< draft-finn-detnet-bounded-latency-02.txt   draft-finn-detnet-bounded-latency-03.txt >
DetNet N. Finn DetNet N. Finn
Internet-Draft Huawei Technologies Co. Ltd Internet-Draft Huawei Technologies Co. Ltd
Intended status: Standards Track J-Y. Le Boudec Intended status: Informational J-Y. Le Boudec
Expires: April 25, 2019 E. Mohammadpour Expires: September 12, 2019 E. Mohammadpour
EPFL EPFL
J. Zhang J. Zhang
Huawei Technologies Co. Ltd Huawei Technologies Co. Ltd
B. Varga B. Varga
J. Farkas J. Farkas
Ericsson Ericsson
October 22, 2018 March 11, 2019
DetNet Bounded Latency DetNet Bounded Latency
draft-finn-detnet-bounded-latency-02 draft-finn-detnet-bounded-latency-03
Abstract Abstract
This document presents a parameterized timing model for Deterministic This document presents a parameterized timing model for Deterministic
Networking (DetNet), so that existing and future standards can Networking (DetNet), so that existing and future standards can
achieve the DetNet quality of service features of bounded latency and achieve the DetNet quality of service features of bounded latency and
zero congestion loss. It defines requirements for resource zero congestion loss. It defines requirements for resource
reservation protocols or servers. It calls out queuing mechanisms, reservation protocols or servers. It calls out queuing mechanisms,
defined in other documents, that can provide the DetNet quality of defined in other documents, that can provide the DetNet quality of
service. service.
skipping to change at page 1, line 43 skipping to change at page 1, line 43
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This Internet-Draft will expire on April 25, 2019. This Internet-Draft will expire on September 12, 2019.
Copyright Notice Copyright Notice
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions Used in This Document . . . . . . . . . . . . . . 4 2. Terminology and Definitions . . . . . . . . . . . . . . . . . 4
3. Terminology and Definitions . . . . . . . . . . . . . . . . . 4 3. DetNet bounded latency model . . . . . . . . . . . . . . . . 4
4. DetNet bounded latency model . . . . . . . . . . . . . . . . 4 3.1. Flow creation . . . . . . . . . . . . . . . . . . . . . . 4
4.1. Flow creation . . . . . . . . . . . . . . . . . . . . . . 4 3.1.1. Static flow creation . . . . . . . . . . . . . . . . 4
4.2. Relay system model . . . . . . . . . . . . . . . . . . . 5 3.1.2. Dynamic flow creation . . . . . . . . . . . . . . . . 5
5. Computing End-to-end Latency Bounds . . . . . . . . . . . . . 7 3.2. Relay node model . . . . . . . . . . . . . . . . . . . . 6
5.1. Non-queuing delay bound . . . . . . . . . . . . . . . . . 7 4. Computing End-to-end Latency Bounds . . . . . . . . . . . . . 9
5.2. Queuing delay bound . . . . . . . . . . . . . . . . . . . 8 4.1. Non-queuing delay bound . . . . . . . . . . . . . . . . . 9
5.2.1. Per-flow queuing mechanisms . . . . . . . . . . . . . 8 4.2. Queuing delay bound . . . . . . . . . . . . . . . . . . . 9
5.2.2. Per-class queuing mechanisms . . . . . . . . . . . . 8 4.2.1. Per-flow queuing mechanisms . . . . . . . . . . . . . 10
6. Achieving zero congestion loss . . . . . . . . . . . . . . . 10 4.2.2. Per-class queuing mechanisms . . . . . . . . . . . . 10
6.1. A General Formula . . . . . . . . . . . . . . . . . . . . 10 4.3. Ingress considerations . . . . . . . . . . . . . . . . . 11
7. Queuing model . . . . . . . . . . . . . . . . . . . . . . . . 11 4.4. Interspersed non-DetNet transit nodes . . . . . . . . . . 11
7.1. Queuing data model . . . . . . . . . . . . . . . . . . . 11 5. Achieving zero congestion loss . . . . . . . . . . . . . . . 12
7.2. Preemption . . . . . . . . . . . . . . . . . . . . . . . 13 5.1. A General Formula . . . . . . . . . . . . . . . . . . . . 12
7.3. Time-scheduled queuing . . . . . . . . . . . . . . . . . 13 6. Queuing model . . . . . . . . . . . . . . . . . . . . . . . . 13
7.4. Time-Sensitive Networking with Asynchronous Traffic 6.1. Queuing data model . . . . . . . . . . . . . . . . . . . 13
Shaping . . . . . . . . . . . . . . . . . . . . . . . . . 13 6.2. Preemption . . . . . . . . . . . . . . . . . . . . . . . 15
7.5. IntServ . . . . . . . . . . . . . . . . . . . . . . . . . 15 6.3. Time-scheduled queuing . . . . . . . . . . . . . . . . . 15
8. Time-based DetNet QoS . . . . . . . . . . . . . . . . . . . . 19 6.4. Time-Sensitive Networking with Asynchronous Traffic
8.1. Cyclic Queuing and Forwarding . . . . . . . . . . . . . . 19 Shaping . . . . . . . . . . . . . . . . . . . . . . . . . 16
8.2. Time Scheduled Queuing . . . . . . . . . . . . . . . . . 19 6.4.1. Flow Admission . . . . . . . . . . . . . . . . . . . 19
9. Parameters for the bounded latency model . . . . . . . . . . 20 6.5. IntServ . . . . . . . . . . . . . . . . . . . . . . . . . 20
9.1. Sender parameters . . . . . . . . . . . . . . . . . . . . 20 7. Time-based DetNet QoS . . . . . . . . . . . . . . . . . . . . 22
9.2. Relay system parameters . . . . . . . . . . . . . . . . . 21 7.1. Cyclic Queuing and Forwarding . . . . . . . . . . . . . . 22
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 21 7.1.1. CQF timing sequence . . . . . . . . . . . . . . . . . 23
10.1. Normative References . . . . . . . . . . . . . . . . . . 21 7.1.2. Dead time computation . . . . . . . . . . . . . . . . 24
10.2. Informative References . . . . . . . . . . . . . . . . . 22 7.1.3. Tc computation . . . . . . . . . . . . . . . . . . . 24
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23 7.1.4. CQF latency calculation . . . . . . . . . . . . . . . 24
7.1.5. CQF parameterization . . . . . . . . . . . . . . . . 25
7.1.6. Ingress conditioning for CQF . . . . . . . . . . . . 25
7.1.7. CQF ingress conditioning timing model . . . . . . . . 27
7.2. Time-scheduled queuing . . . . . . . . . . . . . . . . . 28
8. Parameters for the bounded latency model . . . . . . . . . . 29
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 29
9.1. Normative References . . . . . . . . . . . . . . . . . . 29
9.2. Informative References . . . . . . . . . . . . . . . . . 30
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 31
1. Introduction 1. Introduction
The ability for IETF Deterministic Networking (DetNet) or IEEE 802.1 The ability for IETF Deterministic Networking (DetNet) or IEEE 802.1
Time-Sensitive Networking (TSN, [IEEE8021TSN]) to provide the DetNet Time-Sensitive Networking (TSN, [IEEE8021TSN]) to provide the DetNet
services of bounded latency and zero congestion loss depends upon A) services of bounded latency and zero congestion loss depends upon A)
configuring and allocating network resources for the exclusive use of configuring and allocating network resources for the exclusive use of
DetNet/TSN flows; B) identifying, in the data plane, the resources to DetNet/TSN flows; B) identifying, in the data plane, the resources to
be utilized by any given packet, and C) the detailed behavior of be utilized by any given packet, and C) the detailed behavior of
those resources, especially transmission queue selection, so that those resources, especially transmission queue selection, so that
latency bounds can be reliably assured. Thus, DetNet is an example latency bounds can be reliably assured. Thus, DetNet is an example
of an INTSERV Guaranteed Quality of Service [RFC2212] of an IntServ Guaranteed Quality of Service [RFC2212]
As explained in [I-D.ietf-detnet-architecture], DetNet flows are As explained in [I-D.ietf-detnet-architecture], DetNet flows are
characterized by 1) a maximum bandwidth, guaranteed either by the characterized by 1) a maximum bandwidth, guaranteed either by the
transmitter or by strict input metering; and 2) a requirement for a transmitter or by strict input metering; and 2) a requirement for a
guaranteed worst-case end-to-end latency. That latency guarantee, in guaranteed worst-case end-to-end latency. That latency guarantee, in
turn, provides the opportunity for the network to supply enough turn, provides the opportunity for the network to supply enough
buffer space to guarantee zero congestion loss. To be of use to the buffer space to guarantee zero congestion loss.
applications identified in [I-D.ietf-detnet-use-cases], it must be
possible to calculate, before the transmission of a DetNet flow To be of use to the applications identified in
commences, both the worst-case end-to-end network latency, and the [I-D.ietf-detnet-use-cases], it must be possible to calculate, before
amount of buffer space required at each hop to ensure against the transmission of a DetNet flow commences, both the worst-case end-
congestion loss. to-end network latency, and the amount of buffer space required at
each hop to ensure against congestion loss.
This document references specific queuing mechanisms, defined in This document references specific queuing mechanisms, defined in
other documents, that can be used to control packet transmission at other documents, that can be used to control packet transmission at
each output port and achieve the DetNet qualities of service. This each output port and achieve the DetNet qualities of service. This
document presents a timing model for sources, destinations, and the document presents a timing model for sources, destinations, and the
network nodes that relay packets that is applicable to all of those DetNet transit nodes that relay packets that is applicable to all of
referenced queuing mechanisms. The parameters specified in this those referenced queuing mechanisms. The parameters specified in
model: this model:
o Characterize a DetNet flow in a way that provides externally o Characterize a DetNet flow in a way that provides externally
measurable verification that the sender is conforming to its measurable verification that the sender is conforming to its
promised maximum, can be implemented reasonably easily by a promised maximum, can be implemented reasonably easily by a
sending device, and does not require excessive over-allocation of sending device, and does not require excessive over-allocation of
resources by the network. resources by the network.
o Enable reasonably accurate computation of worst-case end-to-end o Enable reasonably accurate computation of worst-case end-to-end
latency, in a way that requires as little detailed knowledge as latency, in a way that requires as little detailed knowledge as
possible of the behavior of the Quality of Service (QoS) possible of the behavior of the Quality of Service (QoS)
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network, and to select a resource reservation algorithm for that network, and to select a resource reservation algorithm for that
network, so that those elements can work together to provide the network, so that those elements can work together to provide the
DetNet service. DetNet service.
This document does not specify any resource reservation protocol or This document does not specify any resource reservation protocol or
server. It does not describe all of the requirements for that server. It does not describe all of the requirements for that
protocol or server. It does describe requirements for such resource protocol or server. It does describe requirements for such resource
reservation methods, and for queuing mechanisms that, if met, will reservation methods, and for queuing mechanisms that, if met, will
enable them to work together. enable them to work together.
