BACKGROUND Within Internet, functionality for QoS (Quality of Service) and service differentiation is beginning to be introduced. From just providing one type of service"best effort"one wants to be able to differentiate between different flows. At the same time as concepts in order to introduce QoS are produced within IETF (Internet Engineering Task Force), for instance DiffServ (Differentiated Services), functionality to support such services are beginning to be implemented in routers and other network elements. Within the working group DiffServ (within IETF)"A Conceptual Model for DiffServ Routers" (http ://www. ietf. org/internet-drafts/draft-ietf- diffserv-model-Ol. txt) has been produced.

This model is built of"Traffic Conditioning Blocks" (TCBs), where a TCB is used for each interface and direction of the traffic flow. Each TCB consists in its turn of a combination of a number of components, classification, metering, action and queuing. The component classification classifies the packets to divide them into some form of flows. In metering, the transmission speed is metered in number of packets and bits per second to check if it complies with the agreement of how much the customer is allowed to transmit. Depending on whether the traffic is kept within given limits or not, different actions are taken/executed. One action can for instance be to throw away packets if the flow is not kept within given limits.

In the last step, queuing, the packets are queued up to be transmitted in correct order. One also within different fields is beginning to specify more complex services which shall be based on the new functionality.

In W097/48051 a data distribution system for multicast is described, adapted to provide a guaranteed QoS for information distribution over an IP-network. The document, however, does not deal with the bandwidth problem.

In WO 99/53718 a system is described adapted to offer increased control of data flows in a data communication network. This is achieved according to the suggested solution by installing one or more control programs, which for instance can be adapted to multicast control.

In W098/27689 a method and a device for multicasting in an ATM-network is described, at which a TCB is arranged as buffer for each priority class of ATM-cells.

AIM OF THE INVENTION For the survival of an Internet Service Provider, ISP, in the market today considerably more than just offering ordinary"best effort"-surfing on Internet is required. A variety of new services are growing, many based on QoS and/or multicast, that is directed data transmission to a plurality of users. Some services might be possible to realize at moderate costs if they were based on principles based on a shared medium. It can, for instance, be multicast-sessions where one wants that the whole session is allocated a total bandwidth which is shared by the participants in'the session. This means that it will be easier to dimension the QoS-need of a session. When static dimensioning is possible, one does not need to calculate with the dynamics in the number of participants, which can be very expensive. This is an overall aim of the present invention.

One aspect of this aim is to realize a virtual shared medium on IP-level for QoS with regard to policing and

metering-functionality. The technology for this, however, does not exist today, since the solutions of today are lacking connection between incoming and outgoing traffic, a requirement for a shared medium. The TCBs of today are not aware/have no idea of each other.

SUMMARY OF THE INVENTION Above mentioned aims are fulfilled according to a first aspect of the present invention by an arrangement for realization of virtual shared medium for QoS in a communication network. A network unit has an input port and an output port for two-way communication in a session with an opposite party or user of a service, where each port includes a metering device arranged to meter data transmission speed in data flows, and an action device, from a communication point of view connected to respective metering device and arranged to take/execute actions on respective data flows depending on the belonging metering device. The arrangement is characterized in that the metering device in said input port is adapted to metering of data flows belonging to a first service, and the metering device in said output port is adapted to metering of data flows belonging to the same service, at which said output port includes a calculation device arranged to calculate control data depending on the metering device in said input port and the metering device in said output port. Further, the action device in said output port is arranged to, for said service, take/execute actions on the flow through the output port belonging to the service depending on said control data. Preferably, each port further includes a classification device arranged to divide data packets of different services into different flows, from a communication point of view connected between the metering device in respective port and a data input of/for respective port for data incoming via the input port to the network unit, respective data outgoing via the output port

from the network unit to the in the session included party.

In addition each port preferably further includes a queuing device arranged to queue packets from said action device to a data output of/for respective port for outgoing data from the output port to the in the session included party, respective reception from the input port to the network unit.

In a preferred embodiment of the invention, said control data is the sum of data transmission speed of said service, as metered by said metering device in said input port and output port, that is the sum of incoming and outgoing data transmission speed or bandwidth of just that session. The metering device in the output port preferably includes control devices, adapted to check how metered and summed up transmission speed of a service is to agreed bandwidth of the service in question for the in the session included party. The action device in the output port further includes means to throw away data packets if the sum of metered transmission speed of the service and the in the session included party exceeds agreed bandwidth. Said input port further preferably also includes a calculation device arranged to calculate the sum of data transmission speed of said service, as metered by the metering device in said input port and the metering device in said output port, and the action device in said input port is for said service arranged to take/execute actions on the flow in the input port belonging to the service depending on the summed up data transmission speed. At that also the metering device in the input port includes control devices, adapted to check how metered and summed up transmission speed of a service is to agreed bandwidth of the service in question for the in the session included party. The action device in the input port includes means to throw data packets if the sum of metered transmission speed of the service and the in the session included party exceeds agreed bandwidth. In a preferred embodiment said network unit is a DiffServ-

router. The Diff-Serv-router is preferably adapted to multicast sessions with a plurality of included parties, at which the DiffServ-router of respective included party is set up with an input port and an output port for two-way communication, and where the sum of incoming and outgoing data for each session is allocated a given data transmission speed.

