Deterministic Networking (DetNet) Bounded Latency
draft-ietf-detnet-bounded-latency-10
The information below is for an old version of the document that is already published as an RFC.
| Document | Type |
This is an older version of an Internet-Draft that was ultimately published as RFC 9320.
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|---|---|---|---|
| Authors | Norman Finn , Jean-Yves Le Boudec , Ehsan Mohammadpour , Jiayi Zhang , Balazs Varga | ||
| Last updated | 2022-11-30 (Latest revision 2022-04-08) | ||
| Replaces | draft-finn-detnet-bounded-latency | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | Informational | ||
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| Additional resources | Mailing list discussion | ||
| Stream | WG state | Submitted to IESG for Publication | |
| Document shepherd | Lou Berger | ||
| Shepherd write-up | Show Last changed 2021-05-17 | ||
| IESG | IESG state | Became RFC 9320 (Informational) | |
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draft-ietf-detnet-bounded-latency-10
DetNet N. Finn
Internet-Draft Huawei Technologies Co. Ltd
Intended status: Informational J-Y. Le Boudec
Expires: 10 October 2022 E. Mohammadpour
EPFL
J. Zhang
Huawei Technologies Co. Ltd
B. Varga
Ericsson
8 April 2022
DetNet Bounded Latency
draft-ietf-detnet-bounded-latency-10
Abstract
This document presents a timing model for sources, destinations, and
DetNet transit nodes. Using the model, it provides a methodology to
compute end-to-end latency and backlog bounds for various queuing
methods. The methodology can be used by the management and control
planes and by resource reservation algorithms to provide bounded
latency and zero congestion loss for the DetNet service.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 10 October 2022.
Copyright Notice
Copyright (c) 2022 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology and Definitions . . . . . . . . . . . . . . . . . 4
3. DetNet bounded latency model . . . . . . . . . . . . . . . . 4
3.1. Flow admission . . . . . . . . . . . . . . . . . . . . . 4
3.1.1. Static latency-calculation . . . . . . . . . . . . . 5
3.1.2. Dynamic latency-calculation . . . . . . . . . . . . . 6
3.2. Relay node model . . . . . . . . . . . . . . . . . . . . 7
4. Computing End-to-end Delay Bounds . . . . . . . . . . . . . . 9
4.1. Non-queuing delay bound . . . . . . . . . . . . . . . . . 9
4.2. Queuing delay bound . . . . . . . . . . . . . . . . . . . 10
4.2.1. Per-flow queuing mechanisms . . . . . . . . . . . . . 11
4.2.2. Aggregate queuing mechanisms . . . . . . . . . . . . 11
4.3. Ingress considerations . . . . . . . . . . . . . . . . . 12
4.4. Interspersed DetNet-unaware transit nodes . . . . . . . . 13
5. Achieving zero congestion loss . . . . . . . . . . . . . . . 13
6. Queuing techniques . . . . . . . . . . . . . . . . . . . . . 14
6.1. Queuing data model . . . . . . . . . . . . . . . . . . . 15
6.2. Frame Preemption . . . . . . . . . . . . . . . . . . . . 17
6.3. Time-Aware Shaper . . . . . . . . . . . . . . . . . . . . 17
6.4. Credit-Based Shaper with Asynchronous Traffic Shaping . . 18
6.4.1. Delay Bound Calculation . . . . . . . . . . . . . . . 20
6.4.2. Flow Admission . . . . . . . . . . . . . . . . . . . 21
6.5. Guaranteed-Service IntServ . . . . . . . . . . . . . . . 22
6.6. Cyclic Queuing and Forwarding . . . . . . . . . . . . . . 23
7. Example application on DetNet IP network . . . . . . . . . . 24
8. Security considerations . . . . . . . . . . . . . . . . . . . 26
9. IANA considerations . . . . . . . . . . . . . . . . . . . . . 27
10. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 27
11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 27
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 27
12.1. Normative References . . . . . . . . . . . . . . . . . . 27
12.2. Informative References . . . . . . . . . . . . . . . . . 28
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 30
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1. Introduction
The ability for IETF Deterministic Networking (DetNet) or IEEE 802.1
Time-Sensitive Networking [IEEE8021TSN] to provide the DetNet
services of bounded latency and zero congestion loss depends upon
A) configuring and allocating network resources for the exclusive
use of DetNet flows;
B) identifying, in the data plane, the resources to be utilized by
any given packet;
C) the detailed behavior of those resources, especially
transmission queue selection, so that latency bounds can be
reliably assured.
As explained in [RFC8655], DetNet flows are notably characterized by
1. a maximum bandwidth, guaranteed either by the transmitter or by
strict input metering;
2. a requirement for a guaranteed worst-case end-to-end latency.
That latency guarantee, in turn, provides the opportunity for the
network to supply enough buffer space to guarantee zero congestion
loss. It is assumed in this document that the paths of DetNet flows
are fixed. Before the transmission of a DetNet flow, it is possible
to calculate end-to-end latency bounds and the amount of buffer space
required at each hop to ensure zero congestion loss; this can be used
by the applications identified in [RFC8578].
This document presents a timing model for sources, destinations, and
the DetNet transit nodes; using this model, it provides a methodology
to compute end-to-end latency and backlog bounds for various queuing
mechanisms that can be used by the management and control planes to
provide DetNet qualities of service. The methodology used in this
document account for the possibility of packet reordering within a
DetNet node. The bounds on the amount of packet reordering is out of
the scope of this document and can be found in
[PacketReorderingBounds]. Moreover, this document references
specific queuing mechanisms, mentioned in [RFC8655], as proofs of
concept that can be used to control packet transmission at each
output port and achieve the DetNet quality of service.
Using the model presented in this document, it is possible for an
implementer, user, or standards development organization to select a
set of queuing mechanisms for each device in a DetNet network, and to
select a resource reservation algorithm for that network, so that
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those elements can work together to provide the DetNet service.
Section 7 provides an example application of the timing model
introduced in this document on a DetNet IP network with a combination
of different queuing mechanisms.
This document does not specify any resource reservation protocol or
control plane function. It does not describe all of the requirements
for that protocol or control plane function. It does describe
requirements for such resource reservation methods, and for queuing
mechanisms that, if met, will enable them to work together.
2. Terminology and Definitions
This document uses the terms defined in [RFC8655]. Moreover, the
following terms are used in this document:
T-SPEC
TrafficSpecification as defined in Section 5.5 of [RFC9016].
arrival curve
An arrival curve function alpha(t) is an upper bound on the number
of bits seen at an observation point within any time interval t.
CQF
Cyclic Queuing and Forwarding.
CBS
Credit-based Shaper.
TSN
Time-Sensitive Networking.
PREOF
A collective name for Packet Replication, Elimination, and
Ordering Functions.
Packet Ordering Function (POF)
A function that reorders packets within a DetNet flow that are
received out of order. This function can be implemented by a
DetNet edge node, a DetNet relay node, or an end system.