NOTE: This draft is not yet complete, but it is sufficiently so to 2. Terminology and Definitions
share with the Working Group and to obtain opinions and direction.
The present intent of is for this draft to become a normative RFC,
defining how one SHALL/SHOULD provide the DetNet quality of service.
There are still a few authors' notes to each other present in this
draft.
2. Conventions Used in This Document This document uses the terms defined in
[I-D.ietf-detnet-architecture].
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 3. DetNet bounded latency model
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
The lowercase forms with an initial capital "Must", "Must Not", 3.1. Flow creation
"Shall", "Shall Not", "Should", "Should Not", "May", and "Optional"
in this document are to be interpreted in the sense defined in
[RFC2119], but are used where the normative behavior is defined in
documents published by SDOs other than the IETF.
3. Terminology and Definitions There are two models for flow creation, static (Section 3.1.1) and
dynamic (Section 3.1.2). Most of the mathematical analysis provided
in this document is applicable to either flow creation model; any
dependencies on the choice of flow creation model are pointed out in
the text.
This document uses the terms defined in 3.1.1. Static flow creation
[I-D.ietf-detnet-architecture].
4. DetNet bounded latency model The static problem:
Given a network and a set of DetNet flows, compute an end-to-
end latency bound (if computable) for each flow, and compute
the resources, particularly buffer space, required in each
DetNet transit node to achieve zero congestion loss.
4.1. Flow creation In this model, all of the DetNet flows are known before the
calculation commences. This problem is of interest to relatively
static networks, or static parts of larger networks. It gives the
best possible worst-case behavior. The calculations can be extended
to provide global optimizations, such as altering the path of one
DetNet flow in order to make resources available to another DetNet
flow with tighter constraints.
The bounded latency model assumes the use of the following paradigm This calculation may be more difficult to perform than that of the
for provisioning a particular DetNet flow: dynamic model (Section 3.1.2), because the flows passing through one
port on a DetNet transit node affect each others' latency. The
effects can even be circular, from Flow A to B to C and back to A.
1. Perform any configuration required by the relay systems in the On the other hand, the static calculation can often accommodate
network for the classes of service to be offered, including one queuing methods, such as transmission selection by strict priority,
or more classes of DetNet service. This configuration is not that are unsuitable for the dynamic calculation.
tied to any particular flow.
2. Characterize the DetNet flow in terms of limitations on the The static flow creation model is not limited only to static
sender [Section 9.1] and flow requirements [Section 9.2]. networks; the entire calculation for all flows can be repeated each
time a new DetNet flow is created or deleted. If some already-
established flow would be pushed beyond its latency requirements by
the new flow, then either the new flow is refused, or some other
suitable action taken.
3.1.2. Dynamic flow creation
The dynamic problem:
Given a network whose maximum capacity for DetNet flows is
bounded by a set of static configuration parameters applied
to the DetNet transit nodes, and given just one DetNet flow,
compute the worst-case end-to-end latency that can be
experienced by that flow, no matter what other DetNet flows
(within the network's configured parameters) might be created
or deleted in the future. Also, compute the resources,
particularly buffer space, required in each DetNet transit
node to achieve zero congestion loss.
This model is dynamic, in the sense that flows can be added or
deleted at any time, with a minimum of computation effort, and
without affecting the guarantees already given to other flows.
The choice of queuing methods is critical to the applicability of the
dynamic model. Some queuing methods (e.g. CQF, Section 7.1) make it
easy to configure bounds on the network's capacity, and to make
independent calculations for each flow. Other queuing methods (e.g.,
transmission selection by strict priority), make this calculation
impossible, because the worst case for one flow cannot be computed
without complete knowledge of all other flows. Other queuing methods
(e.g. the credit-based shaper defined in [IEEE8021Q] section 8.6.8.2)
can be used for dynamic flow creation, but yield poorer latency and
buffer space guarantees than when that same queuing method is used
for static flow creation (Section 3.1.1).
The dynamic flow creation model assumes the use of the following
paradigm for provisioning DetNet flows:
1. Perform any configuration required by the DetNet transit nodes in
the network for the classes of service to be offered, including
one or more classes of DetNet service. This configuration is
done beforehand, and not tied to any particular flow.
2. Characterize the new DetNet flow in IntServ terms (Section 8).
3. Establish the path that the DetNet flow will take through the 3. Establish the path that the DetNet flow will take through the
network from the source to the destination(s). This can be a network from the source to the destination(s). This can be a
point-to-point or a point-to-multipoint path. point-to-point or a point-to-multipoint path.
4. Select one of the DetNet classes of service for the DetNet flow. 4. Select one of the DetNet classes of service for the DetNet flow.
5. Compute the worst-case end-to-end latency for the DetNet flow. 5. Compute the worst-case end-to-end latency for the DetNet flow.
In the process, determine whether sufficient resources are In the process, determine whether sufficient resources are
available for that flow to guarantee the required latency and to available for that flow to guarantee the required latency and to
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to the flow. This may or may not require adjusting the to the flow. This may or may not require adjusting the
parameters that control the queuing mechanisms at each hop along parameters that control the queuing mechanisms at each hop along
the flow's path. the flow's path.
This paradigm can be static and/or dynamic, and can be implemented This paradigm can be static and/or dynamic, and can be implemented
using peer-to-peer protocols or using a central server model. In using peer-to-peer protocols or using a central server model. In
some situations, backtracking and recursing through this list may be some situations, backtracking and recursing through this list may be
necessary. necessary.
Issues such as un-provisioning a DetNet flow in favor of another when Issues such as un-provisioning a DetNet flow in favor of another when
resources are scarce are not considered. How the path to be taken by resources are scarce are not considered, but are left to the static
a DetNet flow is chosen is not considered in this document. flow creation model (Section 3.1.1). How the path to be taken by a
DetNet flow is chosen is not considered in this document.
4.2. Relay system model 3.2. Relay node model
In Figure 1 we see a breakdown of the per-hop latency experienced by A model for the operation of a DetNet transit node is required, in
a packet passing through a relay system, in terms that are suitable order to define the latency and buffer calculations. In Figure 1 we
for computing both hop-by-hop latency and per-hop buffer see a breakdown of the per-hop latency experienced by a packet
requirements. passing through a DetNet transit node, in terms that are suitable for
computing both hop-by-hop latency and per-hop buffer requirements.
DetNet relay node A DetNet relay node B DetNet transit node A DetNet transit node B
+-------------------------+ +------------------------+ +-------------------------+ +------------------------+
| Queuing | | Queuing | | Queuing | | Queuing |
| Regulator subsystem | | Regulator subsystem | | Regulator subsystem | | Regulator subsystem |
| +-+-+-+-+ +-+-+-+-+ | | +-+-+-+-+ +-+-+-+-+ | | +-+-+-+-+ +-+-+-+-+ | | +-+-+-+-+ +-+-+-+-+ |
-->+ | | | | | | | | | + +------>+ | | | | | | | | | + +---> -->+ | | | | | | | | | + +------>+ | | | | | | | | | + +--->
| +-+-+-+-+ +-+-+-+-+ | | +-+-+-+-+ +-+-+-+-+ | | +-+-+-+-+ +-+-+-+-+ | | +-+-+-+-+ +-+-+-+-+ |
| | | | | | | |
+-------------------------+ +------------------------+ +-------------------------+ +------------------------+
|<->|<------>|<------->|<->|<---->|<->|<------>|<------>|<->|<-- |<->|<------>|<------->|<->|<---->|<->|<------>|<------>|<->|<--
2,3 4 5 6 1 2,3 4 5 6 1 2,3 2,3 4 5 6 1 2,3 4 5 6 1 2,3
1: Output delay 4: Processing delay 1: Output delay 4: Processing delay
2: Link delay 5: Regulation delay 2: Link delay 5: Regulation delay
3: Preemption delay 6: Queuing delay. 3: Preemption delay 6: Queuing delay.
Figure 1: Timing model for DetNet or TSN Figure 1: Timing model for DetNet or TSN
In Figure 1, we see two DetNet relay nodes (typically, bridges or In Figure 1, we see two DetNet transit nodes (typically, bridges or
routers), with a wired link between them. In this model, the only routers), with a wired link between them. In this model, the only
queues we deal with explicitly are attached to the output port; other queues we deal with explicitly are attached to the output port; other
queues are modeled as variations in the other delay times. (E.g., an queues are modeled as variations in the other delay times. (E.g., an
input queue could be modeled as either a variation in the link delay input queue could be modeled as either a variation in the link delay
[2] or the processing delay [4].) There are six delays that a packet [2] or the processing delay [4].) There are six delays that a packet
can experience from hop to hop. can experience from hop to hop.
1. Output delay 1. Output delay
The time taken from the selection of a packet for output from a The time taken from the selection of a packet for output from a
queue to the transmission of the first bit of the packet on the queue to the transmission of the first bit of the packet on the
physical link. If the queue is directly attached to the physical physical link. If the queue is directly attached to the physical
port, output delay can be a constant. But, in many port, output delay can be a constant. But, in many
implementations, the queuing mechanism in a forwarding ASIC is implementations, the queuing mechanism in a forwarding ASIC is
separated from a multi-port MAC/PHY, in a second ASIC, by a separated from a multi-port MAC/PHY, in a second ASIC, by a
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The time taken from the transmission of the first bit of the The time taken from the transmission of the first bit of the
packet to the reception of the last bit, assuming that the packet to the reception of the last bit, assuming that the
transmission is not suspended by a preemption event. This delay transmission is not suspended by a preemption event. This delay
has two components, the first-bit-out to first-bit-in delay and has two components, the first-bit-out to first-bit-in delay and
the first-bit-in to last-bit-in delay that varies with packet the first-bit-in to last-bit-in delay that varies with packet
size. The former is typically measured by the Precision Time size. The former is typically measured by the Precision Time
Protocol and is constant (see [I-D.ietf-detnet-architecture]). Protocol and is constant (see [I-D.ietf-detnet-architecture]).
However, a virtual "link" could exhibit a variable link delay. However, a virtual "link" could exhibit a variable link delay.
3. Preemption delay 3. Preemption delay
If the packet is interrupted (e.g. [IEEE8023br] and [IEEE8021Qbu] If the packet is interrupted in order to transmit another packet
preemption) in order to transmit another packet or packets, an or packets, (e.g. [IEEE8023] clause 99 frame preemption) an
arbitrary delay can result. arbitrary delay can result.
