High-Performance Routing
High-Performance Routing (HPR) is the addition to Advanced Peer-to-Peer Networking (APPN). HPR enhances APPN data routing performance and reliability, especially when higher-speed lower-error links are used.
To support high-speed communications facilities, certain changes to the APPN architecture are required. These changes allow switching in intermediate nodes to be done at a lower layer and enable faster switching than in base APPN support. HPR changes the existing APPN intermediate session routing by using automatic network routing (ANR), which minimizes the storage and processing requirements in intermediate nodes. Each outbound packet has a predetermined path through the network so that intermediate routing nodes do not need to store information about HPR sessions that flow through them. Intermediate routing nodes in HPR route the data based on information that is contained within the packet.
Enterprise Extender (SNA over IP networks using HPR)
Enterprise Extender is a networking architecture that allows Systems Network Architecture (SNA) applications to run over IP networks using High Performance Routing (HPR). This is the preferred way to run SNA applications over IP networks with communications input/output adapters (IOAs), such as Gigabit Ethernet, since these IOAs do not require an input/output processor (IOP) and, therefore, do not natively support SNA. It is suggested that Enterprise Extender be used in place of AnyNet®.
Enterprise Extender uses the following HPR option sets: 1401, 1402, 2006, and 2009. These option sets, as well as 1400, are described as follows.
- HPR Base option (option set 1400): Its primary function is to provide automatic network routing (ANR). Products that only use this function can participate as intermediate nodes in one or more RTP connections. This type of implementation cannot be an endpoint of an RTP connection. An addition to the base option is HPR link-level error recovery. A system that supports high-speed links does not always require link-level error recovery. It is optional because when link-level error recovery is eliminated, faster communications might occur when high-quality data transmission is used.
- RTP Tower option (option set 1401):
Implementations that support this option can act as an endpoint and are able
to transport logical-unit to logical-unit session (LU-LU session) traffic
across HPR networks by using RTP connections. An RTP connection can be made
only between two systems that support RTP. That is, there can be a mix of
systems only in a path of a given RTP connection through the network (systems
that only support the HPR Base option and systems that support the HPR Tower
option). However, at least two endpoints in the path must support the HPR
Tower option; otherwise, APPN is used. Note: An implementation that has the RTP Tower option also supports the base option. These systems can run as intermediate systems in the path.
- Control Flows over RTP Tower option (option set 1402): This option causes control-point to control-point sessions (CP-CP sessions) and route setup messages to flow over special RTP connections. CP-CP sessions are established between adjacent node pairs and are used to broadcast topology flows to the entire network so that every node has the topology for the entire network stored in its topology database. Route setup messages are request messages and reply messages that are used to obtain information about a route over which an RTP connection is established. The route setup request is sent by the origin node to the destination node over the exact route that is to be used. It stops at each intermediate node along the way to gather information associated with the forward path. The route setup reply is returned by the destination node after receiving the route setup request. The reply follows the same path as the request (in the reverse direction) and stops at each intermediate node along the way to gather information about the reverse path. When the origin node receives the reply, it uses the information to establish a new RTP connection or reroute an existing one.
- Logical Data Link Control (LDLC) Support option (option set 2006): LDLC is a Logical Link Control (LLC) type defined to be used with HPR networks in conjunction with the Control Flows over RTP Tower option (option set 1402) over reliable links that do not require link-level error recovery. LDLC is only used for Enterprise Extender links.
- Native IP Data Link Control (DLC) option (option set 2009): Native IP is a DLC option used with option sets 1400, 1401, 1402, and 2006 to allow you to take advantage of APPN and HPR functions, such as class of service (COS), and flow and congestion control that is based on adaptive rate in the IP environment. This option set contains the support for Enterprise Extender links.