]> Huawei Technologies

China c.l@huawei.com

China Mobile

China duzongpeng@chinamobile.com

Orange

France mohamed.boucadair@orange.com

Telefonica

Spain luismiguel.contrerasmurillo@telefonica.com

Independent

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Routing area cats Computing Computing-Aware Traffic Steering User Experience Collaborative Networking Service optimization This document describes a framework for Computing-Aware Traffic Steering (CATS). Specifically, the document identifies a set of CATS components, describes their interactions, and provides illustrative workflows of the control and data planes.

Introduction Computing service architectures have evolved from single service site to multiple, sometimes collaborative, service sites to address various issues such as long response times or suboptimal utilization of service and network resources (e.g., resource under-utilization or exhaustion). The underlying networking infrastructures that include computing resources usually provide relatively static service dispatching, e.g., the selection of the service instances for a request. In such infrastructures, service-specific traffic is often directed to the closest service site from a routing perspective without considering the actual network state (e.g., traffic congestion conditions) or the service site state. As described in , traffic steering that takes into account computing resource metrics would benefit several services, including latency-sensitive services such as immersive services that rely upon the use of augmented reality or virtual reality (AR/VR) techniques. This document provides an architectural framework that aims at facilitating the making of compute- and network-aware traffic steering decisions in networking environments where computing service resources are deployed. The Computing-Aware Traffic Steering (CATS) framework assumes that there might be multiple service instances that are providing one given service, which are running in one or more service sites. Each of these service instances can be accessed via a service contact instance, which is a client-facing service function instance. A single service site may host one or multiple service contact instances. A single service site may have limited computing resources available at a given time, whereas the various service sites may experience different resource availability issues over time. Therefore, steering traffic among different service sites can address the issues of lacking resources in a specific service site. Steering in CATS is about selecting the appropriate service contact instance that will service a request according to a set of network and computing metrics. This selection may not necessarily reveal the actual service instance that will be invoked, e.g., in hierarchical or recursive contexts. Therefore, the metrics of the service contact instance may be the aggregated metrics from multiple service instances. The CATS framework is an overlay framework for the selection of the suitable service contact instance(s) from a set of candidates. The exact characterization of 'suitable' is determined by a combination of networking and computing metrics. Furthermore, this document describes a workflow of the main CATS procedures in , which are executed in both the control and data planes.

Terminology This document makes use of the following terms:

Client:

An endpoint that is connected to a service provider network.

Flow:

A flow is identified by the 5-tuple transport coordinates (source address and destination address, source and destination port numbers, and protocol).

Computing-Aware Traffic Steering (CATS):

A traffic engineering approach that takes into account the dynamic nature of computing resources (e.g., compute and storage) and network state to optimize service-specific traffic forwarding towards a given service contact instance. Various relevant metrics may be used to enable such computing-aware traffic steering policies.

Metric:

A piece of information that provides suitable input to a selection mechanism to determine a CATS egress node.

Computing metrics:

Computing metrics are the metrics that come specifically from the computing side of the system as distinct from other metrics that may be used in a CATS system, such as the metrics from network side. For details, a set of metrics from computing side used for CATS has been defined in .

Service:

An offering that is made available by a service provider by orchestrating a set of resources (networking, compute, storage, etc.).

Which and how these resources are used is part of the service logic which is internal to the service provider. For example, these resources may be:

• Exposed by one or multiple processes.
• Provided by virtual instances, physical, or a combination thereof.
• Hosted within the same or distinct nodes.
• Hosted within the same or multiple service sites.
• Chained to provide a service using a variety of means.

How a service is structured is out of the scope of CATS.

The same service can be provided in many locations; each of them constitutes a service instance.

Computing Service:

An offering is made available by a service provider by orchestrating a set of computing resources.

CATS Service ID (CS-ID):

An identifier representing a service, which the clients use to access it. See .

Service instance:

An instance of running resources according to a given service logic.

Many such instances can be enabled by a service provider. Instances that adhere to the same service logic provide the same service.

An instance is running in a service site. Clients' requests are serviced by one or more of these instances.

Service site:

A location that hosts the resources that are required to offer a service.

A service site may be a node or a set of nodes.

A CATS-serviced site is a service site that is connected to a CATS-Forwarder.

Service contact instance:

A client-facing service function instance that is responsible for receiving requests in the context of a given service.

A service contact instance can handle one or more service instances.

Steering beyond a service contact instance is hidden to both clients and CATS components.

A service request is processed according to the service logic (e.g., handle locally or solicit backend resources).

A service contact instance is reachable via at least one Egress CATS-Forwarder.

A service can be accessed via multiple service contact instances running at the same or different locations (service sites).

A service contact instance may dispatch service requests to one or more service instances (e.g., a service contact instance that behaves as a service load-balancer).

CATS Service Contact Instance ID (CSCI-ID):

An identifier of a specific service contact instance. See .

Service request:

A request to access or invoke a specific service. Such a request is steered to a service contact instance via CATS-Forwarders.

A service request is placed using service-specific protocols.

Service requests are not explicitly sent by clients to CATS-Forwarders.

CATS-Forwarder:

A network entity that steers traffic specific to a service request towards a corresponding yet selected service contact instance according to provisioned forwarding decisions. These decisions are supplied by a C-PS, which may or may not be on the CATS-Forwarder.

A CATS-Forwarder may behave as Ingress or Egress CATS-Forwarder.

Ingress CATS-Forwarder:

An entity that steers service-specific traffic along a CATS-computed path that leads to an Egress CATS-Forwarder that connects to the most suitable service site that host the service contact instance selected to satisfy the initial service request.