3. DetNet bounded latency model
3.1. Flow admission
This document assumes that the following paradigm is used to admit
DetNet flows:
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1. Perform any configuration required by the DetNet transit nodes in
the network for aggregates of DetNet flows. This configuration
is done beforehand, and not tied to any particular DetNet flow.
2. Characterize the new DetNet flow, particularly in terms of
required bandwidth.
3. Establish the path that the DetNet flow will take through the
network from the source to the destination(s). This can be a
point-to-point or a point-to-multipoint path.
4. Compute the worst-case end-to-end latency for the DetNet flow,
using one of the methods, below (Section 3.1.1, Section 3.1.2).
In the process, determine whether sufficient resources are
available for the DetNet flow to guarantee the required latency
and to provide zero congestion loss.
5. Assuming that the resources are available, commit those resources
to the DetNet flow. This may or may not require adjusting the
parameters that control the filtering and/or queuing mechanisms
at each hop along the DetNet flow's path.
This paradigm can be implemented using peer-to-peer protocols or
using a central controller. In some situations, a lack of resources
can require backtracking and recursing through the above list.
Issues such as service preemption of a DetNet flow in favor of
another, when resources are scarce, are not considered here. Also
not addressed is the question of how to choose the path to be taken
by a DetNet flow.
3.1.1. Static latency-calculation
The static problem:
Given a network and a set of DetNet flows, compute an end-to-
end latency bound (if computable) for each DetNet flow, and
compute the resources, particularly buffer space, required in
each DetNet transit node to achieve zero congestion loss.
In this calculation, 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 provides
bounds on latency and buffer size. 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.
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This calculation may be more difficult to perform than the dynamic
calculation (Section 3.1.2), because the DetNet flows passing through
one port on a DetNet transit node affect each other's latency. The
effects can even be circular, from a node A to B to C and back to A.
On the other hand, the static calculation can often accommodate
queuing methods, such as transmission selection by strict priority,
that are unsuitable for the dynamic calculation.
3.1.2. Dynamic latency-calculation
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 calculation is dynamic, in the sense that DetNet flows can be
added or deleted at any time, with a minimum of computation effort,
and without affecting the guarantees already given to other DetNet
flows.
Dynamic latency-calculation can be done based on the static one
described in Section 3.1.1; when a new DetNet flow is created or
deleted, the entire calculation for all DetNet flows is repeated. If
an already-established DetNet flow would be pushed beyond its latency
requirements by the new DetNet flow request, then the new DetNet flow
request can be refused, or some other suitable action taken.
The choice of queuing methods is critical to the applicability of the
dynamic calculation. Some queuing methods (e.g., CQF, Section 6.6)
make it easy to configure bounds on the network's capacity, and to
make independent calculations for each DetNet flow. Some other
queuing methods (e.g., strict priority with the credit-based shaper
defined in [IEEE8021Q] section 8.6.8.2) can be used for dynamic
DetNet flow creation, but yield poorer latency and buffer space
guarantees than when that same queuing method is used for static
DetNet flow creation (Section 3.1.1).
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3.2. Relay node model
A model for the operation of a DetNet transit node is required, in
order to define the latency and buffer calculations. In Figure 1 we
see a breakdown of the per-hop latency experienced by a packet
passing through a DetNet transit node, in terms that are suitable for
computing both hop-by-hop latency and per-hop buffer requirements.
DetNet transit node A DetNet transit node B
+-------------------------+ +------------------------+
| Queuing | | Queuing |
| Regulator subsystem | | Regulator subsystem |
| +-+-+-+-+ +-+-+-+-+ | | +-+-+-+-+ +-+-+-+-+ |
-->+ | | | | | | | | | + +------>+ | | | | | | | | | + +--->
| +-+-+-+-+ +-+-+-+-+ | | +-+-+-+-+ +-+-+-+-+ |
| | | |
+-------------------------+ +------------------------+
|<->|<------>|<------->|<->|<---->|<->|<------>|<------>|<->|<--
2,3 4 5 6 1 2,3 4 5 6 1 2,3
1: Output delay 4: Processing delay
2: Link delay 5: Regulation delay
3: Frame preemption delay 6: Queuing delay
Figure 1: Timing model for DetNet or TSN
In Figure 1, we see two DetNet transit nodes that are connected via a
link. In this model, the only queues, that we deal with explicitly,
are attached to the output port; other 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 (2) or the processing
delay (4).) There are six delays that a packet can experience from
hop to hop.
1. Output delay
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
physical link. If the queue is directly attached to the physical
port, output delay can be a constant. But, in many
implementations, the queuing mechanism in a forwarding ASIC is
separated from a multi-port MAC/PHY, in a second ASIC, by a
multiplexed connection. This causes variations in the output
delay that are hard for the forwarding node to predict or control.
2. Link delay
The time taken from the transmission of the first bit of the
packet to the reception of the last bit, assuming that the
transmission is not suspended by a frame preemption event. This
delay has two components, the first-bit-out to first-bit-in delay
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and the first-bit-in to last-bit-in delay that varies with packet
size. The former is typically measured by the Precision Time
Protocol and is constant (see [RFC8655]). However, a virtual
"link" could exhibit a variable link delay.
3. Frame preemption delay
If the packet is interrupted in order to transmit another packet
or packets, (e.g., [IEEE8023] clause 99 frame preemption) an
arbitrary delay can result.
4. Processing delay
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
(queuing subsystem, if there is no regulator) as shown in
Figure 1. This delay can be variable, and depends on the details
of the operation of the forwarding node.
5. Regulator delay
A regulator, also known as shaper in [RFC2475], delays some or all
of the packets in a traffic stream in order to bring the stream
into compliance with an arrival curve; an arrival curve 'alpha(t)'
is an upper bound on the number of bits observed within any
interval t. The regulator delay is the time spent from the
insertion of the last bit of a packet into a regulation queue
until the time the packet is declared eligible according to its
regulation constraints. We assume that this time can be
calculated based on the details of regulation policy. If there is
no regulation, this time is zero.
6. Queuing subsystem delay
This is the time spent for a packet from being declared eligible
until being selected for output on the next link. We assume that
this time is calculable based on the details of the queuing
mechanism. If there is no regulation, this time is from the
insertion of the packet into a queue until it is selected for
output on the next link.
Not shown in Figure 1 are the other output queues that we presume are
also attached to that same output port as the queue shown, and
against which this shown queue competes for transmission
opportunities.
In this analysis, the measurement is from the point at which a packet
is selected for output in a node to the point at which it is selected
for output in the next downstream node (that is the definition of a
"hop"). In general, any queue selection method that is suitable for
use in a DetNet network includes a detailed specification as to
exactly when packets are selected for transmission. Any variations
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in any of the delay times 1-4 result in a need for additional buffers
in the queue. If all delays 1-4 are constant, then any variation in
the time at which packets are inserted into a queue depends entirely
on the timing of packet selection in the previous node. If the
delays 1-4 are not constant, then additional buffers are required in
the queue to absorb these variations. Thus:
* Variations in output delay (1) require buffers to absorb that
variation in the next hop, so the output delay variations of the
previous hop (on each input port) must be known in order to
calculate the buffer space required on this hop.
