ACC Installation and Configuration Guide

Tuning and Sizing
ZCOM_MEM_SIZE
Appendix B 81
An appropriate value for zcom_mem_size can be estimated using the
following algorithm:
zcom_mem_size = <card> * <rate> * <time> * (<length> + 200) * 1.5
where:
<card> number of mux cards on the system
<rate> maximum number of messages per
second per mux card (Refer to the
calculation shown below.)
<time> average turn-around time for one
message (including transmission
time). This also depends on the SPU
processing power. For most systems, 5
seconds should be adequate.
<length> average message length.
200 memory overhead per message (in
bytes)
1.5 scaling factor to allow for usable gaps
in the buffer pool
The rate value is calculated as follows:
<rate> = (<bps_rate> * <num_ports> * <duplex>) / <msg_len>
where:
<bps_rate> rate of port in bits per second divided
by 8
<num_ports> number of ports in use.
<duplex> half duplex = 1; full duplex = 2
<msg_len> average number of bytes per message
For example, for a system with 5 ports (at 57.6 Kbits per second per port)
running half duplex with a message length of 100 bytes per message:
rate = (((57.6 * 103 / 8) * 5) * 1) / 100 = 576