How can a telecommunications carrier convert his layer 3 transmission network to layer 2 at client site?

Question

Ok, my company has three telco providers, each telco provides data links from the central site to different remote sites. Telco provider 'A' provides layer 2 "dedicated" fiber optic links from the central site to remote sites 1, 2, and 3, and each remote site can be accessed through a distinct port on a layer 2 switch at the central site. My company is then free to place layer 3 devices with IPs from a given subnet at the remote sites and central site. That is the ideal scenario.

Now, telco provider 'B' for remote sites 4, 5, and 6, only has satellite links and they say that their transmission network is layer 3, but they have added extra equipment to convert it to layer 2 as required by my company. The only thing is that they can only give us one physical layer 2 port at the central site through which we can access sites 4-6. Layer 3 devices are again connected to the given layer 2 ports at local and remote ends.

Finally, telco provider 'C' for remote sites 7-9, also only has satellite links and has a layer 3 transmission network, but they are not able to give us access to the remote site through a layer 2 device, instead they can only deliver us layer 3 access to the remote sites.This means that the remote end devices must have IPs from their subnet, and we must create routes to their network from our central site.

(all three scenarios are exemplified in rudimentary attached image)

I am trying to work with providers B and C, so that they can migrate to the same scenario as provider A. Unfortunately, I do not know how provider A is able to deliver this scenario, nor do I know if there is some limitation for satellite networks that makes this more difficult.

In conclusion, my questions are: How can a telecommunications carrier convert his layer 3 transmission network to layer 2 at client site ? Once this is done, how can he deliver a link to each remote site on a different switchport?

Answer 1

Layer 2 over a Layer 3/IP core can be done by using tunnels between the appropriate supported endpoint equipment. Some possible tunneling protocols are:

• L2TP
• GRE
• VPLS (over a MPLS backbone, not strictly L3)
• …

(some disadvantages of using L2 over a global network are growing broadcast traffic and increased difficulty to manage a L2 network with many devices…)

Most of these options would be able to provide a separate interface for each remote site on a switch at your central site, but it really depends on the configuration implemented by the service provider. This includes the equipment that is or will be used, engineering skills, etc.

If the service provider doesn't give you L2 connectivity when you directly ask for it – you should change your ISP or build the L2 connectivity yourself with the assistance of an integrator and your own equipment that can create a L2 extension over L3 (aka, pseudowire).