Quality of Service (QoS) UPDATED
ACTUAL Exam Questions and CORRECT
Answers
Why is Quality of Service important? - CORRECT ANSWER - When looking to
provision Real Time communications across a network that is being shared w/ data.
How does Quality of Service help? - CORRECT ANSWER - All elements in the network (
& WAN provider network) are configured to recognize Real Time communications streams &
give them the treatment or 'priority' they need in order to get to their destination on time.
W/in the LAN & WAN Voice quality is dependent on? - CORRECT ANSWER - Delay,
Jitter, Packet loss & Bandwidth.
For best Voice quality Delay should be? - CORRECT ANSWER - One way end-to-end
should be no more than 150ms. AKA latency.
For best Voice quality Jitter should be? - CORRECT ANSWER - No more the 30ms.
How to test for Delay & Jitter? - CORRECT ANSWER - Ping tests ( -l or -s linx/unix
parameter loads the ping packets to a more realistic size).
In a fully switched Ethernet environment will Delay be a problem? - CORRECT
ANSWER - Delay will not be problem, but routers will insert move delay into a network.
What are Network Delay types? - CORRECT ANSWER - 1. Hardware Delay through the
network.
2. Variable Delay e.g Router queues.
3. Transit Delay (the time to traverse networks)
4. Processing Delay in the end devices.
, Measuring Delay example? - CORRECT ANSWER - Pinging w/ 238 bytes of data to
simulate a G.711 voice frame.
ping -l 238 x.x.x.x
Replay x.x.x.x bytes=238 time=40ms TTL=64
Replay x.x.x.x bytes=238 time=40ms TTL=64
What is Jitter? - CORRECT ANSWER - The variation in delay from the expected value.
What can cause Jitter? - CORRECT ANSWER - 1. Router queues
2. Over utilized devices
3. Poor cabling
(Network problems that cause delay)
How does a IP phone cope with Jitter? - CORRECT ANSWER - Jitter buffer at the
receiving end copes w/ irregularities of the network. This buffer holds each packet just long
enough to allow packets to emerge at the right rate. Therefore taking the irregularity out of the
transmission path.
Jitter example - CORRECT ANSWER - Replay x.x.x.x bytes=238time=*25*ms TTL=64
Replay x.x.x.x bytes=238 time=*120*ms TTL=64
Replay x.x.x.x bytes=238 time=*40*ms TTL=64
Replay x.x.x.x bytes=238 time=*100*ms TTL=64
ACTUAL Exam Questions and CORRECT
Answers
Why is Quality of Service important? - CORRECT ANSWER - When looking to
provision Real Time communications across a network that is being shared w/ data.
How does Quality of Service help? - CORRECT ANSWER - All elements in the network (
& WAN provider network) are configured to recognize Real Time communications streams &
give them the treatment or 'priority' they need in order to get to their destination on time.
W/in the LAN & WAN Voice quality is dependent on? - CORRECT ANSWER - Delay,
Jitter, Packet loss & Bandwidth.
For best Voice quality Delay should be? - CORRECT ANSWER - One way end-to-end
should be no more than 150ms. AKA latency.
For best Voice quality Jitter should be? - CORRECT ANSWER - No more the 30ms.
How to test for Delay & Jitter? - CORRECT ANSWER - Ping tests ( -l or -s linx/unix
parameter loads the ping packets to a more realistic size).
In a fully switched Ethernet environment will Delay be a problem? - CORRECT
ANSWER - Delay will not be problem, but routers will insert move delay into a network.
What are Network Delay types? - CORRECT ANSWER - 1. Hardware Delay through the
network.
2. Variable Delay e.g Router queues.
3. Transit Delay (the time to traverse networks)
4. Processing Delay in the end devices.
, Measuring Delay example? - CORRECT ANSWER - Pinging w/ 238 bytes of data to
simulate a G.711 voice frame.
ping -l 238 x.x.x.x
Replay x.x.x.x bytes=238 time=40ms TTL=64
Replay x.x.x.x bytes=238 time=40ms TTL=64
What is Jitter? - CORRECT ANSWER - The variation in delay from the expected value.
What can cause Jitter? - CORRECT ANSWER - 1. Router queues
2. Over utilized devices
3. Poor cabling
(Network problems that cause delay)
How does a IP phone cope with Jitter? - CORRECT ANSWER - Jitter buffer at the
receiving end copes w/ irregularities of the network. This buffer holds each packet just long
enough to allow packets to emerge at the right rate. Therefore taking the irregularity out of the
transmission path.
Jitter example - CORRECT ANSWER - Replay x.x.x.x bytes=238time=*25*ms TTL=64
Replay x.x.x.x bytes=238 time=*120*ms TTL=64
Replay x.x.x.x bytes=238 time=*40*ms TTL=64
Replay x.x.x.x bytes=238 time=*100*ms TTL=64
