GB2413037A

GB2413037A - Allocating temporary addresses to devices in an ad hoc network

Info

Publication number: GB2413037A
Application number: GB0407930A
Authority: GB
Inventors: Russell John Haines
Original assignee: Toshiba Research Europe Ltd
Current assignee: Toshiba Europe Ltd
Priority date: 2004-04-07
Filing date: 2004-04-07
Publication date: 2005-10-12
Anticipated expiration: 2024-04-07
Also published as: GB0407930D0; GB2413037B

Abstract

A method of allocating variable length network addresses in, for example, an ad hoc network comprises allocating an address of a first minimum length to a first node, determining whether the remaining nodes to be addressed can be done so using addresses of the same length and, if not, allocating addresses of a length one bit more than the first to those nodes. Using the method, the signalling overhead taken up by such addresses is minimised, and increasing numbers of devices can be accommodated.

Description

24 1 3037

NETWORK ADDRESSING

The present invention relates to temporary addressing of devices in a network, for example an ad-hoc or centralised wireless network.

A number of contemporary device addressing schemes for wireless networks are known. The networks may be centralized, for example an infrastructure based wireless local area network (WLAN) in an airport lounge, or distributed ad hoc, such as a personal area network (PAN). Such network addressing schemes are needed to allow the devices to communicate with each other whilst part of the network. In many cases, where communication is established on the basis of an internationally agreed technical standard, each device wild have a permanent unique address assigned to it, but also it may, in the context of the specific network concerned, be allocated a temporary network address as well.

The IEEE 802.11 WLAN system for example uses a 48-bit MAC (Medium Access Control) Address to uniquely identify every device in the world, and then uses that address to direct frames within a WLAN BSS (Basic Service Set, the 802.11 term for a network of WLAN devices sharing a common channel). This approach allows the allocation of network addresses to up to 248 devices, which is considered sufficient given current and anticipated device usage within the lifetime of the communications standard itself.

However, it has been recognised that it is unnecessary to provide a device in a network with the facility to address uniquely 248 other devices. In practice, many networks, such as wireless networks installed in domestic premises to manage communication between personal computing and entertainment devices, may in fact involve as few as two devices in the entire BSS. In such a case, the use of the full 48 bit addressing standard is not optimal, as such long addresses are wasteful of bandwidth, and contribute to the overheads imposed by the MAC that reduce the total data rate offered by the physical layer to the much smaller net data rate offered by the MAC layer to the layers above it.

The Bluetooth_ system gives each node a fixed Bluetooth Device Address (BD_ADDR) of forty-eight bits but, for efficiency reasons, rather than transmitting that entire 48-bit address to address a packet to a node, a temporary 3-bit Active Member Address (AM_ADDR) is allocated to a device whilst it is associated with a piconet.

This arrangement, whilst far more efficient, results in the imposition of a maximum of seven active members that can be supported at any given time, as only seven members can be uniquely addressed using a 3-bit AM_ADDR, as one of the 23 addresses is reserved for broadcast. Thus, a piconet established using the Bluetooth_ standard has to employ relatively complex "park" mechanisms to handle inactive members of the piconet, as well as parking and unparking devices dynamically. This in addition can lead to processing overhead in the management of communication of a network involving a number of devices several orders of magnitude lower than the maximum of 248.

Thus there is a need for an improved device network-addressing scheme for ad-hoc and centralised networks such as WLAN and piconets, such that the number of devices in the addressing scheme is not arbitrarily limited by a fixed allocation of addressing bits.

UK Patent Application No. 0403825.3 provides a method of allocating and using variable length temporary addresses for devices in networks. These networks may be temporary and completely ad hoc such as Bluetooth TM personal piconets; infrastructure based but with highly dynamic membership such as an 802.11 Wi-Fi TM (WLAN) network in an airport lounge or coffee shop (a "hot spot") for example, or they may be essentially fixed and static once set up for example a home entertainment system. By using variable length addresses, the above mentioned problems can be overcome as only as many addresses as necessary are used, thus reducing the overhead and bandwidth efficiency of the network. In addition a network using this method is scalable so that it can accommodate further devices, as the network is not constrained in the way that a Bluetooth TM network is for example.

A first aspect of the invention provides an improved method of allocating and using variable length temporary addresses for devices in a network comprises allocating addresses to devices with the shortest number of bits possible, including an address identity portion and an address length portion, such that, after each allocation of an address, the method comprises checking whether all remaining devices which have not been allocated addresses can be addressed using unallocated addresses of the same length as the previously allocated address.

Preferably the most popular or most active devices utilise the shortest addresses, further enhancing the efficiency benefits. For example, in a typical WEAN infrastructure star topology, all traffic is either from the client stations (STA) to the access point (AP) or vice versa. As a result, every packet or data-frame sent will have the AP's address in it (either as the source or destination address). Given that this address is used so frequently, it should be given the shortest address possible, rather than all devices having the same address length.

A second aspect of the invention provides a method of allocating network addresses for devices in a network, each network address comprising an addressing field of no fixed length, said method including the steps of allocating a value to an addressing field of an address to a first device with an initial minimum length and allocating values to addressing fields of further addresses, of the same length or longer, to further devices thereafter, and determining, after allocating an addressing field of an address to a device, whether remaining devices to be allocated addresses can be allocated addresses with addressing field of the same length as the addressing field of the presently allocated address and, if said devices can be so allocated addresses, then allocating addresses to remaining devices with addressing field of the same length as that of the presently allocated address.

The step of allocating an address to a first device preferably comprises allocating a 1-bit address to the first device.

The method preferably further comprises the initial step of determining an ordered list of devices to be allocated addresses in said network, the order of the list being determined substantially on the basis of anticipated relative usage of said devices.

