Hardware to give IP packets priority

(written by lawrence krubner, however indented passages are often quotes). You can contact lawrence at: lawrence@krubner.com, or follow me on Twitter.

Damn clever.

Let’s use your example – you have a fantastic router with DD-WRT and the best QoS in the world. Your router detects a high #1 priority packet and places it at the top of the egress queue so that the high priority packet immediately exits the router at the “front of the line.” Wonderful! Next, the high priority packet immediately enters the “end of the line” of the modem’s single adaptive rate buffer (ARB). Well, modems have no idea about QoS or prioritization, so your high priority packet must wait in queue behind ALL the previous packets before it exits to the Internet. All packets must wait for their turn – there is no jumping to the front of the line in a modem! Put another way, modems remove any semblance of “prioritization” from packets – all packets are equal in a modem. Democracy in action!
That said, the LagBuster solves the modem lag problem by precisely matching the ingress and egress flow rates, and limiting the modem to only one packet in the ARB at any time. Further, with LagBuster’s dual buffer, the high packet priority status is retained. With no other packets in the ARB to cause queuing delays, the LagBuster can always send high priority packets from the high priority buffer at maximum speed.
Lastly, the dwell time (“lag”) in the modem is basically proportional to the modem’s buffer size and upstream bandwidth. A consumer grade modem may add up to hundreds of milliseconds of delay to the packet stream. For example, a typical modem buffer is about 300KByte, and a typical upstream speed is about 5Mbps, which can result in as much as 500ms delay for a packet flow. QoS routers cannot ever solve that delay. LagBuster does.”

Post external references

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    http://www.cringely.com/2012/10/01/clothing-may-be-optional-but-bufferbloat-isnt/
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