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409 1040_05F9_c2
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© 1999, Cisco Systems, Inc.
Advanced VoIP Tuning and Troubleshooting Session 409
409 1040_05F9_c2
© 1999, Cisco Systems, Inc.
Copyright © 1998, Cisco Systems, Inc. All rights reserved. Printed in USA. 1040_05F9_c2.scr
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Tuning for Voice Quality
Problem Avoidance Analyze problem sources and proper design tool/guidelines to ensure voice quality
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© 1999, Cisco Systems, Inc.
More Than Just Providing Router QoS The World Is Not All Point-to-Point Links Sender
Receiver T1 V
PBX
V
128 kbps V
WAN
Router
Whew, We Made It
409 1040_05F9_c2
PBX Router
Hmmmm, Voice Packets, My Favorite! Chomp, Chomp, Chomp!
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Agenda
• VoIP Requirements and Challenges • Router/Switch Egress QoS Study • WAN QoS Design Considerations • Tuning—Audio Level and Echo • Best Practice Recommendations 409 1040_05F9_c2
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© 1999, Cisco Systems, Inc.
Data and Voice Opposite Needs/Behavior Data
Voice
• Bursty
• Smooth
• Greedy
• Benign
• Drop sensitive
• Drop insensitive
• Delay insensitive
• Delay sensitive
• TCP retransmits
• UDP best effort
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Voice over IP Protocols VoIP Is Not Bound to H.323 (H.323 Is a Signaling Protocol) Many Other Signaling Protocols—MGCP, SGCP, SIP, Etc. Commonality—Voice Packets Ride on UDP/RTP Voice Payload
G.711, G.729, G.723(.1)
Transport
RTP/UDP
Network
IP
Link
MLPPP/FR/ATM AAL1
Physical
–––
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© 1999, Cisco Systems, Inc.
“Payload” Bandwidth Requirements for Various Codecs Encoding/Compression
Resulting Bit Rate
G.711 PCM A-Law/u-Law
64 kbps (DS0)
G.726 ADPCM
16, 24, 32, 40 kbps
G.727 E-ADPCM
16, 24, 32, 40 kbps
G.729 CS-ACELP
8 kbps
G.728 LD-CELP
16 kbps
G.723.1 CELP
6.3/5.3 kbps
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VoIP Packet Format VoIP Packet Link UDP IP Header Header Header X Bytes 20 Bytes 8 Bytes
RTP Header 12 Bytes
Voice Payload X Bytes
• Payload size, PPS and BPS vendor implementation specific • For example: Not Including Link Layer Header or CRTP Cisco Router at G.711 Cisco Router at G.729 Cisco IP Phone at G.711 Cisco IP Phone at G.723.1
= 160 Byte Voice Payload at 50 pps (80 kbps) = 20 Byte Payload at 50 pps (24 kbps) = 240 Byte Payload at 33 pps (74.6 kbps) = 24 Byte Payload at 33 pps (17k bps)
Note—Link Layer Sizes Vary per Media 409 1040_05F9_c2
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© 1999, Cisco Systems, Inc.
Various Link Layer Header Sizes “Varying Bit Rates per Media” Example—G.729 with 60 Byte Packet (Voice and IP Header) at 50 pps (No RTP Header Compression)
Media
Link Layer Header Size
Bit Rate
Ethernet
14 Bytes
29.6 kbps
PPP
6 Bytes
26.4 kbps
Frame Relay
4 Bytes
25.6 kbps
ATM
5 Bytes Per Cell
42.4 kbps
Note—For ATM a Single 60 Byte Packet Requires Two 53 Byte ATM Cells 409 1040_05F9_c2
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Domains of QoS Consideration Requirement - “End to End” Quality of Service (QoS)
IP
Multilayer Campus Router
Multilayer Campus Router
WAN
IP
IP
IP
IP
Campus
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IP
WAN Edge/Egress
WAN Backbone
Avoiding Loss, Delay and Delay Variation (Jitter) Strict Prioritization of Voice 11
© 1999, Cisco Systems, Inc.
Loss Sources of Packet Loss—Congestion
IP
Multilayer Campus Router
IP
Multilayer Campus Router
WAN
IP
IP
IP
Edge/Egress 1. 1. Congestion Congestion on on WAN WAN Link Link 2. 2. Proper Proper QoS QoS Mechanisms Mechanisms Not Not Deployed Deployed 3. 3. Campus Campus Congestion Congestion Less Less Concerning Concerning
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IP
WAN 1. 1. Global Global WAN WAN Congestion Congestion 2. 2. Central Central to to Remote Remote Circuit Circuit Speed Speed Mismatch Mismatch 3. Remote Site to 3. Remote Site to Central Central Site Site over over Subscription Subscription 4. 4. Improper Improper PVC PVC Design/Provisioning Design/Provisioning
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Delay—Fixed Sources of Fixed Delay
IP
Multilayer Campus Router
Multilayer Campus Router
WAN
IP
IP IP
IP
IP
Edge/Egress
WAN
Codec Codec Processing—Packetization Processing—Packetization (TX) (TX) Serialization Serialization De-Jitter De-Jitter Buffer Buffer
409 1040_05F9_c2
Propagation Propagation Delay—6us Delay—6us per per Km Km Serialization Serialization Delay Delay
13
© 1999, Cisco Systems, Inc.
Delay Budget Goal < 150 ms Cumulative Transmission Path Delay Avoid the “Human Ethernet” CB Zone Satellite Quality High Quality 0
100
Fax Relay, Broadcast 200
300
400
500
600
700
800
Time (msec) Delay Target
ITU’s G.114 “Recommendation” = 0–150 msec 1-Way Delay 409 1040_05F9_c2
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Delay—Variable Sources of Variable Delay
IP
Multilayer Campus Router
WAN
IP
Multilayer Campus Router
IP
IP
IP
Edge/Egress
WAN
Queuing Queuing Delay Delay (Congestion) (Congestion) De-Jitter De-Jitter Buffer Buffer No No or or Improper Improper Traffic Traffic Shaping Shaping Config Config Large Large Packet Packet Serialization Serialization on on Slow Slow Links Links Variable Variable Size Size Packets Packets Less Less Common Common in in Campus Campus 409 1040_05F9_c2
IP
Global Global WAN WAN Congestion Congestion Central Central to to Remote Remote Site Site Speed Speed Mismatch Mismatch (Fast (Fast to to Slow) Slow) PVC PVC Over Over Subscription Subscription (Remote (Remote to to Central Central Site) Site) Bursting Bursting Above Above Committed Committed Rates Rates
15
© 1999, Cisco Systems, Inc.
