Patent ID: 12212503

DESCRIPTION OF EMBODIMENTS

The present disclosure describes a method for scheduling TSN flows in a communication system within a time-sensitive network.

The method is implemented at a central network configuration entity.

The method comprises:obtaining, from at least one TSN bridge having internal time constraints, assistance information relating to a time granularity of transmission opportunities, andbased on the obtained assistance information, scheduling a plurality of TSN flows by computing time sequences of said TSN flows down to said time granularity.

The method is applicable to any bridge having internal time constraints, due for example to using a time-splitted transmission medium. Such bridge having internal time constraints, from which assistance information is obtained, is also referred to throughout this document as a “time-constraint TSN bridge”. An example of such bridge is a 5G system acting as a TSN bridge, also referred to as a 5GS bridge. In this case, the transmission medium is a radio medium. Various exemplary embodiments are described hereinafter, accounting for diverse possible time splits of the transmission medium of the time-constraint TSN bridge. Of course, the method does not exclude obtaining additional assistance information from additional TSN bridges, which may also have internal time constraints or on the contrary be devoid thereof, for the shared purpose of scheduling the plurality of TSN flows. Indeed, the time-sensitive network may comprise various subnetworks and various TSN bridges, one, some, or all of which may have internal time constraints.

One possible time split of the transmission medium is shown inFIG.3. The frame (31) is the larger scale. Each frame can be divided in slots (32), and each slot is eventually split in transmission opportunities (TxOps) (33). In the case of a 5GS bridge, 5GS defines several numerologies for the slotting. In a typical example (frequency below 6 GHZ), the frame duration is about 10 ms long, the slot duration is 1 ms, which leads to a transmission opportunity duration around 140 μs. Considering a throughput of 50 Mbit/s, a transmission opportunity can transport about 800 octets of data.

The nature and the depth of the data from a time-constraint TSN bridge that may form relevant assistance information for the CNC may vary depending on the structure of the transmission frame at hand.

Moreover, the opportunities of improvement over the prior art, in terms of taking into account the assistance information at the CNC in view of optimizing the delay at said at least one TSN bridge, are also variable:based on the structure of the transmission frame at hand, as well ason the nature and the depth of the assistance information that is transmitted by the TSN bridge to the CNC.

In the case of the possible time split of the transmission medium shown inFIG.3, a typical resource allocation, as known from the state of the art, at a base station is to define the scheduling for the next slot. It means that all packets (34,35) arriving during slot n are transmitted at the sooner in slot n+1, as shown inFIG.3a.

In the state of the art, the CNC computes its TSN scheduling considering an independent delay and a dependent delay for the TSN bridge provided by the TSN bridge.

The dependent delay is the part of the delay that is load-dependent. The dependent delay Ddepcan be computed for example in case the transmission medium is a radio medium, from the average throughput available in one slot assuming a given radio condition and a given load.

The independent delay is independent of the load, and, in the state of the art, includes the slot duration. Hence, this independent delay Dind, advertised by the time-constraint TSN bridge, is typically defined by (Eq. 1)
Dind=C+Tp+margin  (Eq. 1)
with C and the margin having both constant values and Tpdesignating the full duration of a slot as represented in the example ofFIG.3.

In other words, as can be seen onFIG.3a, in the state of the art, the actual transmission time of a packet (TxDelay) (36), defined as the time interval between the arrival time and the transmission time of the packet, is always strictly greater than the full duration of a slot.

There is a benefit to be able to shift packets arrival time within a given slot to be closer to the beginning of the next slot, in order to reduce the actual transmission time TxDelay (36), as illustrated inFIG.3b.

In order to do so, in this example, the CNC needs to take more efficiently the TSN bridge slotting into account when computing the transmission time of the packets at each network device.

In this regard, for the CNC to be able to consider the independent delay of the time-constraint TSN bridge as being possibly smaller than a full slot duration, it is necessary for the CNC to have access not simply to the full slot duration Tpas defined above, but to more specific information from the TSN bridge.

