Marker device adapted to generate and insert a priority within a data packet

Abstract: In a method for marking data packets of a data transmission flow pertaining to an end-to-end connection within a packet network, the priority value is calculated based on at least one service quality parameter attributed to the data transmission flow, and upon a network feedback parameter indicative of the state of congestion within the packet network. A marker device adapted for performing the subject method, is described as well.

Description: The present invention relates to a marker device adapted to generate a priority and to insert said priority within a data packet of a data transmission flow pertaining to an end-to-end connection as is further described in the preamble of claim 1. In the Internet, which is an example of a packet network, marker devices, in conjunction with drop mechanisms in the routers based on the priorities of the data packets, and in conjunction with the intrinsic properties of the TCP/IP protocol, allow for differentiation of several traffic flows based on their service quality and/or traffic parameters. These service quality parameters are generally agreed between the user and the Internet Service Provider, hereafter abbreviated with ISP, before the actual transmission of data takes place. In the International Patent Application with International Publication Number WO 00/02395 and titled "Method and apparatus for adjustment of TCP slliding window with information about network conditions", a particular mechanism is mentioned for priority generation. Page 8 of this prior art document describes that every data packet is equipped with a priority level, which is determined from a service quality parameter such as the nominal bit rate assigned to the source. The prior art network further provides Priority Level Feedback, wherein a typically accepted priority level serves as an input parameter to a Feedback Infromation Converter, FIC device , which can calculate the TCP transmission window size that will keep the priorities of packets just greater than or equal to this minimum priority . This FIC device puts this adapted window size in acknowledgement packets which, when received by the source, will lead to this source adapting its sending rate by means of the TCP transmission window size method as explained into detail in the remainder of the prior art document. As a result of the adaptation of the transmission rate of the source, the data packets are sent at a different rate, which in its turn controls the calculation of the priority as this is determined from the ratio of the momentary actual bit rate of the source to the nominal bit rate of the source, as is stated in the prior art document on page 8, line 4. The drawback of this priority determining or marking method is that it concerns an indirect method, by first controlling the sending rate of the source, which updated value then later determines the new priority. Such a method is complicated and too slow since it takes a certain time before the priority values are actually adapted in accordance to the network feedback parameters. It is therefore an object of the present invention to provide a marker device of the above know kind, but which allows the priorities to be adapted based on the network feedback parameter in a much quicker and simpler way. According to the invention , this object is achieved by the architecture of the marker device as mentioned in the characterising portion of the first claim. In this way, the congestion check device present in the marker device, determines from the network feedback parameter an output signal serving as a trigger to a token generation rate device, which further controls the priority device. A direct and simple method is thus foreseen which does not longer rely on the rate adaptation of the source for adjusting priorities in response to a network feedback parameter. Another characteristic feature of the present invention is described in claim 2. This claim provides further details about the parameters used. Another characteristic feature of the present invention is described in claims 3 and 4. By further considering other parameters , such as the reduction factor and increase factor, attributed to the end-to-end connections itself, which are thus different from the already mentioned and used service quality parameters as well as from the network feedback parameter indicating congestion, a better level of differentiation with respect to the end-to-end connections itself, is obtained. These other parameters can be negotiated during the service level agreement phase between the user intending to transmit data pertaining to individual TCP flows and the ISP. Yet a further characteristic feature of the present invention is mentioned in the claim 5. This is important in conjunction with claims 6 and 7 whereby the other parameters attributed to the end-to-end connection are used for influencing the rate with which the priority is generated. For instance, a reduction factor is used for decreasing the rate with which a first type of these priorities, for instance the highest priority, is generated. By reducing the rate of generating the highest priority, in accordance with the congestion information as was described in claim 1, and in accordance with this reduction parameter attributed to the end-to-end connection, a much faster, and differentiated reduction of the flow is obtained. Similarly, an increase parameter is used for again increasing the rate , during periods of non-congestion, with which this first type of these priorities, for instance the highest priority, is generated. Again a differentiation with respect to other end-to-end connections is obtained. Since in general end-to-end connections in the Internet are associated to different terminals, the thus obtained marking mechanism also allows for a differentiation with respect to the terminals, taking into account congestion information. As described in claim 8 