Large Packets on Slow Links
56 kbps Line
Real-Time MTU
Elastic Traffic MTU 214 ms Serialization Delay for 1500 Byte Frame at 56 kbps
Large Packets “Freeze Out” Voice—Results in Jitter
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QoS Needs • Campus Bandwidth minimizes QoS issues
• WAN edge QoS “starts” in the WAN—a must
• WAN considerations Often forgotten or misunderstood— a must 409 1040_05F9_c2
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© 1999, Cisco Systems, Inc.
Agenda
• VoIP Requirements and Challenges • Router/Switch Egress QoS Study • WAN QoS Design Considerations • Tuning—Audio Level and Echo • Best Practice Recommendations 409 1040_05F9_c2
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Case Study: End-to-End Quality of Service Headquarters IP
Si
High-Speed WAN Backbone > 2 Mbps
Cisco 7500
Catalyst 6500
IP
Campus
High-Speed Backbone
Regional Office
Point-to-Point 256 kbps
IP
Cisco 2600
Cisco 7200 T1
WAN Provisioning and Design
Cisco 3600
Frame Relay
Low Speed Central Site
128 kbps
IP
ATM
Branch Office’s Cisco 3600
Low Speed Remote Sites
IP
Applying Proper Tools in Proper Location 409 1040_05F9_c2
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© 1999, Cisco Systems, Inc.
Router/Switch Egress QoS Tools “Three Classes of QoS Tools” VoIP
1
1
SNA
2
2
3
3
Data
3
3
Router 2
V 1
3
V 1
2
V 1
• Prioritization Low Speed WAN, High Speed WAN, Campus
• Link Efficiency Fragment and Interleave, Compression, VAD
• Traffic Shaping Speed Mismatches + To Avoid Bursting 409 1040_05F9_c2
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Prioritization Low Speed WAN Egress QoS Two MB or Less • IP precedence • RSVP • Class-cased weighted fair queuing CBWFQ
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Weighted Fair Queuing (WFQ) Treats Flows with same IP Precedence Equally 24 kbps Flow Gets 28 kbps (Only Needs 24 kbps)
Router Queue Structure
24 kbps Voice Flow
Processor
Interface Queues Dynamic Queue Per Flow 11
22
11
22
22
22
11 DeDequeue queue
22 11 22
500 kbps Flow
22
Classify
22
22 Transmit Scheduling
500 kbps Flow Gets 28 kbps Therefore = “Fair” 22
11
22
11
22
11
56 kbps Line Speed
Default on Links 2 MB or Less High Speed Input Ethernet T1 etc.
When Congestion Exists Queues share Bandwidth Equally i.e. “Fair Queuing” in a TDM Fashion
Low Speed Output 56 kbps
“Not as Effective When Many Flows” 409 1040_05F9_c2
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Displaying WFQ Emphasizing the “Fair” in Weighted Fair Queuing Note: The Lower the Weight of a Flow, the More Bandwidth it Gets HUB3640#show queue se 0/0 Input queue: 0/75/0 (size/max/drops); Total output drops: 0 Queuing strategy: weighted fair Output queue: 31/64/0 (size/threshold/drops) Conversations 2/4 (active/max active) Reserved Conversations 0/0 (allocated/max allocated) (depth/weight weight/discards/interleaves) 24/4096 4096/0/0 Conversation 184, linktype: ip, length: 1504 source: 10.1.5.2, destination: 10.1.6.1, id: 0x04CF, ttl: 31, TOS: 0 prot: 6, source port 1503, destination port 21 (depth/weight weight/discards/interleaves) 2/4096 4096/0/0 Conversation 227, linktype: ip, length: 68 source: 10.1.1.2, destination: 10.1.1.1, id: 0xFCCF, ttl: 31, TOS: 0 prot: 17, source port 49608, destination port 49608 409 1040_05F9_c2
Weight = 4096/(1+ IP Prec)
High Bandwidth Flow
VoIP Flow 23
© 1999, Cisco Systems, Inc.
Traffic Differentiation Mechanisms IP Precedence and 802.1p Three Bits Used for CoS (User Priority)
Layer 2 802.1Q/p Data PREAM. SFD Packet
DA
SA
TAG 4 Bytes
PT
DATA
FCS
Layer 3 IPV4 Version ToS Len Length 1 Byte
ID
offset
TTL
Proto
FCS
IP-SA IP-DA
Data
Standard IPV4: Three MSB Called IP Precedence (DiffServ Will Use Six D.S. Bits Plus Two for Flow Control)
• Layer 2 mechanisms are not assured end-to-end • Layer 3 mechanisms provide end-to-end classification 409 1040_05F9_c2
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IP Precedence “Controlling WFQ’s De-queuing Behavior” IP Packet Data
Weight =
4096 (1 + IP Precedence)
IP Precedence
ToS Field 3 Bit Precedence Field
0 1 2 3 4 5 6 7
Weight 4096 2048 1365 1024 819 682 585 512
• IP Precedence Not a QoS Mechanism turned on in the router “In Band” QoS Signaling—Set in the End Point 409 1040_05F9_c2
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© 1999, Cisco Systems, Inc.
Displaying Effects of IP Precedence This Is Using the “Weight” in Weighted Fair Queuing HUB3640#show queue se 0/0 Input queue: 0/75/0 (size/max/drops); Total output drops: 0 Queuing strategy: weighted fair Output queue: 9/64/0 (size/threshold/drops) Conversations 2/7 (active/max active) Reserved Conversations 0/0 (allocated/max allocated)
409 1040_05F9_c2
(depth/weight weight/discards/interleaves) 1/585 585/0/0 Conversation 90, linktype: ip, length: 68 source: 10.1.5.2, destination: 10.1.6.1, id: 0x0064, ttl: 255, TOS: 192 prot: 17, source port 16384, destination port 16384
VoIP Flow
(depth/weight/discards/interleaves) 8/4096/0/0 Conversation 219, linktype: ip, length: 1504 source: 10.1.1.2, destination: 10.1.1.1, id: 0x1C7E, ttl: 31, TOS: 0 prot: 6, source port 49604, destination port 21
FTP Flow
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IP Precedence with WFQ Calculating Given Flow Bandwidth Based on IP Precedence Under Congestion A “Parts” ) X Circuit ( Sum ofFlow Bandwidth all Flow “Parts”
Flow A BW =
Individual Flow “Parts” = 1 + IP Precedence IP Precedence 0 1 2 3 4 5 6 7 409 1040_05F9_c2
Flow “Parts” 1 2 3 4 5 6 7 8 27
© 1999, Cisco Systems, Inc.
