How sensitive is TDMoE to BER?

Question

We are currently looking at connecting two Asterisk servers across a Metro Ethernet. This leads to a couple of questions I haven't been able to find answers to elsewhere.

The first involves bit error rates and cabling. I would expect that TDMoE, by virtue of being timing sensitive would also be very sensitive to bit error rates (i.e. I don't see how missing data could be retransmitted). Is this a correct assumption? Data seems pretty sparse. Should I be basing cabling considerations around BER for the links between the two servers? Should I be asking BER-related questions to the Metro Ethernet provider?

Or is the protocol capable of handling reasonable loss?

I don't have a lot of experience with TDMoE but thinking through this, my concern is that lost ethernet frames would lead to lost PRI frames which might lead to dropped calls and PRI's going into alarm states.

Answer 1

Take a look at https://www.rfc-editor.org/rfc/rfc4553, generally speaking while the transport should provide error information, you'll loose information, there's no way to retransmit something that was sent. The transport itself (CEoIP in Cisco speak, or more generally - L2VPN with TDM transport over it) will be fine as long signalization will work between end nodes, your application however, running it's data over the TDM may encounter errors.

That's why it's critical for the nodes to be able to properly time the transport. If you'll be providing the transport yourself this is also different discussion that if you're asking for transport - for typical ME service, you'll get typical Ethernet BER assurance.