Abstract:
The invention relates to a method and a device for transmitting data in a packet-based transmission network so that a throughput of useful data is kept below a threshold value in that, in particular, pseudo-packets, which do not contain any useful information, are fed into the transmission network. The quality of voice services (for example “Voice over IP”) is thereby impaired as desired. A network element, in particular a DSLAM, which is configured for carrying out the method or comprises the device, is also provided.

Description:
BACKGROUND  
       [0001]     The invention relates to a method for transmitting data in a packet-based transmission network, to a corresponding device and to a network element, in particular a DSLAM, in which the device is used.  
         [0002]     For cell or packet-based data traffic, there have long been technical approaches to ensure absolute, or at least relative, qualities of services or transmission parameters (such as, for example, Delay, Jitter, etc.). Within these approaches, specific classes (for example “Constant Bit Rate”, in the case of ATM, or “Expedited Forwarding”, in the case of IP), for which absolute or relative transmission guarantees may then be ensured, are provided.  
         [0003]     In the past, for various reasons, no absolute resource reservation strategies (for example via broadband signalling protocols), extending over the entire communication path, have been able to establish themselves in practical application for broadband packet-switched services. Instead, a situation has increasingly arisen in which a relative service priorisation, in combination with a sufficient basic broadband provision (via a totality of possible users), has proven sufficient to use services, which are sensitive, inter alia, with respect to transmission parameters, on the network layer (including Layer 3) in a connectionless manner via the Internet, the quality on the application layer being nevertheless sufficient.  
         [0004]     For network operators, what are known as interactive voice services are of central economic interest, as these are a substantial source of revenue. In the past, these interactive voice services have been supported primarily by time slot-based transmission methods (using narrowband switching equipment). This is an earlier method which established operators, in view of the advent of alternative transmission processes, are now calling for to be written off unexpectedly prematurely.  
         [0005]     The established network operators are thus confronted with an economic conflict: on the one hand, there is an economic incentive to develop data networks of increasingly high quality, for example to ensure additional revenue from pure data transmission services and also to remain a general service provider. On the other hand, this gives rise to technical conditions under which revenue from existing voice transmission services is “cannibalised”, and this is undesirable for the established network operators.  
         [0006]     For the upstream industry (Network Equipment Providers), the situation is different, as this industry is divided into two camps, which are largely independent of each other: on the one hand, there are suppliers of typical data equipment (for example Cisco), which have never produced narrowband switching equipment. On the other hand, there are long-established suppliers of telecommunications equipment (for example Siemens), whose initial attempt to enter the data market was unsuccessful. The data equipment supplier industry, which has profited from the migration, is therefore nevertheless able to provide equipment of increasingly high quality for carrying out QoS-dependent services. However, as a result of the technical possibilities, the above-described economic conflict continues to intensify for the established operators.  
       SUMMARY  
       [0007]     One advantage of the present invention is to allow the established operators to develop data networks of increasingly high quality, while at the same time slowing down, if not entirely avoiding, the resultant erosion or revenue from existing voice transmission services.  
         [0008]     The present invention provides a method for transmitting data in a packet-based transmission network, the throughput of useful data being kept below a threshold value.  
         [0009]     As a result of the fact that the throughput of the useful data is kept below the threshold value, it may be ensured, by correspondingly adjusting the threshold value, that a transmission quality of the useful data is never above a specific threshold value. It may thus be ensured in an advantageous manner that an absolute or relative transmission guarantee is not adhered to or cannot be adhered to.  
         [0010]     The throughput of useful data for which a maximum permissible time delay is defined is, in particular, kept below a threshold value, the threshold value being selected such that a throughput below this threshold value inevitably results in an infringement of the maximum permissible time delay.  
         [0011]     Time-critical useful data, such as are used, for example, in “Voice over IP”, are thus delayed (“jittered”) in a sufficiently significant manner that either a jitter, without a subsequent shaping stage, or the delay (“Transfer-Delay”), after any shaping stage for compensating the jitter, for competitive or in any way sufficient voice intelligibility, is exceeded in phases.  
         [0012]     According to the invention, the throughput of the useful data may be kept below the threshold value in that artificial traffic, in particular pseudo-packets, is fed into the transmission network as a function of the current throughput of the useful data. The pseudo-packets do not contain any useful information.  
         [0013]     As a result of the feeding of the pseudo-packets, these pseudo-packets compete with packets containing useful load, as a result of which these packets containing useful load are impeded, thus in turn causing the transmission quality of these packets containing useful load to be reduced. As the pseudo-packets are fed in as a function of the current throughput of the useful data, the pseudo-packets are fed in only if the throughput of the useful data is, for example, above a predetermined threshold value. Conversely, this means that no pseudo-packets are fed in if the packets containing useful load are already sufficiently impeded for other reasons (for example, because an important connection node in the transmission network has failed or because a correspondingly large amount of useful load has to be transmitted).  
