EL MODELO RACIONAL

This section describes the different points within the home and the DOCSIS network in which SFC packet marking can start. The problem statement is to figure out what is needed on the DOCSIS Network (CM/CMTS) to enable Service Function Chaining / Marking of traffic flows, as it crosses the Service Function Edge to the SFC domain

Figure 46 -Traffic Flows from DOCSIS Network through Different Service Chains

The starting points where the traffic is classified and marked may differ as described below but the end point is the same, as all traffic destined for the SFC domain will end at the SFC edge, as shown in Figure 47.

SDN Architecture for Cable Access Networks Technical Report VNE-TR-SDN-ARCH-V01-150625

Figure 47 - Different Starting Point of SFC

11.3.1 SFC Initiating from Application

An application can initiate SFC directly. This option is the most granular and most accurate when it comes to selecting a service chain because there is no second-guessing as to what the application needs. The downside is, of course, that it requires changes to the application software and the host OS it is utilizing.

The application can be the starting point on the SFC. There are two methods from the application. The first is the overlay method which creates a tunnel (or a virtualconnection) from the application to the SFC edge. In this scenario, everything from the application would be sent to the SFC. The DOCSIS network would not be aware of the application contents and there would be no classification done on the DOCSIS Network (CM/CMTS). This method would not work if the application needed to leverage the DOCSIS QoS mechanism or QoS mechanism from the CMTS to the SFC edge.

The second scenario is to mark the application so that the DOCSIS network and core network is aware. An example of this would be an MSO-provided VoIP service. The application would mark the traffic so that proper QoS could be applied on the DOCSIS network, and from the NSI side of CMTS to the SFC edge. Other MSO-provided

applications, such as Video On Demand or home security, can leverage the QoS mechanism on DOCSIS and the rest of the network.

11.3.2 SFC Initiating from Home Gateway

The home gateway is part of the home network and, while it might not have the ability to explicitly tag flows based on applications, it still has good visibility into information, such as the type of devices in the home and some information related to identify the user, for example, by using Wi-Fi authentication. Using this information, it should be relatively easy to tag different flows with different SFCs; for example, devices that are defined as “kid devices” can be tagged with SFC that requires parental control while “parent devices” can skip it.

In the context of a home gateway, it’s important not to confuse a tunnel that the home gateway might initiate with SFC. The two concepts are unrelated. A tunneling option from the home would be to use an overlay technique such as VXLAN or GRE tunnel from the gateway to the SFC edge.

11.3.3 SFC Initiating from CM

Initiating SFC from the CM is not a desirable option. Implementing SFC in the CM would not scale and there is no added value. The SFC Marking functionality that can be done on the CM can also be done on the CMTS (as described in Section 11.3.4). From a granularity and feature point of view, it does not offer advantages over the CCAP/CMTS initiated SFC as described in the next section.

11.3.4 SFC Initiating from CCAP/CMTS

It is fairly straightforward to associate DOCSIS upstream service flows with SFC from a data plane processing point of view. Having said that, one has to remember that service flows and service chains are different (and also

be associated with a particular application. It is possible to tag traffic such that different applications have different service flows that map to corresponding SFC. However, one should be careful not to create an inflation of service flows as a result. It is better to use service flows to create a coarse separation of traffic; for example, video versus data versus voice, that can serve as a “hint” for further analysis in case it is needed (see Section 11.3.5).

On the downstream side, the CMTS terminates a service chain. One can view the QoS that the CMTS applies as the end of the “service” that SFC defines; however, the CMTS would still use packet classification rules rather than inspecting the SFC header directly in order to do that. As a future extension, that CMTS can inspect SFC headers directly.

11.3.5 SFC Initiating from a Proxy Behind CCAP

A proxy behind CCAP, a device such as a DPI appliance (physical or virtual), can analyze packet streams and dynamically assign SFC based on the inspected traffic. The upstream classification to DOCSIS service flows can serve as a hint to the appliance. Most importantly, if the tagging is applied correctly, some flows can skip the appliance altogether, resulting in a simpler and less expensive inspection device. For example, a home surveillance camera with a dedicated service flow can be directed immediately to the correct SFC.