Specifications

58 IBM Voice Over Frame Relay Perform Guide
Figure 24. DLSw and DLC Timeout
DLSw was developed to provide support for SNA and NetBIOS in multiprotocol
routers. Since SNA and NetBIOS are basically connection-oriented protocols, the
data link control procedure that they use on the LAN is IEEE 802.2 Logical Link
Control (LLC) Type 2. DLSw also accommodates SNA protocols over WAN links
via the SDLC protocol. IEEE 802.2 LLC Type 2 was designed with the assumption
that the network transit delay would be small and predictable (for example, a local
LAN). Therefore LLC uses a fixed timer for detecting lost frames. When bridging
is used over wide area lines (especially at lower speeds), the network delay is
larger and can vary greatly based upon congestion. When the delay exceeds the
timeout value, LLC attempts to retransmit. If the frame is not actually lost, only
delayed, it is possible for the LLC Type 2 procedures to become confused, and as
a result, the link is eventually taken down. Given the use of LLC Type 2 services,
DLSw addresses the following bridging problems:
• DLC timeouts
• DLC acknowledgments over the WAN
• Flow and congestion control
• Broadcast control of search packets
• Source-route bridging hop count limits
4.0.3 Voice
IBM 2212 has voice card adapters that work with IP and SNA as follows:
End
System
LAN Bridge
WAN
Cloud
Bridge LAN
End
System
<< Bridging >>
Info
RR
<< Data Link Switching >>
End
System
LAN
DLSw
WAN
Cloud
DLSw
LAN
End
System
TCP/IP
Info
RR
Info
RR