WO2008096908A1

WO2008096908A1 - Method of transmitting packet in low power wireless personal area network and low power wireless personal area network performing the same

Info

Publication number: WO2008096908A1
Application number: PCT/KR2007/000590
Authority: WO
Inventors: Ki-Hyung Kim; Hee-Jung Kim; Byeong-Hee Roh; Seung-Wha Yoo; Woon-Seob Shin; Chae-Seong Lim
Original assignee: Ki-Hyung Kim; Hee-Jung Kim; Byeong-Hee Roh; Seung-Wha Yoo; Woon-Seob Shin; Chae-Seong Lim
Priority date: 2007-02-04
Filing date: 2007-02-04
Publication date: 2008-08-14

Abstract

A method of transmitting a packet in a low-power wireless personal area network (LoWPAN) comprises transmitting a fragmented packet to an intermediate node from a sender node, storing the fragmented packet in the intermediate node for retransmitting the fragmented packet to a receiver node when an error occurs in the fragmented packet or the fragmented packet is lost while the fragmented packet is transmitted to the receiver node, and transmitting the stored fragmented packet to the receiver node. The packet transmission method and a packet transmission system may reduce power consumption and traffic in a LoWPAN and enhance the reliability of the packet transmission.

Description

METHOD OF TRANSMITTING PACKET IN LOW POWER WIRELESS

PERSONAL AREA NETWORK AND LOW POWER WIRELESS

PERSONAL AREA NETWORK PERFORMING THE SAME

Technical Field

The present invention relates to a low-power wireless personal area network (LoWPAN). More particularly, the present invention relates to a method and a system for transmitting a packet in the LoWPAN with reduced traffic and power consumption.

Background Art

A ubiquitous sensor network (USN) corresponds to a wireless network using an apparatus implemented as one chip including a sensor, an antenna, and an integrated circuit for real-time monitoring objects and an environment. In the USN, communication among the objects is possible, regardless of time and place, using radio-frequency identification (RFID) tags attached to the objects.

The most popular type of the USN is the ZigBee standard based on the Institute of Electrical and Electronics Engineers (IEEE) 802.15.4 standard. A personal area network (PAN) may be implemented to have low power consumption. Various applications may not be adapted to the PAN because its own protocol is used. Thus, research for associating an Internet Protocol (IP)-based network with a low-power wireless personal area network (LoWPAN) by applying Internet Protocol version 6 (IPv6) to the LoWPAN is continuing.

FIG. 1 is a configuration diagram illustrating a conventional sensor network associating with an IP network.

Referring to FIG. 1, a sensor node using its own protocol in a sensor network 130 may associate with an IP network 110 through a gateway 120.

FIG. 2 is a diagram illustrating layers of an IPv6-based LoWPAN.

Referring to FIG. 2, an IP-based USN router (hereinafter referred to as IP-USN router) 220 having a dual stack structure converting different protocols of a physical layer may be required for transmitting data from an IP network 210 to a sensor node in a LoWPAN (or sensor network) 230. The IP network 210 includes an application layer, a transport layer and a network layer. The network layer of the sensor network 230 generally uses IPv6. The sensor network 230 may associate with the IP network 210 through the IP-LJSN router 220 because a protocol of the physical layer of the sensor network 230 is different from a protocol of the IP network 210. The sensor node for transmitting an IPv6 packet to a sensor node of the IP network has an adaptation layer between the network layer and the physical layer complying with the IEEE 802.15.4 standard. The adaptation layer may perform an IPv6 packet header compression, a UDP/TCP header compression or mesh routing.

The maximum transmission unit (MTU) size of IPv6 corresponds to 1,280 bytes. The physical data unit size of the IEEE 802.15.4 standard corresponds to 127 bytes. Thus, an IPv6 packet needs to be fragmented to be transmitted by units of the IEEE 802.15.4 standard frame. Additionally, the fragmented packet needs to be recombined at the receiver's end. An adaptation layer may perform the adaptation and the recombination.

The reliability of data transmission consuming low power is important for associating the IP network with the sensor network. Particularly, the power consumption of a packet transmission in the sensor network occupies a large portion of the total power consumption. When retransmission is required due to an error or packet loss, power consumption may be larger due to repetitive retransmission. Thus, a packet transmission method and system reducing errors and power consumption is required.