* Variations in processing delay (4) require additional output
buffers in the queues of that same DetNet transit node. Depending
on the details of the queuing subsystem delay (6) calculations,
these variations need not be visible outside the DetNet transit
node.
4. Computing End-to-end Delay Bounds
4.1. Non-queuing delay bound
End-to-end latency bounds can be computed using the delay model in
Section 3.2. Here, it is important to be aware that for several
queuing mechanisms, the end-to-end latency bound is less than the sum
of the per-hop latency bounds. An end-to-end latency bound for one
DetNet flow can be computed as
end_to_end_delay_bound = non_queuing_delay_bound +
queuing_delay_bound
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-bound per-hop_non_queuing_delay_bound[h] on the sum of the
bounds over the delays 1,2,3,4 of Figure 1. These upper bounds are
expected to depend on the specific technology of the DetNet transit
node at the h-th hop but not on the T-SPEC of this DetNet flow
[RFC9016]. Then set non_queuing_delay_bound = the sum of per-
hop_non_queuing_delay_bound[h] over all hops h.
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Second, compute queuing_delay_bound as an upper bound to the sum of
the queuing delays along the path. The value of queuing_delay_bound
depends on the information on the arrival curve of this DetNet flow
and possibly of other flows in the network, as well as the specifics
of the queuing mechanisms deployed along the path of this DetNet
flow. Note that arrival curve of DetNet flow at source is
immediately specified by the T-SPEC of this flow. The computation of
queuing_delay_bound is described in Section 4.2 as a separate
section.
4.2. Queuing delay bound
For several queuing mechanisms, queuing_delay_bound is less than the
sum of upper bounds on the queuing delays (5,6) at every hop. This
occurs with (1) per-flow queuing, and (2) aggregate queuing with
regulators, as explained in Section 4.2.1, Section 4.2.2, and
Section 6. For other queuing mechanisms the only available value of
queuing_delay_bound is the sum of the per-hop queuing delay bounds.
The computation of per-hop queuing delay bounds must account for the
fact that the arrival curve of a DetNet flow is no longer satisfied
at the ingress of a hop, since burstiness increases as one flow
traverses one DetNet transit node. If a regulator is placed at a
hop, an arrival curve of a DetNet flow at the entrance of the queuing
subsystem of this hop is the one configured at the regulator (also
called shaping curve in [NetCalBook]); otherwise, an arrival curve of
the flow can be derived using the delay-jitter of the flow from the
last regulation point (the last regulator in the path of the flow if
there is any, otherwise the source of the flow) to the ingress of the
hop; more formally, assume a DetNet flow has arrival curve at the
last regulation point equal to 'alpha(t)', and the delay-jitter from
the last regulation point to the ingress of the hop is 'V'. Then,
the arrival curve at the ingress of the hop is 'alpha(t+V)'.
For example, consider a DetNet flow with T-SPEC "Interval: tau,
MaxPacketsPerInterval: K, MaxPayloadSize: L" at source. Then, a
leaky-bucket arrival curve for such flow at source is alpha(t)=r * t+
b, t>0; alpha(0)=0, where r is the rate and b is the bucket size,
computed as
r = K * (L+L') / tau,
b = K * (L+L').
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where L' is the size of any added networking technology-specific
encapsulation (e.g., MPLS label(s), UDP, and IP headers). Now, if
the flow has delay-jitter of 'V' from the last regulation point to
the ingress of a hop, an arrival curve at this point is r * t + b + r
* V, implying that the burstiness is increased by r*V. A more
detailed information on arrival curves is available in [NetCalBook].
4.2.1. Per-flow queuing mechanisms
With such mechanisms, each flow uses a separate queue inside every
node. The service for each queue is abstracted with a guaranteed
rate and a latency. For every DetNet flow, a per-node latency bound
as well as an end-to-end latency bound can be computed from the
traffic specification of this DetNet flow at its source and from the
values of rates and latencies at all nodes along its path. An
instance of per-flow queuing is IntServ's Guaranteed-Service, for
which the details of latency bound calculation are presented in
Section 6.5.
4.2.2. Aggregate queuing mechanisms
With such mechanisms, multiple flows are aggregated into macro-flows
and there is one FIFO queue per macro-flow. A practical example is
the credit-based shaper defined in section 8.6.8.2 of [IEEE8021Q]
where a macro-flow is called a "class". One key issue in this
context is how to deal with the burstiness cascade: individual flows
that share a resource dedicated to a macro-flow may see their
burstiness increase, which may in turn cause increased burstiness to
other flows downstream of this resource. Computing delay upper
bounds for such cases is difficult, and in some conditions impossible
[CharnyDelay][BennettDelay]. Also, when bounds are obtained, they
depend on the complete configuration, and must be recomputed when one
flow is added. (The dynamic calculation, Section 3.1.2.)
A solution to deal with this issue for the DetNet flows is to reshape
them at every hop. This can be done with per-flow regulators (e.g.,
leaky bucket shapers), but this requires per-flow queuing and defeats
the purpose of aggregate queuing. An alternative is the interleaved
regulator, which reshapes individual DetNet flows without per-flow
queuing ([SpechtUBS], [IEEE8021Qcr]). With an interleaved regulator,
the packet at the head of the queue is regulated based on its (flow)
regulation constraints; it is released at the earliest time at which
this is possible without violating the constraint. One key feature
of per-flow or interleaved regulator is that, it does not increase
worst-case latency bounds [LeBoudecTheory]. Specifically, when an
interleaved regulator is appended to a FIFO subsystem, it does not
increase the worst-case delay of the latter; in Figure 1, when the
order of packets from output of queuing subsystem at node A to the
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entrance of regulator at node B is preserved, then the regulator does
not increase the worst-case latency bounds; this is made possible if
all the systems are FIFO or a DetNet packet-ordering function (POF)
is implemented just before the regulator. This property does not
hold if packet reordering occurs from the output of a queuing
subsystem to the entrance of next downstream interleaved regulator,
e.g., at a non-FIFO switching fabric.
