AU662578B2 - A method of transmitting data from a terminal to a digital network transmission line - Google Patents

Description

662 578

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

(ORIGINAL)

Rcguation 32 Name of Applicant: Actual Inventor: Address for Service: TELSTRA CORPORATION LIMITED, A.C.N. 051 775 556, of 242 Exhibition Street, Melbourne, Victoria 3000, Australia Moshe ZUKERMAN DAVIES COLLISON CAVE, Patent Attorneys, of 1 Little Collins Street, Melbourne, Victoria 3000, Australia A METHOD OF TRANSMITTING DATA FROM A TERMINAL TO A DIGITAL NETWORK TRANSMISSION

LINE

0 Invention Title: Details of Associated Provisional Application Nos: PL0108/91, PL1132/92 and PL1415/92 The following statement is a full description of this invention, including the best method of performing it known to us: -1- -2- A METHOD OF TRANSMITTING DATA FROM A TERMINAL TO A DIGITAL NETWORK TRANSMISSION LINE The present invention relates to a method of transmitting data from a terminal to a digital"network transmission line. More specifically, the invention relates to a flow control protocol which can be used to regulate traffic access to the broadband integrated services digital network (B-ISDN).

Discussions have been conducted between interested parties over a number of years to determine the most efficient method of providing access for a user to the B-ISDN, with a view to establishing a standard protocol to be adopted by the standards body CCITT. A telecommunications terminal used to connect the user to the network may form part of a slotted ring or dual bus structure where a group of terminals are connected to one another in a ring or in series via at least one data transmission line.

Data is transmitted on lines of the network in consecutive packets known as cells which may contain user message data and be marked as assigned, or may not contain such data 20 and are marked as unassigned and available. Data is transmitted between nodes under an asynchronous transfer mode (ATM) whereby the cells are equivalent to ATM cells and can be sent separately by the terminal. According to CCITT standards, an ATM cell is 53 octets or bytes in length. If the ring or dual bus structure forms part of a local area network, such as a customer premises network (CPN), connection of the local network to the public network is controlled by a usage parameter control (UPC) circuit connected to the interface. The UPC ensures the local network does not exceed a peak rate allocation for access to the public network, which may be for example one cell per 150 cells. If a number of cells arrive at the UPC together, then the UPC may need to space 4 the cells prior to releasing the cells to the network. Groups of cells which arrive consecutively at a single node are known as clumps, and clumping of cells at the UPC, which may be caused by a traffic effect known as cell delay variation (CDV), is undesirable as it adds a significant burden on the UPC. The protocol to be adopted by 92t22LpMpecdbw.A0TC,6 -3the CCITT should minimise CDV and reduce clumping of cells. The protocol should also provide fair access to users under any load conditions, It is also desirable to be able to control sharing of the bandwidth between different forms of traffic, as the B-ISDN will support a range of telecommunication services, each having a different bandwidth requirement. The requirements imposed by the UPC should only apply to traffic directed to the public network and therefore the protocol should ensure that the local traffic does not interfere with the network orientated traffic. Preferably the bandwidth for the local and network oriented traffic should be different. The protocol should also be flexible, simple to implement and incur minimum cost.

In accordance with the present invention there is provided a method of transmitting data from a terminal to a digital network transmission line, which transmits cells for use by terminals connected thereto, comprising: placing said data in a cell in an initial queue of said terminal; controiling release of said cell from said initial queue by allowing a predetermined number of cells to pass on said transmission line before placing said cell in a transmit queue; and transmitting said cell on said transmission line when an unassigned cell is available ther.'on, or, when the number of cells in said transmit queue exceeds a predeterminca aiit, by replacing an assigned cell on said line with said cell and inserting said assigned cell in a buffer of said terminal.

Preferably assigned cells held in said buffer are released onto said line when they are replaced therein by succeeding assigned cells received on said line or when an unassigned cell is available.

Preferably said predetermined limit is one and said transmit queue transmits a cell on said transmission line whenever another cell is received thereby, and said buffer, if necessary, is adapted to buffer a plurality of assigned cells.

Preferably said predetermined number depends on a priority level allocated to said cell.

9SWo14,p:\oper\JbwOPt$9I i -4- Preferably said cell is assigned a high or low priority level and for high priority level cells access to the transmission line is controlled as described above, whereas for low priority cells access is controlled by a distributed queue protocol, Preferably said cell is assigned one of three priority levels, and for the middle priority level between the high and low priority levels, a cell is queued in a buffer of said terminal, which also queues assigned cells received on said line for the middle and low priority levels when the transmit queue or the buffer of the high priority level is not empty. Preferably cells in the middle priority level buffer are released when the high priority level buffer and queue are emIty. Preferably request signals, according to said distributed queue protocol, 10 are issued on a reverse transmission line connected to said terminal when the cells are released after allowing predetermined number of cells to pass.

