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Deploying Voice Over ATM or FR Networks Session 403
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403 0916_04F9_c3
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© 1999, Cisco Systems, Inc.
Deploying Voice Over ATM or FR Networks Session 403
403 0916_04F9_c3
© 1999, Cisco Systems, Inc.
Copyright © 1998, Cisco Systems, Inc. All rights reserved. Printed in USA. Presentation_ID.scr
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Objectives • Understand the voice quality factors in an integrated data/voice network • Describe integrated data/voice network transport mechanisms • Understand the engineering requirements in data/voice networks to meet voice quality requirements • Know where to look for the “Gremlins” in integrated data/voice networks 403 0916_04F9_c3
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© 1999, Cisco Systems, Inc.
Agenda
• Establishing Target Parameters for Quality • Network Technology Trade-Offs • Voice Over Frame Relay Network Design • Voice Over ATM Network Design 403 0916_04F9_c3
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Establishing Target Parameters
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Voice Quality Factors
• Mean opinion score • Coding • Compression • Delay
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3
Mean Opinion Score Source
Channel Simulation
Impairment Codec “X”
1 2 3 4 5
“Nowadays—a Chicken Leg Is a Rare Dish” Rating
Speech Quality
Level of Distortion
5
Excellent
Imperceptible
4
Good
Just Perceptible—Not Annoying
3
Fair
Perceptible—Slightly Annoying
2
Poor
Annoying but Not Objectionable
1
Unsatisfactory
Very Annoying—Objectionable
1 2 3 4 5
MOS of 4.2 = Toll Quality 403 0916_04F9_c3
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© 1999, Cisco Systems, Inc.
Voice Quality Guidelines MOS Score
Delay (Msec)
Bit Rate (Kbps)
PCM (G.711)
4.4
0.75
64
ADPCM (G.726)
4.1
1
32–24–16
3.65
3–5
16
CS-ACELP (G.729)
3.9
15
8
CS-ACELP (G.729a)
3.65
15
8
3.8
30
6.3–5.3
Compression Method
LD-CELP (G.728)
MPMLQ or ACELP (G.723.1)
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Voice Delay Guidelines One Way Delay (Msec)
Description
0– 150
Acceptable for Most User Applications
150– 150 – 400
Acceptable Provided that Administrations Are Aware of the Transmission Time Impact On the Transmission Quality of User Applications
400 +
Unacceptable for General Network Planning Purposes—However—It Is Recognized that in Some Exceptional Cases this Limit Will Be Exceeded
ITU’s G.114 Recommendation 403 0916_04F9_c3
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© 1999, Cisco Systems, Inc.
Fixed Delay Components Propagation Delay Serialization Delay— Buffer to Serial Link Processing Delay
Munich
1MS 30MS Frankfurt Los Angeles
• Propagation—six microseconds per kilometer • Serialization • Processing Coding/compression/decompression Packetization 403 0916_04F9_c3
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Variable Delay Components Queuing Delay
Queuing Delay
Queuing Delay
Packets
Packets
Packets
Dejitter Delay
• Dejitter buffers • Queuing delay • Variable packet sizes 403 0916_04F9_c3
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© 1999, Cisco Systems, Inc.
Calculate Delay Budget Coder Queuing Delay Delay 30 ms 20 ms
Example
Dejitter Buffer 40 ms
40 ms Network Delay Serialization Delay 3 ms Fixed Delay Propagation Delay Coder Delay G.729 (15 Msec Per 10 Bytes) Packetization Delay—Included in Coder Delay Queuing Delay 64 Kbps Trunk Serialization Delay 64 Kbps Trunk Network Delay (Public Frame Relay Network) Dejitter Buffer Total 403 0916_04F9_c3
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Variable Delay
30 Msec 20 Msec 3 Msec 40 Msec 40 Msec 113 Msec 20 Msec 12
6
Delay—How Much Is Too Much? Cumulative Transmission Path Delay CB Zone Satellite Quality High Quality 0
100
Fax Relay, Broadcast 200
300
400
500
600
700
800
Time (msec) Delay Target
ITU’s G.114 Recommendation = 0 – 150msec 1-way delay
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© 1999, Cisco Systems, Inc.