Figure 2 shows an example of a network with 5 nodes, aggregate
queuing mechanism and interleaved regulators as in Figure 1. An end-
to-end delay bound for DetNet flow f, traversing nodes 1 to 5, is
calculated as follows:
end_to_end_latency_bound_of_flow_f = C12 + C23 + C34 + S4
In the above formula, Cij is a bound on the delay of the queuing
subsystem in node i and interleaved regulator of node j, and S4 is a
bound on the delay of the queuing subsystem in node 4 for DetNet flow
f. In fact, using the delay definitions in 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 1,2,3,6 of node 4. A
practical example of queuing model and delay calculation is presented
Section 6.4.
f
----------------------------->
+---+ +---+ +---+ +---+ +---+
| 1 |---| 2 |---| 3 |---| 4 |---| 5 |
+---+ +---+ +---+ +---+ +---+
\__C12_/\__C23_/\__C34_/\_S4_/
Figure 2: End-to-end delay computation example
REMARK: If packet reordering does not occur, the end-to-end latency
bound calculation provided here gives a tighter latency upper-bound
than would be obtained by adding the latency bounds of each node in
the path of a DetNet flow [TSNwithATS].
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 bounds 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 DetNet flow may be necessary at the ingress
DetNet transit node.
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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, this
simply requires added 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 DetNet-unaware transit nodes
It is sometimes desirable to build a network that has both DetNet-
aware transit nodes and DetNet-unaware transit nodes, and for a
DetNet flow to traverse an island of DetNet-unaware transit nodes,
while still allowing the network to offer delay and congestion loss
guarantees. This is possible under certain conditions.
In general, when passing through a DetNet-unaware island, the island
may cause delay variation in excess of what would be caused by DetNet
nodes. That is, the DetNet flow might be "lumpier" after traversing
the DetNet-unaware island. DetNet guarantees for delay and buffer
requirements can still be calculated and met if and only if the
following are true:
1. The latency variation across the DetNet-unaware island must be
bounded and calculable.
2. An ingress conditioning function (Section 4.3) is 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 latency bound.
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 DetNet-unaware island is
typically the most difficult to achieve. Without such a bound, it is
obvious that DetNet cannot deliver its guarantees, so a DetNet-
unaware 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
sufficient length of time, the queue must overflow. This is
congestion loss, and this is what deterministic networking seeks to
avoid.
To avoid congestion losses, an upper bound on the backlog present in
the regulator and queuing subsystem of Figure 1 must be computed
during resource reservation. This bound depends on the set of flows
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that use these queues, the details of the specific queuing mechanism
and an upper bound on the processing delay (4). The queue must
contain the packet in transmission plus all other packets that are
waiting to be selected for output. A conservative backlog bound,
that applies to all systems, can be derived as follows.
The backlog bound is counted in data units (bytes, or words of
multiple bytes) that are relevant for buffer allocation. For every
flow or an aggregate of flows, we need one buffer space for the
packet in transmission, plus space for the packets that are waiting
to be selected for output.
Let
* total_in_rate be the sum of the line rates of all input ports that
send traffic to this output port. The value of total_in_rate is
in data units (e.g., bytes) per second.
* nb_input_ports be the number input ports that send traffic to this
output port
* max_packet_length be the maximum packet size for packets that may
be sent to this output port. This is counted in data units.
* max_delay456 be an upper bound, in seconds, on the sum of the
processing delay (4) and the queuing delays (5,6) for any packet
at this output port.
Then a bound on the backlog of traffic in the queue at this output
port is
backlog_bound = (nb_input_ports * max_packet_length) +
(total_in_rate * max_delay456)
The above bound is over the backlog caused by the traffic entering
the queue from the input ports of a DetNet node. If the DetNet node
also generates packets (e.g., creation of new packets, replication of
arriving packets), the bound must accordingly incorporate the
introduced backlog.
6. Queuing techniques
In this section, we present a general queuing data model as well as
some examples of queuing mechanisms. For simplicity of latency bound
computation, we assume leaky-bucket arrival curve for each DetNet
flow at source. Also, at each DetNet transit node, the service for
each queue is abstracted with a minimum guaranteed rate and a latency
[NetCalBook].
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6.1. Queuing data model
Sophisticated queuing mechanisms are available in Layer 3 (L3, see,
e.g., [RFC7806] for an overview). In general, we assume that "Layer
3" queues, shapers, meters, etc., are precisely the "regulators"
shown in Figure 1. The "queuing subsystems" in this figure are FIFO.
They are not the province solely of bridges; they are an essential
part of any DetNet transit node. As illustrated by numerous
implementation examples, some of the "Layer 3" mechanisms described
in documents such as [RFC7806] are often integrated, in an
implementation, with the "Layer 2" mechanisms also implemented in the
same node. An integrated model is needed in order to successfully
predict the interactions among the different queuing mechanisms
needed in a network carrying both DetNet flows and non-DetNet flows.
Figure 3 shows the general model for the flow of packets through the
queues of a DetNet transit node. The DetNet packets are mapped to a
number of regulators. Here, we assume that the PREOF (Packet
Replication, Elimination and Ordering Functions) are performed before
the DetNet packets enter the regulators. All Packets are assigned to
a set of queues. Packets compete for the selection to be passed to
queues in the queuing subsystem. Packets again are selected for
output from the queuing subsystem.
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|
+--------------------------------V----------------------------------+
| Queue assignment |
+--+------+----------+---------+-----------+-----+-------+-------+--+
| | | | | | | |
+--V-+ +--V-+ +--V--+ +--V--+ +--V--+ | | |
|Flow| |Flow| |Flow | |Flow | |Flow | | | |
| 0 | | 1 | ... | i | | i+1 | ... | n | | | |
| reg| | reg| | reg | | reg | | reg | | | |
+--+-+ +--+-+ +--+--+ +--+--+ +--+--+ | | |
| | | | | | | |
+--V------V----------V--+ +--V-----------V--+ | | |
| Trans. selection | | Trans. select. | | | |
+----------+------------+ +-----+-----------+ | | |
| | | | |
+--V--+ +--V--+ +--V--+ +--V--+ +--V--+
| out | | out | | out | | out | | out |
|queue| |queue| |queue| |queue| |queue|
| 1 | | 2 | | 3 | | 4 | | 5 |
+--+--+ +--+--+ +--+--+ +--+--+ +--+--+
| | | | |
+----------V----------------------V--------------V-------V-------V--+
| Transmission selection |
+---------------------------------+---------------------------------+
|
V
Figure 3: IEEE 802.1Q Queuing Model: Data flow
Some relevant mechanisms are hidden in this figure, and are performed
in the queue boxes:
* Discarding packets because a queue is full.
* Discarding packets marked "yellow" by a metering function, in
preference to discarding "green" packets [RFC2697].
Ideally, neither of these actions are performed on DetNet packets.
Full queues for DetNet packets occurs only when a DetNet flow is
misbehaving, and the DetNet QoS does not include "yellow" service for
packets in excess of committed rate.
The queue assignment function can be quite complex, even in a bridge
[IEEE8021Q], since the introduction of per-stream filtering and
policing ([IEEE8021Q] clause 8.6.5.1). In addition to the Layer 2
priority expressed in the 802.1Q VLAN tag, a DetNet transit node can
utilize the information from the non-exhaustive list below to assign
a packet to a particular queue:
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* Input port.
* Selector based on a rotating schedule that starts at regular,
time-synchronized intervals and has nanosecond precision.
