CN1282501A - Method and device for delay reduction in communication network - Google Patents

Abstract

A method and a device for reduction of the total delay of ATM traffic in a communication network where a multitude of nodes (2-4) share a common time multiplex physical medium (5) for transmitting ATM cells in an uplink direction (6). The nodes (2-4) comprise a circuit emulator (11) where the ATM cells which are to be transmitted are packed and a network terminal (8) comprising at least one PLL (27), a phase detector (26) and preferably a phase delay unit (24). The nominal frequency for the allocated time slots on the physical medium (5) is the same as the frequency for generation of the ATM cells. By using the above components the generation of ATM cells will be locked in frequency and phase to the allocated time slots in order to minimize the waiting time in the buffer (26) of the node.

Description

Be used for reducing the method and apparatus that communication network postpones

Technical field

The present invention relates to reduce professional total delay in the communication network that transmits the ATM business, wherein a plurality of users share same public physical medium.When use is professional to the lower so-called CBR (constant bit rate) of network delay tolerance limit, this advantageous particularly that reduces.

Prior art

By the telephone network transferring voice time, limit extremely important from the total delay (round-trip delay) of transmitted from transmitter to receiver.If one the delay of phone connection has surpassed about 50ms, just need an echo eliminator, because at this moment because both sides begin speech simultaneously, conversation is just disturbed in delay.When this 50ms was assigned to different this locality, switching and international office in different standards and norms, Access Network then was made up of the twin-(core) cable that does not have to postpone.This makes when also introducing transmission system, exchange and ATM (asychronous transfer mode) at present in Access Network there has not been the assignable time in " delay budget ".This causes the harsh requirement very low to the total delay of Access Network.

The tradition local network generates the reason that postpones and also can express by observing the following fact: transmit big packet and use the storage retransmission technique to need holding time in router and bridge.At first, when collecting data, the user just has delay when filling whole packet.Grouping also can generate identical late effect when being received by bridge or router at every turn, because after must waiting for that whole group arrives, could transmit it to next link.When being grouped in medium the biding one's time of the very heavy link queue of load, delay can change.If the priority of all groupings is identical, the very strict grouping of time requirement just can not surmount this formation.

About the formation problem, ATM has a priority feature, and it makes the grouping of time requirement strictness might surmount a formation.

In addition, it is that channel appointed is distributed a definite bandwidth that terminal can require, and it can guarantee the capacity of needs.It is relevant that this system and business are classified as constant bit rate (CBR), variable bit rate (VBR) or Available Bit Rate (ABR).To must when setting up, connection reserve the bandwidth that needs by the terminal of CBR or VBR transmission video or tonic train.

If all business have identical priority, this problem also will exist naturally.When to transmit the arrowband CBR signal (voice) that is assembled in the ATM cell and when physical layer can only provide one fixing during than low transmission rate, this problem will be very outstanding.When using based on the PON (EPON) of TDM (time division multiplexing) or coaxial cable system, this phenomenon (from the user or/and equipment to one common node, for example business of Local Exchange or what is called " headend equipment ") can usually appear in uplink direction.If postpone also to change in time, will further increase the total delay of receiver end.It is big more to postpone variation, and CDV (call delay variation) buffering area that needs also will be more greatly.

For example, when a plurality of nodes use uplink direction (from user node to the common node) transmit cell of a bus at a TDM network, physical medium (being bus in this example) be exactly one must be with the best public resource that may mode uses.Because user transmit cell on bus can only be arranged at every turn, so the cell at user node place must be waited for " taking turns to their order " before by the physical medium transmission.

In some applications of the shared public physical medium of time division multiplexing of a plurality of users, can generate this problem.The most ready-made example is voice (phone) and the transmission of using low fixed-bandwidth in the ATM connection.Another field is a cable TV.When research this technology standing state the time, we find that most of document all belongs to the technical field of cable TV.But, how to reduce described time of delay without any document description.

United States Patent (USP) 5,546,199 have disclosed and a kind ofly have been used for the method for the carrier wave of cable television system uplink direction by use a reference frequency to generate (synthesizing) in the down link direction.Its objective is provides a kind of low-cost carrier wave with precise frequency.So this carrier wave just can be used for public medium, be a coaxial cable in this example.But the document does not have to disclose the total delay that how to reduce system.Other existing documents, for example United States Patent (USP) 4,553,161, described the synchronous of uplink data business.

