- •QoS Overview
- •“Do I Know This Already?” Quiz
- •QoS: Tuning Bandwidth, Delay, Jitter, and Loss Questions
- •Foundation Topics
- •QoS: Tuning Bandwidth, Delay, Jitter, and Loss
- •Bandwidth
- •The clock rate Command Versus the bandwidth Command
- •QoS Tools That Affect Bandwidth
- •Delay
- •Serialization Delay
- •Propagation Delay
- •Queuing Delay
- •Forwarding Delay
- •Shaping Delay
- •Network Delay
- •Delay Summary
- •QoS Tools That Affect Delay
- •Jitter
- •QoS Tools That Affect Jitter
- •Loss
- •QoS Tools That Affect Loss
- •Summary: QoS Characteristics: Bandwidth, Delay, Jitter, and Loss
- •Voice Basics
- •Voice Bandwidth Considerations
- •Voice Delay Considerations
- •Voice Jitter Considerations
- •Voice Loss Considerations
- •Video Basics
- •Video Bandwidth Considerations
- •Video Delay Considerations
- •Video Jitter Considerations
- •Video Loss Considerations
- •Comparing Voice and Video: Summary
- •IP Data Basics
- •Data Bandwidth Considerations
- •Data Delay Considerations
- •Data Jitter Considerations
- •Data Loss Considerations
- •Comparing Voice, Video, and Data: Summary
- •Foundation Summary
- •QoS Tools and Architectures
- •“Do I Know This Already?” Quiz
- •QoS Tools Questions
- •Differentiated Services Questions
- •Integrated Services Questions
- •Foundation Topics
- •Introduction to IOS QoS Tools
- •Queuing
- •Queuing Tools
- •Shaping and Policing
- •Shaping and Policing Tools
- •Congestion Avoidance
- •Congestion-Avoidance Tools
- •Call Admission Control and RSVP
- •CAC Tools
- •Management Tools
- •Summary
- •The Good-Old Common Sense QoS Model
- •GOCS Flow-Based QoS
- •GOCS Class-Based QoS
- •The Differentiated Services QoS Model
- •DiffServ Per-Hop Behaviors
- •The Class Selector PHB and DSCP Values
- •The Assured Forwarding PHB and DSCP Values
- •The Expedited Forwarding PHB and DSCP Values
- •The Integrated Services QoS Model
- •Foundation Summary
- •“Do I Know This Already?” Quiz Questions
- •CAR, PBR, and CB Marking Questions
- •Foundation Topics
- •Marking
- •IP Header QoS Fields: Precedence and DSCP
- •LAN Class of Service (CoS)
- •Other Marking Fields
- •Summary of Marking Fields
- •Class-Based Marking (CB Marking)
- •Network-Based Application Recognition (NBAR)
- •CB Marking show Commands
- •CB Marking Summary
- •Committed Access Rate (CAR)
- •CAR Marking Summary
- •Policy-Based Routing (PBR)
- •PBR Marking Summary
- •VoIP Dial Peer
- •VoIP Dial-Peer Summary
- •Foundation Summary
- •Congestion Management
- •“Do I Know This Already?” Quiz
- •Queuing Concepts Questions
- •WFQ and IP RTP Priority Questions
- •CBWFQ and LLQ Questions
- •Comparing Queuing Options Questions
- •Foundation Topics
- •Queuing Concepts
- •Output Queues, TX Rings, and TX Queues
- •Queuing on Interfaces Versus Subinterfaces and Virtual Circuits (VCs)
- •Summary of Queuing Concepts
- •Queuing Tools
- •FIFO Queuing
- •Priority Queuing
- •Custom Queuing
- •Weighted Fair Queuing (WFQ)
- •WFQ Scheduler: The Net Effect
- •WFQ Scheduling: The Process
- •WFQ Drop Policy, Number of Queues, and Queue Lengths
- •WFQ Summary
- •Class-Based WFQ (CBWFQ)
- •CBWFQ Summary
- •Low Latency Queuing (LLQ)
- •LLQ with More Than One Priority Queue
- •IP RTP Priority
- •Summary of Queuing Tool Features
- •Foundation Summary
- •Conceptual Questions
- •Priority Queuing and Custom Queuing
- •CBWFQ, LLQ, IP RTP Priority
- •Comparing Queuing Tool Options
- •“Do I Know This Already?” Quiz
