SE513508C2 - Procedures and arrangements for establishing communication channels in a DTM network - Google Patents

Abstract

The present invention relates to methods and an arrangement for establishing communication channels in a DTM network. According to the invention a DTM channel is established from a first node (N4) to a second node (N9) via one or more intermediate nodes (N5, N6, N8). Furthermore, a set of one or more DTM channels are established within said DTM channel, typically using control signaling between said first node and said second node, said one or more intermediate nodes not participating in said control signaling.

Description

Disclosure of the Invention The above and other objects are achieved by the invention as defined in the appended claims.

According to a first aspect of the invention, there is provided a method of establishing communication channels in a DTM network, channel from a first node to a second node in one or comprising the steps of: establishing a DTM - several intermediate nodes; and establishing a set of DTM channels within said DTM channel.

According to a second aspect of the invention, there is provided an arrangement for establishing communication channels in a DTM network, means for establishing a DTM channel from the first comprising a first node; a second node, the node of the second node, which DTM channel is established via one or more intermediate nodes; and means for establishing a set of DTM channels within said DTM channel. The invention is thus based on the idea of treating a plurality of DTM channels, hereinafter sometimes referred to as DTM subchannels, as components of a single DTM, which in the following is sometimes referred to as a DTM main "DTM tunnel". thus, it is possible to control, channel, channel or a With the invention it becomes change, modify, etc. the distribution of time slots among the DTM subchannels without this necessarily having to affect the handling of the DTM main channel, the size of the DTM main channel or the allocation of time slots to the DTM main channel.

When the DTM main channel, and consequently also DTM sub-extends from a transmitting node to a receiving node via one or more intermediate nodes, the intermediate nodes only need to participate in the handling of the DTM main channel and the allocation of time slots to the DTM. the main channel, the channels can be controlled from the endpoints. The division into while the definition of DTM-de1-DTM-subchannels thus only needs to be handled at the 50% transmitting and receiving node but these need to mix in intermediate nodes.

The possibility of not having to involve intermediate nodes in the handling of a plurality of DTM subchannels, all of which extend over the same network path, offers a great advantage in that this significantly reduces the need for signaling, especially when the number of intermediate nodes is large.

According to a preferred embodiment of the invention, the DTM subchannels comprise one or more control channels (signaling channels). In a conventional DTM network, a node will typically have access to a control time slot, which enables the node to send signaling messages to other nodes located on the same link (such as a bus or a ring). However, any form of signaling to nodes on other links must typically take place via the participation of an intermediate node which has access to a control channel on the other link and which can therefore handle the signaling required on this second link. When the channel's handling is not limited to a link, a plurality of intermediate nodes typically have to participate in but instead extend over a plurality of links, the signaling according to a hop-by-hop principle.

By establishing according to the invention a DTM main channel to extend over a plurality of links, and by defining a DTM control channel within this DTM main channel, this DTM control channel will enable a direct signaling path to nodes located on other links. Consequently, the DTM main channel can be considered as a virtual link that connects all the nodes that use the main channel to send / receive control signaling or payload. The intermediate nodes which only participate in the mapping / switching of the DTM main channel without participating in the actual transmission / reception of data in said channel or in DTM sub-channels thereof will not be involved in the handling of channels within 10 15 20 25 30 35 513 508 the main channel, ie in the management of channels on the virtual link.

It is thus clear that the invention significantly reduces the amount of signaling required in a DTM network.

According to another embodiment of the invention, channels received from one or more bit streams are mapped into respective DTM subchannels of the DTM main channel at an "input end" of the DTM main channel. The various DTM subchannels are then mapped to the respective outgoing channels on one or more outgoing bit streams at an "output end" of the main DTM channel. The invention thus provides a method of multiplexing channels into larger channels over large parts of a network.

In addition, the division of a DTM channel into DTM subchannels according to the invention can be used recursively. In other words, according to an alternative embodiment of the invention, a plurality of DTM subchannels are transmitted within a common DTM main channel, which in turn transmits together with other DTM channels in a common "supra-DTM main channel", and so on. The creation of virtual links in the form of DTM main channels according to the invention can thus take place over a plurality of hierarchical link levels.

