From help-file :

TBF queue CONFIG_NET_SCH_TBF Say Y here if you want to use the Simple Token Bucket Filter (TBF) packet scheduling algorithm for some of your network devices or as a leaf discipline for the CBQ scheduling algorithm (see the top of net/sched/sch_tbf.c for a description of the TBF algorithm). This code is also available as a module called sch_tbf.o ( = code which can be inserted in and removed from the running kernel whenever you want). If you want to compile it as a module, say M here and read Documentation/modules.txt

From source-files :

Simple Token Bucket Filter. ======================================= SOURCE. ------- None. Description. ------------ A data flow obeys TBF with rate R and depth B, if for any time interval t_i...t_f the number of transmitted bits does not exceed B + R*(t_f-t_i). Packetized version of this definition: The sequence of packets of sizes s_i served at moments t_i obeys TBF, if for any i<=k: s_i+....+s_k <= B + R*(t_k - t_i) Algorithm. ---------- Let N(t_i) be B/R initially and N(t) grow continuously with time as: N(t+delta) = min{B/R, N(t) + delta} If the first packet in queue has length S, it may be transmited only at the time t_* when S/R <= N(t_*), and in this case N(t) jumps: N(t_* + 0) = N(t_* - 0) - S/R. Actually, QoS requires two TBF to be applied to a data stream. One of them controls steady state burst size, another one with rate P (peak rate) and depth M (equal to link MTU) limits bursts at a smaller time scale. It is easy to see that P>R, and B>M. If P is infinity, this double TBF is equivalent to a single one. When TBF works in reshaping mode, latency is estimated as: lat = max ((L-B)/R, (L-M)/P) NOTES. ------ If TBF throttles, it starts a watchdog timer, which will wake it up when it is ready to transmit. Note that the minimal timer resolution is 1/HZ. If no new packets arrive during this period, or if the device is not awaken by EOI for some previous packet, TBF can stop its activity for 1/HZ. This means, that with depth B, the maximal rate is R_crit = B*HZ F.e. for 10Mbit ethernet and HZ=100 the minimal allowed B is ~10Kbytes. Note that the peak rate TBF is much more tough: with MTU 1500 P_crit = 150Kbytes/sec. So, if you need greater peak rates, use alpha with HZ=1000 :-)