* MAC addresses, VLAN ID, IP addresses, Layer 4 port numbers, DSCP
[RFC8939], [RFC8964].
* The queue assignment function can contain metering and policing
functions.
* MPLS and/or pseudo-wire labels [RFC6658].
The "Transmission selection" function decides which queue is to
transfer its oldest packet to the output port when a transmission
opportunity arises.
6.2. Frame Preemption
In [IEEE8021Q] and [IEEE8023], the transmission of a frame can be
interrupted by one or more "express" frames, and then the interrupted
frame can continue transmission. The frame preemption is modeled as
consisting of two MAC/PHY stacks, one for packets that can be
interrupted, and one for packets that can interrupt the interruptible
packets. Only one layer of frame preemption is supported -- a
transmitter cannot have more than one interrupted frame in progress.
DetNet flows typically pass through the interrupting MAC. For those
DetNet flows with T-SPEC, latency bounds can be calculated by the
methods provided in the following sections that account for the
effect of frame preemption, according to the specific queuing
mechanism that is used in DetNet nodes. Best-effort queues pass
through the interruptible MAC, and can thus be preempted.
6.3. Time-Aware Shaper
In [IEEE8021Q], the notion of time-scheduling queue gates is
described in section 8.6.8.4. On each node, the transmission
selection for packets is controlled by time-synchronized gates; each
output queue is associated with a gate. The gates can be either open
or closed. The states of the gates are determined by the gate
control list (GCL). The GCL specifies the opening and closing times
of the gates. The design of GCL must satisfy the requirement of
latency upper bounds of all DetNet flows; therefore, those DetNet
flows that traverse a network that uses this kind of shaper must have
bounded latency, if the traffic and nodes are conformant.
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Note that scheduled traffic service relies on a synchronized network
and coordinated GCL configuration. Synthesis of GCL on multiple
nodes in network is a scheduling problem considering all DetNet flows
traversing the network, which is a non-deterministic polynomial-time
hard (NP-hard) problem [Sch8021Qbv]. Also, at this writing,
scheduled traffic service supports no more than eight traffic queues,
typically using up to seven priority queues and at least one best
effort.
6.4. Credit-Based Shaper with Asynchronous Traffic Shaping
In this queuing model, it is assumed that the DetNet nodes are FIFO.
We consider the four traffic classes (Definition 3.268 of
[IEEE8021Q]): control-data traffic (CDT), class A, class B, and best
effort (BE) in decreasing order of priority. Flows of classes A and
B are DetNet flows that are less critical than CDT (such as studio
audio and video traffic, as in IEEE 802.1BA Audio-Video-Bridging).
This model is a subset of Time-Sensitive Networking as described
next.
Based on the timing model described in Figure 1, contention occurs
only at the output port of a DetNet transit node; therefore, the
focus of the rest of this subsection is on the regulator and queuing
subsystem in the output port of a DetNet transit node. The input
flows are identified using the information in (Section 5.1 of
[RFC8939]). Then they are aggregated into eight macro flows based on
their service requirements; we refer to each macro flow as a class.
The output port performs aggregate scheduling with eight queues
(queuing subsystems): one for CDT, one for class A flows, one for
class B flows, and five for BE traffic denoted as BE0-BE4. The
queuing policy for each queuing subsystem is FIFO. In addition, each
node output port also performs per-flow regulation for class A and B
flows using an interleaved regulator (IR), called Asynchronous
Traffic Shaper [IEEE8021Qcr]. Thus, at each output port of a node,
there is one interleaved regulator per-input port and per-class; the
interleaved regulator is mapped to the regulator depicted in
Figure 1. The detailed picture of scheduling and regulation
architecture at a node output port is given by Figure 4. The packets
received at a node input port for a given class are enqueued in the
respective interleaved regulator at the output port. Then, the
packets from all the flows, including CDT and BE flows, are enqueued
in queuing subsystem; there is no regulator for CDT and BE flows.
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+--+ +--+ +--+ +--+
| | | | | | | |
|IR| |IR| |IR| |IR|
| | | | | | | |
+-++XXX++-+ +-++XXX++-+
| | | |
| | | |
+---+ +-v-XXX-v-+ +-v-XXX-v-+ +-----+ +-----+ +-----+ +-----+ +-----+
| | | | | | |Class| |Class| |Class| |Class| |Class|
|CDT| | Class A | | Class B | | BE4 | | BE3 | | BE2 | | BE1 | | BE0 |
| | | | | | | | | | | | | | | |
+-+-+ +----+----+ +----+----+ +--+--+ +--+--+ +--+--+ +--+--+ +--+--+
| | | | | | | |
| +-v-+ +-v-+ | | | | |
| |CBS| |CBS| | | | | |
| +-+-+ +-+-+ | | | | |
| | | | | | | |
+-v--------v-----------v---------v-------V-------v-------v-------v--+
| Strict Priority selection |
+--------------------------------+----------------------------------+
|
V
Figure 4: The architecture of an output port inside a relay node with
interleaved regulators (IRs) and credit-based shaper (CBS)
Each of the queuing subsystems for classes A and B, contains a
Credit-Based Shaper (CBS). The CBS serves a packet from a class
according to the available credit for that class. As described in
Section 8.6.8.2 and Annex L.1 of [IEEE8021Q], the credit for each
class A or B increases based on the idle slope (as guaranteed rate),
and decreases based on the sendslope (typically equal to the
difference between the guaranteed and the output link rates), both of
which are parameters of the CBS. The CDT and BE0-BE4 flows are
served by separate queuing subsystems. Then, packets from all flows
are served by a transmission selection subsystem that serves packets
from each class based on its priority. All subsystems are non-
preemptive. Guarantees for classes A and B traffic can be provided
only if CDT traffic is bounded; it is assumed that the CDT traffic
has a leaky bucket arrival curve with two parameters r_h as 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.
Additionally, it is assumed that the classes A and B flows are also
regulated at their source according to a leaky bucket arrival curve.
At the source, the traffic satisfies its regulation constraint, i.e.,
the delay due to interleaved regulator at the source is ignored.
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At each DetNet transit node implementing an interleaved regulator,
packets of multiple flows are processed in one FIFO queue; the packet
at the head of the queue is regulated based on its leaky bucket
parameters; it is released at the earliest time at which this is
possible without violating the constraint.
The regulation parameters for a flow (leaky bucket rate and bucket
size) are the same at its source and at all DetNet transit nodes
along its path in the case where all clocks are perfect. However, in
reality there is clock non-ideality throughout the DetNet domain even
with clock synchronization. This phenomenon causes inaccuracy in the
rates configured at the regulators that may lead to network
instability. To avoid that, when configuring the regulators, the
rates are set as the source rates with some positive margin.
[ThomasTime] describes and provides solutions to this issue.