Disclosure of the Invention Technical Problem

The present invention provides a packet transmission method capable of reducing power consumption and traffic in a low-power wireless personal area network (LoWPAN) and enhancing the reliability of the packet transmission.

Additionally, the present invention provides a system for the packet transmitting reducing power consumption and traffic in the LoWPAN and enhancing the reliability of the packet transmission.

Technical Solution

A method of transmitting a packet in a LoWPAN according to an example embodiment of the present invention includes transmitting a fragmented packet to an intermediate node from a sender node, storing the fragmented packet in the intermediate node for retransmitting the fragmented packet to a receiver node when an error occurs in the fragmented packet or the fragmented packet is lost while the fragmented packet is being transmitted to the receiver node, and transmitting the stored fragmented packet to the receiver node.

The method of transmitting a packet may further include receiving the fragmented packet stored in the intermediate node by requesting the retransmission of the fragmented packet stored in the intermediate node when the error occurs in the fragmented packet or the fragmented packet is lost while the fragmented packet is transmitted to the receiver node.

Receiving the fragmented packet stored in the intermediate node may include receiving information about a plurality of fragmented packets having errors or being lost by one request of retransmission when the plurality of the fragmented packets have the errors or the plurality of the fragmented packets are lost.

The method of transmitting a packet may further include checking whether or not the fragmented packet having the error or being lost is stored in the intermediate node when the intermediate node receives the request of retransmission, and requesting a previous intermediate node to retransmit the fragmented packet having the error or being lost when the fragmented packet having the error or being lost is not stored in the intermediate node. The method of transmitting a packet may further include deleting the fragmented packet when the fragmented packet stored in the intermediate node is successfully transmitted to the receiver node.

A LoWPAN system according to an example embodiment of the present invention includes a receiver node, a sender node configured to fragment and transmit the fragmented packet to the receiver node, and an intermediate node located between the sender node and the receiver node, the intermediate node being configured to store the fragmented packet for retransmitting the fragmented packet to the receiver node when an error occurs in the fragmented packet or the fragmented packet is lost while the fragmented packet is transmitted to the receiver node.

The fragmented packet stored in the intermediate node may be retransmitted to the receiver node by requesting the retransmission of the fragmented packet stored in the intermediate node when the error occurs in the fragmented packet or the fragmented packet is lost while the fragmented packet is transmitted to the receiver node.

The receiver node may receive information about a plurality of fragmented packets having errors or being lost by one request of retransmission when the plurality of the fragmented packets has the error or the plurality of the fragmented packets is lost.

Brief Description of the Drawings

The above and other advantages of the present invention will become more apparent by describing in detail example embodiments thereof with reference to the accompanying drawings, in which:

FIG. 1 is a configuration diagram illustrating a conventional sensor network associating with an Internet Protocol (IP)-based network.

FIG. 2 is a diagram illustrating layers of an Internet Protocol version 6 (IPvό)-based LoWPAN. FIG. 3 is a configuration diagram illustrating a packet transmission system according to an example embodiment of the present invention.

FIG. 4 is a flowchart illustrating a packet transmission method according to an example embodiment of the present invention. FIG. 5 is a flowchart illustrating a transmission of a fragmented packet from a sender node to a receiver node through an intermediate node.

FIGS. 6 and 7 are diagrams illustrating information tables of the fragmented packet in the sender node and the receiver node.

FIG. 8 is a diagram illustrating a format of an acknowledgement signal. FIG 9 is a diagram illustrating a format of a retransmission request signal.

Best Mode for Carrying Out the Invention

Embodiments of the present invention now will be described more fully with reference to the accompanying drawings, in which embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like reference numerals refer to like elements throughout this application.

It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of the present invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

It will be understood that when an element is referred to as being "connected" or "coupled" to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being "directly connected" or "directly coupled" to another element, there are no intervening elements present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., "between" versus "directly between," "adjacent" versus "directly adjacent," etc.).