Target Parameters
• MOS—Business/toll quality • Coding—G.729, G.711 • Compression—8k, 64k • Delay—Calculate network
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Network Technology Trade-Offs
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Technology Trade-Offs
• Frame vs cell • Mesh vs star • Transport vs translate
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TDM vs Frame vs Cell TDM
Frame/Packet
Cell
• TDM—Constant delay, wasted bandwidth • Frame/packet—Variable delay, highly efficient • Cell—Improved delay, less efficient 403 0916_04F9_c3
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© 1999, Cisco Systems, Inc.
Packet Efficiency
Frame/Packet
OH
Payload
OH
4 Bytes
1488 Bytes
4 Bytes
Payload = 1488 OH Cell 5 Bytes
Overhead = 8
Efficiency = 99.5%
Payload 48 Bytes
Payload = 48
Overhead = 5
Efficiency = 89.6%
• Small vs large packet sizes • Fixed vs variable sized packets 403 0916_04F9_c3
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Voice Payload Options
10 ms of voice
10 ms of voice
10 ms of voice
Original Voice Information
• Small Payload crc
Low Delay High Overhead High PPS High CPU Load
10 ms of voice crc
3 Small Frames
hdr
10 ms of voice
hdr
crc 10 ms of voice
hdr
• Large Payload crc
High Delay Low Overhead Low PPS Low CPU Load 403 0916_04F9_c3
10 ms of voice
10 ms of voice
10 ms of voice
hdr
1 Large Frame
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© 1999, Cisco Systems, Inc.
Network Design Options Full Mesh of PVCs
Voice PVCs Go to One Central Site
Site D
Site C
Site D
Site C
Site A
Site B
Site A
Site B
• Separate voice and data PVCs—Maximizes quality of service • Combine voice and data on one PVC—Minimizes recurring costs • Or use some combination 403 0916_04F9_c3
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Transport vs Translate Model Transport
Translate
PBX2
PBX1
PBX2
PBX4
PBX1
PBX3
PBX3
PBX4
Network Understands PBX Signaling
• ATM • Frame Relay • Router-based backbone—such as TCP/IP • Or a mixture of the above 403 0916_04F9_c3
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© 1999, Cisco Systems, Inc.
Design Trade-Offs
• TDM, frame, cell-efficiency, delay, cost • Mesh vs star—Performance vs cost • Transport vs translate—Signaling
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11
Voice Over Frame Relay
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Voice Over Frame Relay Network Design
• A brief tour of FRF.11 • Why FRF.12? • Network design considerations • Bandwidth calculations
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12
Data Over Frame Relay Network VoFR Service User
Data User
Data User
FRF.3.1 Multiprotocol Encapsulation
FRF.3.1 Multiprotocol Encapsulation
Frame Relay Data Link Connection 17
Frame Relay Data Link Connection N
VoFR Service SubSubSubChannel Channel Channel 1 2 3 (Voice) (Voice) (Data)
2500
Frame Relay Carrier Network
7200
SubChannel N
Voice/Data Sub-Channel Multiplexing
Central Site
Frame Relay Data Link Connection 16
7200
7200
Frame Relay Physical Interface
High-Speed Access Port at Central Sites (T1/E1)
2500
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2500 Branch Sites
2500
2500
Low-Speed Access Port at Branch Sites (64Kbps CIR)
25
© 1999, Cisco Systems, Inc.
