Co-Location
Co-location is an arrangement whereby trading firms install their servers in the same data centre as an exchange's matching engine, minimising network latency to microsecond levels and enabling high-frequency and algorithmic trading strategies that depend on speed of execution.
When an order is submitted to an exchange, it travels as an electronic signal from the trading firm's server to the exchange's matching engine. Even at the speed of light, physical distance introduces latency measured in milliseconds or microseconds. Co-location eliminates most of this distance by allowing participating firms to rack their own servers inside the exchange's data centre or an approved third-party facility directly connected to the exchange.
The National Stock Exchange of India (NSE) began offering co-location services in 2010, initially from its Mahape facility in Navi Mumbai. Firms that purchased rack space inside or adjacent to NSE's data centre could route their orders to the matching engine in under 100 microseconds, compared to several milliseconds for firms connecting from remote offices. This latency advantage, small in absolute terms, is decisive in strategies such as statistical arbitrage between NSE and BSE, index arbitrage between the Nifty cash and futures segments, and market making in equity derivatives.
The NSE co-location controversy, which became public in 2015, involved allegations that certain co-location clients were granted preferential access to the tick-by-tick data feed — the 'primary' server connection — before others received the data on the 'secondary' feed, creating a two-tier information hierarchy. SEBI investigated the matter and in a 2019 order found NSE guilty of providing unfair access. NSE was directed to disgorge profits and pay a penalty. The case became one of the most significant market-structure enforcement actions in India's capital market history and prompted a complete overhaul of NSE's co-location policies, including implementation of randomised order sequencing and stricter equal-access protocols.
SEBI's framework for co-location and proximity hosting, outlined in circulars issued following the investigation, mandated equal latency access for all co-location participants, prohibited preferential server connectivity, and required exchanges to publish detailed technical specifications of their connectivity offerings. Firms must register as algorithmic trading participants and obtain SEBI approval before deploying co-located systems.
The economics of co-location are significant: NSE charges annual rack fees that historically ranged from several lakhs to over a crore per rack depending on location and power requirements. Despite the cost, the latency advantages available to co-located high-frequency traders create a structural barrier to entry that has drawn criticism from market participants who argue it creates an uneven playing field. SEBI's ongoing review of HFT and co-location practices continues to refine the regulatory framework.