Hierarchical methods of computing metrics distribution
draft-yi-cats-hierarchical-metric-distribution-02
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| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Authors | Xinxin Yi , Naihan Zhang | ||
| Last updated | 2025-09-11 | ||
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draft-yi-cats-hierarchical-metric-distribution-02
CATS X. Yi, Ed.
Internet-Draft N. Zhang, Ed.
Intended status: Standards Track China Unicom
Expires: 16 March 2026 12 September 2025
Hierarchical methods of computing metrics distribution
draft-yi-cats-hierarchical-metric-distribution-02
Abstract
This document analyzes the necessarity of setting hierarchical
methods of computing metrics distribution. Besides, we propose the
workflow of hierarchical metric distribution for different CATS
frameworks.
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This Internet-Draft will expire on 16 March 2026.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 2
1.2. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 3
3. Definition and requirements of hierarchical metric
distribution . . . . . . . . . . . . . . . . . . . . . . 3
4. Optional hierarchical parameters . . . . . . . . . . . . . . 5
4.1. Geographical distance . . . . . . . . . . . . . . . . . . 6
4.2. Performance of service sites . . . . . . . . . . . . . . 6
4.3. Number of service sites . . . . . . . . . . . . . . . . . 6
4.4. Other Options . . . . . . . . . . . . . . . . . . . . . . 6
5. Workflow of hierarchical metric distribution . . . . . . . . 6
5.1. Distributed model . . . . . . . . . . . . . . . . . . . . 6
5.2. Centralized model . . . . . . . . . . . . . . . . . . . . 7
5.3. Hybrid model . . . . . . . . . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 7
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
8. Normative References . . . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
The path computation needs to process both network and computing
metrics in CATS. As described in [I-D.ietf-cats-framework], after
the computing metrics are collected, they will be distributed to CATS
Path Selector (C-PS) for path computation. The C-PS can be
integrated into ingress CATS-Forwarders or deployed as a functional
component of a centralized controller. Computing metrics are defined
in [I-D.ietf-cats-metric-definition]. And
[I-D.ietf-cats-usecases-requirements] describes the importance of the
representation and encoding of computing metrics. As service scale
increases, the data amount reported to C-PS and size of routing table
increases, which will bring greater processing pressure to network
devices. As a result, the service quality will be affected.
Therefore, it is necessary to set a hierarchical method of computing
metric distribution between service site and different C-PSes. The
hierarchical method can be set according to geographical distance or
performance of service sites, etc.
1.1. Terminology
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1.2. 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.
2. Conventions and Definitions
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. This document uses terms defined in
[I-D.ietf-cats-framework]. We list them below for clarification.
*Computing-Aware Traffic Steering (CATS): An architecture that takes
into account the dynamic nature of computing resources and network
state to steer service traffic to a service instance. This
dynamicity is expressed by means of relevant metrics.
*Ingress CATS-Forwarder: An entity that steers service-specific
traffic along a CATS-computed path that leads to an Egress CATS-
Forwarder that connects to the most suitable service site that host
the service contact instance selected to satisfy the initial service
request.
*Egress CATS-Forwarder: An entity that is located at the end of a
CATS-computed path and which connects to a CATS-serviced site.
*CATS Path Selector (C-PS): A functional entity that selects paths
towards service locations and instances and which accommodates the
requirements of service requests. Such a path selection engine takes
into account the service and network status information.
3. Definition and requirements of hierarchical metric distribution
The hierarchical method of cpmputing metrics is based on the CATS
framework defined in [I-D.ietf-cats-framework](see Figure 1, the
figure is replicated here for better understanding).
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+-----+ +------+ +------+
+------+| +------+ | +------+ |
|client|+ |client|-+ |client|-+
+---+--+ +---+--+ +---+--+
| | |
| +----------------+ | +-----+----------+
'-+ C-TC#1 +-' .-----+ C-TC#2 |
|----------------| | |----------------|
| |C-PS#1 | +------+ |CATS-Forwarder 4|
......| +----------|....|C-PS#2|..| |...
: |CATS-Forwarder 2| | | | | .
: +----------------+ +------+ +----------------+ :
: :
: +-------+ :
: Underlay | C-NMA | :
: Infrastructure +-------+ :
: :
: :
: +----------------+ +----------------+ :
: |CATS-Forwarder 1| +-------+ |CATS-Forwarder 3| :
:.| |..|C-SMA#1|.... | |....:
+---------+------+ +-------+ +----------------+
| | | C-SMA#2 |
| | +-------+--------+
| | |
| | |
+------------+ +------------+
+------------+ | +------------+ |
| Service | | | Service | |
| Contact | | | Contact | |
| Instance |-+ | Instance |-+
+------------+ +------------+
| |
+----------+ +----------+
+----------+ | +----------+ |
+----------+ | | | Service | |
| Service | |-+ | Instance |-+
| Instance |-+ +----------+
+----------+
Service Site 1 Service Site 2
Figure 1: CATS-Functional-Components
The hierarchical metric distribution is defined as reporting
different levels of the computing metric to C-PS in ingress CATS-
Forwarder according to geographical scope (distance or radius) and
performance of service sites, etc. The service sites classified as
high priority report high-level computing metrics (full metric
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information). And the service sites classified as low priority only
report a simple computing metric (i.e. available or unavailable). If
the priorities are classified by distance, then the near service site
can be set to a higher priority. On the one hand, setting a
hierarchical method of computing metric distribution can reduce the
processing pressure of network devices and the size of distribution
data and routing table. On the other hand, the increase in service
delay caused by processing large amounts of data can be avoided. The
impact is particularly obvious when C-PS is deployed in CATS-
Forwader. Therefore, hierarchical method of computing metric
distribution is particularly important in distributed and hybrid
model.
