain higher throughput and lower time delay with lower routing overhead.

The Ad Hoc network that adopts 802.11 agreements, the MAC layer of each node is being safeguarded two variablees: short frame number of retransmissions SSRC (Station Short Retry Count) and long frame number of retransmissions SLRC (Station Long Retry Count).Both are in difference: in the situation that RTS/CTS mechanism is triggered, if the length of Frame is less than the RTS threshold values of regulation, the number of retransmissions of this Frame is indicated with SSRC, otherwise indicate with SLRC.Retransmission counter initial value is 0, and once, this value adds 1 to the every re-transmission of frame.If counter arrives maximum, will abandon this transmission and be discarded in medium this frame waiting for transmission of transmit queue, unison counter is reset to 0 again.In general, the maximum of SSRC and SLRC is set as respectively 6 and 3.Here redefine one and retransmit index SR (Smooth of Retry) to represent the RTS frame of a required re-transmission of frame of a node transmission and the number of times of Frame:

Wherein SSRC is short frame number of retransmissions, and span is the integer between 0 to 6, the long frame number of retransmissions of SLRC, span is the integer between 0 to 3, and t is the weight factor of these two number of retransmissions of balance, and span is between 0 to 1, retransmit index SR and in the time of bust this, obtain maximum, SR _max=6t+4 (1-t).

SR is a parameter of a concentrated expression node access channel capacity and network topology change thereof.T*SSRC in formula (1) has shown that node and active node around seize the ability of channel.If successfully receive CTS frame, represent reservation channel success and start to transmit DATA frame; T*SLRC part has reflected the residing network condition of node when node sends Frame after obtaining channel, because Ad Hoc nodes is random mobile, now may there be some active nodes to move towards this node direction, thereby clash with the transmission of this secondary data, so node will retransmit DATA frame, thereby the Internet resources and the time that while not being wasted in reservation channel, consume, weight coefficient t can obtain certain balance between these two parts.So far, by the number of retransmissions analysis of MAC layer data transmission being obtained characterizing the parameter S R of node access channel capacity.

Below by SR value definition channel allocation tolerance and route metric.

1, based on channel success access probability PSAC(Probability of Successful Access to Channel) method for channel allocation.

Be less than in the scene of the number of channel at number of ports, in order to ensure the connectedness of network, be necessary to ensure by some rational distribution mechanisms the connectedness of network, for example, set a public control channel, be used for sending control bag and other broadcast packet.And the present invention is applicable to the multi-signal-channel and multi-interface AdHoc network that the node number of channel is identical with number of ports.In the situation that the number of channel is identical with number of ports, the connectedness of network does not need to ensure by setting a public control channel.Be used for carrying out the transmission of broadcast packet if set a channel, can increase on the contrary the collision probability of broadcast packet.Therefore,, in the present invention, channel allocation tolerance is divided into channel allocation tolerance and the non-broadcast packet channel allocation tolerance of broadcast packet.It should be noted that in this agreement, the broadcast of HELLO bag does not adopt following channel allocation tolerance, but broadcasts in each channel, and this is conducive to build accurately network topological diagram and upgrades the SR value in Routing Protocol.

(1) channel allocation of broadcast packet tolerance

The neighbours that suppose node A concentrate a N neighbor node, and in node A, the successful access probability PSAC of the channel of the broadcast packet of channel j value is defined as follows:

${\mathrm{PSAC}}_j^{\mathrm{Broadcast}}\left(A\right)=1-\frac{\underset{n=1}{\overset{N}{\mathrm{\Σ}}}\underset{i=0}{\overset{{\mathrm{FC}}_j\left(n\right)}{\mathrm{\Σ}}}{\mathrm{SR}}_i^j\left(n\right)}{\underset{n=1}{\overset{N}{\mathrm{\Σ}}}{\mathrm{FC}}_j\left(n\right)\×{\mathrm{SR}}_{\max }}---\left(2\right)$

Wherein FC _j(n) be illustrated in the bag quantity that one-period interior nodes A transmits to its neighbours n by channel j, be illustrated in i the SR value of wrapping that one-period interior nodes A sends to neighbours n by channel j.Thus, by formula (3), can be easy to obtain value is between 0 and 1.It had reacted node A in the upper T cycle and has transmitted to all neighbours by channel j the average re-transmission situation of bag.This value is larger, can illustrate that to a certain extent to select this channel more reliable as broadcast packet channel.Therefore the best broadcast channel of node A selects tolerance to be:

$\mathrm{BestChannelForBroadcast}\left(A\right)=\left\{j\right|\underset{j\∈[0,K-1]}{\max }\left\{{\mathrm{PSAC}}_j^{\mathrm{Broadcast}}\left(A\right)\right\}\}---\left(3\right)$

Wherein K represents all available numbers of channel in node A.

