P802.1Qcz – Congestion Isolation

This amendment specifies protocols, procedures and managed objects that support the isolation of congested data flows within data center environments. This is achieved by enabling systems to individually identify flows creating congestion, adjust transmission selection for frames of those flows, and signal to neighbors. This mechanism reduces head-of-line blocking for uncongested flows sharing a traffic class in lossless networks. Congestion Isolation is intended to be used with higher layer protocols that utilize end-to-end congestion control in order to reduce packet loss and latency. This amendment also addresses errors and omissions in the description of existing functionality.

There is significant customer interest and market opportunity for large scale, low-latency, lossless Ethernet data centers to support high-performance computing and distributed storage applications. Congestion is the primary cause of loss and delay. These environments currently use higher layer end-to-end congestion control coupled with priority-based flow control at Layer 2 to avoid performance degradation from packet loss due to congestion. As the Ethernet data center network scales in size, speed and number of concurrent flows, the current environment creates head-of-line blocking for flows sharing the same traffic class. Isolating flows that cause congestion reduces latency for flows not causing congestion and improves the scale and performance of the Ethernet data center network. This amendment will support the identification and isolation of the higher layer protocol flows that are creating congestion. The amendment will interoperate with existing congestion management. Use of a consolidated Ethernet data center network will realize operational and equipment cost benefits..

Current Status

Status PAR approved
Current Draft D0.2
PAR & CSD Full title: Standard for Local and Metropolitan Area Networks — Bridges and Bridged Networks — Amendment: Congestion Isolation
PAR approved 27 Sep 2018;
Editor Paul Congdon


Date Document
15 May 2019 802.1Qcz, Draft 0.0

The above list includes only the latest version of (proposed) dispositions. See the project folder for a complete list). The dates listed are the website file dates; they may differ from the creation dates in the documents.


Date Document
22 May 2019 Initial draft review
11 March 2019 Text contribution
12 Sep 2018 Proposed Technical Approach Congestion Isolation
09 Jul 2018 Congestion Isolation update
09 Jul 2018 P802.1Qcz interworking with other data center technologies
10 Jun 2018 P802.1Qcz Changes to 802.1Q
24 May 2018 New Simulation Results of Congestion Isolation
24 May 2018 Need For Advanced Congestion Mitigation In Modern Networks
21 May 2018 Responses to Qcz analysis in March
21 May 2018 Congestion Isolation update
16 Apr 2018 Congestion Isolation review

The above list includes only the latest version of updated documents and omits those superseded by subsequent discussion or inclusion in the current draft (see filenames beginning “cz-” in the 2018 and 2019 public directories for a complete list). The dates listed are the website file dates; they may differ from the creation dates in the documents.

Please contact the Editor if you have comments to the TSN TG page.