The combined use of the telephone or ISDN network (ISDN—Integrated Services Digital Network) and the Internet has made the transport of different communication services on the conventional subscriber line DSL (Digital Subscriber Line) an important technology.
A number of systems are available for connecting the various customer premises equipment for conventional telephony/ISDN or broadband applications. Both time division multiplex and ATM techniques (ATM—Asynchronous Transfer Mode) are used as the transmission format, ADSL (Asymmetric Digital Subscriber Line) and SDSL (Symmetric Digital Subscriber Line) being well-known transmission methods. The present invention relates to both of these methods, ADSL and SDSL. For symmetric digital subscriber line, the abbreviation SHDSL (Symmetric High Bit Rate Digital Subscriber Line) is also commonly used.
With both methods, telephone connections and/or ISDN connections can be operated simultaneously with data links on the subscriber line and can be set up and terminated individually and independently of one another. In the interest of intensive used of the line, it is particularly advantageous, for example, to leave the transmission channel of a just terminated telephone or ISDN connection unused during the period up to the next connection request, using instead a simultaneously active ATM data channel to temporarily increase the throughput volume. The associated allocation or taking-back of the additional channel must not cause any loss of data in the ATM channel. This principle of intensively utilizing transmission channels is known as dynamic channel allocation or dynamic rate repartitioning (DRR).
An object of the present invention is to specify a method for this purpose. This method has the advantage of increasing the data transmission capacity of the ATM channel without loss of data.
The advantage of this, in turn, is that the existing telephone and ISDN connections are unaffected.
The inventive method offers the further advantage that, when the channels additionally carrying ATM are taken back, this taking-back causes no impairment of a new connection setup for ISDN and telephony.
Additional features and advantages of the present invention are described in, and will be apparent from, the following Detailed Description of the Invention and the Figures.
For the following considerations, data transport via an SDSL frame and then viaan ADSL frame will be discussed. Payload bits, signaling bits and service bits are transmitted at defined bit positions in this frame.
It is well known that for various SDSL applications, the service bits and the signaling bits can be transmitted within the frame, in accordance with ETSI standard TS 101 524 or ITU standard G.991.2, in the so-called overhead area where they are also transmitted in the eoc channel (embedded operations channel), or in one or more 8-kbit/s Z-channels provided as an expansion or in one or more 64-kbit/s B-channels. The protocol sequences for controlling telephone and ISDN connections likewise have been standardized in accordance with ETSI EN 300 324-1. Also standardized is the assignment of 64-kbit/s timeslots in the SDSL frame to the payload information of one or more telephone and ISDN connections.
The frame is subdivided into four payload blocks PL1, PL2, PL3 and PL4. Each payload block PL1, PL2, PL3, PL4 is in turn subdivided into 12 payload sub-blocks P01 to P12, P13 to P24, P25 to P36 and P37 to P48.
Each sub-block can be subdivided into up to seven 8-kbit/s Z-channels and up to thirty-six 64-kbit/s B-channels, each Z-timeslot including 1 bit position and each B-timeslot 8 bit positions. Signaling bits as well as operational bits for telephone and ISDN connections can be transmitted in a number of Z-timeslots and/or adjacent B-timeslots specified as required when the SDSL link is configured. The information bits of the B1- and B2-channels of an ISDN connection are transmitted in 2 consecutive B-timeslots of an SDSL frame. The digitized signals of the telephone connections are likewise transmitted in B-timeslots, one B-timeslot being assigned to each telephone connection and the relevant number of telephone B-timeslots and ISDN B-timeslot pairs required likewise being specified when the SDSL link is configured. The data of the ATM connection is concentrated in another configured number of 64-kbit/s timeslots. The total number of B-timeslots is determined by the transmission rate of the current SDSL system and is between 3 and 36 as indicated in
The overhead (OH) accommodates overhead data (data concerning the payload) containing individual bit positions for the operational information, and, with approximately 3.3 kbit/s transport capacity, the eoc channel.
In addition, the frame has at its start a 14 bit long sync word (synchronization word) for frame alignment and two bits at the end of the frame for adapting the frame length.
As has been explained in the frame description in connection with
During operation, not all the reserved telephone and ISDN channels are occupied all the time. According to the present invention, a method for using the temporarily unassigned telephone and ISDN timeslots will now be specified. This has the advantage of increasing the transport capacity of the ATM connection.