Brief summary of the invention

A kind of equipment and the method for the present invention by in the communication network of a public physical medium of a plurality of (n) user/nodes sharing, using, the total delay in the data packet transmission that can reduce to generate with fixed rate.

Best or the simplest situation should be naturally, and the bandwidth that connection should have is much larger than demand, and has a function that is used for Dynamic Bandwidth Allocation, and when packet/cell was ready in a node, this function generated transmission permission immediately.With some difference of this ideal situation be that the bandwidth that several nodes will be shared is generally very limited, and is used for Payload fully.

If all business have identical priority, the dynamic transmission permission distributes useless.When all nodes are ready for sending a cell simultaneously, last cell must wait for one complete cycle T, wherein T is from the time (cycle) between two cells of a specific connection, and every other node all must have a transmission permission at this section in the period.

According to the present invention, solved this problem by a kind of like this equipment and method, wherein the generation that is created on uplink time slot in user side and the public physical medium of ATM cell is synchronous, thereby makes just in time transmission cell when receiving a transmission permission.Its condition is that an ATM cell can be assembled in the time slot.Therefore, need ATM cell to be created in user node place and the uplink channel institute's distributed time slot synchronous.Can realize with some kinds of modes synchronously, but the speed that the ATM cell that importantly generates arrives is identical with time slot on the public physical medium, does not add when lingeringly being assembled on the described medium, can directly transmit with convenient packet.For example use a kind of phase delay equipment and phase detectors or just do not use a cell and on correct phase next cell of beginning, can make the random phase that time slot and ATM cell cause between generating under the initial condition obtain proofreading and correct.Suppose to adopt TDM, and fixing " time slot " transmission ATM cell is used in every connection under the normal condition.One frame can be defined as n time slot, and every connection is with a time slot.Article one, be connected and use " same " time slot in all frames.Frame period is fixed.In the frame of same length, also may not define time slot stream, and just as a fixing time slot stream.The cycle that but importantly is used between two time slots of a specific connection is fixed.

Make in this way the advantage that obtains clearly.Delay in the assembling ATM cell at user node place is very short, helps reducing the total delay in the network.

Can believe that the feature of the present invention that defines all is novel in claims.Yet, can understand enforcement of the present invention, function and other advantages best by specification and accompanying drawing.

The accompanying drawing summary

To inventive embodiment be described with reference to the accompanying drawings below, wherein:

Fig. 1 is according to the prior art state, simply represented uplink service in the PON/ coaxial system with a plurality of nodes and a public physical medium with schematic diagram,

Fig. 2 represents the block diagram of a kind of environment that the following stated the present invention can be worked,

Fig. 3 represents how to realize a user node and the block diagram that carries out synchronous a kind of method according to the present invention,

Fig. 4 represents how to realize a user node and the block diagram that carries out synchronous a kind of addition method according to the present invention.

Preferred embodiment is described

Fig. 1 represents to be used to have the uplink direction of a PON/ coaxial system of n node.According to Fig. 1, postpone mainly to comprise two parts that one is the assembling of ATM cell from the uplink service of a n node to a headend equipment, another is the time of delay before can transmit cell.

For correct understanding background of the present invention and invention itself, can use two examples.Use Dynamic Bandwidth Allocation in first example, what at this moment adopt is the MAC function (medium access control) of active volume being carried out certain form of continuous control and distribution between connection or connection group.Its objective is after a cell is ready to send as quickly as possible that promptly dynamically control bandwidth is distributed.Here we use:

The n=maximum number of connections

T=sends the time of a cell, and it depends on the capacity of connection.

T=is from the time (cycle) between 2 cells of a connection, (the 64kb/s speech connects corresponding T=6ms).

Therefore, can to satisfy the condition that all n bars connect needs be exactly that n * t≤T or equivalence are n≤T/t to connection capacity.

When using current bandwidth to greatest extent, n=T/t.

Stand-by period changes, and when all connections will send a cell (=n cell) simultaneously, maximum latency occurs.Last cell just will have maximum latency T.But this situation unlikely takes place, but available bandwidth is restricted to n on the low like this value usually, makes the stand-by period can not ignore near the probability of T.

