US 7248573 B2
An interface between a wireless node and a network node includes an encapsulator for temporarily converting data frames into Ethernet frames for the link between the two nodes and de-encapsulating the Ethernet frames before the data is processed at the network node.
1. A system for receiving data signals and coupling data signals to an Ethernet network, said system comprising:
a plurality of dumb nodes, each dumb node comprising a radio receiver and an encapsulator, said radio receiver including a baseband processor for providing serial data signals composed of data frames each including a packet payload, and said encapsulator including means for encapsulating said data frames within temporary Ethernet frames, and wherein each dumb node includes a multiplexer for multiplexing host controller interface data with pulse-code modulated voice data into said data frames;
an intelligent node comprising a de-encapsulator, and a protocol processor for providing addressed Ethernet packets for transmission in said network; and
a plurality of physical links, each physical link coupling one of said dumb nodes with said intelligent node;
said encapsulator is coupled to said physical link to send said temporary Ethernet frames across the physical link only to said de-encapsulator;
said de-encapsulator includes means for receiving temporary Ethernet frames from said link and de-encapsulating said temporary Ethernet frames to recover said data frames; and
said protocol processor includes means for converting said data frames into said addressed Ethernet packets.
2. A system as in
3. A system as in
4. A method of receiving signals and transmitting signals over a local area network, comprising:
receiving, at one of a plurality of dumb nodes, a spread-spectrum signal containing message data and converting said spread-spectrum signal into serial data frames conforming to a host controller interface format;
encapsulating said serial data frames into Ethernet frames;
conveying said Ethernet frames over one of a plurality of physical links only, each of said plurality of physical links coupling one of said plurality of dumb nodes to an intelligent node;
receiving, at said intelligent node, said Ethernet frames from said physical link;
de-encapsulating, at said intelligent node, said Ethernet data frames to provide recovered serial data frames;
developing, by means of a protocol processor at said intelligent node, addressed Ethernet data packets from said recovered serial data frames; and
forwarding, from said intelligent node, said addressed Ethernet data packets to said local area network.
This invention relates to packet-based communication networks and particularly those which include a packet processing unit and wireless receivers or transceivers by which radio communication with a communication network is achieved. The present invention particularly relates to an interface link which facilitates separation of the wireless receiving and/or transmitting part of a network node and the high level packet processing functions or ‘protocol stack’.
In recent years much attention has been given to the extension of wireless links to local area networks or other packet-based communication networks which normally consist of various forms of packet generating receiving and processing units linked by physical links constituted by, for example, twisted pair lines, coaxial cable or optical fibres. Various standards are being developed for the wireless communication of data to and from nodes which form part of a packet-based communication network. One such standard is known as ‘Bluetooth’. The present invention in a preferred form is intended to be compatible with a Bluetooth standard but the subject matter of the invention is applicable to other systems.
It is known, from the systems operating in accordance with the Bluetooth standard, to provide a ‘node’ which is capable of receiving and/or transmitting a radio frequency signal, preferably in the form of a spread spectrum signal with ‘frequency-hopped’ coding. Such a node includes high level packet processing functions so that the node is immediately compatible, for example, with an Ethernet network. In such a node, the signals recovered from the baseband processing in the radio receiver are conventionally in a high speed serial data format. The transport layer for this high speed serial data is specified in the Bluetooth specification as using either USB, RS232 or UART. For a variety of reasons it is not feasible to include substantial error detecting or correcting facilities in such a format and accordingly it is not desirable to have any substantial physical separation between the radio section of the node and the high level packet processing section.
The main object of the present invention is to improve the interface between the radio receiving and/or transmitting section of a wireless node and the packet processing section and more particularly to enable a separation of the a wireless node into a ‘dumb’ node, which performs a conversion from the radio frequency signals to a signal format that is robust and can be used to convey data over substantial distances, and an ‘intelligent’ node, which is compatible with the aforementioned signal format and performs the packet processing or switch functions necessary for connection of data packets to a local area network or other network in which the node is connected. There is the further possibility that a multiplicity of ‘dumb’ nodes may share a single ‘intelligent’ node.
The present invention is based on a temporary conversion of passing between the radio receiver and/or transmitter and the intelligent node to an Ethernet format for the purpose of conveyance over a link between a dumb node and an intelligent node.
Further features of the invention will become apparent from the following description with reference to the accompanying drawings.
The RF section 1 of the known node is commonly a spread spectrum receiver and transmitter which, as far the receiver is concerned, accepts a spread spectrum signal having a bandwidth of the order of 80 MHz (in the range 2400 MHz to 2480 MHz), converts the radio frequency signal to an intermediate frequency and after appropriate filtration and amplification converts the intermediate frequency signal to an appropriate lower frequency where the signal is split into I and Q components, preferably converted into digital form and subject to correlation employing a direct sequence code generator employing the same code as was used to spread the spectrum of the original signal. The system will include appropriate synchronizers and baseband processing which provides serial data signals generally in a form of a preamble, an access code section and a payload (i.e. the message data). These packets will normally take the form of a 3 part packet with a 72 bit access code, a 54 bit header followed by a payload of between 0 and 2745 bits. The access code is used for synchronisation, DC offset compensation and identification, and has the format of a 4-bit preamble, an 64-bit sync word and a 4-bit trailer if a header follows. Section B of the Bluetooth specification V1.1 gives a complete list of access code formats and packet header types.
L2CAP is a protocol which is employed in the baseband for the purposes of protocol multiplexing, segmentation and reassembly. The various packet codes conforming to the protocol are embedded within the packet payload.