- •Shaping and Policing Concepts Questions
- •Policing with CAR and CB Policer Questions
- •Shaping with FRTS, GTS, DTS, and CB Shaping
- •Foundation Topics
- •When and Where to Use Shaping and Policing
- •How Shaping Works
- •Where to Shape: Interfaces, Subinterfaces, and VCs
- •How Policing Works
- •CAR Internals
- •CB Policing Internals
- •Policing, but Not Discarding
- •Foundation Summary
- •Shaping and Policing Concepts
- •“Do I Know This Already?” Quiz
- •Congestion-Avoidance Concepts and RED Questions
- •WRED Questions
- •FRED Questions
- •Foundation Topics
- •TCP and UDP Reactions to Packet Loss
- •Tail Drop, Global Synchronization, and TCP Starvation
- •Random Early Detection (RED)
- •Weighted RED (WRED)
- •How WRED Weights Packets
- •WRED and Queuing
- •WRED Summary
- •Flow-Based WRED (FRED)
- •Foundation Summary
- •Congestion-Avoidance Concepts and Random Early Detection (RED)
- •Weighted RED (WRED)
- •Flow-Based WRED (FRED)
- •“Do I Know This Already?” Quiz
- •Compression Questions
- •Link Fragmentation and Interleave Questions
- •Foundation Topics
- •Payload and Header Compression
- •Payload Compression
- •Header Compression
- •Link Fragmentation and Interleaving
- •Multilink PPP LFI
- •Maximum Serialization Delay and Optimum Fragment Sizes
- •Frame Relay LFI Using FRF.12
- •Choosing Fragment Sizes for Frame Relay
- •Fragmentation with More Than One VC on a Single Access Link
- •FRF.11-C and FRF.12 Comparison
- •Foundation Summary
- •Compression Tools
- •LFI Tools
- •“Do I Know This Already?” Quiz
- •Foundation Topics
- •Call Admission Control Overview
- •Call Rerouting Alternatives
- •Bandwidth Engineering
- •CAC Mechanisms
- •CAC Mechanism Evaluation Criteria
- •Local Voice CAC
- •Physical DS0 Limitation
- •Max-Connections
- •Voice over Frame Relay—Voice Bandwidth
- •Trunk Conditioning
- •Local Voice Busyout
- •Measurement-Based Voice CAC
- •Service Assurance Agents
- •SAA Probes Versus Pings
- •SAA Service
- •Calculated Planning Impairment Factor
- •Advanced Voice Busyout
- •PSTN Fallback
- •SAA Probes Used for PSTN Fallback
- •IP Destination Caching
- •SAA Probe Format
- •PSTN Fallback Scalability
- •PSTN Fallback Summary
- •Resource-Based CAC
- •Resource Availability Indication
- •Gateway Calculation of Resources
- •RAI in Service Provider Networks
- •RAI in Enterprise Networks
- •RAI Operation
- •RAI Platform Support
- •Cisco CallManager Resource-Based CAC
- •Location-Based CAC Operation
- •Locations and Regions
- •Calculation of Resources
- •Automatic Alternate Routing
- •Location-Based CAC Summary
- •Gatekeeper Zone Bandwidth
- •Gatekeeper Zone Bandwidth Operation
- •Single-Zone Topology
- •Multizone Topology
- •Zone-per-Gateway Design
- •Gatekeeper in CallManager Networks
- •Zone Bandwidth Calculation
- •Gatekeeper Zone Bandwidth Summary
- •Integrated Services / Resource Reservation Protocol
- •RSVP Levels of Service
- •RSVP Operation
- •RSVP/H.323 Synchronization
- •Bandwidth per Codec
- •Subnet Bandwidth Management
- •Monitoring and Troubleshooting RSVP
- •RSVP CAC Summary
- •Foundation Summary
- •Call Admission Control Concepts
- •Local-Based CAC
- •Measurement-Based CAC
- •Resources-Based CAC
- •“Do I Know This Already?” Quiz
- •QoS Management Tools Questions
- •QoS Design Questions
- •Foundation Topics
- •QoS Management Tools
- •QoS Device Manager
- •QoS Policy Manager
- •Service Assurance Agent
- •Internetwork Performance Monitor
