Service Transparency

Services as far as the eye can see...

If you were to look at all the potential options that could be conceiveably be supported within the world that is Metro Ethernet, it would make your head swim.

Last blog entry I mentioned that there are roughly two categories for ME services; point-to-point and multipoint. I also wrote that point-to-point Ethernet Virtual Connections (EVCs) can be used to provide a replacement for Frame Relay service. And most WAN connections are typically terminated with some type of routed interface.

But since it's ethernet we're talking about, you may be interested in using something other than a routed connection at the edge. In fact, because ethernet is such a simple and inexpensive solution, it's possible for very small customers with just a few sites to get connected together and appear as a single broadcast domain (or VLAN). And that brings us to the switched edge connection rather than routed.

As a switched connection, the enterprise customer will have certain expectations. After all, if the service provider is going to appear to behave as a 'big switch', from the enterprise perspective, it should really behave like a switch.

When I connect two switches together certain things happen. One of those things that happeneds is that certain layer-2 management protocols -- like spanning tree -- are negotiated. A general rule for provider networks is that the provider should not participate with their customers in these layer-2 management protocols: they should tunnel them through the provider network or drop them at the edge. And what this means to the enterprise customer is that if the provider network is going to behave as a 'big switch', it needs to support the spanning tree protocol. Since the provider will not participate with the customer in spanning tree, it really needs to tunnel it. Sometimes this is not clear in the service offering.

Creating a bridged loop, which is to say a layer-2 loop, through the provider network without their knowledge can cause the enterprise customer no end of headaches if they have not discussed this with the provider. So, I encourage all you enterprise customers to make sure you explain exactly how you intend to use the service to your provider so that they may sell you the correct service which will support this.

Next blog I will introduce some of the MEF services and what you could use them for.