Data/Voice Over Frame Relay VoFR Service User
Data User
Data User
FRF.3.1 Multiprotocol Encapsulation
FRF.3.1 Multiprotocol Encapsulation
Frame Relay Data Link Connection 17
Frame Relay Data Link Connection N
VoFR Service
3600
2600
V 7200
Frame Relay Carrier Network V
SubSubSubChannel Channel Channel 1 2 3 (Voice) (Voice) (Data)
Voice/Data Sub-Channel Multiplexing
3600 V
7200
PVC Carrying Voice
Frame Relay Data Link Connection 16
7200 Central Site
Frame Relay PVC (<64K CIR)
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2500
2500 Branch Sites
3600 V
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Frame Relay Physical Interface
High-Speed Access Port at Central Sites (T1/E1)
FRF.11/12 Frame Relay PVC
2600 V
SubChannel N
2500
Low-Speed Access Port at Branch Sites (64Kbps CIR)
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13
VoFR Multiplexing Model VoFR Service User
Data User
Data User
FRF.3.1 Multiprotocol Encapsulation
FRF.3.1 Multiprotocol Encapsulation
Frame Relay Data Link Connection 17
Frame Relay Data Link Connection N
VoFR Service
SubChannel 1 (Voice)
SubChannel 2 (Voice)
SubChannel 3 (Data)
SubChannel N
Voice/Data Sub-Channel Multiplexing Frame Relay Data Link Connection 16
Frame Relay Physical Interface Source: Frame Relay Forum
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FRF.11 Frame Format FLAG Frame Relay Header FRF.11 Sub-Frame Header Payload FCS FLAG 403 0916_04F9_c3
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Voice and Data Encapsulation
Frame Relay Frame
Sub Frame
Sub Frame
Sub Frame
Sub Frame
• Multi frames transport
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Multiple Sub-Channel Payloads in an FRF.11 Frame Voice Payload
1
Voice Payload
Voice Payload
2
Sub-Frame 1
DLCI
Voice Payload
Voice Payload Sub-Frame 2
Information Field
3
Data Payload
Voice Payload Sub-Frame 3
CRC
Frame
4
Data Payload Sub-Frame 1
DLCI
Information Field
CRC
Frame
Source: Frame Relay Forum
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FRF.11 Concept
• Extension of frame relay application support for compressed voice • Multiplexing of up to 255 sub-channels • Support of multiple payloads • Support of data sub-channel 403 0916_04F9_c3
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FRF.11 Equipment Classes
• Class 1 equipment Transmission equipment in high bandwidth environments Requires G.727 EADPCM compliance
• Class 2 equipment Optimizes performance over low bandwidth trunks 403 0916_04F9_c3
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VoFR Services VoFR Service User Voice
Data FAX
Faults Dialed FAX Digits
Primary Payloads
Bits (CAS Signaling)
Silence Information
Signaled Payloads
VoFR Service Service Data Units
Frame Relay Service Source: Frame Relay Forum 403 0916_04F9_c3
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www.cisco.com
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FRF.11 Class 2 Services • Dialed digits transfer syntax (Annex A) • Signaling bit transfer syntax (Annex B) • Data transfer syntax (Annex C) • FAX relay transfer syntax (Annex D) • CS-ACELP transfer syntax (Annex E) • PCM/ADPCM transfer syntax (Annex F) • G.727 D/E EADPCM voice transfer syntax (Annex G) • G.728 LD-CELP transfer syntax (Annex H) • G.723.1 MP-MLQ dual rate speech coder (Annex I) Note: Cisco Does Not Currently Support Annex G
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FRF.11 Annex E, F, G, H, I: Voice Transfer Syntax Voice PKT
PBX
3600
3600
V
Compressed Speech
PBX
V
Annex E—I Voice Transfer Syntax
• Codec syntax specified per annex—ie; Annex E— CS-ACELP G.729 • Annex F—Generic PCM/ADPCM G.711, G.726, G.727 • Annex H—LD-CELP G.728, Annex I—G.723.1 • Sequence number and coding type are optional 403 0916_04F9_c3
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FRF.11 Annex C Data Transfer Syntax PBX
Voice 3600 PKT
