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P-T-P T1 buffering


I freely admit I newbie to T1's, please help, please limit laughing to off line, grin.

We are considering running a point to point T1 from one office to another, so we can run a MS Access DB application across the T1. We have tried other methods of connecting the offices, such as VPN and wireless, but have seen data corruption.

Then I realized the routers on either end of the T1 have memory, and wondered if it would buffer the data stream.

Would the data be buffered?

If we used 2821's, with 256 MB of memory, any ideas what percent of the memory would be used of the IOS, and what percent available to buffer?

What would happen if the buffers were full?

Thanks for any and all help and ideas,



Re: P-T-P T1 buffering

Hi Jeff


The router maintains two different sets of buffers: public pools that the router can use for anything, and interface specific pools that it can only use for processing packets on that interface.

Here is a list of public buffers that are maintained

Buffer size

Buffer pool name

104 bytes

Small buffers

600 bytes

Middle buffers

1536 bytes

Big buffers

4520 bytes

VeryBig buffers

5024 bytes

Large buffers

18024 bytes (default)

Huge buffers

You can configure any size between 18,024 and 100,000 bytes for your huge buffers. Since the router can only use memory in buffer-sized chunks, having extremely large buffers can be useful if you find that you need to manipulate extremely large packets. However, the default value of 18,024 should be large enough to handle the largest MTU values for all standard interface types. It's unlikely that you'll need to adjust this parameter.

As you can see by the range of values I specified, most of the memory out of the 256MB you mentioned will be utilized by the public pools. Interface pools come into play only when data has to be buffered and that too only to the extent specified by the maximum value (1,00,000 bytes)

If you inadvertently overallocate your buffers while trying to improve system performance, you may find that the router does not have enough memory to operate properly when the load increases.

If the buffers are full as is the case with any technology, data will be dropped to a certain extent. If your buffers are constantly hitting 100% utilization, the only way out is probably getting more bandwidth !


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