The present invention further provides a terminal for connection to a digital network transmission line which transmits cells for use by the terminal, comprising: means for placing the data to be transmitted in a cell in an initial queue of said terminal; means for controlling release of said cell from said initial queue by allowing a predetermined number of cells to pass on said transmission line before placing said cell in a transmit queue of said terminal; means for transmitting said cell onto said transmission line when an unassigned cell is available thereon, or, when the number of cells in said transmit queue exceeds a predetermined limit, by replacing an assigned cell on said line with said cell and inserting said assigned cell in a buffet of said terminal.

A preferred embodiment of the present invention is hereinafter d'scribed, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a block diagram of a customer premises network (CPN); and Figure 2 is a block diagram of a first preferred embodiment of a terminal node, according to the present invention, connected to a transmission line on the CPN; and Figure 3 is a block diagram of a dual bus CPN; Figure 4 is a block diagram of a second preferred embodiment of a terminal node, according to the present invention, connected to the dual bus CPN; and Figure 5 is a block diagram of a third preferred embodiment of a terminal node, 95S6Ip:\opetzbw,?1PIO8.91,4 according to the present invention, connected to the dual bus CPN.

A customer premises network 2, as shown in Figure 1, includes a plurality of user terminals 4 connected in a ring structure by a transmission line 6, which transmits data in cells, The network 2 is connected to a UPC 8 which polices connection of the CPN 2 to the public network 10. Appropriate B-ISDN interfaces (not shown) are used to connect the CPN 2 to the UPC 8 which is included in and lies at the edge of the public network 'iO As mentioned previously, thecells transmitted on the line 6 by the network 2 are each equivalent to an ATM cell and have a length of 53 octets. The headers of the cells include data which indicates whether a cell is assigned or unassigned, i.e. whether the respective cell includes message data or is unassigned. The headers may also include data to designate a respective priority level to cells.

A terminal 4, as shown in Figure 2, is connected to the transmission line of the ring by a ring interface 12 which has two operating modes, listen and transmit. In listen mode, the bits received at the input 14 of the terminal 4 are simply copied or passed to the output 16. In transmit mode, the interface 12 breaks the connection between the input 14 and the output 16 and places its own data to be transmaitted onto the ring. Message data to ba transmitted by the terminal 4 is formed into transmission cells of 53 bytes 20 which are each assigned a priority level and are placed in a local queue 18. The cells are released from the queue 18 and inputted to a traffic shaper 20 of the terminal 4, The local queue 18 operates on a first in, first out (FIFO) basis and a local queue 18 and a traffic shaper 20 are provided for each priority level.

4 The shaper 20 is used to regulate the spacing of cells wishing to gain access to the traffic stream of the transmission line 6. For each priority level assigned to a transmission cell, system parameters income, cellcost and creditmax are defined and held in registers 22, 24 and 26, respectively. The shaper 20 as with the local queue 18 operates on a first in, first out (FIFO) basis for each priority level. A credit register 28 is incremented by a number of credit units equal to the parameter income, as each ceil, unassigned or assigned, passes through the interface 12. A transmission cell, if present in the shaper 20, is released by the shaper 20 and passed to the interface 12 from the 92122IprMpt4bw.AT -6shaper 20 when value of the credit register 28 exceeds the value of the corresponding parameter cellcost. On releasing a transmission cell, the credit register 28 is decremented by the parameter cellcost. The parameter creditmax, which is greater than or equal to cellcost, represents the maximum number of credit units which are allowed to be accumulated. When creditmax is reached, no further credit units are added to the credit register 28, which prevents a terminal 4 accumulating an excessive and unfair amount of credit units. The parameters held in the registers 22, 24 and 26 are determined during a call sef'up procedure by a network manager processor so as to ensure that traffic from a particular terminal 4 at the respective priority level does not exceed the bandwidth allocated to the terminal 4. The shaper 20 only permits the terminal 4 to queue cells up to a rate limit defined by the parameters, and the rate limit used corresponds to a peak allocation so the combination of predetermined shaping parameters selected for different service functions on all the terminals for the network 2 is sufficient to keep the CDV for all services within acceptable bounds.

Cells released by the shaper 20 are outputted to the interface 12 and placed in a transmit queue 30 corresponding to the priority level of the cell. A cell held in one of the transmit queues 30 is placed on the transmission line 6, on the basis of highest priority first, when an assigned or unassigned cell is received by the interface 12. The 20 interface 12 also includes a buffer 32 for each priority level which is provided to compensate for any access delay experienced by terminals downstream in the CPN 2 during overload conditions. The buffers 32 are also included to minimise CDV as :required by the network 2, 10, and are served on a highest priority first basis. When an assigned or unassigned cell arrives at the interface 12 of the terminal 4 from the input 14, one of the following occurs: e 9.

If the transmit queues 30 and buffers 32 are empty, the terminal 4 will pass the cell to the output 4 without any change.

,i 2. If the cell is unassigned and more than one cell, or more than an acceptable number of cells, is held in the highest priority transmit queue (being the queue of the highest priority level which is not empty), or at least one cell is held in the 92i21lp:oixbwAOCM0 -7highest priority transmit queue and the corresponding and higher priority insertion I s%'e empty, the interface 12 places the next cell in the head of that queue for output on the transmission line 6. The transmit queues 30 and the buffers 32 also operate on a FIFO basis with respect to each priority level.