6.4.1. Delay Bound Calculation
A delay bound of the queuing subsystem ((4) in Figure 1) of a given
DetNet node for a flow of classes A or B can be computed if the
following condition holds:
sum of leaky bucket rates of all flows of this class at this
transit node <= R, where R is given below for every class.
If the condition holds, the delay bounds for a flow of class X (A or
B) is d_X and calculated as:
d_X = T_X + (b_t_X-L_min_X)/R_X - L_min_X/c
where L_min_X is the minimum packet lengths of class X (A or B); c is
the output link transmission rate; b_t_X is the sum of the b term
(bucket size) for all the flows of the class X. Parameters R_X and
T_X are calculated as follows for class A and class B, separately:
If the flow is of class A:
R_A = I_A * (c-r_h)/ c
T_A = (L_nA + b_h + r_h * L_n/c)/(c-r_h)
where I_A is the idle slope for class A; 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; r_h is the rate and b_h is the bucket size of
CDT traffic leaky bucket arrival curve.
If the flow is of class B:
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R_B = I_B * (c-r_h)/ c
T_B = (L_BE + L_A + L_nA * I_A/(c_h-I_A) + b_h + r_h * L_n/
c)/(c-r_h)
where I_B is the idle slope for class B; L_A is the maximum packet
length of class A; L_BE is the maximum packet length of class BE.
Then, as discussed in Section 4.2.2; an interleaved regulator does
not increase the delay bound of the upstream queuing subsystem;
therefore an end-to-end delay bound for a DetNet flow of class X (A
or B) is the sum of d_X_i for all node i in the path the flow, where
d_X_i is the delay bound of queuing subsystem in node i which is
computed as above. According to the notation in Section 4.2.2, the
delay bound of queuing subsystem in a node i and interleaved
regulator in node j, i.e., Cij, is:
Cij = d_X_i
More information of delay analysis in such a DetNet transit node is
described in [TSNwithATS].
6.4.2. Flow Admission
The delay bound calculation requires some information about each
node. For 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)
must be known. To admit a flow/flows of classes A and B, their delay
requirements must 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 must be
guaranteed. Thus,
The static admission control:
The leaky bucket parameters of all class A or B flows are
known, therefore, for each class A or B flow f, a delay bound
can be calculated. The computed delay bound for every class
A or B flow must not be more than its delay requirement.
Moreover, the sum of the rate of each flow (r_f) must not be
more than the rate allocated to each class (R). If these two
conditions hold, the configuration is declared admissible.
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The dynamic admission control:
For dynamic admission control, we allocate to every node and
class A or B, static value for rate (R) and maximum bucket
size (b_t). In addition, for every node and every class A
and B, two counters are maintained:
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:
R_acc <=R, (Eq. 1)
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:
b_acc <=b_t. (Eq. 2)
A new class A or B 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 class A or
B 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 class A or B 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. The value of R must be set such that
R <= I_X*(c-r_h)/c
where I_X is the idleslope of credit-based shaper for class X={A,B},
c is the transmission rate of the output link and r_h is the leaky-
bucket rate of the CDT class.
6.5. Guaranteed-Service IntServ
Guaranteed-Service Integrated service (IntServ) is an architecture
that specifies the elements to guarantee quality of service (QoS) on
networks [RFC2212].
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The flow, at the source, has a leaky bucket arrival curve with two
parameters r as rate and b as bucket size, i.e., the amount of bits
entering a node within a time interval t is bounded by r * t + b.
If a resource reservation on a path is applied, a node provides a
guaranteed rate R and maximum service latency of T. This can be
interpreted in a way that the bits might have to wait up to T before
being served with a rate greater or equal to R. The delay bound of
the flow traversing the node is T + b / R.
Consider a Guaranteed-Service IntServ path including a sequence of
nodes, where the i-th node provides a guaranteed rate R_i and maximum
service latency of T_i. Then, the end-to-end delay bound for a flow
on this can be calculated as sum(T_i) + b / min(R_i).
The provided delay bound is based on a simple case of Guaranteed-
Service IntServ where only a guaranteed rate and maximum service
latency and a leaky bucket arrival curve are available. If more
information about the flow is known, e.g., the peak rate, the delay
bound is more complicated; the details are available in [RFC2212] and
Section 1.4.1 of [NetCalBook].
6.6. Cyclic Queuing and Forwarding
Annex T of [IEEE8021Q] describes Cyclic Queuing and Forwarding (CQF),
which provides bounded latency and zero congestion loss using the
time-scheduled gates of [IEEE8021Q] section 8.6.8.4. For a given
class of DetNet flows, a set of two or more buffers is provided at
the output queue layer of Figure 3. A cycle time T_c is configured
for each class of DetNet flows c, and all of the buffer sets in a
class of DetNet flows swap buffers simultaneously throughout the
DetNet domain at that cycle rate, all in phase. In such a mechanism,
the regulator, mentioned in Figure 1, is not required.
In the case of two-buffer CQF, each class of DetNet flows c has two
buffers, namely buffer1 and buffer2. In a cycle (i) when buffer1
accumulates received packets from the node's reception ports, buffer2
transmits the already stored packets from the previous cycle (i-1).
In the next cycle (i+1), buffer2 stores the received packets and
buffer1 transmits the packets received in cycle (i). The duration of
each cycle is T_c.
The cycle time T_c must be carefully chosen; it needs to be large
enough to accommodate all the DetNet traffic, plus at least one
maximum packet (or fragment) size from lower priority queues, which
might be received within a cycle. Also, the value of T_c includes a
time interval, called dead time (DT), which is the sum of the delays
1,2,3,4 defined in Figure 1. The value of DT guarantees that the
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last packet of one cycle in a node is fully delivered to a buffer of
the next node in the same cycle. A two-buffer CQF is recommended if
DT is small compared to T_c. For a large DT, CQF with more buffers
can be used, and a cycle identification label can be added to the
packets.
The per-hop latency is determined by the cycle time T_c: a packet
transmitted from a node at a cycle (i), is transmitted from the next
node at cycle (i+1). Then, if the packet traverses h hops, the
maximum latency experienced by the packet is from the beginning of
cycle (i) to the end of cycle (i+h); also, the minimum latency is
from the end of cycle (i) before the DT, to the beginning of cycle
(i+h). Then, the maximum latency is:
(h+1) T_c
and the minimum latency is:
(h-1) T_c + DT.
Ingress conditioning (Section 4.3) may be required if the source of a
DetNet flow does not, itself, employ CQF. Since there are no per-
flow parameters in the CQF technique, per-hop configuration is not
required in the CQF forwarding nodes.
7. Example application on DetNet IP network
This section provides an example application of the timing model
presented in this document to control the admission of a DetNet flow
on a DetNet-enabled IP network. Consider Figure 5, taken from
Section 3 of [RFC8939], that shows a simple IP network:
* The end-system 1 implements Guaranteed-Service IntServ as in
Section 6.5 between itself and relay node 1.
