Advanced Voice Over Ip Tuning And Troubleshooting

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© 1999, Cisco Systems, Inc.

Advanced VoIP Tuning and Troubleshooting Session 409

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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

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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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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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“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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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

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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

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Propagation Propagation Delay—6us Delay—6us per per Km Km Serialization Serialization Delay Delay

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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

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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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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

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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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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)

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(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

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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

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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

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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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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

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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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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

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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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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

55

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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

63

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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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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

73

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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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