Local area network with converting means

The invention relates to a local area, the asynchronous transfer mode (ATM) working network, in particular a uni- or bi-directional ring network, with several stations and these and / or other networks with other stations associated network interface (ATM transceivers), each having a transceiver and having receiving ring terminal, said information exchange digital via ATM cells, in their header field (header) address information, particular bundle identifiers (VPI, Virtual Path Identifier) ​​and connection identifiers (VCI Virtual Channel Identifier), are laid down. The invention also relates to a for use in such a network appropriate ATM cell, and a network interface for such a local Network, and finally a stackable ATM unit consisting of a plurality of network interfaces for the construction of a switching device (switch).

In a local area network, which in the asynchronous transfer mode (ATM) works, are calculated from the information to be transmitted (message) blocks fixed length formed. Each block will be an additional control information a transfer unit adds designated as ATM cell. An ATM cell is composed thus of a cell header (header) and a Information field (payload) in which contain the information to be transmitted are.

The ATM technique is used in different transmission services such as Data transmission services, voice services, video services (eg Video conferencing, video databases) or in the transmission of multimedia information, in which language settings, data and video information to each other are combined. It can be both private and public, an ATM network.

A public ATM network is for example the B-ISDN network (broadband integrated service Digital Network). Private or public ATM networks may due to the predetermined ATM standards to be interconnected.

When ATM cells are continuously transmitted on each transmission section. Just no useful information to send, so be specially marked Empty cells sent. Thus, the ATM useful to one another in time transmitted independently since the time intervals adjacent to the line between Useful cells are usually different. This type of transmission one calls therefore be asynchronous. This provides ATM asynchronous transfer solid of useful cells length represents.

The payload cells distinguish between user cells (user cells), which in an established its information field, such as news or information about the user above containing compound, and control cells (signaling cells), which in its Information field control information, for example for the control unit of a network interface, contain.

In ATM networks, the available transmission capacity (bandwidth) is a In so-called wideband channel. Virtual paths (Virtual Path) divided. A virtual path in turn represents a group of virtual channels (virtual channel). At the Building a virtual connection between a transmitter and a receiver is selected, first the appropriate virtual path. Subsequently, a part the bandwidth as a virtual channel of this path is. For the identification of virtual channel identifier VCI is used the (Virtual Channel Identifier). For the identification of the paths, the identifier VPI (Virtual Path Identifier) ​​is used. Thus, each cell transmitted can be clearly assigned because the combination VPI & VCI is the logical identifier for the specified connection.

In addition, a distinction is made between a single connection (unicast connection) between a single user of a first station and a User a second station is built. If the connection between a first and a plurality of other users takes place, is referred to the compound as a multiple (multicast connection). If it is at such a multiple connection to an arbitrary number of further users is, one speaks of a Verteilverbindung (broadcast connection).

From EP 0614296 A2 is a local ATM network of the aforementioned known type in which useful cells both user cells and control cells are processed. Each network interface is associated with this one station. The user cells included, while the actual information, eg Messages or data of the user of this compound. When a virtual Connection example for transmission of voice signals (phone call) is used, contains the information field of the user cell speech data. In contrast, contains a control cell in its information field control information, the example of the ring internal coordination of the switching function are required, in particular to establish a connection or by the information transmission dismantle again. On the other hand also control cells needed to control information between a station and the network transferred to. In such a case, the control cell from a UNI / NNI prescribed standardized layout.

In such a known network connection is established as follows:

When a connection request of a transmitting station having at least one Receiving station is first at least a control cell with a query generates the state of the receiving station. The at least one receiving station upon receiving the query at least one control cell with the information about their condition. The transmitting station forms after receiving the state information at least one control cell to establish the connection, if the state of at least one receiving station allows a connection. Subsequently, the connection and the transmission of the information. The reduction in Connection is made in the reverse order.

From US 5,600,795 is a according to the asynchronous transfer mode ATM known operating local area network, wherein the connection setup in a similar Way characterized, in that a first of a transmitting station associated control assembly, provided from said transmitting station control cell with a viable Desire for a single (unicast) or multiple (Multicast / broadcast) receives a user of the transmitting station. subsequently done sending the control cell to a user at least one Receiving station, said control cell in its information field at least one Information about the user, the address of the transmitting station and a user-related contains identification for the return link. In one of the receiving stations associated control arrangement is effected after reception of the delivered by the transmitting station Control cell generating a transmitting station to be transmitted control cell which in its information field at least an indication of the address of the associated receiving station and a user-related identification for the forward link contains. Also in this network each station is its own associated network interface.