IP Precedence Flow Bandwidth Calculation Example A “Parts” ) X Circuit ( Sum ofFlow Bandwidth all Flow “Parts”
Flow A BW = Example A
Example B
56 kbps Link
56 kbps Link
2—VoIP Flows A+B at 24 kbps (IP Prec 0) 2—FTP Flows at 56 kbps (IP Prec 0)
2—VoIP Flows A+B at 24 kbps (IP Prec 5) 2—FTP Flows at 56 kbps (IP Prec 0)
14 kbps =
( 14 )
X 56 kbps
24 kbps =
6 ) ( 14
X 56 kbps
14 kbps Not Suitable for a 24 kbps Flow Example of Many Flows with WFQ and Equal Precedence Flows
24 kbps Suitable for a 24 kbps Flow
Weighted “Fair” Queuing
WFQ Preferring IP Precedence
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IP Precedence No Admission Control Moral of the Story: Know Your Environment, Voice Traffic Patterns etc. Recommendations for Certain Bandwidth’s to Follow Example C 56 kbps Link 2—VoIP Flow’s at 24 kbps (IP Prec 5) 4—FTP Flows at 56 kbps (IP Prec 0) 21 kbps =
6 (16)
X 56 kbps
21 kbps Not Suitable for a 24 kbps Flow
RTP Header Compression Would Help Since it Would reduce VoIP Flow to 11.2 kbps Also RSVP or CBWFQ 409 1040_05F9_c2
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Class-Based Weighted Fair Queuing CBWFQ • Queues represent “classes” that have an associated minimum bandwidth in kbps • Traffic assigned to classes via a “policy-map” • Max 64 classes which support: WFQ between classes RED per class 409 1040_05F9_c2
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Class-Based Weighted Fair Queuing CBWFQ class-map data match input-interface Ethernet0/0 class-map class-default match any class-map voice match access-group 101 ! 11 22 22 11 ! policy-map WAN class voice bandwidth 80 class data bandwidth 48 ! interface Serial0/1 ip address 10.1.6.2 255.255.255.0 bandwidth 128 no ip directed-broadcast service-policy output WAN ! access-list 101 permit ip any any precedence critical
Class-Based WFQ Class-Map Voice = 80 kbbs
22
11 11
11
22 22
DeDequeue queue
128 kbps
Classify Class-Map Data = 48 kbbs 31
Any Packet with IP Precedence = 5 Gets Assigned to a Class That will Get a Minimum of 80 kbps on a 128 kbps Circuit
31 409 1040_05F9_c2
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© 1999, Cisco Systems, Inc.
RSVP: Resource Reservation Protocol • IETF signaling protocol
Admit Admit One One
Reservation of bandwidth and delay
• Flow can be signaled by end station or by router (static reservation) • Basically reserves queue space End Points Send Unicast Signaling Messages (RSVP PATH + RESV)
Non RSVP Enabled Routers Pass the VoIP Flow as Best Effort
RSVP PATH Message FXS
FXS RSVP RESV Message RSVP Enabled Router See the PATH and RESERVE Messages and Allocate the Appropriate Queue Space for the Given Flow
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Configuring RSVP Interface Command ip rsvp bandwidth [interface-kbps] [single-flow-kbps] interface Serial0/0 ip address 10.1.1.2 255.255.0.0 ip rsvp bandwidth 96 96 bandwidth 128 fair-queue 64 256 1000 Make Sure the Bandwidth Statement Accurately Reflects the Circuit Bandwidth
bottom#sho ip rsvp installed BPS To From 24K 10.1.1.1 10.1.1.2 409 1040_05F9_c2
RSVP Flow = Weight
Greatest BW Reservation on the link Conversation BW
By Default 75% of the “Bandwidth” Statement Is Reservable
Protoc DPort Sport Weight Conversation UDP 16384 16384 4 264 33
© 1999, Cisco Systems, Inc.
Monitoring RSVP Queue Operation bottom#sho que se 0 Input queue: 0/75/0 (size/max/drops); Total output drops: 0 Queueing strategy: weighted fair Output queue: 23/64/0 (size/threshold/drops) Conversations 3/5 (active/max active) Reserved Conversations 1/1 (allocated/max allocated) (depth/weight/discards/interleaves) 21/4096/0/0 Conversation 195, linktype: ip, length: 1504 source: 10.1.5.1, destination: 10.1.6.1, id: 0xD5E8, ttl: 31, TOS: 0 prot: 6, source port 1503, destination port 21
(depth/weight weight/discards/interleaves) 2/4 4/0/0 Conversation 264, linktype: ip, length: 68 source: 10.1.1.2, destination: 10.1.1.1, id: 0xAFE9, ttl: 31, TOS: 0 prot: 17, source port 16348, destination port 16384 409 1040_05F9_c2
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FTP Flow
Reserved VoIP Flow
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Prioritization High-Speed WAN Egress QoS Greater than 2 MB • Distributed weighted fair queuing • WRED • IP to ATM CoS At High-Speeds Processor Oriented QoS Mechanisms Not Efficient 409 1040_05F9_c2
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© 1999, Cisco Systems, Inc.
