MEF-70 for SD-WAN- A cheat sheet!

This guest blog on MEF-70 is written by Anuradha Udunuwara – My friend and a Subject Matter Expert for Carrier Ethernet, SDN, NFV, and SD-WAN.

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You have probably heard a lot about Software-Defined WAN or SD-WAN.

So, you may know that It falls within the larger scope of SDx and Software-Defined anything ( if you are new, you can check this video to learn more about SDx and SDN)

Depending on the context, SD-WAN could mean a service, technology or an architecture (Just recall “Ethernet” – service (Carrier Ethernet), protocol (Data Link layer), interface etc.).

What is MEF-70 and why so much buzz around it?

With MEF 70, MEF is doing the same thing for SD-WAN ( that it did for Carrier Ethernet); taking SD-WAN as a service and define the required attributes supporting the easy adoption, interoperability or as MEF says, define the “common language for SD-WAN services”. The below from MEF, clearly explains that;

“MEF’s SD-WAN service definition standard describes requirements for an application-aware, over-the-top WAN connectivity service that uses policies to determine how application flows are directed over multiple underlay networks irrespective of the underlay technologies or service providers who deliver them.”

MEF-70 is a great milestone by MEF and a big step towards standardizing how a user can get a standard SD-WAN service from a managed SD-WAN service provider. It enables the deployment of SD-WAN with standard service attributes. More importantly, the buyer and seller of service can refer to the same terms, which will lead to service transparency for both service providers and its customers.

MEF-70 at a high level includes the following two things:

What is Service Attribute?

MEF Services, such as SD-WAN, are specified using Service Attributes. A Service Attribute captures specific information that is agreed on between the Service Provider (an organization that provides services to Subscribers) and the Subscriber (end-user of service) of a MEF Service, and it describes some aspect of the service behavior. SD-WAN Service Attributes includes the enumeration and description of the information that is agreed between the SD-WAN Subscriber and the SD-WAN Service Provider, while SD-WAN Service Framework defines the instances of an SD-WAN Service based on the definitions, service elements, and Service Attributes

For easy understanding, the content of MEF 70 can further be divided into two major areas.

As you can see, Service Attributes is further divided into 3 main areas (small circles);

1. SWVC (SD-WAN Virtual Connection) Service Attributes
2.  SWVC EP (SWVC End Point Service Attributes
3. SD-WAN UNI (SD-WAN User Network Interface) Service Attributes

So Service Attribute is an important part of MEF-70

However, before discussing SD-WAN service attributes, it is worthwhile to discuss the basic components of SD-WAN architecture and basic terms like UCS, TVC, application flows and policies ( also described in MEF-70). After discussing these terms, we will return again to service attributes.

SD-WAN Service Components Architecture

The following diagram shows the association of the components of an SD-WAN service which are also described below and described in MEF-70. SD-WAN Edge is the customer premises equipment also called SD-WAN CPE.

Component 1: SD-WAN Virtual Connection

SWVC or SD-WAN Virtual Connection is an association of SD-WAN Virtual Connection End Points in an SD-WAN Service that provides the logical construct of an L3 Virtual Private Routed Network for a Subscriber.

Component 2: SWVC Endpoint

SWVC End Point or SWVC EP is a logical construct at an SD-WAN UNI that partitions Ingress IP Packets into Application Flows, applies a Policy to each IP Packet based on the associated Application Flow, and selects an appropriate path to transport the IP Packet over the SWVC.

Component 3: UNI

SD-WAN UNI or (User Network Interface) is the demarcation point between the responsibility of the SD-WAN Service Provider and the SD-WAN Subscriber.

UCS and TVC-Two important things on which SD-WAN service is constructed

SD-WAN Services operate over Underlay Connectivity Services (UCS). UCSs are network service offerings that provide connectivity between the Subscriber sites. UCSs can include a variety of services including, but not limited to, Ethernet Services (as defined in MEF 6.2), IP Services (as defined in MEF 61.1), L1 Connectivity Services (as defined in MEF 63), and public Internet Services. Access to these UCSs can be via a variety of networking technologies, such as DSL, HFC, LTE, fiber, Wi-Fi, Ethernet, and the transport can be based on Ethernet switching, IP Routing, MPLS, or other technologies.

In the Fig. 03 above, if traffic is flowing from Site A to Site B, the Site A SD-WAN UNI will become an Ingress SD-WAN UNI and the Site B SD-WAN UNI will become an Egress SD-WAN UNI.