4. Processing delay 4. Processing delay
This delay covers the time from the reception of the last bit of This delay covers the time from the reception of the last bit of
the packet to the time the packet is enqueued in the regulator the packet to the time the packet is enqueued in the regulator
(Queuing subsystem, if there is no regulation). This delay can be (Queuing subsystem, if there is no regulation). This delay can be
variable, and depends on the details of the operation of the variable, and depends on the details of the operation of the
forwarding node. forwarding node.
5. Regulator delay 5. Regulator delay
skipping to change at page 7, line 30 skipping to change at page 9, line 6
on the timing of packet selection in the previous node. If the on the timing of packet selection in the previous node. If the
delays 1-4 are not constant, then additional buffers are required in delays 1-4 are not constant, then additional buffers are required in
the queue to absorb these variations. Thus: the queue to absorb these variations. Thus:
o Variations in output delay (1) require buffers to absorb that o Variations in output delay (1) require buffers to absorb that
variation in the next hop, so the output delay variations of the variation in the next hop, so the output delay variations of the
previous hop (on each input port) must be known in order to previous hop (on each input port) must be known in order to
calculate the buffer space required on this hop. calculate the buffer space required on this hop.
o Variations in processing delay (4) require additional output o Variations in processing delay (4) require additional output
buffers in the queues of that same Detnet relay node. Depending buffers in the queues of that same DetNet transit node. Depending
on the details of the queueing subsystem delay (6) calculations, on the details of the queueing subsystem delay (6) calculations,
these variations need not be visible outside the DetNet relay these variations need not be visible outside the DetNet transit
node. node.
5. Computing End-to-end Latency Bounds 4. Computing End-to-end Latency Bounds
5.1. Non-queuing delay bound 4.1. Non-queuing delay bound
End-to-end latency bounds can be computed using the delay model in End-to-end latency bounds can be computed using the delay model in
Section 4.2. Here it is important to be aware that for several Section 3.2. Here it is important to be aware that for several
queuing mechanisms, the worst-case end-to-end delay is less than the queuing mechanisms, the worst-case end-to-end delay is less than the
sum of the per-hop worst-case delays. An end-to-end latency bound sum of the per-hop worst-case delays. An end-to-end latency bound
for one DetNet flow can be computed as for one DetNet flow can be computed as
end_to_end_latency_bound = non_queuing_latency + queuing_latency end_to_end_latency_bound = non_queuing_latency + queuing_latency
The two terms in the above formula are computed as follows. First, The two terms in the above formula are computed as follows. First,
at the h-th hop along the path of this DetNet flow, obtain an upper at the h-th hop along the path of this DetNet flow, obtain an upper
bound per-hop_non_queuing_latency[h] on the sum of delays 1,2,3,4 of bound per-hop_non_queuing_latency[h] on the sum of delays 1,2,3,4 of
Figure 1. These upper-bounds are expected to depend on the specific Figure 1. These upper-bounds are expected to depend on the specific
technology of the node at the h-th hop but not on the T-SPEC of this technology of the DetNet transit node at the h-th hop but not on the
DetNet flow. Then set non_queuing_latency = the sum of per- T-SPEC of this DetNet flow. Then set non_queuing_latency = the sum
hop_non_queuing_latency[h] over all hops h. of per-hop_non_queuing_latency[h] over all hops h.
5.2. Queuing delay bound 4.2. Queuing delay bound
Second, compute queuing_latency as an upper bound to the sum of the Second, compute queuing_latency as an upper bound to the sum of the
queuing delays along the path. The value of queuing_latency depends queuing delays along the path. The value of queuing_latency depends
on the T-SPEC of this flow and possibly of other flows in the on the T-SPEC of this flow and possibly of other flows in the
network, as well as the specifics of the queuing mechanisms deployed network, as well as the specifics of the queuing mechanisms deployed
along the path of this flow. along the path of this flow.
For several queuing mechanisms, queuing_latency is less than the sum For several queuing mechanisms, queuing_latency is less than the sum
of upper bounds on the queuing delays (5,6) at every hop. This of upper bounds on the queuing delays (5,6) at every hop. This
occurs with (1) per-flow queuing, and (2) per-class queuing with occurs with (1) per-flow queuing, and (2) per-class queuing with
regulators, as explained in Section 5.2.1, Section 5.2.2, and regulators, as explained in Section 4.2.1, Section 4.2.2, and
Section 7. Section 6.
For other queuing mechanisms the only available value of For other queuing mechanisms the only available value of
queuing_latency is the sum of the per-hop queuing delay bounds. In queuing_latency is the sum of the per-hop queuing delay bounds. In
such cases, the computation of per-hop queuing delay bounds must such cases, the computation of per-hop queuing delay bounds must
account for the fact that the T-SPEC of a DetNet flow is no longer account for the fact that the T-SPEC of a DetNet flow is no longer
satisfied at the ingress of a hop, since burstiness increases as one satisfied at the ingress of a hop, since burstiness increases as one
flow traverses one DetNet node. flow traverses one DetNet transit node.
5.2.1. Per-flow queuing mechanisms 4.2.1. Per-flow queuing mechanisms
With such mechanisms, each flow uses a separate queue inside every With such mechanisms, each flow uses a separate queue inside every
node. The service for each queue is abstracted with a guaranteed node. The service for each queue is abstracted with a guaranteed
rate and a delay. For every flow the per-node delay bound as well as rate and a delay. For every flow the per-node delay bound as well as
end-to-end delay bound can be computed from the traffic specification end-to-end delay bound can be computed from the traffic specification
of this flow at its source and from the values of rates and latencies of this flow at its source and from the values of rates and latencies
at all nodes along its path. Details of calculation for IntServ are at all nodes along its path. Details of calculation for IntServ are
described in Section 7.5. described in Section 6.5.
5.2.2. Per-class queuing mechanisms 4.2.2. Per-class queuing mechanisms
With such mechanisms, the flows that have the same class share the With such mechanisms, the flows that have the same class share the
same queue. A practical example is the queuing mechanism in Time same queue. A practical example is the queuing mechanism in Time
Sensitive Networking. One key issue in this context is how to deal Sensitive Networking. One key issue in this context is how to deal
with the burstiness cascade: individual flows that share a resource with the burstiness cascade: individual flows that share a resource
dedicated to a class may see their burstiness increase, which may in dedicated to a class may see their burstiness increase, which may in
turn cause increased burstiness to other flows downstream of this turn cause increased burstiness to other flows downstream of this
resource. Computing latency upper bounds for such cases is resource. Computing latency upper bounds for such cases is
difficult, and in some conditions impossible difficult, and in some conditions impossible
[charny2000delay][bennett2002delay]. Also, when bounds are obtained, [charny2000delay][bennett2002delay]. Also, when bounds are obtained,
they depend on the complete configuration, and must be recomputed they depend on the complete configuration, and must be recomputed
when one flow is added. when one flow is added.
A solution to deal with this issue is to reshape the flows at every A solution to deal with this issue is to reshape the flows at every
hop. This can be done with per-flow regulators (e.g. leaky bucket hop. This can be done with per-flow regulators (e.g. leaky bucket
shapers), but this requires per-flow queuing and defeats the purpose shapers), but this requires per-flow queuing and defeats the purpose
of per-class queuing. An alternative is the interleaved regulator, of per-class queuing. An alternative is the interleaved regulator,
which reshapes individual flows without per-flow queuing which reshapes individual flows without per-flow queuing
([Specht2016UBS], [IEEE8021Qcr]"). With an interleaved regulator, ([Specht2016UBS], [IEEE8021Qcr]). With an interleaved regulator, the
the packet at the head of the queue is regulated based on its (flow) packet at the head of the queue is regulated based on its (flow)
regulation constraints; it is released at the earliest time at which regulation constraints; it is released at the earliest time at which
this is possible without violating the constraint. One key feature this is possible without violating the constraint. One key feature
of per-flow or interleaved regulator is that, it does not increase of per-flow or interleaved regulator is that, it does not increase
worst-case latency bounds [le_boudec_theory_2018]. Specifically, worst-case latency bounds [le_boudec_theory_2018]. Specifically,
when an interleaved regulator is appended to a FIFO subsystem, it when an interleaved regulator is appended to a FIFO subsystem, it
does not increase the worst-case delay of the latter. does not increase the worst-case delay of the latter.
Figure 2 shows an example of a network with 5 nodes, per-class Figure 2 shows an example of a network with 5 nodes, per-class
queuing mechanism and interleaved regulators as in Figure 1. An end- queuing mechanism and interleaved regulators as in Figure 1. An end-
to-end delay bound for flow f, traversing nodes 1 to 5, is calculated to-end delay bound for flow f, traversing nodes 1 to 5, is calculated
as follows: as follows:
end_to_end_latency_bound_of_flow_f = C12 + C23 + C34 + S4 end_to_end_latency_bound_of_flow_f = C12 + C23 + C34 + S4
In the above formula, Cij is a bound on the aggregate response time In the above formula, Cij is a bound on the aggregate response time
of queuing subsystem in node i and interleaved regulator of node j, of queuing subsystem in node i and interleaved regulator of node j,
and S4 is a bound on the response time of the queuing subsystem in and S4 is a bound on the response time of the queuing subsystem in
node 4 for flow f. In fact, using the delay definitions in node 4 for flow f. In fact, using the delay definitions in
Section 4.2, Cij is a bound on sum of the delays 1,2,3,6 of node i Section 3.2, Cij is a bound on sum of the delays 1,2,3,6 of node i
and 4,5 of node j. Similarly, S4 is a bound on sum of the delays and 4,5 of node j. Similarly, S4 is a bound on sum of the delays
1,2,3,6 of node 4. A practical example of queuing model and delay 1,2,3,6 of node 4. A practical example of queuing model and delay
calculation is presented Section 7.4. calculation is presented Section 6.4.
f f
-----------------------------> ----------------------------->
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+
| 1 |---| 2 |---| 3 |---| 4 |---| 5 | | 1 |---| 2 |---| 3 |---| 4 |---| 5 |
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+
\__C12_/\__C23_/\__C34_/\_S4_/ \__C12_/\__C23_/\__C34_/\_S4_/
Figure 2: End-to-end latency computation example Figure 2: End-to-end latency computation example
REMARK: The end-to-end delay bound calculation provided here gives a REMARK: The end-to-end delay bound calculation provided here gives a
much better upper bound in comparison with end-to-end delay bound much better upper bound in comparison with end-to-end delay bound
computation by adding the delay bounds of each node in the path of a computation by adding the delay bounds of each node in the path of a
flow [TSNwithATS]. flow [TSNwithATS].
6. Achieving zero congestion loss 4.3. Ingress considerations
A sender can be a DetNet node which uses exactly the same queuing
methods as its adjacent DetNet transit node, so that the latency and
buffer calculations at the first hop are indistinguishable from those
at a later hop within the DetNet domain. On the other hand, the
sender may be DetNet unaware, in which case some conditioning of the
flow may be necessary at the ingress DetNet transit node.