High-Speed Prioritization Distributed Weighted Fair Queuing (DWFQ) VIP2-40 or Better (Versatile Interface Processor) Flow-Based DWFQ 11
11
22
22
33
33
44 44
44
55 55 55
55
66
66
11
Classify
QoS-Group-Based DWFQ
ToS-Based DWFQ
11
11
22
22
33
33
44 44
44
11 11
DeDequeue queue
11 11 22 22
DeDequeue queue
Classify
1 Queue Per Flow IP Precedence Does Not Get Priority (i.e. “Fair Queuing”)
Classify
DeDequeue queue
Define Queue Classes and weight in Percent
4 Queues Based on ToS 2 MSB
Policy Routing Assigns Flows to Queues
Can Weight the 4 Queues Accordingly to Percent
• Cannot be configured on sub-interfaces—yet 409 1040_05F9_c2
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ToS-Based DWFQ Configuration Example interface Serial1/1/0 ip address 10.1.5.1 255.255.255.0 no ip directed-broadcast ip route-cache distributed fair-queue tos fair-queue tos 1 weight 2 0 fair-queue tos 1 limit 197 fair-queue tos 2 weight 3 0 fair-queue tos 2 limit 197 fair-queue tos 3 weight 4 0 fair-queue tos 3 limit 197
Queue Bandwidth in Percent
7500#sho queu se 1/1/0 Serial1/1/0 queue size 54 packets output 1859402, wfq drops 0, nobuffer drops 0 WFQ: aggregate queue limit 395, individual queue limit 197 max available buffers 395
Data Flow Voice Flow 409 1040_05F9_c2
Class 0: weight 10 limit 197 qsize 61 packets output 600387 drops 0 Class 1: weight 20 limit 197 qsize 1 packets output 529548 drops 0 Class 2: weight 30 limit 197 qsize 0 packets output 1610 drops 0 Class 3: weight 40 limit 197 qsize 0 packets output 0 drops 0 37
© 1999, Cisco Systems, Inc.
Weighted RED • WRED: In the event packets need to be dropped, what class of packets should be dropped Packets Classified as Blue Start Dropping at a 50% Queue Depth. Drop Rate Is Increased as Queue Depth Is Increased
Packets Classified as Gold Are Dropped at 90% Queue Depth
WRED Benefit for VoIP: Maintain Room in Queue, and if Packets Must be Dropped “Avoid” Dropping Voice 409 1040_05F9_c2
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WRED Congestion Avoidance Maximize Data Goodput Adjustable Drop Probabilities (from “show interface”) Queuing strategy: random early detection (RED) mean queue depth: 56 drops: class random tail min-th max-th mark-prob 0 4356 0 20 40 1/10 Data 1 0 0 22 40 1/10 Flow 2 0 0 24 40 1/10 Prec = 0 3 0 0 26 40 1/10 4 0 0 28 40 1/10 5 0 0 30 40 1/10 6 0 0 33 40 1/10 Voice 7 0 0 35 40 1/10 Flow 0 0 37 40 1/10 Prec = 5 rsvp
Uncontrolled Uncontrolled Uncontrolled Congestion Congestion Congestion
Managed Congestion Managed Managed Congestion Congestion
• Accommodate burstiness • “Less” drop probability for higher priority flows (VoIP) • Does not protect against flows that do not react to drop For example, extremely heavy UDP flow can overflow WRED queue 409 1040_05F9_c2
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Make Sure That IP QoS Policies Are Preserved in an ATM Network • IP-ATM CoS: Differentiated services over standard ATM • Requires PA-A3/deluxe PA IP precedence to ATM CoS mapping IP RSVP to ATM services
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Precedence to VC Mapping VC Bundle
Si Si
VC1 VC2 VC3 VC4
ATM Network
Assign to VC Based on:
Note:
IP Precedence RSVP Policy Routing
WAN QoS is Only as Good as Specified ATM VC Parameters
• VC bundle—multiple VCs for each IP adjacency • Separate VC for each IP CoS • WRED, WFQ, or CBWFQ runs on each VC queue 409 1040_05F9_c2
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© 1999, Cisco Systems, Inc.
IP to ATM Egress QoS Tools IP to ATM CoS Interworking Only One Routing Adjacency per “Bundle” Bundle Appears as One Logical Interface
ATM VC1– VC1– 0/35 0/35 VC2–0/36 VC2–0/36
Data PVC Voice PVC
VC Bundle interface ATM0/0/0.7 point-to-point ip address 10.1.40.1 255.255.255.0 no ip directed-broadcast bundle gene protocol ip 10.1.40.2 broadcast encapsulation aal5snap pvc-bundle 0/35 other pvc-bundle 0/36 precedence 5-7
409 1040_05F9_c2
If High Precedence VC Fails, it Can “Bump” Traffic to a Lower Precedence VC, or Entire Bundle Can be Declared Down
Data PVC All Low Priority Traffic Assigned to this PVC Voice PVC High Priority Traffic Assigned to VC Based on IP Precedence (5–7 (5 7 in This Case)
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Prioritization Campus QoS Needs • Catalyst 6XXX Two queues + two drop thresholds per port
Server Farm
Classification + policing
• Catalyst 8500 Four queues
Campus Backbone
• Catalyst 5XXX 1 queue WRED four drop thresholds
Wiring Closet
Reclassification Campus QoS Need Based on Customer Environment 409 1040_05F9_c2
IP
IP
© 1999, Cisco Systems, Inc.
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Link Efficiency Low-Speed WAN QoS Tools
• Fragmentation and interleave (LFI) • RTP header compression (CRTP) • Voice Activity Detection (VAD)
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Fragmentation and Interleave Only Needed on Slow Links Before
Real-Time MTU
Elastic Traffic MTU 214 ms Serialization Delay for 1500 byte Frame at 56 kbps After
Elastic MTU
Elastic MTU
Real-Time MTU
Elastic MTU
Mechanisms Point-to-Point Links—MLPPP with Fragmentation and Interleave Frame Relay—FRF.12 (Voice and Data Can Use Single PVC) ATM—(Voice and Data Need Separate VC’s on Slow Links) 409 1040_05F9_c2
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© 1999, Cisco Systems, Inc.