According to another embodiment of the invention, data transmitted in the DTM main channel is encrypted as a whole, ie not subchannel for subchannel. This makes it more difficult for an unauthorized user to decrypt a DTM subchannel, thereby improving network security and network integrity.

According to a third aspect of the invention, there is provided a method for managing communication channels in a DTM network, which method comprises the steps of: accessing a first link of the DTM network via a first interface; establishing a DTM channel from the first interface to one or more intended receivers, at least one of which is located on another link of the DTM network and is reached via at least one exchange node in the network; defining a virtual link, the connectivity of which is defined by said intended receiver of said DTM channel, and a virtual interface associated with the virtual link and defined by the access to the set of time slots provided. defines said DTM channel on said first link; and establishing one or more DTM channels on said virtual link to one or more of said intended receivers.

This third aspect of the invention thus provides an advantageous way for a node in the network to handle the division of DTM main channels into DTM subchannels according to the first and second aspects of the invention.

By considering a DTM main channel of the kind discussed above as a separate, virtual interface, and by allowing the emergency to operate accordingly, the invention can be relatively easily implemented without having to design separate complicated software processes and / or memory functions dedicated to the management and definition of DTM subchannels. Since virtual interfaces according to the invention can be used recursively, an increased depth of the division into subchannels (ie the division of DTM subchannels into DTM subchannels into DTM subchannels, etc.) can be handled in a preferred manner using one and the same software function. as further described below with reference to Fig. 4.

According to an embodiment of the latter aspect, the one or more DTM subchannels are divided into DTM control channels and DTM data channels, the invention, wherein control signaling for handling said DTM channels on the virtual link is performed using said DTM control channels. for transmitting signaling messages between nodes This provides a mechanism located on different links transparent to intermediate nodes, as discussed above.

The term "intended receivers" refers to the units (nodes) which are arranged to transmit data or receive data (control signaling or payload) using jDTM main channel 513 508 using said DTM main channel or DTM subchannels therefrom. A node which only provides mapping / switching of one (and consequently of the DTM subchannels within the main channel) from one bitstream to another without in fact being arranged to listen to or transmit data within the main channel, and which is not affected by any existing subdivision in subchannels, in other words are not considered as an "intended recipient".

The use of a one-to-one DTM main, ie a point-to-point tunnel for which a single (unicast) channel, node acts as an input and a single other node acts as an output, will probably be the most common I in such a case, the virtual channel formed by the main DTM channel will be the application of the invention. be a one-to-one link. An alternative embodiment, i.e. a DTM main channel accessed and used by a plurality of nodes, which is a multiaccess DTM main channel, is also advantageous. In the latter case, the virtual link formed by the multiaccess DTM main channel can be considered as a multiaccess link. A node having access to the multiaccess DTM tunnel can thus be arranged to read data from and / or transmit data in one or more of the main channel DTM subchannels, and thus act in a similar manner as an add-drop channel. multiplexer in relation to DTM subchannels of the DTM main channel.

By definition, a "DTM network" refers to a circuit-switched time division multiplexed network of the kind in which information is transmitted between the networks' nodes on bit streams. Each bitstream is divided into regularly recurring frames of so-called comprise a number of time slots of fixed size, which fixed length, "DTM frames", each time slots being divided into control time slots (signaling and data time slots), a time slot position in a DTM frame thus defines gaps) At any given time, there will be either a control time slot or a data time slot.

Control time slots are used for signaling between the nodes of the network, and data time slots are used for the transmission of payloads. Note that control time slots and data time slots are basically handled the same at the link level. The only difference -between the two is that they are used in two different ways by the nodes of the network.

In addition, in a DTM network, the write rights to the time slots in a DTM frame are distributed among nodes connected to the bitstream that should be the DTM frame, where each node typically has write rights to at least one respective control time slot and a dynamically varying number of data time slots. the recurring framework. In this case, having the write right to a time slot position in a frame also means having the write right to this time slot position for each recurring frame on the bitstream.

In a DTM network, a node can use the data slots to which it has write access to establish so-called "DTM channels" by allocating one or more of these data time slots to the respective DTM channel. A DTM channel, whether it is a "main channel" or a "subchannel", is thus defined by one or more time slots occupying the same time slot positions within each DTM frame on the bitstream on which said DTM channel is carried. However, if a DTM channel extends over, for example, two bitstreams, the channel can of course be defined by different sets of time slot positions on the two bitstreams. A DTM channel can be a control channel (signaling channel) or a data channel depending on whether control or data time slots define the channel. A DTM channel can also be a single-channel channel (a transmitter to one receiver), a multicast channel (a transmitter to several receivers) or a broadcast channel (a transmitter to all others).

