3com Phones 1 800 544 0059

NBX Group - your source for all 3Com phones.

  • Increase font size
  • Default font size
  • Decrease font size

Echo on external call

E-mail Print PDF

Users complaining of "echo" on external calls will cite symptoms of:

  • being able to hear their own voice echo back while talking
  • clipping of the conversation
  • both parties voice interrupts each others
  • noticeable delay

The telephone lines terminating in the NBX100 can be tested with either a Voice Network Analyzer (Model VNA-70A) manufactured by Metro Tel and available from Specialized Products or a Loop Current Test Set (Model ITC-3004) available from Independent Technologies.

The loop current must be measured on each telephone line before it goes into the NBX 100 line card (3C10114). Acceptable loop current is between 23 - 35 ma .

Symptoms of High Loop Current Include:

  • burned out equipment
  • garbled data
  • modem failures
  • cut-offs squealing on lines
  • crosstalk
  • echo hollow sounding conversations
  • intermittent circuit failures
  • off premise equipment problems

Symptoms of Low Loop Current Problems are:

  • poor voice transmission quality low volume
  • ghost rings
  • wrong numbers
  • lost calls during transfer
  • data loss

The 3Com NBX has latency (delay)of about 120 milliseconds which is higher than traditional telephone systems (20 - 40 ms). This is important to know because you may not of had echo on your previous telephone system. However, you likely had some other problems associated with loop current. When the NBX 100 is installed with foreign exchange (FX) lines or Metro calling area lines that have moderate to extremely high loop current, echo will likely occur. It is important to measure the lines before they terminate into the NBX line card.

Any external telephone lines terminating in the NBX 100 telephone system that have loop current too low or beyond the 23 -35 ma range can be "attenuated" with loop current attenuators. These are available from Mike Sandman or Independent Technologies. Attenuation is just increasing or decreasing power (loop current).

The model LCR-66B from Mike Sandman is easily installed on the 66 style punch down blocks since they are like super sized bridging clips. The model ITC-4001 is also easily installed using modular cords.

Please Note:

  • With any of the Panamax Towermax or Central Office line protection modules installed, you must install the loop current attenuators before the Panamax equipment. Basically, the telephone lines plug into the loop current attenuators; the attenuators plug into the Panamax equipment; then the Panamax equipment plugs into the 3Com NBX 100 line card. This is also true with any other Central Office (CO) line protection equipment.
  • This solution was implemented on a network with Novell, NT, and peer to peer, 41 computer stations running at 10 Mbps, and using three hubs-- not switched. The NBX 100 is configured with 19 NBX telephones, 6 Central Office (CO) lines, and the 6 port x 20 hour APX Voice Messaging System.
  • Loop current issues will very unlikely be removed 100 percent. It is more like an effort of remediation.
  • This site with the installed solution states that approximately 70 percent of the problem is gone. Some echo still occurs. Network switches are not yet in place.
  • The plan of attack was to first reduce the loop current levels then, install two (2) 3Com 1100 switches P/N 3C16950 using a matrix cable between the two switches P/N 3C16965. (24 ports, each with 2 10/100 Mbps ports. Total switched ports 52)
  • Tanscend Network Supervisor version 1.0 is available FREE from 3Com, stock number 300236-002. This is an excellent networking tool and a must have for any toolbox. Transcend will discover your Local Area Network (LAN) and help isolate traffic bottlenecks.
  • This solution was knowingly implemented without the switches. The customer LAN traffic is quite heavy in volume of packets since the files being transferred throughout the business day are voice files from proprietary dictation systems.