GB2355886A

GB2355886A - Determining at a bluetooth node the IP address of a peer bluetooth node

Info

Publication number: GB2355886A
Application number: GB9925174A
Authority: GB
Inventors: Tero Kauppinen
Original assignee: Telefonaktiebolaget LM Ericsson AB
Current assignee: Telefonaktiebolaget LM Ericsson AB
Priority date: 1999-10-26
Filing date: 1999-10-26
Publication date: 2001-05-02
Also published as: GB9925174D0

Abstract

A method of determining at a Bluetooth node, the IP address of a peer Bluetooth node. The method comprises the steps of constructing an echo request message at the Layer 2 Control and Adaptation Protocol (L2CAP) layer of the first mentioned node, the message including in a payload field thereof an IP address query indicator. The echo request message is sent from the first mentioned node to the peer node. At the L2CAP layer of the peer node, an L2CAP echo response message is constructed, the echo response message including in a payload field thereof the IP address of the peer node. The echo response message is sent from the peer node to the first mentioned node and is decapsulated at the L2CAP layer of the first mentioned node to determine the IP address of the peer node.

Description

2355886 SHORT-RANGE WIRELESS COMMUNICATION

Field of the Invention

The present invention relates to short-range wireless communication and in particular to the short-range wireless communication system referred to as "Bluetooth".

Backaound to the Invention A collaboration currently exists between a number of major software, electronic, and telecommunication companies to define an open specification for the wireless communication of data and voice signals. This specification is referred to as "Bluetooth" and is based on a low cost short-range (-10m) radio link, built into small microchips, which facilitates secure ad hoc connections for stationery and mobile communication environments. Bluetooth will allow the replacement of many proprietary wireless links and cables which currently connect devices, with one universal short-range radio link. For example, Bluetooth technology built into both a cellular telephone and a laptop computer would replace the cumbersome cables which are used today. Other devices such as printers, PDA's, desktop computers, facsimile machines, keyboards, joysticks and many other digital devices may be part of a Bluetooth system.

The Bluetooth specification currently specifies the low level requirements of a communication link. The specification includes details of the radio link, for example frequency, TDMA frame and slot length, and the Layer 2 Control and Adaptation Protocol (L2CAP). L2CAP is designed to provide an open interface which may be accessed by a number of different communication protocols. In particular, it is envisaged that Bluetooth may be used to carry IP communications. Figure I illustrates the protocol stack which might exist in a typical Bluetooth scenario in which the communication protocol sitting on top of Bluetooth is Internet Protocol (IP).

As already mentioned, Bluetooth is based around a single specific microchip. In Figure 1, this chip is built into a PCMCIA card which is received by a PCMCIA slot of a computer, PDA, or the like. The microchip includes the Host Controller Interface 2 (HCI) finnware, the Link Manager Protocol, and the baseband requirements. The driver for the PCMCIA is implemented in software in the computer, as is the Host Controller Interface (HCI). The top layer of the Bluetooth system is the Layer 2 Control and Adaptation Protocol (L2CAP) which is also implemented in software running on the computer. The TCPIUDI? and IP layers are interfaced to the L2CA_P layer via a Pointto-Point Protocol (PPP) layer and RFCOMM and Service Discovery Protocol (SDP) layers. The RFCOMM layer provides emulation of RS-232 serial ports over the L2CAP layer whilst the SDP layer is used for locating services provided by, or available through a Bluetooth device.

A user application, such as a Web browser or dedicated Bluetooth control application, may initiate a "physical" connection to a peer Bluetooth "node". Following the establishment of the physical connection, in order to carry out an IP exchange of information, the PPP layer is used. PPP is a complete specification for transmitting datagrams between data communications equipment over dial-up and dedicated serial point-to-point links although PPP does not specify how the physical connection is established (usually this involves sending AT commands to a modem). When the physical connection is established, PPP is responsible for establishing the link between two PPP peers and negotiating configuration options. This involves an exchange of IP addresses between the Bluetooth nodes.

It will be appreciated from Figure 1 that under existing proposals it is only possible to obtain an IP address for a remote Bluetooth node after a PPP connection has been established. There may be circumstances however when a user wishes to obtain this address prior to the establishment of a PPP connection or even in the complete absence of a PPP connection.

SummM of the Invention

It is an object of the present invention to overcome or at least mitigate the disadvantages of the proposed IP over Bluetooth implementation. This and other objects are achieved at least in part by providing a mechanism for exchanging IP addresses between nodes in a Bluetooth system.