Data Voice PKT PKT
Data PKT
V
3600
PBX
V
Annex C—Data Transfer Syntax
• FRF.11 sub-frame headers allow voice and data sub-channels within a PVC • Each packet contains a whole or a fragment of an original data frame • Original frames smaller than the fragmentation threshold are encapsulated with both the B and E bits set 403 0916_04F9_c3
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FRF.11 Annex A Dialed Digit Transfer Syntax Each Packet Contains 20 Msec of Digits with Time Relationship
Voice 3600 PKT
PBX
DTMF Packets are Interleaved with Voice Packets On the Same PVC
Data Voice PKT PKT
Data PKT
V
3600
Speech/Noise Signal with DTMF Digits Overlaid
PBX
V
Sequence Number and Packet Interval (20 Msec) Maintains Inter-Packet Timing Relationship
Speech/Noise Signal is Reconstructed— but Interrupted for DTMF Digit Generation with Correct Durations and Levels
• Supports DTMF transmission for high compression Codecs • Originating VFRAD detects DTMF and codes; destination VFRAD reproduces DTMF • When there has been no DTMF activity for 60 msec, no more Annex A frames are generated until the next DTMF digit is detected 403 0916_04F9_c3
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© 1999, Cisco Systems, Inc.
FRF.11 Interoperability
PBX
Voice 3600 PKT
Data Voice PKT PKT
V
Data PKT
Foreign FRAD PBX V
• In theory FRADs from different vendors can interoperate with FRF.11 • Your mileage may vary 403 0916_04F9_c3
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Why FRF.12? PBX
1500 Byte Packet
Frag
Frag
Frag
1500 Byte Packet
V PBX Cisco 3600
V
Cisco 3600
VoIP with FRF.12 On Frame Relay
Larger Branch Office
Headquarters
• Multiple PVCs—some with FRF3.1 data on same physical interface • Can be used with VoIP • Fragments and interleaves large data frames with voice packets 403 0916_04F9_c3
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© 1999, Cisco Systems, Inc.
Comparison of FRF.11/12 Fragmentation Schemes FRF.12 UNI
VFRAD
Frame Relay Network
V
VFRAD
V
UNI Frame Format Fragmentation Header Frame Relay Header Payload (Fragment)
FRF.12 UNI Fragments Across the UNI Only, Frames are Reassembled at Ingress to Network, and Pass Across the Network Intact (Cisco Does Not Support UNI Fragmentation)
FCS
E-E Frame Format
FRF.12 End-End
VFRAD
Frame Relay Network
V
VFRAD V
Frame Relay Header Fragmentation Header Payload (Fragment) FCS
FRF.12 End-to-End Frames Traverse the Network as Fragments and Are Reassembled at the Terminating VFRAD (DTE)
FRF.11 Annex C
VFRAD
Frame Relay Network
V
FRF.11 Annex C Format VFRAD
V
Frame Relay Header Subframe Header Fragmentation Header Payload (Fragment) FCS
FRF.11 Annex C Frames Traverse the Network as Fragments and Are Reassembled at the Terminating Vfrad (Dte); However, FRF.11 Annex C Allows for a Subframe Header Which Allows Many Different Channels of Different Types to Be Multiplexed Onto a Single Network PVC 403 0916_04F9_c3
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Fragmentation Frame Size Matrix Real Time Packet Interval
Link Speed
10ms
20ms
30ms
40ms
50ms
56kbps
70 Bytes
140 Bytes
210 Bytes
280 Bytes
350 Bytes
700 Bytes
1400 Bytes
64kbps
80 Bytes
160 Bytes
240 Bytes
320 Bytes
400 Bytes
800 Bytes
1600 Bytes
128kbps
160 Bytes
320 Bytes
480 Bytes
640 Bytes
800 Bytes
1600 Bytes
X
3200 Bytes
256kbps
320 Bytes
640 Bytes
960 Bytes
1280 Bytes
1600 Bytes
3200 Bytes
512kbps
640 Bytes
1280 Bytes
1920 Bytes
X
2560 Bytes
X
3200 Bytes
X X
6400 Bytes
6400 Bytes
12800 Bytes
768kbps
1000 Bytes
2000 Bytes
3000 Bytes
4000 Bytes
5000 Bytes
10000 Bytes
20000 Bytes
1536kbs
2000 Bytes
X
X 4000 X Bytes
X 6000 X Bytes
X 8000 X Bytes
X X
X 10000 X Bytes
100ms 200ms
X 20000 X Bytes
X X X X
X X
40000 Bytes
X —Fragmentation not an issue due to BW + Interval Combination 403 0916_04F9_c3
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© 1999, Cisco Systems, Inc.
