Hello, I have been trying to understand how applications should use network QoS. My interest have been mostly from wireless perspective, especially how to utilise WMM and U-APSD properly, but naturally this applicable to all networks. I have done some research about this, but I haven't managed to get anywhere. For example, from my point of view DiffServ is just one big mess and I can't see how in practise it can help applications. I wrote a small wiki page to sum up my findings: http://wireless.kernel.org/en/developers/Documentation/qos I would like to clear up all this by and I'm willing to write a document for application developers about network QoS. But I need help to understand what's the proper way to mark different QoS prioritities. In the wiki page I have tried to come up with different possible solutions (copied below), but I'm sure there are even more ways. Please comment. I would like to get some understanding about this. ---------------------------------------------------------------------- Solution 1: SO_PRIORITY with values 0-7 Easy, applications need to just use setsockopt() and be done with it. It's unknown how widely supported values 0-7 are and the exact meaning of them, but at least they make sense (0 default, 1 lowest priority and 7 highest priority). The problem is that the priority is used only in the first link, rest of the route is not able to benefit from the classification. Pros: * easy for applications * works with both IPv4 and IPv6 Cons: * only visible in in the first L2 link, not visible to upper layers (IP) * no well defined meaning for the priority values Solution 2: SO_PRIORITY with values 256-263 mac80211 uses these values to map the packets to DSCP classes. Most probably non other stack or driver (even non-wifi ones) use these values. Otherwise similar as Solution 1. Pros: * easy for applications * works with both IPv4 and IPv6 Cons: * only visible in in the first L2 link, not visible to upper layers (IP) * no well defined meaning for the priority values * using values over 256 is not intuitive Solution 3: IPv4 DSCP field with values 0-7 Most, if not all, wifi drivers should use it. And, in theory, the receiver should also benefit from the classification, unless ISPs modify it of course. But the standardisation for IPv4 QoS bits is a mess. Pros: * visible in IP layer (but ISPs change the value often?) Cons: * applications need to handle IPv4 and IPv6 separately ---------------------------------------------------------------------- -- Kalle Valo -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
