1 Introduction

A mobile ad hoc network (MANET) [1, 2] is a decentralized type of wireless network that is characterized by the absence of any pre-established infrastructure or centralized administration. In a MANET, mobile nodes communicate with each other directly or through intermediate nodes, forming a dynamic and self-configuring network. This unique feature allows MANETs to be highly flexible and adaptable, making them suitable for various scenarios where traditional infrastructure-based networks may be impractical or unavailable. The characteristics such as Infrastructure-less configuration, dynamic topology, security challenges and resource constraints make MANETs suitable for situations where the deployment of a static infrastructure is challenging in military operations, emergency responses, civilian and certain wireless sensor network applications.

MANETs [1, 2] are used in a wide range of situations, such as wireless sensor networks for environmental monitoring, disaster recovery operations, collaborative work environments, and military communication in dynamic battlefield circumstances. Although MANETs are quite flexible, they still have to deal with concerns like scalability, security in the absence of a centralised authority, and creating efficient routing protocols.

Routing in MANETs is a complex task due to their dynamic nature, requiring specialized protocols like Ad hoc on-demand distance vector (AODV) or dynamic source routing (DSR). Security is also a concern in MANETs, as their open and dynamic nature makes them susceptible to various threats. Encryption and authentication mechanisms are crucial to safeguard against potential attacks. Researchers and engineers continually work on improving the robustness and efficiency of MANETs to meet the demands of diverse applications. Literature review on ad hoc on-demand distance vector (AODV) is shown in Table 1.

Table 1 Literature review on ad hoc on-demand distance vector (AODV)
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The rest of the paper is organized as follows: The popular unipath routing protocol: In Sect. 2, a brief discussion of ad hoc on-demand distance vector (AODV) is provided. Comparably, Sect. 3 presents an illustration of the suggested protocol; Sect. 4 presents the simulation and experimental results; and Sect. 5 concludes with a discussion on future study.

2 Ad hoc on-demand distance vector (AODV)

The loop-free on-demand or reactive routing protocol known as ad hoc on-demand distance vector (AODV)  [9] combines the capabilities of dynamic source routing (DSR)  [10, 11] and destination-sequenced distance vector (DSDV)  [12] to tolerate a variety of network behaviours, including node mobility, packet losses, and connection failures. The efficiency of AODV is well established in dynamic and resource-constrained contexts, where node mobility can cause frequent changes in the network’s architecture. At every node, AODV maintains a routing table. The fields that must be present in a destination’s routing table entry are a sequence number, a hop count, and the next hop node. All packets intended for the destination are received by the next hop node. The sequence number serves as a time-stamp and gauges how recent a route is. The hop count indicates the current distance to the destination node.

When a node i receives an RREQ or RREP, it updates its hop count and next hop for a destination d if its sequence number is less than or equal to the sequence number of RREQ or RREP of node j, or if its sequence number is equal to the sequence number of RREQ or RREP of node j and its hop count is greater than the hop count of RREQ or RREP of node j. The above said rules for AODV route update are shown in Algorithm 1.

Algorithm 1
figure a

Route update rules of AODV protocol  [9]

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Key features of AODV are: (i) On-demand routing—AODV creates routes only when needed, operating on an as-needed basis. Because of the reduction in overhead brought about by the constant updating of routing data, AODV is especially well-suited to situations where energy and bandwidth conservation are vital. (ii) Route discovery—A route discovery procedure is started by a source node that wishes to interact with a destination node but does not yet have a valid route. A Route Request (RREQ) packet is broadcast to its neighbors during this process, and these neighbors forward the request until it reaches the destination or a node that has discovered a new route there. (iii) Route maintenance—AODV monitors the status of active routes. If a link or node failure occurs, a Route Error (RERR) message is generated and propagated through the network, informing affected nodes to invalidate the broken route. This triggers a new route discovery if needed. (iv) Loop avoidance—Routing loops are a prevalent problem in dynamic networks, and AODV has ways to prevent them. Every route has a sequence number assigned to it, which aids nodes in differentiating between outdated and updated routing data. This guarantees that the routing table entries are current and helps to eliminate loops. (v) Optimized route—Finding the best path to the destination is the goal of AODV. The routing table’s sequence numbers and hop counts allow it to make well-informed decisions about which data transmission method is most dependable and effective.