This more specific information is related at least to a time granularity of the transmission opportunities within the transmission frame.

In the case of an alignment at a slot level, depicted inFIG.3b, a time-constraint TSN bridge thus provides to the CNC assistance information which may for example comprise the following indications:per TSN bridge: a transmission period Tpwhich, as already defined, corresponds to the duration of a slot, andalso per TSN bridge: an offset Tocorresponding to the beginning of a slot, relatively to a clock common to the TSN bridge and to the CNC.

According to this example, the assistance information Tpand Toare values that are associated to the TSN bridge as a whole. In other words, Tpand Toare values that are, in this example, common to all the port combinations of the TSN bridge which may be used as ingress and/or as egress ports.

With this assistance information, the independent delay advertised by the TSN bridge to the CNC may be reduced to become as (Eq. 2):
Dind=C+margin  (Eq. 2)

As a result, by knowing the offset Tomarking the beginning of a slot and the time interval Tpbetween the beginning of two consecutive slots, the CNC may compute time sequences of TSN flows that differentiate among the transmission opportunities within each slot. Therefore, contrary to the state-of the-art, such time sequences are computed down to a time granularity that is more precise than simply that of slots within the transmission frame. For example, the arrival time of a packet may be shifted towards the end of a given slot (therefore at a late transmission opportunity within the slot), while the subsequent transmission time of said packet may be scheduled at the beginning of the next slot (therefore at an early transmission opportunity within said slot).

Therefore, the resulting transmission delay may be smaller than the full duration of a slot.

In the above example with a time alignment at slot level, the assistance information does not need to comprise any indication regarding the inner composition of each slot, which may thus be hidden from the CNC.

However, providing to the CNC, as part of the assistance information, indications regarding the inner composition of each slot may allow for further improvements of the estimation of the independent delay at the CNC.

To illustrate this aspect, another example is described thereafter.

In this example, the TSN bridge is considered to be operating in Time Division Duplex (TDD) mode. This means that each slot may be described as a pattern of:a set of transmission opportunities that are usable for an uplink transmission mode (UL TxOps), andanother set of transmission opportunities that are usable for a downlink transmission mode (DL TxOps).

Such a framing may be as depicted inFIG.4, assuming a static UL/DL partitioning. This means that the UL/DL pattern is constant over time, with the period Tpcorresponding to the slot duration, and that UL and DL TxOps are not or little interleaved.

In a known scenario, a scheduler at a base station is able to allocate resources to packets in the current slot. In another known scenario, some pre-allocation of resources is made, assuming a periodic TSC traffic.

In the state of the art, as depicted inFIG.4a, the transmission delay (36) is strictly greater than the full duration of a slot, with the additional constraints that, for a given packet, the transmission of said packet can only occur during transmission opportunities that are usable for the transmission mode (uplink or downlink) of said packet.

In order to align as most as possible the arrival time of the packets with the transmission frame slotting, a possibility is to inform the CNC, through the assistance information from the TSN bridge, that the TxOps are of two different natures, depending on the direction of the data flow.

In such example, the assistance information provided by the TSN bridge to the CNC may thus comprise a transmission period Tp, corresponding to the full duration of a slot, and two offsets To1and To2for respectively marking the beginning of a UL TxOp and the beginning of a DL TxOp. Both offsets are relative to a clock common to the TSN bridge and the CNC. Such type of assistance information is illustrated inFIG.5.

Such assistance information is however not ideal. Indeed, the CNC does not need to be aware of transmission medium details and of details of the internal configuration of the TSN bridge. In particular identifying a usage of a transmission opportunity as an uplink or a downlink usage is, in principle, a notion that the CNC shall not be aware of.

