Enterprise QoS Solution Reference Network Design Guide
Enterprise QoS Solution Reference Network Design Guide
Enterprise QoS Solution Reference Network Design Guide
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Chapter 3 WAN Aggregator <strong>QoS</strong> <strong>Design</strong><br />
<strong>Reference</strong>s<br />
Standards<br />
Books<br />
Cisco Documentation<br />
Version 3.3<br />
<strong>Enterprise</strong> <strong>QoS</strong> <strong>Solution</strong> <strong>Reference</strong> <strong>Network</strong> <strong>Design</strong> <strong>Guide</strong><br />
<strong>Reference</strong>s<br />
For the WAN edges, bandwidth-provisioning guidelines were considered, such as leaving 25 percent of<br />
the bandwidth for the Best-Effort class and limiting the sum of all LLQs<br />
to 33 percent.<br />
Three categories of WAN link speeds and their design implications were presented:<br />
Slow-speed (£ 768 kbps) links, which can support only Three- to Five-Class <strong>QoS</strong> models and require<br />
LFI mechanisms and cRTP.<br />
Medium-speed (£ T1/E1) links, which, likewise, can support only Three- to Five-Class <strong>QoS</strong> Models<br />
but no longer require LFI mechanisms. cRTP becomes optional.<br />
High-speed (multiple T1/E1 or greater) links, which can support 5- to 11-Class <strong>QoS</strong> Models. No LFI<br />
is required on such links. cRTP likely would have a high CPU cost (compared to realized bandwidth<br />
savings) and, as such, generally is not recommended for such links. Additionally, some method of<br />
load sharing, bundling, or inverse multiplexing is required to distribute the traffic across multiple<br />
physical links.<br />
These principles then were applied to certain WAN media designs—specifically, for leased lines, Frame<br />
Relay, ATM, and ATM-to-Frame Relay SIW. The corner case of ISDN as a backup WAN link also was<br />
considered.<br />
RFC 2474 “Definition of the Differentiated Services Field (DS Field) in the IPv4 and IPv6 Headers”<br />
http://www.ietf.org/rfc/rfc2474<br />
RFC 2597 “Assured Forwarding PHB Group” http://www.ietf.org/rfc/rfc2597<br />
RFC 2697 “A Single Rate Three Color Marker” http://www.ietf.org/rfc/rfc2697<br />
RFC 2698 “A Two Rate Three Color Marker” http://www.ietf.org/rfc/rfc2698<br />
RFC 3168 “The Addition of Explicit Congestion Notification (ECN) to IP”<br />
http://www.ietf.org/rfc/rfc3168<br />
RFC 3246 “An Expedited Forwarding PHB (Per-Hop Behavior)” http://www.ietf.org/rfc/rfc3246<br />
Szigeti, Tim and Christina Hattingh. End-to-End <strong>QoS</strong> <strong>Network</strong> <strong>Design</strong>: Quality of Service in LANs,<br />
WANs and VPNs. Indianapolis: Cisco Press, 2004.<br />
Layer 3 queuing:<br />
Class-based weighted fair queuing (Cisco IOS Release 12.0.5T):<br />
http://www.cisco.com/univercd/cc/td/doc/product/software/ios120/120newft/120t/120t5/cbwfq.ht<br />
m<br />
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