It is assumed that, as described above, during configuration of an SDSL link the assignment of the timeslots to the communication services is preset, examples of which are shown in
According to the present invention, the same applies analogously to the ISDN timeslots, as the second example in
For ATM operation, this means that, in the two examples described, the ATM cells must be injected into separate timeslot areas of the frame. It is an advantageous aspect of the present invention that the telephony timeslots and ISDN timeslot pairs temporarily switched to the ATM channel are not jumpered, thereby eliminating interference to existing telephone and ISDN connections.
According to the present invention, the timeslots or timeslot pairs temporarily switched away from the telephone and ISDN area remain assigned to the ATM area until they are again required in their preset area as the result of a connection request for telephony or ISDN.
To initiate the procedures for channel allocation to the ATM link or back to the telephony or ISDN area, commands of standard EN 300 324-1 can be used. These are “Disconnect” for assigning a telephony timeslot to the ATM link, “Deactivate” for assigning an ISDN timeslot pair to the ATM link, “Establish” for returning the telephony timeslot to the telephony area and “Activate” for returning an ISDN timeslot pair to the ISDN area. This definition has the advantage that the assignment and switchover procedures can be seamlessly linked to existing signaling procedures for setting up and terminating connections.
The assignment and switchover procedure initiated by the commands in accordance with EN 300 324-1 is illustrated in an example in
The switchover procedure following the allocation procedure is bit-controlled, so that the conventional duration of telephone and ISDN connection setup is not noticeably extended by the switchover and is frame-synchronized, ensuring that no loss of data occurs in the existing ATM link. The sequence of the switchover procedure is illustrated in an example in
From the idle state of LT and NT, which is defined by Bit24/Bit36=0/0, the LT procedure is initiated by the message Bit24/Bit36=1/0, “Sync Demand”, sent downstream to NT. With the transmission or arrival of the first frame with Sync Demand, the reference or synchronization point for subsequently defining the transmit and receive time of the first downstream frame with a new channel structure in LT or NT, is already fixed in LT and NT respectively. With the CRC-protected receipt of Sync Demand, NT in turn initiates the switchover procedure using the currently valid channel allocation list transmitted with the B Channel Allocate command. After an NT-specific delay according to the present invention, as described below, NT sends the message Bit24/Bit36=1/0, “Sync Response”, upstream to LT. With the transmission or arrival of the first frame with Sync Response, the starting point for subsequently defining the transmit and receive time of the first upstream frame with a new channel structure in NT or LT, is now also fixed in NT and LT respectively. LT answers after the CRC-protected receipt of Sync Response and after an LT-specific delay according to the present invention, as described below, with the message Bit24/Bit36=1/1, “Sync Confirmation”. LT counts the SDSL frames beginning with the first transmitted frame with Sync Demand up to and including the last frame prior to the transmission of Sync Confirmation and therefore knows, for LT, the reference time TRef governing the transmission and receipt of the first frame with the new channel allocation. NT likewise determines the reference time TRef by counting the frames beginning with the first incoming frame with Sync Demand up to and including the last frame prior to the arrival of Sync Confirmation.
As illustrated in
When the procedure is operating properly, according to the present invention the first new frames are transmitted or received by the LT and NT in the time interval 2 TRef according to the previously specified reference points. The time instants for frame switchover in the upstream or downstream direction are defined in LT and NT by the transmission and receipt of the same frame in each case, and therefore ensure a frame-synchronized switchover.
A further advantage of the inventive extending of TRef by the time portions for switching over to the changed channel allocation is that the message exchange up to the execution confirmation described below is terminated with a time lead compared to the predetermined switchover time 2 TRef. As explained below, this lead forms a buffer when the procedure sequence is delayed by transmission disturbances.
Up to this point (i.e., up to the CRC-protected arrival of Sync Response in LT, and of Sync Confirmation in NT), the LT and NT abort the procedure in the event of each CRC-detected fault or each CRC-protected receipt of the reset message Bit24/Bit36=0/0, “Done”, and return to the idle condition with immediate restart by LT. This is illustrated in an example in
The phase thus far described constitutes the synchronizing phase of the switchover procedure, at the end of which the switchover times to the frames with the new channel allocation have been established at both ends for both LT and NT.
The synchronizing phase is followed by the execution phase with the actual frame switchover (cf.,
In the procedural sequence illustrated in
If the transmission line disturbance and therefore the CRC alarm persists for so long that the predetermined switchover time in the LT is overshot, the new frame is formed and sent out immediately after the end of the CRC alarm and recognition of Exec Ack. The predetermined switchover times are retained in the NT. In the time between its own predetermined switchover time and the switchover time delayed in the LT by the disturbed line, the NT receives frames with the old instead of the expected new channel structure. This downstream frame disturbance caused by the line disturbance does not affect the existing telephone and ISDN connections, as their channel allocation (downstream as well as upstream) is not changed. It is also terminated in a “self-healing” manner with the arrival of the new structure in the NT at the end of the transmission disturbance.