and 9 the use of an agreed bandwidth value and an agreed burst tolerance value as service quality parameters, allow for compatibility with existing marker mechanisms such as the token bucket mechanism. The invention relates as well to a terminal and to an edge router which incorporate such a marker device as is described in respective claims 10 and 11. The above and other objects and features of the invention will become more apparent and the invention itself will be best understood by referring to the following description of an embodiment taken in conjunction with the accompanying drawings wherein the figure represents one embodiment of a marker device MD according to the present invention. The marker device MD of the present invention is used in packet networks such as the Internet, aiming for differentiated services. With differentiated services is meant that several service or quality of service classes are supported , whereby within the IP-header of each data packet a specific field, named the Type of Service and abbreviated with ToS field, can be set to a specific value. This allows different types of data packets or data packets belonging to a specific connection, to be distinguished from each other so that they can be forwarded differently. For the standardized DiffServ model this ToS field is renamed as DiffServ Code-Point and abbreviated with DSCP, to indicate the quality of service requirement of the data packet. Each data packet contains its own service parameter, which partly determines the way it should be treated at each hop or router. The way different data packets with different service parameters are treated at such a router or hop, is further determined by another set of bits within this DSCP field, this set representing the value of a priority. The attribution and insertion of the priorities in the data packets is done within a marker device which is situated either in the data packets transmitting terminal itself, or within the routers of the data packet network. Among these routers one can distinguish access or edge routers and core routers, based on their position within the Internet. Access routers are thereby directly coupled to the user terminals and situated in between the user terminals and the core routers. The present invention deals with the initial marking process of the data packets, which takes place either in the data transmitting terminal itself, or within the access router coupled to this data transmitting terminal. Marking devices placed in the core routers and which are adapted for adapting the value of the markers of the incoming packets, are not subject of this invention. The values of these priorities, in conjunction with their quality of service classes, are used within the routers to determine the so-called per-hop behaviour. These per-hop behaviours are generally implemented by means of buffer acceptance mechanisms, also known as active queue management mechanisms, and schedulers, whereby packets pertaining to the several service classes, are dropped or queued on the basis of their priority and of this quality of service, and of other parameters related to the filling of the queue. One of these buffer acceptance mechanisms is for instance the so-called Random Early Detection, abbreviated with RED, algorithm . Extensive descriptions of this mechanism can be found in literature, for instance in the article "Random Early Detection gateways for Congestion Avoidance", by S. Floyd and V. Jacobson, IEEE/ACM transactions on Networking, V.1 N.4, August 1993, p 397-413. It will however also be briefly explained in the next paragraph, since this algorithm can for instance be used in conjunction with the marker device of the present invention, for obtaining service level differentiation. RED is an active queue management scheme, which tries to keep the overall throughput high while maintaining a small average queue length. RED has four configurable parameters. There are two buffer thresholds, between which probabilistic packet drops occur. When the average queue occupancy is below the minimum threshold, no packets are dropped. When the average queue occupancy exceeds the minimum threshold, packets are dropped with an increasing probability. When the average queue size exceeds the maximum threshold all arriving packets are dropped. For service differentiation purposes, the parameters that directly control the average queue lengths are also used. The idea is to have n, with n minimum 2 and related to the amount of priorities used when marking the packets, sets of thresholds, a maximum drop probability and a weigth. The differences in parameter values will then result into different drop probabilities given an average queue length. The marking mechanism of the present invention is used in conjunction with a drop mechanism having at least two, but in general, as much as there are priorities, different drop probability curves for dropping packets with the different priorities in queues pertaining to the service classes. The marker mechanism as well as the marker device of the present invention will now be discussed. A marker device MD is shown in the figure. It includes a memory denoted M for storing service quality parameter values such as an agreed bandwidth BW, an agreed burst tolerance value BT, and two parameters, denoted β and γ , which are also attributed to the end-to-end connection under consideration. This end-to-end connection in the Internet consists of a TCP connection, the corresponding TCP flow being denoted TCPF and being represented by the thick arrow entering the marker device and leaving it as well. All four parameters BW,BT, β and γ were agreed between the user and the ISP, and can be considered as being static parameters for the operation of the marker device for a particular end-to-end connection. They may however be updated regularly, upon which process new values will be stored within M. The TCP flow, of which several packets are indicated as dark rectangles, enters the marker