This read-write enumeration caps the fax transmission rate the gateway will negotiate for T.38 fax relay, with choices such as fx2400bps up through fx14400bps. An admin lowers this ceiling on links with poor quality or limited bandwidth to force fax calls to negotiate down to a rate the connection can reliably sustain. For example, setting t38MaxFaxTxRate to fx9600bps on a congested WAN link prevents fax machines from attempting a 14400bps session that would be more likely to fail or retrain.