Verilink 9000 Series (34-00271) Product Manual - Manual (Page 207)

11
DLP
(D
ATA
L
INK
P
ROTOCOL
)
Introduction This chapter provides specific information for DLPl and how it operates using the
TXPORT MultiPro platform and NMCS software.
DLP Principles
and Concepts This chapter explains how to configure ports which support DLP (Data Link
Protocol) for either an SDLC, a LAPB, or a TUNNEL mode.
In SDLC mode, the port can have two personalities: Primary port or Secondary
port. Primary port (which acts like a FEP port polling the 3x74 or 5250 Cluster
Controllers) or a Secondary port (which acts like a 3x74 or 5250 Cluster
Controller being polled by the FEP).
The SDLC option allows an IBM user to integrate MultiPro communications
platforms into his network to increase performance or extend his network at a lower
cost. The communications platform allows the user to configure it as one or more
SDLC cluster controllers (Devices). This implies that the host, instead of directly
polling the Devices, can poll only the platform, while the other ports of the platform
take care of polling the different Devices. This type of configuration reduces the
number of front end ports used by the mainframe and allows the FEP ports to be
configured for full duplex operation, resulting in a better response time provided by
the MultiPro unit communications platform's FIFO transmission queue.
The SDLC option is intended to be used across two or more ports configured for
the SDLC protocol. If the ports are on different nodes in the network, then either
an X.25 or Frame Relay backbone can transport the SDLC data while the polling
overhead is spoofed locally.
An SDLC mode port can be connected to an IBM host or to an IBM cluster controller.
It must be planned which port is connected to the host and which port is connected to
the cluster controller to correctly configure the application. The host is polling the
communications platform, and the platform is polling the downline 3x74 and/or 5250
controllers. Therefore, a platform port connected to a host is a Secondary port because
it is a secondary station at the SDLC layer, and a platform port connected to the
controllers is a Primary port because it is the primary station which polls the secondary
stations (cluster controllers) on the link. Any device or host that conforms with the
IBM SDLC mode of operation can be connected to the TXPORT platform.
In LAPB mode, the port support the ITU X.25 Level II protocol. The port can be
either a Logical DCE or DTE. In defining an LAPB mode port, there are
parameters which must be set at each level of the protocol (Levels 1 and 2).