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NetForecast ® Quality of Service for IP Telephony and Video John Bartlett NetForecast, Inc. firstname.lastname@example.org
©2004, NetForecast, all rights reserved. NetForecast ® Slide 2 Four Major Tasks Network QoS Implementation Classification Bandwidth Management Testing, Measuring and Monitoring
©2004, NetForecast, all rights reserved. NetForecast ® Slide 3 Enterprise QoS Implementations Enterprises use a broad variety of QoS implementations Over Provision Point to Point Using meshed service provider Full network implementation Overlay network Lets take a look at each one and see how they compare
©2004, NetForecast, all rights reserved. NetForecast ® Slide 4 Over Provision Adding bandwidth allows real-time traffic and data traffic to coexist Simple solution Inexpensive in the LAN, expensive in the WAN Works most of the time …
©2004, NetForecast, all rights reserved. NetForecast ® Slide 5 Point to Point Leased line or Frame Relay link has contention due to limited bandwidth Deploy edge box on both ends (Allot, Packeteer, Sitara, etc) Simple, manageable, works well
©2004, NetForecast, all rights reserved. NetForecast ® Slide 6 Meshed Service Provider Corp Now have a more complex problem QoS box on edge can manage traffic flowing towards ISP Traffic from ISP flowing toward enterprise can become congested at the boundary with the access link Now need ISP to provide QoS capabilities as well Corp Service Provider
©2004, NetForecast, all rights reserved. NetForecast ® Slide 7 Full Network Implementation Whole corporate network has QoS implementation Requires careful design Adds significant complexity
©2004, NetForecast, all rights reserved. NetForecast ® Slide 8 Overlay Network Overlays are a compromise implementation Traffic in constrained areas (WAN) are separated LAN uses over provisioning Real-Time Data
©2004, NetForecast, all rights reserved. NetForecast ® Slide 9 Is QoS Easy to Implement? Easy Simple point to point setup, supporting interactive or real-time traffic Traffic shaping can manage bursts Primary focus, consistency of performance, support interactive traffic responsiveness, maintain quality of real-time traffic More Difficult Full network implementation is complex Managing priority traffic volumes is vital, and complex Set up failure paths, allocating bandwidth during failure Testing, finding micro event problems, isolation Impossible (or not yet possible) Across the Internet, using multiple carriers Primarily a business issue Need arbitration, common terms, contract negotiations, etc. Whole business model needed to make this work
©2004, NetForecast, all rights reserved. NetForecast ® Slide 10 Classification This is the job of deciding which traffic is high priority traffic, and which is not End point vs. network Multimedia clients/servers can mark their traffic with DiffServ code point to identify it as high priority Endpoint is the best place to distinguish between real-time and other traffic, because it is close to the application Network may not want to trust the endpoint to determine priority –Has a more global point of view –Distrust of end user (gamer? hacker?) –Network has to manage total amount of high priority traffic Who gets to decide? Semantic problem Organizational high priority and application requirements should not be confused
©2004, NetForecast, all rights reserved. NetForecast ® Slide 11 Bandwidth Management Priority mechanisms only work if the prioritized traffic is a low percentage of overall traffic
©2004, NetForecast, all rights reserved. NetForecast ® Slide 12 Bandwidth Management Priority mechanisms only work if the prioritized traffic is a low percentage of overall traffic
©2004, NetForecast, all rights reserved. NetForecast ® Slide 13 More Bandwidth Management The good news is: Voice and video have very predictable bandwidth consumption Voice and video understand the concept of a busy signal, and/or can be rerouted through the PSTN The bad news is: Data traffic does not have predictable bandwidth Data applications need significant overhead to perform properly Data traffic must be always connected, no busy signal ATM – has built-in bandwidth management functions MPLS – must have bandwidth management system associated with it IP – has some features in some routers ….
©2004, NetForecast, all rights reserved. NetForecast ® Slide 14 Yet More Bandwidth Management Bandwidth management can be done by the voice/video infrastructure Telecommunications & Video organization vs. IP Network Organization Must have an agreement on bandwidth usage Telecom/Video must stick to their allocation Need a process to negotiate growth Growth over time is natural Real-time will encroach on data, and vice versa
©2004, NetForecast, all rights reserved. NetForecast ® Slide 15 The Testing Problem The TCP/IP Way TCP covers up most low level network problems TCP/IPUDP/IP The real-time problem UDP covers up nothing When network problems exist, applications fail rapidly
©2004, NetForecast, all rights reserved. NetForecast ® Slide 16 Brave New World Network congestion causes TCP-based applications to gracefully degrade their functionality (e.g. slow down) Network often self-heals after a short time Long term traffic volume is managed by listening to user grumbles, or monitoring average link usage. Time constants are long. UDP-based applications fail in a more binary way (works, doesnt work) Real-time applications have an additional disadvantage, user expectations are high: Voice over IP is compared to the toll quality voice we get on the PSTN Videoconferencing is often used by high level execs, hence high visibility Yikes! We better test this network constantly!
©2004, NetForecast, all rights reserved. NetForecast ® Slide 17 Testing, Testing, Testing We have to test the network and monitor the call quality to know what is going on Are we delivering the quality voice/video service we want to? Is the problem with the voice equipment, or the transport? Where and when is the network causing problems? Must test as close to end-to-end as possible Voice is subject to very local problems (echo, local connection, poor equipment) as well as network problems Must isolate problems in the network So this call had poor quality, which part of this complex network caused the problem? Must find problems in time domain Micro-outages cause momentary burst packet loss Testing or sniffing after the fact has little value Monitoring tools, NetIQ, RADCom, Telchemy and more
©2004, NetForecast, all rights reserved. NetForecast ® Slide 18 Does this stuff really work? The priority mechanism works well for low volume high priority traffic What happens when we have higher volumes of high priority traffic? What happens to the applications that fall to the bottom of the priority stack?
©2004, NetForecast, all rights reserved. NetForecast ® Slide 19 Bandwidth Time Priority
©2004, NetForecast, all rights reserved. NetForecast ® Slide 20 Bandwidth Time Priority
©2004, NetForecast, all rights reserved. NetForecast ® Slide 21 Bandwidth Time Priority
©2004, NetForecast, all rights reserved. NetForecast ® Slide 22 More Issues! In a link failure situation, if a back-up link has less BW, what gets dropped? Convergence: How quickly will the new network routing configuration resolve after failure? Marking of traffic is more difficult as more end-points come on-line, soft phones, from peering points, etc. Also, how to distinguish traffic that is in-service or out of service (rogues, illegally marked traffic, etc.) Why would we willingly put ourselves in this complex situation?
©2004, NetForecast, all rights reserved. NetForecast ® Slide 23 Conclusions QoS Mechanisms exist, and work for low volumes of high priority traffic Simple network configurations are simple to implement Whole network convergence is still very complex, difficult to implement and more difficult to manage
©2004, NetForecast, all rights reserved. NetForecast ® Slide 24 Net Forecast Nature abhors leaving money on the table New technologies to aid convergence will arise in the next few years Many folks will separate real-time and data traffic in the low-bandwidth high cost areas (WAN) until new technologies simplify the problem considerably
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