[Just switch off for a minute and ignore the following]
To confuse matters even more, there are three priority marking systems.
1. 802.1p at layer 2 (ethernet) - for use with all kinds of ethernet frames not just IPv4 or IPv6 packets up with other protocols too.
2. With wireless LANs there is a priority system for marking wireless frames called WMM_something eg WMM_BACKGROUND for low priority and various others, important when controlling different things fighting for time on the wireless LAN. Also at layer 2.
3. at layer 3 = IP there is a label called DSCP or DIFFSERV (»differentiated services”) similar kind of thing for indicating the priority of IP packets.
It all gets a bit weird if things are marked with more than one of these things at once. Does the lowest layer’s marking determine what happens ? So maybe L2 markings are considered, and then if L2 markings are equal, then the L3 marking may or may not be considered next?
And apps or operating systems have to somehow decide how to mark PDUs and at which layer or layers do they apply marking? Perhaps someone could enlighten me?
Perhaps in o/s <blah> apps that send eg IP packets find it difficult to specify what kinds of L2 priority marking should be applied to L2 PDUs on wireful ethernet II or wireless 802.11n/a/ac/whatever, because L2 PDUs are one level too many removed, too far down the stack. Could anyone tell me?
