QOS - QOS Models

Question 1

What are the 3 QOS Implementation Models?

Answer 1

• Best effort
• Integrated Services (IntServ)
• Differentiated Services (DiffServ)

Question 2

What was the IntServ model created for?

Answer 2

For real-time applications such as voice and video that require bandwidth, delay, and packet-loss guarantees to ensure both predictable and guaranteed service levels.

Question 3

What do applications do when using IntServ?

Answer 3

Applications signal their requirements to the network to reserve the end-to-end resources (such as bandwidth) they require to provide an acceptable user experience.

Question 4

What protocol does IntServ use to reserve end-to-end resources?

Answer 4

Resource Reservation Protocol - RSVP

Question 5

What 2 things does RSVP do?

Answer 5

• Reserves bandwidth/delay throughout a network for a specific application
• Provides call admission control (CAC) to guarantee that no other IP traffic can use the reserved bandwidth.

Question 6

What happens to the bandwidth reserved by an application if the application is not being used?

Answer 6

It is wasted.

Question 7

What is required of all nodes in order to provide end-to-end QOS using IntServ?

Answer 7

All nodes, including the endpoints running the applications, need to support, build, and maintain RSVP path state for every single flow.

Question 8

What is the biggest drawback to using IntServ?

Answer 8

It cannot scale well on large networks that might have thousands or millions of flows due to the large number of RSVP flows that would need to be maintained.

Question 9

What are the 5 steps showing how RSVP works?

Answer 9

• Sender sends RSVP PATH msgs to receiver
• If each router along the way can guarantee the bandwidth/delay reservation the PATH message is forwarded on to the next hop
• Receiver replies with RSVP RESV message to guarantee bandwidth/delay in the opposite direction
• As each router gets the RSVP RESV message it will determine if it can meet the bandwidth/delay guarantee in the opposite direction and if so, forwards it on to the next hop
• If receiver needs to reserve bandwidth in reverse direction the process is repeated with the receiver sending the RSVP PATH message and the sender replies with the RSVP RESV message

Question 10

What is in an RSVP PATH message?

Answer 10

• Sender source address
• Destination address
• Protocol
• Port
• Bandwidth to be reserved

Question 11

What does each node do when it receives a RSVP PATH message?

Answer 11

Determines if it can meet the bandwidth/delay reservation and if so reserves the resources and forwards it on to the next hop

Question 12

What are 2 types of messages used by RSVP?

Answer 12

• PATH messages
• RESV messages

Question 13

What 3 things make DiffServ different than IntServ?

Answer 13

• No need for a signaling protocol
• No RSVP flow state to maintain on every single node
• With DiffServ QoS characteristics (such as bandwidth and delay) managed on a hop-by-hop basis with QoS policies defined independently at each device

Question 14

Is DiffServ considered an end-to-end QOS solution?

Answer 14

No, because end-to-end QoS guarantees cannot be enforced.