On the contrary,, no matter whether have cell to send if we use existing static bandwidth allocation among the present invention, all with regular time interval T 1 provide continuous transmission permission for every ATM connects.This method will cause with the frequency of f1=1/T1 poll being carried out in every connection.When T1≤T, can obtain sufficiently high connection capacity.In order to use the active volume that connects to greatest extent, select T1 big as far as possible, but can not be greater than T.For 64kb/s voice, T=6ms.In this asynchronous polling method, the stand-by period evenly distributes in interval 0-T1.

Conclusion is: for described two kinds of methods, the stand-by period 0 and 6ms between change continuously.But, the stand-by period is that with the difference of fixing and uncontrollable package delay it is controlled.

When using suggesting method, except that part of delay that assembling generates, most of delay can be avoided.Therefore the total delay of these parts has reduced to about 6ms.But should be pointed out that any additional delay that does not have consideration in transmission or formation, may generate here.

Below describe the transmission of the main 64kb/s of consideration encoded voice, but also can be used for other data rates.

Therefore, condition is to use TDM, and fixing " time slot " transmission ATM cell is used in every connection under the normal condition.One frame definition is a n time slot, and every connects a time slot.Article one, connect " same " time slot that uses in all frames.Frame period is constant.

Also will suppose: the generation of up link on the public medium and down link direction and up link CBR cell (the implicit reference frequency that also is useful on speech coding is generally 8kHz) has a common synchronization source.

Then, if satisfy two conditions, the stand-by period just almost can be reduced to zero.The generation that at first is ATM cell must be synchronous with time slot corresponding, and promptly the cell number in each chronomere is identical with timeslot number.Secondly ATM cell just assembled intact and preparation transmission before the transmission in distributing time slot.Back one conditional request: can control/select corresponding used time slot in the moment (or phase place) that ATM cell prepares to transmit, perhaps can connect the idle time slot that distributes " suitable " for this.A kind of method in back should be avoided using, because it depends on connecting of other.

The speed of ATM cell is by used AAL and the 8kHz signal deciding that is generally used for the voice signal analog/digital conversion, i.e. the cell frequency/generation of nominal is fixing and uncontrollable.Consequently distribute the nominal time cycle of time slot must be suitable with the generation of ATM cell, on the contrary quite different.

Here we discuss voice signal, because the high quality standards of this class signal is required to make and must transmit them with CBR that what can benefit is exactly voice signal from the present invention.But the present invention is not limited to voice signal, and other type signal with constant bit rate can certainly use same basic conception of the present invention to transmit.

When a plurality of user nodes will be to a common node transmit cell, use the term uplink direction, when common node when user node transmits, use term down link direction.If the used time slot in the uplink channel has the identical nominal time cycle with the generation of ATM cell, the generation of ATM cell just can be synchronous with uplink channel in the following manner: at first be Frequency Synchronization, the time cycle that promptly is used to generate ATM cell with distribute the time slots cycle suitable/synchronously, suppose that at this moment time slot and the ATM cell phase place between generating is at random.Next adjusts phase place, makes that the ATM cell of each generation is prepared/moment of assembling just in time is will be in " it " time slot before the transmission, promptly just in time is before this time slot of transmission or on the same time, so that can be loaded into this cell in the time slot.

This method means no matter an ATM cell generates in which node, phase place is all suitable with the distribution time slot.The result can become short arbitrarily the stand-by period.

Fig. 2 represents a kind of applied environment example that the present invention is very useful.The figure shows a HPC (Hybrid Fiber Coax) cable television system 1, wherein a plurality of users/node 2-4 shares a public physical medium, is bus 5 in this example.For for simplicity, only represented three nodes among the figure, but should understand that this number can be much bigger.

Cable television network is mutual, this means the user can be in uplink direction 6 transmission information.This embodiment provides and has used a good example of the present invention, and what it will be represented is a kind of implementation of reality.In fact, a plurality of node/users share a public physical medium and will with network that a common unit is communicated by letter in carry out can using the present invention in all systems of single worker or duplex communication.

In this example, bus 5 can be a common coaxial cable, but light/electricity conversion of carrying out in transducer 7 is usually arranged on the uplink direction 6.