Therefore, to warn the CNC that time constraints can be different depending of data flow direction, it is proposed to indicate a time offset per oriented port pair at the TSN bridge. Hence, an offset Toijis provided for the oriented port pair (Pi, Pj)—assuming Pias ingress port and Pjas egress port, and an offset Tojifor the oriented port pair (Pj, Pi)—assuming Pjas ingress port and Pias egress port. Hence, the TSN bridge is able to provide a different offset value for DL and for UL.

Assistance information provided by the TSN bridge to the CNC may comprise, in this case, the following indications:per TSN bridge: a transmission period Tp, corresponding to the full duration of a slot, andper oriented port pair (Pi, Pj) of such bridge: an offset Toij(51) relative to a clock common to the TSN bridge and to the CNC, with

Pithe ingress port and Pjthe egress port of the port pair (Pi, Pj)

Based on the values of Tpand Toij, the independent delay Dindadvertised by the TSN bridge to the CNC may be computed as defined in (Eq. 2), while the dependent delay Ddepmay be computed for one direction (UL or DL) from the average throughput available in one slot for one direction, assuming a given radio condition and a given load from (Eq. 3) in case the transmission medium is a radio medium.

1/Dd⁢e⁢p=Bdep,dm⁢o⁢y=nsd·CapsdTp(Eq.3)withd indicating the direction: UL or DLnsdbeing the number of TxOps for the direction d in said slotCapsdbeing the capacity in bits of one TxOp, assuming a given radio condition and a given load, andTpbeing the full duration of one slot.

To be noted that in state of the art, the delays are provided by a TSN bridge to the CNC per oriented port pair.

This allows the CNC to minimize the transmission delay (36) at the TSN bridge, by scheduling, for example, an arrival of a packet (34) during a UL TxOp within a given slot and a transmission of such packet during the next UL TxOp of the next slot, as shown inFIG.4b. Conversely, considering an opposite flow, an arrival of another packet (35) may be scheduled during a DL TxOp within a given slot and a transmission of such packet may be scheduled during the next DL TxOp of the next slot.

In yet another example, it may be taken advantage of the flexibility of the 5G standard in terms of dedicating TxOps in a slot to UL and DL.

One such example is depicted inFIG.6.

In such example, in order to align as most as possible packets arrival time with the transmission frame slotting, the CNC should be aware of the details of TxOps inside a slot.

A possibility is to provide to the CNC, for each oriented port pair (Pi, Pj) of a time-constraint TSN bridge, a bit map corresponding to the TxOps that can be used for this oriented port pair. Hence the bit map {1, 1, 0, 1, 0, 0} may indicate that the slot comprises 6 TxOps, but only the first, second and fourth could be used for data flows going from port Pito port Pj.

Assistance information provided to the CNC may comprise, in this example, the following indications:per TSN bridge: a transmission period Tp, corresponding to slot duration and an offset To(51) corresponding to the beginning to a slot, relatively to a clock common to the TSN bridge and the CNC, andper oriented port pair (Pi, Pj) of such TSN bridge, a bit map (62) of available TxOps inside a slot.

Typically, a time-constraint TSN bridge will define in this scenario one TxOp bit map for DL (62) and one TxOps bitmap for UL (63), and will provide in assistance information one or the other for each oriented port pair.

Alternately, it is possible to provide to the CNC a plurality of possible slot configurations for a given TSN bridge combined with, for each oriented port pair (Pi, Pj), a corresponding index pointing towards one of these possible slot configurations.

As a result of such alternative, the assistance information provided to the CNC may comprise the following indications:per TSN bridge, a transmission period Tp, corresponding to slot duration, an offset Tocorresponding to the beginning to a slot, relatively to a clock common to said TSN bridge and the CNC, and different bit maps corresponding to different available TxOps configurations, as well asper oriented port pair (Pi, Pj): an index to the TxOps bitmap to use.

Based on the values of Tpand To, the independent delay (Dind) advertised by the TSN bridge to the CNC may be computed such as defined in (Eq. 2).

