Should routers and modems talk to each other ?

There is a problem looming in the marketplace – more and more people are moving to wireless communication solutions, and Internet Protocol (IP) is pervasive. This is all fine today, but the problem arises when we need to get more from less, as wireless spectrum disappears. In the satellite world solutions such as DVB-S2/ACM vary signal power to meet the current channel conditions (due to clouds for example). On the ground many wireless modems tune to meet the current channel conditions as mobile devices move around dense cities. Again this is fine – however in nearly all networks there is a router, and in order to ensure some level of Quality of Service (QOS) the modem has some level of traffic shaping enabled to prioritise delay or jitter sensitive traffic such as VoIP. This invariably means that the router traffic shapes the traffic going to the modem to a pre defined rate. So when the modem changes speed the router is blissfully unaware and continue to spit out traffic at the old rate regardless of whether the modem has increased or reduced its offered rate. The ubiquitous use of Ethernet has caused a disassociation of not only modem link speed, but also link state and a few other parameters.

So whats the answer – well its actually quite simple – routers and modems should talk to each other. The actual mechanism doesn’t really matter that much, but what is important is that they do talk. This is often called cross-layer design, where a modem which traditionally operates in OSI layer 2 starts to talk out of band to the router that is shaping in OSI layer 3 data rates.

This problem isn’t confined to wireless and satellite modems, modems such as ADSL that auto tune will also need the same feature in the future. It also applies to tunnels such as VPN tunnels where the network state is unknown to the “red” side of the tunnel.

In my previous life many moons ago, a colleague and I tried to start fix this problem. We wrote a few IETF drafts with limited sucess.

However there is a real problem – there exists no standards body that this problem neatly fits into. The layer 3 at the IETF don’t really do much layer 2 anymore. The ANCP people in the IETF only look after DSL (and maybe some wireless networks in the future) but they don’t consider the CPE router as their remit. How can we form a standard interface in which satellite modem vendors, WiFi and WiMax vendors, Military Radio vendors, DSL modem vendors all work together with the multiple Layer 3 vendors when there is no standards body that includes these players at present ?

the technical solution is easy – the politics is a nightmare.


These views are my own and do not represent the views of my employer

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