DetNet Z. Han
Internet-Draft R. Pang
Intended status: Standards Track C. Liu
Expires: 23 August 2025 China Unicom
J. Yan
X. ZHU
ZTE Corporation
19 February 2025
Anomalous Packets Handling for DetNet
draft-han-detnet-anomalous-packets-handling-00
Abstract
In deterministic networking (DetNet), there may be resource conflicts
at the flow aggregation nodes, resulting in network anomalies. The
existing mechanisms for handling anomalous packets in the data plane
are crude, such as discarding or processing them as BE flows, so the
network performance may be worse than applying traditional QoS.
Therefore, in order to handle the anomalous traffic, the data plane
should implement an enhanced handling mechanism.
This document proposes an anomalous packet handling solution for
anomalous traffic in DetNet. This solution includes two policies:
the packet squeezing policy and the packet degrading policy, which
can be applied flexibly to a variety of queuing mechanisms, thereby
ensuring that network traffic for deterministic services is
preferentially scheduled in anomalous situations.
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
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on 23 August 2025.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Anomalous Forwarding Detection . . . . . . . . . . . . . . . 4
4. Anomalous Packets Handling Policy . . . . . . . . . . . . . . 4
4.1. Squeezing Policy . . . . . . . . . . . . . . . . . . . . 5
4.2. Degrading Policy . . . . . . . . . . . . . . . . . . . . 7
4.3. Squeezing Policy and Degrading Policy . . . . . . . . . . 8
5. Anomalous Packets Handling Solution . . . . . . . . . . . . . 8
5.1. Policy Selection and Configuration . . . . . . . . . . . 8
5.2. Anomalous Information Reporting . . . . . . . . . . . . . 9
5.3. Anomalous Packets Handling Procedure . . . . . . . . . . 9
6. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
7. Security Considerations . . . . . . . . . . . . . . . . . . . 12
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
10.1. Normative References . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
1. Introduction
DetNet is capable of providing real-time application services with
deterministic guarantees such as bounded latency, low jitter, and low
packet loss rate, as per [RFC8655]. One of the major technologies of
DetNet is resource allocation, as per [RFC8938]. Resource allocation
reduces the packet loss and jitter caused by network congestion by
allocating available resources to specified DetNet flows. The
control plane orchestrates the paths of DetNet flows to avoid
resource conflicts, while the data plane transmits DetNet flows based
on the orchestration result from the control plane, with traffic
shaping, flow admission control, and encapsulation of forwarding
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information, etc., to maintain QoS.
Each node in the end-to-end path may serve as an aggregation node.
Aggregated flows that belong to the same traffic class will share the
reserved resources at the outgoing port. Ideally, the transmission
of each flow within the same traffic class strictly conforms to the
scheduling of the control plane, thus being able to meet the strict
requirements of a narrowly deterministic network. However, due to
the diversity of deterministic flows—such as occasional microbursts
and packet size fluctuations—this ideal case is often difficult to
fulfill. Allocating resources based on the maximum packet size may
lead to waste, whereas basing them on the average size may cause
resource conflicts. Furthermore, software and hardware limitations
can introduce additional discrepancies. For instance, algorithmic
flaws in the control plane may lead to resource conflicts in extreme
cases, and high-priority protocol messages (e.g., ARP packets under
abnormal conditions) in the data plane may preempt service packets,
causing delays for lower-priority flows.
To address these network anomalies, the control plane should properly
schedule resources to avoid resource conflict at the aggregation
nodes. As defined in [RFC8655], it proposes a service protection
solution such as PREOF based on multi-path transmission. Although
PREOF can prevent performance reduction by reserving a large amount
of redundant resources for the specified service flows, it may cause
a serious waste of resources or even a light load in the network,
which further diminishes the advantage of deterministic technologies.
In the data plane, the existing mechanisms are relatively simple and
crude. For example, the data plane may choose to discard packets
directly or buffer them until the resources allocated to its traffic
class become available. Both of the solutions will result in even
worse QoS than that of BE flows.
Therefore, the processing of anomalous packets from deterministic
services should be automatically optimized in the data plane. The
processing of anomalous packets is an indispensable part of the
future implementation and application of the entire deterministic
network technology.