Egress Blocking/Fragmentation Public Frame Relay Potential Egress Blocking
Site C FRF.12 Prevents Potential Blocking Point
Site D
FRF.12 Applied Here Even though No Voice
Site A
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Site B
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VoFR Network Design Considerations Network Queue Increasing Delay
Router Data + Voice V
BECN = 1
V
V
D
D
D
D
D
D
BECN Threshold Discard Eligible
• If network queues are filling… Voice may experience excessive delay Voice may be discarded Router throttles back on BECN—but it’s too late— queues are full and voice packets are dropped
• Voice quality may be negatively affected 403 0916_04F9_c3
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© 1999, Cisco Systems, Inc.
VoFR Design Considerations— Queuing (WFQ) Flows Share Bandwidth Equally Configurable Queues Two 100-Byte Voice Packets
11
11
Therefore = “Fair”
22 11
22
DeDequeue queue
11
Two 100-Byte Packets Transmitted for Every One 200 Byte Packet
2
11
11
Classify One 200-Byte Data Packet
Interface Buffer Resources Flow Flow Classification/Sorting Classification/Sorting •• Source Source and and destination destination address address •• Protocol Protocol •• Session Session identifier identifier (port/socket) (port/socket) 403 0916_04F9_c3
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Transmit Scheduling
Weighted Weighted Fair Fair Scheduling Scheduling •• Requested Requested QoS QoS (IP (IP Precedence, Precedence, RSVP) RSVP) •• Frame Frame Relay Relay FECN, FECN, BECN, BECN, DE DE •• Flow Flow throughput throughput (Weighted-Fair) (Weighted-Fair) 44
22
Frame Relay Traffic Shaping Port Speed Rate CIR
=Bc>Bc
Time
• Traffic shaping provides voice and data quality of service • Allows better utilization of CIR by shaping data 403 0916_04F9_c3
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© 1999, Cisco Systems, Inc.
Single PVC Design Considerations Line Rate
Router Interface
Line Rate 128k
CIR: 80k Min CIR: 58k
0k
CIR 64k
Carrier Interface
0k
• Goal is best voice quality, NOT data volume • Contract CIR to meet calculated requirements • Shape conservatively • Have carrier set BECN threshold to a smaller setting • Set traffic shaping parameters for finest granularity 403 0916_04F9_c3
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Multiple PVC Design Considerations Network Queue
Router
Discard Eligible BECN Threshold Increasing Delay
BECN = 1 Data
D
D
D
D
D
Voice
D
D
D
D
V
V
V
V
• Separate queues maintain voice quality More deterministic—voice won’t burst
• Priority PVCs from Carrier for Voice 403 0916_04F9_c3
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Calculating VoFR Bandwidth • Assumptions • G.729 Codec at 8Kbps • 50 PPS (using 2–10ms samples) • 2 bytes of DLCI header • 2 bytes of FRF.11 header • 1 byte of sequence number • 2 byte CRC 403 0916_04F9_c3
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Calculating VoFR Bandwidth • Voice payload calculation 20 Msec voice sample * 8 Kbps (for G.729)/ 8 bits/byte = 20 bytes Note: to derive the payload for G.711, substitute 64 kbps = 160 bytes
• Packet size calculations 20 byte payload + 7 byte Header = 27 bytes (Header = DLCI/FRF.11/seqn/CRC)
• Bandwidth calculations 27 b/voice packet * 8 bits/byte * 50 pps = 10.8 Kbps per call 403 0916_04F9_c3
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© 1999, Cisco Systems, Inc.
