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There are buffers within DAHDI that get filled with data from Asterisk. When the driver has the ability to interrupt the CPU, it pushes the data out over the PCI bus to the Digium card.
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Note: This is seperate from the 'latency' kernel module option and also seperate separate from the jitter buffering than can be done on DAHDI channels within Asterisk.
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Buffer Policy Information
Immediate Buffer Policy | This policy means that as soon as data arrives in the buffer within DAHDI, it is immediately pushed out even if the kernel is doing something else. If the kernel is busy with something else, the data is lost and never gets to the Digium card.
Pros: Low latency Cons: Data loss
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Full Buffer Policy | This policy means that DAHDI will wait until all it's buffers are full before it pushes any data out to the Digium card.
Pros: Little chance of data loss Cons: High latency |
Half Full Buffer Policy | This policy is a balance between the immediate and full policies. It will wait until half of the DAHDI buffers are filled before pushing the data out to the Digium card.
Pros: Less chance of data loss when compared to immediate. Lower latency when compared to full. Cons: More chance of data loss when compared to full. Higher latency when compared to immediate. |
Configuration
As of DAHDI-LINUX 2.2.0 there are a total of three buffer polcies: Immediate, Full and Half. The default policy that is used is the immediate policy with 4 buffers .
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