Differences
This shows you the differences between two versions of the page.
| Both sides previous revision Previous revision Next revision | Previous revision Next revisionBoth sides next revision | ||
| docs:guide-user:network:traffic-shaping:sqm-details [2022/01/15 20:42] – [SQM: Link Layer Adaptation Tab] moeller0 | docs:guide-user:network:traffic-shaping:sqm-details [2022/11/17 20:00] – [SQM: Link Layer Adaptation Tab] moeller0 | ||
|---|---|---|---|
| Line 10: | Line 10: | ||
| Smart Queue Management (SQM) is our name for an intelligent combination of better packet scheduling (flow queueing) techniques along with with active queue length management (AQM). | Smart Queue Management (SQM) is our name for an intelligent combination of better packet scheduling (flow queueing) techniques along with with active queue length management (AQM). | ||
| - | OpenWrt/ | + | OpenWrt/ |
| Current versions of OpenWrt/ | Current versions of OpenWrt/ | ||
| Line 91: | Line 91: | ||
| * Choose **ATM: select for e.g. ADSL1, ADSL2, ADSL2+** and set the Per-packet Overhead to 44 bytes if you use any kind of DSL/ADSL connection to the Internet other than a modern VDSL high speed connection (20+Mbps). In other words if you have your internet service through a copper telephone line at around 1 or 2Mbps. | * Choose **ATM: select for e.g. ADSL1, ADSL2, ADSL2+** and set the Per-packet Overhead to 44 bytes if you use any kind of DSL/ADSL connection to the Internet other than a modern VDSL high speed connection (20+Mbps). In other words if you have your internet service through a copper telephone line at around 1 or 2Mbps. | ||
| * Choose **Ethernet with overhead: select for e.g. VDSL2** and set the Per-packet Overhead to 34 if you know you have a VDSL2 connection (this is sometimes called Fiber to the Cabinet, for example in the UK). VDSL connections operate at 20-100Mbps over higher quality copper lines. If you are sure that PPPoE is not in use, you can reduce this to 26. | * Choose **Ethernet with overhead: select for e.g. VDSL2** and set the Per-packet Overhead to 34 if you know you have a VDSL2 connection (this is sometimes called Fiber to the Cabinet, for example in the UK). VDSL connections operate at 20-100Mbps over higher quality copper lines. If you are sure that PPPoE is not in use, you can reduce this to 26. | ||
| - | * If you have a cable modem, with a coaxial cable connector, you can try 22 bytes, or see the **Ethernet with Overhead** details below. | + | * If you have a cable modem, with a coaxial cable connector, you can try 22 bytes, or see the **Ethernet with Overhead** details below. If your contracted rate is greater than 760 Mbps set overhead 42 (mpu 84) as the ethernet link to the modem now affects worst case per-packet-overhead. |
| * Choose **Ethernet with overhead** if you have an actual Fiber to the Premises or metro-Ethernet connection and set the Per-Packet Overhead to 44 bytes. This can be reduced somewhat for example if you know you are not using VLAN tags, but will usually work well. | * Choose **Ethernet with overhead** if you have an actual Fiber to the Premises or metro-Ethernet connection and set the Per-Packet Overhead to 44 bytes. This can be reduced somewhat for example if you know you are not using VLAN tags, but will usually work well. | ||
| * Choose **none (default)** if you have some reason to not include overhead. All the other parameters will be ignored. | * Choose **none (default)** if you have some reason to not include overhead. All the other parameters will be ignored. | ||
| Line 104: | Line 104: | ||
| * **ATM:** It is especially important to set the Link Layer Adaptation on links that use ATM framing (almost all DSL/ADSL links do), because ATM adds five additional bytes of overhead to a 48-byte frame. Unless the SQM algorithm knows to account for the ATM framing bytes, short packets will appear to take longer to send than expected, and will be penalized. For true ATM links, one often can measure the real per-packet overhead empirically, | * **ATM:** It is especially important to set the Link Layer Adaptation on links that use ATM framing (almost all DSL/ADSL links do), because ATM adds five additional bytes of overhead to a 48-byte frame. Unless the SQM algorithm knows to account for the ATM framing bytes, short packets will appear to take longer to send than expected, and will be penalized. For true ATM links, one often can measure the real per-packet overhead empirically, | ||
| - | * **Ethernet with Overhead:** SQM can also account for the overhead imposed by VDSL2 links - add 22 bytes of overhead (mpu 68). Cable Modems (DOCSIS) set both up- and downstream overhead to 18 bytes (6 bytes source MAC, 6 bytes destination MAC, 2 bytes ether-type, 4 bytes FCS), to allow for a possible 4 byte VLAN tag it is recommended to set the overhead to 18 + 4 = 22 (mpu 64). | + | * **Ethernet with Overhead:** SQM can also account for the overhead imposed by //VDSL2// links - add 22 bytes of overhead (mpu 68). Cable Modems (//DOCSIS//) set both up- and downstream overhead to 18 bytes (6 bytes source MAC, 6 bytes destination MAC, 2 bytes ether-type, 4 bytes FCS), to allow for a possible 4 byte VLAN tag it is recommended to set the overhead to 18 + 4 = 22 (mpu 64); if you want to set shaper rates greater than 760 Mbps set overhead 42 (mpu 84) as now the worst case per-packet-overhead is on the ethernet link to the modem. For //FTTH// the answer is less clear cut, since different underlaying technologies have different relevant per-packet-overheads; |
| - | * **None: | + | * **None: |
| Line 298: | Line 298: | ||
| Also to make things even more complicated, | Also to make things even more complicated, | ||
| + | ** How do I get cake to consider IPv6 traffic in a 6in4 tunnel as separate flows?** | ||
| + | See [[: | ||
| ===== Troubleshooting SQM ===== | ===== Troubleshooting SQM ===== | ||