3 According to a first aspect of the present invention there is provided a method of determining at a Bluetooth node, the EP address of a peer Bluetooth node, the method comprising the steps of:

constructing a request message at the Layer 2 Control and Adaptation Protocol (L2CAP) layer of the first mentioned node, the message including in a payload field thereof an EP address query indicator; sending the request message from the first mentioned node to the peer node; constructing at the L2CAP layer of the peer node an L2CAP response message, the response message including in a payload field thereof the IP address of the peer node; sending the response message from the peer node to the first mentioned node; and decapsulating the response message at the L2CAP layer of the first mentioned node to determine the IF address of the peer node.

It will be appreciated that the decapsulated IP address may be made available to an application at the first node. The application may be for example a modified web browser. The application may subsequently use the IP address of the peer Bluetooth node to direct IP traffic to that node.

Preferably, said request message is an L2CAP echo request message, and said response message is an L2CAP echo response message. Alternatively however, the request message may be an L2CAP information request message (code OxOA) whilst the response message may be an L2CAP information response message (code OxOB).

Preferably, the first mentioned node additionally incorporates into a payload field of the transmitted request message, it's own IEP address. The request message may then be decapsulated at the L2CAP layer of the peer node to determine the IP address of the first mentioned node. The peer node may subsequently direct IP datagrams to the first mentioned node using the determined IP address of the first mentioned node.

According to a second aspect of the present invention there is provided a node for use in a Bluetooth wireless communication system, the node comprising:

4 a Layer 2 Control and Adaptation Protocol (L2CAP) layer processor arranged to construct a request message including in a payload field thereof an IP address query indicator; transmission means for sending the request message to a peer Bluetooth node; and receiving means for receiving an L2CAP response message from the peer node, said L2CAP layer processor being further arranged to decapsulate the received response message to deten-nine the IP address of the peer node.

According to a third aspect of the present invention there is provided a method of transmitting data between two nodes of a Bluetooth wireless communication system where each node is allocated an EP address, the method comprising the steps of; establishing a physical connection between the two Bluetooth nodes over the wireless interface; sending an L2CAP request message from a first of the nodes to a second of the nodes, the message including an IP address query; returning from the second node to the first node an L2CAP request message containing the IP address of the second node; and subsequently exchanging IP traffic between the two nodes.

IP traffic may be exchanged between the Bluetooth nodes over a PPP connection or directly over the L2CAP connection.

Brief Description of the Drawings

Figure I illustrates a currently proposed IP over Bluetooth hardware/software protocol stack; Figure 2a illustrates the structure of the L2CAP echo request message; Figure 2b illustrates the structure of the L2CAP echo response message; Figure 3 is a flow diagram illustrating a method of exchanging IP addresses in a Bluetooth system; and Figure 4 illustrates an IP over Bluetooth hardware/software protocol stack which may be used after establishing IP addresses using the method illustrated in Figure 3.

Detailed Desqdption of a Preferred Embodiment The current proposal for using IP over Bluetooth has been briefly described above with reference to Figure 1. The inventor of the present invention has recognised that, under this current proposal, in order to obtain the IP address of a remote Bluetooth node it is first necessary to establish both the physical connection and a PPP connection. The latter step involves a relatively large number of protocol layers and is both computationally complex and time consuming. The inventor has fiu-ther recognised that within the currently specified L2CAP protocol there already exists messages which may be used to conduct a negotiation between peer Bluetooth nodes for the purpose of determining IP addresses, prior to the establishment of a PPP connection. In particular, L2CAP defines an echo request message and an echo response message (identified respectively with codes OxO8 and OxO9). The structure of these messages are illustrated respectively in Figures 2a and 2b.

The echo request message includes a field arranged to carry a payload ("da&'). The nature of the payload is implementation dependent and is available for carrying any data specified by that implementation. The echo response message, which is generated by a Bluetooth node following receipt of an echo request message, similarly comprises a field for carrying a payload.

Consider now a Bluetooth node, which may be for example a laptop computer or palmtop computer having a PCMCIA card fitted into a PCMCIA slot of the computer. The card implements the lower protocol layers of Bluetooth including the baseband requirements. The upper layers of Bluetooth, including the L2CAP layer, are implemented by software run on the computer's processor. When the Bluetooth node is initialised, it seeks to identify other Bluetooth nodes which are located within a given communication range (-10m). In particular, the newly initialised Bluetooth node broadcasts an inquiry message which may include a restriction on the class of Bluetooth devices which should respond. Active Bluetooth devices which receive the inquiry 6 message respond by returning answer messages. The answer messages include the respective Bluetooth addresses of the answering nodes. Details of the Bluetooth nodes which respond are provided by the HCI layer (the HCI layer obtains the information from the HCI firmware, which sends an event packet to the host when it has discovered 5 a new device). It is possible to provide this information to an application similar to the DialUp networking dialog of Windows. The application may then display the results of an inquiry as well as provide the means for the user to establish a physical connection to a selected Bluetooth device.

