Patent Application: US-86808601-A

Abstract:
in a packet - switching network , a stable quality grade is achieved for data services by virtue of the fact that , during the transmission of data packets which are associated with a data service and are assigned to a quality class for the purposes of possible preferential treatment , the transmitter , generally a computer of a service provider , and / or at least one intermediate node establishes the quality of the transmission on the basis of acknowledgements indicating the quality grade and compares it with the quality grade demanded by the data service , and , on the basis of the result of the comparison , the data packets associated with the data service are possibly assigned to another quality class , of which the quality grade demanded by the data service is expected .

Description:
referring to fig1 , a subscriber terminal tln is connected to the packet - switching network pn , e . g . the internet , via an access node zk . the indicated packet - switching network pn also could be a private packet - switching network , e . g . a company network . in the case of a private packet - switching network , the access node zk is usually integrated into the subscriber terminal or into the private branch exchange . such a private packet - switching network can also have a point of access to another private or public packet - switching network ; e . g ., to a company network or to the internet . the packet - switching network pn in fig1 can then be regarded as a communication network comprising all the private and public packet - switching networks . fig1 also shows a computer dk , e . g . of a service provider , which provides subscribers with data services , such as video on demand or voice over ip , and is situated in the packet - switching network pn . the intermediate nodes zw 1 to zw 4 connected in between the computer dk and the access node zk indicate that there can be a number of connection options between the computer dk and the access node zk . thus , on the internet , for example , as already mentioned in the introduction , it is customary for data packets to get to their destination independently of one another on different paths . in the example , a subscriber uses his / her subscriber terminal tln , e . g . a personal computer , to dial into the packet - switching network pn via the connection to the access node zk , and uses an application program provided on his subscriber terminal to set up a connection to a computer dk , providing data services , of a service provider , e . g . via the intermediate nodes zw 1 to zw 4 . the subscriber requests a video transmission service , for example , which requires a transmission bandwidth of 100 kbit / s . accordingly , the data packets associated with the video transmission service are assigned to a mean quality class , for example , by setting a particular bit pattern in the ‘ tos byte ’ of such a data packet . assuming that there are quality classes of a ( e . g . premium ), b ( e . g . normal ) and c ( e . g . best effort ), with a distinguishing the highest class , then the data packets associated with the video transmission service are assigned to the class b in the example . ideally , the quality classes are subdivided further into priority classes , e . g . 1 ( low ) to 8 ( high ). by way of example , the data packets associated with the video transmission service are assigned to the priority class 4 , with the priority class likewise being able to be characterized in the ‘ tos byte ’ of such data packets . at the start of transmission of the video transmission service , the data packets are thus sent with the quality class b and the priority class 4 . during transmission , an intermediate node , e . g . zw 1 , or the receiver , e . g . zk or tln , acknowledges to the transmitter , in the example the computer of a service provider dk , the quality grade , such as the bandwidth , delay times to the network node and the packet loss rate for the transmission , using a protocol , e . g . the rtp / rtcp protocol mentioned in the introduction , and then compares the acknowledged quality grade with the demanded quality grade . preferably , at least one upper limit and at least one lower limit are stipulated for the comparison . if the limits are exceeded or undershot by the difference between the demanded quality grade ( nominal value ) and the acknowledged quality grade ( actual value ), for example for the transmission bandwidth , a change to another quality class or possibly priority class is triggered . in this case , the actual value can be determined , by way of example , by the average value with , if appropriate , a stipulated permissible discrepancy ( e . g ., +/− 5 %) from quality grade values acknowledged cyclically over a particular period of time ( e . g ., 1 second ). accordingly , the levels for the difference between the nominal value and the actual value can be set as triggers for a change to a higher / lower quality class or priority class such that , by way of example , the following rules are produced : 1 . if a positive difference between nominal and actual value has a value of more than 128 kbit / s , then a change to the highest quality class a is made . 2 . a corresponding negative difference of less than − 128 kbit / s triggers a change to the lowest quality class c . 3 . with a positive difference of more than 64 kbit / s , there is a change to the next highest quality class . 4 . with a corresponding negative difference of less than − 64 kbit / s , there is a change to the next lowest quality class . 5 . if the positive difference constitutes less than 64 kbit / s , or the negative difference constitutes more than − 64 kbit / s , then the quality class is retained . 6 . a positive or negative difference of more than 8 kbit / s or less than − 8 kbit / s results in a change to the next highest or lowest priority class ( max . 8 priority classes ). similar rules can be stipulated for other quality grade features than for the transmission bandwidth , such as for the delay time , the packet loss rate and the throughput . particularly with a voice data service such as voice over ip , the transmission bandwidth would be less of a crucial factor for a change of quality class than the delay time and possibly the packet loss rate . by way of example , a transmission bandwidth of 76 kbit / s obtained at the receiver , e . g . tln , is acknowledged to the transmitter , e . g . dk , instead of the demanded transmission bandwidth of 100 kbit / s . the transmitter then rearranges the data packets associated with the video transmission service from the priority class 4 into the priority class 5 ; for example , on the basis of the rules 5 and 6 indicated above . if the transmission bandwidth of 100 kbit / s is now detected , the priority class can be retained . otherwise , reassignment to a higher priority class is repeated until the demanded transmission bandwidth is reached . under the circumstance in which the highest priority class in the quality class has already been assigned and only a transmission bandwidth of , by way of example , 85 kbit / s could be achieved , it is appropriate to assign the data packets associated with the video transmission service to the next highest quality class , e . g . a . preferably , these data packets in the next highest quality class are then first assigned to the lowest priority class , e . g . 1 , so as not to impair the quality of the transmission of data packets associated with other data services within this quality class . if the influence on the transmission quality is too great , the data packets associated with the video transmission service can , if appropriate , be removed from this quality class and assigned to the original quality class again . advantageously , the network utilization level can also be used to determine the quality or priority class . thus , in addition to the transmission bandwidth obtained at the receiver , the delay times or fluctuations in the delays can also be acknowledged . accordingly , after repeated assignment to a higher priority class and with a subsequently acknowledged short delay time , it would be possible to try to assign the data packets associated with the video transmission service to a lower priority class or possibly to a lower quality class again . in the case of a long delay time , which indicates a high network utilization level , the data packets associated with the video transmission service are more readily assigned to even higher priority classes or are predominantly assigned to a higher quality class . in addition , the data packets associated with other data services in the packet - switching network could be prevented from changing to a higher priority class or quality class . expediently , the quality classes are implemented in the form of separate queues in the network nodes ( intermediate nodes , e . g . zw 1 to zw 4 ) of the packet - switching network . the data packets arriving at the intermediate nodes are temporarily stored in a queue which is based on their quality class before being forwarded . the priority classes are usefully produced by a ‘ drop level ’ mechanism . that is , the data packets arriving at an intermediate node are provided with a marker which is based on their priority class and are temporarily stored in a queue which is based on their quality class . if the queue overflows , the data packets associated with a low priority class are discarded first . although the present invention has been described with reference to specific embodiments , those of skill in the art will recognize that changes may be made thereto without departing from the spirit and scope of the invention as set forth in the hereafter appended claims 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