* Sub-network 1 is a TSN network. The nodes in subnetwork 1
implement credit-based shapers with asynchronous traffic shaping
as in Section 6.4.
* Sub-network 2 is a TSN network. The nodes in subnetwork 2
implement cyclic queuing and forwarding with two buffers as in
Section 6.6.
* The relay nodes 1 and 2 implement credit-based shapers with
asynchronous traffic shaping as in Section 6.4. They also perform
the aggregation and mapping of IP DetNet flows to TSN streams
(Section 4.4 of [RFC9023]).
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DetNet IP Relay Relay DetNet IP
End-System Node 1 Node 2 End-System
1 2
+----------+ +----------+
| Appl. |<------------ End-to-End Service ----------->| Appl. |
+----------+ ............ ........... +----------+
| Service |<-: Service :-- DetNet flow --: Service :->| Service |
+----------+ +----------+ +----------+ +----------+
|Forwarding| |Forwarding| |Forwarding| |Forwarding|
+--------.-+ +-.------.-+ +-.---.----+ +-------.--+
: Link : \ ,-----. / \ ,-----. /
+......+ +----[ Sub- ]----+ +-[ Sub- ]-+
[Network] [Network]
`--1--' `--2--'
|<--------------------- DetNet IP --------------------->|
|<--- d1 --->|<--------------- d2_p --------------->|<-- d3_p -->|
Figure 5: A Simple DetNet-Enabled IP Network, taken from RFC8939
Consider a fully centralized control plane for the network of
Figure 5 as described in Section 3.2 of
[I-D.ietf-detnet-controller-plane-framework]. Suppose end-system 1
wants to create a DetNet flow with traffic specification destined to
end-system 2 with end-to-end delay bound requirement D. Therefore,
the control plane receives a flow establishment request and
calculates a number of valid paths through the network (Section 3.2
of [I-D.ietf-detnet-controller-plane-framework]). To select a proper
path, the control plane needs to compute an end-to-end delay bound at
every node of each selected path p.
The end-to-end delay bound is d1 + d2_p + d3_p, where d1 is the delay
bound from end-system 1 to the entrance of relay node 1, d2_p is the
delay bound for path p from relay node 1 to entrance of the first
node in sub-network 2, and d3_p the delay bound of path p from the
first node in sub-network 2 to end-system 2. The computation of d1
is explained in Section 6.5. Since the relay node 1, sub-network 1
and relay node 2 implement aggregate queuing, we use the results in
Section 4.2.2 and Section 6.4 to compute d2_p for the path p.
Finally, d3_p is computed using the delay bound computation of
Section 6.6. Any path p such that d1 + d2_p + d3_p <= D satisfies
the delay bound requirement of the flow. If there is no such path,
the control plane may compute new set of valid paths and redo the
delay bound computation or reject the DetNet flow.
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As soon as the control plane selects a path that satisfies the delay
bound constraint, it allocates and reserves the resources in the path
for the DetNet flow (Section 4.2
[I-D.ietf-detnet-controller-plane-framework]).
8. Security considerations
Detailed security considerations for DetNet are cataloged in
[RFC9055], and more general security considerations are described in
[RFC8655].
Security aspects that are unique to DetNet are those whose aim is to
provide the specific QoS aspects of DetNet, specifically bounded end-
to-end delivery latency and zero congestion loss. Achieving such
loss rates and bounded latency may not be possible in the face of a
highly capable adversary, such as the one envisioned by the Internet
Threat Model of BCP 72 [RFC3552] that can arbitrarily drop or delay
any or all traffic. In order to present meaningful security
considerations, we consider a somewhat weaker attacker who does not
control the physical links of the DetNet domain but may have the
ability to control or change the behavior of some resources within
the boundary of the DetNet domain.
Latency bound calculations use parameters that reflect physical
quantities. If an attacker finds a way to change the physical
quantities, unknown to the control and management planes, the latency
calculations fail and may result in latency violation and/or
congestion losses. An example of such attacks is to make some
traffic sources under the control of the attacker send more traffic
than their assumed T-SPECs. This type of attack is typically avoided
by ingress conditioning at the edge of a DetNet domain. However, it
must be insured that such ingress conditioning is done per-flow and
that the buffers are segregated such that if one flow exceeds its
T-SPEC, it does not cause buffer overflow for other flows.
Some queuing mechanisms require time synchronization and operate
correctly only if the time synchronization works correctly. In the
case of CQF, the correct alignments of cycles can fail if an attack
against time synchronization fools a node into having an incorrect
offset. Some of these attacks can be prevented by cryptographic
authentication as in Annex K of [IEEE1588] for the Precision Time
Protocol (PTP). However, the attacks that change the physical
latency of the links used by the time synchronization protocol are
still possible even if the time synchronization protocol is protected
by authentication and cryptography [DelayAttack]. Such attacks can
be detected only by their effects on latency bound violations and
congestion losses, which do not occur in normal DetNet operation.
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9. IANA considerations
This document has no IANA actions.
10. Acknowledgement
We would like to thank Lou Berger, Tony Przygienda, John Scudder,
Watson Ladd, Yoshifumi Nishida, Ralf Weber, Robert Sparks, Gyan
Mishra, Martin Duke, Eric Vyncke, Lars Eggert, Roman Danyliw, and
Paul Wouters for their useful feedback on this document.
11. Contributors
RFC 7322 limits the number of authors listed on the front page to a
maximum of 5. The editor wishes to thank and acknowledge the
following author for contributing text to this document
Janos Farkas
Ericsson
Email: janos.farkas@ericsson.com
12. References
12.1. Normative References
[IEEE8021Q]
IEEE 802.1, "IEEE Std 802.1Q-2018: IEEE Standard for Local
and metropolitan area networks - Bridges and Bridged
Networks", 2018,
<https://ieeexplore.ieee.org/document/8403927>.
[RFC2212] Shenker, S., Partridge, C., and R. Guerin, "Specification
of Guaranteed Quality of Service", RFC 2212,
DOI 10.17487/RFC2212, September 1997,
<https://www.rfc-editor.org/info/rfc2212>.
[RFC2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.,
and W. Weiss, "An Architecture for Differentiated
Services", RFC 2475, DOI 10.17487/RFC2475, December 1998,
<https://www.rfc-editor.org/info/rfc2475>.
[RFC6658] Bryant, S., Ed., Martini, L., Swallow, G., and A. Malis,
"Packet Pseudowire Encapsulation over an MPLS PSN",
RFC 6658, DOI 10.17487/RFC6658, July 2012,
<https://www.rfc-editor.org/info/rfc6658>.
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[RFC7806] Baker, F. and R. Pan, "On Queuing, Marking, and Dropping",
RFC 7806, DOI 10.17487/RFC7806, April 2016,
<https://www.rfc-editor.org/info/rfc7806>.
[RFC8655] Finn, N., Thubert, P., Varga, B., and J. Farkas,
"Deterministic Networking Architecture", RFC 8655,
DOI 10.17487/RFC8655, October 2019,
<https://www.rfc-editor.org/info/rfc8655>.