Configuring Multilink PPP Fragmentation and Interleave Hub
interface Virtual-Template1 ip unnumbered Loopback0 bandwidth 128 fair-queue 64 256 1000 ppp multilink ppp multilink fragment-delay 10 ppp multilink interleave ! interface Serial0 Desired Max Blocking no ip address Delay in ms encapsulation ppp bandwidth 128 Fragmentation Size a Result of this and “Bandwidth” no fair-queue Statement ppp multilink
Remote
interface Virtual-Template1 ip unnumbered Loopback0 bandwidth 128 fair-queue 64 256 1000 ppp multilink ppp multilink fragment-delay 10 ppp multilink interleave ! interface Serial0 no ip address encapsulation ppp bandwidth 128 no fair-queue ppp multilink
Note: Issues with multiple links in a bundle and CRTP at the same time 409 1040_05F9_c2
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Low Speed Frame Relay FRF.12 Configuration Hub3640#
Remote3640#
interface Serial0/0 no ip address encapsulation frame-relay bandwidth 1300000 frame-relay traffic-shaping ! interface Serial0/0.1 point-to-point ip address 10.1.1.1 255.255.255.0 no ip directed-broadcast bandwidth 1300000 frame-relay class gene
interface Serial0/0 no ip address encapsulation frame-relay bandwidth 56000 frame-relay traffic-shaping ! interface Serial0/0.1 point-to-point ip address 10.1.1.2 255.255.255.0 no ip directed-broadcast bandwidth 56000 frame-relay class gene
map-class frame-relay gene frame-relay fragment 70 no frame-relay adaptive-shaping frame-relay bc 2000 frame-relay mincir 56000 frame-relay fair-queue
map-class frame-relay gene frame-relay fragment 70 no frame-relay adaptive-shaping frame-relay bc 2000 frame-relay mincir 56000 frame-relay fair-queue
Note: Bc set lower than the default of 1/8th the CIR Lower interval better on high speed links with low CIR (can result in quicker credit exhaustion) 409 1040_05F9_c2
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Setting Fragment Size Based on Minimum Desired Blocking Delay 70 70 Byte Byte Frag Frag
56kbps
A
B
If Fragment Gets De-Queued Right Before Voice Packet
C 70 Byte Packet Takes 10 ms to De-Queue at 56 kbps
A
56kbps
20 ms
B
70 70 Byte Byte Frag Frag
C
20 ms + Frag 30 ms total
Note: Blocking delays are always present 409 1040_05F9_c2
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Fragment Size Matrix Assuming 10 ms Blocking Delay per Fragment Link Speed
10 ms Time for 1 Byte at BW
Fragment Size =
Fragment Size
56 56 kbps kbps
70 70 Bytes Bytes
Example: 4 G.729 Calls on 128 kbps Circuit Fragment Blocking Delay = 10 ms (160 bytes)
64 64 kbps kbps
80 80 Bytes Bytes
Q = (Pv*N/C) + LFI
128 128 kbps kbps
160 160 Bytes Bytes
256 256 kbps kbps 512 512 kbps kbps 768 768 kbps kbps
1000 1000 Bytes Bytes
1536 1536 kbs kbs
2000 2000 Bytes Bytes
409 1040_05F9_c2
Q = (480 bits*4/128000) + 10 ms = 25 ms
320 320 Bytes Bytes 640 640 Bytes Bytes
Worst Case Queuing Delay = 25 ms Q = Worst Case Queuing Delay of Voice Packet in ms Pv = Size of a Voice Packet in Bits (at Layer 1) N = Number of Calls C = Is the Link Capacity in bps LFI = Fragment Size Queue Delay in ms
X
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When Is Fragmentation Needed? Frame Size 64 1 128 Bytes Bytes Byte 256 143 us 14364 us 99128 ms 18 ms 18 ms ms Bytes Bytes Bytes
1024 256 512 Bytes Bytes Bytes 1024 144 512 1500 36 36 ms ms 72 ms 72 ms ms 144 ms Bytes Bytes Bytes
1500 Bytes
125 125 us us
88 ms ms
16 16 ms ms
32 32 ms ms
64 64 ms ms
128 ms
187 ms
Link 128 kbps Speed 256 kbps
62.5 62.5 us us
44 ms ms
88 ms ms
16 16 ms ms
32 32 ms ms
64 64 ms ms
93 93 ms ms
31 31 us us
22 ms ms
44 ms ms
88 ms ms
16 16 ms ms
32 32 ms ms
46 46 ms ms
512 kbps
15.5 15.5 us us
56 kbps 64 kbps
768 kbps
9ms 8ms 4ms 2ms
10 10 us us
18ms 16ms 8ms
11 ms ms
4ms
36ms 32ms 16ms
22 ms ms
64ms
32ms
44 ms ms
8ms
640 640 us us 1.28 1.28 ms ms
72ms
16ms
214 214 ms ms
128 ms 187 ms 144ms 214ms
128ms 187ms 64ms
88 ms ms
32ms
93ms 16 16 ms ms
23 23 ms ms
46ms
2.56 15 ms ms 2.56 ms ms 5.12 5.12 ms ms 10.24 10.24 ms ms 15
1ms 2ms 8ms 16ms 23ms 4ms 640 55 us 640 us us 1.28 1536 kbs us 320 2.56 ms ms 5.12 5.12 ms ms 7.5 320 us us 1.28 ms ms 2.56 7.5 ms ms 768kbps 10us 640us 1.28ms 2.56ms 5.12ms 10.24ms 15mss
• Depends on the queuing delay caused by large 1536kbs 640us 1.28ms 2.56ms 5.12ms 5usat a given frames 320us speed—fragmentation generally 7.5ms
not needed above 768 kbps 409 1040_05F9_c2
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RTP Header Compression • Overhead 20 ms @ 8 kbps yields 20 byte payload
Version
IHL
Type of Service
Identification Time to Live
40bytes per packet IP header 20; UDP header 8; RTP header 12
Total Length Flags
Fragment Offset
Protocol
Header Checksum
Source Address Destination Address Options
Padding
Source Port
2X payload!
