HDLC
High-Level Data Link Control (HDLC) is a framing protocol used to encapsulate other network protocols such SS7, ISDN, X.25, PPP and others.
An HDLC controller, essentially special-purpose circuitry on a motherboard, provides the ability to receive HDLC packets. For a full-duplex (FDX) SS7 link, 2 HDLC controllers are required.
TelcoBridges and HDLC
TelcoBridges supports HDLC via its Tmonitor family of products that support activities such as network monitoring, lawful intercept, and location-based services. The entry-level TM1000 device features up to 512 HDLC controllers, while the TM3000 devices support up to 2048 HDLC controllers.