connect error: "connection refused"

[VFT]

config.json：

{
    "threads":4,                                 // number of miner threads
    "pools": [
        {
            "url": "stratum+tcp://u1pool.com:18888",
            "user": "------", 
            "pass": "x"
        }
    ]
}

can't connect to pool：

root@h01:~/UlordRig# ./ulordrig 
 * VERSIONS:     ulordrig/1.2.0 libuv/1.8.0 gcc/5.4.0
 * HUGE PAGES:   available, disabled
 * CPU:          Intel(R) Xeon(R) Gold 6161 CPU @ 2.20GHz (1) x64 AES-NI
 * CPU L2/L3:    2.0 MB/30.2 MB
 * THREADS:      4, cryptohello 
 * POOL #1:      u1pool.com:18888
 * COMMANDS:     hashrate, pause, resume
[2018-09-04 17:51:07] [u1pool.com:18888] connect error: "connection refused"
[2018-09-04 17:51:13] [u1pool.com:18888] connect error: "connection refused"