The terminology used herein is for the purpose of describing particular embodiments and is not intended to be limiting of the invention. As used herein, the singular forms "a," "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises," "comprising," "includes" and/or "including," when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

It should also be noted that in some alternative implementations, the functions/acts noted in the blocks may occur out of the order noted in the flowcharts. For example, two blocks shown in succession may in fact be executed substantially concurrently or the blocks may sometimes be executed in the reverse order, depending upon the functionality/acts involved.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. FIG. 3 is a configuration diagram illustrating a packet transmission system according to an example embodiment of the present invention.

Referring to FIG. 3, a packet transmission system according to an example embodiment of the present invention includes Internet Protocol (IP) networks 310 and 330 and a sensor network associating the IP networks 310 and 330. The packet transmission system may include IP-ubiquitous sensor network (USN) routers 321 and 327 between the IP networks 310 and 330 and the sensor network 320 for a protocol conversion.

When a packet is transmitted from an IP network 310 illustrated in a left part of FIG. 3 to the IP network 330 illustrated in a right part of FIG. 3 through the sensor network 320 illustrated in a middle part of FIG. 3, a router 321 illustrated in the left side of FIG. 3 corresponds to an ingress router, and a router

327 illustrated in the right side of FIG. 3 corresponds to an egress router.

The IP network 310 and 330 may use Internet Protocol version 4 (IPv4) and Internet Protocol version 6 (IPv6), and may include various kinds of network devices capable of being connected to the Internet.

The ingress router 321 may be required for transmitting the data from the IP network 310 to the sensor network 320. When the data size of data being transmitted from the Internet or a backbone network to the sensor network 320 is larger than the maximum transmission unit (MTU) allowable in the sensor network 320, the data needs to be fragmented. A fragmented packet may be transmitted to nodes in the sensor network 320.

The egress router 327 may be required for transmitting the data from the sensor network 320 to the IP network 330. The egress router 327 recombines the fragmented packet transmitted from the sensor network 320 to generate data adaptable to a transmission unit of the IP network 330.

The ingress router 321 and the egress router 327 may have the dual stack structure for mediating the different protocols. According to example embodiments, various kinds of protocol conversion devices including a gateway may be used.

The packet transmission in the sensor network may be performed through a plurality of sensor nodes 322 to 326. Some parts of the sensor nodes 323 to 325 may include intermediate nodes 323 and 325 for enhancing transmission reliability. In the description of an example embodiment of the present invention, an intermediate buffer node does not represent a node storing received data merely for transmitting the received data. The intermediate buffer node represents a node storing the received data for retransmission according to the retransmission request. The packet transmission in the sensor network may be performed through at least one intermediate buffer node. In an example embodiment, most sensor nodes 322 to 326 in the sensor network 320 may have functions of the intermediate buffer node 323 and 325. In another example embodiment, some parts of a transmission path may be implemented with intermediate buffer nodes. When the fragmented packet is transmitted from the sender node such as ingress router 321 to the intermediate nodes 323 and 325, the intermediate nodes 323 and 325 store the received fragmented packet in storage areas and send the received fragmented packet to receiver node. The receiver node may correspond to another node in the sensor network 320 or an egress router 327. The receiver node checks whether or not the packet transmission is successful. When the fragmented packet is transmitted successfully, the receiver node sends an acknowledgement signal ACK to the intermediate node or the sender node. When the fragmented packet is not transmitted successfully, the receiver node sends a retransmission request signal NACK to the intermediate node or the sender node. In the conventional art, to the contrary, the receiver node generally sends the acknowledgement signal and the retransmission request signal only to the sender node.

According to an example embodiment, a fragmented packet may be stored in the intermediate buffer node during the packet transmission. When the intermediate buffer node receives the retransmission request signal NACK, the intermediate buffer node retransmits the stored fragmented packet. Thus, when the fragmented packet is not transmitted successfully, the retransmission request signal NACK does not need to be directly transmitted to the sender node. Therefore, traffic and power consumption may be reduced due to a relatively short retransmission path, and the reliability may be enhanced.

FIG. 4 is a flowchart illustrating a packet transmission method according to an example embodiment of the present invention.