3. If the cell is assigned and only one cell, or an acceptable number of cells, is held in the h i ghest priority transmit queue which is not empty, the terminal 4 allows the assigned cell to pass directly to the output 16. If the buffers 32 are not empty, the assigned cell is placed into the tail or end of the corresponding buffer 32, and is replaced by the head of the highest priority buffer which is not empty, which is allowed to pass to the output 16 instead.

4. If the cell is assigned and more than one cell, or more than an acceptable number of cells, are held in the highest priority transmit queue which is not empty, the interface 12 copies the cell into the tail or end of the corresponding insertion buffer 32, and replaces the cell on the transmission line 6 with the head of that highest priority transmit queue.

e 5. If the cell is unassigned and either all of the transmit queues 30 are empty, or 20 only one cell, or an acceptable number of cells is held in the highest priority transmit queue which is not empty, and the insertion buffers 32 are not empty, the interface 12 places the head of the highest priority insertion buffer 32, which is not empty, onto the transmission line 6.

The ab6ve access control procedure ensures that the right to transmission access S' on the network is always given to the highest priority cells.

Overload of the baffers 32 can be prevented by ensuring that the sum of the cells transmitted by all of the shapers 20 in the CPN 2 is less than the number of unassigned cells generated by the CPN 2.

The terminal 4 has a node structure which is microprocessor based and is of the 91211,p.bwAOCAI -8type described in the paper "SILK: An Implementation of a Buffer Insertion Ring" by Daniel E. Huber, Walter Steinlin and Peter J. Wild, IEEE Journal on Selected Areas in Communications, VOL. SAC-1, No. 5, November 1983, which is herein incorporated by reference. The registers 22, 24, 26 and 28, and the queues 18, 20 and 30 and the buffers 32 can be implemented by allocating respective areas of memory in the node, and by altering the operating software of the node. Alternatively, specific register circuits and queue memory can be added to the node. The transmit and local queues 18 and 30 and the shaper 20 for each priority level are preferably implemented using a signal queue with an address pointer which is moved, in accordance with the algorithm of the shaper to indicate the end of the transmit queue 30 and the start of the local queue Traffic in the CPN 2 can be placed in one of three classes, outgoing to the network 10, incoming from the network 10 and local. To meet different CDV and priority requirements of each class, use of the insertion buffers 32 may only be applied to the outgoing and incoming traffic whilst a cyclic control procedure can be applied to the local traffic, such as those described in R.M. Falconer and J.L. Adams, "Orwell: A protocol for an Integrated Services Local Network", Br Telecom Technol Vol. 3, Nov.

4, October 1985; H, Ohnishi, N. Morita and S. Suzuki, Proceedings, ICC89, Boston, June 1989; "Proposal For Enhanced GFC Protocol", NTT contribution to CCITT SGXVIII, 20 D.1860, Melbourne, December 1991; and "BT/NTT Protocol Proposal for GFC", BT Scontribution to CCITT SGXVIII, D.1958, Melbourne, December 1991. Alternatively, local traffic can be depressed by not allowing a terminal 4, which is transmitting data to another terminal 4, to insert a cell in place of a cell already on the transmission line 6, and these local cells are only transmitted when unassigned cells are available, and all cells directed to the public network 10 have been transmitted. Also, bandwidth balancing parameters, as described in IEEE Standard 802.6 Distributed Queue Dual Bus (DQDB) Sub-network of a Metropolitan Area Network (MAN), Final Draft D15, 6 December ,1990, can be used to prevent local traffic Interrupting cells which are destined for the public network 10, Bandwidth balancing (BWB) can also be implemented to ensure fair usage of cells and control sharing of the available bandwidth in addition to that provided by the shaper 20, For example, local traffic may be given a different BWB parameter 3 from that of the traffic directed to the network 10. The parameter 8 is set so that after 92I22IprkpdbwA01t6,S -9the terminal 4 has transmitted a number p of cells, the terminal 4 defers its right to access cells by letting one unassigned cell pass.

The above protocol can also be adapted to a CPN 40, as shown in Figure 3, which employs a dual bus structure. The terminals 44 of the CPN 40 connected to one another by two unidirectional buses 45 and 46 which transmit cells in respective opposite directions. The buses 45 and 46 are terminated by respective head of bus (HOB) and end of bus (EOB) units 50, 52 and 54, 56. Unassigned cells are continuously generated by the HOBs 50 and 52 of the two buses 45 and 46. When a terminal 44 writes data to be transmitted into a cell, the cell is marked as assigned. The cells transmitted on the buses and 46 are, again, each equivalent to an ATM cell and have a length of 53 octets.