Egress CATS-Forwarder:

An entity that is located at the end of a CATS-computed path and which connects to a CATS-serviced site.

CATS Path Selector (C-PS):

A functional entity that selects paths towards service locations and instances and which accommodates the requirements of service requests. Such a path selection engine takes into account the service and network status information. See .

CATS Service Metric Agent (C-SMA):

A functional entity that is responsible for collecting service capabilities and status, and for reporting them to a CATS Path Selector (C-PS). See .

CATS Network Metric Agent (C-NMA):

A functional entity that is responsible for collecting network capabilities and status, and for reporting them to a C-PS. See .

CATS Traffic Classifier (C-TC):

A functional entity that is responsible for determining which packets belong to a traffic flow for a specific service request. It is also responsible for forwarding such packets along a C-PS computed path that leads to the relevant service contact instance. See .

CATS Framework and Components

Assumptions CATS assumes that there are multiple service instances running on different service sites, which provide a given service that is represented by the same service identifier (see ). However, CATS does not make any assumption about these instances other than they are reachable via one or multiple service contact instances.

CATS Identifiers CATS uses the following identifiers:

CATS Service ID (CS-ID):

An identifier (ID) representing a service, which the clients use to access it. Such an ID identifies all the instances of a given service, regardless of their location.

The CS-ID is independent of which service contact instance serves the service request.

Service requests are spread over the service contact instances that can accommodate them, considering the location of the initiator of the service request and the availability (in terms of resource/traffic load, for example) of the service instances resource-wise among other considerations like traffic congestion conditions.

CATS Service Contact Instance ID (CSCI-ID):

An identifier of a specific service contact instance.

Framework Overview A high-level view of the CATS framework, without expanding the functional entities in the network, is illustrated in .

Main CATS Interactions | C-SMA | | Control Plane | | | | +----------------------------------+ | +---+----+ /\ | | || | | \/ | | +----------------------------------+ | +--------+ | Data Plane | | | +--------+ +----------------------------------+ |<=======>| |Service | | +-|Contact | | |Instance| | +--------+ | | | +--------+ | | +--------+ | | |Service | | +-|Instance| | +--------+ ]]>

For the sake of illustration, "Service Instance" is shown as a single box in . However, this does not imply that a service instance is hosted in a single node. Whether a service instance is realized by invoking resources within a same node or by chaining resources exposed by several nodes is deployment specific. The following planes are defined:

• CATS Management Plane: Responsible for monitoring, configuring, and maintaining CATS network devices.
• CATS Control Plane: Responsible for scheduling services based on computing and network information. It is also responsible for making decisions about how packets should be forwarded by involved forwarding nodes and communicating such decisions to the CATS Data Plane for execution.
• CATS Data Plane: Responsible for computing-aware routing, including handling packets in the data path, such as packet forwarding.

Depending on implementation and deployment, these planes may consist of several functional elements/components, and the details will be described in the following sections.

CATS Functional Components CATS nodes make forwarding decisions for a given service request that has been received from a client according to the capabilities and status information of both service contact instances and network. The main CATS functional elements and their interactions are shown in .

CATS Functional Components

Service Sites, Services Instances, and Service Contact Instances Service sites are locations that host resources (including computing resources) that are required to offer a service. A compute service (e.g., for face recognition purposes or a game server) is identified by a CATS Service Identifier (CS-ID). The CS-ID does not need to be globally unique, but must be sufficiently unique to unambiguously identify the service at all of the components of a CATS system. A single service can be represented and accessed via several contact instances that run in same or different regions of a network. As service instances are accessed via a service contact instance, a client will not see the service instances but only the service contact instance. shows two CATS nodes ("CATS-Forwarder 1" and "CATS-Forwarder 3") that provide access to service contact instances. These nodes behave as Egress CATS-Forwarders ().

• Note: "Egress" is used here in reference to the direction of the service request placement. The directionality is called to explicitly identify the exit node of the CATS infrastructure.

CATS Service Metric Agent (C-SMA) The CATS Service Metric Agent (C-SMA) is a functional component that gathers information about service sites and server resources, as well as the status of the different service instances. A C-SMA may be co-located or located adjacent to a service contact instance, hosted by or adjacent to an Egress CATS-Forwarder (), etc. shows one C-SMA embedded in "CATS-Forwarder 3", and another C-SMA that is adjacent to "CATS-Forwarder 1".

CATS Network Metric Agent (C-NMA) The CATS Network Metric Agent (C-NMA) is a functional component that gathers information about the state of the underlay network. The C-NMAs may be implemented as standalone components or may be hosted by other components, such as CATS-Forwarders or CATS Path Selectors (C-PS) (). C-NMA is likely to leverage existing techniques (e.g., , , and ). shows a single, standalone C-NMA within the underlay network. There may be one or more C-NMAs for an underlay network.

CATS Path Selector (C-PS) The C-SMAs and C-NMAs share the collected information with CATS Path Selectors (C-PSes) that use such information to select the Egress CATS-Forwarders (and potentially the service contact instances) where to forward traffic for a given service request. C-PSes also determine the best paths (possibly using tunnels) to forward traffic, according to various criteria that include network state and traffic congestion conditions. The collected information is encoded into one or more metrics that feed the C-PS path selection logic. Such information also includes CS-ID and possibly CSCI-IDs. There might be one or more C-PSes used to select CATS paths in a CATS infrastructure. A C-PS can be integrated into CATS-Forwarders (e.g., "C-PS#1" in ) or may be deployed as a standalone component (e.g., "C-PS#2" in ). Generally, a standalone C-PS can be a functional component of a centralized controller (e.g., a Path Computation Element (PCE) ). Refer to for a discussion on metric distribution (including, interaction with routing protocols).

