This document discusses Cisco Systems Network Architecture (CSNA)
support on the Channel Interface Processor (CIP) in a Cisco 7000/7500 Router
and the Channel Port Adapter (CPA) in a Cisco 7200 Router.
There are no specific requirements for this document.
The information in this document is based on the Cisco 7000, 7200 and
The information in this document was created from the devices in a
specific lab environment. All of the devices used in this document started with
a cleared (default) configuration. If your network is live, make sure that you
understand the potential impact of any command.
Technical Tips Conventions for more information on document
CSNA support on the CIP in a Cisco 7000/7500 router and the CPA in a
Cisco 7200 router provides mainframe connectivity to Systems Network
Architecture (SNA) network nodes. The CIP/CPA supports both ESCON Channel
Adapter (ECA) and Parallel Channel Adapter (PCA) connections to an SNA
The CSNA feature is designed to provide an SNA LAN gateway to virtual
telecommunications access method (VTAM) with the help of a high speed channel
Figure 1 illustrates the LAN/WAN
connectivity options that the CSNA feature provides between SNA network nodes
and channel-attached mainframes. The CSNA feature also allows you to replace
currently-installed IBM 3172 Interconnect Controllers with a either a Cisco
7000/7500 series router equipped with a CIP or a Cisco 7200 series router
equipped with a CPA; with no loss of functionality. In fact, you gain
functionality, with minimal or no changes to VTAM or site configuration.
Likewise, there are many configurations in which a Cisco 7000/7500 router with
a CIP or a Cisco 7200 router with a CPA can replace an IBM 3745 or 3746.
Figure 1 – LAN/WAN Connectivity Options
The CSNA feature is a software product and does not introduce any
hardware features. However, this feature has a specific hardware requirement.
The CSNA feature runs only on a Cisco 7000/7500 series router equipped with one
or more CIPs or a Cisco 7200 series router equipped with one or more
The CSNA feature allows the router to support connections between a
channel-attached SNA mainframe and local LAN-attached SNA nodes, Synchronous
Data Link Control (SDLC)- and Qualified Logical Link Control (QLLC)-connected
devices, and remotely-connected SNA nodes through remote source-route bridging
(RSRB) and data-link switching (DLSw+). Connections between mainframes that are
channel-attached to the same router are also supported.
Figure 2 depicts the architecture for the
CSNA feature. This feature consists of the CTA driver, ported Cisco Link
Services (CLS), Logical Link Control 2 (LLC2) stack, and MAC Encapsulation
Layers that run on the CIP/CPA. The CTA driver implements the channel protocol
and the primitives necessary to communicate with VTAM over the channel
interface and allows VTAM to activate and deactivate SNA nodes through LLC2 as
the link level communications. The CLS module provides the interface between
the CTA driver and the LLC2 stack which provides the IEEE 802.2 elements of
procedure for link level connection establishment and data transfer. The LLC2
stack provides a link station end point for all SNA network nodes that
communicate with the channel-attached hosts.
The LLC2 stack on the Route-Switch Processor (RSP) provides LLC2
connection services for QLLC and SDLC Logical Link Control (SDLLC), and RSRB
and DLSw+ when local acknowledgment is configured.
The MAC Encapsulation layers provide processing for the LAN media types
that the CIP card can accept. There is a MAC encapsulation layer for each media
type that you can configure for the CSNA feature, Token Ring, Ethernet, and
FDDI. This layer parses the MAC header of every LLC2 frame forwarded to the CIP
and destined for the mainframe. The destination MAC address and start of the
LLC2 header are determined in the MAC encapsulation layer before the frame is
passed to the LLC2 protocol stack. The MAC encapsulation layer also builds the
appropriate MAC header type on all LLC2 frames before the layer forwards the
frame through the router out onto the network.
Figure 2 – Architecture for the CSNA Feature