linux command ab for benchmark on nodejs concurrent processes

Option at ab linux command for benchmark is described at http://linux.die.net/man/1/ab,

-n number of request -c number of concurrency

for example command to get statistic result on requesting index.html (file size=5937 bytes)

  ab -n 1000 -c 1000 http://localhost:8000/ and show the output as follows

My question is the command execute 1000 concurrent process to get the index.html in 1000 times from one nodejs process at the same start time Right ? Why I need to specify -n 1000 ? How to describe the command with -n 1000 and -c 1000 together ? I believe -n option is set just for number of request re-try if previous request is failed for one process request. Right ?

    The command output on apache Centos
    ==================================
    Server Hostname:        localhost
    Server Port:            8000

    Document Path:          /
    Document Length:        5937 bytes

    Concurrency Level:      1000
    Time taken for tests:   0.725 seconds
    Complete requests:      1000
    Failed requests:        0
    Write errors:           0
    Total transferred:      6052000 bytes
    HTML transferred:       5937000 bytes
    Requests per second:    1378.45 [#/sec] (mean)
    Time per request:       725.455 [ms] (mean)
    Time per request:       0.725 [ms] (mean, across all concurrent requests)
    Transfer rate:          8146.83 [Kbytes/sec] received

    Connection Times (ms)
                min  mean[+/-sd] median   max
    Connect:        0   21  30.0      0      83
    Processing:    25  135  74.2     94     286
    Waiting:       24  135  74.2     93     286
    Total:         54  156  80.3    131     351

    Percentage of the requests served within a certain time (ms)
    50%    131
    66%    227
    75%    238
    80%    242
    90%    257
    95%    266
    98%    269
    99%    272
    100%    351 (longest request)