CATS Traffic Classifier (C-TC) The CATS Traffic Classifier (C-TC) is a functional component that is responsible for associating incoming packets from clients with service requests. CATS classifiers also ensure that packets that are bound to a specific service contact instance are all forwarded towards that same service contact instance, as instructed by a C-PS. To that aim, a C-TC uses CS-IDs (or their resolution of CS-ID to network locators) to calssify service requests. Refer to for more details about provisioning of classification rules. Note that CS-IDs may be carried in packets if mechanisms such as TLS Server Name Indication extension (SNI) () are used. CATS classifiers are typically hosted in CATS-Forwarders.

CATS-Forwarders Ingress CATS-Forwarder are resposnible for steering service-specific traffic along a CATS-computed path that leads to an Egress CATS- Forwarder. Egress CATS-Forwarders are the endpoints that behave as an egress for service requests that are forwarded over a CATS infrastructure. A service site that hosts service instances may be connected to one or more Egress CATS-Forwarders (e.g., multi-homing design). If a C-PS has selected a specific service contact instance and the C-TC has marked the traffic with the CSCI-ID related information, the Egress CATS-Forwarder then forwards traffic to the relevant service contact instance accordingly. In some cases, the choice of the service contact instance may be left open to the Egress CATS-Forwarder (i.e., traffic is marked only with the CS-ID). In such cases, the Egress CATS-Forwarder selects a service contact instance using its knowledge of service and network capabilities as well as the current load as observed by the CATS-Forwarder, among other considerations. In the absence of an explicit policy, an Egress CATS-Forwarder must make sure to forward all packets that pertain to a given service request towards the same service contact instance. Note that, depending on the design considerations and service requirements, per-service contact instance computing-related metrics or aggregated per-site computing related metrics (and a combination thereof) can be used by a C-PS. Using aggregated per-site computing related metrics appears as a preferred option scalability-wise, but relies on Egress CATS-Forwarders that connect to various service contact instances to select the proper service contact instance. An Egress CATS-Forwarder may choose to aggregate the metrics from different sites as well. In this case, the Egress CATS-Forwarder will choose the best site by itself when the packets arrive at it.

Underlay Infrastructure The "underlay infrastructure" in indicates an IP and/or MPLS network that is not necessarily CATS-aware. The CATS paths that are computed by a C-PS will be distributed among the CATS-Forwarders (), and will not affect the underlay nodes. Underlay nodes are typically P routers ().

CATS Framework Workflow The following subsections provide an overview of a typical CATS workflow. In order to enable CATS in a given domain, some provisioning is needed; see more details in . describes several deployment options (distributed, centralized, and hybrid model) to accommodate a variety of contexts.

Service Announcement A service is associated by the service provider with a unique identifier called a CS-ID. A CS-ID may be a network identifier, such as an IP address. The mapping of CS-IDs to network identifiers may be learned through a name resolution service (e.g., DNS ). Note that CATS framework does not assume nor preclude any specific name resolution service.

Metrics Distribution As described in , a C-SMA collects both computing-related capabilities and metrics, and associates them with a CS-ID that identifies the service. The C-SMA may aggregate the metrics for multiple service contact instances, or maintain them separately or both. The C-SMA then advertises CS-IDs along with metrics to related C-PSes in the network. Depending on deployment choice, CS-IDs with metrics may be distributed in different ways. For example, in a distributed model, CS-IDs with metrics can be distributed from the C-SMA to an Egress CATS-Forwarder firstly and then be redistributed by the Egress CATS-Forwarder to related C-PSes that are integrated into Ingress CATS-Forwarders. In the centralized model, CS-IDs with metrics can be distributed from the C-SMA to a centralized control plane, for instance, a standalone C-PS. In the hybrid model, the metrics can be distributed to C-PSes in combination of distributed and centralized ways. The specific combination of metric distribution is an implementation choice, which is determined by the requirements of specific services. The Computing metrics include computing-related metrics and potentially other service-specific metrics like the number of end-users who access the service contact instance at any given time, etc. Computing metrics may change very frequently (see for a discussion). How frequently such information is distributed is to be determined as part of the specification of any communication protocol (including routing protocols) that may be used to distribute the information. Various options can be considered, such as (but not limited to) interval-based updates, threshold-triggered updates, policy-based updates, or using normalized metrics . Regarding using the normalized metrics, provides some suggestions to implement computing metrics normalization and aggregation in CATS framework, to reduce the impact of the routing system. Additionally, the C-NMA collects network-related capabilities and metrics. These may be collected and distributed by existing measurement protocols and/or routing protocols, although extensions to such protocols may be required to carry additional information (e.g., link latency). The C-NMA distributes the network metrics to the C-PSes so that they can use the combination of service and network metrics to determine the best Egress CATS-Forwarder to provide access to a service contact instance and invoke the compute function required by a service request. Similar to computing-related metrics, the network-related metrics can be distributed using distributed, centralized, or hybrid schemes. This document does not describe such details since this is deployment-specific. Network metrics may also change over time. Dynamic routing protocols may take advantage of some information or capabilities to prevent the network from being flooded with state change information (e.g., Partial Route Computation (PRC) of OSPFv3 ). C-NMAs should also be configured or instructed like C-SMAs to determine when and how often updates should be notified to the C-PSes. shows an example of how CATS metrics can be disseminated in the distributed model. There is a client attached to the network via "CATS-Forwarder 1". There are three service contact instances of the service with CS-ID "1": two service contact instances with CSCI-IDs "1" and "2", respectively, are located at "Service Site 2" attached via "CATS-Forwarder 2"; the third service contact instance is located at "Service Site 3" attached via "CATS-Forwarder 3" and with CSCI-ID "3". There is also a second service with CS-ID "2" with only one service contact instance located at "Service Site 3". In , the C-SMA collocated with "CATS-Forwarder 2" distributes the computing metrics for both service contact instances (i.e., (CS-ID 1, CSCI-ID 1) and (CS-ID 1, CSCI-ID 2)). Note that this information may be aggregated into a single advertisement, but in this case, the metrics for each service contact instance are indicated separately. Similarly, the C-SMA agent located at "Service Site 3" advertises the computing metrics for the two services hosted by "Service Site 3". The computing metric advertisements are processed by the C-PS hosted by "CATS-Forwarder 1". The C-PS also processes network metric advertisements sent by the C-NMA. All metrics are used by the C-PS to select the most relevant path that leads to the Egress CATS-Forwarder according to the initial client's service request, the service that is requested ("CS-ID 1" or "CS-ID 2"), the state of the service contact instances as reported by the metrics, and the state of the network.