This document proposes an anomalous packet handling policy and
solution for DetNet, supporting two anomalous packet handling
policies, packet squeezing and packet degrading, which can be enabled
individually or together. The control plane and users can configure
the policies’ activation and associated parameters. Detailed
procedures for implementing these policies across various queuing
mechanisms are also provided.
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1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
2. Terminology
The terminology is defined as [RFC8655].
3. Anomalous Forwarding Detection
The real-time detection in the data plane aims to identify anomalous
forwarding behaviors. Upon detection, enhanced processing policies,
such as packet squeezing and degrading, are applied to ensure that
deterministic flows are scheduled preferentially, even under abnormal
conditions.
The detection process is closely associated with the queuing
mechanisms employed. Typically, for
TQF[I-D.peng-detnet-packet-timeslot-mechanism], the target output
timeslot of a packet at the current node can be determined based on
the upstream timeslot label carried by the packet and the basic
timeslot mapping.
For EDF[I-D.peng-detnet-deadline-based-forwarding], the target output
timeslot at the current node is calculated based on the budget and
delay target carried in the packet. Each output timeslot is
associated with a queue. When a packet arrives, it is enqueued in
the corresponding queue. For CQF, if the current scheduling timeslot
is 1 and the target timeslot is 5, the packet for target output
timeslot 5 will be preemptively placed into the corresponding queue.
Before the packet enters the output queue, the queue depth is
checked. If it does not exceed the allowable packet capacity of the
queue, the packet is enqueued normally. If it exceeds the allowable
capacity, it indicates an anomaly.
4. Anomalous Packets Handling Policy
The proposed solution supports two enhanced anomalous packet handling
policies in the data plane:
* Squeezing Policy: Temporarily delays anomalous packets by
“squeezing” them into the next timeslot while retaining their
original scheduling information.
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* Degrading Policy: Redirects packets to a lower-priority queue and
modifies the scheduling parameters when the accumulation of
anomalous packets exceeds a predefined threshold.
These policies provide flexibility in terms of activation; they can
be enabled concurrently, selectively, or not at all. If neither
policy is enabled, the default mechanism, such as discarding the
packets or treating them as a BE flow will be utilized.
4.1. Squeezing Policy
The data plane can support the squeezing policy by allowing the
configuration of the squeezing threshold. When anomalous traffic
causes the queue occupancy to exceed its permitted capacity—but
remains below the squeezing threshold—the system applies the
squeezing policy. Specifically, the system will enqueue the packets
and record the number of squeezed bits. According to the squeezing
policy, packets that can not be sent within the allocated time should
be squeezed into the next timeslot until the queue gets empty. It
should be noted that the squeezing policy is compatible with various
queuing mechanisms, although it may not be available in all.
Regarding different queuing mechanisms, the implementation of the
squeezing policy varies.
Assume that each timeslot permits 4000 bits, and the squeezing
threshold is set to 2000 bits. Consider a service flow where the
size of each packet is fixed at 1000 bits. Packets 1 to 4 are
assigned to timeslot 1, while packets numbered 5 to 7 are assigned to
timeslot 2. Due to the presence of aggregated traffic, assume that
the current depth of queue 1 is 2000 bits.
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|<----timeslot1---->|<----timeslot2---->|<----timeslot3---->|
+---------+---------+-------------------+-------------------+
|/////////| | | |
+---------+---------+-------------------+-------------------+
packet sequence of the flow
+----+----+----+----+----+----+----+
| P7 | P6 | P5 | P4 | P3 | P2 | P1 | --->
+----+----+----+----+----+----+----+
P1 P2 P3 P4 -> target timeslot ： 1
P5 P6 P7 -> target timeslot ： 2
|
\/
+---------+----+----+----+----+
queue 1 |/////////| P1 | P2 | P3 | P4 |
+---------+----+----+----+----+
+----+----+----+
queue 2 | P5 | P6 | P7 |
+----+----+----+
|-----timeslot1-----|-----timeslot2-----|-----timeslot3-----|
+---------+----+----+----+----+----+----+----+--------------+
|/////////| P1 | P2 | P3 | P4 | P5 | P6 | P7 | |
+---------+----+----+----+----+----+----+----+--------------+
|<------->|
squeezing threshold
Figure 1: Squeezing policy based on timeslot-based queuing mechanism
Figure 1 illustrates the processing of packets in the service flow
with serial numbers 1 through 7. Packets 1 and 2 are put into queue
1 sequentially. Therefore, queue 1 has reached the permitted
carrying threshold of 4000 bits. When packets 3 and 4 arrive, they
are determined to be anomalous packets.
