Currently, I/O memory is set at a level of available DRAM (10 percent). In many cases, this is a poor allocation of DRAM because in most customer environments I/O memory can be established at much lower portion of available DRAM.
T.37 is a store-and-forward method, and it needs packet memory to store fax messages. This puts a requirement of 2.0 MB of iomem and 8.0 MB of process memory to be free before admitting any T.37 fax call.
This problem is solved by increasing the I/O memory manually. To increase the I/O memory, issue the memory-size iomempercentage command in global configuration mode.
By default, the I/O memory size is 10 percent. It can be increased to 15 percent or more depending on the application that is running. You can issue show memory summary command to verify the memory allocated.