An Example of CATS Metric Dissemination in a Distributed Model Service CS-ID 1, contact instance CSCI-ID 2 :<----------------------: : : +---------+ : : |CS-ID 1 | : : .--|CSCI-ID 1| : +----------------+ | +---------+ : | C-SMA |----| Service Site 2 : +----------------+ | +---------+ : |CATS-Forwarder 2| '--|CS-ID 1 | : +----------------+ |CSCI-ID 2| +--------+ : | +---------+ | Client | : Network +----------------------+ +--------+ : metrics | +-------+ | | : :<---------| C-NMA | | | : : | +-------+ | +---------------------+ | | |CATS-Forwarder 1|C-PS|----| | +---------------------+ | Underlay | : | Infrastructure | +---------+ : | | |CS-ID 1 | : +----------------------+ .---|CSCI-ID 3| : | | +---------+ : +----------------+ +-------+ : |CATS-Forwarder 3|--| C-SMA | Service Site 3 : +----------------+ +-------+ : : | +-------+ : : '---|CS-ID 2| : : +-------+ :<-------------------------------: Service CS-ID 1, contact instance CSCI-ID 3 Service CS-ID 2, ]]>

The example in mainly describes a per-instance computing-related metric distribution. In the case of distributing aggregated per-site computing-related metrics, the per-instance CSCI-ID information will not be included in the advertisement. Instead, a per-site CSCI-ID may be used in case multiple sites are connected to the Egress CATS-Forwarder to explicitly indicate the site from where the aggregated metrics come. If the CATS framework is implemented using a centralized model, the metric can be, e.g., distributed as illustrated in .

An Example of CATS Metric Distribution in a Centralized Model Service CS-ID 1, instance CSCI-ID 2 Service CS-ID 1, instance CSCI-ID 3 Service CS-ID 2, +------+ :<------| C-PS |<------------------------------------. : | |<------. | : +------+ | +---------+ | : ^ | +---|CS-ID 1 | | : | | | |CSCI-ID 1| | : | +----------------+ | +---------+ | : | | C-SMA |---| Service Site 2 | : | +----------------+ | +---------+ | : | |CATS-Forwarder 2| +---|CS-ID 1 | | : | +----------------+ |CSCI-ID 2| | +--------+ : | | +---------+ | | Client | : Network | +----------------------+ | +--------+ : metrics | | +-------+ | | | : +----| C-NMA | | +-----+ | | : | | +-------+ | |C-SMA|--+ +----------------+ | | | | |<-. |CATS-Forwarder 1|<---' | | +-----+ | | |<------| | ^ | +----------------+ | Underlay | | | | Infrastructure | +---------+| | | |CS-ID 1 || +----------------------+ +-|CSCI-ID 3|| | | +---------+| +----------------+ | | |CATS-Forwarder 3|------------+ | +----------------+ Service Site 3 | | +-------+ | +--------------|CS-ID 2|-----+ +-------+ ]]>

In , the C-SMA collocated with "CATS-Forwarder 2" distributes the computing metrics for both service contact instances (i.e., (CS-ID 1, CSCI-ID 1) and (CS-ID 1, CSCI-ID 2)) to the centralized C-PS. In this case, the C-PS is a logically centralized element deployed independently with the CATS-Forwarder 1. Similarly, the C-SMA agent located at "Service Site 3" advertises the computing metrics for the two services hosted by "Service Site 3" to the centralized C-PS as well. Furthermore, the C-PS receives the network metrics sent from the C-NMA. All metrics are used by the C-PS to select the most relevant path that leads to the Egress CATS-Forwarder. The selected paths will be sent from the C-PS to CATS-Forwarder 1 to indicate traffic steering. If the CATS framework is implemented using an hybrid model, the metric can be distributed, e.g., as illustrated in the . For example, the metrics 1,2,3 associated with the CS-ID1 are collected by the centralized C-PS, and the metrics 4 and 5 are distributed via distributed protocols to the ingress CATS-Forwarder directly. For a service with CS-ID2, all the metrics are collected by the centralized C-PS. The CATS-computed path result will be distributed to the Ingress CATS-Forwarders from the C-PS by considering both the metrics from the C-SMA and C-NMA. Furthermore, the Ingress CATS-Forwarder may also have some ability to compute the path for the subsequent service accessing packets.