CIR Critical Factors • PVC design Full mesh vs star Shared vs separate PVCs for voice and data
• Potential concurrent calls Bandwidth per call Switched through calls
• Pre-existing data environment Utilization prior to adding voice 403 0916_04F9_c3
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VoFR Summary • FRF.11 standards-based voice and function syntax • FRF.12 standards-based fragmentation for data, mitigates delay and delay variation • Proper PVC design for network requirements • Balance voice quality, delay, bandwidth, CIR 403 0916_04F9_c3
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VoFR Summary • Avoid Tandem (multiple) conversions • Calculate delay for chosen design • Check for Egress blocking • Calculate CIR for total potential voice and/or data per PVC • Configure queuing and traffic shaping 403 0916_04F9_c3
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References • [1] FRF.3.1, R. Cherukuri (ed), Multiprotocol Encapsulation Implementation Agreement, June 22–1995 • [2] FRF.9, D. Cantwell (ed), Data Compression Over Frame Relay Implementation Agreement, January 22–1996 • [3] FRF.11.1 K. Rehbehn, R. Kocen, T. Hatala (eds), Voice Over Frame Relay Implementation Agreement, December 1998 • [4] FRF.12, A. Malis (ed), Frame Relay Fragmentation Implementation Agreement, 1997 • [5] ITU Recommendation Q.922, ISDN Data Link Layer Specification for Frame Mode Bearer Services, 1992 403 0916_04F9_c3
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Web Sites
• Cisco http://www.cisco.com—search on VoFR
• Frame Relay Forum http://www.frforum.com/
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Voice Over ATM
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Voice Over ATM Network Design • ATM reference model • ATM service categories • Circuit emulation • Packetized voice • Network designs • Bandwidth calculations 403 0916_04F9_c3
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VoATM Signalling
Non-ATM Network PVC for Non-ATM Signaling
ATM Network
Non-ATM Network
N x 64 Kbps PVC for Voice
PVC for ATM Signaling
ATM Network
PVC for ATM Signaling
Non-ATM Network
Non-ATM Network
CBR SVCs for Voice
Network Interworking (Transport)
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Network Interworking (Translate) Service Interworking (Translate) 57
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ATM Service Criteria Contract
Contract
ATM Network
• Contract Traffic descriptors Peak cell rate Sustainable cell rate Maximum burst size Minimum cell rate Quality of service Delay Cell loss 403 0916_04F9_c3
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ATM Protocol Model Data Class
Class A
Class B
Class C
Class D
Service
TDM Channel (DS-1—DS-3)
Variable Rate (Compressed Video)
Blocked Data (Frame Relay)
Data Service (SMDS)
Bit Rate
Constant
Variable
End-to-End
Timing Adaption Layer
AAL-1
AAL-2
Convergence Sublayer
1 Byte
User Payload
47 Bytes
Variable AAL-5
AAL-3/4
1 -3 Bytes
0 Bytes
4 Bytes
45-47 Bytes
48 Bytes
44 Bytes
ATM Layer
5 Bytes ATM Physical Interface
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ATM Cell
48 Byte Payload 53 Bytes
ATM Adaptation Layer (AAL) ATM Layer 5 Byte Header
Physical Layer
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ATM Reference Model ATM Adaptation Layer (AAL) ATM Adaptation Layer (AAL)
• Two sublayers Convergence Sublayer (CS)
ATM Layer
Segmentation and Reassembly (SAR)
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Physical Layer
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AAL Cell Tax AAL-1 Cell Tax
AAL-2 Cell Tax
5 Byte Header
5 Byte Header 1 Byte
47 Byte Payload
1–47 Byte Payload
AAL-3/4 Cell Tax
AAL-5 Cell Tax
5 Byte Header
5 Byte Header
44 Byte Payload
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4 Bytes
