Signaling System #7 (SS7) was derived from the earlier SS6, which explains the similarities. SS7 provides much more capability than SS6. Where SS6 used fixed-length signal units, SS7 uses variable-length signaling units (with a maximum sized length), providing more versatility and flexibility. SS7 also uses high-speed data links (56 kbps). This makes the signaling network much faster than SS6. In international networks, the data links operate at 64 kbps. Study is under way to increase this in the United States to 1.544 Mbps, and internationally to 2.046 Mbps.

As of 1983, SS6 was still being deployed throughout the United States telephone network, even though SS7 was being introduced. As SS7 began deployment in the mid-1980s, SS6 was phased out of the network. SS7 was used in the interoffice network and was not immediately deployed in the local offices until many years later.

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