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© 1999, Cisco Systems, Inc.
Introduction to QoS in Campus Networks Session 502
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Agenda • Networking Trends • QoS Demystified • QoS in Campus: Justifications • QoS Model and Techniques • Implementing QoS • Summary • Q&A 502 0943_05F9_c2
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© 1999, Cisco Systems, Inc.
Networking Trends Evolution
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Bridges to First Generation Routers
Early 1980’s
Multiprotocol Router, Dynamic Routing Protocols
Mid 1980’s
Multicast, Switching, Scaling, DHCP
1990’s
Single Network for Delay Sensitive (Voice), High Bandwidth (Video), Standard Data (E-mail) and MissionCritical Data (ERP)
Mid 1990’s–2000
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Voice, Data, Video Communications You Have Mail
Ring ng i R
[email protected] Voice
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E-Mail
Internal Web
Video
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Mission Critical
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What Is Mission Critical?
• ERP applications • SNA applications • Selected physical ports • Selected hosts/clients
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Enterprise Resource Planning (ERP) Networked Applications • Order entry • Finance • Manufacturing • Human Resources • Supply chain management • Sales force automation 502 0943_05F9_c2
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Trend—Integrated Multiservice Network: Data, Voice, Video Data Voice
Video Internet
Single Infrastructure
Packet-Based Multiservice Network
• Integration of data, voice, and video services into a single packet-based infrastructure using IP • Both in enterprise and public service provider networks infrastructure 502 0943_05F9_c2
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Data, Voice, Video Benefits of Integration Short Term
Benefits
Medium Term
Business/ Application Enablement
Long Term
Infrastructure/ Information Convergence
Budget Leverage 1998 502 0943_05F9_c2
2000
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© 1999, Cisco Systems, Inc.
Agenda • Networking Trends • QoS Demystified • QoS in Campus: Justifications • QoS Model and Techniques • Implementing QoS • Summary • Q&A 502 0943_05F9_c2
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QoS—What Is It ? • A traditional network is best-effort • All traffic get the same service, i.e., the forwarding behavior by a network device is FIFO • QoS prioritizes traffic into different service levels and provides preferential forwarding treatment to some data traffic at the expense of lower priority traffic • QoS = Preferential treatment 502 0943_05F9_c2
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QoS—Why Is It Needed? Motivation for QoS Is Manifold • Integrated networks carry different traffic types from a variety of business-enabling applications • Business drivers and policies dictate preferential treatment for some type of traffic over other(s) • Convergence of voice and data networks force us to consider servicing two different types of traffic on a single wire 502 0943_05F9_c2
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Different Requirements Data
Voice
• Bursty
• Smooth
• Greedy
• Benign
• Loss Sensitive
• Loss Insensitive
• Delay Insensitive
• Delay Sensitive
• TCP Retransmits
• UDP Best Effort
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QoS Components
Bandwidth Loss Delay Delay Variation (Jitter)
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Not All Traffic Is Created Equal Data (Best-Effort)
MissionCritical Data
Voice
Video
Low to Moderate
Moderate to High
Moderate to High
Low to Moderate
Random Drop Sensitivity
Low
Low
High
Moderate to High
Delay Sensitivity
High
High
Low
Moderate to High
Jitter Sensitivity
High
High
Low
Low to Moderate
Bandwidth
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© 1999, Cisco Systems, Inc.
What Is Driving the Need for Preferential Treatment in Networks ? Mission-Critical Apps Voice Video None Other
0
20
40
60
80
100
Source: Forrester, August ’98 Fortune 1000
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Example: Evolving Campus Network Existing Network
New Additions
Voice
Video Surveillance
PCs
Mission Critical
MissionCritical Servers
E-mail Servers
Protect Mission-Critical Traffic! 502 0943_05F9_c2
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Consolidated Network Distribution
Wiring Closet
Voice
PCs 502 0943_05F9_c2
Server Farm
MissionCritical Application
Video Surveillance
MissionCritical Application
Web Servers
Four Different Traffic Types PCs, Voice, Video, Mission Critical
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Agenda • Networking Trends • QoS Demystified • QoS in Campus: Justifications • QoS Model and Techniques • Implementing QoS • Summary • Q&A 502 0943_05F9_c2
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QoS in Campus Networks?
“
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Why Not Just Increase the Link Speed? Throw More Bandwidth at the Problem! © 1999, Cisco Systems, Inc.
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Maybe You Can, Maybe You Can’t • QoS in the campus is primarily about buffer management • Buffer management is required to control delay or drops • TCP will eventually retransmit dropped packets • Do you care about delay or drops? 502 0943_05F9_c2
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Buffers Fill for Various Reasons
• Rate mismatch (1000M to 10M Ethernet) • Many to one (multiple interfaces talking to the same interface all with the same rate) • Aggregation points 502 0943_05F9_c2
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TCP Traffic Behavior
Media Sender
Receiver Ack 21 1Ack’s Ack 4 Ack’s
Buffers are available at Sender and Receiver. Media is a buffer of sorts as well because of RTT Because of Almost Zero RTT in LAN, Switch Has to Buffer the TCP Window 502 0943_05F9_c2
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TCP Traffic Behavior Example: Transmission of a 13 Segment Window Round Trip Time (RTT) of 100ms
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TCP Traffic Behavior Window Perfectly Matched with RTT Example: Link Holds 12 IP Segments Worth of Data Which Is Equal to TCP Window 13
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10
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2
1
Ack
Next Window Is Transmitted upon the Receipt of Segment 1 Acknowledgement 502 0943_05F9_c2
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© 1999, Cisco Systems, Inc.
TCP Traffic Behavior Window Not Perfectly Matched
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Ack
Link Buffers, Less Than the TCP Window Which Causes Transmit Buffer to Fill 502 0943_05F9_c2
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Buffer Congestion Speed Mismatch Most Traffic Is Server to Client Smaller Percentage of Traffic Is Client to Server 10 Meg
1000 Meg
Speed Mismatch
Speed Mismatch: Most Likely Point of Congestion on Output Ports of 10 Meg Interface
10 Mbps
1000 Mbps
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Buffer Congestion Many to One
Switching Fabric
• Required when multiple ports are contending for the same port 502 0943_05F9_c2
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Buffer Congestion Aggregation Point • Links oversubscribed
Aggregation
• Buffers full (clue: packets dropped) • Buffering reduces loss but delaysensitive application could be negatively impacted 502 0943_05F9_c2
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Result Packets that Made through; Rest Are Dropped
Even though the Average Link Utilization Is Below 100%, Buffers Can Still Fill up
Buffers Link Utilization 60%
Example: 100 Mbps Link
Packets from Different Applications
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What Happens When Multiple Packets Are Dropped Within the Same Window?
• Window size is reduced exponentially since it is halved for each failed ACK • TCP window may be reduced to the minimum • Transmitter of the sender tends to lock-up 502 0943_05F9_c2
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© 1999, Cisco Systems, Inc.
Voice Delay Budget: 150 ms Cumulative Transmission Path Delay CB Zone Satellite Quality High Quality 0
100
Fax Relay, Broadcast 200
300
400
500
600
700
800
Time (msec) Delay Target
ITU G.114 Recommendation
