 T.4 and related fax standards were published by the ITU in 1980, before the rise of the Internet.In the late 1990s, VoIP, or Voice over IP, began to gain ground as an alternative to the conventional Public Switched Telephone Network (PSTN).However, because most VoIP systems are optimized (through their use of aggressive lossy bandwidth-saving compression) for voice rather than data calls, conventional fax machines worked poorly or not at all on them due to the network impairments such as delay, jitter, packet loss, and so on.