Since the squeezing policy is enabled with a threshold of 2000 bits,
packets 3 and 4 are enqueued in queue 2, while retaining their
timeslot label of 1. Based on the squeezing policy, packets 3 and 4
are squeezed into timeslot 2 for transmission. At this point, the
buffer depth of the queue increases to 2000 bits. Subsequently,
packets 5, 6, and 7 which are targeted for timeslot 2, are allowed to
enter queue 2. However, when queue 2 reaches its upper limit of 4000
bits, packet 7 is marked as an anomalous packet. It is enqueued in
queue 2 and postponed for transmission in timeslot 3.
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At the aggregation node, continuous bursts may lead to successive
squeezing, which in turn may trigger a chain reaction. Without
safeguards, packets squeezed from one timeslot into the next may
accumulate indefinitely, undermining deterministic transmission
guarantees. To prevent unbounded accumulation caused by consecutive
squeezing, the following two safeguard mechanisms are introduced:
* Synchronization Threshold Mechanism: A "synchronization threshold"
is defined as the maximum number of consecutive timeslots that may
be affected by squeezing. For example, if the threshold is set to
N timeslots, once squeezing has occurred over N consecutive slots,
the current queue must be re-synchronized with the timeslot
schedule. This re-synchronization restores scheduling consistency
and prevents indefinite delay accumulation.
* Exponential Decay Mechanism: In scenarios with consecutive
squeezing, the allowed squeezing capacity decays exponentially.
Specifically, the first affected timeslot permits a predefined
squeezing capacity T; for each subsequent consecutive timeslot,
the allowed squeezing capacity is reduced by 50% compared to the
previous slot. This decay continues until the permitted capacity
falls below the minimum packet size, at which point further
squeezing is disallowed, and alternative handling (e.g.,
degrading) is triggered.
|----timeslot1----|----timeslot2----|----timeslot3----|----timeslot4----|
|---------queue1---------|-----queue2------|----queue3-----|---queue4---|
|<--------------------------------------------------------------------->|
synchronization threshold
Figure 2: Illustration of synchronization threshold
4.2. Degrading Policy
The data plane supports the degrading policy and allows for the
configuration of degrading parameters, and can be used either in
combination or independently. When the degrading policy is used in
conjunction with the squeezing policy, it processes anomalous traffic
that exceeds the squeezing threshold. The degrading policy can also
be deployed on its own. For anomalous packets that go beyond the
allowed buffer capacity, the degrading policy can be directly
applied.
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For EDF, packets are delayed based on the target sending time. The
delayed period can be flexibly configured due to the level of
busyness at the current outgoing port. For TAS/CQF and their
variations, packets are redirected to a queue with a lower priority.
4.3. Squeezing Policy and Degrading Policy
When both squeezing and degrading policies are enabled, the node
shall perform the following steps:
1. Upon packet arrival, determine whether is anomalous packet.
2. If the abnormal accumulation is below the squeezing threshold T,
process the packet by applying the squeezing policy.
3. If the abnormal accumulation exceeds T (or if consecutive
squeezing has reached the synchronization threshold N or the
exponential decay limit), immediately trigger the degrading
policy. This involves modifying the packet’s internal scheduling
parameters (as detailed above) and redirecting it to the
appropriate lower-priority queue.
5. Anomalous Packets Handling Solution
5.1. Policy Selection and Configuration
The following anomaly handling policies are involved in this
document:
* Degrading Policy: Process packets according to the degrading
policy, which includes degrading the packets to be treated as BE
flow.
* Squeezing Policy: Process packets according to the squeezing
policy. This policy provides temporary capacity expansion to
avoid data loss due to unexpected traffic.
* Postponement Policy: Postpone packets to the next cycle.
* Redirection Policy: Redirect packets to a regular QoS queue.