From "Telekommunkation currently, ATM applications, multimedia communication via information highways, VDE Verlag GmbH 1995 ", pages 11-16, is the fundamental known structure of ATM cells according to the prescribed standard ATM. Accordingly, there is the ATM cell from an information part of a length of 48 Byte and a head part (header) of a length of 5 bytes. The cell header is structured differently, depending on whether it is an ATM cell, the via an interface between a station and the network (UNI, user network interface) or between two different networks (NNI network network interface) is transmitted.

If there is a UNI-contained cabin that form the first 4 bits of the cell header the GFC function (generic flow control). This enables overload situations in power due to exceeding a predetermined bandwidth to prevent. Followed by a bit string of 8-bit VPI and VCI 16 bits to Definition of the virtual channel or the virtual path. The following Info header cell refer to the type of cell (PT, payload type) A distinction is made with in this prior art between user cells and control cells. More information by the cell loss priority (CLP, cell loss priority) and the Zellenkopfprüfsumme (HEC, header error control) made. The latter areas PT, CLP, HEC are at UNI / NNI cell identical. In contrast, the NNI cell differs from the UNI-cell in that, instead of the intended in the UNI-cell GFC-range of the range for the path identifier (VPI) is extended from 8 to 12 bits.

The invention is based on the object, a network or a network interface of the aforementioned type, as well as for use in a to further develop such a network suitable ATM-cell, that the ring internal communications is simplified without the ring externally set Standard is violated.

This object is in a network or a network interface of the kind mentioned in that the at least one network interface Conversion means are assigned to at least partially and reversible reaction of available data bytes in the header field of the ATM cell in a network-specific identifier.

When an ATM cell for use in a network of the aforementioned Art done the inventive solution in that it is a one port extender forming multiplexer / demultiplexer is associated, via which the data transfer is carried out to a plurality of connection ports arranged on stations.

The invention is in principle over the prior art by from that by the reaction of the available data bytes within the header bit the ATM cell in the network-specific identifier is a much more flexible data transfer can be carried out within the network. The inventive solution based on the approach that a standardization in accordance with the UNI / NNI Standard Only there must be upheld where it due to the ambient conditions is required.

Within the network, thus seen from the network on this side of the interfaces must contrast the prescribed standard to stations not be respected. Rather, a system-specific header format be used. Both of these formats differ in meaning the header bits, but not in the length of the header. Upon entry into the Network is thus the invention of the UNI / NNI nonstandard Header in the network-specific header bit translated. Conversely, when the Cell leaving the network, whose header specific to the UNI / NNI format transformed back. used The selection of specific ring for identification Header bits can be freely selected.

Because preferred implementation means a during the call setup phase or updated during the week reduction phase header translation table (Header translation table) include such that at least a Part of not occupied by the standardized VPI & VCI bit sequence header area with the network-specific identifier is overwritten, resulting in a simple Adjustment. The header translation table during Signaling (call setup) defined so that on one hand the VPI & VCI bit sequence obtained for the connection identifier remains and on the other hand the desired network-specific information is included in the identifier. On First Part of the identifier can preferably for distinguishing unicast (Individual compounds), multicast (multiple connections) and broadcast (Verteilverbindungen) be used. Another, further in the following subsection II called Section of network-specific identifier is used for the target indication of ATM cell, that is, for determining that the network interface on which Destination station is connected.

Finally, may include information on the priority and the Eige nschaft a Cell (control cell) be laid down in the network-specific header format.

In Unicastbetrieb located in the other section of the network-specific Identifier specifying the jenigen network interface to which the desired destination lies.

