6LoWPAN technology has attracted extensive attention recently. It is because 6LoWPAN is one of Internet of Things standard and it adapts to IPv6 protocol stack over low-rate wireless personal area network, such as IEEE 802.15.4. One view is that IP architecture is not suitable for low-rate wireless personal area network. It is a challenge to implement the IPv6 protocol stack into IEEE 802.15.4 devices due to that the size of IPv6 packet is much larger than the maximum packet size of IEEE 802.15.4 in data link layer. In order to solve this problem, 6LoWPAN provides header compression to reduce the transmission overhead for IP packets. In addition, two selected routing schemes, mesh-under and route-over routing schemes, are also proposed in 6LoWPAN to forward IP fragmentations under IEEE 802.15.4 radio link. The distinction is based on which layer of the 6LoWPAN protocol stack is in charge of routing decisions. In route-over routing scheme, the routing distinction is taken at the network layer and, in mesh-under, is taken by the adaptation layer. Thus, the goal of this research is to understand the performance of two routing schemes in 6LoWPAN under error-prone channel condition.
6LoWPAN [
Mesh-under and route-over routing schemes can be considered as end-to-end and hop-by-hop transmission, respectively. Hop-by-hop fragmentation and reassembly generate more delay but achieve better fragment arrival ratio. Whereas end-to-end scheme has less latency, but fragment loss has high probability. Therefore, the goal of this research is to understand the performance of two routing schemes in 6LoWPAN under error-prone channel condition.
In 6LoWPAN protocol stack, the last two layers are based on IEEE 802.15.4 physical and data-link layers. A two-dimensional discrete-time Markov chain for unslotted CSMA/CA mechanism in 6LoWPAN is used to analyze the performance in unsaturated 6LoWPAN for rout-over and mesh-under routing schemes. Based on this Markov chain, the packet successful transmission probability for route-over and mesh-under routing schemes is evaluated under different numbers of competing nodes and wireless channel condition. To the best of our knowledge, this study is not yet reported in the literature. Finally, we attempt to compare route-over against mesh-under routing schemes in 6LowPAN in terms of goodput for IP end-to-end communication.
The rest of the paper is organized as follows. Next section describes related research works. Section
In the case of the WLAN, Bianchi [
In WSN, [
In [
6LoWPAN protocol stack adopts IEEE 802.15.4 standard PHY and MAC layers which are specified in [
6LoWPAN unslotted CSMA/CA algorithm [
The random backoff mechanism is used to decrease the probability of collisionsand ensure that the channel is clear for a node to access it. The channel clear assessment in unslotted CSMA/CA is one backoff period (in slotted CSMA/CA, which performs two channel clear assessments before transmission). If the channel is detected to be busy, BE is increased by 1, and the new backoff stage begins before channel sensing. This process is repeated until BE equals upperbounded macMaxBE (maximum value of BE, the default is 5), and then the BE is frozen at macMaxBE. When the number of backoff stage is equal to macMaxCSMABackoffs (the default value is 4), the node access channel is failure.
To enable the transmission of large IPv6 packets over size constrained link layer payload size (102 bytes of payload) in IEEE 802.15.4, the 6LoWPAN adaptation layer provides IP packet fragmentation mechanism [
As mentioned in the previous section, 6LoWPAN divides routing schemes into mesh-under and route-over [
Routing decision layer for both mesh-under and route-over routing schemes in 6LoWPAN [
In the mesh-under routing scheme, the routing functions are placed at the link layer based on IEEE 802.15.4 frame structure and the 6LoWPAN header [
In route-over scheme, each sensor node inside the route path acts as an IP router. The IP packet is forwarded hop by hop from the source node to the destination node [
In this section, we propose mathematical models to analyze the IP packet successful transmission probability for route-over and mesh-under, respectively. In addition, we present the goodput analysis to compare the performance of these two routing schemes under error-prone channel condition.
In Figure
The Discrete-time Markov chain model for unslotted CSMA/CA mechanism in 6LoWPAN under error-prone channel condition.
Let the stationary probabilities of the Markov chain be
The sum of probabilities of all the states should be equal to 1, and we have
Assume that the system has
According to the proposed Markov chain model, we can get the probability to enter transmission stage which is
While a node access channel is successful, it will transmit data, and the transmission task is completed in data link layer. But this transmission cannot ensure that the packet arrival to receiver is correctly. It is possible occurring interference in air propagation. Hence, a successful transmission will not have any FER from sender to receiver. We can get
Consider
Equation (
To evaluate the goodput, we consider that a cycle of transmission includes idle, contention, and transmission states. These states define as the duration, and each one is normalized which contains probability. The equations are shown as follows.
The procedure of data transmission in 6LoWPAN using the acknowledged and unacknowledged transmission.
Figure
The goodput analysis model for unacknowledged transmission in both route-over and mesh-under routing schemes is presented in this section. We first obtain the expected transmission time for route-over and mesh-under routing schemes.
Consider
Thus, the transmission goodput of route-over and mesh-under routing schemes can be obtained from (
In this section, we first obtain the expected transmission time for route-over and mesh-under routing schemes for acknowledged transmission:
In this section, we present the numerical analysis results for 6LoWPAN routing schemes in error-prone channel condition. Our probabilistic model was emulated by PRISM [
Numerical evaluation parameters.
IPv6 packet size | 1280 bytes |
Number of fragments | 14 |
Number of competing nodes | 3, 5, and 7 |
Hop counts | From 1 to 7 |
BER | From 0 to 1E-3 |
From results in figures
The successful IP packet transmission probability with 3 competing nodes for mesh-under and route-over routing schemes in 6LowPAN under error-prone channel condition.
Mesh-under
Route-over
The successful IP packet transmission probability with 5 competing nodes for mesh-under and route-over routing schemes in 6LowPAN under error-prone channel condition.
Mesh-under
Route-over
The successful IP packet transmission probability with 7 competing nodes for mesh-under and route-over routing schemes in 6LowPAN under error-prone channel condition.
Mesh-under
Route-over
In Figure
Goodput for mesh-under and route-over routing schemes in 6LowPAN under error-prone channel condition.
In this paper, we investigate the 6LoWPAN transmission performance by using the proposed mathematical model in 6LowPAN under varying number of competing nodes and error-prone channel condition. Analysis results show that route-over scheme has higher transmission probability than mesh-under.
This research was partially supported by the National Science Council of Republic of China, Taiwan under contracts, NSC102-2221-E-142-005 and NSC 101-2119-M-142-001 as well as National Taichung University regarding the MoE project (No. 1020035480A).