         [0014]     In particular, the pseudo-packets within a node of the transmission network are fed in and removed from this node once they have sufficiently impeded packets containing useful load, so the throughput of the useful data remains below the threshold value.  
         [0015]     As no pseudo-packets leave the node, the pseudo-packets occur only at predetermined points, i.e. in predetermined nodes, in the transmission network, as a result of which it advantageously becomes more difficult, in comparison to a method in which the pseudo-packets occur on connection lines between the nodes of the transmission network, to discover the fact that the pseudo-packets are fed into the transmission network in the first place.  
         [0016]     According to the invention, the pseudo-packets may be generated in that they are copied from packets comprising useful data and marked as pseudo-packets.  
         [0017]     Apart from their marking, the pseudo-packets therefore correspond to, and may hardly be distinguished from, packets comprising useful data. Precisely because the packets comprising useful data differ substantially with respect to their length, the copying of packets comprising useful data is advantageous if it is to be concealed that pseudo-packets are fed into the transmission network, as the artificially fed-in pseudo-packets therefore do not differ, with respect to their length, from naturally occurring packets comprising useful data.  
         [0018]     The pseudo-packets of a specific packet type may, in particular, be fed into the transmission network only if a throughput of packets of this specific packet type is above a threshold value determined for this packet type. The specific packet type may, in particular, designate packets containing time-critical useful data, the threshold value determined for this packet type being in this case adjusted such that a throughput of packets of this packet type below this threshold value results in an infringement of the maximum permissible time delay that is defined for the time-critical useful data.  
         [0019]     It is thus advantageously possible to impede only packets of one packet type or to force a throughput of packets of this packet type below the threshold value determined for packets of this packet type. It is thus advantageously possible, for example, to impede only time-critical packets by means of the pseudo-packets, while leaving other packets, which transmit time-uncritical data, almost unimpeded.  
         [0020]     According to the invention, the pseudo-packets may be fed in only at specific times, which are determined at random.  
         [0021]     As a result of the fact that pseudo-packets are fed into the transmission network only at times selected at random, packets comprising useful data are also impeded only at these times selected at random. It is thus even harder to demonstrate whether packets comprising useful data are deliberately impeded, since it is, for example, impossible externally to simulate (from outside the node) a situation that inevitably always results in an impeding of useful data.  
         [0022]     According to the invention, the throughput of the useful data is below the threshold value if, in particular, one or more of the following conditions are fulfilled: 
        a packet throughput, which is defined by a number of packets comprising useful data that pass per unit of time through a node of the transmission network, is below a first threshold value.     an average delay, which a packet comprising useful data experiences on passing through the node of the transmission network, is above a second threshold value.     a maximum delay, which occurs at a quantity of packets comprising useful data that pass per unit of time through the node of the transmission network, is above a third threshold value.        
 
         [0026]     Since, according to the invention, the throughput of packets comprising useful data is kept below the threshold value, in particular, by means of the feeding of pseudo-packets, pseudo-packets are fed into the transmission network or packets comprising useful data impeded, as a result of the above-described, somewhat more complex definition of the threshold value, if one or more of the above-described conditions are met. If, for example, it is defined that the throughput of the useful data is below the threshold value only if the average delay is above the second threshold value, the packets comprising useful data are, according to the invention, impeded, in particular by means of the feeding of pseudo-packets, such that the average delay is above the second threshold value even if the packet throughput is, for example, significantly below the first threshold value, even without impeding. According to the invention, the packets comprising useful data may thus be impeded per unit of time, irrespective of the number of the packets comprising useful data, such that the average delay of the packets comprising useful data is above the second threshold value. A protocol that presupposes that the packets comprising useful data at their centre do not require longer than a predetermined period for a specific distance within the transmission network may thus, according to the invention, not be implemented if the method according to the invention is used. Corresponding considerations apply to the condition with respect to the maximum delay. In other words, even a protocol that presupposes that the packets comprising useful data do not exceed the maximum delay per unit of time may not be applied if the method according to the invention is correspondingly in use. According to the invention, the use of an interactive voice service is thus not possible if the method according to the invention is active.  
         [0027]     The present invention also provides a device for transmitting data in a packet-based transmission network. This device is configured such that, as a function of a throughput of useful data, it feeds pseudo-packets into the transmission network such that the pseudo-packets prevent forwarding of the useful data.  
