Internet DRAFT - draft-zhu-detnet-ldn-mapping
draft-zhu-detnet-ldn-mapping
DetNet X. Zhu
Internet-Draft J. Yu
Intended status: Informational C. Gao
Expires: 26 November 2023 Q. Xiong
ZTE Corporation
25 May 2023
LDN CYCLE MAPPING LEARNING PROCESS
draft-zhu-detnet-ldn-mapping-00
Abstract
The Large-scale Deterministic Network(LDN) technology based on cyclic
queuing and scheduling is expected to solve the scalability problem
of DetNet, and is hoped to extend the adaptive domain of DetNet to
wide area network or even backbone network. One of the keys of this
technology is to accurately obtain the cyclic mapping relationship
between adjacent nodes, based on which DetNet packets can be end-to-
end deterministically forwarded . This draft proposes a method for
LDN nodes to learn the cycle mapping relationship through sending
learning messages.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on 26 November 2023.
Copyright Notice
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document authors. All rights reserved.
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.
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions used in this document . . . . . . . . . . . . . . 4
2.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2.2. Requirements Language . . . . . . . . . . . . . . . . . . 4
3. Cycle Mapping Learning Message . . . . . . . . . . . . . . . 4
3.1. Based on special purpose message . . . . . . . . . . . . 4
3.2. Based on DetNet flow packets . . . . . . . . . . . . . . 5
3.3. Based on enhanced DetNet flow packets . . . . . . . . . . 5
4. Cycle mapping learning principle . . . . . . . . . . . . . . 6
4.1. Obtain the maximum processing delay of the DN . . . . . . 6
4.2. DN determines the ingress cycle of learning msg . . . . . 7
4.3. DN determines the message sending cycle . . . . . . . . . 7
4.4. DN cycle mapping relationship maintenance . . . . . . . . 8
5. Problems discussion in detail . . . . . . . . . . . . . . . . 9
5.1. Cycle learning based on DetNet flow packets . . . . . . . 9
5.2. Monitoring of UN and DN mapping relationships . . . . . . 11
5.3. Cycle Mapping Relationship Storage . . . . . . . . . . . 11
5.4. UN and DN concurrently support multiple cycle
templates . . . . . . . . . . . . . . . . . . . . . . . . 12
6. Security Considerations . . . . . . . . . . . . . . . . . . . 12
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12
9. Normative References . . . . . . . . . . . . . . . . . . . . 13
10. Informative References . . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14
1. Introduction
[I-D.ietf-detnet-scaling-requirements] proposes the requirements for
deterministic forwarding of services in large-scale networks.
Typical characteristics of large-scale networks include long single-
hop delay, no time sync, and large network dimensions (typically,
greater than 16 hops), etc., these requirements cannot be met by the
DetNet architecture and technology proposed by [RFC8655], because the
architecture andtechnology proposed by RFC8655 are mainly intend for
limited-scale networks. In order to provide deterministic services
in large-scale networks, the industry has proposed a variety of
improving ideas, such as [SR-TSN], [Deadline] and [TCQF], and one of
the promising and first-deployed solutions is based on the idea of
cyclic scheduling and forwarding from [IEEE802.1Qch].
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Representatives of such solutions include [DIP], etc., which are
collectively referred to as LDN schemes.
In this draft, for two adjacent nodes, one is called upstream node (
UN) and the other downstream node (DN).The cycle-mapping relationship
refers to the correspondence between the cycle label carried by the
upstream node`s egress packet and the cycle label encapsulated by the
downstream node`s egress port. The packet is forwarded under the
guidance of the cycle mapping relationship. For example, as shown in
Figure 1, if there is a cycle mapping relationship x->z between UN
and DN, when the packet with the cycle label x arrives at the
downstream node , the downstream node will obtain the downstream
egress cycle label according to the mapping relationship x->z, then z
will be encapsulated into and the packet will be scheduled and
forwarded according to the cycle slot z.
| cycle x | |
UN +-----------+-----------+
\
\ Packet
\ received with x
| V | | cycle z |
DN +-----------+ ... ... +-----------+
\
\ Packet
\ sent with z
V
Figure 1: LDN cycle forwarding paradigm
To obtain the cycle mapping relationship, we have many optional
methods, for example, one can use control plane for calculation and
configure the result to forwarding node, and one can also leave the
task to forwarding plane self-learning. In the forwarding plane
learning mode, cycle mapping learning messages are exchanged between
upstream node and downstream node, and the downstream node have to
calculate and store the cycle mapping relationship according to the
learning messages.