The CPN 40 is based on the DQDB network described in International Patent Publication WO 86/03639 (PCT/AU85/00304) and Australian Patent Application No. 45968/89, which are herein incorporated by reference. The CPN 40 includes a B-ISDN interface 49, such as a customer switch, to connect the network 40 to the UPC 48 of the public network The cells handled by the terminals 44 and placed on the CPN 40 are assigned one of three access delay priorities, denoted zero, one and two, Priority zero is the lowest priority and is used for services which are not delay sensitive, such as a standard data 20 transmission, whereas priorities one and two are utilised by delay sensitive services, such I as voice and a video transmission. The highest priority, priority two, is used mainly for traffic streams which use more than a predetermined pcrcc(tage of the bus capacity. The distinction is based on traffic volume in crder to reduce the CDV in high rate services which may be caused by simultaneous access to the CPN 40 by a large number of low rate services. Preferably, transmissions using more than 2% of the total bus capacity are assigned to priority two.

The headers of the cells include a four bit generic flow control (GFC) field comprising one assigned bit, one priority bit and two request bits. The assigned bit indicates whether a cell is assigned or unassigned. Alternatively, assigned and unassigned cells can be distinguished on the basis of the contents of a virtual circuit identifier (VCI) field of the cells. The VCI field indicates whether the cell has been assigned to a virtual 9O2IpIppebwAOM6.9 circuit for data transmission. Use of the VCI field to indicate whether a cell is assigned allows the assigned bit to be used for other purposes, for example as a monitor bit in distributed queue ring architectures of the type described in "The Swiss PTT GFC Protocol: New Features, in Response to Questions Raised in Geneva June 1991", Contribution to CCITT SG XVIII D.1684, Melbourne, Dec. 1991, and Bealer Potts M. and Rao "D3Q The Dynamic Distributed Dual Queue, an Optimised Distributed Queuing Protocol" Paper No. A4.2 in Proceedings of ISS90 Stockholm, Sweden, May 1990. The priority bit indicates the cell's priority level and is set high for cells of priority two, and set to low for cells of priority zero or one. One of the request bits is used to request cells, on the reverse bus, for high priority traffic (priorities one or two) and the other request bit is used to request cells for low priority traffic (priority zero).

A terminal 44 of the network 40, as shown in Figure 4, has the same configuration as a DQDB station, as described in International Patent Publication WO 86/03639 (PCT/AU85/00304) and Australian Patent Application No. 45968/89, which is modified to include traffic shapers 20 for each priority level and bus interfaces which provide a buffer insertion facility and control access to respective buses 45 and 46.

As will be apparent from the following description, the terminal 44 enables distributed queuing to be implemented with buffer insertion and may be referred to as a distributed 20 queue buffer insertion (DQBI) station. The remaining description of the station is restricted, for the purposes of clarity, to accessing cells on bus 45 only.

Transmission cells formed by the station 44 are handled in the same manner as for the terminals 4 of Figure 2 up until they are released from a traffic shaper 20 to the bus interface 60. For priority two cells, the interface 60 includes a transmit queue Q.2 62 and an insertion buffer IB_02 64. Priority two cells released from their respective traffic shaper 20 are held in the transmit queue 62. The interface 60 includes a second insertion buffer 66 which also acts as a transmit queue for priority one cells, and is designated IB.0_1jQ_.. The buffer 66 queues assigned cells of priorities zero and one which have been received on the bus 45 when cells are held in the priority two buffer 64 or queue 62 or when buffer 66 itself is not empty.

921221,ppet\dbwAOTO.A0= 11 Within the terminal 44, a priority rule determines which of the transmit queues and insertion buffers has right of access to an outgoing cell on the bus 45. The priority rule is as follows: The highest priority is the priority two insertion buffer 64, except when the priority two transmit queue 62 contains more than a specified number, Q_2 Limit, of cells, then thd transmit queue 62 is the highest priority.

(ii) The second highest priority is the priority two transmit queue 62, except when that queue contains more than Q_2 Limit cells, as described above, then the priority two insertion buffer 64 is the second highest priority.

(iii) The next highest priority is the insertion buffer IB_0_1_Q_1 66.

(iv) The lowest priority is the priority zero transmit queue 68.

o When the highest priority buffer or queue is empty then the right of access passes 20 to the next highest priority etc. until the highest priority non-empty buffer or queue is selected.

When a cell arrives at the interface 60 of the terminal 44, one of the following occurs: 1. If all of the queues and buffers 62 to 68 are empty, then the cell passes unchanged to the output 2. If the arriving cell is unassigned and one or more of the transmit queues or buffers 62 to 68 contains at least one cell, then a cell is selected from these according to the priority rule for delivery to the bun 92i22 .p-AopPNb WAOM .'1B 1 12- 3. If the arriving cell is assigned and of priority two then the cell to be delivered to the bus 45 is determined by appending the arriving cell to the tail or end of the priority two insertion buffer 64 and then applying the priority rule. Of course physically there will be instances, according to the priority rule, where the assigned priority two cell is allowed to pass directly through the interface 4. If the arriving cell is assigned and of priority zero or one then the cell to be delivered to the bus 45 is determined by appending the arriving cell to the tail of the insertion buffer IB_0_1_Q 1 66 and then applying the priority rule.

