按照信息传送的时间和方向，数据通信系统有（ ）几种方式。

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SQL Error: select id,body,options from ***_enewstiku where sourceid='29462' and id < 2399410 and id<>'2399410' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku where sourceid='29462' and id > 2399410 and id<>'2399410' order by id asc limit 5