In contrast, corresponds to multicast or broadcast mode, in other Portion of the network-specific identification information stored address the transmitting network interface (Port ID = SENDER ID). The ATM cell is So passed within the network of interface to interface to they finally returned to their Ausgangangspunkt, ie the transmission network interface arrives and is deleted there. In broadcast mode needs doing to be made, no further distinction, as the ATM cell for each Network interface is determined. In contrast, should the multicast operation in advance be determined whether the ATM cell is determined for each network interface is because there is a proper connection to the station, or whether the cell without submitting it to the station to the output of the network interface is forwarded. This purpose, a mapping table (small broadcast / multicast table), called during the signaling phase from. Call handler on the basis of for the compound desired stations is defined. This mapping table on Output station is necessary because of a particular broadcast / multicast connection associated cells a global, that is, substantially identical, use VPI & VCI pattern. In contrast have to UNI / NNI Standard different connection participants also different VPI & VCI values. The Allocation table (broadcast / multicast table) therefore matches the global VPI & VCI Pattern of a compound in the ring network to the subscriber-specific VPI & VCI Pattern of UNI / NNI standard. This adjustment takes place during the signaling phase. The effect of this mapping table is that a deletion notice is read for the cell in this table for the case that it is in the Multicast operation is a cell that is not to the network interface belonging station belongs.

A particular embodiment of the inventive solution is that at least one network interface comprises a multiplexer / demultiplexer, over which two or more stations together to network interface are connected. Accordingly, each network interface are now accordingly the multiplicity of the multiplexer or demultiplexer several stations assigned which are each served by the same network interface from can. Thus, the network interface the status of so-called. Port Extenders on which a fixed number of connection ports for the individual stations contains. The incident with comparable slow speed of the stations Cells are selected by the multiplex operation on the high speed link transformed to the transmitting ring ports of the network interface. In the reverse direction of the network interface to be arriving cells to the various terminal ports of the stations in the distributed sense of demultiplexing. These multiplexing and demultiplexing function the Port Extenders can be realized without the above-described basic Construction, the network interface device must be changed. There are only to take measures to further the portion of the network-specific Identifier to store additional information, the basis of which the Fact is taken into account that now each network interface not only a but over the Port Extender several stations are connected. at this solution using the Port Extender is particularly advantageous in that UNI / NNI standard at the input and the output of the port extender is present, ie is displaced at the network interface there.

For this purpose is provided in the case of a Unicastbetriebs in that the further partial region II the network-specific identification of two bit portions x, y, said the a bit portion x to identify the type of the multiplexer / demultiplexer connected terminal ports and the other bit portion y to identify the Network interface is used for which the ATM cell is determined. Compared to the previously described basic system without Port Extender is now the first bit portion x updated and shortened the second bit portion y. This is another assignment table from which the call handler receives the information, which connection ports on the respective network interface in which way addressed. Thus, if in a particular Unicastbetrieb the transmitting station Receiving station selects the call handler is about him known association the coding information for the bit portion x given. The data bit then so filled that in the x-range information for each connection port and-containing the identification of this terminal port in the y-range Network interface is stored.

In the case of a multicast / broadcast operation is - as in the basic system without port Extender - the further partial region (II) of the network-specific identifier with the Indication of the transmitting network interface (SENDER ID) provided. here, too, thus runs the ATM cell interface to interface until they finally again arrives at its starting point.

Also in the broadcast operation resulting in the use of the Port Extenders no substantial difference.

In multicast mode, however, provided that any person participating in the compound Network interface defined during the call set-up assignment pattern a (Pattern) for the selection of within this network interface at the having connection terminal participating ports, the network interface internally the other part II of the network-specific identifier respectively overwritten becomes. This measure reflects the fact that in multicast operation one hand the information must be maintained, whether the respective network interface has ever connection ports, that pertains to the compound Stations provide, and, if so, in addition, the further information which the stations are affected by the compound. The first information is the call handler known about the system configuration. The second information containing allocation pattern is accordingly during the signaling phase set participating in the connection stations, serving later as Distribution algorithm for the arriving cells to the output ports of the associated Port Extenders.

A particular use way finds the solution of the invention by that a network interface is set up, the local blocking free N x N Switching unit forms, when the data rate of the connection between port Extender and transceivers is greater than the sum of the individual data rate port Extender A. or outputs.

