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NetForecast ®
Quality of Service for IP Telephony and Video
John Bartlett
NetForecast, Inc.
Slide 2©2004, NetForecast, all rights reserved.
NetForecast ®Four Major Tasks
Network QoS Implementation
Classification
Bandwidth Management
Testing, Measuring and Monitoring
Slide 3©2004, NetForecast, all rights reserved.
NetForecast ®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
Slide 4©2004, NetForecast, all rights reserved.
NetForecast ®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 …
Slide 5©2004, NetForecast, all rights reserved.
NetForecast ®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
Slide 6©2004, NetForecast, all rights reserved.
NetForecast ®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 enterprisecan become congested at the boundary with the access link
Now need ISP to provide QoS capabilities as well
Corp
Corp
ServiceProvider
Slide 7©2004, NetForecast, all rights reserved.
NetForecast ®Full Network Implementation
Whole corporate network has QoS implementation
Requires careful design
Adds significant complexity
Slide 8©2004, NetForecast, all rights reserved.
NetForecast ®Overlay Network
Overlays are a compromise implementation
Traffic in constrained areas (WAN) are separated
LAN uses over provisioning
Real-Time
Data
Slide 9©2004, NetForecast, all rights reserved.
NetForecast ®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
Slide 10©2004, NetForecast, all rights reserved.
NetForecast ®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
Slide 11©2004, NetForecast, all rights reserved.
NetForecast ®Bandwidth Management
Priority mechanisms only work if the prioritized traffic is a low percentage of overall traffic
Slide 12©2004, NetForecast, all rights reserved.
NetForecast ®Bandwidth Management
Priority mechanisms only work if the prioritized traffic is a low percentage of overall traffic
Slide 13©2004, NetForecast, all rights reserved.
NetForecast ®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 functionsMPLS – must have bandwidth management system
associated with it IP – has some features in some routers ….
Slide 14©2004, NetForecast, all rights reserved.
NetForecast ®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
Slide 15©2004, NetForecast, all rights reserved.
NetForecast ®The Testing Problem
The TCP/IP Way TCP covers up most low level network problems
TCP/IP UDP/IP
The real-time problemUDP covers up nothing When network problems exist, applications fail rapidly
Slide 16©2004, NetForecast, all rights reserved.
NetForecast ®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, doesn’t 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!
Slide 17©2004, NetForecast, all rights reserved.
NetForecast ®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
Slide 18©2004, NetForecast, all rights reserved.
NetForecast ®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?
Slide 19©2004, NetForecast, all rights reserved.
NetForecast ®
Ban
dwid
th
Time
Priority
Slide 20©2004, NetForecast, all rights reserved.
NetForecast ®
Ban
dwid
th
Time
Priority
Slide 21©2004, NetForecast, all rights reserved.
NetForecast ®
Ban
dwid
th
Time
Priority
Slide 22©2004, NetForecast, all rights reserved.
NetForecast ®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?
Slide 23©2004, NetForecast, all rights reserved.
NetForecast ®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
Slide 24©2004, NetForecast, all rights reserved.
NetForecast ®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