On 8/Jul/16 04:43, Manuel Marín wrote:

Dear Nanog community

We are currently experimenting TCP degradation issues in some metro markets where there are multiple POPs and the IP packets have to pass multiple L3 access devices (routers) before reaching the core router. The more L3 hops that it goes through the more degradation we see in the Internet service. L3 routers have the capacity in terms of pps and BW and we are using just a small percentage of that capacity but anyway the service is degraded (No CRC/Input errors in the links). A couple of vendors are recommending using OTN or MPLS-TP to backhaul the connections from the access to the core but obviously deploying OTN means a considerable amount of capex. The flexibility and simplicity of the L3 based access network is great but given the performance issues we are experimenting I would appreciate if you can share your experience/recommendation with either OTN or MPLS-TP. Does it really make sense to use a OTN/Photonic layer to backhaul the L3 connections in a metro network?

Are you running your Metro-E networks on dark fibre all the way into your core, or are you leasing a lit service from another carrier for this? If the former, you should not have any issues with performance considering a well-designed network. If the latter, you are in the hands of your carrier, and you would need to qualify that they know what they are doing before you overlay your network on top of theirs. I cannot find any benefit in running your Metro-E network on dark fibre vs. OTN into the core apart from when you hit the port bandwidth limits in your Metro-E network and need to go to DWDM to upgrade that so as to keep the fibre-count down while increasing bandwidth. We run a large dark-fibre-based Metro-E network without any DWDM equipment between most rings and our core, and there is no tangible difference in performance between services delivered on those rings or services delivered upstream in the core data centres. There is also no difference in performance between the dark fibre rings vs. the DWDM rings (although, depending on your equipment vendor, some platforms could introduce quite a bit of serialization delay, but not enough to affect actual performance). Sounds like your vendors are trying to sell you boxes... Mark.