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1–48 Bytes
No Tax
48 Byte Payload
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ATM Adaptation Layer—AAL ATM Adaptation Layer (AAL)
AAL PBX CS
ATM Layer
S A R
Physical Layer
• AAL = CS + SAR • CS—cell tax • SAR—cell <-> packet 403 0916_04F9_c3
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ATM Classes of Service • Service criteria Traffic descriptors QoS parameters
• Service categories Constant Bit Rate (CBR) Variable Bit Rate (VBR) Unspecified Bit Rate (UBR) Available Bit Rate (ABR) 403 0916_04F9_c3
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ATM Service Criteria Traffic Parameters • Peak Cell Rate—PCR—Maximum data rate a connection can handle without losing data • Sustainable Cell Rate—SCR—Average ATM cell throughput the application is permitted • Maximum Burst Size—MBS—Size of the maximum burst of contiguous cells that can be transmitted • Minimum Cell Rate—MCR—Rate of an application’s ability to handle latency 403 0916_04F9_c3
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ATM Service Criteria QoS Parameters • Maximum Cell Transfer Delay—MCTD how long the network can take to transmit a cell from one endpoint to another • Cell Delay Variation Tolerance—CDVT line distortion caused by change in interarrival times between cells aka jitter
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ATM Service Criteria QoS Parameters • Cell Loss Ratio—CLR acceptable percentage of cells that the network can discard due to congestion
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ATM Classes of Service • Service criteria Traffic descriptors QoS parameters
• Service categories Constant Bit Rate (CBR) Variable Bit Rate (VBR) Unspecified Bit Rate (UBR) Available Bit Rate (ABR) 403 0916_04F9_c3
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ATM Service Categories Constant Bit Rate (CBR) Application Real Time Voice and Video
Traffic Descriptor
QoS Tolerance
PCR
Low
High
Peak Cell Rate Cell Loss Cell Delay 403 0916_04F9_c3
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ATM Service Categories Variable Bit Rate (VBR-RT/VBR-NRT) Application Packetized Voice/Video—SNA
Traffic Descriptor
QoS Tolerance
PCR Peak Cell Rate
SCR
Low
High
Sustainable Cell Rate
MBS Maximum Burst Size 403 0916_04F9_c3
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Cell Loss Cell Delay
Cell Delay (NRT) 70
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ATM Service Categories Available Bit Rate (ABR) Application LAN Interconnect for Data
Traffic Descriptor
QoS Tolerance
PCR
Low
Peak Cell Rate
High
MCR Minimum Cell Rate
Cell Loss
Cell Delay
Also Uses Congestion Feedback Mechanisms 403 0916_04F9_c3
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ATM Service Categories Unspecified Bit Rate (UBR) Application Data Transfer
Traffic Descriptor
QoS Tolerance
No Guarantees Send and Pray
Low
High
Cell Delay Cell Loss 403 0916_04F9_c3
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Characteristics of ATM Voice Data Cells
Video
• Uses small—fixed-sized cells • Connection-oriented • Supports multiple service types • Applicable to LAN and WAN 403 0916_04F9_c3
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CES Reference Model CBR Service Interface
ATM Network
PBX
PBX
CBR Equipment
CBR Equipment ATM Access Interface
ATM CES Interworking Function
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ATM CES Interworking Function
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ATM Voice Transport Choices ATM Cell 47 Byte Payload
ATM Cell 47 Byte Payload
• Unstructured circuit emulation service • Entire payload filled with one voice channel • Or a continuous stream of bytes from an E1 circuit is placed into cells