For priority zero cells released from their respective traffic shaper 20, the buffer interface 60 includes a priority zero transmit queue 68. The queue 68 has the lowest access priority of all of the other queues and buffers 62, 64 and 66 maintained by the interface 60, and the cells of the queue are only allowed to access an available cell received on the bus 45 when the priority two and priority one queues and buffers 62, 64 and 66 are empty. Access from the transmit queue 68 is then based on its position in a distributed queue according to the DODB protocol, in that priority zero request and countdown counters are maintained to record requests of il priorities received from succeeding stations on the other bus 46.

Once a cell is released for transmission by priority two or one shaper 20, a request is queued for transmission on the reverse bus 46, as for DQDB. For priorities two and one, more than one outstanding request is allowed to be queued in the station 44. For *priority zero, only one outstanding request is allowed per terminal 44 and on releasing a cell froM the priority zero Ahaper 20, a request is queued for transmission only after any outstanding request has been satisfied.

Cells received on the buses 45 and 46 are delayed by the insertion buffers 64 and 66 in tho respective bus intertces 60, and in order to avoid such delays in the processing and retransmission of requests provided by the received cells, the requests are processed using a separate patt through the terminal 44. This is achieved by removing the two request bits in the GFC field of a cell when it arrives on a bus 45 or 46, processing the 92122Ip1.0 .bWAOIV.G.12 13 received requests in the terminal 44 according to the DQDB protocol, and outputting the request bits on the bus 45 or 46 in the next outgoing cell.

Bandwidth bll4ancing (BWB), as described in the IEEE 802.6 $tandard, can be implemented to ensure fairness and control sharing of the bandwidth 1or priority zero amongst all of the terminals 44. For instance, after a terminal 44 'has transmitted a number 3 of priority zero cells, the terminal 44 counts an additional high priority request in its request or countdown counters, effectively foregoing a priority zero cell it could have used. The terminals 44 may be assigned different BWB parameters 1 according to different capacity allocations.

A terminal 70, as shown in Figure 5, is a second form of DQBI station which is essentially the same as the terminal 44 of Figure 4 except adjustments have been made to allow the terminal 70 to implement mixed priorityi connections. The B-ISDN will allow connections to be establishc4 for variable bit rate traffic, such as variable bit rate video, where only a portion of the traffic's peak capacity is guaranteed, the remaining ceils being non-guaranteed and transmitted when the transmission lines are not being used for higher priority connections. For example, a video connection may have a pek capacity of 15 Mbs and only a capacity of 5 Mbs can be guaranteed. An advantageous way of dealing with such traffic is to prov-d'a mixed priority connection, where the guaranteed capacity portion is transmitted at a high priority level, one or two, and the remainder is allocated for transmission in accordance with low priority level standards, priority zero. This allows the traffic to be dealt with using a single connection, without exceeding a guaranteed capacity allocation. The mixed connections may be denoted for priority two and priority zero mixed connections, and 1/0 for priority one and priority .0 zero mixed connections.

STo facilitate the mixed priority connections, the DQBI terminal 44 is altered to form the terminal 70 by including a 2/0 flag register 78, and a 1/0 flag register 76 and splitting the insertion buffer 66 into a priority one and zero insertion buffer IBl 0172, and a priority one transmit queue Q_1 74, Consideritg first a 2/0 connection, cells for the connection are queued to enter the priority two shaper 20. If more than a specified 921221,pMpet'bwAO=td6la 14 number of cells for the connection arc held in the shaper 20, preferably the specified number will be one, a priority zero request is queued to be sent by the terminal subject to the normal DQDB restriction that only one request can be outstanding for each priority level at the terminal 70. The request and countdown counters associated with a priority zero request are therefore used and maintained. The cell at the head of the traffic shaper is then allowed to move direct to the transmit queue 62 by either disregarding the credit requirement or simply adding a credit amount equal to ccllcost to the respective credit register 28 which is then subsequently deducted.

The cell passing to the transmit queue 62 may be referred to as a non-guaranteed cell, and on being received by the transmit queue 62, ths 2/0 flag 78 is set to one to indicate that the transmit queue 62 now holds a non-guaranteed cell. Similar procedures are invoked for access by cells of a 1/0 connection to the priority one transmit queue 74.

Only one of the flags 78 or 76, however, is set at any one time as the terminal 70 can only have one priority zero request outstanding.

As cells are received by the transmit queues 62 and 74, the last cell held in the queues whenever the respective flag 78 or 76 is set is designated as the non-guaranteed cell. Therefore a non-guaranteed cell on entering one of queues 62 or 74 will become 20 guaranteed when another cell is received from the respective shaper 20. The flags 78 and 76 are not reset until their respective queues 62 and 74 arc emptied.