Advantages of AODV are: (i) Low overhead—AODV minimizes control packet overhead by initiating the route discovery process when needed. This leads to efficient use of network resources and reduces congestion. (ii) Adaptability to dynamic environments—AODV is well-suited for MANETs due to its ability to adapt to dynamic network topologies caused by node mobility. The on-demand nature of the protocol ensures that routes are only established when necessary, accommodating changes in the network structure. (iii) Quick Route Establishment—AODV is known for its relatively quick route establishment process. This is crucial in scenarios where communication needs to be established promptly, such as in military operations or emergency response situations.

3 Proposed protocol: link reliable on-demand distance vector (LRODV)

Communication nodes are susceptible to connection failures and route breakdowns because AODV routing chooses a route between any source and destination pair based on the least possible hop count, which does not ensure end-to-end reliable data transmission. A novel node disjoint routing protocol called Link Reliable On-demand Distance Vector (LRODV) protocol is introduced as a remedy for these problems by extending AODV  [9].

3.1 Routing metrics

Routing metrics are the measurements that are used to determine the best route, out of all the options. It falls into two categories: (i) node-based routing metrics, which select the best feasible path based on available information from participating nodes, such as energy and hop count; and (ii) link-based routing metrics, which select the best feasible path based on available information from participating links, such as throughput and reliability.

Every routing protocol measures link stability by default using link expiration time (LET). When a link between nodes are active (its LET is not expired) but outside of the transmission range, it has failed to send data. The scope of our protocol is to dynamically measure enhanced CETX using PROBE Packets in order to guarantee connection stability.

3.2 General Procedure

The suggested protocol is an improved variant of AODV that uses the enhanced Cumulative Expected Transmission Count (enh-CETX) to choose a link trustworthy route between a source and destination pair. This protocol introduces a new received signal strength indicator (RSSI) called PROBE Packet along with RREQ/RREP Packets in order to measure the trustworthy link between nodes. This PROBE Message Format is illustrated in Table 4.

The following is the general procedure of LRODV protocol:

  1. 1.

    Determining enhanced expected transmission count (enh-ETX)

  2. 2.

    Determining enhanced cumulative expected transmission count (enh-CETX)

  3. 3.

    Route selection based on enh-CETX

3.2.1 Determining enhanced expected transmission count (enh-ETX)

The number of PROBE packets sent over a period of time known as the enhanced expected transmission count (enh-ETX) is used to assess the quality of a link between participating nodes in the path.

The LRODV protocol calculates \({{mPRR}_{forward(i,j)}}\), \({{mPRR}_{backward(i,j)}}\), and \({{enh\text {-}ETX}_{link(i,j)}}\) during route discovery phase as follows:

$$\begin{aligned}&{{mPRR}_{forward(i,j)}}\nonumber \\&= \frac{Number\;of\;PROBE\;messages\;i\;received\;from\;j}{w\;seconds} \end{aligned}$$
(1)

The number of PROBE messages generated from the sender j to the receiver i over a given amount of time, say w seconds, is known as the modified Packet Reception Rate, or \({{mPRR}_{forward(i,j)}}\), of uplink quality from the sender to the receiver.

$$\begin{aligned}&{{mPRR}_{backward(i,j)}}\nonumber \\&= \frac{Number\;of\;PROBE\;messages\;j\;received\;from\;i}{w\;seconds} \end{aligned}$$
(2)

The number of PROBE messages generated from sender i to receiver j over a given amount of time, say w seconds, is known as the modified Packet Reception Rate, or \({{mPRR}_{backward(i,j)}}\), of downlink quality from the sender to the receiver.

3.2.2 Determining enhanced cumulative expected transmission count (enh-CETX)

Table 3 shows the enhanced Cumulative Expected Transmission Count (enh-CETX), a new field added to each RREQ and RREP in the LRODV protocol. When both \({{mPRR}_{forward(i,j)}}\) and \({{mPRR}_{backward(i,j)}}\) are 1 and the link between i and j is perfect, so the \({{enh\text {-}ETX}_{link(i,j)}}\) is 1. The summation of the enh-ETX values of all participating links in the node-disjoint path is the enh-CETX value of a path from a source node S to a destination node D. This value is computed as follows after determining the enh-ETX of links in a wireless network:

$$\begin{aligned} {{enh\text {-}ETX}_{link(i,j)}} = \frac{1}{{{mPRR}_{forward(i,j)}} * {{mPRR}_{backward(i,j)}}} \end{aligned}$$
(3)

Both the downlink quality (\({{mPRR}_{backward(i,j)}}\)) from the receiver to the sender and the uplink quality (\({{mPRR}_{forward(i,j)}}\)) from the sender to the receiver are used to determine the value of \({{enh\text {-}ETX}_{link(i,j)}}\).

$$\begin{aligned} {{enh\text {-}CETX}_{path(S,D)}} = \sum _{link(i,j)\in path(S,D)} {{enh\text {-}ETX}_{link(i,j)}} \end{aligned}$$
(4)

Where path(S, D) is a set of successive links in the path from node S to D such as: path(S, D) = \({\{(S, I_1), (I_1, I_2),..., (I_{k-1}, I_k), (I_k, D)\}}\).

