Method for reserving isochronous resources in a wireless network

ES 2 246 325 T3

DESCRIPTION

Method of reserving isochronous resources in a wireless network.

The invention relates to a method for reserving isochronous resources in a wireless network. It is especially applicable to a HIPERLAN 2 network among whose devices include an IEEE 1394 convergence layer.

The IEC 61883 documents, in their parts 1 to 5, define a digital interface for audio and video devices in an IEEE 1394 wired connected bus-based network. Specifically, these documents describe the packet and record formats to be used in conjunction with the isochronous resource reservation mechanism defined by IEEE 1394.

IEC 61883-1 defines an isochronous packet (“Source packet”) that encapsulates the data of the audio / video stream to be transmitted. An isochronous source packet is divided into one or more data blocks for insertion into IEEE 1394 isochronous packets ("Bus Packets"). Depending on the available bandwidth, one or more blocks of data may be inserted into a bus packet. A bus packet can also remain empty, when no data blocks are available.

Special registers (“Connector registers”) are defined in the source and collector devices. An output connector control register (oPCR) is defined for each output connector (source), while an input connector control register is defined for each input connector (collector). A device can have several connectors of each type. More specifically, each connector control register defines the number of "quadlets" that can be supplied by a source or absorbed by a collector, for each isochronous packet.

Bandwidth reservation, as such, for the IEEE 1394 bus is known from EP 0971509 A (Sony International (Europe) GmbH et al.), Published on January 12, 2000.

When an IEEE 1394 controller reserves isochronous bandwidth, it will reserve for the maximum bandwidth defined by the connector control registers. The maximum bandwidth is expressed as the maximum number of “quadlets” that can be sent by a source device during a 125 jus bus cycle. This reservation is valid for every cycle, which means that even in case of not sending data blocks during a cycle, this bandwidth is lost, since it is not available for other devices.

The ETSI BRAN HIPERLAN 2 draft standard aims to define a high-speed local area network for multimedia applications. The use of HIPERLAN 2 has been proposed to interconnect IEEE 1394 buses or IEEE 1394 devices. Therefore, for HIPERLAN 2 a specific IEEE 1394 convergence sublayer is required, to act as an interface for the 1394 devices and facilitate the services of a IEEE 1394 link layer.

HIPERLAN 2 is based on a TDMA / TDD (Time Division Multiple Access / Time Division Duplex Mode) scheme, in which the TDMA frame has a periodicity of 2 ms.

Taking into account that the bandwidth reservation, according to the IEC 61883 rules, can only be done in discrete stages (1.5, 3.6,12,24, 36 ... Mbit / s), regardless of the width actual bandwidth required, applying these rules to the 2 ms HIPERLAN frame would result in a loss of bandwidth efficiency, compared to a tighter scheme. For example, if an MPEG 2 transport stream is to be transmitted at 7 Mbit / s, then 12 Mbit / s should actually be reserved.

Considering that network resources in a wireless network are especially scarce, a more efficient wireless bandwidth reservation mechanism is required than that of IEC 61883.

The object of the invention consists of a method for reserving isochronous resources in a wireless network, which comprises at least one wireless source device and one wireless collecting device, said wireless network being based on a TDMA frame transmission scheme, said method including the following stages:

- providing an output connector on a wired source device connected to the wireless source device, said output connector being associated with a register of output connectors that defines a maximum amount of data that outputs through said output connector during a wired bus frame;

- reserving on the wired bus an amount of bandwidth corresponding to said maximum amount of data to be sent in a frame through the wired bus;

- providing an output connector on said wireless source device, said output connector being associated with a record of output connectors, wherein said record of output connectors defines a maximum amount of data output for said output connector during a wireless frame;

- reserving in the wireless network an amount of bandwidth corresponding to said maximum amount of data to be sent in a wireless frame with an isochronous resource manager of the wireless network;

ES 2 246 325 T3

- providing the wireless source device with isochronous data to be sent over the wireless network from the wired source device.

The amount of bandwidth to reserve over the wireless link is based on the characteristics (for example, duration) of the wireless frame, and thus is not dependent on the cycles of the wired buses or other means used to provide data for its transmission to the source device.

For the HIPERLAN 2 wireless link, a frame duration of 2 ms is used instead of the 125 ps cycle of IEEE 1394.