A non-guaranteed cell has the status of a priority zero cell and can only access the bus 45 when the priority zero countdown counter for the bus 45 is zero, the higher priority buffers 64 and 72 are empty and when an unassigned cell passes on the bus Q_2 limit is increased by one when the 2/0 flag 78 is set, so as to ensure a non-guaranteed cell is not allowed to access the bus 45 in the same manner as guarateed priority two cells, Similarly, a non-guaranteed cell in the priority one :transmit queue 74 has the status of a priority zero cell and is not able to join the queue of thi buffer 72. Access is gained only after the higher priority buffers 64 and 72 and the priority two transmit queue 62 are all empty. Only guaranteed priority one cells are able to join the tail of the queue established in the insertion buffer 72, which, as 911221,pAopttbw.AOTXI%14 15 discussed for the terminal 44, is used to buffer priority one and priority zero cells received on the bus 45. Priority one cells in the transmit queue 74 are able to access unassigned cells that pass through the interface 60 when Q_2, IB_02 and IB_01, 62, 64 and 72, are empty, otherwise, they join the end of IB_01 72 at the first available opportunity. With regard to the priority rule discussed previously, the priority of the transmit queue 74 is between the insertion buffer IB_01 72 and the priority zero transmit queue 68.

Two small intermediate buffers, of two cells storage capacity each, can be implemented to assist priority one guaranteed cells gaining access to the end of the insertion buffer 72 from the transmit queue 74 in situations where heavy priority one and zero traffic is received on the bus 45. One intermediate buffer is placed between the bus 45 and IB_01 72, and the other buffer is placed between Q_1 74 and IB_01, 72. Both intermediate buffers are written to and read from at a rate greater then twice the transmission rate of the bus 45, with the intermediate buffer between the bus and the s o. insertion buffer 72 being served before the other intermediate buffer.

5 0 If a non-guaranteed cell is held in the priority two or one transmit queue 62 or 64, and there are no cells held in the respective shaper 20, the cell is allowed to change 20 its status to a guaranteed cell if the credit available in the respective credit register 28 is greater than or equal to cellcost. A credit amount, equal to cellcost, is then deducted :from the credit register 28.

0 For the terminal 70 to implement connections at mixed priorities 2/0 and/or S 25 as well as priority level zero, all require access to the priority level zero request outstanding queue, and each is allocated sequential access to the queue in a round robin or cyclical manner so as to allow each fair access to issue priority zero requests. Each connection is allowed to transmit a number of requests per access cycle in proportion to which provides the best quality of service for the different connections, for example, depending on the bit rate of a connection.

In the protocols described above cells are reused to increase the capacity of the 9t222I.P.PetbwA=6,S 16transmission lines 6, 45 and 46. This is particularly advantageous when there is a significant degree of local traffic on the CPNs 2, 4. If not employed, local traffic competes for transmission resources with the incoming or outgoing traffic from the network interface 8. Cell reuse can be achieved by implementing destination release, whereby after a terminal 4, 44 or 70 receives a cell destined for itself, it removes the contents of the cell and then treats it as being an unassigned cell. The terminal 4 then follows the access control procedure described previously. Preferably, the destination release protocol implemented is the protocol described in the specification of the Australian Patent Application No. 27195/92 entitled "An Improved Method of Erasing Slots", which is herein incorporated by reference, The above protocols are particularly advantageous as they incur minimal CDV due to the combined use of the shapers and the insertion buffers so that cells are appropriately spaced and can then access cells on a busy CPN. The combination reduces the formation 15 of clumps at the public network interface. The traffic shaping performed by the shapers provides fairness and the desired bandwidth allocation can be obtained by properly selecting the shaping parameters, and if necessary, bandwidth balancing parameters. By judicious use of priority levels, network directed traffic can be made privileged over local traffic so that jitter for the former can be kept within acceptable bounds. Access control S 20 is fully distributed throughout the CPN.

S.

*T 921221,pA

Claims (37)

1. A method of transmitting data from a terminal to a digital network transmission line, which transmits cells for use by terminals connected thereto, comprising: placing said data in a cell in an initial queue of said terminal; controlling release of said cell from said initial queue by allowing a predetermined number of cells to pass on said transmission line before placing said cell in a transmit queue; and transmitting said cell on said transmission line when an unassigned cell is S 10 available thereon, or, when the number of cells in said transmit queue exceeds a .predetermined limit, by replacing an assigned cell on said line with said cell and inserting said assigned cell in a buffer of said terminal.

2. A method as claimed in claim 1, including releasing said assigned cell held in said buffer onto said line when said assigned cell is replaced therein by a succeeding assigned cell received on said line or when an unassigned cell is available on said line.

3. A method as claimed in claim 2, wherein an assigned cell in said buffer is released onto said line when the cells in said transmit queue do not exceed said 20 predetermined limit.

4. A method as claimed in claim 3, wherein said predetermined limit is one and said S*cell is transmitted on said transmission line whenever another cell is received by said transmit queue, and said buffer is adapted to buffer a plurality of assigned cells. A method as claimed in claim 4, including maintaining a count of cells passing through said terminal on said transmission line, and decrementing said count by said predetermined number when said cell is released by said initial queue.

6. A method as claimed in claim 5, wherein said count is incremented by a predetermined amount when said cells pass on said transmission line and the count can not exceed a predetermined maximum. 9O614,pe:\perLdbw.lI'15A91,l7 18

7. A method as claimed in claim 6, wherein said cell is assigned a priority level from one of a plurality of priority levels and one of said initial queue is provided for each priority level.

