Lync Server 2013 Stress and Performance Tool — Best Practices and Configuration Tips

Troubleshooting Performance Issues with the Lync Server 2013 Stress and Performance ToolThe Lync Server 2013 Stress and Performance Tool (S&PT) is a Microsoft-provided utility designed to simulate real-world usage and load against Lync Server 2013 environments. When properly configured, it can reproduce call/conference, IM, presence, and conferencing scenarios at scale. But because it interacts with many moving parts (clients, network, servers, databases, and certificates), performance issues during testing are common. This article walks through systematic troubleshooting steps, diagnostic checks, and practical fixes to get reliable, actionable results from the S&PT.

1. Understand what “performance issue” means in your test

Before troubleshooting, clarify the symptom you see:

• Slow session establishment (calls or IMs take long to setup)
• High failure rate (connection/authentication/registration errors)
• Abrupt session drops or media quality problems
• Low simulated user density compared to expected
• High CPU, memory, disk I/O, or network utilization on S&PT clients or Lync servers

Having a concrete failure mode will guide which logs and metrics to collect.

2. Validate test topology and scenario design

• Confirm your S&PT topology reflects the production-like elements you intend to test: Front End (or Front End Pool), Edge servers (if external users simulated), SQL back-end, mediation/voice gateways, and certificate and DNS configuration.
• Ensure client roles and workloads match expected real usage (registration, IM, audio/video, AV conferencing, desktop sharing). Over- or under-specified scenarios produce misleading results.
• If possible, start with a small scale test (5–10 simulated users) to validate basics before scaling to hundreds or thousands.

3. Check S&PT client host health and configuration

S&PT runs on one or more client machines that generate load. Problems on these hosts often look like server-side performance issues.

• Hardware and OS:
  • Ensure S&PT hosts meet or exceed recommended CPU, RAM, disk, and network specs.
  • Disable CPU frequency scaling and power-saving modes during tests to avoid throttling.
• Network:
  • Place S&PT clients on the same LAN or on equivalent network paths to the Lync servers you intend to test. Avoid NAT/transit links unless testing WAN scenarios.
  • Verify NIC drivers are up-to-date and that jumbo frames / offloads are configured consistently if used.
• Software:
  • Use the same .NET Framework and Windows updates on S&PT machines as documented for the tool.
  • Ensure antivirus exclusions for S&PT processes and any generated log directories to avoid I/O slowdowns.
• S&PT configuration:
  • Validate user pools, agent counts per machine, endpoints per agent, and scenario timing. Overloading a single S&PT host with too many agents will saturate the host before reaching server limits.
  • Check S&PT logging levels — verbose logging increases CPU/disk usage; lower it for large-scale tests unless debugging.

4. Examine Lync Server resource utilization

Collect real-time and historical counters while tests run:

• CPU: High sustained CPU on Front End or Edge may indicate too much signaling or media processing load.
• Memory: Watch for paging or memory pressure on Front End, Director, or Edge.
• Network: Monitor bytes/sec and packet drops on server NICs. Congestion or duplex mismatches cause severe media degradation.
• Disk I/O: SQL back-end and file stores (for conferencing) need adequate throughput and low latency. High disk queue lengths indicate bottlenecks.
• OS-level counters:
  • Processor: % Processor Time, Processor Queue Length
  • Memory: Available MBytes, Pages/sec
  • Network Interface: Output/Input Queue Length, Bytes/sec
  • Disk: Avg. Disk sec/Read, Avg. Disk sec/Write
• Lync-specific performance counters:
  • RTCSRV counters (user registrations, calls/sec)
  • AV Conferencing counters (packets dropped, channels opened)
  • Registrar and Presence counters Collect these with PerfMon or other monitoring tools and correlate with test timeline.

5. Inspect Lync and S&PT logs

• S&PT logs:
  • Check the log directory of S&PT for scenario failures, registration errors, or agent crashes.
  • Look for consistent error messages like authentication failures, TLS/SSL negotiation errors, SIP errors (4xx/5xx), or media negotiation failures.
• Lync Server logs:
  • Use Snooper (from the Microsoft SDK) to analyze SIP traces captured on Front End and Edge servers. Snooper can show SIP flows and reveal where registrations or call setups fail.
  • Check Event Viewer on Lync servers for warnings/errors tied to SIP stack, SQL connectivity, certificate issues, or service crashes.
• SQL logs:
  • If you see high latency for user lookups or conference scheduling, check SQL Server wait stats and blocking. Ensure maintenance and indexes are healthy.
• Network traces:
  • Use netsh trace, Message Analyzer, or Wireshark to capture SIP and RTP traffic. Look for retransmissions, TLS handshake failures, or packet loss patterns.

