Verilink 9000 Series (34-00271) Product Manual - Manual (Page 153)

8
NCR
Introduction This chapter provides specific information for the NCR protocol and how it
operates using TXPORT MultiPro platforms and NMCS software.
Poll/Select
Basics The NCR protocol belongs to the poll/select protocol family. These protocols are a
strong component for any network application that requires one or more branch
office sites to convey information to a central-site location. The banking industry,
retail chain-store franchises, and the freight-hauling industry are examples of
applications that have used poll/select networks for many years.
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 NCR 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.