8. A method as claimed in claim 7, wherein said predetermined number, amount and maximum are based on the priority level for the respective one of said initial queue.

9. A method as claimed in claim 8, wherein one of said transmit queue and said buffer is provided for each priority level and access to said transmission line is determined on the basis of the priority level assigned to said cell. e4 A method as claimed in claim 8 or 9, wherein the sum of cells released by all of said initial queues of a digital network comprising a plurality of said terminal is less than the number of unassigned cells generated by said network.

11. A method as claimed in claim 10, includes giving priority for access to said line to cells destined for a public network over cells destined to form part of local traffic on said digital network.

12. A method as claimed in any one of claims 1 to 8, which applies to said cell when assigned a high priority level, whereas access to said line is controlled by a distributed queue protocol if said cell is assigned a low priority level.

13. A method as claimed in claim 12, wherein said cell is assigned one of at least three priority levels, high, middle and low and said buffer and said transmit queue are provided for the high level, and a further buffer is provided for said middle and low levels, said further buffer queuing assigned cells of said middle and low levels when said buffer or said transmit queue include at least one cell.

14. A method as claimed in claim 13, including queuing a request signal, according to said distributed queue protocol, for transmission on a reverse transmission line connected to said tetminal when said cell is released from said initial queue. 9614,00dpdbPWADID8.9I,19

19- A method as claimed in claim 14, wherein cells in said further buffer are placed on said digital network transmission line when said buffer and said transmit queue are empty, in place of an unassigned cell or an assigr d cell of said middle or low level, which is queued in said further buffer. 16. A method as claimed in claim 15, wherein said cell is queued in said further buffer when assigned said middle or low level. 17. A method as claimed in claim 15, wherein said cell is released from said initial S 10 queue as a non-guaranteed cell when the cells in said initial queue exceed another predetermined number and said cell is for a mixed priority connection. 18. A method as claimed in claim 17, wherein said non-guaranteed cell is placed in said transmit queue, a low priority request signal is queued for said reverse transmission line, and a flag set, and access for said non-guaranteed cell to said transmission line is controlled on the basis of said distributed queue protocol. 19, A method as claimed in claim 18, wherein said non-guaranteed cell reverts to a guaranteed cell when a further cell is placed in said transmit queue, and said further cell becomes a non-guaranteed cell. A method as claimed in claim 18 or 19, wherein said flag is reset and said non- guaranteed cell reverts to a guaranteed cell when said predetermined number of cells have passed through said terminal, and said initial queue is empty.

21. A method as claimed in claim 20, wherein if said mixed priority connection is high/low, said non-guaranteed cell is placed in said transmit queue for said high level and said predetermined limit for said transmit queue is increased.

22. A method as claimed in claim 21, wherein if said mixed priority connection is middle/low, said non-guaranteed cell is placed in a said transmit queue for said middle level, and guaranteed cells released from the middle level transmit queue are placed in 94W14,p:\alerr/la~rSIX~llk191;19 20 said further buffer.

23. A method as claimed in claim 22, wherein a request outstanding queue for request signals is accessed on a cyclic basis for each cell priority level.

24. A method as claimed in any one of the preceding claims, wherein all of the buffers and queues operate on a FIFO basis. A method as claimed in any one of the preceding claims, including further controlling access to said transmission line by using bandwidth balancing (BWB) and providing said terminal with BWB parameters.

26. A terminal for connection to a digital network transmission line which transmits cells for use by the terminal, comprising: means for placing the data to be transmitted in a cell in an initial queue of said terminal; *.means for controlling release of said cell from said initial queue by allowing a predetermined number of cells to pass on said transmission line before placing said cell in a transmit queue of said terminal; means for transmitting said cell onto said transmission line when an unassigned cell is available thereon, or, when the number of cells in said transmit queue exceeds a *predetermined limit, by replacing an assigned cell on said line with said cell and inserting said assigned cell in a buffer of said terminal.

27. A terminal as claimed in claim 26, wherein said assigned celt is held in said buffer is released onto said line when said assigned cell is replaced in said buffer by a succeeding assigned cell received on said line or when an unassigned cell is avalbble on said line.

28. A terminal as claimed in claim 27, wherein an assigned cell in said buffer is released onto said line when the cells in said transmit queue do 1iot exceed said predetermined limit. 950614 ~piJdbw.IrW1OU.B1,2%) 21

29. A terminal as claimed in claim 28, wherein said predetermined limit is one and said transmitting means transmits said cell on said transmission line whenever another cell is received by said transmit queue, and said buffer is adapted to buffer a plurality of assigned cells. A terminal as claimed in claim 29, including means for maintaining a count of cells passing through said terminal on said transmission line, and means for decrementing said count by said predetermined number when said cell is released by said initial queue.

31. A terminal as claimed in claim 30, wherein said count is incremented by a Spredetermined amount when said cells pass on said transmission line and said count can not exceed a predetermined maximum. .J2. A terminal as claimed in claim 31, wherein said cell is assigneu a priority level from one of a plurality of priority levels and said terminal includes one of said initial queue for each priority level.

