Voice over HDLC | Non-IP Alternatives to Traditional Telephony

If your particular network situation involves a point-to-point T-1 circuit, you might want to consider voice over High-level Data Link Control (VoHDLC). HDLC is a Layer 2 protocol typically used for point-to-point circuits. VoHDLC is similar to VoFR in that it allows multiple calls to be placed over the T-1 using compression. In the instance of tie-line replacement using T-1s and Cisco equipment, VoHDLC can be an attractive alternative. One of the major drawbacks to VoHDLC is that it has very limited scalability. It was originally designed for point-to-point connections between Cisco routers (Figure 1).

Figure 1: VoHDLC Configuration

As you can see, you have a fair selection of technologies at your disposal for bypassing or supplementing your PSTN needs. No one technology is the "best"; instead, your requirements determine which you will need. VoIP best leverages the investment that you have likely made in your data network to handle your voice needs.