This draft gives the general idea, problems and corresponding
solutions for cycle mapping self-learning. This draft only considers
the general learning process of the forwarding plane , and does not
consider the underlying protocol (e.g., OAM) and protocol extension
format of the learning message, nor does it consider the interaction
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protocol extension between the control plane and the forwarding
plane. The consideration of related extensions will be described in
detail in future drafts.
2. Conventions used in this document
2.1. Terminology
LDN: Large-scale Deterministic Network
UN: Upstream Node
DN: Downstream Node
2.2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Cycle Mapping Learning Message
The cycle mapping learning process requires UN to send learning
messages to DN. No restriction is put on the detailed encapsulation
format, the sending frequency, sending times and how the downstream
node can identify the message, for example, it can be configured by
the control plane.
At least three optional cycle mapping learning message types can be
used.
3.1. Based on special purpose message
In order to clearly mark the egress cycle slot boundary, the UN can
constructs and sends special protocol messages (such as PAUSE, TWAMP)
as learning messages at the beginning and the ending of the cycle.
In order to avoid occupying too much bandwidth, special messages are
sent at a reasonable frequency, for example, sent once a physical
cycle. The start time of cycle learning may be the time of system
startup, controller configuration time, user triggering and so on.
When a learning message arrives at a DN, it can be used to clearly
mark the boundary of the UN egress cycle at local, which is called a
UN virtual cycle.
Advantages: easy to mark cycle boundaries, out-of-band, flexible and
controllable;
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Disadvantages: Bandwidth consumption is required, and special message
construction brings hardware overhead;
3.2. Based on DetNet flow packets
Before DetNet flow packets enters the network, the cycle mapping
relationship does not work and is meaningless. At the same time, in
order to avoid bandwidth consumption in the active mode, learning can
be based on actual DetNet flow packets, because when deterministic
packets are sent from the source node, they will inevitably carry the
egress cycle label of the UN egress. There is no restriction on the
packet type, for example, it may be an SRv6 extended packet or an SR-
MPLS extended packet.
Advantages: In-band mode can realize packets multiplexing;
Disadvantages: The number and time of sending actual flow packets are
uncertain, resulting in uncertain positions of flow packets within
the cycle, and cannot be directly used to calibrate the cycle
boundary;
3.3. Based on enhanced DetNet flow packets
In this manner, the field of the flow packet is extended, and the
value of "deviation from the beginning of the cycle slot" is
additionally encapsulated, which can be used to clearly identify the
position of the flow packet in the UN egress cycle, thereby assisting
the DN to determine the virtual cycle boundary where the flow packet
is located.
Advantages: In-band mode, multiplexing can be realized, and
downstream nodes are easy to learn;
Disadvantage: The purpose of the extra encapsulation field is only
for periodic learning, occupying the effective field of the business
message. Both encapsulation and decapsulation logic need to be
modified, increasing hardware resource consumption.
According to specific scenarios, one of the above methods can be
selected for cycle mapping learning messages.
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4. Cycle mapping learning principle
The cycle mapping self-learning process is carried out by the DN,
relying on the cycle mapping learning message sent by the UN. It is
assumed that the number of queues and cache capacity configured by
the UN are sufficient. The functions of packet routing and
forwarding are independent from learning process described here and
will not be described.
4.1. Obtain the maximum processing delay of the DN
According to the latency reference model proposed in the [RFC9320],
the node regulation subsystem must be able to absorb the maximum node
processing delay. Typically, the processing delay variation scope
only depends on the hardware implementation of a specific device,
including shaping, table lookup algorithm, the packet counter
resources and etc. For a specific network device, the maximum value
of processing delay is determined at the product, and usually
includes two components, namely the packet length related part and
packet length independent part. For instance, packet-length-
independent part include forwarding table lookup, CRC check, etc.,
and the packet length-related part includes packet cache and
scheduling and so on. If the processing delay is known and can be
queried by the self-learning module, no active OAM probing is
required.
Though processing delay may depend on enabled functions (such as
shaping, packet slicing) and packet length, the processing delay
range can also be obtained through some active detection tools.
