APS (automatic protection switching): a feature in ATM suggests that two cables can be made redundant--one protects the other. If one fails, the connection is switched to the ready protection fiber.
Connect Code: generally used to handle connection services to higher layers.
DS3: based on DS0, a transmission rate of 64Kbps, the bandwidth normally used for one telephone voice channel; transfer rate is 44.736Mbps.
HAL (hardware access layer): the part of the device driver in which the interfaces and constants are based upon the physical hardware.
HSL (hardware shielding layer): the part of the device driver whose interfaces and constants are based upon the needs of the resource layer.
ISR: interrupt service routine or request.
POS: packet-over-sonnet interface.