Destination Port
Length
Header compression 40 Bytes to 2–4 much of the time
V=2 V=2
P P
X X
CC CC M M
Checksum PT PT
Sequence Sequence Number Number
Timestamp Timestamp Synchronization Synchronization Source Source (SSRC) (SSRC) Identifier Identifier
Hop-by-hop on slow links CRTP—compressed real-time protocol
409 1040_05F9_c2
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Traffic Shaping Why? Result: Buffering = Delay or Dropped Packets 128 kbps 256 kbps
Remote Sites
512 kbps
T1 Frame Relay, ATM
768 kbps T1
Central Site
• Central to remote site speed mismatch • Remote to central site over-subscription • Prohibit bursting above committed rate What are you guaranteed above you committed rate? 409 1040_05F9_c2
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Understanding Shaping Parameters Frame Relay Traffic Shaping “Average” Traffic Rate Out of an Interface Challenge—Traffic Still Clocked Out at Line Rate CIR (Committed Information Rate) Average Rate over Time, Typically in Bits per Second
Bc (Committed Burst) Amount Allowed to Transmit in an Interval, in Bits
Be (Excess Burst) Amount Allowed to Transmit Above Bc per Second
Interval Equal Integer of Tme Within 1 sec, Typically in ms. Number of Intervals per Second Depends on Interval Length Bc and the Interval Are Derivatives of Each Other
Bc CIR
Interval = 409 1040_05F9_c2
Example
125 ms =
8000 bits 64 kbps 53
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Example—Traffic Shaping in Action High Volume Data Flow Towards a 128 kbps Line Rate Shaping to 64 kbps Bc CIR
Interval =
125 ms Interval =
8000 bits 64000 bps
Cisco Default Bc=1/8 CIR = 125 ms Interval 0 bits
Bits per Interval of Time at 128 kbps Rate
16000 bits
32000 bits
48000 bits
64000 bits
80000 bits
96000 bits
112000 bits
128,000 bits
Line Rate 128 kbps
Net Result: 8000 X 8 = 64 bkps 62.5 ms
0 ms
125 ms 250 ms 375 ms 500 ms 625 ms
When 8000 bits (Bc) Transmitted Credits Are Exhausted and No More Packet Flow in that Interval. This Happens at the 62.5 ms Point of the Interval.
409 1040_05F9_c2
75 0ms 875 ms 1000 ms
Time —1 Second When a New Interval Begins Bc (8000 bit). Credits Are Restored and Transmission May Resume. Pause in Transmission Is 62.5 ms in the Case.
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Bc setting Considerations for VoIP Set Bc Lower if Line Rate to CIR Ratio Is High Example: T1 Line Rate Shaping to 64 kbps Bc = 8000 8000 Bc 64kbps CIR
Bc = 1000 1000 Bc 64kbps CIR
125ms Interval =
15ms Interval =
T1 can transmit 193,000 bits in 125 ms 0 bits
193000 bits
T1 can transmit 23,000 bits in 15 ms 0 bits
Bits per increment of time at 128kbps
23000 bits
125 ms Interval Traffic Flow
Time
120 120 ms ms
Traffic Flow
5 ms 0 ms 125 ms
At T1 Rate 8000 Bits (Bc) Are Exhausted in 5 ms. Halting Traffic Flow for that PVC for the Rest of that Interval. Even for Voice! 409 1040_05F9_c2
15 ms Interval
120 ms of Potential Delay for Voice Until New Interval Begins and Bc Credits Are Restored
Time
10 10 ms ms
.6 ms 0 ms 15 ms
At T1 Rate 1000 Bits (Bc) Still Are Exhausted in 5 ms. Halting Traffic Flow for that PVC for the Rest of that Interval. Even for Voice!
10 ms of Potential Delay for Voice Until New Interval Begins and Bc Credits Are Restored
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Traffic Shaping Configuration Shaping to 56 kbps with No Bursting FRTS#
GTS#
interface Serial0/0 no ip address encapsulation frame-relay bandwidth 1300000 frame-relay traffic-shaping ! interface Serial0/0.1 point-to-point ip address 10.1.1.1 255.255.255.0 bandwidth 56000 frame-relay class gene
interface Serial0/0 ip address 10.1.1.2 255.255.255.0 bandwidth 512 traffic-shape rate 56000 2000 0
map-class frame-relay gene frame-relay fragment 70 no frame-relay adaptive-shaping frame-relay bc 2000 frame-relay cir 56000 frame-relay mincir 56000 frame-relay fair-queue
Can Work on “Non” Frame Relay Interfaces Anywhere Throttling Needs to Occur
traffic shape rate [average] [interval] [burst]
Frame Relay Traffic Shaping 409 1040_05F9_c2
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Generic Traffic Shaping 56
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Verifying Traffic Shaping Operation HUB3640#sho frame pvc 100 PVC Statistics for interface Serial0/0 (Frame Relay DTE) DLCI = 100, DLCI USAGE = LOCAL, PVC STATUS = STATIC, INTERFACE = Serial0/0.1 input pkts 149427 output pkts 835851 in bytes 9948250 out bytes 1042695469 dropped pkts 622090 in FECN pkts 0 in BECN pkts 0 out FECN pkts 0 out BECN pkts 0 in DE pkts 0 out DE pkts 0 out bcast pkts 1325 out bcast bytes 110227 pvc create time 013442, last time pvc status changed 013145 fragment type end-to-end fragment size 70 cir 56000 bc 2000 be 0 limit 250 interval 35 mincir 56000 byte increment 250 BECN response no pkts 48669 bytes 4146936 pkts delayed 24334 bytes delayed 2072716 shaping active Byte Increment = Bc Amount to be Credited to Bc for Next Upcoming Interval. Value Gets Decreased Upon Receipt of BECN or CLLM Messages. This Is How Router Gets Throttled Back Due to Congestion Indication. 409 1040_05F9_c2
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Cisco IOS Support
• WFQ—11.0
• FRF.12—12.0(4)T
• IP Precedence—11.0
• WRED—12.0
• RSVP—11.2
• DWFQ—12.0(3)T
• MLPPP + Frag—11.3
• IP to ATM QoS—12.0(3)T
• Traffic Shaping—11.2
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Agenda