Specifically, for a given device with enabled function sets, one can
randomly send packets that meet the packet length limit and up to
wire-speed, and then it is easy to measure the maximum processing
delay. Further, the delay value can be configured in a device-
specific field , and then can be used by the cycle mapping self-
learning module.
The processing delay can also be configured by the control plane as
needed. For example, when the control plane needs to control the
end-to-end delay of the LDN domain, it may actively increase the
single-hop process delay of the device.
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4.2. DN determines the ingress cycle of learning msg
Suppose that the special purpose cycle learning message described in
Section 2.1 is sent by UN, it is easy for DN to correctly identify
the boundary of UN egress virtual cycle slot. Different from the
IEEE802.1Qch mechanism, since the upstream and downstream nodes are
not time synchronized and there are long links, the packets carrying
the same UN egress cycle label x, may not necessarily fall into the
same DN cycle y-1, in fact some packets may also fall into cycle y,
as shown in Figure 2.
| cycle x | |
UN +-----------------+-----------------+
\ \
\ \
\ learning msg \learning msg
\ P1 received \P2 received
\ in cycle y-1 \in cycle y
| V | V | |
DN +-----------------+-----------------+-----------------+
y-1 y y+1
Figure 2: Figure 2: DN determines ingress cycle
In order to correctly obtain the egress cycle number of the
downstream node, it is necessary to take the arrival time of the
latest packet belonging to UN egress cycle x as the baseline, that
is, y as the final receiving cycle. In the implementation, it is
necessary to have a table storing the cycle mapping relationship
between the UN egress and the DN ingress cycle label. When the first
learning message P1 carrying the cycle label x is received, the
mapping relationship x->y-1 is obtained and stored. When the second
learning message carrying cycle label x is received , UN will obtain
x->y relationship and update the table.
4.3. DN determines the message sending cycle
The DN calculates the local ingress->egress port cycle mapping
relationship according to the maximum processing delay obtained in
Section 4.1, as shown in Figure 3.
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UN | cycle x | |
egress +-----------------+-----------------+
\ \
\P1(x) \P2(x)
\ \
V V
<--virtual cycle-->
DN ingress+-----------------+--*--------------+ ....+-----------------+
| | * | | |
| | <-max process delay->| |
| cycle y-1 | cycle y | | * cycle z |
DN egress +-----------------+-----------------+ ....+-*---------------+
\ \
\P1(z) \P2(z)
\ \
V V
Figure 3: DN determines egress cycle
The calculation method of the egress cycle label of DN is no very
simple and intuitive, it needs to consider the cycle slot size, the
slot offset of the P2 message falling in the cycle and the maximum
processing delay of UN at the same time. Assuming that the cycle
slot size is T and the receiving cycle is y, the formula is as
follows:
UN egress cycle z=y+ ceil((processing delay-T+offset)/T) + 1
In formula above, ceil means to round-up the division result.
In particular, if (processing delay-T+offset) happens to be an
integer multiple of T, in order to avoid the last flow packet of
cycle x sent to thez queue cannot be forwarded in time and cause an
error, because, for example, hardware implementationprecision, z can
be proactively increased by 1 for redundant configuration .
Then can get the DN ingress and egress cycle mapping relationship
y->z.
4.4. DN cycle mapping relationship maintenance
After obtaining the mapping relationship x->y from the upstream
egress to the downstream ingress and the mapping relationship y->z
from the downstream ingress to the egress, the mapping relationship
x->z can be easily obtained. Since there are multiple circular
queues, assuming that the number of circular queues of template T is
N, the final cycle mapping relationship can be further obtained:
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(x+i) MOD N -> (z+i) MOD N
For example, the UN and DN concurrently maintain a eight-cycle-queue
template. Through learning, the cycle mapping relationship between
the upstream egress and the downstream egress port is 4->6, then the
mapping relationship maintained at the DN is:
4->6, 5->7, 6->0, 7->1,0->2,1->3,2->4,3->5.
5. Problems discussion in detail
5.1. Cycle learning based on DetNet flow packets
Among the three cycle self-learning messages mentioned in Section 2,
both 3.1 and 3.3 can accurately identify the virtual cycle boundary
where the message is located at the downstream node. When learning
based on flow packets proposed in 3.2, since the arrival frequency
and time of flow packets are random in cycle slot, flow packets
cannot be directly used to accurately identify cycle boundaries.
