Architecture and Message in Flight Settings

Each FIX order handler process will allow a single TCP connection from a member. Connection attempts from unknown source IP ranges will be blocked to prevent unauthorized access to FIX ports. The Cboe NOC should be contacted in the event that a Member desires to connect from a new source IP range.

Each FIX order handler will connect, using a proprietary UDP protocol, to all matching units. Connections from order handlers to matching engines are latency equalized. The connections between order handlers and matching units are governed by an internal flow control mechanism to control burst rates.

The maximum number of messages in flight between a FIX or BOE order handler and a CFE matching engine is 64. In addition, when the total number of unacknowledged messages between an order handler and all CFE matching engines exceeds 1024, the order handler will stop reading from the TPH-facing TCP socket. This will cause the order handler to stop removing bytes from the TCP receive buffer and will prevent the TPH from sending more TCP data through the order handler once the TPH's own configured send buffer is full.

When the total number of unacknowledged messages falls below 960, the order handler will resume reading from the TPH-facing TCP socket.

Messages in flight are defined as messages that have been sent by an order handler to a CFE matching engine that have not yet been acknowledged. Each application message sent by a CFE TPH (e.g., a new order, quote update, cancel/replace, cancel, or purge message) counts as one message for this purpose. An order handler includes a CFE FIX or unitized BOE order or quoting match capacity allocation or purge port.

CFE may update either the message in flight or the total number of unacknowledged messages settings with notice. Changes to reduce either limit will be made with a notice period of at least two weeks. CFE reserves the ability to increase either limit immediately with notice.