When the demand for network capacity varies, DTM channels can be set up, taken down or modified dynamically, the latter by changing the number of time slots allocated to the DTM channel. The distribution of write rights to time slots among different nodes can be dynamically modified as different nodes develop different needs for signaling and data transmission.

The above and other aspects of and features of the invention, such as the use of a memory-based exchange core shared by all ports and the use of routing memory shared by all channels accessed by routing means, will be further apparent from the following description of embodiments thereof.

Brief Description of the Drawings Exemplary embodiments of the invention will now be described with reference to the accompanying drawings, in which: Fig. 1 schematically shows a DTM network operating in accordance with an embodiment of the invention; Figs. 2a-2c schematically show the allocation of time slots to DTM channels on a bitstream in accordance with the prior art.

Figs. 2d-2e schematically show the allocation of time slots to DTM channels on a bitstream in accordance with an embodiment of the invention; Fig. 3 is a block diagram schematically showing a node in the network of Fig. 1; and Fig. 4 schematically shows a simplified view of the DTM network in Fig. 1.

Detailed description_of preferred embodiments A circuit-switched, time-multiplexed network operating according to a DTM protocol (Dynamic synchronous Transfer Mode) will now be described with reference to Fig. 1.

The DTM network in Fig. 1 comprises a plurality of nodes N1-N11 which are interconnected via four unidirectional bit streams B1-B4. Each of the bit streams B1-B4 will typically be used together with a respective bit stream (not shown) which propagates in the opposite direction, thus together forming a bidirectional link interconnecting all nodes connected to 15 20 25 30 35 513 508 link. The nodes N1-N4 are connected to the bitstream B1, the nodes N4-N7 are connected to the bitstream B2, the nodes N6, N8 and N9 are connected to the bitstream B3 and the nodes N9-N11 are connected to the bitstream B4.

The nodes in Fig. 1 typically give end users (not shown) access to the network. However, the network also includes nodes that do not give end users access to the network, but which e.g. only provides switching between different of the network's links, such as switching nodes N4, N6 and N9. In addition, one or more of the nodes can connect the DTM network NW with an external network (not shown) separate from the DTM network NW in Fig. 1, such as e.g. an Ethernet network.

The data transfer format used on the bit streams B1-B4 in Fig. 1, using the bit stream B2 as an example, will now be described with reference to Figs. 2a-2e.

As shown in Fig. 2a, the bitstream B2 is divided into recurring frames of substantially fixed length, where the start of each frame is defined by a frame synchronization time slot F. For example, each frame may have a length of 125 ps. As shown in Figs. 2b and 2c, each frame is divided into a number of time slots of fixed size, typically 64 bits.

For example, if you use a frame length of 125 ps, time slots of 64 bits and a bit rate of 2 Gbps, the total number of time slots in each frame will amount to approximately 3900.

The time slots in a frame are generally divided into control time slots C4-C7 and data time slots D4-D7. The control time slots use fl åâ for signaling between the network nodes, while the data time slots are used for transmission of payload. At the start-up of the network, at least one node connected to the bitstream B2 is typically allocated at least one control time slot, at the same time as the data time slots are distributed between the nodes connected to the bitstream. The node N4 will thus initially have access to a control time slot CÃ Sch to a set of data time slots D4 within each frame of the bitstream, the node N5 will have access to a control time slot C5 and to a set of data time slots D5 within each frame of the bitstream, etc., as shown in Fig. 2b. The time slots that are allocated to a node as control time slots (one or more) and / or data time slots (one or more) occupy the same time slot positions within each frame of the bitstream. Consequently, the control time slot C4 belonging to the node N4 will occupy the second time slot in each frame of the bitstream in the current example.

During network operation, each node can increase or decrease its access to time slots, thereby redistributing access to data time slots or control time slots among the nodes. A node that has a set need for transmission capacity can e.g. give away their writing right to time slots to a node that has a greater need for transmission capacity. As shown below, time slots allocated to a node do not have to lie next to each other, but can lie anywhere in the frame.