device within a device denoted ME. The latter device is adapted to, upon arrival of a new data packet denoted DP, to give a trigger PA to another device TBM, to extract the length L, in bytes, of this data packet, and to calculate Δt being the time between the previous packet arrival and the current one. This value, as well as the length of the packet L is as well delivered to the device TBM, whose operation will be described in a next paragraph. The marker device MD further receives information from the packet network under the form of a network feedback parameter NFB, which contains information related to the state of congestion within the network. This parameter can be related to the state of congestion on the end-to-end connection, and as such may for instance consist of the TCP-duplicate or normal acknowledgement signal. Another example of congestion information within the network can consist of the ECN -bit, in case the network is ECN capable. ECN thereby is the abbreviation of Explicit Congestion Notification, which mechanism is also described in the current literature, for instance in the article "A proposal to add Explicit Congestion Notification (ECN) to IP", by K.K. Ramakrishnan and S. Floyd, RFC 2481. However this network feedback parameter NFB can also contain information related to the status of congestion within a core router, generated and transmitted by this core router itself. In the latter case several of these signals, generated by several congested core routers can enter the marker device. In the next paragraphs an embodiment of the marker device will be described which is adapted to receive the normal and duplicate acknowledgements of the TCP connection for each transmitted packet. Upon receipt of one of these signals by the marker device, they are checked for congestion within a congestion check device CC. Dependent of the result of this check, the output signal Cl of this congestion check device will be indicative of congestion or not. This signal is an input signal for a token generation rate device TGR which derives from it and from the value of the agreed bandwidth BW, of the parameters γ and β related to the TCP connection under consideration, and of a previous or starting value of a token generation rate, an updated value TGRu of this token generation rate. This updated value is temporarily stored in a token generation rate memory TGRM. Upon arrival of a new network feedback signal NFB, CI is updated and will trigger TGR to calculate a new value of TGRu . TGR is thus triggered or activated by the arrival of NFB signals. In order to distinguish between the previous value TGRp and the updated value TGRu of the token generation rate variable used and generated within TGR, the old value TGRp, is denoted as a separate signal from TGRu. The updated value TGRu is as well requested from TGRM and used by a token bucket marker device TBM, upon arrival of a new data packet DP from the TCP flow TCPF. As already explained in a previous paragraph of this document, this arrival is triggered by a signal PA. This token bucked marker device generates from TGRu, from L being the length of the packet, and from the already mentioned Δt, a priority P. This priority, or marker, is delivered back to the device ME, which inserts it in the data packet DP, which arrival was last detected. It is to be remarked that this priority generation occurs at minimum the speed of the data arrival transmission, thus buffering of packets is thereby reduced to a minimum. In the following a possible algorithm for calculating the token generation rate and the priority will be described. The initial value of the token generation rate is set to BW. Upon arrival of a network feedback signal, for instance a TCP acknowledgement or duplicate acknowledgement, a check is performed within CC to determine whether there is congestion or not. An updated value of the variable Cl is thereby generated. In case of non-congestion the updated value TGRu of the token generation rate is calculated as its previous value TGRp, multiplied by β+1), whereby β is a positive number, larger than zero. β is therefore also named an increase factor. In case of congestion, the updated value TGRu of the token generation rate is calculated from the previous value TGRp, multiplied by γ , with γ larger than zero and smaller than one. γ is therefore also named a decrease factor. Upon arrival of a data packet DP, the PA signal triggers the TBM. An internal variable, being the token count TC, will then be updated according to the following equation : TC <-- min(TC+TGRu/Δt, BT) whereby TGRu represents the value requested by TBM from the memory TGRM. Next TC is compared with L. In case TC is lower than L, the priority P is set to be low. In case TC exceeds or is equal to L, the value of TC is reduced with L, and the priority is set to be high. Remark that the intial value of the TC is set as BT. The embodiment and algorithm described thus used two priority values, High or Low. In order to use this marker algorithm within a service differentiation method, the per-hop behaviour in the routers need to be compliant to two priorities, and thus need to provide for two different drop behaviours, one for each priority. The already mentioned 2-RED method as well as the RIO which stands for the RED In and OUT algorithm and which is also described in the literature can thus be used for this. It is however to be noted that marker devices according to the invention exist with more than two priorities. For n priorities, the Per Hop behaviour within the routers can than for instance consist of n-RED. It is also to be remarked that other algorithms and consequently other marker device embodiments exist whereby the priority generation is based purely on a network feedback congestion parameter, in conjunction with BW and BT. While the principles of the invention have been described above in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of the invention, as defined in the appended claims.