This ingress conditioning typically consists of a FIFO with an output
regulator that is compatible with the queuing employed by the DetNet
transit node on its output port(s). For some queuing methods, simply
requires added extra buffer space in the queuing subsystem. Ingress
conditioning requirements for different queuing methods are mentioned
in the sections, below, describing those queuing methods.
4.4. Interspersed non-DetNet transit nodes
It is sometimes desirable to build a network that has both DetNet
aware transit nodes and DetNet non-aware transit nodes, and for a
DetNet flow to traverse an island of non-DetNet transit nodes, while
still allowing the network to offer latency and congestion loss
guarantees. This is possible under certain conditions.
In general, when passing through a non-DetNet island, the island
causes delay variation in excess of what would be caused by DetNet
nodes. That is, the DetNet flow is "lumpier" after traversing the
non-DetNet island. DetNet guarantees for latency and buffer
requirements can still be calculated and met if and only if the
following are true:
1. The latency variation across the non-DetNet island must be
bounded and calculable.
2. An ingress conditioning function (Section 4.3) may be required at
the re-entry to the DetNet-aware domain. This will, at least,
require some extra buffering to accommodate the additional delay
variation, and thus further increases the worst-case latency.
The ingress conditioning is exactly the same problem as that of a
sender at the edge of the DetNet domain. The requirement for bounds
on the latency variation across the non-DetNet island is typically
the most difficult to achieve. Without such a bound, it is obvious
that DetNet cannot deliver its guarantees, so a non-DetNet island
that cannot offer bounded latency variation cannot be used to carry a
DetNet flow.
5. Achieving zero congestion loss
When the input rate to an output queue exceeds the output rate for a When the input rate to an output queue exceeds the output rate for a
sufficient length of time, the queue must overflow. This is sufficient length of time, the queue must overflow. This is
congestion loss, and this is what deterministic networking seeks to congestion loss, and this is what deterministic networking seeks to
avoid. avoid.
6.1. A General Formula 5.1. A General Formula
To avoid congestion losses, an upper bound on the backlog present in To avoid congestion losses, an upper bound on the backlog present in
the regulator and queuing subsystem of Figure 1 must be computed the regulator and queuing subsystem of Figure 1 must be computed
during resource reservation. This bound depends on the set of flows during resource reservation. This bound depends on the set of flows
that use these queues, the details of the specific queuing mechanism that use these queues, the details of the specific queuing mechanism
and an upper bound on the processing delay (4). The queue must and an upper bound on the processing delay (4). The queue must
contain the packet in transmission plus all other packets that are contain the packet in transmission plus all other packets that are
waiting to be selected for output. waiting to be selected for output.
A conservative backlog bound, that applies to all systems, can be A conservative backlog bound, that applies to all systems, can be
skipping to change at page 10, line 51 skipping to change at page 13, line 20
o nb_input_ports be the number input ports that send traffic of any o nb_input_ports be the number input ports that send traffic of any
class to this output port class to this output port
o max_packet_length be the maximum packet size for packets of any o max_packet_length be the maximum packet size for packets of any
class that may be sent to this output port. This is counted in class that may be sent to this output port. This is counted in
data units. data units.
o max_delay45 be an upper bound, in seconds, on the sum of the o max_delay45 be an upper bound, in seconds, on the sum of the
processing delay (4) and the queuing delays (5,6) for a packet of processing delay (4) and the queuing delays (5,6) for a packet of
any class at this ouput port. any class at this output port.
Then a bound on the backlog of traffic of all classes in the queue at Then a bound on the backlog of traffic of all classes in the queue at
this output port is this output port is
backlog_bound = ( nb_classes + nb_input_ports ) * backlog_bound = ( nb_classes + nb_input_ports ) *
max_packet_length + total_in_rate* max_delay45 max_packet_length + total_in_rate* max_delay45
7. Queuing model 6. Queuing model
7.1. Queuing data model 6.1. Queuing data model
Sophisticated queuing mechanisms are available in Layer 3 (L3, see, Sophisticated queuing mechanisms are available in Layer 3 (L3, see,
e.g., [RFC7806] for an overview). In general, we assume that "Layer e.g., [RFC7806] for an overview). In general, we assume that "Layer
3" queues, shapers, meters, etc., are precisely the "regulators" 3" queues, shapers, meters, etc., are precisely the "regulators"
shown in Figure 1. The "queuing subsystems" in this figure are not shown in Figure 1. The "queuing subsystems" in this figure are not
the province solely of bridges; they are an essential part of any the province solely of bridges; they are an essential part of any
DetNet relay node. As illustrated by numerous implementation DetNet transit node. As illustrated by numerous implementation
examples, some of the "Layer 3" mechanisms described in documents examples, some of the "Layer 3" mechanisms described in documents
such as [RFC7806] are often integrated, in an implementation, with such as [RFC7806] are often integrated, in an implementation, with
the "Layer 2" mechanisms also implemented in the same system. An the "Layer 2" mechanisms also implemented in the same node. An
integrated model is needed in order to successfully predict the integrated model is needed in order to successfully predict the
interactions among the different queuing mechanisms needed in a interactions among the different queuing mechanisms needed in a
network carrying both DetNet flows and non-DetNet flows. network carrying both DetNet flows and non-DetNet flows.
Figure 3 shows the general model for the flow of packets through the Figure 3 shows the general model for the flow of packets through the
queues of a DetNet relay node. Packets are assigned to a class of queues of a DetNet transit node. Packets are assigned to a class of
service. The classes of service are mapped to some number of service. The classes of service are mapped to some number of
regulator queues. Only DetNet/TSN packets pass through regulators. regulator queues. Only DetNet/TSN packets pass through regulators.
Queues compete for the selection of packets to be passed to queues in Queues compete for the selection of packets to be passed to queues in
the queuing subsystem. Packets again are selected for output from the queuing subsystem. Packets again are selected for output from
the queuing subsystem. the queuing subsystem.
| |
+--------------------------------V----------------------------------+ +--------------------------------V----------------------------------+
| Class of Service Assignment | | Class of Service Assignment |
+--+------+----------+---------+-----------+-----+-------+-------+--+ +--+------+----------+---------+-----------+-----+-------+-------+--+
skipping to change at page 12, line 49 skipping to change at page 14, line 49
o Discarding packets marked "yellow" by a metering function, in o Discarding packets marked "yellow" by a metering function, in
preference to discarding "green" packets. preference to discarding "green" packets.
Ideally, neither of these actions are performed on DetNet packets. Ideally, neither of these actions are performed on DetNet packets.
Full queues for DetNet packets should occur only when a flow is Full queues for DetNet packets should occur only when a flow is
misbehaving, and the DetNet QoS does not include "yellow" service for misbehaving, and the DetNet QoS does not include "yellow" service for
packets in excess of committed rate. packets in excess of committed rate.
The Class of Service Assignment function can be quite complex, even The Class of Service Assignment function can be quite complex, even
in a bridge [IEEE8021Q], since the introduction of [IEEE802.1Qci]. in a bridge [IEEE8021Q], since the introduction of per-stream
In addition to the Layer 2 priority expressed in the 802.1Q VLAN tag, filtering and policing ([IEEE8021Q] clause 8.6.5.1). In addition to
a DetNet relay node can utilize any of the following information to the Layer 2 priority expressed in the 802.1Q VLAN tag, a DetNet
assign a packet to a particular class of service (queue): transit node can utilize any of the following information to assign a
packet to a particular class of service (queue):
o Input port. o Input port.
o Selector based on a rotating schedule that starts at regular, o Selector based on a rotating schedule that starts at regular,
time-synchronized intervals and has nanosecond precision. time-synchronized intervals and has nanosecond precision.
o MAC addresses, VLAN ID, IP addresses, Layer 4 port numbers, DSCP. o MAC addresses, VLAN ID, IP addresses, Layer 4 port numbers, DSCP.
([I-D.ietf-detnet-dp-sol-ip], [I-D.ietf-detnet-dp-sol-mpls]) (Work ([I-D.ietf-detnet-dp-sol-ip], [I-D.ietf-detnet-dp-sol-mpls]) (Work
items are expected to add MPC and other indicators.) items are expected to add MPC and other indicators.)
o The Class of Service Assignment function can contain metering and o The Class of Service Assignment function can contain metering and
policing functions. policing functions.
o MPLS and/or pseudowire ([RFC6658]) labels. o MPLS and/or pseudowire ([RFC6658]) labels.
The "Transmission selection" function decides which queue is to The "Transmission selection" function decides which queue is to
transfer its oldest packet to the output port when a transmission transfer its oldest packet to the output port when a transmission
opportunity arises. opportunity arises.
7.2. Preemption 6.2. Preemption
In IEEE Std 802.1Q, preemption is modeled as consisting of two MAC/ In [IEEE8021Q] and [IEEE8023], the transmission of a frame can be
PHY stacks, one for packets that can be interrupted, and one for interrupted by one or more "express" frames, and then the interrupted
packets that can interrupt the interruptible packets. The Class of frame can continue transmission. This frame preemption is modeled as
Service (queue) determines which packets are which. Only one layer consisting of two MAC/PHY stacks, one for packets that can be
of preemption is supported. DetNet flows pass through the interrupted, and one for packets that can interrupt the interruptible
interrupting MAC. Only best-effort queues pass through the packets. The Class of Service (queue) determines which packets are
interruptible MAC, and can thus be preempted. which. Only one layer of preemption is supported -- a transmitter
cannot have more than one interrupted frame in progress. DetNet
flows typically pass through the interrupting MAC. Best-effort
queues pass through the interruptible MAC, and can thus be preempted.
7.3. Time-scheduled queuing 6.3. Time-scheduled queuing
In [IEEE8021Qbv], the notion of time-scheduling queue gates were In [IEEE8021Q], the notion of time-scheduling queue gates is
introduced. On below every output queue (the lower row of queues in described in section 8.6.8.4. Below every output queue (the lower
Figure 3) is a gate that permits or denies the queue to present data row of queues in Figure 3) is a gate that permits or denies the queue
for transmission selection. The gates are controlled by a rotating to present data for transmission selection. The gates are controlled
schedule that can be locked to a clock that is synchronized with by a rotating schedule that can be locked to a clock that is
other relay nodes. The DetNet class of service can be supplied by synchronized with other DetNet transit nodes. The DetNet class of
queuing mechanisms based on time, rather than the regulator model in service can be supplied by queuing mechanisms based on time, rather
Figure 3. These queuing mechanisms are discussed in Section 8, than the regulator model in Figure 3. These queuing mechanisms are
below. discussed in Section 7, below.
