双同步：
BISYNC 代表二进制同步通信。它是一种半双工链路协议，取代了代表同步发送-接收的 SRT。
高密度脂蛋白：
HDLC 代表高级数据链路控制。它适用于 OSI 参考模型的数据链路层。它支持面向连接和无连接服务。
HDLC 和 BISYNC 的特点：
| BISYNC Features | HDLC Features |
|---|---|
| It supports serial transmission. | It also supports serial transmission. |
| Communication mode of BISYNC is synchronous. | Communication mode of HDLC is both synchronous and asynchronous. |
| It uses TWA directional mode. | It uses TWA and TWS directional mode. |
| It supports both point to point and point to multipoint configuration. | It also supports both point to point and point to multipoint configuration. |
| It follows stop and wait flow control protocol. | It follows sliding window flow control protocol. |
| To content errors it uses LRC/CRC method. | To content errors it uses CRC method. |
| It uses SYN SYN frame identifier in framing. | It uses Flag frame identifier in framing. |
| EBT/ETX frame delimiter in framing. | Flag frame delimiter in framing. |
| Multiple bytes information field in framing. | Multiple bits information field in framing. |
| For Framing transparency it follows DLE stuffing. | For Framing transparency it follows ZERO stuffing. |