An Example of CATS Metric Distribution in Hybrid Model Service CS-ID 1, instance CSCI-ID 2 Service CS-ID 1, instance CSCI-ID 3 Service CS-ID 2, +------+ :<------| C-PS |<-------------------------------------. : | |<-------. | : +------+ | +---------+ | : ^ | +---|CS-ID 1 | | : | | | |CSCI-ID 1| | : | +----------------+ | +---------+ | : | | C-SMA |---| Service Site 2 | : | +----------------+ | +---------+ | : | |CATS-Forwarder 2| +---|CS-ID 1 | | : | +----------------+ |CSCI-ID 2| | +--------+ : | | +---------+ | | Client | : Network | +----------------------+ | +--------+ : metrics | | +-------+ | | | : +-----| C-NMA | | +-----+ | | : | | +-------+ | |C-SMA|--+ | : | | | | |<-. +----------------+ | | | +-----+ | |CATS-Forwarder 1|<----' | | ^ | | |---------| Underlay | | | |----------------+ | Infrastructure | +---------+| |C-PS| : | | |CS-ID 1 || +----+ : +----------------------+ +-|CSCI-ID 3|| : | | +---------+| : +----------------+ | | : |CATS-Forwarder 3|------------+ | : +----------------+ Service Site 3 | : | +-------+ | : '-------+------|CS-ID 2|-----' : : +-------+ :<-------------------------------: Service CS-ID 1, contact instance CSCI-ID 3, ]]>

Service Access Processing A C-PS selects paths that lead to Egress CATS-Forwarders according to both service and network metrics that were advertised. A C-PS may be collocated with an Ingress CATS-Forwarder (as shown in ) or logically centralized (in a centralized model or hybrid model). This document does not specify any specific algorithm for path selection purposes to be supported by C-PSes in order to not constrain the CATS framework to one possible selection only. Instead, it is expected that a service request or local policy may feed the C-PS with appropriate information on that selection logic that takes the suitable metric information as input and the selected service contact instance as output. Such "appropriate information" may be utilized to differentiate selection mechanisms to enable service-specific selections. In the example shown in , the client sends a service access via the network through the "CATS-Forwarder 1", which is an Ingress CATS-Forwarder. Note that, a service access may consist of one or more service packets (e.g., Session Initiation Protocol (SIP) , HTTP , IPv6 , SRv6 or Real-Time Streaming Protocol (RTSP) ) that carry the CS-ID and potential parameters. The Ingress CATS-Forwarder classifies the packets using the information provided by the CATS classifier (C-TC). When a matching classification entry is found for the packets, the Ingress CATS-Forwarder encapsulates and forwards them to the C-PS selected Egress CATS-Forwarder. When these packets reach the Egress CATS-Forwarder, the outer header of the possible overlay encapsulation will be removed and the inner packets will be sent to the relevant service contact instance.

• Note that multi-homed clients may be connected to multiple CATS infrastructures that may be operated by the same or distinct service providers. This version of the framework does not cover multihoming specifics.

Service Contact Instance Affinity Service contact instance affinity means that packets that belong to a flow associated with a service should always be sent to the same service contact instance. Furthermore, packets of a given flow should be forwarded along the same path to avoid mis-ordering and to prevent the introduction of unpredictable latency variations. The CATS framework must ensure that service instance selection and path steering decisions remain consistent for a flow. Specifically, the same Egress CATS-Forwarder need to be solicited to forward the packets. The affinity is configured on the C-PS when the service is deployed, or is determined at the time of newly formulated service requests. Note that different services may have different notions of what constitutes a 'flow' and may, thus, identify a flow differently. Typically, a flow is identified by the 5-tuple transport coordinates (source address and destination address, source and destination port numbers, and protocol). However, for instance, an RTP video stream may use different port numbers for video and audio channels: in that case, affinity may be identified as a combination of the two 5-tuple flow identifiers so that both flows are addressed to the same service contact instance. Hence, when specifying a protocol to communicate information about service contact instance affinity, the protocol should support flexible mechanisms for identifying flows. Or, from a more general perspective, there should be a mechanism to specify and identify the set of packets that are subject to a service contact instance affinity. More importantly, the means for identifying a flow for ensuring instance affinity should be application-independent to avoid the need for service-specific instance affinity methods. However, service contact instance affinity information may be configurable on a per-service basis. For each service, the information can include the flow/packets identification type and means, affinity timeout value, etc. This document does not define any mechanism for defining or enforcing service contact instance affinity.

Operational and Mangeability Considerations

Provisioning of CATS Components Enabling CATS in a network can be done incrementally. That is, not all ingress routers need to be upgraded to support CATS. In addition the CATS steering policies that are communicated by a C-PS to an Ingress CATS-Forwarder, some provisioning tasks are required. This includes, but not limited to:

• Provide C-PS elements with the locators of available Ingress CATS-Forwarder. Such locators may also be discovered from the network.
• Enable required setup to connect C-PS elements with C-NMA and C-SMA.
• Allocate various identifiers CS-ID/CSCI-ID and bind them to specific service contact instances.
• Provide C-PS element with the set of optimization metrics (per service) and an optimization policy.
• Expose Encapsulation capabilities supported by CATS-Frowarders.
• Configure specific encapsulation capabilities of CATS-Forwarders for use, including any credentials for mutual authentication between peer CATS-Forwarders.
• Expose classification capabilities of C-TC elements.
• Retrieve active classification table of C-TC elements.
• Reset the classification table of C-TC elements.
• Set the traffic counter at CATS-Forwarders to ease correlation between both Ingress and Egress CATS-Forwarders. Such correlation is needed to help identify issues induced by the underlying encapsulation.
• Enable tools to check the correct behavior of various entities (e.g., classification rules, steering rules, and forwarding behavior)

The above task can be enabled using a variety of means (NETCONF , IPFIX , etc.). It is out of scope to discuss required CATS extension to these protocols.

