Egress-edge multi-hop quality-of-service fairness enabler by backpropagation and auto-configuration of service level quotas
Publication Date: 2015-Sep-06
The IP.com Prior Art Database
Maintaining accurate quality-of-service delivery rates is an important and challenging problem that appears in practially every data-center infrastructure, where multiple users or applications, each with different prioritizations, must share a common infrastructure while maintaining service delivery rates and latencies within previously set ranges. For multi-hop networks a challenge appears which is that the enforcement of service rates in middle hops might prevent egress-edge switches to actually receive enough packets from all service levels as to maintain the service rates promised. This invention provides a feedback mechanism for egress-edge switches to be able to satisfy the quality of service demands given that enough packets for each service level are present in the network, by promoting, through feedback signals, packets of under-represented service levels to reach the egress side.
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The invention relates to the maintenance of multi-hop fairness across quality of service levels (called "Service Lanes" in InfiniBand), and in particular to the maintenance of such quality of service levels at egress.
Systems implementing some sort of quality-of-service mechanisms today strive to ensure that the quality of service configuration set is maintained at the local level at each switch . However what the users are really interested is in maintaining these service levels at egress. Guaranteeing quality of service levels in multi-hop network is very difficult to achieve; let's imagin imagine an output buffered switch that receives packets in different service level from many input ports; let's assume that all but one of the input ports send packets to a particular quality of service level, while only one input port transmit packets to a different quality of service level; assuming that both service levels have been configured with the same quota (so the egress of both should be balanced), due to the decisions at the previous hops, the egress at this port would be biased towards one of the quality of service levels.
Instead of rate-limiting sources by sending rate-limiting notifications (like PFC), which are prone to cause a global loss of performance if not used with extreme care (innocent flows might be unsuspecting victims of the rate-limiting mechanisms), we propose back-propagate information about the quality-of-service levels that are not meeting their quotas at egress to cause a back-propagation re-configuration of the quality-of-service parameters in the previous hops such that push the system to an state where the egress maintains the desired quality -of-service configuration. Quota-based QoS mechanisms such as InfiniBand are not prone to loss of performance, if the under-represented traffic at egress is not present elsewhere in the network, increasing its quota does not cause any negative impact on the other traffic classes, as there is no bandwidth-reservation, and any empty slots are always distributed according to the QoS rules to the traffic classes already present.
For instance, in the previous case, one could implement the "request to change the configuration" as a bit-mask with the quality-of-service levels under-represented at egress (let's say 01, because QoS level 1 was under-represented), that would cause, in the previous hops to increase (by addition or by a factor) the quota assigned to that service level (*) such that it can help the egress to maintain its quota - if this previous-to-last switch cannot still maintain its quota it would again back-propagate this information. When a switch receives such information with a '0' it should reset the quota assigned to the (original) egress value, and if all values were 1s, maintain the current quota values.
The invention consists in the addition of a dynamic configuration factor to the QoS parameters of the service levels of InfiniBand tables...