The step of determining an ordered list may include the step of receiving information about each device on introduction of said device to said network, said information including predicted usage information and processing said predicted usage information to derive anticipated relative usage of said devices.

The step of determining an ordered list preferably includes the step of measuring previous usage of devices in said network and, on the basis of previous usage, determining a list of said devices in order of rate of use in said network.

In a preferred embodiment, each address further comprises an address length field of predetermined length, and the method further comprises the step of assigning, to an address length field of an address, a value denoting the number of bits in the

corresponding addressing field.

The method may then include the step of determining the number of devices in the network, the length of the address length field being dependent on the number of devices in the network.

In an alternative arrangement, a predetermined bit pattern could be appended to the variable length address instead of prepending the fixed length field.

In the case where legacy devices exist in the network, allocation of variable length addresses will just be to those devices in the network which can read these.

Preferably the network is a wireless network of the type used by personal communications devices such as wireless local area networks and personal area network. Examples of such networks include those utilising the IEEE802. 11 and Bluetooth TM protocols. Such devices typically exchange large amounts of data such as computer files, multimedia content including web content and voice traffic as well as control commands. Examples of such devices include laptop computers, smart or mobile phones, MP3 players and other home entertainment equipment such as television sets, speakers, set-top boxes, sound reproduction equipment and remote control devices.

According to a preferred embodiment of the invention, the method comprises the steps of determining, from the allocated addresses, the minimum value stored in the address length field of an allocated address, subtracting this minimum value from each value stored in the address length field of each allocated address and, if said step of subtracting results in the largest value of the address length field being less than the value associated with the most significant bit allocated to the address length field, then de-allocating said most significant bit from the address for all allocated addresses.

The method may further comprise determining an activity profile for each device, said activity profile corresponding with a measure or estimation of the frequency of communication of said device within the network compared with the other said devices; and placing said devices in a list ordered on the basis of their activity profile prior to said step of allocating values to said addressing fields, such that addresses of lower allocated length correspond substantially with devices with a more active activity profile than do addresses of higher allocated length.

The measure or estimation may comprise a frequency parameter wherein the device having the highest frequency parameter is allocated the first address of minimum predetermined length.

Said step of allocating comprises assigning a preliminary addressing code to each device, considering each preliminary addressing code and, if the length of said preliminary addressing code is insufficient to allow addressing of all further devices with addressing codes of the same length, then allocating said preliminary addressing code to the addressing field of said device, otherwise allocating to the addressing field of each remaining device an addressing code of length the same as the length of the preliminary addressing code under consideration, each such allocated addressing code being distinct.

In one embodiment, the step of allocating a preliminary addressing code may comprise applying a Huffman code to each device, the devices being ordered substantially in terms of frequency of addressing in the network.

In this embodiment, the step of allocating, in the event that the length of said preliminary addressing code is sufficient to allow addressing of all further devices with addressing codes of the same length, may comprise allocating, as the value stored in the addressing field for the device under consideration, the preliminary addressing code, and allocating as the value stored in the addressing field for all further devices to be considered, other values of the same bits.

In another embodiment, the step of allocating comprises sequentially allocating values to addressing fields of devices such that all combinations of values for a given length of addressing field are allocated to devices before allocating an addressing field of longer length and, on allocating a value to an addressing field of a device wherein the addressing field is longer than the previously allocated addressing field, determining if all remaining devices can be addressed using addressing field of the same length and if so then performing the same.

According to a third aspect of the invention, apparatus for allocating network addresses for devices in a network, each network address comprising an addressing field of no fixed length, comprises addressing field value allocation means for allocating a value to an addressing field of an address to a first device with an initial minimum length and for allocating values to addressing fields of further addresses, of the same length or longer, to further devices thereafter, and allocation process management means for determining, after said addressing field value allocation means has allocated an addressing field of an address to a device, whether remaining devices to be allocated addresses can be allocated addresses with addressing field of the same length as the addressing field of the presently allocated address and, if said devices can be so allocated addresses, then causing said addressing field value allocation means to allocate addresses to remaining devices with addressing field of the same length as that of the presently allocated address.

The addressing field value allocation means may preferably be operable to allocate a 1- bit address to the first device.

The apparatus may further comprise ordering means for determining an ordered list of devices to be allocated addresses in said network, the order of said list being determined substantially on the basis of anticipated relative usage of said devices.

The ordering means may be operable to receive information about each device on introduction of said device to said network, said information including predicted usage information, and operable to process said predicted usage information to derive anticipated relative usage of said devices.

The ordering means may include measuring means for measuring previous usage of devices in said network and, on the basis of previous usage, said ordering means may then be operable to determine a list of said devices in order of rate of use in said network.

Activity profile determining means may be provided for determining an activity profile for each device, said activity profile corresponding with a measure or estimation of the frequency of communication of said device within the network compared with the other said devices; and said ordering means may thus be operable to place said devices in a list ordered on the basis of their activity profile prior to said step of allocating values to said addressing fields, such that addresses of lower allocated length correspond substantially with devices with a more active activity profile than do addresses of higher allocated length.

The measure or estimation may comprise a frequency parameter; the device having the highest frequency parameter being allocated the first address of minimum predetermined length.

Each address may further comprise an address length field of predetermined length, and addressing field value allocation means being further operable to assign, to an address length field of an address, a value denoting the number of bits in the corresponding

addressing field.

The apparatus may then further comprise means for determining the number of devices in the network, the length of the address length field being dependent on the number of devices in the network.