Referring to FIG. 4, data is fragmented in a sender node (step S401). The fragmentation may be performed when a transmission data unit of the sender node is larger than a transmission data unit of the sensor network. When a transmission data unit of the sender node is sufficiently smaller, the transmission data may be transmitted within one packet. Generally, the fragmented packet may be transmitted to the receiver node through a plurality of sensor nodes (step S402). The fragmented packet may be transmitted through the intermediate node. When the intermediate buffer node receives fragmented packet, the intermediate buffer node stores the fragmented packet in a storage area step (S403).

When the transmission of the fragmented packet is successful (step S404), the receiver node sends an acknowledgement signal ACK (step S410). When an error occurs during the transmission of the fragmented packet, the receiver node generates a retransmission request signal (step S405). When errors or packet losses occur in a plurality of packets, information about errors and packet losses about the plurality of packets may be included in one retransmission request signal NACK. Thus, even when errors or packet loss occurs in many packets, the number of transmissions may be reduced and power consumption and traffic also may be reduced.

The retransmission request signal NACK may be transmitted to the receiver node or intermediate node (step S406) via a reversed path of transmission.

When the intermediate buffer node receives the retransmission request signal NACK, the intermediate buffer node checks whether a requested packet is stored in the storage area (step S407). When the requested packet is stored in the intermediate node, the intermediate buffer node retransmits the lost packet to the receiver node without transmitting the retransmission request signal to the sender node (step S408).

When the intermediate buffer node does not have the requested packet, the intermediate node transmits the retransmission request signal to another node located closer to the sender node (step S411). For example, the intermediate buffer node may transmit the retransmission request signal to another intermediate buffer node located closer to the sender node. The transmission of the retransmission request signal may be repeated until the retransmission request signal is transmitted to the sender node. Repeating the transmission of retransmission request signal is omitted in FlG. 4.

When the fragmented packet is transmitted to the receiver node successfully, the receiver node sends acknowledgement signal ACK to the intermediate buffer node or the sender node (step S409). The acknowledgement signal ACK also may be transmitted through the intermediate buffer node. When the intermediate node receives the acknowledgement signal ACK, the intermediate buffer node deletes the stored packet to increase storage area (step S412).

FIG. 5 is a flowchart illustrating a transmission of a fragmented packet among a sender node, an intermediate node and receiver node. Referring to FIG. 5, a sender and a receiver are divided into a plurality of layers according to functions. When the sender node transmits data 501, an adaptation layer fragments the data 502. The fragmented packet may be transmitted 503 to the intermediate buffer node by a MAC/PHY layer 504. The packet is generally transmitted through a plurality of sensor nodes. When the intermediate buffer node receives the fragmented packet, the intermediate node stores the received packet in its temporary storage area and sends the received packet to the receiver node 505. The MAC/PHY layer receives the fragmented packet 506. The adaptation layer recombines the fragmented packet 507. When the fragmented packet is not able to be recombined due to an error or a packet loss, the receiver node sends the retransmission request signal NACK and extends a waiting time 508.

According to an example embodiment of the present invention, more than one packet are lost or have error, information about a plurality of packets having errors or being lost may be included in one retransmission request signal NACK

509 to be transmitted to the intermediate buffer node. Thus, the more than one packet may be retransmitted by one retransmission request signal NACK.

The retransmission request signal may be transmitted 510 through the intermediate buffer node before the receiver node. When the intermediate buffer node receives the retransmission request signal NACK, the intermediate buffer node checks whether or not the fragmented packet is stored in the storage area

511.

When the requested packet is stored in the intermediate buffer node, the intermediate buffer node itself transmits the requested packet 512. Thus, a retransmission path may be shortened without sending a retransmission request signal to the sender node. Additionally, trafiϊc and power consumption may be lowered by retransmitting only a requested packet rather than using a Go-Back-N method.

A retransmitted packet is recombined with other packets arrived in the receiver node 514. Retransmission and recombination may be repeated until the recombination is completed. When the requested packet is not stored in the intermediate buffer node, the intermediate buffer node transmits the retransmission request signal to another node. The other node may correspond to the sender node, a normal node or another intermediate buffer node. When the fragmented packet is transmitted to the receiver node successfully, the receiver node sends an acknowledgement signal ACK to the intermediate buffer node or the sender node 516. The acknowledgement signal ACK also may be transmitted through the intermediate buffer node. When the intermediate node receives the acknowledgement signal ACK, the intermediate buffer node deletes the stored packet to increase storage area 517. Thereafter, the intermediate buffer node sends the acknowledgement signal ACK to the sender node 518.