• VoIP Requirements and Challenges • Router/Switch Egress QoS Study • WAN QoS Design Considerations • Tuning—Audio Level and Echo • Best Practice Recommendations 409 1040_05F9_c2
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WAN QoS Considerations
• High-speed to low circuits • Remote to central site over subscription • Over subscription—carrier • To burst or not to burst? 409 1040_05F9_c2
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Anatomy of a Carrier Customer Premises Equipment
Access Lines
Inter-Node Trunks
“The Cloud/Carrier” Frame Relay, ATM WAN Switch Fabric
Inter-Node Trunk Over Subscription Often 3:1 or Higher 409 1040_05F9_c2
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WAN Queuing and Buffering Router
WAN Switch Access IGX/8400 T1
Ingress
T1 Queue
WAN Switch IGX/8400 Access Inter-Nodal Trunk
Trunk Queue
Packets Arrive at Line Rate Placed in Ingress Queue
Router
56kbps
Trunk Queue
Egress 56 Queuekbps
Packets De-Queue at Line Rate
Packets Leak into Trunk at PIR—(Peak Information Rate) Typically Lowest Access Rate—56 kbps 409 1040_05F9_c2
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Where WAN Congestion and Delay Can Occur Router
WAN Switch Access IGX/8400 T1
Ingress
T1 Queue
T1
Inter-Nodal Trunk
Trunk Queue
Router
56kbps
Trunk Queue
Egress 56 Queuekbps
Ingress Queue
Packets Arrive at Greater than PIR or CIR PIR = Peak Information Rate 409 1040_05F9_c2
WAN Switch IGX/8400 Access
Global Trunk Congestion
Egress Port Congestion VC Over Subscription
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Bursting—What Is Your Guarantee? Options Router
WAN Switch Access IGX/8400 T1
Ingress
T1 Queue
Mark Mark Data Data DE DE (Discard (Discard Eligible) Eligible)
The The Safest Safest
Only Only Drop Drop Data Data Upon Upon Congestion Congestion Data Data Gets Gets Dropped Dropped 1st 1st Compared Compared to to Other Other Subscribers Subscribers
409 1040_05F9_c2
Inter-Nodal Trunk
Trunk Queue
Shape Shape to to CIR CIR— — No No Bursting Bursting
Not Not Popular Popular
WAN Switch IGX/8400 Access
Router
56kbps
Trunk Queue
Egress 56 Queuekbps
Two Two PVC’s PVC’s— —Data Data ++ Voice Voice
Active Active Traffic Traffic Management Management
Voice Voice— —Keep Keep Below Below CIR CIR Data Data— —Allow Allow for for Bursting Bursting
ABR, ABR, FECN/BECN, FECN/BECN, ForeSight ForeSight
Need Need DLCI DLCI Prioritization Prioritization at at WAN WAN Egress Egress
Only Only Invoked Invoked when when congestion/Delays congestion/Delays has has Already Occurred Already Occurred
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Congestion Detection and Feedback Effectiveness Depends on Round Trip Delay Router
WAN Switch Access IGX/8400 T1
Ingress
T1 Queue
WAN Switch IGX/8400 Access Inter-Nodal Trunk
Trunk Queue
Egress 56 Queuekbps
Trunk Queue
ABR/ ABR/ Foresight Foresight
Router
56kbps
ABR/ Foresight
FECN/ BECN
ABR—Available ABR—Available Bit Bit Rate Rate
FECN/BECN FECN/BECN Notification Notification
Foresight/CLLM Foresight/CLLM
Can Can Send Send aa Rate Rate Down Down from from Point Point of of Congestion Congestion
Requires Requires Far Far End End to to Reflect Reflect aa FECN FECN and and Send Send and and BECN BECN Back Back to to Source Source Indicating Indicating aa Rate Rate Down Down
Can Can Send Send aa Rate Rate Down Down from from Point Point of of Congestion Congestion Speeds Speeds up up Rate Rate Down Down Time Time over over FECN/BECN FECN/BECN
Congestion Must Occur to Invoke, Congestion Relief Can be as Long as One Round Trip Time 409 1040_05F9_c2
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FRF.8 ATM/FR Service Interworking From a Frame Relay Perspective ATM ATM Sites Sites Logically Logically Look Look Like Like aa Frame Frame Relay Relay Site Site FRF.8 Service Inter-working Occurs in the Carrier—SAR
ATM Frame Relay
From an ATM Perspective Frame Frame Relay Relay Sites Sites Logically Logically Look Look Like Like an an ATM ATM Site Site
Caution: If FRF.12 needed at remote then its fragment re-assembly must occur before SAR in carrier Two PVC’s required for Interleaving ATM must not interleave cells from different packets 409 1040_05F9_c2
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Agenda
• VoIP Requirements and Challenges • Router/Switch Egress QoS Study • WAN QoS Design Considerations • Tuning—Audio Level and Echo • Best Practice Recommendations 409 1040_05F9_c2
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Audio Level Adjustment/Tuning Sender
Receiver Router
PBX
T1
WAN
0db
PBX -12db
1. 0DB from Tone Generator 2. Set for -3DB “into” network. If input or output adjustment made hang up call and measure again “show call active voice”
409 1040_05F9_c2
56 kbps Router
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3. Set for—12DB at phone. Set output attenuation accordingly “show call active voice”
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Echo—How Does it Happen? Echo Is Due to a Reflection Central Office/ PBX
Receive Direction
2 Wire Local Loop Rx and Tx Superimposed
2w-4w Hybrid
4 Wire Circuit
Transmit Direction
• Impedance mismatch at the 2w-4w hybrid is the most common source of echo • Echo is always present. A function of the echo delay, and the magnitude of the echo 409 1040_05F9_c2
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© 1999, Cisco Systems, Inc.