The invention is explained in more detail below with reference to drawings. there show: <dl tsize="7" compact="compact"><dt>Fig. 1</dt><dd>a local, in the asynchronous transfer mode (ATM) working Network as to its basic structure from the prior is known to the art,</dd><dt>FIG. 2</dt><dd>another, after its basic structure from the prior Art-known local area in the asynchronous transfer mode ATM network operating,</dd><dt>Fig. 3</dt><dd>a local ATM network with a network interface, which a port extender includes,</dd><dt>Fig. 4</dt><dd>Explanation sketches for the construction of ATM cells,</dd><dt>FIG. 4a</dt><dd>the overall construction of a conventional ATM cell,</dd><dt>Fig. 4b</dt><dd>the ATM cell header according to the UNI-standard,</dd><dt>Fig. 4c</dt><dd>the ATM cell header after the NNI-standard and</dd><dt>Fig. 4d</dt><dd>the basic structure of the ATM cell header region according to Embodiment of the invention represent,</dd><dt>Fig. 5</dt><dd>an explanation sketch of the ATM cell transfer, namely</dd><dt>Fig. 5a</dt><dd>Unicastbetrieb in the network of FIG. 1 or 2,</dd><dt>Fig. 5b</dt><dd>in multicast or broadcast operation of the network of FIG. 1 or 2,</dd><dt>Fig. 5c</dt><dd>Unicastbetrieb in the network according to Fig. 3,</dd><dt>Fig. 5d</dt><dd>in multicast operation of the network of FIG. 3</dd></dl>

The illustrated in Fig. 1, which in terms of its basic structure from The art-known local in the asynchronous transfer mode ATM working network provides four stations 1-4, which each have a network interface 5-8 are connected to a ring network. The data connection between one of the stations 1-4 to a receiving station within the network carried respectively by the ATM transmission method. For this purpose, each network interface 5-8 transmit and receive ring compounds on which to transfer are provided by cells. Each network interface has a 5-8 (not shown in detail) on the coupling device, on the buffer memory with the ring compounds and the station is coupled and the cell stream relayed. Details of the structure of such a network interface, the prior Technique of EP 0614296 A2.

Fig. 2 shows a local network assembly consisting of two local ATM networks I, II consists. Each of the networks each comprises a plurality of stations 1, 3, 4 or 9, 10, 11, each connected to separate network interfaces 5, 7, 8 and 13, 14, 15 with the mapped network are connected. Both networks are mutually about each other coupled network interface 6 and 12 associated. In such coupled networks, the transmission of the ATM cells, for example, by a Transmitting station in the area of ​​the network i to a receiving station in the area of Network carried II (or vice versa).

Fig. 3 shows the basic structure of another local ATM network. in the Contrast to the networks shown in Figs. 1 and 2 are connected to a network interface 5 several stations 1a, 1b, 1c connected. To this end, the network interface 5 extended to include a multiplexer or demultiplexer 20 having a Coupling the ATM cells from the parallel at the network interface 5 adjacent station 1a, 1b, 1c in the ring ports of the network interface 5 allows. Conversely, the on the net at the receiving terminal ring of Network Interface 5 received ATM cells in the demultiplexing Multiplexer / demultiplexer 20 is again the desired stations 1a, 1b, 1c assigned. In this way, the network interface 5 is called a. Port equipped Extender, to its port number corresponding to a plurality of stations 1a, 1b, 1c connected. The illustrated in Fig. 3 Port Extender for the network interface 5 is also realized in the same way for any other of the illustrated Network interfaces. Also, the multiplicity of each port extender not limited in principle.

Starting from the basic structure of ways shown in the figures 1 to 3 a local ATM network is the basic function of the present invention Solution will be explained below:

FIG. 4a shows the structure in principle of an ATM cell according to standard, which consists of a total of 53 bytes, with 48 bytes for the transmission of information (Payload) and 5 bytes for the control of the transmission in the form of header data are provided. These 5 bytes make up the so-called. Cell header (header).

Fig. 4b shows the envisaged under standardization Strukur of the cell header for a cell from a station (user) to the network (network) is transmitted. This standard is referred to as UNI (user network interface). Here are the first 4 bits of the GFC function (generic flow control) formed to prevent the emergence of overload situations are in the network. The following 8 Bit used to define the virtual path (VPI), while the subsequent following 16 bits for the definition of the virtual channel (VCI) are provided. Other bits in the header are provided for the identification of Cell type (PT, payload type), the cell loss priority (CLP, cell loss priority) and the Zellenkopfprüfsumme (HEC, header error control).

Fig. 4c shows, in contrast to the construction of the cell header in the event that the ATM cell through a network network interface (NNI, network network Interface) are transmitted from a local ATM network to another shall, (comp., for example, Fig. 2). For the NNI standard are the first 4 bits, which are reserved in the UNI cell for the GFC function added to the VPI field, so that the entire available for VPI &amp; VCI area a Length of eg 28 bits obtained.