         [0028]     The device comprises, in particular, a throughput measuring unit and a pseudo-packet generator, the throughput measuring unit determining a throughput of packets through the device and the pseudo-packet generator generating and feeding pseudo-packets if it is advised by the throughput measuring unit that the throughput is above a threshold value. The pseudo-packet generator generates and feeds the pseudo-packets such that the throughput of the packets comprising useful data is forced below the threshold value.  
         [0029]     Since a node of the transmission network according to the prior art usually comprises a throughput measuring unit, only the pseudo-packet generator, in an advantageous manner, has additionally to be introduced in a suitable manner into the node and correspondingly coupled to the throughput measuring unit.  
         [0030]     Moreover, the device may also comprise a classifier, which is configured such that it allocates a packet type to each packet that reaches the device. The throughput measuring unit may thus determine the throughput of the packets for each packet type, as a result of which the device may in turn detect if the throughput of a specific packet type is above a threshold value determined for this packet type. In this case, the pseudo-packet generator may generate and feed pseudo-packets of this packet type such that the throughput of the packets of this specific packet type is forced below the threshold value determined for this packet type.  
         [0031]     Since a node according to the prior art generally also has a classifier, the device has merely to provide a corresponding coupling of the throughput measuring unit and the classifier to the pseudo-packet generator. As a result of the fact that the device forces only the throughput of specific packet types below the respective threshold value determined for this packet type, the device is able to impede only the packets of these specific packet types, whereas the packets of other packet types are able to pass through the device almost unimpeded.  
         [0032]     The device may also comprise a filter, which filters out the pseudo-packets before the pseudo-packets leave the node.  
         [0033]     Precisely for reasons of cost, it is in turn also advantageous that the node according to the prior art generally comprises a filter, so this filter has merely to be adjusted such that it also detects and filters out pseudo-packets.  
         [0034]     The present invention also provides a network element of a packet-based transmission network, which element is configured for carrying out the above-described method according to the invention and/or is configured such that it comprises an above-described device according to the invention. The network element is, in particular, an access network element, usually a DSLAM, which provides access to the transmission network to at least one subscriber.  
         [0035]     A packet-based transmission network consists of nodes or network elements and links or connection lines, which connect the network elements. The network elements forward packets, which have reached them via connected connection lines, to connection lines, which are also connected to them. Precisely the access network elements, in particular DSLAMs, form an excellent access point, from the point of view of network development strategy, into the transmission network and have generally been technically mastered by the traditional suppliers of conventional telecommunications equipment. A DSLAM (“Digital Subscriber Line Access Multiplexer”) is generally taken to be a device comprising at least one port for lines leading to subscribers. One port is connected to a suitable modem (usually a DSL modem) on the subscriber side.  
         [0036]     Since the “Quality of Service” property is a property that is related to a total respective transmission path and has to be ensured over each node or point in this transmission path, it can, conversely, also be influenced in a crucially disadvantageous manner at an individual node. Since a transmission path between two subscribers necessarily extends via at least one access network element, it is sufficient, according to the invention, for each access network element to comprise one device according to the invention in order to be able to prevent the transmission of packets on any desired transmission path.  
         [0037]     The present invention is suitable, in particular, for impeding time-critical useful data in a packet-based transmission network such that, for example, a telephone conversation conducted via the transmission network exhibits a desired poor voice intelligibility. The invention is not, of course, limited to this preferred field of application, but may also be used, for example, to check, directly and independently of an external traffic situation, a desired configuration of a transmission network. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0038]     The present invention will be described below in greater detail, using a preferred embodiment and with reference to the accompanying drawings, in which:  
         [0039]      FIG. 1  shows a device according to the invention for transmitting data in a packet-based transmission network; and  
         [0040]      FIG. 2  shows a DSLAM according to the invention. 
     
    
     DESCRIPTION  
       [0041]     A device according to the invention illustrated in  FIG. 1  for transmitting data in a packet-based transmission network comprises a throughput measuring unit  2 , a classifier  3 , a sequence control system  4 , a filter  5 , a signal transmitter  6  and a pseudo-packet generator  7 , which will be described below in greater detail.  
         [0042]     The classifier  2  allocates, on the basis of specific properties, each packet  11  entering the device  1  to a specific packet type, as a result of which each packet is in turn associated with what is known as a flow, properties of a head of the respective packet generally being evaluated above all. The classifier  2  thus substantially provides a grouping function, which assists uniform treatment of packets sharing specific properties. For this purpose, the classifier  2  applies rules to fields of the packet and provides a corresponding result, generally as an item of meta data based on the packet. Using this item of meta data or the information provided thereby, the following processing steps may be carried out.  