(2) non-broadcast packet channel allocation tolerance

Different from broadcast packet channel allocation tolerance, non-broadcast packet channel allocation tolerance only considers to transmit the average SR value of bag to down hop.Suppose that node A works as front jumping, and Node B is down hop, in defined node A, channel j is as follows for the channel success access probability PSAC of non-broadcast packet:

${\mathrm{PSAC}}_j^{\mathrm{Data}}(A,B)=1-\frac{\underset{i=0}{\overset{{\mathrm{FC}}_j\left(B\right)}{\mathrm{\Σ}}}{\mathrm{SR}}_i^j\left(B\right)}{{\mathrm{FC}}_j\left(B\right)\×{\mathrm{SR}}_{\max }}---\left(4\right)$

Wherein FC _j(B) be illustrated in the bag quantity that one-period interior nodes A transmits to Node B by channel j, be illustrated in i the SR value of wrapping that one-period interior nodes A sends to Node B by channel j.Similarly, value also between 0 to 1, its reaction be the quality of node A link condition while using channel j to Node B.Value more approaches 1, represents that interference is fewer, and link condition is also just better.Therefore,, in the time of a non-broadcast packet of transmission, Routing Protocol first will be learnt its down hop, then calculates the corresponding PSAC value of each channel, and selects the maximum channel of PSAC value as optimum channel.

2, based on link transmission ability LTC(Link Transmitting Capacity) route metric

Assumption set PATHS={P ₁, P ₂... ..P _mcomprise all m paths from source node S to destination node D, gather represent path P _tin point sequence, altogether l jumps, path P _tq jump be from node h _q-1to node h _q.Definition link transmission ability LTC(Link Transmitting Capacity) as follows:

$\mathrm{LTC}(h_{q-1},h_q)=\mathrm{\β}\×{\mathrm{PSAC}}_j^{\mathrm{Data}}(h_{q-1},h_q)+(1-\mathrm{\β})(1-\frac{C_j}{C_{\max }})---\left(5\right)$

Wherein β is a weight factor of two parts in balance equation the right, and β ∈ (0,1), can get different value according to different network topology situations.J represents the channel number for transmission package in q jumping, C _jrepresent the current buffer queue length of interface j, C _maxrepresent the maximum of egress buffer queue.From formula (6), can find out, LTC is dimeric.Part I represents the link-quality of this jumping, and it can effectively weigh this link disturbed condition around.What Part II characterized is the loading condition of current link, and obviously, queue length is longer, and explanation will be used the bag quantity of this link transmission more, and link load is also just higher.Also can find out easily by formula (6), the LTC value of forward link and the LTC value of reverse link are different.Therefore, be different from other major parts and regard link as symmetrical method, the link characterizing by LTC is asymmetrical, thereby LTC can reflect the quality of link more accurately.

By LTC defined above, routing metric RM of the present invention (Routing Metric) is defined as follows:

$\mathrm{RM}\left(P_t\right)=\underset{q=\mathrm{1,2}..l}{\min }\left\{\mathrm{LTC}(h_{q-1},h_q)\right\}---\left(6\right)$

RM (P _t) react path P _tthe bottleneck value of the link that passes through, obviously, this bottleneck value is larger, and path is better.Therefore,, in the time that source node finds that there is mulitpath, select the maximum path of RM value as optimal path.

3, the realization of Routing Protocol

Routing Protocol of the present invention is to make improvements realization on the basis of AODV, except retaining routing table entry in AODV Routing Protocol, has increased this entry of channel using to down hop.For the SR value information that ensures to preserve in Routing Protocol effective, in certain cycle T, in the time that node is received the HELLO bag of certain neighbor node for the first time, no matter this bag by which channel receives, and all will respectively reply an ACK information by each interface to this neighbor node immediately.By sending this ACK information, node can obtain up-to-date each channel SR value to this neighbor node.Thus, can periodically refresh the SR information of preserving in route, ensure the validity of SR value.Otherwise if do not send packet to this neighbor node by certain channel in a upper T cycle interior nodes, the SR value of this neighbor node of preserving will be 0 or certain expired invalid value.For simplicity, in agreement, the time of setting cycle T is consistent with the broadcast cycle of HELLO bag.And in fact this value is the same with the HELLO packet broadcast cycle, all should adjust according to the concrete condition of network topology change.

