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diff --git a/docs/development/design/specs/High-Priority-Traffic-Path.rst b/docs/development/design/specs/High-Priority-Traffic-Path.rst new file mode 100644 index 0000000..f330a9d --- /dev/null +++ b/docs/development/design/specs/High-Priority-Traffic-Path.rst @@ -0,0 +1,257 @@ +.. This work is licensed under a Creative Commons Attribution 4.0 International License. +.. http://creativecommons.org/licenses/by/4.0 + +========================================== +High Priority Traffic Path +========================================== + +https://wiki.opnfv.org/display/ovsnfv/OVSFV+Requirement+-+High+Priority+Traffic+Path + +Problem description +=================== + +A network design may need to adequately accommodate multiple classes of traffic, each +class requiring different levels of service in critical network elements. + +As a concrete example, a network element managed by a service provider may be +handling voice and elastic data traffic. Voice traffic requires that the end-to-end +latency and jitter is bounded to some numerical limit (in msec) accuracy in order to ensure +sufficient quality-of-service (QoS) for the participants in the voice call. +Elastic data traffic does not impose the same demanding requirements on the network +(there will be essentially no requirement on jitter. For example, when downloading a +large file across the Internet, although the bandwidth requirements may be high there +is usually no requirement that the file arrives within a bounded time interval. + +Depending on the scheduling algorithms running on the network element, +frames belonging to the data traffic may get transmitted before frames +belonging to the voice traffic introducing unwanted latency or jitter. +Therefore, in order to ensure deterministic latency and jitter characteristics +end-to-end, each network element through which the voice traffic traverses +must ensure that voice traffic is handled deterministically. + +Hardware switches have typically been designed to ensure certain classes +of traffic can be scheduled ahead of other classes and are also +over-provisioned which further ensures deterministic behavior when +handling high priority traffic. However, software switches (which includes +virtual switches such as Open vSwitch) may require modification in order +to achieve this deterministic behavior. + +Use Cases +--------- + +1. Program classes of service + +The End User specifies a number of classes of service. Each class of service +will be represented by the value of a particular field in a frame. The class +of service determines the priority treatment which flows in the class will +receive, while maintaining a relative level of priority for other classes and +a default level of treatment for the lowest priority class of service. As +such, each class of service will be associated with a priority. The End User +will associate classes of service and priorities to ingress ports with the +expectation that frames that arrive on these ingress ports will get +scheduled following the specified priorities. + +Note: Priority treatment of the classes of service cannot cause any one of +the classes (even the default class) from being transferred at all. In other +words, a strict priority treatment would likely not be successful for serving +all classes eventually, and this is a key consideration. + +2. Forward high priority network traffic + +A remote network element sends traffic to Open vSwitch. The remote network +element, indicates the class of service to which this flow of traffic belongs +to by modifying a pre-determined but arbitrary field in the frame as specified +in Use Case 1. Some examples include the Differentiated Services Code Point +(DSCP) in an IP packet or the Priority Code Point (PCP) in an Ethernet frame. +The relative priority treatment that frames get processed by Open vSwitch can be guaranteed by the +values populated in these fields when the fields are different. If the fields +are the same, ordering is not deterministic. + +For example: Packet A is sent with a DSCP value of 0 and packet B is sent +with a value of 46; 0 has a lower priority than 46. Packet A arrives +before packet B. If Open vSwitch has been configured as such, Packet +B will be transmitted before Packet A. + +Proposed change +=============== + +TBD + +Alternatives +------------ + +TBD + +OVSDB schema impact +------------------- + +TBD + +User interface impact +--------------------- + +TBD + +Security impact +--------------- + +TBD + +Other end user impact +--------------------- + +TBD + +Performance Impact +------------------ + +TBD + +Other deployer impact +--------------------- + +TBD + +Developer impact +---------------- + +TBD + +Implementation +============== + +Assignee(s) +----------- + +Who is leading the writing of the code? Or is this a blueprint where you're +throwing it out there to see who picks it up? + +If more than one person is working on the implementation, please designate the +primary author and contact. + +Primary assignee: + <email address> + +Other contributors: + <email address> + +Work Items +---------- + +TBD + +Dependencies +============ + +TBD + +Testing +======= + +In order to test how effectively the virtual switch handles high priority traffic +types, the following scheme is suggested.:: + + +---------------------------+ Ingress Traffic Parameters + | | +-------------------------------------------+ + | | + | | Packet Size: The size of the Ethernet frames + | | + | | Tmax: RFC2544 Max. Throughput for traffic of + | PHY0 <-------+ "Packet Size" + | | + | | Total Offered Rate: The offered rate of both + | | traffic classes combined expressed as a % of + | | Tmax + | | + | | Ingress Rates are expressed as a percentage + | | of Total Offered Rate. + | | + | | Class A: + | OVS | Ethernet PCP = 0 (Background) + | (BR0) | Ingress Rate : rate_ingress_a(n) Mfps + | | + | | Class B: + | | Ethernet PCP = 7 (Highest) + | | Ingress Rate : rate_ingress_b(n) Mfps + | | + | | Egress Traffic Measurements + | | +-------------------------------------------+ + | | Class A: + | | Egress Throughput : rate_egress_a(n) Mfps + | | Egress Latency : max_lat_egrees_a(n) ms + | | Egress Jitter : max_jit_egress_a(n) ms + | PHY1 +-------> + | | Class B: + | | Egress Throughput : rate_egress_b(n) Mfps + | | Egress Latency : max_lat_egrees_b(n) ms + +---------------------------+ Egress Jitter : max_jit_egress_b(n) ms + + +Open vSwitch is configured to forward traffic between two ports agnostic to the +traffic type. For example, using the following command: + +ovs-ofctl add-flow br0 in_port=0,actions=output:1 + +The test will be carried out with the functionality to enable high-priority +traffic enabled and disabled in order to guage the change in performance for +both cases. + +Two classes of traffic will be generated by a traffic generator. In the example +above, the classes are differentiated using the Ethernet PCP field. However, +another means for differentiating traffic could be used, depending the +prioritization scheme that is developed. + +Tests should be performed for each combination of: + +* Packet Sizes in (64, 512) +* Total Offered Rate in (80, 120, 150) +* rate_ingress_b(n) / rate_ingress_a(n) in (0.1, 0.2, 0.5) + +For each set, the following metrics should be collected for each traffic +class over a specified time period: + +Egress Throughput (Mfps) +Maximum Egress Latency (ms) +Maximum Egress Jitter (ms) + +Documentation Impact +==================== + +TBD + +References +========== + +Please add any useful references here. You are not required to have any +reference. Moreover, this specification should still make sense when your +references are unavailable. Examples of what you could include are: + +* Links to mailing list or IRC discussions + +- http://lists.opnfv.org/pipermail/opnfv-tech-discuss/2015-December/007193.html +- http://ircbot.wl.linuxfoundation.org/meetings/opnfv-ovsnfv/2016/opnfv-ovsnfv.2016-03-07-13.01.html + +* Links to relevant research, if appropriate + +- https://wiki.opnfv.org/download/attachments/5046510/qos_mechanisms.pdf?version=1&modificationDate=1459187636000&api=v2 + +* Related specifications as appropriate + +* Anything else you feel it is worthwhile to refer to + + +History +======= + +Optional section intended to be used each time the spec +is updated to describe new design, API or any database schema +updated. Useful to let reader understand what's happened along the +time. + +.. list-table:: Revisions + :header-rows: 1 + + * - Release Name + - Description + * - Colorado + - Introduced |