The apparatus preferably comprises minimum address length determination means for determining, from the allocated addresses, the minimum value stored in the address length field of an allocated address, and address length adjustment means for subtracting this minimum value from each value stored in the address length field of each allocated address and, if said subtracting results in the largest value of the address length field being less than the value associated with the most significant bit allocated to the address length field, then operable to de-allocate said most significant bit from the

address length field for all allocated addresses.

In one embodiment of the invention, the addressing field value allocation means comprises preliminary addressing means for assigning a preliminary addressing code to each device, and address confirmation means for considering each preliminary addressing code and, if the length of said preliminary addressing code is insufficient to allow addressing of all further devices with addressing codes of the same length, then for allocating said preliminary addressing code to the addressing field of said device, otherwise for allocating to the addressing field of each remaining device an addressing code of length the same as the length of the preliminary addressing code under consideration, each such allocated addressing code being distinct.

The preliminary addressing means may be operable to apply a Huffman code to each device.

The address confirmation means may be operable, in the event that the length of said preliminary addressing code is sufficient to allow addressing of all further devices with addressing codes of the same length, to allocate, as the value stored in the addressing field for the device under consideration, the preliminary addressing code, and to allocating as the value stored in the addressing field for all further devices to be considered, other values of the same bits.

In another embodiment of the invention, the addressing field value allocation means is operable to sequentially allocate values to addressing fields of devices such that all combinations of values for a given length of addressing field are allocated to devices before allocating an addressing field of longer length and, on allocating a value to an addressing field of a device wherein the addressing field is longer than the previously allocated addressing field, to determine if all remaining devices can be addressed using addressing field of the same length and if so then to perform the same.

According to a further aspect of the invention, there is provided a method of allocating temporary addresses to a plurality of networking devices, each temporary address comprising a fixed length portion and an addressing portion, said fixed length portion being comprised of bits describing, in use, the number of bits of which the addressing portion is comprised, the method comprising establishing a ranking of the devices according to a performance criterion, allocating interim Huffman-based codes to said devices in order of the ranking, and iteratively allocating an interim code as the addressing portion of the corresponding device following which assessing whether remaining devices can be addressed by codes of the same length as the recently allocated code and if so terminating the iterative allocating of codes and instead allocating unique codes of the same length as the recently allocated code to the remaining devices.

According to yet a further aspect of the invention, there is provided a method of allocating temporary addresses to devices in a communications network, each temporary address comprising a fixed length portion and an addressing portion, the method comprising ranking the devices in an order based on a performance criterion, and allocating temporary addresses in an order starting from the highest with respect to the performance criterion, assigning to the addressing portion of the temporary address of the highest ranking device an initial value and initial length, incrementing the initial value by a predetermined amount and, if the incremented value can be expressed in an addressing portion of the same length as the most recently allocated addressing portion, then allocating the incremented value of the addressing portion of the next ranked device, otherwise assigning to the addressing portion of the next ranked device an initial value and a length increased by a predetermined number of bits from the previously allocated addressing portion, iteratively allocating addressing portions of successively ranked devices until addressing portions of all devices have been so allocated.

Preferably, the predetermined amount by which the initial value may be incremented and subsequently further incremented is 1. The predetermined number of bits by which the length of the address portion is selectively increased from one allocation to the next is 1.

Further aspects and advantages of the invention will be apparent from the following description of specific embodiments of the invention, provided by way of example only and with reference to the accompanying drawings, in which: Figure I illustrates a distributed network according to an embodiment of the invention; Figure 2 illustrates a process, in accordance with a first specific embodiment of the invention, for allocating addresses for the network of Figure 1; Figure 3 illustrates a process for allocating initial short addresses to devices in the network of Figure l, as called in the process illustrated in Figure 2; Figure 4 illustrates a process for allocating revised addresses to devices in the network, in the process illustrated in Figure 2; Figure 5 illustrates a process, in accordance with a second specific embodiment of the invention, for allocating addresses to devices in the network illustrated in Figure 1; and Figure 6 illustrates packets of data, one prepared in accordance with IEEE802. 11 and one prepared in accordance with one or other of the described embodiments of the present invention.

Referring to Figure 1, a distributed network 10 comprises a set of home entertainment devices, namely an amplifier (AMP) 12, a DVD player (DVD) 14, two speakers (SPKRA, SPKRB) 16, a television (TV) 18 and a CD player (CD) 20. In such a distributed network, each device 12 to 20 in the network 10 is operable to execute, in a distributed manner, a process to establish wireless communication between it and one or more of the other devices, to enable the exchange of data and thereby the networking functioning of each device. In this embodiment, therefore, no single device is nominated as a "network controller" as the overall functionality that a network controller will provide is distributed between the various devices.

In the described embodiment, the devices are capable of being distinguished by their level of "popularity", i.e. the regularity with which they are used. By the exchange of data between the devices, a ranking list of the devices can be established in a straightforward manner. This ranking process is carried out in a distributed manner, so that each device stores the same ranking information. The specific steps carried out in the establishment and maintenance of this ranking information wild be described in due course.

In operation, the network in Figure 1 is established by means of each device 12 to 20, on joining the network, being configured to send an authentication request including (amongst any other parameters required for the operation of the system as a whole) the full unique address (IEEE 48-bit MAC address) of the device and an indication of the activity profile of the device. In this embodiment, the request is achieved using an IEEE802. 11 authentication request/response exchange in a conventional manner.

The unique address of each device is typically set at the time of manufacture and uniquely distinguishes the device from all other devices anywhere in the world. The profile of a device contains information which allows the network to estimate, in a distributed manner, the "popularity" or activity of that device during the operation of the system. Once the "popularity" or activity of the devices has led to a ranking of the devices, then local network addresses are established in a distributed manner. These are then sent to the devices to enable establishment of communication in the network 10.