If “I” Hear Echo, its “Your” Problem Receiver
Talker: Boy, this Echo Is Bad
PBX
Router A
WAN/PSTN
Router B
Echo Echo
Echo Echo
Echo Echo
PSTN
Echo Echo
“Tail Circuit”
“4 Wire Circuit”
“Tail Circuit”
Where 4w to 2w Conversion Takes Place PBX, PSTN, 2w Port on Router
Low Delays Here Can Mask Echo Problems
Where 4w to 2w Conversion Takes Place (PBX, PSTN, 2w Port on Router)
Possible Echo Sources
• ERL (Echo Return Loss) ITU-T G.131 states ERL of a device should be greater than 15 dbmo Echo cancellers typically give 25 db additional echo reduction 409 1040_05F9_c2
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Types of Echo Tail Circuit
“Loud Echo” WAN/PSTN
Router
0DB
PBX
Echo Echo
Echo Echo
-7DB
• ERL should be greater than 15 DB • Typical echo canceller adds about 25 DB of echo reduction • Solution—fix echo source
“Long Echo” 0DB at Time 0
WAN/PSTN
Router
PSTN Echo Echo
Echo Echo
-30DB 100 ms Later
• Echo exceeds coverage range—Cisco echo coverage is 32 ms 409 1040_05F9_c2
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Echo Loudness to Echo Delay Relationship 60 db 50 db 40 db
Irritation Zone ITU-T G.131
30 db 20 db 10 db 0 db 0 ms
409 1040_05F9_c2
Low Delay Masking: Side Tone + Low WAN/Terrestrial Link Delay
50 ms
100 ms
150 ms
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200 ms
250 ms
300 ms
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Echo Troubleshooting Example “Loud Echo” Inject 1000 Hz Philadelphia TX Audio Test Tone Philadelphia at 0DB Cisco AS5300 PBX
Belgium Cisco 3640 PBX
IP Network
4W E+M
Philadelphia#sho call active voice
Belgium#sho call active voice
CoderTypeRate=g729r8 NoiseLevel=0 ACOMLevel=0 OutSignalLevel=-79 InSignalLevel=-3
CoderTypeRate=g729r8 NoiseLevel=0 ACOMLevel=0 OutSignalLevel=-7 InSignalLevel=-14 InfoActivity=2 ERLLevel=7
Note Input Level from Test Set
409 1040_05F9_c2
Level “OUT” of Router Level “IN” from Router
(-7) - (-14) = 7DB ERL >15DB needed Result = Noticeable Echo
Note Output Level and Insufficient ERL
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Solution: Router Performs 4w to 2W Conversion Inject 1000 Hz Philadelphia TX Audio Test Tone Philadelphia at 0DB Cisco AS5300 PBX
Belgium Cisco 3640 PBX
IP Network
FXS
Reading#sho call active voice
Belgium#sho call active voice
CoderTypeRate=g729r8 NoiseLevel=0 ACOMLevel=0 OutSignalLevel=-79 InSignalLevel=-3
CoderTypeRate=g729r8 NoiseLevel=0 ACOMLevel=0 OutSignalLevel=-7 InSignalLevel=-27 InfoActivity=2 ERLLevel=20
Note Output Level and Sufficient ERL
(-7) - (-27) = 20DB ERL ERL >15DB—Good Result—No Noticeable Echo 409 1040_05F9_c2
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Agenda
• VoIP Requirements and Challenges • Router/Switch Egress QoS Study • WAN QoS Design Considerations • Tuning—Audio Level and Echo • Best Practice Recommendations 409 1040_05F9_c2
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Summary: QoS Best Practice Example Headquarters IP
Si
Catalyst 6500
IP
Campus
Cisco 7500
High-Speed WAN Backbone > 2 Mbps
High-Speed Backbone
Regional Office
Point-to-Point 256 kbps
IP
Cisco 2600
Cisco 7200 T1
WAN Provisioning and Design
Cisco 3600
Frame Relay
Low-Speed Central Site
128 kbps
IP
ATM
Branch Office’s Cisco 3600
Low-Speed Remote Sites
IP
Applying Proper Tools in Proper Location 409 1040_05F9_c2
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Low-Speed WAN Frame Relay Example Remote Branch Considerations • Prioritization
Regional Office
IP Prec/RSVP
Cisco 7200
• Link efficiency FRF.12
Central site considerations • Prioritization
VAD (If desired)
T1
CRTP (If desired)
• Traffic shaping
Frame Relay
IP Prec/RSVP
• Link efficiency
Frame Relay traffic shaping 128 kbps
FRF.12 PVC’s to low speed remotes must use FRF.12
Shape to CIR on Voice PVC
Cico 3600
VAD (If desired)
IP
CRTP (If desired)
Branch Office
• Traffic shaping Frame Relay traffic shaping Shape to CIR on Voice PVC 409 1040_05F9_c2
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Low Speed WAN ATM Example Central Site + Remote Branch Considerations (ATM Typically Greater than T1)
Regional Office Cisco 7200
• Prioritization IP-ATM CoS
• Link efficiency
ATM
T1 and above “typically” not needed
• Traffic shaping Cico 3600
Shape to VC parameters
IP
Branch Office 409 1040_05F9_c2
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Low Speed WAN Pt to Pt Example Point-to-Point Considerations
Regional Office
• Prioritization
Cisco 7200
IP Prec/RSVP
• Link efficiency MLPPP with fragmentation and interleave
256 kbps
VAD (if desired) CRTP (if desired)
Cico 3600 IP
• Traffic shaping
Branch Office 409 1040_05F9_c2
N/A
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High Speed WAN Backbone Frame Relay/ATM Example > 2 MB Cisco 7500
Cisco 7200 High-Speed WAN
Headquarters
IP
Regional Office
ATM
Frame Relay
Point to Point
• Prioritization
• Prioritization
• Prioritization
IP-ATM CoS
IP Prec/RSVP
IP Prec/RSVP
• Link efficiency
• Link efficiency
• Link efficiency
N/A
FRF.12 if remote low-speed
• Traffic shaping Shape to VC parameters
• Traffic shaping Frame Relay traffic shaping
N/A
• Traffic shaping N/A
Shape to CIR
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WAN Provisioning/ Design Considerations 128 kbps 256 kbps
Remote Sites
512 kbps
T1 Frame Relay, ATM
768 kbps T1
Central Site
Central to Remote Speed Mismatch Traffic Shaping—Prevents Delay or Loss in WAN—A A Must Remote to Central Over Subscription—Do Do Not Add additional T1’s at Central Site, or Traffic Shaping—from Remotes at Reduced Rate (< Line Rate) 409 1040_05F9_c2
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Bursting Considerations “Guidelines” • Single PVC—limit bursting to committed rate (CIR) The safest—you are guaranteed what you pay for
• Single PVC—mark data discard eligible Your data gets dropped first upon network congestion
• Single PVC—utilize BECN’s, foresight or ABR Only invoked when congestion has already occurred Round trip delays—Congestion indication must get back to source
• Dual PVCs—one for voice and one for data One for data (may burst), one for voice (keep below CIR) Must Perform PVC prioritization in frame cloud (Cisco WAN gear does) Fragmentation rules still apply for data PVC
Moral of the Story—“Know Your Carrier” 409 1040_05F9_c2
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In Conclusion
• Prioritization • Link efficiency mechanisms • Traffic shape • Know your WAN!
409 1040_05F9_c2
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Please Complete Your Evaluation Form Session 409
409 1040_05F9_c2
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