SFC's OAM Management framework

1, Introduction SFC

Service function Chain (SFC): A series of sequential combinations of services functions, primarily for packet/frame categorization in the network, as well as network functions that can be dynamically sequenced for deployment, independent of the topological structure of these network functions, and the ability to exchange metadata between participating network entities.

2. SFC Hierarchy model

Deploying SFC requires a number of layers of coordination, including the service layer, network layer, Transport layer, physical link layer, and so on, as an SFC hierarchy model:

Service layer mainly consists of: classifier and some service functions, using transmission network to transfer data between classifier and service function or service function; transmission network: Refers to the transport layer and Network layer, is the transmission medium between service functions, almost to the service function transparent, Through a variety of coverage network technology to connect the service function and establish a service function path; physical link layer: Depends on the physical technology, this layer is widely deployed Ethernet, the other is POS, DWDM and so on.

3, SFC monitoring aspects of OAM

SFC's operations are primarily at the service level, and are based on this to define the SFC's OAM framework, and the following are some aspects that SFC must be able to monitor:

1> Service function

Service functions can be divided into SFC-aware and SFC-aware, an SFC-aware service function is able to parse an SFC packet with a service function forwarding component and a service function sub-component, and the SFC is not aware of the service function is just the opposite, And the need for a separate service function forwarding node (SFF) access, whether based on the SFC-aware service or SFC-aware, requires SFF access, so SFC's OAM must be able to monitor and service the function-linked SFF.

2> Services function Path (service function path)

SFP refers to the set of service functions, and the SFC's OAM framework must be able to monitor the SFP and the service path that can render a particular packet.

3> classifier

The classifier determines which packages will be mapped to an SFP, and SFC's OAM must also be able to monitor the operation of the classifier.

The SFC monitoring aspects of OAM are as follows:

3.1 operation and performance of service functions

Operation of the 1> monitoring service function

SFC's OAM obtains information about service functional components by monitoring an SFC-aware network device (SFF). The General Monitoring service functional component operation is not in the scope of the SFC's OAM, because service functions provide services that are not covered by SFC, and the service functions have their own monitoring tools. But SFF also provides an optional feature to monitor the operation of its connected service functions and feedback monitoring information.

Performance measurement of 2> service functions

SFC detects packet drops and delays for specific service functions through SFC-aware network devices, which can be deployed on local network devices or on other network devices.

3.2 Operation and performance of the service function path

1> Monitoring Service function path operation

SFC's OAM must be able to monitor the SFP to obtain SFC and report links, providing fault isolation.

In order to perform the service link authentication of the SFP, the OAM tool must be able to detect either an end-to-end path from any of the SFC-aware network devices or a partial path that terminates to the specific network function of the SFP. The function of the OAM is to ensure connectivity of the service functions that are connected, and to define the necessary return information in the OAM response package to authenticate the interconnection. For a given SFC when there is an equivalent route for the service layer, the OAM must be sufficient to discover and traverse all available paths.

2> Service function Chain performance measurement

SFC's ingress or SFC-aware network devices must be capable of measuring the loss and delay of SFC packets.

3> monitoring Classifier

A classifier defines a stream to a specific SFC, so the classifier will correctly map the incoming stream to SFC, so SFC's OAM must be able to test the definition and function of the test flow to the expected SFC.

4, SFC's OAM function

1> connection function (Connectivity Functions)

Connectivity is used to verify the connectivity of network elements and the availability of service functions, and Ping is a tool used to measure connectivity, and when probing an SFC component, the OAM message that is sent should encapsulate the SFC's header and the identity of the OAM. The OAM message that is sent may encapsulate the SFC's header and the identity of the OAM when the Service feature component is probed.

2> continuity (Continuity Function)

Continuity is the ability to confirm the accessibility of SFC or to a given service function by periodically sending OAM messages, which requires the operator to monitor network equipment and quickly detect faults (link failure, network failure, service interruption, SFC interrupt), The function of the OAM continuity check informs other OAM functions of detected faults and takes proper recovery measures. The BFD is a fast fault detection tool.

3> Routing Capabilities

The routing feature is an important OAM feature that triggers an action (resulting in a response) on the transport device on the test layer, which is typically used to collect information about the transmission device, isolate the point of failure to the service function, or SFC.

4> Performance measurement function

Performance management functions involve measuring the loss rate, latency, etc. of SFC packages, which should be active on-demand measurements. A statistical method is used to measure the packet loss rate of a given SFC. SFC delay is the packet from the SFC port to the port of the time difference, since SFC is usually unidirectional, so it is important to measure the one-way delay, the measurement delay requires clock synchronization, NTP,GPS, etc.

5, the existence of deficiencies

1> presence of OAM functions

Various OAM tools provide OAM functionality at the Network layer, protocol layer, and link layer, these tools support different network types, such as Ip,mpls,trill, but providing links and continuity testing in the overlay network still needs to be researched. The following are the OAM tools, but none of these tools have a uniform standard:

2>oam Functional Requirements

The current main OAM functions are in the network layer, transport layer, and link layer. Configuration, orchestration, management service functions and service function chains all require CLI, netconf, etc.

6. Unresolved issues

1, the performance measurement needs more refinement

2. Call out which OAM functions can is achieved by protocol design vs requiring synthetic traffic.

7. Security

1. Prevent DDoS attacks through OAM channels

2. Prevent the leakage of OAM packets between two service function chains

3. Prevent information from leaking outside of the SFC's management domain

SFC's OAM Management framework