Figure 2 illustrates the process by which local short addresses can be derived for a network 10 in accordance with a first specific embodiment of the invention. In the distributed network described here, it will be appreciated that this process will be executed in a distributed manner, involving the exchange of a plurality of messages between individual devices to ensure consistency of addressing in the network. It will also be appreciated that a centralised network, with a nominated access point (AP) could enable this process to be performed at the access point and merely to send relevant addressing information to the remaining devices.

Firstly, in Step S 1-2, initial short addresses are allocated to devices. This is achieved using a Huffman code algorithm, and the manner in which this is achieved will be described in due course with reference to Figure 3.

Then in Step S 1-4, an address compression algorithm is applied to the set of initial addresses allocated to the devices. The manner in which this is achieved in accordance with the first embodiment will be described in due course with reference to Figure 4.

Finally, in Step S 1-6, the revised set of addresses, as derived in Step S 1-4, are applied to the set of devices.

As illustrated in Figure 3, the process of allocating initial short addresses to the devices 12 to 20 of the network 10 commences, in Step S2-2 by ranking the devices in order of frequency and use. This is achieved initially by, on introduction of a device into the network, taking account of profile information included in an authentication message to establish the anticipated 'popularity' of the introduced device.

In this example, the results of this step is to determine that the devices, ranked in order of popularity, with most popular first, rank as AMP, DVD, SPKRA, SPKRB, TV, CD.

Then, in Step S2-4, a Huffman based address is allocated to each device in turn, such that the most popular device receives the initial Huffman code and thus the shortest address.

The result of this step is set out in Table 1 below:

Table 1

Device Initial Huffman-Based Address AMP 1 DVD 01 SPKRA 001 SPKRB 0001 TV 00001

_

CD 00000 then, in Step S2-6, the length of each allocated Huffman-Based address is measured, leading to an address length field in the above table:

Table 2

Device Huffman-Based Address Address Length (bits) AMP 1 DVD l 01 2 SPKRA 001 3 SPKRB 0001 4 TV 00001 5 CD 00000 5 In Step S2-8, the maximum value of the address length field is established, to identity how many bits should be allocated to the address length field in short addresses as the result of this method. These bits are ultimately prepended to each Huffman based address ascertained in Step S2-4. In Step S2-10, the actual address length values are prepended to the corresponding initial Huffman based addresses, to produce initial short addresses for further processing in the process of Figure 2. These resultant initial short addresses are set out in Table 3.

Table 3

Device Initial Address AMP 001 1 DVD 010 01 SPKRA 011001 SPKRB 100 0001 TV 10100001 CD 101 00000 The address length field is allocated 3 bits in all cases, in order to provide sufficient range of values to accommodate the addresses comprising the most bits. However, this has the undesirable consequence that shorter addresses comprise a high proportion of their length that does not bear data but instead defines the length of the address. For example, the address for the amplifier (AMP) 12 is 0011 using the above method; in this case 75% of the bits in the address are used to define the length of the address and only the remaining 25% (a single bit) comprise addressing data. This demonstrates that the above method alone adds overheads to the shorter addresses.

It will be appreciated that this inefficiency is a direct result of prepending address length bits to the Huffman codes which are otherwise inherently a highly efficient way of addressing but which are susceptible to error and require some form of error checking (such as an address length field) to avoid malfunction in a practical system. Further, without the address length field, the receiver of a data packet structured in this way would not be able to establish the length of the address field, as other bits follow the address field and would be otherwise indistinguishable therefrom.

The process illustrated in Figure 4, called in Step S 1-4 of the process illustrated in Figure 2, provides a first embodiment of the invention to improve upon this situation.

This process processes the Huffman-based codes allocated in the previously described method, such that the inefficiency introduced by prependingaddress length bits to the Huffman codes can to some extent be ameliorated.

The process commences, in Step S3-2, by considering the first address in the list. As illustrated in Table 3, each initial address listed in Table 3 comprises a 3-bit Address Length field, followed by addressing data. Then, in Step S3-4, the number of bits in the address is measured. In Step S3-6, the number of possible other addresses available, with the same number of bits as the current address under consideration, is determined.

In Step S3-8, the number of devices remaining to be provided with an address is counted.

In Step S3-1 O. the number of possible same-length addresses available for allocation is compared with the number of devices to which addresses remain to be allocated. If the number of possible same-length addresses is less than the number of devices presently lacking an address, then it is determined that the remaining devices cannot be re- addressed with addresses of the same length as the address currently under consideration. Therefore, in Step S3-12, a check is made as to whether any further initial addresses remain to be processed and potentially shortened. If not, then the procedure ends, on the basis that the Huffman-based codes applied to the devices did not result in undue redundancy through unnecessarily long address codes.

However if further initial addresses remain for consideration, then in Step S3-14, the next device, with its initial address, is considered and the procedure continues from Step S3-4 onwards.

If, in Step S3-10, it is established that the number of possible addresses remaining available for allocation, of the same length as the current address under consideration, is greater than or equal to the number of devices remaining to be addressed, then in Step S3-16, spare addresses are allocated arbitrarily to the remaining devices. The procedure then ends. This step ensures that, if all further devices can be addressed without using longer addresses than the one presently being considered, then this should be effected - though this may be theoretically less efficient as it prevents pure Huffman-type coding and thus instant recognition of higher ranked devices, in fact in practice this latter technique is not employed as it is prone to error hence the introduction of bits allocated to describe the length of the address. The presence of the address length bits, and their number in the practical case, are communicated to devices in the system by means of an authentication message, in accordance with conventional techniques.

A worked example of this process as applied to the devices, with their initial addresses, set out in Table 3, will now follow.

