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| -rw-r--r-- | specs/High-Priority-Traffic-Path.rst | 219 |
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diff --git a/specs/High-Priority-Traffic-Path.rst b/specs/High-Priority-Traffic-Path.rst index 8dfd2ae..25f6361 100644 --- a/specs/High-Priority-Traffic-Path.rst +++ b/specs/High-Priority-Traffic-Path.rst @@ -10,171 +10,115 @@ High Priority Traffic Path https://wiki.opnfv.org/display/ovsnfv/OVSFV+Requirement+-+High+Priority+Traffic+Path -Introduction paragraph -- why are we doing anything? A single paragraph of -prose that operators can understand. The title and this first paragraph -should be used as the subject line and body of the commit message -respectively. - -Some notes about the process: - -* The aim of this document is first to define the problem we need to solve, - and second agree the overall approach to solve that problem. - -* This is not intended to be extensive documentation for a new feature. - -* You should aim to get your spec approved before writing your code. - While you are free to write prototypes and code before getting your spec - approved, its possible that the outcome of the spec review process leads - you towards a fundamentally different solution than you first envisaged. - -* But, API changes are held to a much higher level of scrutiny. - As soon as an API change merges, we must assume it could be in production - somewhere, and as such, we then need to support that API change forever. - To avoid getting that wrong, we do want lots of details about API changes - upfront. - -Some notes about using this template: - -* Your spec should be in ReSTructured text, like this template. - -* Please wrap text at 79 columns. - -* Please do not delete any of the sections in this template. If you have - nothing to say for a whole section, just write: None - -* For help with syntax, see http://sphinx-doc.org/rest.html - -* To test out your formatting, build the docs using sphinx - -* If you would like to provide a diagram with your spec, ascii diagrams are - required. http://asciiflow.com/ is a very nice tool to assist with making - ascii diagrams. The reason for this is that the tool used to review specs is - based purely on plain text. Plain text will allow review to proceed without - having to look at additional files which can not be viewed in gerrit. It - will also allow inline feedback on the diagram itself. - Problem description =================== -A detailed description of the problem. What problem is this blueprint -addressing? +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 --------- -What use cases does this address? What impact on actors does this change have? -Ensure you are clear about the actors in each use case: Developer, End User, -Deployer etc. +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 =============== -Here is where you cover the change you propose to make in detail. How do you -propose to solve this problem? - -If this is one part of a larger effort make it clear where this piece ends. In -other words, what's the scope of this effort? - -At this point, if you would like to just get feedback on the problem and -proposed change, you can stop here and post this for review to get -preliminary feedback. If so please say: -Posting to get preliminary feedback on the scope of this spec. +TBD Alternatives ------------ -What other ways could we do this thing? Why aren't we using those? This doesn't -have to be a full literature review, but it should demonstrate that thought has -been put into why the proposed solution is an appropriate one. +TBD OVSDB schema impact ------------------- -Changes which require modifications to the data model often have a wider impact -on the system. The community often has strong opinions on how the data model -should be evolved, from both a functional and performance perspective. It is -therefore important to capture and gain agreement as early as possible on any -proposed changes to the data model. - -Questions which need to be addressed by this section include: - -* What new data objects and/or database schema changes is this going to - require? +TBD User interface impact --------------------- -Each user interface that is either added, changed or removed should have the -following: - -* Specification for the user interface - -* Example use case including typical examples for both data supplied - by the caller and the response +TBD Security impact --------------- -Describe any potential security impact on the system. Some of the items to -consider include: - -* Does this change touch sensitive data such as tokens, keys, or user data? - -* Does this change alter the interface in a way that may impact security, such as - a new way to access sensitive information? - -* Does this change involve cryptography or hashing? - -* Does this change require the use of sudo or any elevated privileges? - -* Does this change involve using or parsing user-provided data? This could - be directly at the API level or indirectly such as changes to a cache layer. - -* Can this change enable a resource exhaustion attack, such as allowing a - single interaction to consume significant server resources? +TBD Other end user impact --------------------- -Aside from the user interfaces, are there other ways a user will interact with this -feature? +TBD Performance Impact ------------------ -Describe any potential performance impact on the system, for example -how often will new code be called, and is there a major change to the calling -pattern of existing code. - -Examples of things to consider here include: - -* Will the change include any locking, and if so what considerations are there - on holding the lock? +TBD Other deployer impact --------------------- -Discuss things that will affect how you deploy and configure Open vSwitch -that have not already been mentioned, such as: - -* What config options are being added? Should they be more generic than - proposed? Are the default values ones which will work well in - real deployments? - -* Is this a change that takes immediate effect after its merged, or is it - something that has to be explicitly enabled? - -* If this change is a new binary, how would it be deployed? - -* Please state anything that those doing continuous deployment, or those - upgrading from the previous release, need to be aware of. Also describe - any plans to deprecate configuration values or features. +TBD Developer impact ---------------- -Discuss things that will affect other developers working on Open vSwitch, -such as: +TBD Implementation ============== @@ -197,45 +141,22 @@ Other contributors: Work Items ---------- -Work items or tasks -- break the feature up into the things that need to be -done to implement it. Those parts might end up being done by different people, -but we're mostly trying to understand the timeline for implementation. - +TBD Dependencies ============ -* If this requires functionality of another project that is not currently used - document that fact. - -* Does this feature require any new library dependencies or code otherwise not - included in Open vSwitch? Or does it depend on a specific version of library? - +TBD Testing ======= -Please discuss the important scenarios needed to test here, as well as -specific edge cases we should be ensuring work correctly. For each -scenario please specify if this requires specialized hardware. - -Please discuss how the change will be tested: Open vSwitch unit tests, VSPERF -performance tests, Yardstick tests, etc. - -Is this untestable in gate given current limitations (specific hardware / -software configurations available)? If so, are there mitigation plans (3rd -party testing, gate enhancements, etc). - +TBD Documentation Impact ==================== -Which audiences are affected most by this change, and which documentation -should be updated because of this change? Don't -repeat details discussed above, but reference them here in the context of -documentation for multiple audiences. If a config option -changes or is deprecated, note here that the documentation needs to be updated -to reflect this specification's change. +TBD References ========== |