Some sessions might have routes consisting of both APPN segments and RTP segments. In Figure 1, for example, the VTAM® on HOSTC might not have been defined to provide HPR support. In this case, for a session between HOSTB and HOSTE, HPR is used where possible (between HOSTB and HOSTA and between HOSTD and HOSTE). Otherwise, APPN routing is used (between HOSTA and HOSTC and between HOSTC and HOSTD).