Deployment Considerations This document does not make any assumption about how the various CATS functional elements are implemented and deployed. Concretely, whether a CATS deployment follows a fully distributed design or relies upon a mix of centralized (e.g., a C-PS) and distributed CATS functions (e.g., CATS traffic classifiers) is deployment-specific and may reflect the preferences and policies of the (CATS) service provider. For example, in a centralized design, both the computing related metrics from the C-SMAs and the network metrics are collected by a (logically) centralized path computation logic (e.g., a PCE). In this case, the CATS computation logic may process incoming service requests to compute paths to service contact instances. More generally, the paths might be computed before the service request comes. Based on the metrics and computed paths, the C-PS can select the most appropriate path and then synchronize with CATS traffic classifiers (C-TCs). According to the method of distributing and collecting the computing related metrics, three deployment models can be considered for the deployment of the CATS framework:

• Distributed model:

  Computing metrics are distributed among network devices directly using distributed protocols without interactions with a centralized control plane. Service scheduling function is performed by the CATS-Forwarders in the distribution model, Therefore, the C-PS is integrated into an Ingress CATS-Forwarder.

• Centralized model:

  Computing metrics are collected by a centralized control plane, and then the centralized control plane computes the forwarding path for service requests and syncs up with the Ingress CATS-Forwarder. In this model, C-PS is implemented in the centralized control plane.

• Hybrid model:

  Is a combination of distribution and centralized models.

  A part of computing metrics are distributed among involved network devices, and others may be collected by a centralized control plane. For example, some static information (e.g., capabilities information) can be distributed among network devices since they are quite stable (change infrequently). Frequent changing information (e.g., resource utilization) can be collected by a centralized control plane to avoid frequent flooding in the distributed control plane. Service scheduling function can be performed by a centralized control plane and/or the CATS-Forwarder. The entire or partial C-PS function may be implemented in the centralized control plane, depending on the specific implementation and deployment.

Implementation Consideration on Using CATS Metrics According to the metric definition in , computing metrics need to be normalized and/or aggregated in order to low down the scalability impact of the existing route system while providing sufficient detail for effective decision-making. Depeding on the resources and processing capabilities of CATS components, the normalization and aggregation functions can be located in different CATS components. The suggested solution is to implement the normalization and aggregation functions located away from the decision maker, CATS Path Selector (C-PS), especially when C-PS is co-located with CATS-Forwarders. With this in mind, the normalization and aggregation functions of CATS metrics can be placed at Service contact instance or CATS Service Metric Agent (C-SMA). When the C-SMA is co-located with CATS-Forwarders where there is limited resource for processing, the placement of normalization functions in the C-SMA may bring too much overhead and may influence the routing efficiency. Therefore, this document suggests to implement the normalization function at the service contact instance. Regarding the aggregation functions, it can be implemented in the C-SMA, or the service contact instance. In the case of service contact instances and C-SMAs are provided by different vendors, it is needed to use the same common normalization function and aggregation functions, so that the service contact instance selection result can be fair among all the service contact instances.

Verify Correct Operations CATS may be implemented by extending some existing control plane protocols, such as BGP or PCEP. A CATS implementation must log error events for better network management and operation. Means to assess the reachability and trace CATS paths should be supported.

Impact on Network Operations Computing metrics are collected and distributed in CATS. A new function is needed to be deployed to manage the cooperation between network elements and computing elements. For example, this function may be provided by an orchestrator connecting with C-SMA and C-NMA. This might bring more complexity of the network management, especially if this function is not leveraged for other purposes beyond CATS.

Security Considerations The computing resource information changes over time very frequently, especially with the creation and termination of service instances. When such information is carried in a routing protocol, too many updates may affect network stability. This issue could be exploited by an attacker (e.g., by spawning and deleting service contact instances very rapidly). CATS solutions must support guards against such misbehaviors. For example, these solutions should support aggregation techniques, dampening mechanisms, and threshold-triggered distribution updates. The information distributed by the C-SMAs and C-NMAs may be sensitive. Such information could indeed disclose intelligence about the network and the location of compute resources hosted in service sites. This information may be used by an attacker to identify weak spots in an operator's network. Furthermore, such information may be modified by an attacker resulting in disrupted service delivery for the clients, even including misdirection of traffic to an attacker's service implementation. CATS solutions must support authentication and integrity-protection mechanisms between C-SMAs/C-NMAs and C-PSes, and between C-PSes and Ingress CATS-Forwarders. Also, C-SMA agents need to support a mechanism to authenticate the services for which they provide information to C-PS computation logics, among other CATS functions.

Privacy Considerations CATS solutions must support preventing on-path nodes in the underlay infrastructure to fingerprint and track clients (e.g., determine which client accesses which service). More generally, personal data must not be exposed to external parties by CATS beyond what is carried in the packet that was originally issued by the client. In some cases, the service will need to know about applications, clients, and even user identity. This information is sensitive and should be encrypted. To prevent the information leaking between CATS components, the C-PS computed path information should be encrypted in distribution. The specific encryption method may be applied at the network layer, transport layer, or at the application/protocol level depending on the implementation, so this is out of the scope of this document. For more discussion about privacy, refer to and .

IANA Considerations This document makes no requests for IANA action.

