Business Phone Systems Troubleshooting & Maintenance 2

Question 1

What should you check if phones on a specific subnet are experiencing call quality issues while others are not?

Accepted Answer

QoS configuration on the network switch or router serving that subnet

Answer

Whether those phones have an active voicemail plan

Answer

The firmware version on the affected phones only

Answer

Whether the SIP trunk has enough channels

Question 2

What is a common cause of calls dropping after exactly 30 or 32 seconds on a VoIP system?

Accepted Answer

A firewall with a short SIP ALG or UDP session timeout killing the RTP stream

Answer

Maximum call duration limit set to 30 seconds

Answer

Insufficient codec bandwidth for the call

Answer

A licensing limit on the number of call minutes

Question 3

What does SIP ALG (Application Layer Gateway) do and why is it often disabled for VoIP?

Accepted Answer

Modifies SIP packets passing through a router, often corrupting them and causing call failures

Answer

Accelerates SIP call setup by caching registration data

Answer

Encrypts SIP traffic between the router and provider

Answer

Prioritizes SIP packets over other traffic types

Question 4

What is the recommended approach when a firmware update breaks IP phone functionality?

Accepted Answer

Roll back to the previous stable firmware version from the manufacturer's portal

Answer

Replace the phone with a newer model

Answer

Factory reset the phone and re-provision it with the new firmware

Answer

Disable auto-update and leave the broken firmware in place

Question 5

What information should be collected before contacting VoIP provider support about a call quality issue?

Accepted Answer

Affected extension numbers, time and date of issue, call recordings, and network test results

Answer

Only the account number and billing contact

Answer

The model of every phone in the office and their purchase dates

Answer

The names of all employees who reported the problem

Question 6

What does a '503 Service Unavailable' SIP error response indicate?

Accepted Answer

The SIP server is overloaded or temporarily unavailable

Answer

The destination extension does not exist

Answer

The caller is not authorized to make outbound calls

Answer

The called number is busy on another call