- •Service Management Solution
- •QoS Management Tool Summary
- •QoS Design for the Cisco QoS Exams
- •Four-Step QoS Design Process
- •Step 1: Determine Customer Priorities/QoS Policy
- •Step 2: Characterize the Network
- •Step 3: Implement the Policy
- •Step 4: Monitor the Network
- •QoS Design Guidelines for Voice and Video
- •Voice and Video: Bandwidth, Delay, Jitter, and Loss Requirements
- •Voice and Video QoS Design Recommendations
- •Foundation Summary
- •QoS Management
- •QoS Design
- •“Do I Know This Already?” Quiz
- •Foundation Topics
- •The Need for QoS on the LAN
- •Layer 2 Queues
- •Drop Thresholds
- •Trust Boundries
- •Cisco Catalyst Switch QoS Features
- •Catalyst 6500 QoS Features
- •Supervisor and Switching Engine
- •Policy Feature Card
- •Ethernet Interfaces
- •QoS Flow on the Catalyst 6500
- •Ingress Queue Scheduling
- •Layer 2 Switching Engine QoS Frame Flow
- •Layer 3 Switching Engine QoS Packet Flow
- •Egress Queue Scheduling
- •Catalyst 6500 QoS Summary
- •Cisco Catalyst 4500/4000 QoS Features
- •Supervisor Engine I and II
- •Supervisor Engine III and IV
- •Cisco Catalyst 3550 QoS Features
- •Cisco Catalyst 3524 QoS Features
- •CoS-to-Egress Queue Mapping for the Catalyst OS Switch
- •Layer-2-to-Layer 3 Mapping
- •Connecting a Catalyst OS Switch to WAN Segments
- •Displaying QoS Settings for the Catalyst OS Switch
- •Enabling QoS for the Catalyst IOS Switch
- •Enabling Priority Queuing for the Catalyst IOS Switch
- •CoS-to-Egress Queue Mapping for the Catalyst IOS Switch
- •Layer 2-to-Layer 3 Mapping
- •Connecting a Catalyst IOS Switch to Distribution Switches or WAN Segments
- •Displaying QoS Settings for the Catalyst IOS Switch
- •Foundation Summary
- •LAN QoS Concepts
- •Catalyst 6500 Series of Switches
- •Catalyst 4500/4000 Series of Switches
- •Catalyst 3550/3524 Series of Switches
- •QoS: Tuning Bandwidth, Delay, Jitter, and Loss
- •QoS Tools
- •Differentiated Services
- •Integrated Services
- •CAR, PBR, and CB Marking
- •Queuing Concepts
- •WFQ and IP RTP Priority
- •CBWFQ and LLQ
- •Comparing Queuing Options
- •Conceptual Questions
- •Priority Queuing and Custom Queuing
- •CBWFQ, LLQ, IP RTP Priority
- •Comparing Queuing Tool Options
- •Shaping and Policing Concepts
- •Policing with CAR and CB Policer
- •Shaping with FRTS, GTS, DTS, and CB Shaping
- •Shaping and Policing Concepts
- •Congestion-Avoidance Concepts and RED
- •WRED
- •FRED
- •Congestion-Avoidance Concepts and Random Early Detection (RED)
- •Weighted RED (WRED)
- •Flow-Based WRED (FRED)
- •Compression
- •Link Fragmentation and Interleave
- •Compression Tools
- •LFI Tools
- •Call Admission Control Concepts
- •Local-Based CAC
- •Measurement-Based CAC
- •Resources-Based CAC
- •QoS Management Tools
- •QoS Design
- •QoS Management
- •QoS Design
- •LAN QoS Concepts
- •Catalyst 6500 Series of Switches
- •Catalyst 4500/4000 Series of Switches
- •Catalyst 3550/3524 Series of Switches
- •Foundation Topics
- •QPPB Route Marking: Step 1
- •QPPB Per-Packet Marking: Step 2
- •QPPB: The Hidden Details
- •QPPB Summary
- •Flow-Based dWFQ
- •ToS-Based dWFQ
- •Distributed QoS Group–Based WFQ
- •Summary: dWFQ Options
Link Fragmentation and Interleaving 525
show no packets have been in the low-latency queue. This example shows a perfect case where you have a VC (R3 to R2) that does not really need FRF for itself; FRF should be enabled, however, so that the small packets from other VCs can be interleaved.
