The H.323 protocol is specified so that it interoperates with other networks. The most popular H.323 interworking is IP telephony, when the underlying network of H.323 is an IP network and the interoperating network is SCN (see Figure 10). SCN includes PSTN and ISDN networks.

Figure 10. IP Telephony: H.323 Interworking with SCN

H.323 is compatible with various other H.32x networks. Figure 11 shows an H.323 zone interworking with all H.32x networks. The ITU–T recommendation H.246 specifies interworking among various H.32x networks.

Figure 11. H.323 Interworking with Other H.32x Networks