ECNs
Over time, more fully automated markets have gained market share at the expense of
less automated ones, in particular, the NYSE. Brokers that have an affiliation with an
ECN have computer access and can enter orders in the limit order book. As orders are
stock exchanges
Secondary markets where
already-issued securities are
bought and sold by members.
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received, the system determines whether there is a matching order, and if so, the trade is
immediately crossed.
Originally, ECNs were open only to other traders using the same system. But following
the implementation of Reg NMS, ECNs began listing limit orders on other networks.
Traders could use their computer systems to sift through the limit order books of many ECNs
and instantaneously route orders to the market with the best prices. Those cross-market links
have become the impetus for one of the more popular strategies of so-called high-frequency
traders, which seek to profit from even small, transitory discrepancies in prices across
markets. Speed is obviously of the essence here, and ECNs compete in terms of the speed they
can offer. Latency refers to the time it takes to accept, process, and deliver a trading order.
CBOE Global Markets, which acquired the BATS platform, advertises average latency times
of about 100 microseconds, that is, 0.0001 second.

概括

随着时间推移，自动化程度更高的市场（尤其是电子通讯网络ECN）不断蚕食纽约证券交易所等低自动化市场的份额。与ECN关联的经纪商可通过计算机系统将指令输入限价订单簿，系统实时匹配订单并即刻成交。

最初ECN仅限内部交易，但《全国市场系统监管条例》实施后，ECN开始跨网络显示限价订单。交易者能同时检索多个ECN的订单簿，并自动将指令路由至最优报价市场。这种跨市场联动催生了高频交易的流行策略——通过捕捉各市场间微小短暂的价格差异获利。

交易速度成为竞争核心，ECN以处理延迟时间为指标展开较量。收购BATS平台的芝加哥期权交易所全球市场宣称其平均延迟仅100微秒（0.0001秒）。