The show queueing interface serial 0/0 command shows incrementing counters for both the High queue and the Normal queue. Because one voice call is using the VC from R3 to R1, the voice packets get placed into the R3-to-R1 VC’s low-latency queue, and then placed into the Dual FIFO High queue. (Interestingly, I did a few repetitive show queueing commands, once every 5 seconds, and saw the High queue counter increment about 250 packets per 5-second interval. With 20 ms of payload, each G.729 call sends 50 packets per second, so the counters reflected the fact that the voice packets from the low-latency queue were being placed into the Dual FIFO High queue.)
FRF.11-C and FRF.12 Comparison
Most of the coverage of LFI over Frame Relay has focused on FRF.12. However, IOS offers another Frame Relay LFI service called FRF.11-C. You can use each of these two LFI options only when you use particular types of Frame Relay VCs. To appreciate how the two options differ, you first need to understand these two types of VCs.
The Frame Relay Forum (FRF) created data VCs originally to carry multiprotocol data traffic, as defined in the FRF.3 Implementation Agreements. Service providers around the world offer Frame Relay FRF.3 data VCs.
Later, with the advent of packetized voice, the Frame Relay Forum decided to create a new type of VC that would allow for better treatment of voice traffic. The FRF created the FRF.11 Implementation Agreement, which defines Voice over Frame Relay (VoFR) VCs. These VCs still pass data traffic, but they also pass voice traffic. Therefore, if a Frame Relay switch knows that one frame is data, and another is voice, for example, the switch can implement some form of queuing to give the voice frame low latency. FRF.11 headers include a field that identifies the frame as voice or data, making it possible for the cloud to perform QoS for the voice traffic.
The key to understanding the difference between the two basic types of VCs is to look at the headers used when the frames cross the Frame Relay network. It helps to understand when VoFR VCs can be useful, and when they cannot. Figure 7-18 shows the framing when FRF.3 and FRF.11 are used, both for IP telephony traffic and for local voice gateway traffic.
In all cases in the figure, G.729 codecs are used. With FRF.3 VCs, the IP Phone and voice gateway traffic sits inside IP/UDP/RTP headers. In other words, the IP Phones encapsulate the G.729 payload using VoIP, and the routers do the same for the analog and digital voice trunks. Although the packets traverse the Frame Relay network, all the voice traffic is considered to be VoIP traffic when you use FRF.3 data VCs.
