New CIR Support for NCP-Controlled 3746 Model 900 Frame Relay Lines

By Joyce Anne Porter (jbraswel@us.ibm.com)

NCP-controlled 3746 Model 900 Frame Relay lines can now take advantage of Committed Information Rate (CIR) algorithms available for Network Node Processor (NNP)-controlled Frame Relay lines. Prior to this enhancement, a Communications Rate (COMRATE) bandwidth management algorithm was provided for NCP-controlled 3746 Model 900 Frame Relay lines. Now, both CIR and COMRATE bandwidth management algorithms are provided for an NCP-controlled 3746 Model 900 Frame Relay line, allowing you to choose which bandwidth management algorithm is optimum for your environment.

The Committed Information Rate is the subscriber data throughput that the network commits to supporting under normal network conditions. CIR is averaged over the Committed Rate Measurement Interval (Tc). The CIR algorithms can be beneficial in an environment where there is a bandwidth mismatch between the Frame Relay lines that the data is flowing over. For example, in the configuration shown here, the access rate to and from the 3745/3746 is 2 Mbps but the access rate of the 2210 is 64 Kbps. The CIR algorithms can be used to adjust the data flow on the DLCI to the 2210 so that the 2210 access rate is not exceeded. This prevents unnecessary congestion and ultimately the discarding of frames.

Initial Committed Information Rate support for NCP-controlled 3746 Model 900 Frame Relay lines is provided via PTF to NCP V7R3 through V7R6 and SSP V4R3 through V4R6 (see specific APAR information in the table). This support allows CIR algorithms to be used for NCP-controlled 3746 Model 900 Frame Relay lines. The 3746 Model 900/950's automatically adjusting CIR algorithms manage the bandwidth for individual DLCIs on the Frame Relay line.

NCP V7R7 and SSP V4R7 extended the Committed Information Rate support for NCP-controlled 3746 Model 900 Frame Relay lines. This enhancement allows you to specify the committed burst size (Bc), the excess burst size (Be), and the committed rate measurement interval (Tc) for specific DLCIs on a Frame Relay line (instead of relying on the automatically adjusting CIR algorithms).

CIR support is also provided for NCP-controlled 3746 ISDN lines with NCP V7R7 and SSP V4R7. For ISDN lines, the choice of bandwidth management algorithms (CIR or COMRATE) is specified at the physical line level and affects all of the B-channels on the physical line. The 3746 Model 900/950's automatically adjusting CIR algorithm manages the bandwidth for individual DLCIs for ISDN lines.

Consolidated Link Layer Management (CLLM) support is also being extended to NCP-controlled 3746 Model 900 Frame Relay lines with NCP V7R7 and SSP V4R7. CLLM is an optional Frame Relay function that provides management information to DTEs attaching to a network. CLLM, as described in standard ANSI T1.618, provides cause codes that can indicate events such as network congestion, equipment failure, maintenance action, and so on.

The planning guide, 3745 Communication Controller Models A, 3746 Nways Multiprotocol Controller Models 900 and 950 Planning Guide, GA33-0457, provides a more detailed explanation of the 3746 Model 900/950's implementation of the CIR algorithm.

Joyce Anne Porter is a member of the NCP Design/Development Team. She has contributed to NCP's support of the 3746 attachments to NCP.