Claims: Marker device (MD) adapted to generate a priority (P) and to insert said priority (P) within a data packet (DP) of a data transmission flow (TCPF) pertaining to an end-to-end connection within a packet network , said marker device (MD) including a priority device (TBM) being adapted to generate said priority (P) based on at least one service quality parameter (BW) attributed to said data transmission flow (TCPF) for delivery to an inserting device (ME) adapted to insert said priority (P) into said data packet (DP), said marker device further including a congestion check device (CC) adapted to receive a network feedback parameter (NFB) indicative of the state of congestion within said packet network, characterised in that said congestion check device (CC) is further adapted to determine from said network feedback parameter (NFB) a trigger signal (CI) for further delivery to a token generation rate device (TGR) included in said marker device, the token generation rate device (TGR) being adapted to determine a rate (TGRu) with which said priority (P) is generated within said priority device (TBM) and to deliver said rate (TGRu) as an input parameter to said priority device (TBM). Marker device (MD) according to claim 1 wherein said device (ME) for inserting said priority to said data packet further includes means for receiving said data transmission flow (TCPF), for extracting data parameters (PA,Δt,L) from said data packet (DP) of said data transmission flow (TCFP), and for delivering said data parameters to said priority device (TBM), which is adapted to further generate said priority from said data packet parameters (PA,Δt,L). Marker device (MD) according to claims 1 or 2 wherein said token generation rate device (TGR) is further adapted to generate said priority (P) from a reduction factor (γ) attributed to said end-to-end connection and from said at least one service parameter (BW) Marker device (MD) according to any of the previous claims wherein said token generation rate device (TGR) is further adapted to generate said priority rate (TGRu) from an increase factor (β) attributed to said end-to-end connection and from said at least one service parameter (BW). Marker device (MD) according to any of the previous claims wherein said priority device is further adapted to generate said priority (P) so as to have one of a predetermined set of priority values HI and L0. Marker device (MD) according to claim 5 wherein said token generation rate device (TGR) is further adapted to decreases the rate of generating a first type of priority having a first predetermined value, HI, of said set, based on said reduction factor (γ). Marker device (MD) according to claim 6 wherein said token generation rate device (TGR) is further adapted to increase the rate of generating said first type of priority, based on said increase factor (β). Marker device (MD) according to any of the previous claims wherein said at least one service quality parameter consists of an agreed bandwidth value (BW). Marker device (MD) according to any of the previous claims wherein said priority device (TBM) is further adapted to generate said priority based upon another service quality parameter (BT). Terminal coupled to a packet network and adapted to transmit data packets of a data transmission flow (TCPF) pertaining to an end-to-end connection within said packet network to at least one other terminal coupled to said packet network, said terminal including a marker device (MD) adapted to generate a priority (P) and to insert said priority within a data packet (DP) of said data transmission flow (TCPF), wherein said marker device (MD) further includes the features in accordance to any of the previous claims 1 to 9. Access router apparatus of a packet network, said access router apparatus being adapted to receive data packets from a terminal coupled to said access router, said data packets pertaining to an end-to-end connection within said packet network between said terminal and another terminal coupled to said packet network, said access router apparatus including a marker device (MD) adapted to generate a priority (P) and to insert said priority within a data packet (DP) of a data transmission flow (TCPF) pertaining to said end-to-end connection, wherein said marker device (MD) further includes the features in accordance to any of the previous claims 1 to 9.

Inventors: DE CNODDER STEFAAN, ELLOUMI OMAR, DE CNODDER, STEFAAN, ELLOUMI, OMAR
Applicants: CIT ALCATEL, ALCATEL
Application year: 2000
Main classification: H04L12
IPC codes: H04L12