Referring to FIG. 6, an information table of the sender node may include a

DST field representing an IP address of the receiver node, an ET field representing an effective time, a DGS field representing a size of fragmented packet size, a DO field representing an offset of the fragmented packet and a FP field for a payload.

Referring to FIG. 7, an information table of the receiver node may include fields illustrated in FIG. 6, and additional fields including a SRC field representing an IP address of the sender node and a RV field representing whether data transmission is successful. Whether the transmission is successful is recognized by referring to the RV field.

For example, when the fragmented packet is transmitted successfully, the RV field may be set to T. When the fragmented packet is not transmitted successfully, the RV field may be set to O'. After performing an AND operation on all RV fields of received packets, when the operation result corresponds to ' I ', the receiver node sends an acknowledgement signal to the intermediate node or the sender node because all packets arrive successfully at the receiver node. Then, fragmented packets are recombined to be transmitted to an upper layer and information on the table is deleted. When the operation result corresponds to O', the receiver node sends a retransmission request signal including information about packets having errors or being lost.

FIG. 8 is a diagram illustrating a format of an acknowledgement signal and FIG 9 is a diagram illustrating a format of a retransmission request signal.

An LF field represents a type of the fragmented packet. A PT field represents a characteristic of a datagram. An M field represents whether a final destination field is used. An RSV field is space for later versions. A field for a payload may not be required. An ACK field and an NAC field represent an acknowledgement signal and a retransmission request signal, respectively.

An INF field in FIG. 9 has information about the request fragmented packet. One INF field may have information about a plurality of requested packets.

Industrial Applicability

As described above, a packet transmission method and a packet transmission system may reduce power consumption and traffic in a low-power wireless personal area network (LoWPAN) and enhances the reliability of the packet transmission.

Claims

1. A method of transmitting a packet in a low-power wireless personal area network (LoWPAN), comprising: transmitting a fragmented packet to an intermediate node from a sender node; storing the fragmented packet in the intermediate node for retransmitting the fragmented packet to a receiver node when an error occurs in the fragmented packet or the fragmented packet is lost while the fragmented packet is transmitted to the receiver node; and transmitting the stored fragmented packet to the receiver node.

2. The method of claim 1, further comprising: receiving the fragmented packet stored in the intermediate node by requesting the retransmission of the fragmented packet stored in the intermediate node when the error occurs in the fragmented packet or the fragmented packet is lost while the fragmented packet is transmitted to the receiver node.

3. The method of claim 2, wherein receiving the fragmented packet stored in the intermediate node comprises: receiving information about a plurality of fragmented packets having errors or being lost by one request of retransmission when the plurality of the fragmented packets have the errors or the plurality of the fragmented packets are lost.

4. The method of claim 3, further comprising: checking whether or not the fragmented packet having the error or being lost is stored in the intermediate node when the intermediate node receives the request of retransmission; and requesting a previous intermediate node to retransmit the fragmented packet having the error or being lost when the fragmented packet having the error or being lost is not stored in the intermediate node.

5. The method of claim 4, further comprising: deleting the fragmented packet when the fragmented packet stored in the intermediate node is successfully transmitted to the receiver node.

6. A LoWPAN system comprising: a receiver node; a sender node configured to fragment and transmit the fragmented packet to the receiver node; and an intermediate node located between the sender node and the receiver node, the intermediate node being configured to store the fragmented packet for retransmitting the fragmented packet to the receiver node when an error occurs in the fragmented packet or the fragmented packet is lost while the fragmented packet is transmitted to the receiver node.

7. The system of claim 6, wherein the fragmented packet stored in the intermediate node is retransmitted to the receiver node by requesting the retransmission of the fragmented packet stored in the intermediate node when the error occurs in the fragmented packet or the fragmented packet is lost while the fragmented packet is transmitted to the receiver node.

8. The system of claim 7, wherein the receiver node receives information about a plurality of fragmented packets having errors or being lost by one request of retransmission when the plurality of the fragmented packets has the error or the plurality of the fragmented packets is lost.