If there is not the route of certain destination node in source node routing table, it can be by inundation RREQ(routing request packet) bag carries out route discovery.In the time that intermediate node is received RREQ bag, first it set up reverse route in routing table.If it is less than the LTC value of storing in RREQ to the LTC value of previous dive, upgrade the LTC value in RREQ bag by this value.Obviously, the LTC value in RREQ is by the route weight of calculating reverse path.After this, node should check to look at whether oneself is destination node, if not, forward this RREQ bag.Intermediate node is not allow to reply RREP(routing reply bag) bag, even if it has the effective routing to destination node, reason is that the value of each the LTC in path is real-time change.If destination node is replied RREP bag along reverse link, the LTC value update mechanism in RREP bag is similar with RREQ.Thus, the LTC value of the RM value of forward link in can being wrapped by RREP determined.Different from AODV, source node should wait for a period of time to obtain more routing information after receiving RREP bag, finally selects the maximum path of RM value as optimal path.

Claims (1)

1. the method for routing based on cross-layer design in self-organizing network, is characterized in that the method comprises following content:

A. determine the channel allocation tolerance of broadcast packet: the neighbours that establish node A concentrate N neighbor node, in node A, the channel of the broadcast packet of channel j success access probability PSAC is wherein FC _j(n) be illustrated in the bag quantity that one-period interior nodes A transmits to its neighbor node n by channel j, be illustrated in i the re-transmission index SR value of wrapping that one-period interior nodes A sends to neighbor node n by channel j, SR _maxre-transmission index during for bust this, the best broadcast channel of node A selects tolerance to be:

$\mathrm{BestChannelForBroadcast}\left(A\right)=\left\{j\right|\underset{j\∈[0,K-1]}{\max }\left\{\mathrm{PSA}{C}_j^{\mathrm{Broadcast}}\left(A\right)\right\}\},$ Wherein K represents all available numbers of channel of node A;

B. determine the channel allocation tolerance of non-broadcast packet: non-broadcast packet channel allocation tolerance only considers to transmit the average re-transmission index SR value of bag to down hop, suppose that node A works as front jumping, and Node B is down hop, in node A, channel j for the channel success access probability PSAC of non-broadcast packet is:

wherein FC _j(B) be illustrated in the bag quantity that one-period interior nodes A transmits to Node B by channel j, be illustrated in i the re-transmission index SR value of wrapping that one-period interior nodes A sends to Node B by channel j, calculate the PSAC value of all K channel, the maximum channel of PSAC value is as optimum channel;

C. determine the route metric based on link transmission ability LTC: establish set PATHS={P ₁, P ₂... ..P _mcomprise all m paths from source node S to destination node D, gather represent path P _tin point sequence, altogether l jumps, path P _tq jump be from node h _q-1to node h _q, node h _q-1to node h _qlink transmission ability LTC is:

$\mathrm{LTC}(h_{q-1},h_q)=\mathrm{\β}{\×\mathrm{PSAC}}_j^{\mathrm{Data}}(h_{q-1},h_q)+(1-\mathrm{\β})(1-\frac{C_j}{C_{\max }}),$ Wherein β is weight factor, β ∈ (0,1), and j represents the channel number for transmission package in q jumping, C _jrepresent the current buffer queue length of the interface that channel j is corresponding, C _maxrepresent the maximum of egress buffer queue, routing metric is rM (P _t) react path P _tthe bottleneck value of the link that passes through, in the time that source node finds that there is mulitpath, selects the maximum path of RM value as optimal path;

D. within certain cycle, in the time that node is received the HELLO bag of certain neighbor node for the first time, no matter by which channel receive when this bag, all will be immediately reply an ACK information by each interface to this neighbor node is each, the time in cycle is identical with the broadcast cycle that HELLO wraps;

E. optimal path discovery procedure is as follows:

Step 1: if there is not the route of destination node in source node routing table, carry out route discovery by inundation routing request packet, in the time that intermediate node is received routing request packet, first it set up reverse route in routing table, if it is less than the LTC value of storing in routing request packet to the LTC value of previous dive, upgrade the LTC value in routing request packet by this value, the route weight of reverse link is characterized by the LTC value in routing request packet;

Step 2: whether node inspection oneself is destination node, if not, directly forward this routing request packet, if so, go to step 3;

Step 3: reply routing reply bag along reverse link, the LTC value update mechanism in routing reply bag is the same with routing request packet, the routing metric RM value of forward link can be determined by the LTC value in routing reply handbag;

Step 4: source node is received after the routing reply bag in all paths, selects the maximum path of routing metric RM value as optimal path.