Note further that each frame begins with said frame synchronization time slot, which defines the frame rate of the bitstream, and ends with one or more padding time slots G.

After accessing at least one control time slot and a plurality of data time slots, the node N4 may, for example, establish DTM channels on the bitstream B2 by allocating a subset of these data time slots to these DTM channels, but using the control time slot C4 for transmission of signaling messages relating to the management of said DTM channels.

Fig. 2c shows the situation according to the prior art when the node N4, with its access to its control time slot C4 and its data time slots D4 on the bitstream B2, has establishments CH2, CH3 and CH4.

In this example, it is assumed that the channel CH4 is a DTM-rated four channels CH1, a channel extending from the node N4 to the node N7, the node N4 having allocated seven of its data time slots within each frame of the bitstream B2 to the channel and having 5 35 513 508 ll informed the receiving node N7, using the control time slot C4, and the presence of the channel CH4.

The node N4 has further set up a DTM channel CH1 to the node N9 by allocating time slots within each frame on the bitstream B2 and by asking the switching node N6 to allocate a corresponding set of time slots on the bitstream B3, which channel comprises four time slots within each frame on bitstream B2.

After receiving requests for channel establishments from the nodes N1 and N2 on the bitstream B1, the node N4 has also established DTM channels CH2 and CH3 on the bitstream B2, the channel CH2 forming a multi-hop channel from the node N1 to the node N11 and the channel CH3 forming a multi-hop channel from the N2 to the node N10. It will be appreciated that corresponding time slots for channels CH2 and CH3 are also allocated on bitstreams B1, B3 and B4.

In the example in Fig. 2c, the transmission capacity of the channel CH4 is greater than the transmission capacity of the channel CH1, since the number of time slots allocated to the channel CH4 is greater than the number of time slots allocated to the channel CH1. The time slots allocated to a DTM channel occupy the same time slot positions within each recurring frame on the bitstream. after noting the many channels going to / via the node N9, Fig. 2d shows the situation when the node N4, in addition to the previously mentioned channel CH4 to a DTM main channel CH10 from the node N4 to the node All_trafik in time slots within the channel CH10 on the bitstream B2 is thus mapped by the node N6 established, the node N7, N9 via the node N6. to a corresponding channel segment on the bitstream B3 to reach the node N9. In the DTM main channel CH10, three DTM subchannels CH11, CH12 and CH13 are defined, corresponding to the above-mentioned channels CH1, CH2 and CH3 in Fig. 2c. Similar to Fig. 2c, each DTM subchannel is defined to include a respective set of time slots within each frame of the bitstream. The node N4 has furthermore converted a time slot 10 within the channel (the first time slot within the main channel i into a control time slot C4v, said control time slot for sending signaling message to the node N9. The node N4 thus now has access to a control time slot C4 received by all nodes on each frame) utilizing bitstream B2 and a control time slot C4v transmitted within the main channel CH10 and received by node N9.

When allocating etc. of time slots to channels within the main channel CH10, the node N4 no longer needs to be exchanged with the node N6 as Instead, the node N4 can now send signaling messages directly for signaling via the control time slot C4, intermediate negotiator to reach the node N9. the node N9 via the control time slot C4v, which is defined within said main channel CH10. Consequently, the main channel CH10 can be considered as a virtual link offering a virtual direct connection between the nodes N4 and N9. Similarly, node N4 access to the time slots defining the main channel CH1O on bitstream B2 can be considered as defining a virtual interface that provides access to the virtual link.

As an example, Fig. 2e shows the situation when the definition of DTM subchannels within the DTM main channel has changed as In Fig. 2e, the channel CH12 is unchanged, and the bandwidth of the channel CH13 has been increased. However, the size of the main channel CH1O is unchanged. Because all necessary signaling due to changes in demand for capacity. the channel CH11 has been taken down, and the allocation of time slots to, between the nodes N4 and N9 has been possible using the control time slot C4v, and since all changes relate to the allocation of time slots to channels on bit streams B2 and B3 have taken place within the main channel CH10 , none of these changes have required informing or interference with, for example, node N6.