Informative References China Mobile Telefonica Huawei Technologies China Unicom Alibaba Group Distributed computing is a computing pattern that service providers can follow and use to achieve better service response time and optimized energy consumption. In such a distributed computing environment, compute intensive and delay sensitive services can be improved by utilizing computing resources hosted in various computing facilities. Ideally, compute services are balanced across servers and network resources to enable higher throughput and lower response time. To achieve this, the choice of server and network resources should consider metrics that are oriented towards compute capabilities and resources instead of simply dispatching the service requests in a static way or optimizing solely on connectivity metrics. The process of selecting servers or service instance locations, and of directing traffic to them on chosen network resources is called "Computing-Aware Traffic Steering" (CATS). This document provides the problem statement and the typical scenarios for CATS, which shows the necessity of considering more factors when steering traffic to the appropriate computing resource to better meet the customer's expectations. This document describes the principles of traffic engineering (TE) in the Internet. The document is intended to promote better understanding of the issues surrounding traffic engineering in IP networks and the networks that support IP networking and to provide a common basis for the development of traffic-engineering capabilities for the Internet. The principles, architectures, and methodologies for performance evaluation and performance optimization of operational networks are also discussed. This work was first published as RFC 3272 in May 2002. This document obsoletes RFC 3272 by making a complete update to bring the text in line with best current practices for Internet traffic engineering and to include references to the latest relevant work in the IETF. China Mobile Huawei Technologies Telefonica Qualcomm Europe, Inc. Huawei Technologies Computing-Aware Traffic Steering (CATS) is a traffic engineering approach that optimizes the steering of traffic to a given service instance by considering the dynamic nature of computing and network resources. In order to consider the computing and network resources, a system needs to share information (metrics) that describes the state of the resources. Metrics from network domain have been in use in network systems for a long time. This document defines a set of metrics from the computing domain used for CATS. In certain networks, such as, but not limited to, financial information networks (e.g., stock market data providers), network performance information (e.g., link propagation delay) is becoming critical to data path selection. This document describes common extensions to RFC 3630 "Traffic Engineering (TE) Extensions to OSPF Version 2" and RFC 5329 "Traffic Engineering Extensions to OSPF Version 3" to enable network performance information to be distributed in a scalable fashion. The information distributed using OSPF TE Metric Extensions can then be used to make path selection decisions based on network performance. Note that this document only covers the mechanisms by which network performance information is distributed. The mechanisms for measuring network performance information or using that information, once distributed, are outside the scope of this document. In certain networks, such as, but not limited to, financial information networks (e.g., stock market data providers), network-performance criteria (e.g., latency) are becoming as critical to data-path selection as other metrics. This document describes extensions to IS-IS Traffic Engineering Extensions (RFC 5305). These extensions provide a way to distribute and collect network-performance information in a scalable fashion. The information distributed using IS-IS TE Metric Extensions can then be used to make path-selection decisions based on network performance. Note that this document only covers the mechanisms with which network-performance information is distributed. The mechanisms for measuring network performance or acting on that information, once distributed, are outside the scope of this document. This document obsoletes RFC 7810. This document defines new BGP - Link State (BGP-LS) TLVs in order to carry the IGP Traffic Engineering Metric Extensions defined in the IS-IS and OSPF protocols. Constraint-based path computation is a fundamental building block for traffic engineering systems such as Multiprotocol Label Switching (MPLS) and Generalized Multiprotocol Label Switching (GMPLS) networks. Path computation in large, multi-domain, multi-region, or multi-layer networks is complex and may require special computational components and cooperation between the different network domains. This document specifies the architecture for a Path Computation Element (PCE)-based model to address this problem space. This document does not attempt to provide a detailed description of all the architectural components, but rather it describes a set of building blocks for the PCE architecture from which solutions may be constructed. This memo provides information for the Internet community. This document provides specifications for existing TLS extensions. It is a companion document for RFC 5246, "The Transport Layer Security (TLS) Protocol Version 1.2". The extensions specified are server_name, max_fragment_length, client_certificate_url, trusted_ca_keys, truncated_hmac, and status_request. [STANDARDS-TRACK] The widespread interest in provider-provisioned Virtual Private Network (VPN) solutions lead to memos proposing different and overlapping solutions. The IETF working groups (first Provider Provisioned VPNs and later Layer 2 VPNs and Layer 3 VPNs) have discussed these proposals and documented specifications. This has lead to the development of a partially new set of concepts used to describe the set of VPN services. To a certain extent, more than one term covers the same concept, and sometimes the same term covers more than one concept. This document seeks to make the terminology in the area clearer and more intuitive. This memo provides information for the Internet community. This RFC is the revised basic definition of The Domain Name System. It obsoletes RFC-882. This memo describes the domain style names and their used for host address look up and electronic mail forwarding. It discusses the clients and servers in the domain name system and the protocol used between them. This document describes the modifications to OSPF to support version 6 of the Internet Protocol (IPv6). The fundamental mechanisms of OSPF (flooding, Designated Router (DR) election, area support, Short Path First (SPF) calculations, etc.) remain unchanged. However, some changes have been necessary, either due to changes in protocol semantics between