In Fig. 4d, the structure of an ATM cell is now in principle shown as represented by the implementation of the UNI / NNI standard in the network-specific standard is obtained. First, it must be assumed that the areas PT, CLP and HEC of the cell head against the standardized format remain unchanged.

Within the reserved VPI &amp; VCI header area, for example, 28 bits includes, is a located in the standardized use of unused section for example, 16 bits because 10 bits for VPI &amp; VCI information in building 1024 compounds sufficient. The remaining bit range is UNI / NNI set default to zero.

According to the invention will now be this bit range (see Fig. 4d.) For the network-specific (Ring internal) identifier used, ie the free bit overwritten.

The identifier consists of a first section I (UMB), in which the information is stored, whether it is a a unicast, multicast or to a Broadcast connection is. The other portion II (DEST ID) includes the essentially the address information for the ATM cell. This will be in detail later be discussed. Finally, another section III (CP) for Pioritätsangaben or reserved for the cell type.

The FIG. 4d modified header area thus has the appropriate VPI &amp; VCI areas on as well as the original. The remaining under Standard unused portion of the bit string, however, can be freely selected programmed will. The implementation of the header from the UNI / NNI format into the ring specific Header structure takes place when the cell enters the network interface. there be carried out the following steps:<sl><li>1. The existing header VPI &amp; VCI bit according to UNI / NNI are Standard detected and thus stored in the network interface mapping table addressed. In this table, the correspondence between the connection identifier VPI &amp; VCI and the desired destination on the network deposited. The definition This table takes place during the signaling phase, ie during the Call setup.</li><li>2. The new (ring specific) Header format of the mapping table read and overwrite the incoming cell header with this format.</li><li>3. On the basis of is stored in the overwritten cell header information decided whether the ATM cell from the local processor of the network interface is received (if there is one for this imaginary control cell), or whether the cell to return to the station or to enter the ring of the network.</li></sl>

As described above, indicates the first section I of the network-specific Header format, the property of the cell, whether it is a Unicast Multicast or broadcast connection cell is. Depending on the type of connection and further depending on whether a network interface a port extender according Fig.3 contains or not, the cell structure used in the further partial region II vary as follows:

First, the case of Fig. 5a considered that to get an Unicastbetrieb acts and each network interface of FIG. 1 and 2 exactly a station is assigned. In this case located in Section II, the address those network interface where the desired destination station is connected (Port-ID).

Fig. 5b shows the cell structure in region II, when it is in contrast to FIG. 5a is a multicast or broadcast mode. Then located in Section II the address of the network interface from which the ATM cell is emitted (SENDER ID). This results in that the ATM cell starting from the sending station passes through the entire network until they eventually return to the Transmitter arrives.

In Fig. 5c, the structure of the further partial region II of the network-specific ID shown when in the case of Unicastbetriebs a network interface is equipped in accordance with FIG. 3 with a port extender. For this case, a Subdivision provided in a first sequence x and a second bit sequence y. In the first bit sequence x is the identifier is stored for the connection port on which the desired destination station is connected. In contrast, shows the second bit sequence y the identifier of the network interface on which the connection port of the Destination is.

Fig. 5d shows the cell structure in the case of a multicast operation for a Port Extender equipped network interface according to FIG. 3. The section II Bit pattern illustrated account which connection ports within a mentioned network interface for the connection to be desired, for example, Here, the connection ports 0, 2, 4, 6, while the remaining connection ports 1, 3, 5, 7 on the multicast connection should not take part.

For the case that by using a port Extenders a broadcast operation is to take place, resulting in principle from that in Fig. 5b shown Structure without using a port extender no difference. As well as FIG. the station ID 5b used as the destination address of the ATM cell, as all connected within the network stations in the connection are involved.

The detailed operation of the inventive solution is in Follow this procedure:

The following cases are distinguished:

1. Unicastbetrieb without Port Extender

To define the mapping table in the network interface is the call handler known in the signaling phase to which network interface to that station is, with which the connection should be recorded. at the implementation of the header bits in the ATM cell at the transition to the network interface thus in the free bit in Section II, the address (port ID) enrolled those network interface, connected to the station is. If there is a control cell, according to the target for this control cell enrolled in the free bit range. This may be for example, to a control cell for the CPU in the same network interface act.

