Communications Server supports high performance routing (HPR) over Enterprise Extender (IP), synchronous data link control (SDLC), LAN, WAN, channel, Multi-Path Channel (MPC), and X.25 connections.
HPR automatic network routing (ANR) minimizes the storage and processing requirements in intermediate nodes, which is an improvement over APPN intermediate session routing (ISR) for high-speed networks with low error rates.
Communications Server HPR support includes support for rapid transport protocol (RTP) and automatic network routing (ANR).
To provide the benefits listed above, HPR assumes that data links provide low rates of lost frames. HPR recovers from conditions that cause lost frames, but if the conditions persist for long periods, HPR assumes that network congestion is too high and HPR throughput is lowered. Achieving good HPR throughput on a given link involves proper configuration of the sending node, the facilities that constitute the link between the two nodes, and the receiving node.
|Note:||You might want to set ERP values in cases where LAN line facilities have high
If your network has a high error rate, systems administrators may notice lower than expected throughput on HPR connections.
The HPR features are achieved by including additional information in frame headers. If you do not need the HPR features, the additional overhead may reduce your network performance. The HPR features are an advantage whenever there are intermediate nodes or alternate routes. However, if you require high performance between two nodes connected by a single link without non-disruptive recovery during a link failure, you should disable HPR when you configure that link.
HPR implements priority queuing. In general, interactive traffic passes through the network faster than lower priority batch traffic. Adapters that queue frames do so without regard to priority and may interfere with HPR's priority queueing. You may need to reduce the adapter's queue depth to prevent low priority traffic from delaying high priority traffic. (See the adapter documentation for instructions on setting the adapter queue depth.)
Many PCs now have advanced power management features that will suspend power to devices (like disk drives) and reduce the clock rate on a CPU significantly to save power if the keyboard or mouse is not being used. On a workstation, this is a good feature, but on a server platform, this can occur while it is routing data from one adapter to another (and no disk activity is occurring). For Communications Server, disable advanced power management and hardware power management by entering the BIOS configuration during boot up (usually pressing F1 while initializing hardware) and disable these options.
HPR will use more of the LAN adapter memory due to increased performance and queueing. Many shared RAM adapters default to using 8 kilobytes of shared RAM. It is required that the shared RAM size is 16 kilobytes. To adjust this configuration, refer to the adapter configuration manual. This setting is located in either your machine BIOS, or on the adapter switch settings.
|Note:||If you do not increase the shared RAM to 16 kilobytes, network performance is degraded.|
Do not adjust the shared RAM value above 16 kilobytes, the optimal setting for the adapter memory.
If HPR links are failing under heavy traffic, you can set your receive timers to a higher value. This allows more time for the links to receive an acknowledgement for sent frames.
For SDLC links, this is the Primary Receive Timer. The receive timer can be set on either the DLC or a logical link statement.
To calculate the minimum receive timer value in tenths of seconds, use the following formula:
[(send_window_count * max_i_field_size * 8) /actual line speed]* 10
You can specify eight parameters to affect how quickly Communications Server handles recovery and failure of LAN links. You might need to adjust these parameters to achieve the best results if you are using slow links, HPR, or backup host connections.
You should consider the following parameters when defining a LAN device in SNA Node Configuration:
Under the Advanced tab:
The default value is 8.
The default value is 5.
The default value is 65535.
Under the Performance tab:
The default value is 30 seconds.
The default value is 100 milliseconds.
The poll response timeout specifies the time that the LAN device waits for a response to a frame sent with the POLL bit set.
The default value is 8 000 milliseconds.
The default value is 16 frames.
The default value is 32 buffers.
HPR provides a non-disruptive path switch to a different connection if one connection fails. A retry of the failed connection is attempted before a path switch occurs. An explanation of the parameters involved in determining whether a connection has failed and the time to initiate a path switch follows.
When the value specified for Idle timeout is reached, a keepalive frame is sent. The default for Idle timeout is 30 seconds.
The value specified for Poll response timeout determines the time that the device waits for a response to the keepalive frame. The default for Poll response timeout is eight seconds (8 000 milliseconds). A keepalive frame is retried 10 times. This retry count can not be changed.
If there is no response to the keepalive frame, TEST commands are sent to the partner system. The value specified for Test retry interval determines the time between TEST command attempts, and the value specified for Test retry limit determines the maximum number of TEST command attempts. The default for Test retry interval is 8 seconds, and the default for Test retry limit is five attempts.
The following calculation indicates the time required to determine whether a connection has failed and initiate a path switch:
(Idle timeout) + (Poll response timeout * 10 retries) + (Test retry interval * Test retry limit) + 1
Using the defaults for the parameters, the time required to determine a connection failure and initiate a path switch can be up to 151 seconds.
(30 seconds) + (8 seconds * 10 retries) + (8 seconds * 5 attempts) + 1 = 151 seconds
If you are experiencing long path switch times (or failures) with HPR when a connection fails, you can reduce the time by decreasing the values for the parameters in the calculation.