As mentioned above, bus 5 is connected with a plurality of users or node 2-4.A node 4 is exaggerated, and among the figure it has been made more detailed description, and everybody can be from seeing an example how connecting here.The network terminal 8 is connected as an interface to bus 5.Hereinafter the network terminal will be described in more detail.If this is to use as cable television network, television set 9 is suitably connected as the external unit of receiving downlink data 10.For at uplink direction 6 transmitting datas, as shown in the figure, a circuit emulator 11 can be connected with the network terminal 8.Circuit emulator 11 installs to the data set that the user produces in the ATM cell with regard to can be used for.For at uplink direction 6 transmitting datas, the user can use computer 12 or the common phone 13 that links to each other with node 4.Certainly, phone also needs an A/D converter 29.

System has common antenna 14, is used to receive to be transferred to user's TV signal thereafter.Module 15 is represented a headend equipment in the hfc plant, and provides telephony feature in the interface that leads to PSTN 16 or similar network.This module comprises a MAC (medium access control).To determine to allow which user to transmit and when carry out at this.In same module 15, can also carry out carrier modulation.Usually down link uses the QAM modulation, and up link is used the QPSK demodulation.By using combiner 17 to merge, can in same medium 19, transmit them from the signal of module 15 with from the signal of antenna 14.

Fig. 3 has represented the network terminal 8 and circuit emulator 11 in more detail.Circuit emulator 11 also comprises a transmitter 22 and an A/D converter 29 that generates ATM cell except that comprising an ATM cell receiver 20 and a PLL21 (phase-locked loop).In this embodiment, A/D converter 29 is by the data of link 18 receptions from phone 13 (see figure 2)s.Therefore, simulator 11 links to each other with the network terminal 8, and the latter is connected with bus 5 again.

Can under the condition that does not add delay, adjust the audio digital signals phase place that is generated, make the ATM cell of each generation on the best time, be ready to transmission, so that the stand-by period in the network terminal 8 in the buffering area 23 are reduced to hour, its starting point is always from the information of the phase detectors 26 at buffering area 23 places in the network terminal 8.Detector 26 detects from the phase place of distributing on the input ATM cell of transmitter 22 and the bus 5 between the time slot.Like this, supposition signal of needing x ms to assemble has arrived in the circuit of this programme.The transmission permission that accompanies with down link data also is that every x ms arrives once.Therefore, purpose is to use the phase control of downlink traffic, and is assembled good and be sent to buffering area 23 before just in time the transmission in public medium 5 is carried out with the ATM cell that guarantee to generate.

The optional method that the control ATM cell generates has many.A kind of method illustrated in fig. 3 is to use clock in the down link direction 10 simultaneously as the reference (here by network reference 31 representatives) of uplink service 6.Just can use controllable phase delay cell 24 then, according to adjusting the phase place of down link direction 10 from the information of above-mentioned phase detectors 26, obtain an appropriate phase (an aforesaid the best time prepare/assemble) corresponding with its distributed time slot up to the up link cell to circuit emulator 11 via connection 28.This is that phase place by the down link direction business in the module in the delay network terminal 8 25 realizes, so that the PLL 21 in the circuit emulator 11 carries out clock synchronization to A/D converter 29 best, so that cell can assemble in transmitter 22, and just in time before arriving, prepares the transmission permission that is used for public physical medium time slot to buffering area 26 transmission.

This is called as a kind of indirect method, because circuit emulator 11 can not " be seen " phase change.It just follows the tracks of the phase place of down link direction.In the embodiment that the up link ATM cell generates in the integrated unit, also can use this indirect method in the network terminal 8.At this moment do not need an independent PLL, but can use output signal from phase delay 24 as clock signal.

In another embodiment shown in Figure 4, can use the phase place of control channel 30 controls from PLL21 '.PLL 21 ' the transmission and the top identical phase control information that at this moment must allow phase detectors 26 ' always generate from cell by control channel 30 is so that arrive an aforesaid appropriate location to phase control.This method is called as direct method, directly provides the information that needs to the PLL 21 ' of circuit emulator because at this moment be.

Preferred embodiment shown in described method is not limited to can use these methods at every kind under will be by the situation of a physical medium based on TDM (for example coaxial, optical fiber or wireless channel) transmission from the ATM cell of many diverse location information sources.Should be understood that the embodiment in Fig. 3 and 4 has only represented the possible mode that realization is invented.The essence of invention is to control according to a corresponding institute distributed time slot generation of ATM cell, to reduce the stand-by period of cell.