Isochronous traffic generally takes place in bursts: Taking the example of a partial MPEG2 stream, the bursting of the partial stream depends on the location of the MPEG2 TS packet within the full MPEG2 TS. IEC 61883 specifies a packet fragmentation method for data transfer rate rationalization so that some data can be sent every 1394 cycles. However, since the reserved bandwidth on a 1394 bus is expressed as a maximum number of “quadlets” of data to send in a period of 125 ps, the bursts of traffic imply the underutilization of the bandwidth, due to the short cycle length 1394.

For example, an isochronous flow can generate the following profile: cycle (N): 1 source packet, cycle (N + 1): 2 source packets, cycle (N + 2): 1 source packet, cycle (N + 3): 2 source packages,

In this example, the amount of reserved bandwidth through a 1394 bus will be 2 source packets for every 125 ps, resulting in a reserved bandwidth of 2 * 192 * 8 bits / 125 ps = 24,576 Mb / s (without the CIP and 1394 overhead).

If we increase the time interval during which the maximum number of “quadlets” of data to be sent is calculated for the same class of bursts, then the maximum number of “quadlets” of data to be sent decreases. When the time interval is infinite, the bandwidth to be reserved (maximum number of “quadlets” over a period, divided by the period) converges towards the average transfer rate.

Taking the previous example, if we calculate the bandwidth to reserve as the maximum number of “quadlets” to send over 2 ms, we have the following:

ms = 16 cycles of 125 ps

In this way, in 2 ms we will have 24 source packets, with which it turns out that the bandwidth to be reserved is 24 * 192 * 8/2 = 18.432 Mb / s (not counting the CIP and the 1394 overhead).

Thus, when the time interval over which the maximum number of data is calculated for a given type of burst is increased, a value closer to the mean is obtained, and therefore a lower value.

According to one embodiment of the invention, a maximum amount of data is defined in units larger than quadlets.

More specifically, these units can be 48 octets, which represents the amount of useful data of the Data Service Units of the SAR layer.

According to an embodiment of the invention, the wireless network is a HIPERLAN 2 network, in which the data to be sent through the wireless network is provided to said source device through a wired bus in isochronous data packets with a duration less than that of a wireless network frame.

Through the description of a non-limiting embodiment, described with the aid of the following figures, other characteristics and advantages of the invention will become apparent:

- figure 1 is a diagram representing a wireless network with two devices,

Figure 2 is a diagram of the Hiperlan 2 protocol stack of each device, said stack, as such, belonging to the prior art,

ES 2 246 325 T3

- figure 3 represents the format of a control register of output connectors corresponding to the prior art,

figure 4 represents the format of an output connector control register according to the present embodiment.

The wireless network of figure 1 comprises audio / video devices 1 and 2. Device 1 has two output connectors, respectively, 3 and 4, and one input connector 5. Device 2 has only one input connector 6. Both devices are wireless devices and are connected to a HIPERLAN 2 network. Each connection is associated with the corresponding connector control register (oPCR (x) or iPCR (y)).

Figure 2 represents the protocol stack of each of the devices 1 or 2. This stack comprises a physical layer, a data link control layer and a convergence layer. The convergence layer includes a component common to the convergence layers of all HIPERLAN 2 devices. This component is called CPCS, or common component convergence sub-layer. Another common component is the Segmentation and Reassembly (SAR) component. The SAR segments the packets received from the CPCS into fixed-size data units, and transfers them to the data link control layer.

The stack also includes a service-specific convergence sub-layer (SSCS). The function of this layer is to establish a correlation between the specific requirements of the upper layers and the services offered by the data link control layer. In this embodiment, this layer is specific to IEEE 1394 and IEC 61883 (although the invention is also applicable to different environments). Other SSCS can coexist with SCSS IEEE 1394.

Top layers include, for example, a 1394 application.

In the following paragraphs, the acronyms SDU and PDU will be used. These acronyms designate, respectively, Service Data Units and Protocol Data Units. The single layer SDU, for example SSCS SDU, can be described as the data packet format between the SSCS layer and the layer above the SSCS layer, while the single layer PDU designates the data packet format intended for exchange with an underlayer.

According to the invention, a connector control register includes an element that determines the maximum amount of data that a connector can generate or absorb during a period of 2 ms - that is, the period of the wireless frame - instead of during the 125ps of IEEE 1394 cycle time.