The same applies upstream even if the line disturbance and therefore the CRC alarm in the LT persists beyond the predetermined time for receiving the first new upstream frame. After a delay, the LT switches over to receiving new frames as soon as, in an error-free pause in the transmission disturbance, at least one valid frame is received with Exec Ack or, because of the already performed frame switchover in the NT, with Exec Ack New. Consequently, the upstream frame disturbance caused by the line disturbance is also terminated in the LT in a self-healing manner. The message Exec Ack New, Bit24/Bit36=0/0, is transmitted by NT with the new frames if, because of the transmission disturbance, NT has not yet received an Exec Complete message prior to switchover to transmission of the new frames. This is illustrated in
If transmission disturbances produce a CRC alarm only in the NT, frame switchover takes place at both ends as if there were no disturbance, as NT (by—definition) and LT (because no CRC alarm is present) do not change the predetermined switchover times. In this case it is only the return of NT to the idle state that is delayed by the line disturbance due to the late detection of Exec Complete or Done (cf.,
The described cases of temporary but self-healing frame disturbance caused by lengthy continuous transmission disturbances occur very rarely during normal operation due to the low permissible bit error rate. In a further embodiment according to the present invention, the probability of a frame disturbance can be further minimized to any required extent. As described above, a transmission disturbance has no effect on frame switchover if Exec Ack is detected in the LT with a delay but still before the switchover time defined by TRef. Naturally, the longer this buffer, the more effective it is, as the probability of continuous transmission disturbances reduces markedly with their length. In another embodiment according to the present invention, TRef is therefore extended by a configurable buffer time, thereby reducing the probability of frame disturbances to any required extent. In a further embodiment according to the present invention, the probability of disturbances is reduced by lengthening the buffer time by shifting the switchover time to new frames by configurable integral multiples of TRef.
In the described example of
In a further embodiment of the present invention, a dynamic channel allocation solution is specified for ADSL transport. With ADSL, the time-division-multiplex-based services are preferably termed “Channelized Voice over DSL” (CVoDSL) because of their channel orientation. Standardization of CVoDSL is currently underway on the basis of the ITU G.Voice standard. This is being done primarily because CVoDSL enables the delay compensation costs associated with ATM-based voice communication, VoDSL (Voice over DSL), to be avoided.
The ADSL frame can normally be broken down into interleaved and non-interleaved sections. The non-interleaved section is, in principal, as with SDSL, subdivided into areas for CVoDSL and ATM, the individual CVoDSL channels for telephony and ISDN being identified by their position in the ADSL frame and preset when configuring an ADSL link. According to the present invention, a CVoDSL channel which, as in the case of SDSL, is identified by a message to establish or terminate a connection, is switched to the ATM area or switched back to the CVoDSL area. According to the present invention, commands of standard EN 300 324-1 are used, as in the case of SDSL, to initiate the procedures for switching channels to the ATM link and switching channels back to the telephony or ISDN area. As described for SDSL, these are “Disconnect”, “Deactivate”, “Establish” and “Activate”. This specification has the advantage that the same link signaling can be used for CVoDSL and VoDSL transport, as the signaling has already been standardized for VoDSL in accordance with EN 300 324-1. To transport the CVoDSL signaling for ADSL, an HDLC channel in the overhead area of the ADSL frame has already been proposed in ITU for G.Voice. Cf. ITU document IC-045, 2001. This channel is used for transmitting the channel allocation commands according to the present invention. As in the case of SDSL, these commands are “B Channel Allocate” and “B Channel Allocate Ack”, the message content including, structured byte-wise for telephony or ISDN, the position(s) of the CVoDSL-B channel(s) to be switched over which are mirrored back in the confirmation message. The confirmation message, as in the case of SDSL, is followed by the bit-controlled switchover procedure, including the possibility of extending it by an additional buffer (cf.,
The procedure described in
Indeed, although the present invention has been described with reference to specific embodiments, those of skill in the art will recognize that changes may be made thereto without departing from the spirit and scope of the present invention as set forth in the hereafter appended claims.
Number | Date | Country | Kind |
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101 22 419.2 | May 2001 | DE | national |
Filing Document | Filing Date | Country | Kind |
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PCT/DE02/01473 | 4/22/2002 | WO |