The overridden with the ring-specific address information ATM cell occurs now in which a ring network.

If the destination address of the arrived next network interface not with the registered port ID matches, the ATM cell to the ring output forwarded (in case of a bi-directional ring network to both outputs). If it comes to that network interface associated with the port ID agrees, the cell is passed to the output station. There the Backtranslating the header bit in the standardized format in which the in the non- used VPI &amp; VCI area existing bits are set to zero.

An appropriate mode occurs when the cells in the reverse direction to run.

2. Multicast mode without Port Extender

During the signaling phase of the call handler determines to which network interfaces is to be transmitted, that is, which stops in the connection are involved. This is taken into account in the allocation table, by means of which standardized UNI / NNI format in the network-specific header bit structure is implemented.

Due to the defined in section I of the network-specific identification information Multicast is the section II as the address identifier for the ATM cell deposited address of the sender.

During the exchange of information is now passed through the ring with the specific Header format provided ATM cells the ring network and in each network interface the cell is copied and forwarded to the output ring until the Cell finally reaches back to the broadcast network interface and deleted there becomes.

Each network interface is checked whether the cell is intended for them. If this is not the case, the copied cell is erased. If this is the case, the copied cell forwarded to the output of the network interface to the station.

The check whether the particular cell belongs to the network interface or not, carried out by the further allocation table previously determined in the signaling phase (Small broadcast / multicast table).

3. Broadcast operation without Port Extender

During the signaling phase is determined that to all of the network located network interface cells to be transferred, since each connected Station takes part in the connection. However here is under 2. as Address identifier in Strand II of the network-specific identifier, the port ID of the Transmitter deposited, so that here again the ATM cell passes through the entire network, until it finally arrives back in the transmitter and will be deleted there.

4. Unicastbetrieb with using the Port Extenders

As an extension to the processing method described in 1. Call the handler initially informed as the assignment of the individual to the terminal ports the Port Extender connected stations to the respective network interfaces is designed. This is the system-specific structure, which is communicated to the call handler, for example in the form of a database.

Knowing that the call handler sets during the signaling phase, over which network interface to connect to the desired destination station must take place. In Strand II of the network-specific identifier will not be only bit of data in the area y for marking the network interface but data bit area also in the x provided that include an identifier which, the connected to the network interface connection ports to the desired Station belongs.

Moreover, the cell transfer is effected as described under 1. Also the inverse transform the network-specific header format into the standardized Format is again by resetting the bit in the field x and y to zero.

5. Multicast operation using a port extender

In this mode is again defined in the signaling phase initially, which stations are involved in the connection. The call handler is now known to which network interface the connection ports for the connection to the are to be involved stations. Consequently, during the signaling phase set in each network interface a bit pattern characteristic is for which the connection ports of Port Extenders ATM cells should receive. Each network interface receives thus depends on the board to be Connection ports each have different bit patterns such.

It is still set during the signaling phase which network interfaces are anyway involved in the connection, ie, those defined network interfaces, to which at least one connection port for a Station needs to be addressed. For this, in turn, is an allocation table (Small broadcast / multicast table) defined.

In Strand II of the network-specific identifier as an address, as described in 2. and 3. described, again indicated the sender's address as the port-ID.

The transfer of cells is now as follows:

Each cell is from the transmitter terminal port on the high-speed line, the leads to the network interface, and passed from there occurs a the network. If Now the cell has entered the next following network interface depends the Further processing depends on whether at least one of the connection ports this network interface is involved in the connection.

If this is not the case, the cell is forwarded to the ring output and enters the next network interface a.

Is recognized by the existing mapping table that the cell for at least a the connection ports of the network interface is determined, is that in this Network interface stored bit patterns used to further process the cell. Here, all x + y bits are provided for in section II data bit used so that a corresponding multiplicity of the Port Extenders is considered. With the bit pattern will now be given to the respective Connection port directed demultiplexing treatment of the individual cells, so that they arrive at the desired included in the connection stations.

The processing as described is now equally in each of the ATM cell arrived at network interfaces, until the cell back into the transmitter interface is reached and deleted there.

6. Broadcast operation with use of a port extender

Compared to the procedure described in section 5, the broadcast operation no special Bitmusterangabe necessary as connected with each transmitter to communicate. Hence also arises when using a port Extenders that operation, as described under 3.