Based on the assistance information as a whole, the dependent delay (Ddep) may preferably be computed as an ‘instantaneous’ delay, i.e. computed from the throughput of a single TxOp, assuming a given radio condition and a given load (Eq. 4) in case the transmission medium is a radio medium.

1/Ddep=Bd⁢ep,di⁢n⁢s⁢t=CapsdtT⁢x⁢O⁢p=nstot·CapsdTp(Eq.4)withd the direction, UL or DLnstotthe total number of TxOps in one slotCapsdthe capacity in bits of one TxOp (assuming a given radio condition and a given load)Tpthe duration of one slot, andtTxOpthe duration of a TxOp.

Yet another example illustrating the high flexibility of the 5G standard is depicted inFIG.7. As a further variation of UL/DL patterns as shown inFIGS.4to6,FIG.7further introduces the notion of flexible TxOps (F). A flexible TxOp is allocated either to UL or DL transmission by a base station at the last moment, i.e. the slot structure can be indicated in the control part at the beginning of each slot.

In this embodiment, the frame structure is still considered as periodic, i.e. the slot structure is constant among time, but the TSN bridge indicates which slots can be flexible. The TSN bridge further indicates the direction (UL or DL) of each oriented port pair. With those pieces of information, CNC can determine the best UL/DL structure for a given stream set.

Hence, in this example, the assistance information provided by the TSN to the CNC may comprise the following indications:per TSN bridge, a transmission period Tp, corresponding to the duration of a slot, and an offset To(61) marking the beginning of said slot, relatively to a clock common to 5GS bridge and the CNC,per TSN bridge, a set of values (71) indicating a structure of the TxOps within said slot, with each value being for example coded as:0: TxOp not available1: TxOp available for direction d1(e.g. DL TxOp)2: TxOp available for direction d2(e.g. UL TxOp)3: TxOp available for both directions (flexible TxOp), andper oriented port pair (Pi, Pj), a value (84) indicating the direction d1or d2of the oriented port pair.

These assistance information are further illustrated inFIG.8.

The set of values indicating a structure of the TxOps within a slot is a type of descriptive assistance information which is similar to the bitmap in the example ofFIG.6, with the addition that the present example allows a greater number of possible values, in order to allow signalling, in particular, specific TxOps as being flexible.

Of course, instead of providing a single set of values describing a structure of the TxOps within a given slot, it is also possible, as an alternative, for a TSN bridge to provide to the CNC a plurality (81,82) of possible such sets of values. In addition, to allow the CNC to select one specific, relevant, set of values for any given oriented port pair of such TSN bridge, it is also possible for the TSN bridge to provide to the CNC an index (83), per oriented port pair, pointing to a corresponding one of these possible such sets of values.

Similarly to the example ofFIG.6, the independent delay Dindadvertised by the TSN bridge to the CNC may be computed as defined in (Eq. 2), while the dependent delay Ddepwould preferably be computed as an ‘instantaneous’ delay, i.e. computed from the throughput of one TxOp, assuming a given radio condition and a given load (Eq. 4) in case the transmission medium is a radio medium.

In addition, optionally, the CNC may indicate the slot structure that it has chosen back to the TSN bridge having issued such assistance information. This indication may for instance be under the form of one or several sets of values describing at least the flexible TxOps. The encoding may be similar to that of the set of values indicating the structure of the TxOps which has previously been provided by the TSN bridge as part of the assistance information.

A further possibility that may be encountered in any of the previous examples is that a TSN bridge may be internally built with several base stations. Hence, potentially, there may be one different TDD frame configuration per base station.

However, it may be required on the contrary, for example by radio spectrum regulation rules in case the transmission medium is a radio medium, or in order to limit inter-base station interferences, that all base stations in a given TSN bridge have the same TDD frame configuration.

Such specific requirement may also be indicated by the TSN bridge to the CNC. To do so, for example, a unique TxOp description may be indicated, by convention, as part of the assistance information.