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Monitor IBM Z network performance by matching each symptom to the right data: session response-time metrics for user-facing delay, TCP/IP and interface statistics for connection or throughput behavior, and targeted traces when packet-level detail is needed. z/OS Communications Server provides these views through Network Management Interfaces (NMIs), SMF, and related interfaces; IBM Z OMEGAMON Network Monitor can collect performance data across monitored LPARs.
Start by defining the symptom and scope
Before collecting data, identify the affected workload or service, the time window, the LPAR and TCP/IP stack, and the observed symptom. Separate user response time from reduced transfer rate, packet loss or retransmission, and host-side resource pressure: these point to different measurements.
Capture a baseline under comparable workload conditions before attributing a change to a configuration or hardware feature. A measurement without workload and time context is difficult to compare meaningfully.
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Choose the data that matches the question
| Question | Useful data | Collection approach |
|---|---|---|
| Are users or sessions experiencing slow responses? | TN3270E connection performance and response-time information | Configure the applicable Telnet MONITORGROUP; use NMI or an established monitoring product. |
| Are TCP connections, UDP endpoints, or interfaces behaving unusually? | Connection and endpoint activity, interface attributes and statistics, and global TCP/IP stack information | Use the relevant NMI data, SNMP MIBs, command displays, or SMF services. |
| What is happening at packet or data level? | TCP/IP packet, OSAENTA, or data traces | Collect a targeted real-time trace to answer a specific diagnosis question. |
| Could VTAM networking be involved? | VTAM Enterprise Extender (EE) and High Performance Routing (HPR) information | Use Communications Server interfaces and applicable VTAM performance data. |
| Is adapter or host-interface behavior a factor? | OSA adapter and stack/interface statistics | Inspect the relevant statistics, then consult release-matched configuration and best-practices documentation. |
IBM’s z/OS 3.2 Network Management Interfaces reference describes programmatic access to information about IP and SNA (VTAM) components. It lists real-time traces, TCP connection and UDP endpoint activity, interface statistics, TN3270E performance, sysplex networking information, and VTAM EE/HPR data. Depending on the collection method, related information is also available through SNMP MIBs, command displays, VTAM PMI, or SMF services.
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Use NMIs and SMF for Communications Server data
Network Management Interfaces let monitoring applications obtain information about TCP/IP and VTAM processing. Use the interface or record type appropriate to the layer under investigation. SMF is useful when the task calls for event or historical analysis; real-time NMI data and traces are more appropriate for observing current behavior.
A custom NMI client has an important deployment constraint: IBM documents that network-management clients must run on the same z/OS image as Communications Server. Plan collector placement accordingly when monitoring multiple images.
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Traces can expose protocol detail that summary statistics do not, but collect them with a specific diagnostic question in mind. IBM documents the trace capabilities; it does not prescribe a universal sampling rate or retention period for every workload.
Enable the prerequisites for response-time collection
OMEGAMON collection depends on the Communications Server interfaces and configuration being enabled for the information you need. IBM’s setup guidance for IBM Z OMEGAMON Network Monitor 6.1 specifies the following for FTP and TN3270 monitoring:
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- Configure
NETMONitor SMFServicein the TCP/IP profile for FTP and TN3270 monitoring. - For TN3270 response-time information, add an applicable
MONITORGROUPto the Telnet profile. IBM’s example calls for theAVERAGEandBUCKETScharacteristics. - Check that the selected client identifier and its mapping cover the sessions whose response times you intend to collect.
Follow the release-specific instructions in IBM’s OMEGAMON NMI configuration documentation; do not assume a profile example applies unchanged to a different release or deployment.
Use OMEGAMON for managed multi-LPAR monitoring
IBM Z OMEGAMON Network Monitor collects TCP/IP and VTAM performance data on each monitored LPAR. IBM documents data sources that include NMIs, SNMP MIBs, and the VTAM Performance Monitor Interface (PMI). Its listed coverage includes TCP/IP address spaces, TN3270 sessions, HPR and EE connections, FTP sessions and transfers, OSA adapters, TCP/IP connections and interfaces, gateways, CSM, VTAM buffer pools, and the VTAM environment.
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IBM’s OMEGAMON Network Monitor 5.6 collection overview says the agent runs on every LPAR being monitored. Data-space use varies with the number of address spaces and monitored resources, as well as the configured collection types. Capacity-plan for the actual deployment and observe agent overhead rather than assuming one fixed footprint.
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Investigate throughput and OSA behavior
If stack and interface measurements point toward adapter or interrupt behavior, consult the IP Configuration Guide for the z/OS release in use, along with IBM’s OSA-Express guidance. IBM describes optimized latency mode for OSA-Express QDIO as adjusting inbound and outbound interrupt processing to reduce latency and potentially increase throughput for high-volume, interactive, non-streaming workloads. It is not a universal throughput setting: confirm that the workload and hardware fit, and verify the exact configuration syntax in the applicable release documentation before making a change.
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IBM’s OSA-Express best-practices checklist is supplementary guidance, not a replacement for formal configuration publications. Its version 1.2, modified August 15, 2023, added material on OSA sharing and OSA-Express7S Enhanced Inbound Blocking.
Compare monitoring approaches before deploying
| Approach | Best fit | Deployment and operational considerations |
|---|---|---|
| NMIs | Programmatic access to TCP/IP and VTAM data, including real-time information | A custom client must run on the same z/OS image as Communications Server. |
| SMF | Event and historical analysis | Select the records and services relevant to the question; availability depends on configuration. |
| Real-time traces | Protocol-level diagnosis of a specific symptom | Use selectively; detailed collection volume and retention should be determined for the deployment. |
| OMEGAMON Network Monitor | Managed collection of TCP/IP and VTAM performance data across LPARs | An agent runs on each monitored LPAR; data-space use depends on the resources and collection types configured. |
Decide based on the layer you need to see, whether you need live or historical data, where collectors must run, and how much detail is worth collecting. IBM’s Communications Server Performance Index points to release-specific performance reports. Read any reported result in the context of its particular workload and hardware; it should not be treated as a general IBM Z latency or throughput expectation.
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