The link management section 3 of the known receiver is arranged to control the LMP Link Manager Protocol. This is used for link setup security and control. LMP messages have priority over the L2CAP data and are filtered out at the receiving side and are not propagated to the higher levels. Serial data is passed over the interface (known as the HCI or host controller interface). The section 5 decodes the L2CAP data and encapsulates it as packets conforming to a point-to-point protocol. These packets are conveyed to section 6. The RFCOMM protocol provides emulation of serial ports over the L2CAP protocol. This is based on ETSI standard TS 07.10. The purpose of RFCOMM is to provide a complete communications path between applications. RFCOMM is intended to cover applications that make use of the serial ports of the devices in which they reside. In a simple configuration the communication segment is a Bluetooth link from one device to another (direct connect). Where the communications segment is another network RFCOMM connects using a null modem type connection. In section 7 each of the RFCOMM stacks is terminated. An application running on top of this stack converts the PPP type data into valid Ethernet packets with correct source and destination addresses, so that they can be processed by the Ethernet bridge which is illustrated with transmit and receive links 9.
The known system and other systems rely on a high speed serial link This is specified in the Bluetooth specification as either USB, RS232 or UART between a radio receiver and a packet processor.
The existence of this serial link is a physical constraint on the separation of the dumb or transducing part of the node and the ‘intelligent’ or packet processing part of the node. It is the object of the present invention to increase this physical separation by means of converting the serial data to Ethernet packets and reconverting them at the end of the link between the dumb and intelligent nodes.
The link setup for a voice in a Bluetooth system is done via TCS Binary (Telephony Control Protocol Specification). These signals appear as normal Bluetooth data and are sent through the Bluetooth stack as normal L2CAP data. This TCS Binary link is used to establish a separate PCM connection to the Bluetooth baseband section.
For the purpose of the Ethernet encapsulation, these PCM signals need to be tagged and multiplexed along with the HCI signals into Ethernet packets. The multiplexing can be carried out using a simple time division scheme. However to maintain a suitable quality of service for the voice connection, it is preferable that the voice data be given priority. At the receiving end the de-encapsulation logic needs to be able to recognise the tagged PCM data and be able to separate it from the other Bluetooth traffic and send it to either a handset at one end or some type of digital exchange at the other. At either end of the link there will normally be some form of echo cancellation carried out using a simple digital signal processor.
In this particular system, there is provision not only for the conveyance of HCI data in high speed serial form and its encapsulation as Ethernet packets for the physical link between the dumb node and the intelligent node but also provision for sending PCM voice data.
The encapsulator shown in
This arrangement allows more than one HCI or PCM packet to be encapsulated in an Ethernet packet and ensures that the Ethernet packet is at least its prescribed minimum length.
When the counter signals the end of an HCI packet the packet buffer is signalled to provide an output to a demultiplexer 33
Multiplexer 33 also has an input of line 21-3 which is coupled to the manager. Also coupled to the multiplexer are Ethernet header registers 31.
When the system is switched on, a control signal will initialize the header registers 31. The purpose of these is to supply headers for Ethernet packets made up of those headers and packet data taken from the buffer 32. Such Ethernet packets are passed through a CRC generator 38 which computes the CRC code in ordinary manner and adds the CRC data at the end of the Ethernet packet in normal manner.
As a preliminary to the encapsulation of HCI data to Ethernet packets, the link manager on start up of the node will generate what are known as ‘negotiation’ packets which are dedicated multicast packets that are coupled by way of the multiplexer 33 to the link 23. The purpose of these packets is to elicit a response which identifies the MAC address of the processor 26 so that the Ethernet packets may be properly headed with a MAC destination address.
If however the packets received over line 23 are not negotiation packets, the Ethernet header is detected by detector 45 in order to provide a control for the removal of the Ethernet header as the packets are read into buffer 44 splitting the Ethernet packet into an HCI packet and/or pulse code modulation signals to be fed out on lines 25-1 and 25-2 respectively. Once the Ethernet header has been removed, the tags appended to the front of each of the HCI or PCM packets determine whether the packets are sent out on line 25-1 (for HCI packets) or 25-2 (For PCM packets).
There are several different types of HCI packets, for example Command Packets, ACL data packets, SCO data packets and negotiation packets. These are all specified in detail in the Bluetooth specification. For the purpose of this invention the HCI packets are transmitted to the encapsulation logic in their RS232 transport format which consists of an 8 bit packet identifier, and 8 bit sequence and finally the packet payload, the length of which can be determined by the packet identifier. The Ethernet frame 51, shown in somewhat simplified form, consists of a start of frame delimiter (SFD) a destination address (typically a 48-bit MAC address), a source address (typically a 48-bit MAC address), the rest of the header, which is in a generally prescribed form not relevant to the present invention, the tag added by module 32, a section which corresponds to the HCI packet, denoted HCI #1, padding, a CRC section and an end of frame section. The description of
The receiving part of the node comprises an antenna 60, a bandpass filter 61 (restricting the input signal to the range 2.400 GHz to 2.480 GHz), amplified by RF amplifier 62, again bandpass filtered in filter 63 and coupled to a first mixer 64, which receives a signal from a frequency-hopping synthesizer 65 controlled by a frequency-hopping sequence generator 66. The output from the first mixer (either 10 MHz or a low-frequency intermediate frequency such as a 4 MHz) is bandpass filtered by a channel filter 67, amplified by intermediate frequency amplifiers 68 and 69 and demodulated in a demodulator 70, the baseband output being processed in baseband processor 20 (see
The transmitter section is in ordinary form and consists of a baseband processor 71, converting HCI data and PCM voice data to an appropriate modulated form, and a spread spectrum transmitter 72 coupled to an antenna 73. The spread spectrum transmitter will include a mixer receiving the baseband signal and the output of a sequence generator, and up converters for converting the spread spectrum signal to the appropriate radio frequency band.