7.4. Time-Sensitive Networking with Asynchronous Traffic Shaping 6.4. Time-Sensitive Networking with Asynchronous Traffic Shaping
Consider a network with a set of nodes (switches and hosts) along Consider a network with a set of nodes (DetNet transit nodes and
with a set of flows between hosts. Hosts are sources or destinations hosts) along with a set of flows between hosts. Hosts are sources or
of flows. There are four types of flows, namely, control-data destinations of flows. There are four types of flows, namely,
traffic (CDT), class A, class B, and best effort (BE) in decreasing control-data traffic (CDT), class A, class B, and best effort (BE) in
order of priority. Flows of classes A and B are together referred to decreasing order of priority. Flows of classes A and B are together
as AVB flows. It is assumed a subset of TSN functions as described referred to AVB flows. It is assumed a subset of TSN functions as
next. described next.
It is also assumed that contention occurs only at the output port of It is also assumed that contention occurs only at the output port of
a TSN node. Each node output port performs per-class scheduling with a TSN node. Each node output port performs per-class scheduling with
eight classes: one for CDT, one for class A traffic, one for class B eight classes: one for CDT, one for class A traffic, one for class B
traffic, and five for BE traffic denoted as BE0-BE4 (according to TSN traffic, and five for BE traffic denoted as BE0-BE4 (according to TSN
standard). In addition, each node output port also performs per-flow standard). In addition, each node output port also performs per-flow
regulation for AVB flows using an interleaved regulator (IR), called regulation for AVB flows using an interleaved regulator (IR), called
Asynchronous Traffic Shaper (ATS) in TSN. Thus, at each output port Asynchronous Traffic Shaper (ATS) in TSN. Thus, at each output port
of a node, there is one interleaved regulator per-input port and per- of a node, there is one interleaved regulator per-input port and per-
class. The detailed picture of scheduling and regulation class. The detailed picture of scheduling and regulation
skipping to change at page 14, line 48 skipping to change at page 17, line 31
| | | | | | | | | | | | | | | |
+-v--------v-----------v---------v-------V-------v-------v-------v--+ +-v--------v-----------v---------v-------V-------v-------v-------v--+
| Strict Priority selection | | Strict Priority selection |
+--------------------------------+----------------------------------+ +--------------------------------+----------------------------------+
| |
V V
Figure 4: Architecture of a TSN node output port with interleaved Figure 4: Architecture of a TSN node output port with interleaved
regulators (IRs) regulators (IRs)
The CBFS includes two CBS subsystems, one for each class A and B. The CBFS includes two Credit-Based Shaper (CBS) subsystems, one for
The CBS serves a packet from a class according to the available each class A and B. The CBS serves a packet from a class according
credit for that class. The credit for each class A or B increases to the available credit for that class. The credit for each class A
based on the idle slope, and decreases based on the send slope, both or B increases based on the idle slope, and decreases based on the
of which are parameters of the CBS. The CDT and BE0-BE4 flows in the send slope, both of which are parameters of the CBS. The CDT and
CBFS are served by separate FIFO subsystems. Then, packets from all BE0-BE4 flows in the CBFS are served by separate FIFO subsystems.
flows are served by a transmission selection subsystem that serves Then, packets from all flows are served by a transmission selection
packets from each class based on its priority. All subsystems are subsystem that serves packets from each class based on its priority.
non-preemptive. Guarantees for AVB traffic can be provided only if All subsystems are non-preemptive. Guarantees for AVB traffic can be
CDT traffic is bounded; it is assumed that the CDT traffic has an provided only if CDT traffic is bounded; it is assumed that the CDT
affine arrival curve r t + b in each node, i.e. the amount of bits traffic has leaky bucket arrival curve with two parameters r_h as
entering a node within a time interval t is bounded by r t + b. rate and b_h as bucket size, i.e., the amount of bits entering a node
within a time interval t is bounded by r_h t + b_h.
[[ EM: THE FOLLOWING PARAGRAPH SHOULD BE ALIGNED WITH Section 9.2. ]] Additionally, it is assumed that the AVB flows are also regulated at
their source according to leaky bucket arrival curve. At the source
hosts, the traffic satisfies its regulation constraint, i.e. the
delay due to interleaved regulator at hosts is ignored.
Additionally, it is assumed that flows are regulated at their source, At each DetNet transit node implementing an interleaved regulator,
according to either leaky bucket (LB) or length rate quotient (LRQ). packets of multiple flows are processed in one FIFO queue; the packet
The LB-type regulation forces flow f to conform to an arrival curve at the head of the queue is regulated based on its leaky bucket
r_f t+b_f . The LRQ-type regulation with rate r_f ensures that the parameters; it is released at the earliest time at which this is
time separation between two consecutive packets of sizes l_n and possible without violating the constraint. The regulation parameters
l_n+1 is at least l_n/r_f. Note that if flow f is LRQ-regulated, it for a flow (leaky bucket rate and bucket size) are the same at its
satisfies an arrival curve constraint r_f t + L_f where L_f is its source and at all DetNet transit nodes along its path. A delay bound
maximum packet size (but the converse may not hold). For an LRQ of CBFS for an AVB flow f of class A or B can be computed if the
regulated flow, b_f = L_f. At the source hosts, the traffic following condition holds:
satisfies its regulation constraint, i.e. the delay due to
interleaved regulator at hosts is ignored.
At each switch implementing an interleaved regulator, packets of sum of leaky bucket rates of all flows of this class at this node
multiple flows are processed in one FIFO queue; the packet at the <= R, where R is given below for every class.
head of the queue is regulated based on its regulation constraints;
it is released at the earliest time at which this is possible without
violating the constraint. The regulation type and parameters for a
flow are the same at its source and at all switches along its path.
Details of end-to-end delay bound calculation in such a system is If the condition holds, the delay bound is:
described in [TSNwithATS].
7.5. IntServ d_f = T + (b_t-L_min_f)/R - L_min_f/c
In this section, a worst-case queuing latency calculating method is where L_min_f is the minimum packet length of flow f; c is the output
provided. In deterministic network, the traffic of a flow is link transmission rate; b_t is the sum of the b term (bucket size)
constrained by arrival curve. Queuing mechanisms in a DetNet node for all the flows having the same class as flow f at this node.
can be characterized and constrained by service curve. By using Parameters R and T are calculated as follows for class A and class B,
arrival curve and service curve with Network Calculus theory separately:
[NetCalBook], a tight worst-case queuing latency can be calculated.
Considering a DetNet flow at output port, R(s) is the cumulative If f is of class A:
arrival data until time s. For any time period t, the incremental
arrival data is constrained by an arrival curve a(t)
R(s+t)-R(s) <= a(t), \any s>=0, t>=0 R = I_A (c-r_h)/ c
The scheduling that a relay node performs to a DetNet flow can be T = L_nA + b_h + r_h L_n/c)/(c-r_h)
abstracted as service curve. It describes the minimal service the
network can offer. The service curve b(t) of a node is defined as
below, if the accumulative input data R and output data R_out of the
node satisfies
R_out(t) >= inf(R(s) + b(t-s) ), \any s <=t where L_nA is the maximum packet length of class B and BE packets;
L_n is the maximum packet length of classes A,B, and BE.
where the operator "inf" calculates the greatest lower bound in If f is of class B:
period t.
By calculating the maximum vertical deviation between arrival curve R = I_B (c-r_h)/ c
a(t) and service curve b(t), one can obtain the backlog bound in data
unit
Backlog_bound = sup_t(a(t) - b(t) ) T = (L_BE + L_A + L_nA I_A/(c_h-I_A) + b_h + r_h L_n/c)/(c-r_h)
where operator "sup_t" calculates the minimum upper bound with where L_A is the maximum packet length of class A; L_BE is the
respect to t. The buffer space at a node should be no less than the maximum packet length of class BE.
backlog bound to achieve zero congestion loss.
NOTE: Section 6.1 gives a general formula for computing the buffer Then, an end-to-end delay bound is calculated by the formula
requirements. This is an alternative calculation based on the Section 4.2.2, where for Cij:
arrival curve and service curve.
By calculating the maximum horizontal deviation between arrival curve Cij = max(d_f')
a(t) and service curve b(t), one can obtain the delay bound as below
Delay_bound = sup_s( inf_t( t>=0 | a(s) <= b(s+t) ) where f' is any flow that shares the same CBFS class with flow f at
node i and the same interleaved regulator as flow f at node j.
where the operator " inf_t" calculates the maximum lower bound with More information of delay analysis in such a DetNet transit node is
respect to t, the operator "sup_s" calculates the minimum upper bound described in [TSNwithATS].
with respect to s. Figure 5 shows an example of arival curve,
service curve, backlog bound h, and delay bound v.
+ bit . * 6.4.1. Flow Admission
| . *
| . *
| *
| * .
| * .
| * | . .. Service curve
*-----h-|---. ** Arrival curve
| v . h Delay_bound
| | . v Backlog_bound
| |.
+-------.--------------------+ time
Figure 5: Computation of backlog bound and delay bound. Note that The delay calculation requires some information about each node. For
arrival and service curves are not necessary to be linear. each node, it is required to know the idle slope of CBS for each
class A and B (I_A and I_B), as well as the transmission rate of the
output link (c). Besides, it is necessary to have the information on
each class, i.e. maximum packet length of classes A, B, and BE.
Moreover, the leaky bucket parameters of CDT (r_h,b_h) should be
known. To admit a flow/flows, their delay requirements should be
guaranteed not to be violated. As described in Section 3.1, the two
problems static and dynamic are addressed separately. In either of
the problems, the rate and delay should be guaranteed. Thus,
Note that in the formula of Delay_bound, the service curve b(t) can The static admission control:
describe either per-hop scheduling that a DetNet node offers to a The leaky bucket parameters of all flows are known,
flow, or concatenation of multiple nodes that represents end-to-end therefore, for each flow a delay bound can be calculated.
scheduling that DetNet path offers to a flow. In the latter case, The computed delay bound for every flow should not be more
the obtained delay bound is end-to-end worst case delay. To than its delay requirement. Moreover, the sum of the rate of
calculate this, we should at first derive the concatenated service each flow (r_f) should not be more than the rate allocated to
curve. each class (R). If these two conditions hold, the
configuration is declared admissible.
Consider a flow traverse two DetNet nodes, which offer service curve The dynamic admission control:
b1(t) and b2(t) sequentially. Then concatenation of the two nodes For dynamic admission control, we allocate to every node and
offers a service curve b_concatenated as below class A or B, static value for rate (R) and maximum
burstiness (b_t). In addition, for every node and every
class A and B, two counters are maintained:
b_concatenated(t) =inf_s (b1(s) + b2(t-s) ) , \any 0 <=s <=t R_acc is equal to the sum of the leaky-bucket rates of all
flows of this class already admitted at this node; At all
times, we must have:
The concatenation of service curve can be directly generalized to R_acc <=R, (Eq. 1)
include more than two nodes.
a_out(t) = sup_u( a(t+u) - b(u) ), \any u>=0 b_acc is equal to the sum of the bucket sizes of all flows
of this class already admitted at this node; At all times,
we must have:
In DetNet, the arrival curve and service curve can be characterized b_acc <=b_t. (Eq. 2)
by a group of parameters, which will be defined in Section 8.
