TCP/IP (Parallel Library) Configuration and Management Manual

Configuring Parallel Library TCP/IP for Complex and
Heavy-Use Environments
HP NonStop TCP/IP (Parallel Library) Configuration and Management Manual—522271-006
3-7
Distributor Listening Model
PATHSEND allows load-balancing algorithms to distribute the data to the back-end
server instances.
The distributor model achieves some parallelism and load-balancing because of the
use of the multiple, back-end server instances. However, the distributor model is
limited by the fact that all data must flow through the distributor to the back-end server
processes through PATHSEND. This situation creates a potential bottle-neck in the
distributor.
Figure 3-3 on page 3-8 shows the distributor listener model in conventional TCP/IP. To
scale to accommodate growing computing needs in this conventional TCP/IP example,
three instances of the distributor are running in three processors (3, 4, and 5)
distributing connections to three sets of server instances in three different processors
(0, 1, and 2). While you can achieve scalability in the conventional TCP/IP model by
running multiple distributors in this manner, there are two hops involved in data flow
(one inter-process hop between the distributor and the server and one between the
distributor and the TCP/IP process). In addition, each processor must have its own
physical interface (PIF) on the adapter. Finally, having run a TCP/IP process for each
distributor, each distributor appears to be on a different IP host to the outside world.