526 Chapter 7: Link-Efficiency Tools
Figure 7-18 Framing of Voice Traffic with FRF.3 and FRF.11 VCs
|
|
|
|
With Data VC |
|
|
|
|
|
|
|
|
|
|
|
|
||
|
|
|
|
|
|
|
|
|
IP Telephone Traffic |
|
|
|
|
|
||||
|
|
|
|
|
|
FRF.3 |
IP |
UDP |
RTP |
G.729 |
FRF.3 |
|
|
|
|
|
||
|
|
|
|
|
|
Header |
Voice |
Trailer |
|
|
|
|
|
|||||
|
|
|
|
|
|
|
|
|
Voice Gateway Traffic |
|
|
|
|
|
||||
|
|
|
|
|
|
FRF.3 |
IP |
UDP |
RTP |
G.729 |
FRF.3 |
|
|
|
|
|
||
|
|
IP |
|
|
Header |
Voice |
Trailer |
|
|
|
|
|
||||||
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
SW1 |
R1 |
T/1 R2 |
SW2 |
IP |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
With VoFR VC |
|
|
|
|
|
|
|
|
IP Telephone Traffic |
|
||||
FRF.3 |
FRF.11 |
IP |
UDP |
RTP |
G.729 |
FRF.3 |
|
|
||||||
|
|
|
||||||||||||
|
Header |
Header |
Voice |
Trailer |
|
|
||||||||
|
|
|
|
|
Voice Gateway Traffic |
|
|
|
|
|||||
|
FRF.3 |
FRF.11 |
G.729 |
FRF.3 |
|
|
|
|
|
|||||
|
Header |
Header |
Voice |
Trailer |
|
|
|
|
|
With FRF.11 VCs, some voice traffic can be VoIP, and some can be VoFR traffic. The traffic to and from the directly attached analog and digital voice links can be encapsulated using VoFR, as shown in the lowest of the four example frames. The IP telephony traffic, however, still must be encapsulated first in IP, because the traffic must pass across other links besides this single Frame Relay cloud. The VoFR encapsulation requires far less overhead, because the IP, RTP, and UDP headers are not needed. However, VoFR you can use encapsulation only when the Frame Relay-attached routers are the endpoints for the packets holding the voice payload. Because the larger percentage of packetized voice over time will be from IP Phones and the like, VoFR services are not typically offered by Frame Relay providers.
FRF.11-C provides for LFI over VoFR VCs, similarly to how FRF.12 provides LFI services for FRF.3 data VCs. Just like FRF.12, FRF.11-C uses Dual FIFO interface output queues, with PQ logic applied to the two queues. However, FRF.11-C uses a different classification logic, as follows:
•
•
VoFR frames are placed into the High queue on the interface.
All data frames are placed into the Normal queue.
In the preceding figure, the VoFR frames created for the voice gateway would be placed in the High queue, but the IP Phone packets would be placed into the Normal queue, because they would be considered to be data.
Link Fragmentation and Interleaving 527
The other main difference between FRF.11-C and FRF.12 has to do with how the tools decide what to fragment, and what not to fragment. FRF.12 fragments all packets over a certain length. FRF.11-C, however, never fragments VoFR frames, even if they are larger than the fragment size. FRF.11-C fragments data frames only, and only if they are larger than the fragment size.
Table 7-15 summarizes some of the key comparison points about FRF.12 and FRF.11-C.
Table 7-15 FRF.11-C and FRF.12 Comparison
Function |
FRF.12 Behavior |
FRF.11-C Behavior |
|
|
|
Queuing option on the interface |
Dual FIFO |
Dual FIFO |
output queues |
|
|
|
|
|
Classification into the interface |
Based on queuing tool used for |
Voice frames placed in High |
output queues |
shaping, with LLQ and IP RTP |
queue, all others in Normal |
|
Priority putting packets into the |
queue, regardless of shaping |
|
high-priority queue |
queue configuration |
|
|
|
Fragmentation based on size or |
Based only on size; must be |
Non-VoFR (VoIP and data) |
type of packet |
careful not to fragment voice |
frames fragmented if they |
|
packets |
exceed the fragmentation size; |
|
|
voice frames are not, regardless |
|
|
of size |
|
|
|
Frame Relay network aware of |
No |
Yes |
voice vs. nonvoice frames, and |
|
|
acts accordingly |
|
|
|
|
|
Underlying type of VC, and |
FRF.3, available from most if |
FRF.11, not generally available |
general public availability. |
not all public Frame Relay |
from public Frame Relay |
|
services |
services |
|
|
|