* Discarding Policy: Discard anomalous packets.
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If the data plane does not enable either the squeezing or degrading
policy, or if neither policy is applicable, anomalous packets will be
processed by the existing default methods, such as discarding. When
the data plane supports multiple anomalous packets handling policies,
the enabled policies and related parameters can be configured by the
control plane.
5.2. Anomalous Information Reporting
Once the data plane automatically handles anomalies using either the
squeezing policy or the degrading policy, it should promptly report
these anomalies to the controller. This enables the controller to
perceive detailed insights into the network anomalies and take
appropriate actions, such as re-orchestration, flow entry re-
configuration, resource expansion, etc. In addition to reporting to
the controller, the data plane should also transmit the anomaly
information to the downstream nodes. This allows downstream nodes
adjust their forwarding behavior or restore the original parameters
of the packets according to the received anomaly information. The
anomaly information reported by the data plane includes, but is not
limited to:
* Basic information: node ID, port ID, etc.
* Anomalous packet information: flow ID and packet sequence number,
etc.
* Anomalous packet handling policy information:
- Policy Type: Specifies the handling policy employed, which
could be the squeezing policy, the degrading policy, or other
default policies (e.g., discarding).
- Related parameters: For squeezing policy: Includes data such as
the number of squeezed bits and the quantity of squeezed
packets. For the degrading policy: Includes data such as the
priority levels before and after degrading, and the number of
degraded packets. For default policies: Includes information
such as the number of discarded packets or treated as BE flows.
5.3. Anomalous Packets Handling Procedure
When a node in the data plane receives a DetNet packet, it first
checks for anomalies. If an anomaly is detected, the node initiates
the procedure for anomalous packets.
1. Identify Supported Policies. The node needs to determine which
anomalous packets handling policies are supported locally.
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2. Policy-based Packet Processing.
* No Enhanced Policies Enabled: If the enhanced anomalous
packets handling policies (i.e., the squeezing policy and the
degrading policy) are not enabled, the packets will be
processed by the default mechanisms which may be directly
discarding, treating the packets as BE flow, processing them
in a normal QoS queue, or postponing them to the next period.
* Single Policy Enabled: Process the anomalous packet using the
enabled policy.
* Both Policies Enabled: If both the squeezing policy and
degrading policy are enabled, the local node first checks
whether the number of anomalous packets exceeds the squeezing
threshold. If not, process the packet using the squeezing
policy; otherwise, apply the degrading policy.
3. Information Transmission
After processing the anomalous packets, the node sends the anomaly
information to the controller and/or the downstream node.
6. Example
This illustrates the anomaly detection and handling policy in the
forwarding plane when the TQF is employed.
It is assumed that TQF mechanism supports three cycles (A, B, and C)
at the egress ports. In these cycles, the timeslot size increases in
powers of 2 while the number of timeslots decreases in powers of 2.
Cycle A supports eight queues, and in addition, a low-priority BE
queue is provided. For Cycle A, the timeslot mapping is defined as 0
-> 5; for the Cycle B, the mapping is 0 -> 3. It is assumed that
each TQF timeslot in Cycle A allows a maximum capacity of 10,000
bits, Cycle B 20,000 bits, and Cycle C 40,000 bits. When the queue
depth of Cycle A exceeds 10,000 bits, it indicates that an abnormal
condition has occurred.
Furthermore, the control plane is configured to enable the squeezing
policy on the forwarding plane with a squeezing threshold set to
15,000 bits and to enable the degrading policy, which is configured
in a stepwise degrading mode.
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Consider a certain service flow where each packet is 1,000 bits in
size. Packets 1 to 10 use cycle cycle A and carry a timeslot value
of 0; packets with sequence numbers 11 to 15 also use cycle cycle A,
but carry a timeslot value of 2. When packet 1 arrives at the node,
the current queue depth of timeslot 5 is 8,000 bits, and that of
timeslot 7 is 0 bits.