An SD-WAN Service Provider typically builds point-to-point paths called Tunnel Virtual Connections (TVCs) across UCSs that compose an SD-WAN Service. TVCs define the logical forwarding topology of the SD-WAN Service. Each TVC is built over a single UCS with a well-defined set of characteristics, many of which are inherited from the UCS. To forward each ingress IP packet, SD-WAN Edge has to select a TVC.  By building point-to-point TVCs, a Service Provider creates a virtual topology that can be different from the physical topology of the UCS. For example, if one of the UCS is an EP-LAN service connecting all of the SD-WAN Edges, but the Service Provider only builds TVCs from the Headquarters site to each remote site (and not between the remote sites) then the SD-WAN Service is, effectively, a hub and spoke even though the UCS provides a full mesh.

As TVCs are internal to the Service implementation, they do not have Service Attributes.

We now move to internet breakout, which is also an important concept and part of MEF-70

Internet Breakout

When one or more of the UCSc in the SD-WAN Service is an Internet Service (assume UCS2 above), some Application Flows can be forwarded directly to the Internet without being sent over a TVC delivering to another SD-WAN UNI. This capability is called Internet Breakout.

Application Flows and Policies

One of the major characteristics of an SD-WAN service is the forwarding of IP Packets across different UCSs with different attributes based on Policies applied to Application Flows.

Let’s take an example to understand the Application Flows, Flow Groups, and Policies. Assume there are three Application Flows; strawberry, raspberry and blackberry in the Application Flow Group berries. A Policy can be assigned to the group berries, which becomes the Policy for the three Application Flows. Each Application Flow in the group can nonetheless have an explicit Policy assignment that supersedes the group Policy.

Suppose a Policy smoothie is assigned to the berries Application Flow Group at an SWVC EP, then the three listed flows will be forwarded over the SD-WAN using Policy smoothie. However, if at the SWVC EP the Policy pie is assigned to Application Flow strawberry, then raspberry and blackberry will be forwarded using Policy smoothie, and strawberry will be forwarded using Policy pie.

After describing the important terms, lets come back to describe the service attributes.

SWVC Service Attributes

As identified, this has 3 sections. Let’s look at them one by one.

Service Attribute 1: SWVC (SD-WAN Virtual Connection) Service Attributes

Service Attribute 1: SWVC (SD-WAN Virtual Connection) Service Attributes

As shown in the below diagram, the SWVC Service attribute has further seven sub-attributes. There is one instance of these attributes for each SWVC.

SWVC List of Policies Service Attribute includes 6 Policy Criterion as described in the below table taken from MEF-70.

Table 01 – Policy Criteria

Policy Criteria Name	What does it indicate?
ENCRYPTION	Whether or not the Application Flow requires encryption
PUBLIC-PRIVATE	Whether the Application Flow can traverse Public or Private UCS (or both)
INTERNETBREAKOUT	Whether the Application Flow should be forwarded to an Internet destination
BILLING-METHOD	Whether the Application Flow can be sent over an UCS that has usage-based or flat-rate billing
BACKUP	Whether this Application Flow can use a TVC designated as “backup”
BANDWIDTH	Specifies a rate limit on the Application Flow

Even though MEF 70 defines the above Policy Criteria, the Service Provider, if required can have its own additional criterion defined by them.

Application Flows that can be recognized by the SD-WAN service and information about how to identify IP Packets in each Application Flowis specified by the SWVC List of Application Flows Service Attribute. MEF 70 defines 15 Application Flow Criteria that can be used to describe Application Flows.

Service Attribute 2: SWVC EP Service Attributes

As described in Fig. 03, SWVC EP is the construct that represents the attachment of an SWVC to a UNI. The SWVC EP provides a container for attributes of the SWVC that can differ at each UNI. There are 3 attributes defined by MEF 70 as below.

Fig. 05 – SWVC End Point Service Attributes

Service Attribute 3: UNI (User Network Interface) Service Attributes

At any given UNI there is only a single Subscriber and a single Service Provider.  MEF 70 defines 5 SD-WAN UNI Service Attributes (shown in the below diagram). SD-WAN Service delivers IP packets between multiple Subscriber Network locations. Therefore, if you carefully see, you can identify that most of the attributes are adapted from the UNI Services Attributes and UNI Access Link Service Attributes section of the MEF Service Attributes for Subscriber IP Services Technical Specification (MEF 61.1). This has been done to achieve the commonality between MEF IP Services and MEF SD-WAN Services.

That’s my answer to the question What is MEF 70 and a brief cheat sheet. If you have any questions or comments, I’m happy to answer them.

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Anuradha Udunuwara, ARC Tube