2. Traditional data traffic characteristics:
◦ Bursty data flow
◦ First-come, first-served access
◦ Mostly not time-sensitive – delays OK
◦ Brief outages are survivable
3. Converged traffic characteristics:
◦ Constant small-packet voice flow competes
with bursty data flow
◦ Critical traffic must get priority
◦ Voice and video are time-sensitive
◦ Brief outages not acceptable
4. ◦ Telephone Call: “I cannot understand you; your
voice is breaking up.”
◦ Teleconferencing: “The picture is very jerky.
Voice not synchronized.”
◦ Brokerage House: “I needed that information two
hours ago. Where is it?”
◦ Call Center: “Please hold while my screen
refreshes.”
5. Video Lacking
Proper QoS
◦ Lack of bandwidth: multiple flows compete
for a limited amount of bandwidth
◦ End-to-end delay (fixed and variable):
packets have to traverse many network
devices and links that add up to the overall
delay
◦ Variation of delay (jitter): sometimes there is
a lot of other traffic, which results in more
delay
◦ Packet Loss: packets may have to be dropped
when a link is congested
6. Bad Voice Due to
Lack of BW
Bandwidth max = min (10 Mbps, 256 kbps, 512 kbps, 100 Mbps) =
256kbps
Bandwidth avail = bandwidth max / flows
◦ Maximum available bandwidth equals the bandwidth of the
weakest link.
◦ Multiple flows are competing for the same bandwidth, resulting in
much less bandwidth being available to one single application.
7.
8. Bad Voice Due to
Delay Variation
Delay = P1 + Q1 + P2 + Q2 + P3 + Q3 + P4 = X
ms
• End-to-end delay equals a sum of all propagation,
processing, and queuing delays in the path.
• In Best-Effort networks, propagation delay is fixed,
processing and queuing delays are unpredictable.
9. ◦ Processing Delay: The time it takes for a router to take the packet from an
input interface, examine it, and put it into the output queue of the output
interface
◦ Queuing Delay: The time a packets resides in the output queue of a router
◦ Serialization Delay: The time it takes to place the “bits on the wire”
◦ Propagation Delay: The time it takes to transmit a packet
10. ◦ Upgrade the link; the best solution but also the most
expensive.
◦ Forward the important packets first.
◦ Compress the payload of Layer 2 frames (it takes time).
◦ Compress IP packet headers.
11. Bad Voice Due
to Packet Loss
◦ Tail-drops occur when the output queue is full. These are
common drops, which happen when a link is congested.
◦ Many other types of drops exist, usually the result of router
congestion, that are uncommon and may require a hardware
upgrade (input drop, ignore, overrun, frame errors).
12. ◦ Upgrade the link; the best solution but also the most
expensive.
◦ Guarantee enough bandwidth to sensitive packets.
◦ Prevent congestion by randomly dropping less important
packets before congestion occurs.
13.
14.
15. ◦ Network audit
Identify traffic on the
network
◦ Business audit
Determine how each type
of traffic is important for
business
◦ Service levels required
Determine required
response time
16. • Latency < 150 ms*
–
• Jitter < 30 ms*
–
• Loss < 1%*
–
• 17-106 kbps
guaranteed priority
bandwidth
per call
• 150 bps (+ Layer 2
overhead) guaranteed
bandwidth for voice-
control traffic per call
*one-way requirements
17. • Latency ≤ 150 ms
• Jitter ≤ 30 ms
• Loss ≤ 1%
• Minimum priority
bandwidth guarantee
required is:
– Video-Stream + 20%
– For example, a 384 kbps
stream would require 460
kbps of priority bandwidth
*one-way requirements
18. • Different applications have
different traffic characteristics.
• Different versions of the same
application can have different
traffic characteristics.
• Classify data into relative-priority
model with no more than four- to
five-classes:
– Mission-Critical Apps: Locally
defined critical applications
– Transactional: Interactive
traffic, preferred data service
– Best-Effort: Internet, e-mail,
unspecified traffic
– Less-Than-Best-Effort
(Scavenger): Napster, Kazaa,
peer-to-peer applications
19.
20. ◦ Set minimum
bandwidth guarantee
◦ Set maximum
bandwidth limits
◦ Assign priorities to
each class
◦ Manage congestion
21. A network-wide
definition of the
specific levels of
quality of service
assigned to
different classes of
network traffic
