Traditional data traffic characteristics: ◦ Bursty data flow ◦ First-come, first-served access ◦ Mostly not time-sensitive – delays OK ◦ Brief outages are survivable
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
◦ 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.”
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
Bad Voice Due to Lack of BWBandwidth max = min (10 Mbps, 256 kbps, 512 kbps, 100 Mbps) =256kbpsBandwidth 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.
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.
◦ 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
◦ 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.
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).
◦ 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.
◦ 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
• 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
• 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
• 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
◦ Set minimum bandwidth guarantee◦ Set maximum bandwidth limits◦ Assign priorities to each class◦ Manage congestion
A network-wide definition of the specific levels of quality of service assigned to different classes of network traffic
Align Network Resources with Business Priorities