3.2.3 Route selection based on enh-CETX

The enhanced ETX value of each link that an RREQ or RREP has travelled is added to each RREQ and RREP of the LRODV protocol. This field is known as enh-CETX, and it is displayed in Table 3. Table 2 presents the structure of the routing table entries for the AODV and LRODV routing protocols. Table 5 displays the notations and their descriptions that are used in this paper.

Table 2 Structure of routing table entries of AODV and LRODV routing protocols
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Table 3 Extended RREQ/RREP message format
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Table 4 PROBE message format
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Table 5 Notations and their descriptions
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Similar to the AODV routing protocol, a node in LRODV instantly rebroadcasts an RREQ packet upon receiving it for the first time. The enh-CETX of RREQ/RREP is initialised to 0 when a source S floods RREQ to a destination D or a destination D sends back RREP to a source S. The intermediate nodes determine the enh-ETX value in terms of the quantity of PROBE packets sent across the ends of the link upon receiving the RREQs or RREPs, and Algorithm 2 is used to update the enh-CETX on a regular basis.

Algorithm 2
figure b

Route update rules of LRODV protocol

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As shown in Algorithm 2, a node i uses LRODV route update rules to set up both forward and reverse routes whenever it gets a route advertisement to a destination d from a neighbour j. Sequence number, hop count and enhanced cumulative expected transmission count for a destination d at node i or node j are denoted by the variables \({{seqnum}^{d}_{i}}\), \({{hopcount}^{d}_{i}}\) and \({{enh\text {-}cetx}^{d}_{j}}\) respectively.

Fig. 1
figure 1

Route selection process of LRODV protocol

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The LRODV protocol’s route selection procedure is shown in Fig. 1. S and D stand for source and destination in this instance. Among the available paths S-B-E-I-D with enh-CETX=0.7, S-A-C-F-H-D with enh-CETX=0.9, and S-B-C-F-H-D with enh-CETX=0.9, the path S-A-F-H-D with enh-CETX=0.6 is chosen as the primary route for data transmission. The enhanced Expected Transmission Count (enh-ETX) of a link between the participating nodes along the path defined in terms of the amount of PROBE packets, and the least enhanced Cumulative Expected Transmission Count (enh-CETX) are the sole factors considered when selecting routes in LRODV.

4 Simulation environment and experimental results

The process of building a model for a real system and running experiments on it to compare various operating strategies or gain a better understanding of the system’s behaviour is known as simulation  [13]. Figure 2 illustrates the simulation model  [14].

Fig. 2
figure 2

Overview of the simulation model  [14]

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4.1 Environmental setup

With varying network flows on the widely used scenario pattern random way-point mobility (RWM) model  [15] under CBR  [16] traffic using NS2 [13, 17, 18], the performance of LRODV is compared with the commonly used unipath routing protocol AODV. The simulation parameters are shown in Table 6.

Table 6 Simulation parameters
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4.2 Performance metrics

Performance metrics are a group of qualitative measurements that are used to assess the quality of service (QoS) of any MANET routing protocol [19,20,21,22,23,24]. The seven distinct performance metrics that are listed below were assessed:

  1. (i)

    The ratio of data packets created by the sources to those that are not delivered to the destination is known as the packet loss ratio (%). The formula is as follows:

    $$\begin{aligned}{} {} Packet\;Loss = (No.\;of\;Data\;pkts.\;Sent\; \nonumber - \; No.\;of\;Data\;pkts.\;Received) \end{aligned}$$
    (5)
    $$\begin{aligned}{} & {} {Packet\;Loss\;Ratio =\frac{Packet\;Loss}{No.\;of\;Data\;pkts.\;Sent} * 100} \end{aligned}$$
    (6)
  2. (ii)

    The number of routing packets transported per data packet towards the destination during simulation is denoted by the phrase normalised routing overhead (%). Here’s how one obtains it:

    $$\begin{aligned}&Normalized\;Routing\;Overhead \nonumber \\&=\frac{No.\;of\;Routing\;pkts.\;Transmitted}{No.\;of\;Data\;pkts.\;Received} \end{aligned}$$
    (7)
  3. (iii)