         [0043]     The throughput measuring unit  3  ascertains specific flow properties and is able to evaluate said properties against a filed profile. The throughput measuring unit  3  can, for example, ascertain when limits, which designate a specific throughput of packets, are exceeded or undershot. The throughput measuring unit  3  may then provide this information to subsequent elaboration units or processing steps, similarly to the classifier  2 , explicitly as an item of meta data. In the case of the present embodiment, the sequence control system  4  is what is known as a “Weighted Fair Queuing Scheduler”, which uses a generally known sequence control process that ensures, in phases of the congestion of a path, that individual FIFO queues  41  outlined schematically in  FIG. 1  experience at least a specific operating rate, as a fixed proportion of a maximum total rate possible at a point denoted by reference numeral  34 . If no packets are ordered in individual queues  41 , a bandwidth, which is otherwise provided as an operating rate for this queue, is divided fairly, i.e. proportionally, over other queues  41 , without places (what are known as “Working-Slots”) becoming lost in the process. A procedure of this type is also known as “Work-conserving Behaviour”. On the other hand, this procedure ensures that, at times of congestion, there may not be any operating rates above it for individual queues.  
         [0044]     The pseudo-packet generator  7  generates artificial packet traffic in that it generates pseudo-packets, labels them as such and multiplexes them into a packet flow of packets comprising useful data.  
         [0045]     The signal transmitter  6  supplies, in a random sequence for a specific period, an active signal  37 , which the pseudo-packet generator  7  also evaluates in order to decide whether artificially generated packet traffic should be multiplexed into the packet flow of the packets comprising useful data.  
         [0046]     The filter  5  rejects packets that exhibit specific, explicitly labelled properties. The filter  5  rejects, in particular, pseudo-packets generated artificially by the pseudo-packet generator  7 .  
         [0047]     The mode of operation of the device  1  will be described below.  
         [0048]     Useful data traffic enters the device  1  at point  31 . The useful data traffic flows onward via the throughput measuring unit  2  and is labelled as useful data traffic at the output  32  of the throughput measuring unit  2 . Individual packets may also be allocated to specific queues  41  of the sequence control system  4  via the meta data associated with the packets. “Voice over IP” traffic may, for example, be identified unambiguously by using specific protocols (for example RTP or UDP) in conjunction with specific port regions.  
         [0049]     In certain load situations, the throughput measuring unit  3  ascertains that a specific, previously fixed load limit has been undershot and signals this to the pseudo-packet generator  7  via a first signal  36 . If the pseudo-packet generator  7  receives a second signal, in addition to the first signal  36 , from the signal transmitter  6 , the pseudo-packet generator  7  provides at its output  38  pseudo-packets, the statistical properties of which correspond to the packets comprising useful data occurring at the input  31  of the classifier  2 . This is brought about in that, in the event of time intervals of a high useful data load, packets are copied from the throughout measuring unit  3  to the pseudo-packet generator  7 , in order then at a later point in time to be fed in, labelled as pseudo-packets.  
         [0050]     The throughput measuring unit multiplexes the pseudo-packets into the stream of the useful data and evaluates a characteristic of a sum from the useful data stream and a sum of the pseudo-packets with respect to load limits. The first signal  36  is set to “inactive” only if a total packet stream, as a result of a sufficient feeding-in of pseudo-packets, again exhibits a characteristic above a specific limit.  
         [0051]     The sequence control system  4  operates its various queues in a conventional manner. However, as pseudo-packets are now also contained, distributed over the queues, a situation of excess bandwidth, as a result of which the useful data traffic is actually delayed (jittered), only occurs to a limited extent, as the pseudo-packets, for their part, also claim places in the queues.  
         [0052]     The pseudo-packets are subsequently filtered out in the filter  5 , so they do not leave the device  1  via an output  12  of the device  1 .  
         [0053]     The above-described device may be used, inter alia, in conjunction with purposeful packet classification such that voice services, for example, exhibit only a reduced quality. In practical terms, a repercussion thereby intended may not be distinguished from effects that may occur as a consequence of natural congestion as a result of overload situations, which are generally short-term. An application of the device  1  may be demonstrated only with considerable production costs and with authorisation to have physical measuring points provided even in regions of foreign network height.  
         [0054]      FIG. 2  shows a DSLAM  21 , which comprises the above-described device  1 . The DSLAM  21  connects a subscriber  22  to a node  23 , which is located further within the transmission network. As each transmission path that the subscriber  22  constructs passes via the DSLAM  21 , each transmission path may accordingly be disturbed by the DSLAM  21 . A telephone call conducted by the subscriber  22  and passing via the DSLAM  21  may thus, for example, be disturbed by the device  1  within the DSLAM  21  at any time and to any degree.