A new flow is admitted at this node, if Eqs. (1) and (2)
continue to be satisfied after adding its leaky bucket rate
and bucket size to R_acc and b_acc. A flow is admitted in
the network, if it is admitted at all nodes along its path.
When this happens, all variables R_acc and b_acc along its
path must be incremented to reflect the addition of the flow.
Similarly, when a flow leaves the network, all variables
R_acc and b_acc along its path must be decremented to reflect
the removal of the flow.
The choice of the static values of R and b_t at all nodes and classes
must be done in a prior configuration phase; R controls the bandwidth
allocated to this class at this node, b_t affects the delay bound and
the buffer requirement. R must satisfy the constraints given in
Annex L.1 of [IEEE8021Q].
6.5. IntServ
Integrated service (IntServ) is an architecture that specifies the Integrated service (IntServ) is an architecture that specifies the
elements to guarantee quality of service (QoS) on networks. To elements to guarantee quality of service (QoS) on networks. To
satisfied guaranteed service, a flow must conform to a traffic satisfied guaranteed service, a flow must conform to a traffic
specification (T-spec), and reservation is made along a path, only if specification (T-spec), and reservation is made along a path, only if
routers are able to guarantee the required bandwidth and buffer. routers are able to guarantee the required bandwidth and buffer.
Consider the traffic model which conforms to token bucket regulator Consider the traffic model which conforms to token bucket regulator
(r, b), with (r, b), with
o Token bucket depth (b). o Token bucket depth (b).
o Token bucket rate (r). o Token bucket rate (r).
The traffic specification can be described as an arrival curve a(t) The traffic specification can be described as an arrival curve:
alpha(t) = b + rt alpha(t) = b + rt
This token bucket regulator requires that, during any time window of This token bucket regulator requires that, during any time window t,
width t, the number of bit for the flow is limited by alpha(t) = b + the number of bit for the flow is limited by alpha(t) = b + rt.
rt.
If resource reservation on a path is applied, IntServ model on a If resource reservation on a path is applied, IntServ model of a
router can be described as a rate-latency service curve beta(t). router can be described as a rate-latency service curve beta(t).
beta(t) = max(0, R(t-T)) beta(t) = max(0, R(t-T))
It describes that bits might have to wait up to T before being served It describes that bits might have to wait up to T before being served
with a rate greater or equal to R. with a rate greater or equal to R.
It should be noted that, the guaranteed service rate R is a share of It should be noted that, the guaranteed service rate R is a share of
link's bandwidth. The choice of R is related to the specification of link's bandwidth. The choice of R is related to the specification of
flows which will transmit on this node. For example, in strict flows which will transmit on this node. For example, in strict
skipping to change at page 18, line 40 skipping to change at page 21, line 17
flows traversing this node. For example, in a generalized processor flows traversing this node. For example, in a generalized processor
sharing (GPS) node, T = L / R + L_max/c, where L is the maximum sharing (GPS) node, T = L / R + L_max/c, where L is the maximum
packet size for the flow, L_max is the maximum packet size in the packet size for the flow, L_max is the maximum packet size in the
node across all flows. Other choice of R and T are also supported, node across all flows. Other choice of R and T are also supported,
according to the specific scheduling of the node and flows traversing according to the specific scheduling of the node and flows traversing
this node. this node.
As mentioned previously in this section, delay bound and backlog As mentioned previously in this section, delay bound and backlog
bound can be easily obtained by comparing arrival curve and service bound can be easily obtained by comparing arrival curve and service
curve. Backlog bound, or buffer bound, is the maximum vertical curve. Backlog bound, or buffer bound, is the maximum vertical
derivation between curves alpha(t) and beta(t), which is x=b+rT. derivation between curves alpha(t) and beta(t), which is v=b+rT.
Delay bound is the maximum horizontal derivation between curves Delay bound is the maximum horizontal derivation between curves
alpha(t) and beta(t), which is d = T+b/R. Graphical illustration of alpha(t) and beta(t), which is h = T+b/R. Graphical illustration of
the IntServ model is shown in Figure 5. the IntServ model is shown in Figure 5.
+ bit . *
| . *
| . *
| *
| * .
| * .
| * | . .. Service curve
*-----h-|---. ** Arrival curve
| v . h Delay_bound
| | . v Backlog_bound
| |.
+-------.--------------------+ time
Figure 5: Computation of backlog bound and delay bound. Note that
arrival and service curves are not necessary to be linear.
The output bound, or the next-hop arrival curve, is alpha_out(t) = b The output bound, or the next-hop arrival curve, is alpha_out(t) = b
+ rT + rt, where burstiness of the flow is increased by rT, compared + rT + rt, where burstiness of the flow is increased by rT, compared
with the arrival curve. with the arrival curve.
We can calculate the end-to-end delay bound, for a path including N We can calculate the end-to-end delay bound for a path including N
nodes, among which the i-th node offers service curve beta_i(t), nodes, among which the i-th node offers service curve beta_i(t),
beta_i(t) = max(0, R_i(t-T_i)), i=1,...,N beta_i(t) = max(0, R_i(t-T_i)), i=1,...,N
According to [Section 5.1], by concatenating those IntServ nodes, an By concatenating these IntServ nodes, an end-to-end service curve can
end-to-end service curve can be computed as be computed as
beta_e2e (t) = max(0, R_e2e(t-T_e2e) ) beta_e2e (t) = max(0, R_e2e(t-T_e2e) )
where where
R_e2e = min(R_1,..., R_N) R_e2e = min(R_1,..., R_N)
T_e2e = T_1 + ... + T_N T_e2e = T_1 + ... + T_N
Similarly, delay bound, backlog bound and output bound can be Similarly, delay bound, backlog bound and output bound can be
computed by using the original arrival curve alpha(t) and computed by using the original arrival curve alpha(t) and
concatenated service curve beta_e2e(t). concatenated service curve beta_e2e(t).
8. Time-based DetNet QoS 7. Time-based DetNet QoS
8.1. Cyclic Queuing and Forwarding 7.1. Cyclic Queuing and Forwarding
[IEEE802.1Qci] and [IEEE802.1Qch] describe Cyclic Queuing and Annex T of [IEEE8021Q] describes Cyclic Queuing and Forwarding (CQF),
Forwarding (CQF), which provide the bounded latency and zero which provides bounded latency and zero congestion loss using the
congestion loss using the time-scheduled gates of [IEEE8021Qbv]. For time-scheduled gates of [IEEE8021Q] section 8.6.8.4. For a given
each different DetNet class of service, a set of two or three buffers DetNet class of service, a set of two or three buffers is provided at
is provided at the out queue layer of Figure 3. A cycle time is the output queue layer of Figure 3. A cycle time Tc is configured
configured for each class, and all of the buffer sets in a class swap for each class c, and all of the buffer sets in a class swap buffers
buffers simultaneously throughout the DetNet domain at that cycle simultaneously throughout the DetNet domain at that cycle rate, all
rate. The choice of using two or three buffers depends on the link in phase.
lengths and forwarding delay times; two buffers can be used if the
delay from hop to hop is nearly an integral number of cycle times,
and three are required if not. Flows are assigned to a class of
service only until the amount of data to be transmitted in one cycle
would exceed the cycle time for some interface. Every packet dwells
either two or three cycles at each hop, so the calculation of worst-
case latency and latency variation is trivial.
8.2. Time Scheduled Queuing 0 time --> 0.7 1 (units of Tc) 2 3
DetNet transit node A out port 1
| a <-DT->| b | c | d
+------------+------+-------------------+-------------------+--------
\_____ \_____
\_____ \_____ queue-to-queue delay = 1.3 Tc
\_____ \_____
\_____ \_____ DetNet transit node B
\_ \_ queue assignment, in
| | |<-DT->| port 2 to out 3 |
-------+-------------------+------------+------+-------------------+-
0.3 time--> 1.3 2.0 2.3 3.3
[IEEE8021Qbv] specifies a time-aware queue-draining procedure for window to transfer
transmission selection at egress port of a relay node, which supports to buffer c ---> VVVVVVVVVVVV
up to eight traffic classes. Each traffic class has a separate if dead time not window to transfer
queue, frame transmission from each queue is allowed or prevented by excessive VVVVVVVVVVVVVVVVVVV <--- to buffer d
a time gate. This time gate controlled scheduling allows time- DetNet transit node B out port 3
sensitive traffic classes to transmit on dedicate time slots. Within | a | b | c | d
the time slots, the transmitting flows can be granted exclusive use +-------------------+-------------------+-------------------+--------
of the transmission medium. Generally, this time-aware scheduling is 0 time--> 1 2 3
a layer 2 time division multiplexing (TDM) technique.
Figure 6: CQF timing diagram and dead time computation
Figure 6 shows two DetNet transit nodes A and B, including three
timelines for:
1. The output queues on port 1 in node A.
2. The input gate function ([IEEE8021Q], 8.6.5.1) that assigns
packets received on port 1 of transit node B to output queues on
port 2 of transit node B.
3. The output queues on port 2 of node B.
In this figure, the output ports on the two nodes are synchronized,
and a new buffer starts transmitting at each tick, shown as 0, 1, 2,
... The output times shown for timelines 1 and 3 are the times at
which packets are selected for output, which is the start point of
the output time (1) of Figure 1. The queue assignments times on
timeline 3 take place at the beginning of the queuing delay (6) of
Figure 1. Time-based CQF, as described here, does not require any
regulator queues. In the shown in the figure, the total time for
delays 1 through 6 of Figure 1 is 1.3Tc. Of course, any value is
possible.
7.1.1. CQF timing sequence
In general, as shown in Figure 6, the windows for buffer assignment
do not align perfectly with the windows for buffer transmission. The
input gates (the center timeline in Figure 6) must switch from using
one buffer to using another buffer in sync with the (delayed)
received data, at times offset by the dead time from the output
buffer switching (the bottom timeline in Figure 6).
If the dead time DT in Figure 6 is not excessive, then it is feasible
to subtract the dead time from the cycle time Tc, and use the
remainder as the input window. In the example in Figure 6, packets
from node A buffer a can be transferred from the input port to node
B's buffer "c" during the window shown by the upper row "VVVV...".
Input must cease by time = 2.0, because that is when transit node B
starts transmitting the contents of buffer c. In this case, only two
output buffers are in use, one filling and one outputting.