In Step S3-2, the first address in the list, which corresponds with the AMP 12, is considered. This address is the single bit 1. In Step S3-4, the number of bits in the address is measured, the result being 1.

In Step S3-6, it is determined that the number of possible other addresses available for allocation, given the number of bits of the address under consideration, is also 1; another device could be allocated the single bit address 0.

In Step S3-8, the number of devices to which revised addresses remain to be allocated, is found to be 5. Thus, in Step S3-10, it is determined that the number of devices remaining to be addressed (5) exceeds the number of possible addresses available for allocation (1), and so the method continues in Step S3-12.

Further addresses remain to be considered, so in Step S3-14, the next address, 01, corresponding with the DVD device 14, is considered. In Step S3-4, the address for the DVD is found to be a 2-bit address and thus, in Step S3-6, three other 2-bit addresses are available for allocation (00, 10 and 11). In Step S3-8, it is found that four devices remain to be considered, and so a further iteration of the process is necessary. Thus, in Step S3-14, the next address on the list is selected for consideration, being the address 001 for the speaker SPKRA 16.

In this case, the address under consideration is found, in Step S3-4, to be a 3-bit address.

This means that the number of possible other 3-bit addresses is 7. However, the number of devices remaining to be addressed is 3, as established in Step S3-8. Therefore, the number of possible addresses is greater than the number of devices remaining to be addressed, and so in Step S3-16, 3-bit addresses are allocated to the remaining devices, SPKRB 16, the TV device 18, and the CD device 20.

The process illustrated in Figure 4 then ends, with newly allocated addresses for devices such that the number of bits in the longest address is reduced. Table 4 illustrates this in relation to the worked example:

Table 4

Device Old, Huffman-Based Address New Address AMP 1 1 DVD 01 01 SPKRA 001 001 SPKRB 0001 000 TV 00001 010 CD 00000 011 For each newly allocated address, the address length is measured, and an appropriate number of bits is prepended to each address to produce a revised short address for each device, as set out in Table 5.

Table 5

Device Address Address Length (bits) Short Address l AMP 1 1 01 1 DVD 01 10 01 SPKRA 001 11 001 SPKRB 1 000 11 000 TV I 010 _ _ 11 010 CD 011 11011 Since, in addition to the overall shortening of the address code, the address length field is now 2 bits long, instead of 3. Thus, in the case of the lowest ranked device, this results in the number of bits in the short address to have been reduced from 8 to 5 bits, which represents a 37.5% saving. Further, in the case of the highest ranked and thus most frequently used short address, the process has shortened the shortest (most frequently used) address from 4 to 3 bits, which represents a 25% saving.

Figure 5 illustrates a second embodiment of a process to establish addresses for devices in the network illustrated in Figure 1. The process of Figure 5 commences with consideration of a ranked list of devices, as set out above. In Step S4-2, an address count is set to zero, and in Step S4-4, a bit count is set to 1. These are initial values for quantities used in the execution of the process as will be understood from the following

description.

In Step S4-6, the device at the head of the list of devices is selected for consideration.

In Step S4-8, an address is assigned to the device under consideration. The assigned address has numerical value equal to the numerical value of the address count variable, and is allocated a number of bits governed by the bit-count variable.

In Step S4-10, an assessment is made as to whether any more addresses can be allocated with the number of bits stored in the bit count. That is, given the number of bits (n) in the previously allocated address, was the previously allocated address less than 2n-1. If so, then in Step S4-12, the address count is incremented by 1 in readiness for the next allocation. Otherwise, in Step S4- 14, the number of bits in the bit count is incremented by 1, and the address count is set to zero in Step S4-16.

On execution of either Step S4-12 or Step S4-16, the process continues in Step S4-18 by considering the next device in the ordered list of devices.

If, in Step S4-20, it is established that no devices remain to be considered, then the procedure ends. Otherwise, the procedure continues in Step S4-6 by consideration of the next device. This process continues until all devices have been considered and an address has been allocated thereto.

A worked example, in relation to the list of devices set out above, with reference to Figure 1, will now be described.

Initially, in Steps S4-2 and S4-6, the address-count and bit-count values are set to zero and 1 respectively. Then, in Step S4-6, the AMP device 12 is considered and, in Step S4-8, the device is allocated with an address of 0. This is in accordance with the current values of address count (O) and bit count (1). In Step S4-10, it is established that other addresses remain to be allocated without increasing the number of bits per address.

Thus, in Step S4-12, the address count is incremented by 1, and thus now equals 1.

In Step S4-18, consideration moves to the next device on the list, as it is confirmed that further devices remain to be addressed. The DVD device 14 is then considered in Step S4-8, and a single bit address 1 is allocated thereto.

In Step S4-10, it is now established that no further addresses are available with this number of bits, and so in Step S4-14, the bit count is incremented by 1 and the address count is returned to zero.

The process continues until the addresses are all allocated. Then, short addresses are constructed, with the address length expressed in a suitable number of bits prepended to each address in accordance with Table 6.

Table 6

Device Address Address Length Short Address | AMP O I 010 DVD 1 01 1 SPKRA 00 2 10 00 SPKRB 01 2 10 01 TV 10 1010 CD 11 1011 In comparison with the initial Huffman codes allocated to devices in the process of the first embodiment, substantial shortening of address lengths are achieved. For example, the Huffman code based address allocated to the CD player is 8 bits in length, whereas the address allocated according to this second embodiment is only 4 bits in length.

As the variation on the process of the second embodiment, a modified address-length value can be derived from each value in the address-length field, each modified address length value being one less than the corresponding address-length value. This is shown in Table 7. As the number of bits in the longest address is 2, the highest value of the modified address-length quantity is 1. This means that the modified address length can be described by 1 bit, thus reducing the overall length of the allocated short addresses by a further bit.