Assume now that the Bluetooth node is provided with a suitably modified web browser and that the user wishes to conduct an IP session with a Bluetooth node with which a physical link has already been established. The web browser issues an instruction to the L2CAP layer to transmit an echo request message, including an IP address request indicator, to a peer Bluetooth node which the browser identifies by way of a Bluetooth address. The IP address request indicator is encapsulated into the payload field of the echo request message, as is the IP address of the sending Bluetooth node. The L2CAP layer then selects the correct physical connection on the basis of the Bluetooth address and the constructed echo request message is passed from the L2CAP layer, through the HCI layer and the driver, to the PCMCIA card. The message is then transmitted over the physical (wireless) link to the peer Bluetooth node, where the message is forwarded to the L2CAP layer of the peer node.

Upon receipt of the message at the L2CAP layer of the peer node, the IP address request indicator is decapsulated from payload field of the message, together with the IP address of the sending node. The latter is made available by the L2CAP layer to an application at the peer node. In response to receipt of the echo request message, the IP address of the peer node is provided to the L2CAP layer which constructs an echo response message including this 1P address in its payload field. The echo response message is passed through the HCI/driver layers to the PCMCIA card for transmission to the originating Bluetooth node. At the originating node, the L2CAP layer decapsulates the payload field of the message to recover the EP address and make it available to the Web browser.

7 The IP address determination process described above is further illustrated in the flow diagram of Figure 3.

Figure 4 illustrates an IP over a Bluetooth hardware/software protocol stack which may be utilised at a Bluetooth node once the IP address of a peer Bluetooth node has been made available to the originating node. In addition to the TCP/LJDP, IP, PPP, RFCOMM, and SDP layers, there is provided a parallel protocol stack above the L2CAP layer comprising a TCP/UDP/IP/network adaptation layer protocol stack. The TCP/UDP and IP layers perform their known functions whilst the network adaptation layer acts as an interface between the IP layer and the L2CAP layer. In particular, it is noted that the PPP layer is no longer required when determining an IP address. This IP address may be included in the header of the IP data packets which are passed to the L2CAP layer either via the NAL or the PPP layer.

It will be appreciated by the person of skill in the art that modifications may be made to the above described embodiment without departing from the scope of the present invention. In particular, it will be appreciated that the various protocol layers of the IP over Bluetooth implementation may be implemented in hardware or in software or any combination of both hardware and software. The software hardware-boundary indicated in the protocol stack of Figure 4 may be located either higher or lower in that stack as appropriate.

8

Claims

1. A method of determining at a Bluetooth node, the IP address of a peer Bluetooth node, the method comprising the steps of:

constructing a request message at the Layer 2 Control and Adaptation Protocol (L2CAP) layer of the first mentioned node, the message including in a payload field thereof an IP address query indicator; sending the request message from the first mentioned node to the peer node; constructing at the L2CAP layer of the peer node an L2CAP response message, the response message including in a payload field thereof the IF address of the peer node; sending the response message from the peer node to the first mentioned node; and decapsulating the response message at the L2CAP layer of the first mentioned node to determine the IP address of the peer node.

2. A method according to claim 1, wherein the first mentioned node additionally incorporates into a payload field of the transmitted request message, it's own IP address.

3. A method according to claim 2, wherein the request message is decapsulated at the L2CAP layer of the peer node to determine the IP address of the first mentioned node.

4. A method according to any one of the preceding claims, wherein said request message is an L2CAP echo request message, and said response message is an L2CAP echo response message.

5. A method according to any one of claims I to 3, wherein said request message is an L2CAP information request message, and said response message is an L2CAP information response message.

6. A node for use in a Bluetooth wireless communication system, the node comprising:

9 a Layer 2 Control and Adaptation Protocol (L2CAP) layer processor arranged to construct a request message including in a payload field thereof an IP address query indicator; transmission means for sending the request message to a peer Bluetooth node; and receiving means for receiving an L2CAP response message from the peer node, said L2CAP layer processor being further arranged to decapsulate the received response message to determine the IP address of the peer node.

7. A method of transmitting data between two nodes of a Bluetooth wireless communication system where each node is allocated an IP address, the method comprising the steps of; establishing a physical connection between the two Bluetooth nodes over the wireless interface; sending an L2CAP request message from a first of the nodes to a second of the nodes, the message including an IP address query; returning from the second node to the first node an L2CAP request message containing the IP address of the second node; and subsequently exchanging IP traffic between the two nodes. 20