The construction of a node in the network in Fig. 1, using the node N4 as an example, will now be described with reference to Fig. 3. The node 100 in Fig. 3, which in this example is assumed be the node N4 in Fig. 1, comprises four 2-port interfaces 10, 20, 30 and 40, the first and third interfaces 10 providing write / read access to the bit stream B1 and B2, respectively, and the second and fourth interfaces 20 and 40 provide write / read access to respective unidirectional bit streams (not shown in Fig. 1) which propagate in opposite directions with respect to bit streams near and B2, respectively.

All interfaces are connected to a common memory 50 which is used to effect time and space exchange of data among the links connected to the node, time slot by time slot. The common memory includes frame buffers for each of the received bitstreams. For example, the frames received via the interface 10 are sequentially written into the common memory 50 to be temporarily stored there. At the same time, write the frames received via the interface 20 sequentially into another part of the common memory 50 to be temporarily stored there, and so on. Each interface 10, 20, 30 and 40 further comprises a respective time slot mapping table 11, 21, 31 and 41 which are used in transmitting data on the respective bitstream. Each time slot mapping table includes a table row for each outgoing time slot of the respective outgoing bitstream frame, and each table row contains pointers indicating from which field in the common memory 50 data is to be retrieved for the current outgoing time slot.

The contents of the time slot mapping table are indirectly controlled by a node controller 60. The node controller 60 is arranged to read data from one or more fields in the common memory 50, which fields correspond to control time slots defining other nodes' control channels, to receive signaling messages from other nodes. Similarly, the node controller 60 is arranged to enter data in one or more fields of the common memory 50, which fields correspond to control time slots defining the node's own control channels to other nodes, for sending signaling messages to other nodes. nodes.

When establishing a new channel, for example based on a channel establishment request received from another node and consequently read from defined fields of the common memory 50, the node controller can access a routing table 70 which provides, inter alia, information about which receivers can can be accessed via which interfaces, which can then be either physical interfaces (such as interfaces 10, 20, ...) or virtual interfaces (as discussed above). Based on such information, the node controller will set up a channel by defining a table row in a channel table 80 and by sending a channel set message to other nodes (by writing the message in the field of the common memory 50 corresponding to an outgoing control channel).

The channel table 80 contains a list of table rows, one for each channel handled by the node N4. such a table row provides table 80 with information indicating from which interface (physical or virtual) is received for the respective channel, on each and from which time slot positions thereof, as data and which interface (physical or virtual), and which time slot positions thereof, which shall be used for the transmission of data within the current channel.

The channel table 80 is connected to an interface mapping unit 90 which provides mapping between virtual channels / time slots and physical channels / time slots.

For example, the interface mapping unit contains one which e.g. (virtual) (physical) table (not shown) indicates that the time slots 2-20 of the interface 5 correspond to the time slots 12-30 of the interface 1.

When using virtual interfaces recursively, i.e. when a main channel comprises a number of subchannels, at least one of which in turn also contains a number of sub-subchannels, etc., the interface mapping table used by the interface mapping unit 90 will be 513 508 may be provided with recursive mapping instructions, for example by a table row indicating that the (virtual) interface 6 time slots 2-4 correspond to the (virtual) interface 5 time slots 6-8 and another table row indicating that the (virtual) interface 5 time slots 6-8 correspond to the (physical) interface 1 time slots 100- 102.

If the establishment of a channel indicates that it would be appropriate to define a virtual link and an associated virtual interface, as discussed above, the node controller will ensure that the channel table 80 and the interface mapping unit 90 are updated accordingly.

The interface mapping unit 90 will, with the aid of the interface mapping table, translate the channel list of the channel table 80 and, based on that, make sure to create necessary pointers of the time slot mapping tables 11, 21, 31 and 41. The time slot mapping tables will thus always be updated with correct mappings. Fig. 4 Schematically shows a simplified view of the DTM network in Fig. 1. In Fig. 4 it is assumed that the node N4, in a similar manner as described above, has established a main channel CH30 to the node N9 via the node N6, which main channel contains the time slots_1, 2, 4, 5, 6, 9, 10, 11 and 12 in each frame on the bitstream B2 and the time slots 5, 6, 7, 8, 9, 10, 12, 13 and 14 in each frame on the bitstream B3.

