The ability to transmit fax, modem, and TTY calls over IP trunks or LANs and WANs assumes that the endpoints sending and receiving the calls are connected to a private network that uses H.323 trunking or LAN connections between gateways and/or port networks. This type of transmission also assumes that calls can either be passed over the public network using ISDN-PRI trunks or passed over an H.323 private network to Communication Manager switches that are similarly enabled. As a result, it is assumed that you have assigned, or will assign, to the network gateways the IP codec you define in this procedure. As an example, assign codec set 1 to the network region to enable handling of fax, modem, and TTY calls.