Considering the scenario shown in the figure 4 upper half, since all
packets of cycle 1 arrive at the downstream node, they all fall in
the cycle 3, so the mapping relationship of UN egress and DN ingress,
1->3 is formed. In Figure 4 lower half, when the number of service
packets increases, some packets fall into cycle 4. According to
Section 4.2, it must be considered that the packet receiving cycle is
4, and the mapping relationship is adjusted to 1->4.
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| cycle 1 | |
UN +-----------------+-----------------+
\ \ \ \
\ \ \ \
\ \ \ \
\ \ \ \
\ \ \ \
| V V V V | | |
DN +-----------------+-----------------+-----------------+
3 4 5
| cycle x | |
UN +-----------------+-----------------+
\ \ \ \\ \ \ \
\ \ \ \\ \ \ \
\ \ \ \\ \ \ \
\ \ \ \\ \ \ \
\ \ \ \\ \ \ \
| V V V VV| V V V | |
DN +-----------------+-----------------+-----------------+
3 4 5
Figure 4: Ambiguous ingress cycle example
Which add a T to the single-hop jitter after adjustment in figure 4 .
From the perspective of the entire service flow, the end-to-end
jitter requirement of 2T cannot be met.
Idea 1 . When learning the mapping relationship for the first time,
if all the UN egress cycle packets fall into the same DN ingress
cycle, for example, fall into cycle y, then take the automatic
adjustment and supposed it to fall into cycle y+1. At this time, by
introducing a redundancy delay of T, the uncertainty introduced by
flow packets can be avoided . The end-to-end delay increases by N*T,
where N is the number of hops, and the max end-to-end jitter is still
2T.
Idea 2. Reshape the business message, and if there is more than flow
packets in the cycle, since the queue is a FIFO, there will always be
a flow packets to be sent at the beginning of the cycle, so only one
message needs to be reserved and be used to mark the end of the cycle
There is always a message at every moment. This method does not
affect packet forwarding characteristics and bandwidth occupation.
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Idea 3. The network construction is divided into two phases: testing
and operation. When the flow packets requests access, it is required
to send test flow packets at random or full flow for a predefined
period. After the period, actual DetNet flow packets are sent
according to the requirements of the traffic characteristics.
5.2. Monitoring of UN and DN mapping relationships
After the cycle mapping relationship is established, flow packets can
directly search the mapping table to obtain the egress cycle label,
and then deterministic forwarding can be obtained. However, when
some problems occur, for example, the fiber switching occurs ,
forwarding node restarts, link attenuation occurs, or the learning
process is re-triggered by the control plane or user, the mapping
relationship of the upstream and downstream nodes may change. If
such anomalies are not detected in time, errors will occur in the
cycle mapping process, and DetNet flow determinism cannot be
guaranteed.
In order to detect changes in time and update the mapping
relationship,for each receiving flow packets, the DN still needs to
detect ingress cycle, and compare it with the cycle mapping
relationship maintained in Section 4.4. If it is inconsistent, it
indicates that cycle mapping relationship has changed. For example,
if the mapping relationship 2->5 is maintained in 4.4, when a UN flow
packet is received and the ingress cycle of the DN is 4 or 5, it is
considered correct, and in other cases it is considered problems has
take place, it is necessary to re-execute the cycle mapping
relationship calculation process described in Sections 4.
5.3. Cycle Mapping Relationship Storage
Consider the situation where multiple upstream nodes establish a
cycle mapping to a single downstream node . When the downstream node
maintains the mapping relationship, it needs to ensure the uniqueness
of the table key value.
i.For point-to-point links, you can simply use {DN ingress port, DN
egress port} as the key value;
ii.In the case of LAN (many-to-many or many-to-one) , multiple UN may
reach Dn through the same ingress port, as shown in the figure 5, at
this time, the downstream node entry is the same for multiple
upstream nodes and cannot be used as a key value. Considering that
in routing and forwarding, the MAC address of the upstream node will
be carried in the message, so the MAC address can uniquely identify
the upstream node. At this time, the UN egress source mac can be
added to the key value:{mac, DN ingress port , DN egress port}.
