Abstract

Alcatel commissioned The Tolly Group to evaluate the capabilities of its OmniCore 5022 Routing Switch, OmniPCX 4400 (a multi-application VoIP server with integrated H.323 and VoIP gateway functionality), and the OmniStack 6024 (a Layer 2 10/100 Mbit/s Fast Ethernet switch) in VoIP quality-of-service tests.

This Tolly Group evaluation examines an Alcatel converged voice-and-data solution built around the OmniCore 5022 Routing Switch, OmniPCX 4400 VoIP server/gateway, and OmniStack 6024 Fast Ethernet switch. The test focused on whether the platform could preserve voice quality and application performance in heavily congested IP networks, a key requirement for organizations migrating legacy circuit-based voice services to Voice over IP. Testing in March 2000 included severe congestion scenarios, voice compression using both A-law and µ-law, and simultaneous mission-critical application traffic. 

Tolly found that the Alcatel solution maintained voice capacity even under stress. In tests of roughly 500 concurrent calls, the system sustained about 494 to 495 simultaneous calls across multiple traffic scenarios, including severe congestion and combined voice plus SAP R/3 application loads, as shown in the chart on page 1. The report also states that the network sustained 9,600 calls per hour in VoIP testing.   

The solution also protected mission-critical application traffic when QoS was enabled. With high transaction volumes from 32 simulated SAP R/3 sessions, throughput remained at 3,099 transactions per second during severe congestion with voice traffic present, compared with only 29tps under severe congestion when QoS handling was disabled. With moderate application loads, throughput reached 514tps during severe congestion with voice, versus just 4tps without QoS. These results indicate that the system could prioritize both packet voice and important business traffic during overload conditions.   

Voice quality was also strong. Using Hammer Technologies PSQM measurements converted to MOS, the report cites an average MOS of about 4.5 for compressed voice streams, exceeding Tolly’s “business-quality audio” threshold of 4.0.   

The test bed used dual OmniCore 5022 switches connected by Fast Ethernet or Gigabit Ethernet, dual OmniPCX 4400 systems with VoIP gateways, OmniStack 6024 access switches, SmartBits congestion generation, Chariot SAP R/3 traffic, Alcatel UA Simulator voice generation, and analog call equipment. Overall, the report presents the Alcatel platform as an effective QoS-enabled VoIP infrastructure that preserved call volume, maintained business-quality voice, and protected mission-critical application throughput during severe congestion.