If the dead time is too large (e.g., if the delays placed the middle
timeline's switching points at n+0.9, instead of n+0.3), three
buffers are used by node B. This case is shown by the lower row
"VVVV..." in Figure 6. In this case, node B places the data received
from node A buffer a into node B buffer d between the times 1.3 and
2.3 in Figure 6. Buffer b starts outputting at time = 2.0, while
buffer d is filling. Thus, three buffers are in use, one filling,
one waiting, and one emptying.
7.1.2. Dead time computation
The time for switching input packet buffer assignments is equal to
the minimum possible offset from transmission selection in node A to
buffer assignment in node B, which is the sum of the minimum values
for all of the delays 1 through 5 in Figure 1 (the queue-to-queue
delay). All packets must be received and assigned to an output
buffer before the next switching point, which means that all must be
transmitted in time for them to arrive at buffer assignment even if
worst-case (longest delay) is encountered for the queue-to-queue
delay. Thus, the minimum dead time for the 3-buffer case is the sum
of the worst-case variation in the queue-to-queue delay, plus the
worst-case difference between the two transit nodes' buffer switching
clocks.
For the 2-buffer case, we must add the offset (shown as "DT" in
Figure 6) from the end of node B's output switch to the end of node
B's input switch.
7.1.3. Tc computation
Given the dead time DT, there remains a transmit window of (Tc - DT -
Int). The DT was explained in (Section 7.1.2). "Int" is the worst-
case interference with the start of transmission, when the output
buffers switch, caused by lower-priority traffic. This is equal to
one worst-case transmission time, which means that the size of the
packets in all lower-priority queues must be bounded. If Ethernet
preemption ([IEEE8023] clause 99) is employed for lower-priority
queues, then this worst-case interference is reduced to the size of
the largest unfragmentable Ethernet frame.
The bandwidth requirement of any given DetNet flow has to be
translated to CQF terms, in order to determine whether that flow can
be accommodated at each port. A flow has to be characterized as
using a maximum number of bit times on the wire per cycle time Tc.
For Ethernet, for example ([IEEE8023]), this includes the preamble (8
bytes), destination MAC address through CRC (minimum 64 bytes) and
the inter-packet gap (12 bytes). The total bit times per cycle Tc
required by all of the DetNet flows passing through a given port
cannot exceed the available transmit window (Tc - DT - Int).
7.1.4. CQF latency calculation
The per-hop latency is trivially determined by the wire delay plus
the queuing delay. Since the wire delay is either absorbed into the
queueing delay (dead time is small and two buffers are used) or
padded out to a whole cycle time Tc (three buffers are used) the per-
hop latency is always an integral number of cycle times Tc, with a
latency variation at the output of the final hop of Tc.
Ingress conditioning may be required if the source of a DetNet flow
does not, itself, employ CQF. See Section 7.1.6.
7.1.5. CQF parameterization
The transmit window for a given DetNet transit node running CQF, for
example the transmit window for node A in Figure 6, depends on the
interference (Int in section Section 7.1.3), the value of Tc, and the
dead time required by the following node B. The size of the transmit
window determines how many total bits can be reserved per period Tc
by DetNet flows.
Part of the dead time derives from delays and delay variations such
as output delay (1) and link delay (2) and preemption delay (3) of
Figure 1, all of which are known to node A. However, the dead time
also depends on the processing delay (4) of node B and the upon
whether node B is using 2 or 3 output buffers, which is not
necessarily known to node A.
The information in DetNet transit node B necessary to compute the
dead time to be observed by transit node A must be known to the
entity responsible for making reservation decisions, whether that is
node A itself, or a central controller. A decision can be made, by
the controller or by the node, whether to use the dead time and two
buffers, in order to reduce the per-hop latency by one cycle time, or
to use three buffers and eliminate the dead time and increase the
total allocable bandwidth.
If the packet sizes of a DetNet flow are variable, or perhaps even
unknown beyond the imposition of a maximum size, then some degree of
overprovisioning is required. The measurement used to allocate
bandwidth to a given DetNet flow is bit times in one cycle time Tc.
Therefore, one extra maximum packet time (less one bit) has to be
allocated to a flow per cycle time Tc in order to ensure that, no
matter what mix of packet sizes are presented, the flow will get its
guaranteed latency.
7.1.6. Ingress conditioning for CQF
Assuming that a DetNet domain is using CQF, it is always possible
that the previous node (or sender) may not support the queuing method
of CQF, or may support CQF but not use the same configuration in
accordance of the current DetNet domain. In this case, ingress
conditioning is helpful to shape the flow according to the TSPEC in
the current DetNet domain and transmission cycle of CQF, thus control
the burstiness and reduce overprovisioning.
A DetNet node running CQF satisfies that a maximum number of
max_number_packet_per_cycle packets, each with length no larger than
max_packet_size, can be transmitted during a CQF cycle Tc. Also, the
dead time Dt, during which the former node cannot transmit to the
later node (See Section 7.1.1), should be considered. Here we use
the notation max_number_packet_per_cycle, max_packet_size to describe
the maximum amount of transmitting data during the available transmit
window Tc-Dt.
An ingress conditioner typically consists with a FIFO queue with an
output regulator. Every incoming packet enters the FIFO queue, which
passes it on if and only if the packet conforms to the CQF
requirement. For this purpose, two criteria below is suggested to
follow.
o The incoming flow's average rate would be no more than the average
output queue rate at ingress conditioner, to avoid overflow and
congestion loss.
o The queueing buffer at ingress conditioner is suggested to be
large enough, to cover burstiness and jitter of bit rate from the
previous node (or sender).
The output regulator controls the transmitting of packets, with
credit function for instance. At the start of a CQF cycle, credit is
set to the maximum bits to transmit in a cycle, max_bit_per_cycle =
max_number_packet_per_cycle * max_packet_size. When a packet is
transmitted from the node, the credit is reduced by length(packet).
The operation of the output regulator can be described as below.
credit = max_bit_per_cycle; % Initial credit
t = 0; % Initial time offset within a cycle
outputRegulate(packet){
if (t>=0 && t< Tc-Dt) % during a transmit window
{
if ~isEmpty(queue) % if queue is not empty
{
if credit >= length(packet);
{
dequeue(packet);
credit = credit - length(packet);
}
}
}
elseif (t >= Tc) % when a cycle end, reset t and credit.
{
t = t - Tc; % reset t to [0, Tc-Dt)
credit = max_bit_per_cycle; % credit is refilled
}}
Other instance of output regulator may also meet the CQF requirement.
7.1.7. CQF ingress conditioning timing model
Consider the input traffic conforms to variable bit rate (VBR)
constraint (p, M, r, b), which can be modeled as arrival curve:
alpha(t) = min(pt+M, rt+b)
where p is the peak rate, M is the maximum size of a packet, (r, b)
stand for token bucket rate and burst. Note that, if N flows enter
the ingress conditioner, each flow f_i conforms to token bucket
(r_i,b_i), the arrival curve parameters are of the superposition
form: r = sum(r_i), b = sum(b_i), i=1,...,N.
Ingress conditioner, which transmit packets as soon as possible if
conformance is satisfied, does not increase worst-case queuing
latency, if we consider the latency from the input of ingress
conditioner to the first output of CQF node. The CQF node, which
transmits at most max_bit_per_cycle bits during a cycle Tc, offers a
service curve
beta(t) = max_bit_per_cycle * floor(t-Dt) + min(p*mod(t-Dt, Tc),
max_bit_per_cycle)
where Dt is the dead time (see Section 7.1.1), p is the peak rate,
max_bit_per_cycle = max_number_packet_per_cycle * max_packet_size is
the maximum transmitting data in a CQF cycle, floor(x) calculates the
nearest integer less than or equal to x, and mod(x,y)=x-floor(x/y).
According to network calculus, the worst-case queuing delay for
ingress conditioner and CQF node, denoted delay_bound, is the maximum
horizontal distance between arrival curve and service curve.
Specifically, in general assumptions, ingress conditioner's average
output rate r2 = max_bit_per_cycle/Tc is always no less than input
traffic rate r (or else congestion loss would happen). In such
conditions, the queuing delay up-bound for ingress conditioner and
first CQF node is derived as ingress_delay_bound = max(t : beta(t) =
(pb-rm) / (p-r)). Therefore, considering a path traverses ingress
conditioner and H CQF nodes, the total delay up-bound is H*Tc +
ingress_delay_bound.
7.2. Time-scheduled queuing
[IEEE8021Q] section 8.6.8.4 specifies a time-aware queue-draining
procedure for transmission selection at egress port of a DetNet
transit node, which supports up to eight traffic classes. Each
traffic class has a separate queue, frame transmission from each
queue is allowed or prevented by a time gate. This time gate
controlled scheduling allows time-sensitive traffic classes to
transmit on dedicate time slots. Within the time slots, the
transmitting flows can be granted exclusive use of the transmission
medium. Generally, this time-aware scheduling is a layer 2 time
division multiplexing (TDM) technique.
Consider the static configuration of a deterministic network. To Consider the static configuration of a deterministic network. To
provide end-to-end latency guaranteed service, network nodes can provide end-to-end latency guaranteed service, network nodes can
support time-based behavior, which is determined by gate control list support time-based behavior, which is determined by gate control list
(GCL). GCL defines the gate operation, in open or closed state, with (GCL). GCL defines the gate operation, in open or closed state, with
associated timing for each traffic class queue. A time slice with associated timing for each traffic class queue. A time slice with
gate state "open" is called transmission window. The time-based gate state "open" is called transmission window. The time-based
traffic scheduling must be coordinated among the relay nodes along traffic scheduling must be coordinated among the DetNet transit nodes
the path from sender to receiver, to control the transmission of along the path from sender to receiver, to control the transmission
time-sensitive traffic. of time-sensitive traffic.
Ideally all network devices are time synchronized and static GCL Ideally all network devices are time synchronized and static GCL
configurations on all devices along the routed path are coordinated configurations on all devices along the routed path are coordinated
to ensure that length of transmission window fits the assigned to ensure that length of transmission window fits the assigned
frames, and no two time windows for DetNet traffic on the same port frames, and no two time windows for DetNet traffic on the same port
overlap. (DetNet flows' windows can overlap with best-effort overlap. (DetNet flows' windows can overlap with best-effort
windows, so that unused DetNet bandwidth is available to best-effort windows, so that unused DetNet bandwidth is available to best-effort
traffic.) The processing delay, link delay and output delay in traffic.) The processing delay, link delay and output delay in
transmitting are considered in GCL computation. Transmission window transmitting are considered in GCL computation. Transmission window
for a certain flow may require that a time offset on consecutive hops for a certain flow may require that a time offset on consecutive hops
be selected to reduce queueing delay as much as possible. In this be selected to reduce queueing delay as much as possible. In this
case, TSN/DetNet frames transmit at the assigned transmission window case, TSN/DetNet frames transmit at the assigned transmission window
at every node through the routed path, with zero congestion loss and at every node through the routed path, with zero congestion loss and
bounded end-to-end latency. Then, the worst-case end-to-end latency bounded end-to-end latency. Then, the worst-case end-to-end latency
of flow can be derived from GCL configuration. For a TSN or DetNet of the flow can be derived from GCL configuration. For a TSN or
frame, denote the transmission window on last hop closes at DetNet frame, denote the transmission window on last hop closes at
gate_close_time_last_hop. Assuming talker supports scheduled traffic gate_close_time_last_hop. Assuming talker supports scheduled traffic
behavior, it starts the transmission at gate_open_time_on_talker. behavior, it starts the transmission at gate_open_time_on_talker.
