draft-ietf-tsvwg-tunnel-congestion-feedback-02.txt   draft-ietf-tsvwg-tunnel-congestion-feedback-03.txt 
Internet Engineering Task Force X. Wei Internet Engineering Task Force X. Wei
INTERNET-DRAFT Huawei Technologies INTERNET-DRAFT Huawei Technologies
Intended Status: Informational L.Zhu Intended Status: Informational L.Zhu
Expires: January 9, 2017 Huawei Technologies Expires: April 3, 2017 Huawei Technologies
L.Deng L.Deng
China Mobile China Mobile
July 8, 2016 September 30, 2016
Tunnel Congestion Feedback Tunnel Congestion Feedback
draft-ietf-tsvwg-tunnel-congestion-feedback-02 draft-ietf-tsvwg-tunnel-congestion-feedback-03
Abstract Abstract
This document describes a mechanism to calculate congestion of a This document describes a mechanism to calculate congestion of a
tunnel segment based on RFC6040 recommendations, and a feedback tunnel segment based on RFC6040 recommendations, and a feedback
protocol by which to send the measured congestion of the tunnel from protocol by which to send the measured congestion of the tunnel from
egress to ingress . A basic model for measuring tunnel congestion egress to ingress . A basic model for measuring tunnel congestion
and feedback is described, and a protocol for carrying the feedback and feedback is described, and a protocol for carrying the feedback
data is outlined. data is outlined.
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provide congestion control at all. provide congestion control at all.
In order to have a better control on network congestion status, it's In order to have a better control on network congestion status, it's
necessary for the network side to do certain kind of traffic control. necessary for the network side to do certain kind of traffic control.
For example, ConEx [ConEx] provides a method for network operator to For example, ConEx [ConEx] provides a method for network operator to
learn about traffic's congestion contribution information, and then learn about traffic's congestion contribution information, and then
congestion management action can be taken based on this information. congestion management action can be taken based on this information.
Tunnels are widely deployed in various networks including public Tunnels are widely deployed in various networks including public
Internet, datacenter network, and enterprise network etc. A tunnel Internet, datacenter network, and enterprise network etc. A tunnel
consists of ingress, an egress and a set of interior routers. For the consists of ingress, egress and a set of interior routers. For the
tunnel scenario, a tunnel-based mechanism which is different from tunnel scenario, a tunnel-based mechanism which is different from
ConEx is introduced for network traffic control to keep the network ConEx is introduced for network traffic control to keep the network
from persistent congestion. Here, tunnel ingress will implement from persistent congestion. Here, tunnel ingress will implement
congestion management function to control the traffic entering the congestion management function to control the traffic entering the
tunnel. tunnel.
In order to perform congestion management at ingress, the ingress In order to perform congestion management at ingress, the ingress
must first obtain the inner tunnel congestion level information. Yet must first obtain the inner tunnel congestion level information. Yet
the ingress cannot use the locally visible traffic rates, because it the ingress cannot use the locally visible traffic rates, because it
would require additional knowledge of downstream capacity and would require additional knowledge of downstream capacity and
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predefined threshold, the routers will drop both the ECN-capable predefined threshold, the routers will drop both the ECN-capable
packets and the not-ECT packets with the probability proportional to packets and the not-ECT packets with the probability proportional to
the queue length. It's assumed all routers in the tunnel support ECN. the queue length. It's assumed all routers in the tunnel support ECN.
Faked ECN-capable transport (ECT) is used at ingress to defer packet Faked ECN-capable transport (ECT) is used at ingress to defer packet
loss to egress. The basic idea of faked ECT is that, when loss to egress. The basic idea of faked ECT is that, when
encapsulating packets, ingress first marks tunnel outer header encapsulating packets, ingress first marks tunnel outer header
according to RFC6040, and then remarks outer header of Not-ECT packet according to RFC6040, and then remarks outer header of Not-ECT packet
as ECT, there will be three kinds of combination of outer header ECN as ECT, there will be three kinds of combination of outer header ECN
field and inner header ECN field: CE|CE, ECT|N-ECT, ECT|ECT (in the field and inner header ECN field: CE|CE, ECT|N-ECT, ECT|ECT (in the
form of outer ECN| inner ECN). form of outer ECN| inner ECN); when decapsulating packets at egress,
RFC6040 defined decapsulation behavior is used, and according to
RFC6040, the packets marked as CE|N-ECT will be dropped by egress.
In case all interior routers support ECN, the network congestion In case all interior routers support ECN, the network congestion
level could be indicated through the ratio of CE-marked packet and level could be indicated through the ratio of CE-marked packet and
the ratio of packet drop, the relationship between these two kinds of the ratio of packet drop, the relationship between these two kinds of
indicator is complementary. If the congestion level in tunnel is not indicator is complementary. If the congestion level in tunnel is not
high enough, the packets would be marked as CE instead of being high enough, the packets would be marked as CE instead of being
dropped, and then it is easy to calculate congestion level according dropped, and then it is easy to calculate congestion level according
to the ratio of CE-marked packets. If the congestion level is so high to the ratio of CE-marked packets. If the congestion level is so high
that ECT packet will be dropped, then the packet loss ratio could be that ECT packet will be dropped, then the packet loss ratio could be
calculated by comparing total packets entering ingress and total calculated by comparing total packets entering ingress and total
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