Table 7

Device Address Address Length Modified Address Length Short Address

AMP O O O

DVD 1 01 SPKRA 00 2 1 100 SPKRB 01 2 1 1 01 TV 10 2 1 1 10 CD 11 2 1 1 11 It will be appreciated that this last modification will not necessarily bring about a reduction, in all cases, in the number of bits allocated to describe the length of the allocated addresses. For example, in the event that the maximum address length is not capable of being expressed as 2n (n being an integer), then the length of the longest address length field will not be reduced on subtracting 1 from it.

However, to take advantage of the potential saving in the event that the maximum address length is an integer power of 2, it may be found to be useful to apply the technique in all cases.

In the initial authentication stage of operation of a device in the network, partially unique addresses could alternatively be used, for example regionally unique addresses or perhaps company specific addresses.

Another embodiment of the invention can be envisaged, in which Bluetooth TM enabled personal devices such as a mobile phone, a palm-top computer, an MP3 player and a laptop computer, are in networking communication with each other, with the laptop acting as the access point (AP). Various protocols for deciding which device to elect as the access point are known to those skilled in the art. In such an embodiment, the process of assigning short addresses may be performed solely in the nominated access point, in a distributed manner, or each device could have its individual process for addressing all other devices, agreeing addressing with each other device individually.

The profiles associated with each device could be very simple (e.g. in the case of a WEAN, they could be just "AP" or "STA"). In this case where a number of devices (STA) have the same profile, an additional parameter can be used to order the list of full addresses - such as a simple alphanumeric ordering of the full addresses. Alternatively, the profiles could be much more complex, for example in a home entertainment network, the profile could say "amplifier with fourteen parallel connections", "speaker with one connection", "DVD recorder with three connections", "TV with one connection", "CD player with one connection". The alphanumeric listing "backup" approach may still be required to resolve conflicts where several devices have the same profile.

Even if the addresses were listed entirely on the basis of an alphanumeric ordering, there would still be efficiency savings because there would only be as many short addresses as there are devices, so the length of the address fields are optimised.

In the situation where new devices may join the network (centralised or ad-hoc) fairly frequently, it may be undesirable to have to recalculate the entire addressing scheme every time that a new device joins the network.

In this case a management algorithm can be used to inspect the current range of the address-length field, and determines whether there is sufficient space to simply add an extra address of greater length than the current one. In the distributed ad hoc network case, this new address pairing would simply be broadcast to all devices; and in the centralised case, the access point would simply have to inform the new device.

In another alternative, the address-length field could be lengthened by a single bit, with a suitable sequence of messages exchanged and broadcast around the network to do this in a controlled fashion.

Where a device leaves a network, the simplest solution for the removal of the device would be to carry on with the current addressing scheme for the time being.

Alternatively or periodically a dynamic re-allocation scheme (described further below) can re-evaluate the current mapping.

The Huffman algorithm is described in Huffman, D. A. "A Method for the Construction of Minimum-Redundancy Codes." Proc. Inst. Radio Eng. 40, 1098-1101, 1952; and is normally used in file compression. It typically ensures that the calculation of addresses is minimally weighted, but this is at the cost of not only a slightly larger overhead in terms of the minimum length of any address, but also in terms of the requirement for repeated invocations of a sorting (or, at least, search + insertion) algorithm (rather than just on the first iteration as in the low complexity "simple" algorithm described above). The Huffman algorithms application to short address generation requires a more quantitative evaluation of the "popularity" of each device such that an actual numerical weight, relative to the other devices, can be derived. The algorithm builds up an extended binary tree by determining the two smallest weights (we and w2) and combining them to produce a temporary weight (internal to the algorithm) of wit = (w' + w2). This new weight wit is then inserted into the ordered list appropriately, and this process continued until no further combinations are possible (i.e. the root of the tree has been reached).

The ranking of devices, carried out as a precursor to the assignment of short addresses thereto, is based on an initial assessment of the anticipated popularity of a particular device over another. A further enhancement observes the activity of all of the devices during operation. This may be achieved by maintaining a running list of the devices in "most recently used" order, or statistics on the percentage of activity observed at each device. Then, either periodically or if the situation has become such that the current addressing scheme is sub-optimal beyond a threshold, then the addressing scheme could be changed.

One approach to the re-allocation of short addresses is to repeat the allocation from the beginning, by recalculating the network addresses. A second approach is to implement messages that could inform a device (or all devices in the case of the distributed scheme) of its new address and the time at which it should start using the new address.

This second approach would permit the system to continue functioning with only gradual degradation (i.e. only the current reconfiguring device would be affected).

An additional factor, when considering extensions to the EEE802.11/a/blg standards, is that of backwards compatibility. By altering the structure of the frame header in a drastic manner such as this, all older legacy devices will be unable to understand the frame format. The IEEE802. 11 standard defines a "fail-safe" reaction to the reception of corrupted frames (which, to all intents and purposes, these frames will appear to be), whereby the device backs off from attempting to access the medium for a very large amount of time (the Extended Inter Frame Space, EIFS), or until such time as it is able to correctly decode a frame. Whilst this is irrelevant to the new devices embodying this information, it would be problematic with the legacy devices, and is as such undesirable. To mitigate this problem, a "legacy friendly" mode of operation can be employed whereby only the data frame is sent using these variable length, shorter addresses - the acknowledgements (and any RTS/CTS handshakes) are sent with full 48-bit addresses. This results in a less optimum use of bandwidth, but the trade off is used to protect the legacy devices. In the event of the system determining that there are no legacy devices within the BSS, then a "native" mode could be employed with short addressing applied to all frames (data, ACK, RTS and CTS).

