WebRTC Softphone 408 on high concurrency

Quick question, has anyone seen this weird error? with the WebRTC softphone connection stability. We are pushing 200 concurrent JMeter threads and getting 408 timeouts on the WebSocket handshake.

WebSocket connection failed: 408 Request Timeout

The JMeter config uses a constant throughput timer at 50/sec. Is there a specific rate limit on the signaling server for softphone init?