Furthermore, it has been defined, by means of control signaling between nodes N4 and_N9, that the first two time slots, among the main channel's set of nine time slots in each frame on both bitstreams, are allocated to a subchannel CH31, that the following two time slots are allocated to a subchannel CH32, and that the last four time slots are allocated to a subchannel CH33, the fifth of the main channel time slots being unallocated. Tables I and II show an example of the contents of the node N4 channel table and interface table in the position described with reference to Fig. 4.

Table I - Interface mapping table Outgoing Doors Outgoing Doors Interface Interface 2 1-9 l 1,2,4,5,6,9, 10, l1, l2 Table II - Channel table Channel Outgoing Doors Interface CH3O ll, 2,4,5,6 , 9, 10, ll, l2 CH3l 2 1,2 CH32 2 3,4 CH33 2 5,6,7,8 As shown in Table I, the node N4 considers the main (in this case the physical interface to the bitstream B2) time slots l , 2, 4, 5, 6, 9, 10, ll and l2, a virtual interface 2 that offers time slots l-9. the channel, which is defined by the interface 1 as forming Furthermore, the channel CH31 is defined to include the (virtual) which with the time slots 1 and 2 of the interface 2, can be translated by the table I to the time slots 1 and 2 of the physical interface 1. Correspondingly, the channel CH 32 defined to comprise the time slots 3 and 4 of the (virtual) interface 2, which can be translated by means of Table I into the time slots 4 and 5 of the physical interface 1.

Tables III and IV show an example of the contents of the node's N6 channel table and interface table in the same mode as discussed above. 10 15 20 25 515 508 17 Table III - Interface mapping table Outgoing Gaps Outgoing Time Gaps Interface Interface Table IV - Channel Table Channel Incoming Gates Outgoing Gaps Interface Interface g CH 30 ll, 2,4,5,6, 2 5,6,7,8, 9, 9, 10, ll, l2 l0, l2,13, l4 As can be seen from Table III, the node N6 in this mode has not defined any virtual interfaces. In addition, Table IV shows that the channel CH30 is defined to include the time slots 1, 2, 4, 5, 6, 9, 10, 11 and 12 of the interface 1 (the physical interface to the bitstream B2) and the interface 2 (the physical interface to the bitstream B2). B3) time slots 5, 6, 7, 8, 9, 10, 12, 13 and 14. As shown in Tables III and IV, the node N6 in this position has no knowledge of the presence of subchannels within the channel CH30. Although the invention has been described above with reference, these should not be considered to limit the scope of the invention. As will be apparent from exemplary embodiments thereof, will be appreciated by those skilled in the art, various modifications, combinations, and changes may be made within the scope of the invention, as defined by the appended claims.

Claims (32)

