Verilink 9000 Series (34-00271) Product Manual - Manual (Page 107)

5
U
NISYS
P
OLL
/S
ELECT
Introduction This chapter provides specific information for the Unisys Poll/Select protocol and
how it operates using the TXPORT MultiPro platforms and NMCS software.
Poll/Select
Basics The basic concept of poll/select operation is simple. All information is stored at
the central site for all branch sites to use. The centralized mainframe where this
information is stored is commonly referred to as the host. All branch-site locations
extract and send information commonly from terminals, therefore these locations
are referred to as terminals. Two examples of non-terminal devices are ATM
machines and printers. They communicate with the network poll/select protocol
being used. The host site polls all terminal devices at the branch sites, querying
whether there is data to receive from them. Upon being polled, the terminal device
transmits some indication to the host as to whether there is information to be
transmitted or received. The host, having an indication of a terminal device
needing service, selects that terminal device, and the transaction is completed.
Polling then resumes from the host site.
TXPORT MultiPro platforms support the Unisys Poll/Select protocol. This
protocol follows the same concepts as other poll/select-type protocols. If a port is
connected to a host end on the TXPORT device, that port should be configured
using that particular protocol’s host port parameters. If the port selected is
connected to a terminal end on the TXPORT device, that port should be configured
using that particular protocol’s terminal parameters. All host TXPORT device ports
must have a list of which terminal addresses to service. Likewise, each terminal
TXPORT device port must have a unique host name where the terminal data
should be sent.
All host and terminal TXPORT device ports emulate a host or terminal
respectively, thereby only passing non-polling sequences through the transport
(WAN) connection. This protocol emulation is commonly referred to as spoofing.
Spoofing allows more efficient use of the WAN connection, freeing up bandwidth
as well as keeping bandwidth costs down, particularly in the frame relay
environment.
Figure 5-1 on page 86 shows a typical Unisys Poll/Select network using Frame
Relay as the transport medium. This figure shows addressing information as
address table information for Port 4 on unit 002 and unit 003, Port 1 Frame Relay
Endpoint Lists for all units, and the Host name field on unit 001’s Port 4.