Compared with the Bluetooth _ three-bit AM_ADDR scheme, the described embodiments are extendable or scaleable, whereas Bluetooth TM runs out of addresses (ignoring the juggling of active and parked devices) after seven devices (one of the eight addresses being reserved for broadcast).

The embodiments also compare favourably with the 802.11 WLAN system, which uses a 48-bit MAC address even for small networks. A typical 802.1 1 data frame comprises three address fields: the source, destination and the BSS ID (which identifies the BSS as a whole, so that transmissions can be distinguished in the case of mutually collocated, coexisting BSSs). The BSS ID would be dangerous to abbreviate as there can be no coordination between the unrelated but overlapping BSSs, but the other two address fields (source and destination addresses) are both 48-bit addresses. Thus for practical wireless networks the embodiments will offer a considerable improvement.

As illustrated in figure 6, the described embodiments provide substantial improvement over the 48-bit IEEE802. 11 MAC addresses, in that addresses using the first approach will be 3- or 4-bit sequences (including the address length field) and addresses using the second approach will be 2or 3-bit sequences. Not only does this reduce the overheads associated with addressing, particularly with regard to command packets, it also allows further space for accommodation of data in a data packet of given length.

The skilled person will recognise that the above-described apparatus and methods may be embodied as processor control code, for example on a carrier medium such as a disk, CD- or DVD-ROM, programmed memory such as read only memory (Firmware), or on a data carrier such as an optical or electrical signal carrier. For many applications embodiments of the invention will be implemented on a DSP (Digital Signal Processor), ASIC (Application Specific Integrated Circuit) or FPGA (Field Programmable Gate Array). Thus the code may comprise conventional programme code or microcode or, for example code for setting up or controlling an ASIC or FPGA. The code may also comprise code for dynamically configuring reconfigurable apparatus such as re programmable logic gate arrays. Similarly the code may comprise code for a hardware description language such as Verilog _ or VHDL (Very high speed integrated circuit Hardware Description Language). As the skilled person will appreciate, the code may be distributed between a plurality of coupled components in communication with one another. Where appropriate, the embodiments may also be implemented using code running on a field-(re)programmable analogue array or similar device in order to configure analogue hardware.

The skilled person will also appreciate that the various embodiments and specific features described with respect to them could be freely combined with the other embodiments or their specifically described features in general accordance with the above teaching. The skilled person will also recognise that various alterations and modifications can be made to specific examples described without departing from the scope of the appended claims.