6. Common problem areas and targeted fixes

1. Authentication/certificate errors

   • Symptom: Frequent registration failures, TLS handshake errors.
   • Fixes:
     • Verify certificates are valid, trusted by S&PT hosts, and contain required SANs (FQDNs).
     • Ensure correct root/intermediate CAs installed on S&PT machines.
     • Check time synchronization (NTP) across all hosts; clock skew breaks TLS and token-based auth.

2. DNS and topology misconfigurations

   • Symptom: Agents cannot locate services or intermittent routing failures.
   • Fixes:
     • Validate SRV/A records and internal DNS resolution for Front End, Edge, and SIP domains.
     • Confirm topology builder settings and that simple URLs/FQDNs resolve to the intended IPs.

3. Network saturation and packet loss

   • Symptom: High media jitter, packet drops, RTP retransmissions.
   • Fixes:
     • Increase NIC bandwidth, segregate test traffic on a dedicated VLAN or physical link.
     • Tune QoS to prioritize RTP and signaling traffic.
     • Fix duplex mismatches and replace faulty switches/cables.

4. SQL or back-end latency

   • Symptom: Slow user registration, conference creation delays, call setup slowness.
   • Fixes:
     • Ensure SQL Server performance (proper memory, tempdb configuration, disk I/O).
     • Offload reporting or heavy DB operations during tests.
     • Check SQL clustering and network paths to the Front End.

5. Overloaded S&PT hosts

   • Symptom: Agent crashes, large gap between intended and actual simulated users.
   • Fixes:
     • Distribute agents across more client hosts or reduce agents per machine.
     • Reduce logging verbosity and disable non-essential background services on S&PT hosts.

6. Improper scenario timing or resource ramp-up

   • Symptom: Sudden spikes in failures when ramping load.
   • Fixes:
     • Use a gradual ramp-up schedule. Allow servers to reach steady state before increasing agents.
     • Monitor and pause on threshold breaches to investigate before continuing.

7. Media path misrouting (bypassed media vs. server-relayed)

   • Symptom: Media quality differences, unexpected server CPU usage for media.
   • Fixes:
     • Verify network topology, federation, and ICE/STUN/TURN behavior if simulating external clients.
     • Check policies controlling media bypass and ensure server roles and network routes support intended media paths.

7. Reproduce, isolate, and iterate

• Reproduce: Narrow a failing test to the smallest scenario that still shows the issue (single user or small group).
• Isolate: Change one variable at a time (move agent to different VLAN, switch S&PT client machine, change codec, disable conferencing features) to identify the root cause.
• Iterate: Apply fixes and rerun repeating the same metrics and log captures to validate changes.

8. Advanced diagnostics

• Use Lync Quality of Experience (QoE) and Call Quality Methodology reports to analyze media characteristics across calls.
• Use Perfmon Data Collector Sets to capture long-running tests and automatically archive for analysis.
• Consider capturing kernel-level ETW traces for server processes if regular logs don’t reveal the cause.
• If suspecting S&PT internal bugs, check Microsoft KBs, official forums, or support channels for known issues or hotfixes for the tool.

9. Practical example — registration failures at scale

Scenario: At ~2,000 simulated users, 30% registration failures appear with SIP ⁄₄₀₁ errors.

Troubleshooting steps:

1. Check S&PT logs for exact SIP error codes and timestamps.
2. Confirm certificate validity and that S&PT hosts trust the issuing CA.
3. Review Front End CPU and authentication service counters — high CPU may cause token timeouts.
4. Capture SIP traces with Snooper to see whether registration requests reach the Front End and whether responses are generated or dropped.
5. Validate SQL performance for user info lookups — slow DB responses can delay registration processing.
6. Split load across additional S&PT hosts; ramp more slowly to see if rate-limiting or throttling occurs.

Outcome: In many cases, the root cause will be either trust/certificate issues or S&PT client host saturation; fixes are typically certificate renewal or distributing agents across more machines and reducing logging.

10. Final checklist

• Start small, validate basics, then scale.
• Ensure S&PT hosts are healthy, correctly sized, and configured.
• Verify certificates, DNS, and time synchronization.
• Monitor server and SQL resource counters during tests.
• Capture and analyze SIP/RTP traces and Lync-specific logs.
• Ramp load gradually and isolate variables to find root causes.

Troubleshooting S&PT performance is about methodical elimination: validate client and server health, gather metrics and logs, and change one variable at a time. With disciplined testing and the diagnostics above, you can move from confusing failures to concrete infrastructure or configuration fixes that yield repeatable, trustworthy performance results.