[RFC8939] Varga, B., Ed., Farkas, J., Berger, L., Fedyk, D., and S.
Bryant, "Deterministic Networking (DetNet) Data Plane:
IP", RFC 8939, DOI 10.17487/RFC8939, November 2020,
<https://www.rfc-editor.org/info/rfc8939>.
[RFC8964] Varga, B., Ed., Farkas, J., Berger, L., Malis, A., Bryant,
S., and J. Korhonen, "Deterministic Networking (DetNet)
Data Plane: MPLS", RFC 8964, DOI 10.17487/RFC8964, January
2021, <https://www.rfc-editor.org/info/rfc8964>.
[RFC9016] Varga, B., Farkas, J., Cummings, R., Jiang, Y., and D.
Fedyk, "Flow and Service Information Model for
Deterministic Networking (DetNet)", RFC 9016,
DOI 10.17487/RFC9016, March 2021,
<https://www.rfc-editor.org/info/rfc9016>.
12.2. Informative References
[BennettDelay]
J.C.R. Bennett, K. Benson, A. Charny, W.F. Courtney, and
J.-Y. Le Boudec, "Delay Jitter Bounds and Packet Scale
Rate Guarantee for Expedited Forwarding",
<https://dl.acm.org/citation.cfm?id=581870>.
[CharnyDelay]
A. Charny and J.-Y. Le Boudec, "Delay Bounds in a Network
with Aggregate Scheduling", <https://link.springer.com/
chapter/10.1007/3-540-39939-9_1>.
[DelayAttack]
S. Barreto, A. Suresh, and J.-Y. Le Boudec, "Cyber-attack
on packet-based time synchronization protocols: The
undetectable Delay Box",
<https://ieeexplore.ieee.org/document/7520408>.
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[I-D.ietf-detnet-controller-plane-framework]
A. Malis, X. Geng, M. Chen, F. Qin, and B. Varga,
"Deterministic Networking (DetNet) Controller Plane
Framework draft-ietf-detnet-controller-plane-framework-
01", <https://datatracker.ietf.org/doc/html/draft-ietf-
detnet-controller-plane-framework>.
[IEEE1588] IEEE Std 1588-2008, "IEEE Standard for a Precision Clock
Synchronization Protocol for Networked Measurement and
Control Systems", 2008,
<https://ieeexplore.ieee.org/document/4579760>.
[IEEE8021Qcr]
IEEE 802.1, "IEEE P802.1Qcr: Bridges and Bridged Networks
- Amendment: Asynchronous Traffic Shaping", 2017,
<https://1.ieee802.org/tsn/802-1qcr/>.
[IEEE8021TSN]
IEEE 802.1, "IEEE 802.1 Time-Sensitive Networking (TSN)
Task Group", <http://www.ieee802.org/1/>.
[IEEE8023] IEEE 802.3, "IEEE Std 802.3-2018: IEEE Standard for
Ethernet", 2018,
<http://ieeexplore.ieee.org/document/8457469>.
[LeBoudecTheory]
J.-Y. Le Boudec, "A Theory of Traffic Regulators for
Deterministic Networks with Application to Interleaved
Regulators",
<https://ieeexplore.ieee.org/document/8519761>.
[NetCalBook]
J.-Y. Le Boudec and P. Thiran, "Network calculus: a theory
of deterministic queuing systems for the internet", 2001,
<https://leboudec.github.io/netcal/>.
[PacketReorderingBounds]
E. Mohammadpour, and J.-Y. Le Boudec, "On Packet
Reordering in Time-Sensitive Networks",
<https://ieeexplore.ieee.org/document/9640523>.
[RFC2697] Heinanen, J. and R. Guerin, "A Single Rate Three Color
Marker", RFC 2697, DOI 10.17487/RFC2697, September 1999,
<https://www.rfc-editor.org/info/rfc2697>.
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[RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC
Text on Security Considerations", BCP 72, RFC 3552,
DOI 10.17487/RFC3552, July 2003,
<https://www.rfc-editor.org/info/rfc3552>.
[RFC8578] Grossman, E., Ed., "Deterministic Networking Use Cases",
RFC 8578, DOI 10.17487/RFC8578, May 2019,
<https://www.rfc-editor.org/info/rfc8578>.
[RFC9023] Varga, B., Ed., Farkas, J., Malis, A., and S. Bryant,
"Deterministic Networking (DetNet) Data Plane: IP over
IEEE 802.1 Time-Sensitive Networking (TSN)", RFC 9023,
DOI 10.17487/RFC9023, June 2021,
<https://www.rfc-editor.org/info/rfc9023>.
[RFC9055] Grossman, E., Ed., Mizrahi, T., and A. Hacker,
"Deterministic Networking (DetNet) Security
Considerations", RFC 9055, DOI 10.17487/RFC9055, June
2021, <https://www.rfc-editor.org/info/rfc9055>.
[Sch8021Qbv]
S. Craciunas, R. Oliver, M. Chmelik, and W. Steiner,
"Scheduling Real-Time Communication in IEEE 802.1Qbv Time
Sensitive Networks",
<https://dl.acm.org/doi/10.1145/2997465.2997470>.
[SpechtUBS]
J. Specht and S. Samii, "Urgency-Based Scheduler for Time-
Sensitive Switched Ethernet Networks",
<https://ieeexplore.ieee.org/abstract/document/7557870>.
[ThomasTime]
L. Thomas and J.-Y. Le Boudec, "On Time Synchronization
Issues in Time-Sensitive Networks with Regulators and
Nonideal Clocks",
<https://dl.acm.org/doi/10.1145/3393691.3394206>.
[TSNwithATS]
E. Mohammadpour, E. Stai, M. Mohiuddin, and J.-Y. Le
Boudec, "Latency and Backlog Bounds in Time-Sensitive
Networking with Credit Based Shapers and Asynchronous
Traffic Shaping",
<https://ieeexplore.ieee.org/document/8493026>.
Authors' Addresses
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Norman Finn
Huawei Technologies Co. Ltd
3101 Rio Way
Spring Valley, California 91977
United States of America
Phone: +1 925 980 6430
Email: nfinn@nfinnconsulting.com
Jean-Yves Le Boudec
EPFL
IC Station 14
CH-1015 Lausanne EPFL
Switzerland
Email: jean-yves.leboudec@epfl.ch
Ehsan Mohammadpour
EPFL
IC Station 14
CH-1015 Lausanne EPFL
Switzerland
Email: ehsan.mohammadpour@epfl.ch
Jiayi Zhang
Huawei Technologies Co. Ltd
Q27, No.156 Beiqing Road
Beijing
100095
China
Email: zhangjiayi11@huawei.com
Balázs Varga
Ericsson
Budapest
Konyves Kálmán krt. 11/B
1097
Hungary
Email: balazs.a.varga@ericsson.com
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