Processing Procedure:
packet sequence (from right to left)
+---+---+---+---+---+---+--+--+--+--+--+--+--+--+--+
|P15|P14|P13|P12|P11|P10|P9|P8|P7|P6|P5|P4|P3|P2|P1| --->
+---+---+---+---+---+---+--+--+--+--+--+--+--+--+--+
P1 P2 P3 P4 P5 P6 P7 P8 P9 P10 : Cycle A timeslot 0->5
P11 P12 P13 P14 P15 ：Cycle A timeslot 2->7
|
\/
Cycle A
+-----------+--+--+--+--+--+--+--+
queue 5 |///////////|P1|P2|P3|P4|P5|P6|P7|
+-----------+--+--+--+--+--+--+--+
+---+---+---+---+---+
queue 7 |P11|P12|P13|P14|P15|
+---+---+---+---+---+
Cycle B
+--+--+---+
queue 3 |P8|P9|P10|
+--+--+---+
Cycle A
|------timeslot5------|------timeslot6------|------timeslot7------|
+---------------+--+--+--+--+--+--+--+------+---+---+---+---+---+-|
|///////////////|P1|P2|P3|P4|P5|P6|P7| |P11|P12|P13|P14|P15| |
+---------------+--+--+--+--+--+--+--+------+---+---+---+---+---+-|
Cycle B
---timeslot2----------|-----------------timeslot3-----------------|
+---------------------+--+--+---+---------------------------------+
| |P8|P9|P10| |
+---------------------+--+--+---+---------------------------------+
Figure 3: Example of Using the Anomalous Packets Handling
Mechanism with TQF
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When packets 1 and 2 are enqueued into queue 5 according to the Cycle
A timeslot mapping 0 -> 5, the depth of queue 5 reaches 10,000
bits.Upon the arrival of packet 3, if it were to be enqueued using
the same mapping (0 -> 5), the queue depth would exceed the
10,000-bit threshold, thereby indicating the presence of abnormaly.
Since the squeezing policy is enabled with a threshold of 15,000
bits, packets 3 to 7 are processed in squeezing mode and are enqueued
into queue 5, retaining the output timeslot label 5.
When packet 8 arrives, enqueuing it in queue 5 would cause the
cumulative bits to exceed the 15,000-bit squeezing threshold.
Consequently, the degrading policy is triggered. Packets 8 to 10 are
degraded from Cycle A to Cycle B. Based on the Cycle A transmission
timeslot value(0) carried in the packet, which is converted to Cycle
B transmission timeslot 0, the Cycle B mapping (0 → 3) is applied so
that packets 8–10 are enqueued into Cycle B’s Queue 3. Packets 11 to
15 mapped using timeslot 2 -> 7, are enqueued normally as the queue
depth remains within the 10,000-bit capacity.
7. Security Considerations
TBA
8. IANA Considerations
TBA
9. Acknowledgements
TBA
10. References
10.1. Normative References
[I-D.peng-detnet-deadline-based-forwarding]
Peng, S., Du, Z., Basu, K., cheng, Yang, D., and C. Liu,
"Deadline Based Deterministic Forwarding", 20 June 2024,
<https://datatracker.ietf.org/doc/html/draft-peng-detnet-
deadline-based-forwarding-10>.
[I-D.peng-detnet-packet-timeslot-mechanism]
Peng, S., Liu, P., Basu, K., Liu, A., Yang, D., and G.
Peng, "Timeslot Queueing and Forwarding Mechanism", 20
June 2024, <https://datatracker.ietf.org/doc/html/draft-
peng-detnet-packet-timeslot-mechanism-07>.
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[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>.
[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>.
[RFC8938] Varga, B., Ed., Farkas, J., Berger, L., Malis, A., and S.
Bryant, "Deterministic Networking (DetNet) Data Plane
Framework", RFC 8938, DOI 10.17487/RFC8938, November 2020,
<https://www.rfc-editor.org/info/rfc8938>.
Authors' Addresses
Zhengxin Han
China Unicom
Beijing
China
Email: hanzx21@chinaunicom.cn
Ran Pang
China Unicom
Beijing
China
Email: pangran@chinaunicom.cn
Chang Liu
China Unicom
Beijing
China
Email: liuc131@chinaunicom.cn
Jinjie Yan
ZTE Corporation
China
Email: yan.jinjie@zte.com.cn
Xiangyang Zhu
ZTE Corporation
China
Email: zhu.xiangyang@zte.com.cn
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