IPv4 and IPv6, or simply to handle the increased address size of IPv6. These modifications will necessitate incrementing the protocol version from version 2 to version 3. OSPF for IPv6 is also referred to as OSPF version 3 (OSPFv3). Changes between OSPF for IPv4, OSPF Version 2, and OSPF for IPv6 as described herein include the following. Addressing semantics have been removed from OSPF packets and the basic Link State Advertisements (LSAs). New LSAs have been created to carry IPv6 addresses and prefixes. OSPF now runs on a per-link basis rather than on a per-IP-subnet basis. Flooding scope for LSAs has been generalized. Authentication has been removed from the OSPF protocol and instead relies on IPv6's Authentication Header and Encapsulating Security Payload (ESP). Even with larger IPv6 addresses, most packets in OSPF for IPv6 are almost as compact as those in OSPF for IPv4. Most fields and packet- size limitations present in OSPF for IPv4 have been relaxed. In addition, option handling has been made more flexible. All of OSPF for IPv4's optional capabilities, including demand circuit support and Not-So-Stubby Areas (NSSAs), are also supported in OSPF for IPv6. [STANDARDS-TRACK] This document describes Session Initiation Protocol (SIP), an application-layer control (signaling) protocol for creating, modifying, and terminating sessions with one or more participants. These sessions include Internet telephone calls, multimedia distribution, and multimedia conferences. [STANDARDS-TRACK] The Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext information systems. This document specifies the HTTP/1.1 message syntax, message parsing, connection management, and related security concerns. This document obsoletes portions of RFC 7230. This document specifies version 6 of the Internet Protocol (IPv6). It obsoletes RFC 2460. Segment Routing can be applied to the IPv6 data plane using a new type of Routing Extension Header called the Segment Routing Header (SRH). This document describes the SRH and how it is used by nodes that are Segment Routing (SR) capable. This memorandum defines the Real-Time Streaming Protocol (RTSP) version 2.0, which obsoletes RTSP version 1.0 defined in RFC 2326. RTSP is an application-layer protocol for the setup and control of the delivery of data with real-time properties. RTSP provides an extensible framework to enable controlled, on-demand delivery of real-time data, such as audio and video. Sources of data can include both live data feeds and stored clips. This protocol is intended to control multiple data delivery sessions; provide a means for choosing delivery channels such as UDP, multicast UDP, and TCP; and provide a means for choosing delivery mechanisms based upon RTP (RFC 3550). The Network Configuration Protocol (NETCONF) defined in this document provides mechanisms to install, manipulate, and delete the configuration of network devices. It uses an Extensible Markup Language (XML)-based data encoding for the configuration data as well as the protocol messages. The NETCONF protocol operations are realized as remote procedure calls (RPCs). This document obsoletes RFC 4741. [STANDARDS-TRACK] This document specifies the IP Flow Information Export (IPFIX) protocol, which serves as a means for transmitting Traffic Flow information over the network. In order to transmit Traffic Flow information from an Exporting Process to a Collecting Process, a common representation of flow data and a standard means of communicating them are required. This document describes how the IPFIX Data and Template Records are carried over a number of transport protocols from an IPFIX Exporting Process to an IPFIX Collecting Process. This document obsoletes RFC 5101. On December 8-9, 2010, the IAB co-hosted an Internet privacy workshop with the World Wide Web Consortium (W3C), the Internet Society (ISOC), and MIT's Computer Science and Artificial Intelligence Laboratory (CSAIL). The workshop revealed some of the fundamental challenges in designing, deploying, and analyzing privacy-protective Internet protocols and systems. Although workshop participants and the community as a whole are still far from understanding how best to systematically address privacy within Internet standards development, workshop participants identified a number of potential next steps. For the IETF, these included the creation of a privacy directorate to review Internet-Drafts, further work on documenting privacy considerations for protocol developers, and a number of exploratory efforts concerning fingerprinting and anonymized routing. Potential action items for the W3C included investigating the formation of a privacy interest group and formulating guidance about fingerprinting, referrer headers, data minimization in APIs, usability, and general considerations for non-browser-based protocols. Note that this document is a report on the proceedings of the workshop. The views and positions documented in this report are those of the workshop participants and do not necessarily reflect the views of the IAB, W3C, ISOC, or MIT CSAIL. This document is not an Internet Standards Track specification; it is published for informational purposes. This document offers guidance for developing privacy considerations for inclusion in protocol specifications. It aims to make designers, implementers, and users of Internet protocols aware of privacy-related design choices. It suggests that whether any individual RFC warrants a specific privacy considerations section will depend on the document's content. China Mobile Ruijie Networks China Mobile New H3C Technologies New H3C Technologies This document describes a Computing and Network Information Awareness (CNIA)system architecture for Computing-Aware Traffic Steering (CATS). Based on the CATS framework, this document further describes a proposal detailed awareness architecture about the network information and computing information. It includes a new component and the corresponding interfaces and workflows in the CATS control plane.

Acknowledgements The authors would like to thank Joel Halpern, John Scudder, Dino Farinacci, Adrian Farrel, Cullen Jennings, Linda Dunbar, Jeffrey Zhang, Peng Liu, Fang Gao, Aijun Wang, Cong Li, Xinxin Yi, Jari Arkko, Mingyu Wu, Haibo Wang, Xia Chen, Jianwei Mao, Guofeng Qian, Zhenbin Li, Xinyue Zhang, Weier Li, Ines Robles and Nagendra Kumar for their comments and suggestions. Some text about various deployment models was originally documented in .

Contributors ZTE

huang.guangping@zte.com.cn

Verizon Inc.

hayabusagsm@gmail.com

China Mobile

yaohuijuan@chinamobile.com

Huawei Technologies

liyizhou@huawei.com

Huawei Technologies

dirk.trossen@huawei.com

Huawei Technologies

luigi.iannone@huawei.com

Huawei Technologies

shihang9@huawei.com

New H3C Technologies

linchangwang.04414@h3c.com

CICT

xswang@fiberhome.com

Ruijie Networks

wangxuewei1@ruijie.com.cn

Orange

christian.jacquenet@orange.com