This allows a 1394 application to examine the contents of a record and make adequate bandwidth reservation in the HIPERLAN network. A method to carry out this type of reservation is described in European patent application 00400220, filed on January 27, 2000 in the name of THOMSON multimedia, and the corresponding PCT application EP01 / 00941, filed on January 26, 2001 .

Preferably, in order to adhere to the principles of IEC 61883, the maximum amount of data in the connector control registers corresponding to HIPERLAN 2 is expressed in “quadlets”.

Figure 3 shows the format of an output connector control record according to IEC 61883. The meaning of the various fields is as follows:

The bit "online" indicates whether the corresponding output connector is online (value one) "offline" (value zero).

The broadcast connection counter indicates whether there is a broadcast connection with the output connector (value one) or not (value zero).

The point-to-point connection counter indicates the number of point-to-point connections with the output connector.

The use of reserved bits is not defined at the moment.

The channel number indicates the actual channel number used by the output connector.

The data transfer rate indicates the actual data transfer rate used by the output connector (that is, S100, S200, or S400, according to IEEE 1394 terminology).

The overload ID indicates the maximum number of overload quadlets to transmit on the output connector in an isochronous packet.

The useful data indicates the maximum number of “quadlets” of useful data to be transmitted by the output connector in an isochronous packet.

ES 2 246 325 T3

As can be seen in figure 3, this last element is encoded in 10 bits for IEC 61883. Although this is sufficient for a 125 ps cycle, it is not sufficient for a 2 ms frame. According to the present embodiment, other bits of the oPCR register are used, in addition to the 10 bits of the useful data field, in order to increase the coding possibilities of the number of "quadlets".

Considering that the data transfer rate indicated on the oPCR connector is related only to an IEEE 1394 wired bus, this information is meaningless in the context of HIPERLAN 2. For this reason, these two bits can be used for the same purpose. than the bits of the useful data field. This is true in a purely wireless network (when the devices are not connected to a wired bus), but also in the case that a wireless network is used as a bridge between two - or more - wired buses. In fact, the transmission data transfer rate of each wired bus may be different from that of the other wired buses. Devices 1 and 2 in Figure 1 can be used as the two portals of a bridge. In this case, the respective devices would be connected to the respective 1394 wired buses.

The two reserved bits are also used to encode the useful data.

In this way, the maximum number of “quadlets” in a 2 ms frame can be encoded using 14 bits.

Figure 4 shows the format of the new oPCR record.

Of course, the useful data field can indicate the maximum data output required in units other than quadlets.

According to the present embodiment of the invention, the Overload ID field of the oPCR record is used as defined in IEC 61883.

In this case, the useful data field represents the maximum total amount of data that can be generated during a 2 ms frame. This includes the SSCS Service Data Unit (SSCS SDU), the overhead of the SSCS 1394 Protocol Data Unit (SSCS PDU) added by the SSCS layer, and the overhead added by the CPCS / SAR layer. By convention, it does not include data link control layer overhead.

In this case, there is no limitation on the number of CPCS packets within the overhead of the wireless frame (there could be more than one), as long as the overhead induced by the headers of the CPCS packets is reflected in the data field. tools.

Given that the segmentation and reassembly component of the convergence layer segments payload data into 48-octet Service Data Units (SAR SDUs), the new payload field uses the size of a SAR SDU as the unit instead. of "quadlets", as a variant of the main embodiment of the invention.

According to a variant embodiment, the oPCR record usage overhead ID field is redefined to correspond to wireless transmission. The overhead ID will define the amount of overhead added by the HIPERLAN 2 packet-based convergence layer within a 2ms frame (i.e. the SSCS PDU overhead and the CPCS / SAR overhead).

Again, by convention, DLC overload is not included.

In this case, the user data field will contain the maximum number of user data quadlets within a 2 ms frame, that is, the total amount of SSCS SDU data, without the 1394 SSCS PDU overhead or CPCS overhead. /HE.

The invention has the advantage of allowing efficient bandwidth reservation in a wireless network without the process being constrained by the restrictions imposed by IEEE 1394 125ps cycles. It also allows maximum bandwidth reservation without using a limited number of default and discrete bandwidth values, as defined by IEC 61883.