user manual

Configuring Data-Link Switching Plus
Technology Overview
BC-284
Cisco IOS Bridging and IBM Networking Configuration Guide
78-11737-02
• UDP unicast support
• Load balancing
• Support for LLC1 circuits
• Support for multiple bridge groups
• Support for RIF Passthrough
• SNA type of service feature support
• Local acknowledgment for Ethernet-attached devices and media conversion for SNA PU 2.1 and
PU 2.0 devices
• Conversion between LLC2 to SDLC between PU 4 devices
• Local or remote media conversion between LANs and either SDLC Protocol or QLLC
• SNA View, Blue Maps, and Internetwork Status Monitor (ISM) support
MIB enhancements that allow DLSw+ features to be managed by the CiscoWorks Blue products, SNA
Maps, and SNA View. Also, new traps alert network management stations of peer or circuit failures. For
more information, refer to the current Cisco IOS release note for the location of the Cisco MIB website.
Local Acknowledgment
When you have LANs separated by wide geographic distances, and you want to avoid sending data
multiple times, and the loss of user sessions that can occur with time delays, encapsulate the source-route
bridged traffic inside IP datagrams passed over a TCP connection between two routers with local
acknowledgment enabled.
Logical Link Control, type 2 (LLC2) is an ISO standard data-link level protocol used in Token Ring
networks. LLC2 was designed to provide reliable sending of data across LAN media and to cause
minimal or at least predictable time delays. However, DLSw+ and WAN backbones created LANs that
are separated by wide, geographic distances-spanning countries and continents. As a result, LANs have
time delays that are longer than LLC2 allows for bidirectional communication between hosts. Local
acknowledgment addresses the problem of unpredictable time delays, multiple sendings, and loss of user
sessions.
In a typical LLC2 session, when one host sends a frame to another host, the sending host expects the
receiving host to respond positively or negatively in a predefined period of time commonly called the T1
time. If the sending host does not receive an acknowledgment of the frame it sent within the T1 time, it
retries a few times (normally 8 to 10). If there is still no response, the sending host drops the session.
Figure 127 illustrates an LLC2 session in which a 37x5 on a LAN segment communicates with a 3x74
on a different LAN segment separated via a wide-area backbone network. Frames are transported
between Router A and Router B by means of DLSw+. However, the LLC2 session between the 37x5 and
the 3x74 is still end-to-end; that is, every frame generated by the 37x5 traverses the backbone network
to the 3x74, and the 3x74, on receipt of the frame, acknowledges it.