Then worst case end-to-end delay of this flow is bounded by Then worst case end-to-end delay of this flow is bounded by
gate_close_time_last_hop - gate_open_time_on_talker + gate_close_time_last_hop - gate_open_time_on_talker +
link_delay_last_hop. link_delay_last_hop.
It should be noted that scheduled traffic service relies on a It should be noted that scheduled traffic service relies on a
synchronized network and coordinated GCL configuration. Synthesis of synchronized network and coordinated GCL configuration. Synthesis of
GCL on multiple nodes in network is a scheduling problem considering GCL on multiple nodes in network is a scheduling problem considering
all TSN/DetNet flows traversing the network, which is a non- all TSN/DetNet flows traversing the network, which is a non-
deterministic polynomial-time hard (NP-hard) problem. Also, at this deterministic polynomial-time hard (NP-hard) problem. Also, at this
writing, scheduled traffic service supports no more than eight writing, scheduled traffic service supports no more than eight
traffic classes, typically using up to seven priority classes and at traffic classes, typically using up to seven priority classes and at
least one best effort class. least one best effort class.
9. Parameters for the bounded latency model 8. Parameters for the bounded latency model
9.1. Sender parameters
9.2. Relay system parameters
[[NWF This section talks about the parameters that must be used hop- The use of the TSPEC parameters defined in [RFC2212] and related
by-hop by a resource reservation protocol.]] documents for IntServ are well-established and adequate for DetNet
purposes. The parameterization used by [IEEE8021Q] are somewhat
different, as discussed above (Section 7.1.6). These parameters are
maximum number of frames per interval, interval size, and maximum
frame size. They are more suitable for the physical determination of
compliance by a sender than for resource reservation purposes.
10. References 9. References
10.1. Normative References 9.1. Normative References
[I-D.ietf-detnet-architecture] [I-D.ietf-detnet-architecture]
Finn, N., Thubert, P., Varga, B., and J. Farkas, Finn, N., Thubert, P., Varga, B., and J. Farkas,
"Deterministic Networking Architecture", draft-ietf- "Deterministic Networking Architecture", draft-ietf-
detnet-architecture-08 (work in progress), September 2018. detnet-architecture-08 (work in progress), September 2018.
[I-D.ietf-detnet-dp-sol-ip] [I-D.ietf-detnet-dp-sol-ip]
Korhonen, J. and B. Varga, "DetNet IP Data Plane Korhonen, J. and B. Varga, "DetNet IP Data Plane
Encapsulation", draft-ietf-detnet-dp-sol-ip-00 (work in Encapsulation", draft-ietf-detnet-dp-sol-ip-00 (work in
progress), July 2018. progress), July 2018.
[I-D.ietf-detnet-dp-sol-mpls] [I-D.ietf-detnet-dp-sol-mpls]
Korhonen, J. and B. Varga, "DetNet MPLS Data Plane Korhonen, J. and B. Varga, "DetNet MPLS Data Plane
Encapsulation", draft-ietf-detnet-dp-sol-mpls-00 (work in Encapsulation", draft-ietf-detnet-dp-sol-mpls-00 (work in
progress), July 2018. progress), July 2018.
[I-D.ietf-detnet-use-cases] [I-D.ietf-detnet-use-cases]
Grossman, E., "Deterministic Networking Use Cases", draft- Grossman, E., "Deterministic Networking Use Cases", draft-
ietf-detnet-use-cases-19 (work in progress), October 2018. ietf-detnet-use-cases-20 (work in progress), December
2018.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC2212] Shenker, S., Partridge, C., and R. Guerin, "Specification [RFC2212] Shenker, S., Partridge, C., and R. Guerin, "Specification
of Guaranteed Quality of Service", RFC 2212, of Guaranteed Quality of Service", RFC 2212,
DOI 10.17487/RFC2212, September 1997, DOI 10.17487/RFC2212, September 1997,
<https://www.rfc-editor.org/info/rfc2212>. <https://www.rfc-editor.org/info/rfc2212>.
[RFC6658] Bryant, S., Ed., Martini, L., Swallow, G., and A. Malis, [RFC6658] Bryant, S., Ed., Martini, L., Swallow, G., and A. Malis,
"Packet Pseudowire Encapsulation over an MPLS PSN", "Packet Pseudowire Encapsulation over an MPLS PSN",
RFC 6658, DOI 10.17487/RFC6658, July 2012, RFC 6658, DOI 10.17487/RFC6658, July 2012,
<https://www.rfc-editor.org/info/rfc6658>. <https://www.rfc-editor.org/info/rfc6658>.
[RFC7806] Baker, F. and R. Pan, "On Queuing, Marking, and Dropping", [RFC7806] Baker, F. and R. Pan, "On Queuing, Marking, and Dropping",
RFC 7806, DOI 10.17487/RFC7806, April 2016, RFC 7806, DOI 10.17487/RFC7806, April 2016,
<https://www.rfc-editor.org/info/rfc7806>. <https://www.rfc-editor.org/info/rfc7806>.
10.2. Informative References 9.2. Informative References
[bennett2002delay] [bennett2002delay]
J.C.R. Bennett, K. Benson, A. Charny, W.F. Courtney, and J.C.R. Bennett, K. Benson, A. Charny, W.F. Courtney, and
J.-Y. Le Boudec, "Delay Jitter Bounds and Packet Scale J.-Y. Le Boudec, "Delay Jitter Bounds and Packet Scale
Rate Guarantee for Expedited Forwarding", Rate Guarantee for Expedited Forwarding",
<https://dl.acm.org/citation.cfm?id=581870>. <https://dl.acm.org/citation.cfm?id=581870>.
[charny2000delay] [charny2000delay]
A. Charny and J.-Y. Le Boudec, "Delay Bounds in a Network A. Charny and J.-Y. Le Boudec, "Delay Bounds in a Network
with Aggregate Scheduling", <https://link.springer.com/ with Aggregate Scheduling", <https://link.springer.com/
chapter/10.1007/3-540-39939-9_1>. chapter/10.1007/3-540-39939-9_1>.
[IEEE802.1Qch]
IEEE, "IEEE Std 802.1Qch-2017 IEEE Standard for Local and
metropolitan area networks - Bridges and Bridged Networks
Amendment 29: Cyclic Queuing and Forwarding (amendment to
802.1Q-2014)", 2017,
<http://www.ieee802.org/1/files/private/ch-drafts/>.
[IEEE802.1Qci]
IEEE, "IEEE Std 802.1Qci-2017 IEEE Standard for Local and
metropolitan area networks - Bridges and Bridged Networks
- Amendment 30: Per-Stream Filtering and Policing", 2017,
<http://www.ieee802.org/1/files/private/ci-drafts/>.
[IEEE8021Q] [IEEE8021Q]
IEEE 802.1, "IEEE Std 802.1Q-2014: IEEE Standard for Local IEEE 802.1, "IEEE Std 802.1Q-2018: IEEE Standard for Local
and metropolitan area networks - Bridges and Bridged and metropolitan area networks - Bridges and Bridged
Networks", 2014, <http://standards.ieee.org/getieee802/ Networks", 2018,
download/802-1Q-2014.pdf>. <http://ieeexplore.ieee.org/document/8403927>.
[IEEE8021Qbu]
IEEE, "IEEE Std 802.1Qbu-2016 IEEE Standard for Local and
metropolitan area networks - Bridges and Bridged Networks
- Amendment 26: Frame Preemption", 2016,
<http://standards.ieee.org/getieee802/
download/802.1Qbu-2016.zip>.
[IEEE8021Qbv]
IEEE 802.1, "IEEE Std 802.1Qbv-2015: IEEE Standard for
Local and metropolitan area networks - Bridges and Bridged
Networks - Amendment 25: Enhancements for Scheduled
Traffic", 2015, <http://standards.ieee.org/getieee802/
download/802.1Qbv-2015.zip>.
[IEEE8021Qcr] [IEEE8021Qcr]
IEEE 802.1, "IEEE P802.1Qcr: IEEE Draft Standard for Local IEEE 802.1, "IEEE P802.1Qcr: IEEE Draft Standard for Local
and metropolitan area networks - Bridges and Bridged and metropolitan area networks - Bridges and Bridged
Networks - Amendment: Asynchronous Traffic Shaping", 2017, Networks - Amendment: Asynchronous Traffic Shaping", 2017,
<http://www.ieee802.org/1/files/private/cr-drafts/>. <http://www.ieee802.org/1/files/private/cr-drafts/>.
[IEEE8021TSN] [IEEE8021TSN]
IEEE 802.1, "IEEE 802.1 Time-Sensitive Networking (TSN) IEEE 802.1, "IEEE 802.1 Time-Sensitive Networking (TSN)
Task Group", <http://www.ieee802.org/1/>. Task Group", <http://www.ieee802.org/1/>.
[IEEE8023br] [IEEE8023]
IEEE 802.3, "IEEE Std 802.3br-2016: IEEE Standard for IEEE 802.3, "IEEE Std 802.3-2018: IEEE Standard for
Local and metropolitan area networks - Ethernet - Ethernet", 2018,
Amendment 5: Specification and Management Parameters for <http://ieeexplore.ieee.org/document/8457469>.
Interspersing Express Traffic", 2016,
<http://standards.ieee.org/getieee802/
download/802.3br-2016.pdf>.
[le_boudec_theory_2018] [le_boudec_theory_2018]
J.-Y. Le Boudec, "A Theory of Traffic Regulators for J.-Y. Le Boudec, "A Theory of Traffic Regulators for
Deterministic Networks with Application to Interleaved Deterministic Networks with Application to Interleaved
Regulators", <http://arxiv.org/abs/1801.08477/>. Regulators", <http://arxiv.org/abs/1801.08477/>.
[NetCalBook] [NetCalBook]
Le Boudec, Jean-Yves, and Patrick Thiran, "Network Le Boudec, Jean-Yves, and Patrick Thiran, "Network
calculus: a theory of deterministic queuing systems for calculus: a theory of deterministic queuing systems for
the internet", 2001, <https://arxiv.org/abs/1804.10608/>. the internet", 2001, <https://arxiv.org/abs/1804.10608/>.
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