The endpoints sending and receiving calls must be connected to a private network that uses H.323 trunking or LAN connections between gateways and/or port networks. Calls must be able to 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.

Therefore, you must assign the IP codec you define in this procedure to the network gateways. For our example, the network region 1 will be assigned codec set 1, which you are enabling to handle fax and TTY calls.