10 15 20 25 30 35 513 508 18 PATENT REQUIREMENTS A method of establishing communication channels in a DTM network, establishing a DTM channel comprising the steps of: (CH10) from a first node to a second node via one or more intermediate nodes; and establishing a set of DTM channels (CH11, CH13) within said DTM channel. CH12, A method according to claim 1, wherein said set of DTM channels is established within said DTM channel by control signaling between the first node and the second node, said one or more intermediate nodes not participating in said control signaling. A method according to claim 2, wherein said control signaling is performed within said DTM channel. A method according to claim 1, 2 or 3, wherein signaling with respect to said set of DTM channels is performed using one or more of the DTM channels (C4v) forming said set of DTM channels. A method according to any one of the preceding claims, wherein said DTM channel is a one-to-one channel, the first node and the second node forming the end points of the channel. A method according to any one of claims 1-4, wherein said DTM channel is a one-to-several channel extending past at least one of the first node and the second node. 10 15 20 25 30 35 513 508 19 A method according to any one of the preceding claims, wherein said DTM channel extends over a plurality of intermediate nodes. A method according to any one of the preceding claims, wherein one or more of the DTM channels included in said set of DTM channels extends beyond one of the endpoints of said DTM channel. A method according to any one of the preceding claims, wherein each of the intermediate nodes that provide switching of said DTM channel between two bit streams in the DTM network performs mapping from time slot to time slot between the sets of time slots defining said DTM channel on the two bitstreams. A method according to any one of the preceding claims, wherein each of the one or more intermediate nodes which causes switching of said DTM channel from one bit stream to another bit stream in said DTM network participates in said step of establishing said DTM channel by allocating a set of time slots to said channel on the second bitstream. 11. ll. A method according to any one of the preceding claims, comprising transmitting a number of isochronous channels from one or more first bitstreams to one or more second bitstreams via said DTM channel, which isochronous bitstreams are switched to a respective DTM channel of said set of DTM channels. A method according to any one of the preceding claims, comprising encrypting the information transmitted in said DTM channel as a whole. io 15 20 25 30 35 513 508 20 A method according to any one of the preceding claims, comprising dynamically resizing said DTM channel. A method according to any one of the preceding claims, wherein the size of said DTM channel changes as a result of a change in said set of DTM channels' total capacity requirements. An arrangement for establishing communication- comprising: 100); 100); for establishing a DTM channel from transmission channels in a DTM network, a first node (N4; a second node (N9; means (60, 80) the first node to the second node, which DTM channel is established via one or more intermediate nodes, and means (60, 80, 90) DTM channels within said DTM channel for establishing a set An arrangement according to claim 15, wherein said set of DTM channels is established within said DTM channel by control signaling between the first node and the second node, said one or more intermediate nodes not participating in said control signaling. 17. l7. An arrangement according to claim 16, wherein said control signaling is performed within said DTM channel. An arrangement according to claim 15, 16 or 17, wherein signaling with respect to said set of DTM channels is performed using one or more of the DTM channels forming said set of DTM channels. An arrangement according to claim 15, 16, 17 or 18, wherein said DTM channel is a one-to-one channel, the first node and the second node forming the end points of the channel. 10 15 20 25 30 35 513 508 21 An arrangement according to claim 15, 16, 17 or 18, wherein said DTM channel is a one-to-several channel extending past at least one of the first node and the second node. An arrangement according to any one of claims 15-20, wherein said DTM channel extends over a plurality of intermediate nodes (N5, N6, N8). An arrangement according to any one of claims 15-21, wherein one or more of the DTM channels included in said set of DTM channels extends beyond one of the end points of said DTM channel. An arrangement according to any one of claims 15-22, wherein each (N6) of the intermediate nodes that effect switching of said DTM channel between two bitstreams in said DTM network performs switching from time slot to time slot between the sets time slots defining said DTM channel on the two bitstreams. An arrangement according to any one of claims 15-23, wherein each (N6) of the one or more intermediate nodes that provide switching of said DTM channel from one bitstream to another bitstream in said DTM network participates in said step of establishing said DTM channel by allocating a set of time slots to said channel on the second bitstream. An arrangement according to any one of claims 15-24, wherein said organ establishment of a set of DTM channels is arranged to switch one or more isochronous channels received at said first node to respective DTM channels of said set DTM channels 10 15 20 25 30 35 513 508 22 An arrangement according to any one of claims 15-25, wherein said means for establishing a set of DTM channels is arranged to switch one or more of said set of DTM channels to respective isochronous channels transmitted from said second node. An arrangement according to any one of claims 15-26, wherein said means for establishing a DTM channel is arranged to dynamically change the size of said DTM channel. An arrangement according to any one of claims 15-27, wherein said means for establishing a DTM channel is arranged to change the magnitude of said DTM channel as a result of a change in said set of DTM channels' total capacity needs. A method of managing communication channels in a DTM network, comprising the steps of: accessing a first link of the DTM network via a first interface; establishing a DTM channel from the first interface to one or more intended receivers, at least one of which is located on another link of the DTM network and is accessed via at least one exchange node in the network; defining a virtual link, the connectivity of which is defined by said intended receiver of said DTM channel, and a virtual interface associated with the virtual link and defined by the access to the set of time slots defining said DTM channel on said first link; and establishing one or more DTM channels on said virtual link to one or more of said intended receivers. 10 15 20 513 508 23 A method according to claim 29, comprising the step of dividing the data time slots forming said DTM channel into control time slots and data time slots. A method according to claim 29 or 30, wherein said one or more DTM channels comprise a DTM control channel and a 'ends for signaling with respect to said one or more DTM channels within said DTM channel. A method according to claim 29, 30 or 31, comprising the steps of: - accessing a second link of the DTM network via a second interface; receiving one or more DTM channels on said second link; and switching said one or more DTM channels received on said second link to respective DTM channels established on said virtual link.