In the distributed model，all computing metrics are processed in C-PS
in the ingress CATS-Forwarder. It is better to set a suitable
priority for each service site. Therefore, the processing pressure
of the CATS-Forwarder can be relieved while maintaining sufficient
service resource utilization.
In the centralized model, all computing metrics are processed in
centralized C-PS. A centralized C-PS may have a hierarchical control
system, and different levels of controllers can be set to receive
different levels of the computing metric.
In the hybrid model, computing metrics can be chosen to be processed
in the ingress CATS-Forwarder or centralized C-PS according to
service types. [I-D.yi-cats-hybrid-solution] has discussed how to
choose the appropriate processing location in different scenarios.
Because not all computing metrics need to be processed in the CATS-
Forwarder in hybrid model, the hierarchical method can be more
flexible.
4. Optional hierarchical parameters
The priority of service sites is determined by parameters of service
sites, such as geographical distance and performance. When
calculating the priority, different parameters of service sites are
assigned different weights based on the service type. The parameter
scores of different service site parameters are obtained first. The
sum of all products of parameter scores and corresponding weights is
the priority score.The higher the priority score, the higher the
priority of the service site.
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4.1. Geographical distance
Geographical distance is the distance between ingress CATS-Forwarder
and egress CATS-Forwarder. If prioritizing based on geographic
distance, whether the distance between each network device is known
needs to be considered. If the distance is unknown, the distance can
be measured through the network packet transmission delay. Parameter
score of distance is negatively correlated with the distance.
4.2. Performance of service sites
The performance of a service site is related to the processing speed
and resource idle rate of the service site. Parameter score of
service site performance is positively correlated with the
performance.
4.3. Number of service sites
TBD
4.4. Other Options
TBD
5. Workflow of hierarchical metric distribution
The ingress CATS-Forwarder receives service request and send it to
egress CATS-Forwarder connected to the service site. Then the egress
CATS-Forwarder calculates the priority of service sites according to
the obtained parameters of service sites and send instruction
messages to them. Instruction messages are used to indicate the
priority of the corresponding service site. The egress CATS-Forwader
recieves computing metrics from service sites and send computing
metrics to C-PS (CATS Path Selector). The computing metrics of a
service site is determined based on the priority of the service
site.. For different CATS frameworks, the workflow of hierarchical
metric distribution is different.
5.1. Distributed model
When an egress CATS-Forwarder establishes a one-to-one neighbor
relationship with an ingress CATS-Forwarder, the egress CATS-Forwader
determines what level of computing metric to report to C-PS in this
ingress CATS-Forwarder.
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5.2. Centralized model
The egress CATS-Forwader determines what level of computing metric to
report to the different level of controller in the centralized C-PS.
5.3. Hybrid model
The hierarchical policies are set in both egress CATS-Forwarder and
centralized C-PS.
Firstly, the egress CATS-Forwarder determine whether to report the
collected computing metrics to centralized C-PS or C-PS in the
ingress CATS-Forwarder according to the requirements (delay or global
utilization, etc.) of different service types.
If the CATS-Forwarder is selected, the hierarchical metric
distribution workflow follows the distributed model mentioned above.
If there is hierarchical control in hybrid model, the hierarchical
metric distribution workflow follows the centralized model mentioned
above.
6. Security Considerations
TBD
7. IANA Considerations
TBD
8. Normative References
[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>.
[I-D.ietf-cats-framework]
Li, C., Du, Z., Boucadair, M., Contreras, L. M., and J.
Drake, "A Framework for Computing-Aware Traffic Steering
(CATS)", Work in Progress, Internet-Draft, draft-ietf-
cats-framework-13, 3 September 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-cats-
framework-13>.
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[I-D.ietf-cats-usecases-requirements]
Yao, K., Contreras, L. M., Shi, H., Zhang, S., and Q. An,
"Computing-Aware Traffic Steering (CATS) Problem
Statement, Use Cases, and Requirements", Work in Progress,
Internet-Draft, draft-ietf-cats-usecases-requirements-07,
10 June 2025, <https://datatracker.ietf.org/doc/html/
draft-ietf-cats-usecases-requirements-07>.
[I-D.ietf-cats-metric-definition]
Yao, K., Li, C., Contreras, L. M., Ros-Giralt, J., and H.
Shi, "CATS Metrics Definition", Work in Progress,
Internet-Draft, draft-ietf-cats-metric-definition-03, 7
July 2025, <https://datatracker.ietf.org/doc/html/draft-
ietf-cats-metric-definition-03>.
[I-D.yi-cats-hybrid-solution]
Yi, X., Pang, R., and H. Shi, "Hybrid Computing and
Network Awareness and Routing Solution for CATS", Work in
Progress, Internet-Draft, draft-yi-cats-hybrid-solution-
03, 24 July 2024, <https://datatracker.ietf.org/doc/html/
draft-yi-cats-hybrid-solution-03>.
Authors' Addresses
Xinxin Yi (editor)
China Unicom
Beijing
China
Email: yixx3@chinaunicom.cn
Naihan Zhang (editor)
China Unicom
Beijing
China
Email: zhangnh12@chinaunicom.cn
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