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/-----\
| UN1 | ________
+--+--+ _____ / \
| / \__/ \
| / \_____
| / \_____
+-->| \
| |
+-->| LAN |
| \ | /-----\
| \ |------>| DN1 |
| \ | +--+--+
/-----\ \ /
| UN2 | \___ /
+--+--+ \ /
\_____/ \___________/
Figure 5: UN and DN connected by LAN
5.4. UN and DN concurrently support multiple cycle templates
If the upstream and downstream nodes support multiple cycle templates
at the same time, for each cycle template, a mapping relationship can
be formed through cycle self-learning process described in this
draft, and the process of cycle mapping self -learning is exactly the
same as that of a single cycle template.
In order to identify the periodic template at the downstream node, in
addition to the time slot number, the periodic template T needs to be
encapsulated in the learning message . The downstream node first
extracts T and then performs learning based on the corresponding
template. In addition, after the periodic self-learning calculation
is completed, the entry key needs to be added with a template when
storing, that is, {T, mac, DN ingress port , DN egress port} .
6. Security Considerations
TBA
7. IANA Considerations
TBA
8. Acknowledgements
TBA
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9. Normative References
[Deadline] Peng, S., Tan, B., and P. Liu, "Deadline Based
Deterministic Forwarding", Work in Progress, Internet-
Draft, draft-peng-detnet-deadline-based-forwarding-05, 1
March 2022, <https://www.ietf.org/archive/id/draft-peng-
detnet-deadline-based-forwarding-05.txt>.
[IEEE802.1Qch]
IEEE, "IEEE Standard for Local and metropolitan area
networks -- Bridges and Bridged Networks - Amendment 29:
Cyclic Queuing and Forwarding", IEEE 802.1Qch-2017,
DOI 10.1109/IEEESTD.2017.7961303, 28 June 2017,
<https://doi.org/10.1109/IEEESTD.2017.7961303>.
[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>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[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>.
[TCQF] Eckert, T. T., Bryant, S., Malis, A. G., and G. Li,
"Deterministic Networking (DetNet) Data Plane - Tagged
Cyclic Queuing and Forwarding (TCQF) for bounded latency
with low jitter in large scale DetNets", Work in Progress,
Internet-Draft, draft-eckert-detnet-tcqf-02, 6 November
2022, <https://datatracker.ietf.org/doc/html/draft-eckert-
detnet-tcqf-02>.
10. Informative References
[DIP] Qiang, L., Geng, X., Liu, B., Eckert, T. T., Geng, L., and
G. Li, "Large-Scale Deterministic IP Network", Work in
Progress, Internet-Draft, draft-qiang-detnet-large-scale-
detnet-05, 2 September 2019,
<https://datatracker.ietf.org/doc/html/draft-qiang-detnet-
large-scale-detnet-05>.
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[I-D.ietf-detnet-scaling-requirements]
Liu, P., Li, Y., Eckert, T. T., Xiong, Q., Ryoo, J.,
zhushiyin, and X. Geng, "Requirements for Scaling
Deterministic Networks", Work in Progress, Internet-Draft,
draft-ietf-detnet-scaling-requirements-01, 1 March 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-detnet-
scaling-requirements-01>.
[RFC9320] Finn, N., Le Boudec, J.-Y., Mohammadpour, E., Zhang, J.,
and B. Varga, "Deterministic Networking (DetNet) Bounded
Latency", RFC 9320, DOI 10.17487/RFC9320, November 2022,
<https://www.rfc-editor.org/info/rfc9320>.
[SR-TSN] Stein, Y. (., "Segment Routed Time Sensitive Networking",
Work in Progress, Internet-Draft, draft-stein-srtsn-01, 29
August 2021, <https://www.ietf.org/archive/id/draft-stein-
srtsn-01.txt>.
Authors' Addresses
Xiangyang Zhu
ZTE Corporation
No.50 Software Avenue
Nanjing
Jiangsu, 211100
China
Email: zhu.xiangyang@zte.com.cn
Jinghai Yu
ZTE Corporation
Nanjing
Jiangsu,
China
Email: yu.jinghai@zte.com.cn
Chenqiang Gao
ZTE Corporation
Nanjing
China
Email: gao.chenqiang@zte.com.cn
Quan Xiong
ZTE Corporation
Wuhan
China
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Email: xiong.quan@zte.com.cn
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