Claims (10)

1. reduce a kind of method of ATM traffic delay in the communication network, the a plurality of nodes (2-4) that wherein generate ATM cell use a public time division multiplexing physical medium (5) to transmit, the method is characterized in that, the cycle that is used for cycle that described node (2-4) ATM cell generates and physical medium time slot on frequency and phase place synchronously, make cell in these nodes (2-4) just in time in the corresponding distributed time slot of a specific node, will transmit this cell in or before assembled intact.

2. reduce the method for ATM traffic delay according to claim 1, it is characterized in that, be by using down link to connect clock in 10 synchronously simultaneously as the synchronisation source of uplink direction, thereby generation cycle of ATM cell and the distribution slot cycle on the public physical medium uplink channel (6) are realized synchronously.

3. reduce the method for ATM traffic delay according to claim 1 or 2, it is characterized in that, use to detect phase detectors (26), determine that moment that the ATM cell preparation transmits is with respect to the phase place of distributed time slot separately from phase place between the input ATM cell of transmitter (22) and the distribution time slot on the bus (5).

4. reduce the method for ATM traffic delay according to claim 3, it is characterized in that, adjust the down link clock phase with phase delay cell (24), make the ATM cell that generates in the transmitter (22) assembled good and when buffering area (23) transmit, go up these cells of transmission stand-by period minimum before at public medium (5).

5. reduce the method for ATM traffic delay according to claim 3, it is characterized in that, from the transmission of the control channel (30) of phase detectors (26 ') relevant from transmitter (22) and arrive the ATM cell of phase detectors (26 ') and bus (5) on the information of phase place between the distributed time slot, the PLL (21 ') that this channel control links to each other with transmitter (22), make the ATM cell that generates in the transmitter assemble and when buffering area (23) transmits, the stand-by period minimum before public medium (5) is gone up these cells of transmission.

6. reduce a kind of method of ATM traffic delay in the communication network, the a plurality of nodes (2-4) that wherein generate ATM cell use a public time division multiplexing physical medium (5) to transmit, the method is characterized in that, being used for cycle that described node (2-4) ATM cell generates is provided by down link direction (10) clock of physical medium (5), the physical medium time slot of uplink direction (6) is subjected to same clock control, make cell generate and the distribution time slot of uplink direction between phase place be at random, adjust this phase place, make the ATM cell of each generation will be just in time for when will transmit this cell in this specific connection distributed time slot or before assembled intact.

7. reduce a kind of equipment of ATM traffic delay in the communication network, this communication network comprises a plurality of nodes (2-4) and a public time division multiplexing physical medium (5) that is attached thereto, up link (6) and down link (10) are professional just goes up transmission at this medium (5), and uplink service (6) generates in described node (2-4), this equipment is characterised in that, node (2-4) comprises that the network terminal (8) that at least one is connected with described public physical medium (5) and at least one carry out the module (a for example circuit emulator (11)) that ATM cell generates, wherein the generation of cell is controlled, and makes ATM cell just in time go up to when will transmit in its distributed time slot or assembled before intact and prepare to transmit in public physical medium (5).

8. reduce to comprise the equipment of ATM traffic delay in the communication network of a plurality of nodes (2-4) according to claim 7, it is characterized in that node comprises a kind of device, be used to control ATM cell and prepare moment of transmitting with respect to the phase place of distributed time slot separately.

9. reduce to comprise the equipment of ATM traffic delay in the communication network of a plurality of nodes (2-4) according to Claim 8, it is characterized in that, these devices comprise the phase delay cell (24) of at least one phase detectors (26) and a control down link direction data phase, with the generation of ATM cell in the control circuit simulator (11), make cell just in time will be on the physical medium uplink direction for when transmitting in its distributed time slot or before assembled intact.

10. reduce to comprise the equipment of ATM traffic delay in the communication network of a plurality of nodes (2-4) according to Claim 8, it is characterized in that, these devices comprise phase detectors (26 ') and a control channel (30), this channel transmits phase information from phase detectors to a PLL (21 ') who links to each other with transmitter (22), to be used for controlling transmitter the generation of (22) ATM cell, make the assembled intact moment of cell occur in just in time will be on physical medium for when transmitting in its distributed time slot or before.

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