RTP can switch automatically and reroute data around a failed node or link without disrupting the LU-LU sessions. This is called nondisruptive path switching because LU-LU sessions survive link failures. Nondisruptive path switching within the HPR portion of the network automatically occurs in an HPR subnet to bypass link and node failures if an acceptable alternate path is available.

Link failure is detected by the RTP end points when the first link on the RTP pipe fails or data packets that were sent are not acknowledged. One or both RTP endpoints detect the failure and redrive the RTP setup. If necessary, another APPN search is initiated to locate the best path available to the partner LU.

Figure 1 shows a failed RTP and the alternate RTP that traverses different ANR nodes.

Figure 1. Non-disruptive path switching