3 1 Introducing Qo S 2006 Cisco Systems

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3. 1: Introducing Qo. S © 2006 Cisco Systems, Inc. All rights reserved.

3. 1: Introducing Qo. S © 2006 Cisco Systems, Inc. All rights reserved.

Objectives § Explain why converged networks require Qo. S. § Identify the major quality

Objectives § Explain why converged networks require Qo. S. § Identify the major quality issues with converged networks. § Calculate available bandwidth given multiple flows. § Describe mechanisms designed to use bandwidth more efficiently. § Describe types of delay. § Identify ways to reduce the impact of delay on quality. § Describe packet loss and ways to prevent or reduce packet loss in the network. © 2006 Cisco Systems, Inc. All rights reserved.

Traditional Nonconverged Network § Traditional data traffic characteristics: Bursty data flow FIFO access Not

Traditional Nonconverged Network § Traditional data traffic characteristics: Bursty data flow FIFO access Not overly time-sensitive; delays OK Brief outages are survivable © 2006 Cisco Systems, Inc. All rights reserved.

Converged Network Realities § Converged network realities: Constant small-packet voice flow competes with bursty

Converged Network Realities § Converged network realities: Constant small-packet voice flow competes with bursty data flow. Critical traffic must have priority. Voice and video are time-sensitive. Brief outages are not acceptable. © 2006 Cisco Systems, Inc. All rights reserved.

Converged Network Quality Issues § Lack of bandwidth: Multiple flows compete for a limited

Converged Network Quality Issues § 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; this travel adds up to the overall delay. § Variation of delay (jitter): Sometimes there is a lot of other traffic, which results in varied and increased delay. § Packet loss: Packets may have to be dropped when a link is congested. © 2006 Cisco Systems, Inc. All rights reserved.

Measuring Available Bandwidth § The maximum available bandwidth is the bandwidth of the slowest

Measuring Available Bandwidth § The maximum available bandwidth is the bandwidth of the slowest link. § Multiple flows are competing for the same bandwidth, resulting in much less bandwidth being available to one single application. § A lack in bandwidth can have performance impacts on network applications. © 2006 Cisco Systems, Inc. All rights reserved.

Increasing Available Bandwidth § § Upgrade the link (the best but also the most

Increasing Available Bandwidth § § Upgrade the link (the best but also the most expensive solution). Improve Qo. S with advanced queuing mechanisms to forward the important packets first. Compress the payload of Layer 2 frames (takes time). Compress IP packet headers. © 2006 Cisco Systems, Inc. All rights reserved.

Using Available Bandwidth Efficiently Voice 1 1 2 2 3 3 3 4 4

Using Available Bandwidth Efficiently Voice 1 1 2 2 3 3 3 4 4 4 (Highest) Data (High) Data (Medium) Data (Low) 4 Voice • LLQ • RTP header compression 4 3 2 1 1 Data • CBWFQ • TCP header compression § Using advanced queuing and header compression mechanisms, the available bandwidth can be used more efficiently: Voice: LLQ and RTP header compression Interactive traffic: CBWFQ and TCP header compression © 2006 Cisco Systems, Inc. All rights reserved.

Types of Delay § Processing delay: The time it takes for a router to

Types of Delay § Processing delay: The time it takes for a router to take the packet from an input interface, examine the packet, and put the packet into the output queue of the output interface. § Queuing delay: The time a packet 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 for the packet to cross the link from one end to the other. © 2006 Cisco Systems, Inc. All rights reserved.

The Impact of Delay and Jitter on Quality § End-to-end delay: The sum of

The Impact of Delay and Jitter on Quality § End-to-end delay: The sum of all propagation, processing, serialization, and queuing delays in the path § Jitter: The variation in the delay. § In best-effort networks, propagation and serialization delays are fixed, while processing and queuing delays are unpredictable. © 2006 Cisco Systems, Inc. All rights reserved.

Ways to Reduce Delay § § § Upgrade the link (the best solution but

Ways to Reduce Delay § § § Upgrade the link (the best solution but also the most expensive). Forward the important packets first. Enable reprioritization of important packets. Compress the payload of Layer 2 frames (takes time). Compress IP packet headers. © 2006 Cisco Systems, Inc. All rights reserved.

Reducing Delay in a Network § Customer routers perform: TCP/RTP header compression LLQ Prioritization

Reducing Delay in a Network § Customer routers perform: TCP/RTP header compression LLQ Prioritization § ISP routers perform: Reprioritization according to the Qo. S policy © 2006 Cisco Systems, Inc. All rights reserved.

The Impacts of Packet Loss § Telephone call: “I cannot understand you. Your voice

The Impacts of Packet Loss § Telephone call: “I cannot understand you. Your voice is breaking up. ” § Teleconferencing: “The picture is very jerky. Voice is not synchronized. ” § Publishing company: “This file is corrupted. ” § Call center: “Please hold while my screen refreshes. ” © 2006 Cisco Systems, Inc. All rights reserved.

Types of Packet Drops § Tail drops occur when the output queue is full.

Types of Packet Drops § Tail drops occur when the output queue is full. Tail drops are common and happen when a link is congested. § Other types of drops, usually resulting from router congestion, include input drop, ignore, overrun, and frame errors. These errors can often be solved with hardware upgrades. © 2006 Cisco Systems, Inc. All rights reserved.

Ways to Prevent Packet Loss § Upgrade the link (the best solution but also

Ways to Prevent Packet Loss § Upgrade the link (the best solution but also the most expensive). § Guarantee enough bandwidth for sensitive packets. § Prevent congestion by randomly dropping less important packets before congestion occurs. © 2006 Cisco Systems, Inc. All rights reserved.

Traffic Rate Policing Traffic Policing and Traffic Shaping Time Traffic Rate Shaping Time ©

Traffic Rate Policing Traffic Policing and Traffic Shaping Time Traffic Rate Shaping Time © 2006 Cisco Systems, Inc. All rights reserved. Traffic Time Traffic Rate Time

Reducing Packet Loss in a Network § Problem: Interface congestion causes TCP and voice

Reducing Packet Loss in a Network § Problem: Interface congestion causes TCP and voice packet drops, resulting in slowing FTP traffic and jerky speech quality. § Conclusion: Congestion avoidance and queuing can help. § Solution: Use WRED and LLQ. © 2006 Cisco Systems, Inc. All rights reserved.

Summary § Converged networks carry different types of traffic over a shared infrastructure. This

Summary § Converged networks carry different types of traffic over a shared infrastructure. This creates the need to differentiate traffic and give priority to time-sensitive traffic. § Various mechanisms exist that help to maximize the use of the available bandwidth, including queuing techniques and compression mechanisms. § All networks experience delay. Delay can effect time sensitive traffic such as voice and video. § Without proper provisioning and management, networks can experience packet loss. Packet loss is especially important with voice and video, as no resending of lost packets can occur. © 2006 Cisco Systems, Inc. All rights reserved.