Claims

CLAIMS: 1. A method of allocating network addresses for devices in a

network, each network address comprising an addressing field of no fixed length, said method including the steps of: allocating a value to an addressing field of an address to a first device with an initial minimum length and allocating values to addressing fields of further addresses, of the same length or longer, to further devices thereafter, determining, after allocating an addressing field of an address to a device, whether remaining devices to be allocated addresses can be allocated addresses with addressing field of the same length as the addressing field of the presently allocated address and, if said devices can be so allocated addresses, then allocating addresses to remaining devices with addressing field of the same length as that of the presently allocated address.
2. A method in accordance with claim 1 wherein said step of allocating an address to a first device comprises allocating a l-bit address to said first device.
3. A method in accordance with claim 1 or claim 2 and further comprising the initial step of determining an ordered list of devices to be allocated addresses in said network, the order of said list being determined substantially on the basis of anticipated relative usage of said devices.
4. A method in accordance with claim 3 and wherein the step of determining an ordered list includes the step of receiving information about each device on introduction of said device to said network, said information including predicted usage information and processing said predicted usage information to derive anticipated relative usage of said devices.
5. A method in accordance with claim 3 or claim 4 and wherein the step of determining an ordered list includes the step of measuring previous usage of devices in said network and, on the basis of previous usage, determining a list of said devices in order of rate of use in said network.
6. A method in accordance with any preceding claim wherein each address further comprises an address length field of predetermined length, and the method further comprises the step of assigning, to an address length field of an address, a value denoting the number of bits in the corresponding addressing field.
7. A method according to claim 6 further comprising determining the number of devices in the network, the length of the address length field being dependent on the number of devices in the network.
8. A method according to claim 6 or claim 7, comprising the steps of determining, from the allocated addresses, the minimum value stored in the address length field of an allocated address, subtracting this minimum value from each value stored in the address length field of each allocated address and, if said step of subtracting results in the largest value of the address length field being less than the value associated with the most significant bit allocated to the address length field, then de-allocating said most significant bit from the address for all allocated addresses.
9. A method according to any preceding claim further comprising determining an activity profile for each device, said activity profile corresponding with a measure or estimation of the frequency of communication of said device within the network compared with the other said devices; and placing said devices in a list ordered on the basis of their activity profile prior to said step of allocating values to said addressing fields, such that addresses of lower allocated length correspond substantially with devices with a more active activity profile than do addresses of higher allocated length.
10. A method according to claim 9 wherein the measure or estimation comprises a frequency parameter and wherein the device having the highest frequency parameter is allocated the first address of minimum predetermined length.
11. A method according to any preceding claim wherein said step of allocating comprises assigning a preliminary addressing code to each device, considering each preliminary addressing code and, if the length of said preliminary addressing code is insufficient to allow addressing of all farther devices with addressing codes of the same length, then allocating said preliminary addressing code to the addressing field of said device, otherwise allocating to the addressing field of each remaining device an addressing code of length the same as the length of the preliminary addressing code under consideration, each such allocated addressing code being distinct.
12. A method according to claim 11 wherein the step of allocating a preliminary addressing code comprises applying a Huffman code to each device, the devices being ordered substantially in terms of frequency of addressing in the network.
13. A method according to claim 11 or claim 12 wherein the step of allocating, in the event that the length of said preliminary addressing code is sufficient to allow addressing of all further devices with addressing codes of the same length, comprises allocating, as the value stored in the addressing field for the device under consideration, the preliminary addressing code, and allocating as the value stored in the addressing field for all further devices to be considered, other values of the same bits.
14. A method according to any of claims 1 to 10 wherein the step of allocating comprises sequentially allocating values to addressing fields of devices such that all combinations of values for a given length of addressing field are allocated to devices before allocating an addressing field of longer length and, on allocating a value to an addressing field of a device wherein the addressing field is longer than the previously allocated addressing field, determining if all remaining devices can be addressed using addressing field of the same length and if so then performing the same.
15. A computer readable storage medium storing information defining a computer program which, when executed in a computer, causes said computer to perform the method of any preceding claim.
16. A computer receivable signal carrying information defining a computer program which, when executed in a computer, causes said computer to perform the method of any preceding claim.
17. Apparatus for allocating network addresses for devices in a network, each network address comprising an addressing field of no fixed length, including: addressing field value allocation means for allocating a value to an addressing field of an address to a first device with an initial minimum length and for allocating values to addressing fields of further addresses, of the same length or longer, to further devices thereafter, allocation process management means for determining, after said addressing field value allocation means has allocated an addressing field of an address to a device, whether remaining devices to be allocated addresses can be allocated addresses with addressing field of the same length as the addressing field of the presently allocated address and, if said devices can be so allocated addresses, then causing said addressing field value allocation means to allocate addresses to remaining devices with addressing field of the same length as that of the presently allocated address.
18. Apparatus in accordance with claim 17 wherein said addressing field value allocation means is operable to allocate a 1-bit address to said first device.
19. Apparatus in accordance with claim 17 or claim 18 and further comprising ordering means for determining an ordered list of devices to be allocated addresses in said network, the order of said list being determined substantially on the basis of anticipated relative usage of said devices.
20. Apparatus in accordance with claim 19 and wherein the ordering means is operable to receive information about each device on introduction of said device to said network, said information including predicted usage information, and operable to process said predicted usage information to derive anticipated relative usage of said devices.
21. Apparatus in accordance with claim 19 or claim 20 and wherein the ordering means includes measuring means for measuring previous usage of devices in said network and, on the basis of previous usage, said ordering means is operable to determine a list of said devices in order of rate of use in said network.
22. Apparatus in accordance with any of claims 19 to 21 further comprising activity profile determining means for determining an activity profile for each device, said activity profile corresponding with a measure or estimation of the frequency of communication of said device within the network compared with the other said devices; and said ordering means is operable to place said devices in a list ordered on the basis of their activity profile prior to said step of allocating values to said addressing fields, such that addresses of lower allocated length correspond substantially with devices with a more active activity profile than do addresses of higher allocated length.
23. Apparatus in accordance with claim 22 wherein the measure or estimation comprises a frequency parameter and wherein the device having the highest frequency parameter is allocated the first address of minimum predetermined length.
24. Apparatus in accordance with any of claims 17 to 23 wherein each address further comprises an address length field of predetermined length, and addressing field value allocation means is further operable to assign, to an address length field of an address, a value denoting the number of bits in the corresponding addressing field.
25. Apparatus in accordance with claim 24 further comprising means for determining the number of devices in the network, the length of the address length field being dependent on the number of devices in the network.
26. Apparatus in accordance with claim 24 or claim 25, comprising minimum address length determination means for determining, from the allocated addresses, the minimum value stored in the address length field of an allocated address, and address length adjustment means for subtracting this minimum value from each value stored in the address length field of each allocated address and, if said subtracting results in the largest value of the address length field being less than the value associated with the most significant bit allocated to the address length field, then operable to de-allocate said most significant bit from the address length field for all allocated addresses.
27. Apparatus according to any of claims 17 to 26 wherein said addressing field value allocation means comprises preliminary addressing means for assigning a preliminary addressing code to each device, and address confirmation means for considering each preliminary addressing code and, if the length of said preliminary addressing code is insufficient to allow addressing of all further devices with addressing codes of the same length, then for allocating said preliminary addressing code to the addressing field of said device, otherwise for allocating to the addressing field of each remaining device an addressing code of length the same as the length of the preliminary addressing code under consideration, each such allocated addressing code being distinct.
28. Apparatus according to claim 27 wherein the preliminary addressing means is operable to apply a Huffman code to each device.
29. Apparatus according to claim 26 or claim 27 wherein the address confirmation means is operable, in the event that the length of said preliminary addressing code is sufficient to allow addressing of all further devices with addressing codes of the same length, to allocate, as the value stored in the addressing field for the device under consideration, the preliminary addressing code, and to allocating as the value stored in the addressing field for all further devices to be considered, other values of the same bits.
30. Apparatus according to any of claims 17 to 26 wherein the addressing field value allocation means is operable to sequentially allocate values to addressing fields of devices such that all combinations of values for a given length of addressing field are allocated to devices before allocating an addressing field of longer length and, on allocating a value to an addressing field of a device wherein the addressing field is longer than the previously allocated addressing field, to determine if all remaining devices can be addressed using addressing field of the same length and if so then to perform the same.
31. A computer readable storage medium storing information defining a computer program which, when executed in a computer, causes said computer to operate as apparatus according to any of claims 17 to 30.
32. A computer receivable signal carrying information defining a computer program which, when executed in a computer, causes said computer to as apparatus according to any of claims 17 to 30.
33. A method of addressing devices in a network substantially as described herein with reference to the accompanying drawings.
34. Apparatus for addressing devices in a network substantially as described herein with reference to the accompanying drawings.