33. A terminal as claimed in clatm 32, wherein said predetermined nunber, amount and maximum are based on the priority level for the respective one of said initial queue.

34. A terminal as claimed in claim 33, including one of said transmit queue and said buffer for each priority level, wherein access to said transmission line is determined on the basis of the priority level assigned to said cell.

35. A terminal as claimed in claim 33 or 34, wherein said terminal is part of a digital network comprising a plurality of said terminal and the sum of cells released by all of said initial queues in said network is less than the number of unassigned cells generated by said network.

36. A terminal as claimed hi claim 35, including means for giving priority for access to said line to cells destined for a public network over cells destined to form part of local traffic on said digital network, 95OGI4,Ip;\opetIj,.O89i. 22

37. A terminal as claimed in any one of claims 26 to 33, wherein said transmitting means controls access to said line using said transmit queue and said buffer when said cell is assigned a high priority level, and controls access to said line on the basis of a distributed queue protocol when said cell is assigned a low priority level.

38. A terminal as claimed in claim 37, wherein said cell is assigned one of at least three priority levels, high, middle and low, and said buffer and said transmit queue are included for the high level, and said terminal further includes a further buffer for said middle and low levels, said further buffer queuing assigned cells of said middle and low levels when said buffer or said transmit queue include at least one call, t

39. A terminal as claimed in claim 38, including means for queuing a request signai, according to said distributed queue protocol, for transmission on a reverse transmission line connected to said terminal when said cell is released from said initial queue. S' A terminal as claimed in claim 39, wherein said transmitting means places cells from said further buffer on said digital network transmission line when said buffer and said transmit queue are empty, in place of an unassigned cell or an assigned cell of said 'n middle or low priority level, which is queued in said further buffer, S41. A terminal as claimed in claim 40, wherein said cell is queued in said further buffer when said cell is assigned said middle or low level, I. 2 42. A terminal as claimed in claim 40, wherein said initial queue releases said cell as a non-guaranteed cell when the cells in said initial queue exceed another predetermined number and said cell is for a mixed priority connection.

43. A terminal as claimed In claim 42, wherein said transmit queue receives said non-guaranteed cell, and said terminal Includes flag register means which is set to indicate said non-guaranteed cell is in said transmit queue, and a low priority request signal is queued In said request signal queuing means, said transmitting means thereby controlling access for said non-guatanteed cell to said transmission line on the basis of OW14.104OA&Wr.MM91 1 UB~Pf~ 23 said distributed queue protocol.

44. A terminal as claimed in claim 43, wherein said non-guaranteed cell reverts to a guaranteed cell when a further cell is placed in said transmit queue, and said further cell becomes a non-guaranteed cell. A terminal as claimed in claim 43 or 44, wherein said flag register means is reset and said non-guaranteed cell reverts to a guaranteed cell when said predetermined number of cells have passed through said terminal, and said initial queue is empty.

46. A terminal as claimed in claim 45, wherein when said mixed priority connection Is high/low, said transmit queue for said high level receives said non-guaranteed cell, and said predetermined limit for said transmit queue of said high level is increased,

47. A terminal as claimed in claim 46, wherein when said mixed priority connection is middle/low, said transmit queue for said middle level receives said non-guaranteed cell, and guaranteed cells released from the middle level transmit queue are placed in said further buffer. *1

48. A terminal as claimed in claim 47, wherein said request signal queuing means is accessed on a cyclic basis for each cell priority level,

49. A terminal as claimed in any one of claims 26 to 48, wherein all of the buffers and queues operate on a FIFO basis, A terminal as claimed in any one of claims 26 to 49, wherein said transmitting means further controls access to said transmission line on the basis of bandwidth balancing (BWB) parameters stored therein.

51. A method of transmitting data from a terminal to a digital network transission line substantially as hereinbefore described with reference to the accompanying drawings, 9306 14 ;airt~ 4b,''U Io&91,2 24

52. A terminal substantially as hereinbef ore described with reference to the accompanying drawings. DATED this 14th day of June, 1995 TELSTRA CORPORATION LIMITED By its Patent Attorneys DAVIES COLLISON CAVE 9WO14,pAopezdbwW118,91a4 ABSTRACT A method of transmitting data from a terminal (4,44,70) to ri digital network transmission line (6,45,46), which transmits cells for use by terminals (4,44,70) connected S thereto, comprising: placing the data in a cell in a queue (18,20) of the terminal (4,44,70); controlling release of the cell from the queue (18,20) by allowing a predetermined number of cells to pass on the transmission line (6,45,46) before placing the cell in a C transmit queue and 10 transmitting the cell on the transmission line (6,45,46) when an unassigned cell is available thereon, or when the number of cells in the transmit queue (30) exceeds a predetermined limit, by replacing an assigned cell on the line (6,45,46) with the cell and inserting the assigned cell in a buffer (32) of the terminal (4,44,70). to I eq t 15 A terminal (4,45,70) for connection to a digital network transmission line (6,45,46) which includes means for executing the steps of the method. 0e*** O* 92 1 M,p-M pe b wokj~dI j