PTP670/PTP450i - RFC 4938?


Does PTP670/PTP450i support RFC 4938? We are trying to achieve something based on the attached document - Radio Aware routing.


Thanks for asking the question. I'll provide some information relating to PTP 670, and I'll ask a colleague to answer for PMP 450i.

The short answer is that PTP 670 doesn't support Radio Aware Routing using RFC 4938.

Radio Aware Routing is often applied as a general term for an approach to routing where route selection depends on link quality and capacity of wireless links attached to the router. RAR might also include enhancements to accelerate convergence when links come up or go down, and/or flow control to restrict the amount of data buffered in a wireless node. Of course, there are really good reasons for wanting to do this when the network has multiple routes. There's not much to be achieved in a network that is a simply-connected tree topology.

Several different protocols have been proposed in the industry for the link between the router and the attached wireless link. Some protocols worth looking at in more detail are:

- RFC 4938. This RFC (released in 2007) describes a means of communication between the router and the wireless node. RFC 4938 is based on PPPoE. The RFC has a stern warning from the Internet Engineering Steering Group (IESG) saying that the method proposed violates important layer principles and shouldn't be used.

- RFC 5578. This RFC (released in 2010) replaced RFC 4938. The IESG were still not happy.

- RFC 8175. This RFC (released in 2017) describes an approach called Dynamic Link Exchange Protocol (DLEP). DLEP has been a work in progress for at least 10 years. DLEP is quite different from the PPPoE approach described above.

- ITU-T Rec. G.8013/Y.1731 Amendment 1. This standard introduces a new bandwidth notification message at the Ethernet layer, known (logically enough) as ETH-BN.

Finally, we already implemented a proprietary Cisco bandwidth notification technique in PTP 650 and PTP 670. This is known as Microwave Adaptive Bandwidth (MAB). It's fair to say that this has not so far achieved widespread application in the PTP products. We can share details of this with you if you think it's an interesting approach.


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HI Mark,

Thanks for the in-depth sharing on multiple types of protocol. I have attach the logical diagram of our wireless network that will be implemented soon. We are currently using a layer 3 switches at every location and will be enabling the OSPF and ERP switching system for redundancy. Also, we have enhanced the link SLA availability using bigger antenna (high performance) @ 99.99% 100Mbps with noise floor of -73dBm. With all that, there are still some possibility that some of the wireless links may have fluctuation of modulation mode, thus, inconsistent bandwidth that may affect the overall performance of user experience. We all know that OSPF and ERP switching can't be of any help to decide which path is best to go because the bandwidth is unknown to them. 

Can you provide some solution to overcome this?

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