According to a second aspect of the present invention is related to a procedure for realization of virtual shared medium for QoS in a communication network, in which network a network unit for a service communicates two-way in a session with another party, and where to the network unit incoming data is flowing via an input port and from the network unit outgoing data is flowing via an output port, including the steps to meter the transmission speed of said service in said input port, meter the transmission speed of said service in said output port, calculate control data depending on metered transmission speed in said input port and in said output port of said service, and to take/ execute actions on the flow of the service in the output port depending on said control data. Said control data are preferably the sum of metered data transmission speed in said input port and said output port.

In one embodiment is further included the step to, for the service, check how metered and summed up transmission speed is to agreed bandwidth of/for the second party, and to throw away data packets belonging to the service if the metered transmission speed of the service exceeds agreed bandwidth. The procedure preferably also includes the step to take/execute actions on the flow of the service in the input port depending on said control data, for instance throw away data packets.

BRIEF DESCRIPTION OF THE DRAWINGS A preferred embodiment of the invention is described in detail below with reference to the only figure, at which

Figure 1 shows an arrangement at a network unit according to the present invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT The idea of the invention is to introduce functionality to combine, preferably sum up, the meter- functionality in a first TCB in one direction with the meter-functionality in a second TCB in the other direction of the same interface of a network unit. In Figure 1 a first TCB 1 is drawn, arranged for input of data to a network unit 6, and a second TCB 7, arranged for output of data from the network unit 6. TCB 1 for input of data serves as an input port 1 to the network unit 6, and includes a classification device 2, that is a classifier, which, from a communication point of view, is connected to the data input 12 of the input port 1 for a data flow including data for a number of different services. The classification device 2 has in the illustrated embodiment three output ports, this, however, shall only be regarded as an example. To these three output ports the classification device 2 divides data flows belonging to different services. The data flows are each flowing to a metering device, that is a meter, but in the figure only one 3 of these is drawn. The service which is classified to the drawn metering device 3 is in the following called the service. The metering device 3 is arranged to meter the data transmission speed, that is occupied bandwidth, of the belonging flow/service. Depending on if metered data transmission speed exceeds agreed available bandwidth of the service, different actions can be taken/executed by different action devices, of which only one 4 is drawn.

That the result can be different in the metering devices is represented by different arrows which are aiming out from the metering device 3. In the queuing device 5, the data packets from the different action devices are queued, so

that they are transmitted in correct order from the output port 13 of TCB 1 to the network unit 6.

TCB 7 for output of data functions as an output port 7 of the network unit 6, and includes in equivalent way as TCB 1 a classification device 11, which, from a communication point of view, is connected to the data input 15 of the output port 7 for a data flow including data for several different services. Also here applies that the in the illustrated embodiment three output ports at the classification device 11 only shall be regarded as an example. TCB 7 further includes one or more metering devices, one of which 10 is drawn, and one or more action devices for each metering device, of which one 9 is shown.

A queuing device 8 is arranged to queue the data packets from the different action devices, so that they are transmitted in correct order from the output port 14 at TCB 7.

The input port 1 and the output port 7 are arranged for two-way communication in a session between the network unit and an opposite party or user of the service.

According to the invention, the metering devices 3,10 are combined by calculation devices Eo, Ei being arranged in each port 1, 7. The calculation devices Eo, E1 are arranged to calculate control data by summing up by the metering devices 3,10 metered transmission speed of incoming data 12 and outgoing data 15 in the session. The action devices 4,9 by that can take/execute actions based on the same amount of traffic, but on traffic flows running in opposite directions. This results in that a virtual shared medium for QoS is possible to realize. This is particularly useful at multicast sessions. To make it possible to, to a multicast session, allocate a total bandwidth which is shared by the participants of the session is required that the different TCBs are aware of each other. In the access router, which includes the network unit 6, input port 1 and output port 7, the multicast traffic which flows in both

directions and which belongs to the same multicast session, is filtered out, classified. The metering devices 3,10 in the TCBs 1,7, for incoming 12 and outgoing 15 traffic sum by respective calculation devices Eo, E1 up the two flows.

If the sum exceeds promised bandwidth, the flow out on the communication network, for instance the DiffServ-network, is limited by the action device 9 in the output port throwing away outgoing packets. In this way, according to the present invention, is controlled that a session does not use too much bandwidth. In one embodiment the metered flows are summed up only in one in the output port 7 arranged calculation device Po, where also the possible action is taken/executed by the action device 9. In another embodiment, the metered flows are also summed up in one in the output port 1 arranged calculation device Xi, where also the possible action is taken/executed by the action device 4.

The invention can be used in routers in general, and can with advantage be applied to edge routers in the DiffServ-architecture. It is particularly suitable for services which are based on shared media. One example of such a service might be video conference via multicast sessions.

It is to the expert within the field evident that a number of variants and modifications of the described preferred embodiment are conceivable, without for that reason end up outside the scope of the invention, which is only limited by the patent claims below.