    The total energy consumed by all nodes in the simulation environment is given by the value total energy consumed (in Joules). The following formula can be used to determine the total amount of energy used:

    $$\begin{aligned}&{Total\;Energy\;Consumed} \nonumber \\&=\sum _{i=1}^{n}{(Initial\;Energy_i - Residual\;Energy_i)} \end{aligned}$$
    (8)
  4. (iv)

    The number of bytes received successfully is known as Throughput (in Kbps). It is acquired through

    $$\begin{aligned} {Throughput} = \frac{No.\;of\;Bytes\;Received * 8}{Simulation\;Time * 1000} kbps \end{aligned}$$
    (9)
  5. (v)

    The ratio of data packets delivered to the destination to those generated by the sources is known as the packet delivery ratio (%). The following formula is used to compute the Packet Delivery Ratio:

    $$\begin{aligned}&{Packet\;Delivery\;Ratio} \nonumber \\&=\frac{No.\;of\;Data\;pkts.\;Received}{No\;of\;Data\;pkts.\;Sent} * 100 \end{aligned}$$
    (10)
  6. (vi)

    The total amount of control or routing packets created by the routing protocol during simulation is known as routing overhead (Pkts) and is calculated as follows:

    $$\begin{aligned} {Routing\;Overhead} = {No.\;of\;RTR\;pkts.} \end{aligned}$$
    (11)
  7. (vii)

    The average time for a data packet to be successfully transferred over a MANET from source to destination is defined as the average end-to-end delay (in ms). It covers all conceivable delays such as buffering during route discovery latency, queuing at the interface queue, retransmission delay at the MAC, propagation, and transfer time. It is determined as follows:

    $$\begin{aligned} {Average\;End-to-end\;Delay} =\frac{\sum _{i=1}^{n}{(R_i - S_i)}}{n} \end{aligned}$$
    (12)

    Where n is the number of data packets successfully transported across the MANET, ‘i’ represents the unique packet identifier, \({{R}_{i}}\) represents the time when a packet with unique identifier ‘i’ is received, and \({{S}_{i}}\) represents the time when a packet with unique identifier ‘i’ is sent. For high performance, the average end-to-end delay should be reduced.

4.3 Experimental results and discussion

The performance of LRODV protocol is compared with AODV protocol with varying network flows on random way-point mobility (RWM) model under Constant Bit Rate (CBR) traffic pattern using NS 2.35 in terms of Quality of Service (QoS) metrics. When there is a hike in network flows, the LRODV reduces 4.822741 % of routing overhead as shown in Table 10 and Fig. 3f, 2.938256 % of packet loss ratio as shown in Table 7 and Fig. 3a, 7.429350 % of normalized routing overhead as shown in Table 7 and Fig. 3b and 0.609278 % of energy consumption as shown in Table 8 and Fig. 3c. Additionally, compared to the AODV routing protocol, it enhances throughput by 2.741449 % and packet delivery ratio by 2.938256 %, as indicated in Table 9 and Fig. 3e and d.

Table 7 Packet loss ratio (%) and Normalized routing overhead (%) of AODV & LRODV on RWM under CBR Traffic
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Table 8 Total energy consumed (in Joules) and average end-to-end delay (in ms) of AODV & LRODV on RWM under CBR Traffic
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Table 9 Packet delivery ratio (%) and throughput (in kbps) of AODV & LRODV on RWM under CBR Traffic
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Table 10 Routing overhead (in Pkts) of AODV & LRODV on RWM under CBR traffic
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Fig. 3
figure 3

Varying network flows in CBR traffic on RWM

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5 Conclusions and future work

Using NS 2.35, the performance of the LRODV and AODV protocols is compared in terms of quality of service (QoS) metrics with changing network flows on the random way-point mobility (RWM) model under the Constant Bit Rate (CBR) traffic pattern. The LRODV lowers 4.822741% of routing overhead, 2.938256% of packet loss ratio, 7.429350% of normalised routing overhead, and 0.609278% of energy usage as network traffic increase. In comparison to the AODV routing protocol, it also boosts throughput by 2.741449% and packet delivery ratio by 2.938256%. The performance of the suggested protocol will also be evaluated in Cognitive Radio Ad hoc Networks due to its scope in link reliability, and in the future, the average end-to-end delay will be reduced by adding one or more unique routing metric.