• Structured circuit emulation service • Entire payload filled with many voice channels • DS0 structure information is maintained
Note: AAL1 Uses One Byte for Overhead
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CES Voice Network Leased T3/OC3 Lines or ATM Carrier 7200 PBX
PBX
Large Location (PBX with T1 Trunks)
7200
Large Location
Application
Advantages
Provides ATM Standard T1 CES (Emulates Up to 4 T1’s) Large Sites: T3 Trunks Where Consolidating Traffic On an ATM Backbone Is Important Usually Campus/MAN Applications
Consolidates Voice/Data On Backbone Where Voice Compression Is Not Important Eliminates Need for a Separate ATM Mux
KEY
Small Location 403 0916_04F9_c3
7200
PBX
Large Location
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Structured vs Unstructured CES Structured
Unstructured
Nx64
DS1
DS1
ATM Network
DS1
ATM Network DS1
Nx64
• Intended to emulate pointto-point fractional DS1 or E1 circuit • Allows Nx64 Kbps independent emulated circuits to share one DS1 • Can be configured to minimize ATM bandwidth 403 0916_04F9_c3
• Intended to emulate point-to-point DS1 or E1 circuit • Allows one 1.54 or 2.04 Mbps emulated circuit per DS1 • Can be used with equipment with non-standard framing • Allows simple configuration of service 77
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Data/Voice Over ATM (AAL5)
V
Public ATM Network
V V Central Site 403 0916_04F9_c3
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Inverse Multiplexing (IMA)
V
Public ATM Network
V
V
Central Site
Multiple T1 or E1 Connections
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• Uses AAL5; 48 bytes for data • Binds multiple PVCs to a single logical interface • Prioritizes voice cells over data cells 79
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ATM AAL5 Voice and Data Cells
Data
Data Voice PKT
Data PKT
Voice PKT
V
PBX Voice
• • • • 403 0916_04F9_c3
Data PKT V
PBX Voice
AAL 5 does not require convergence sub-layer 48 Byte payload available for voice/data Voice payload = voice sample + padding = 48 bytes 5 byte ATM header
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ATM AAL5 Voice Cells 53 Bytes
28 Byte Padding
20 Byte Voice Payload
ATM Layer 5 Byte Header
48 Bytes
• G.729 compression with 20 ms voice sample • No AAL5 CS “cell tax” • 28 Bytes “overhead” due to padding 403 0916_04F9_c3
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VoATM Bandwidth
• Voice payload calculation 20 msec voice sample * 8 Kbps (for G.729)/8 bits/byte = 20 bytes Note: to derive the payload for G.711, substitute 64 Kbps = 160 bytes
• Packet size calculations 20 byte payload + 28 byte pad +5 byte header = 53 bytes
• Bandwidth calculations 53 b/voice packet * 8 bits/byte * 50 pps = 21.2 Kbps per call
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Priority Queuing ATM Node VCQ PVC VCQ
VCQ VCQ VCQ
PBX
High Pri Queue
VCQ
Control ID Manager
Low Pri Queue
VCQ VCQ VCQ
PVC VCQ
PVC VCQ
Quality of Service (QoS) Extends Across Entire Network 403 0916_04F9_c3
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Regional Office—ATM Over T1/E1 Regional Office
Headquarters T1/E1 ATM Access MC3810
MC3810
Service Provider
T1/E1 Digital PBX
• • • • • 403 0916_04F9_c3
PSTN
ISP
LAN data Internet connection Voice traffic Video application C.O. circuit via CES (future) © 1999, Cisco Systems, Inc.
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VC1—512k VBRnrt, LAN Data VC2—256k VBRrt , 24 Voice Calls VC3—768k CBR , Video VC4—VC8 80k CBR, Voice Circuits
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Frame Relay/ATM Interworking Regional Office
Headquarters
256k Cisco Frame Relay MC3810
T1/E1 ATM
Cisco MC3810
Service Provider
T1/E1 Digital PBX
PSTN
ISP
• Network interworking FRF.5 Frame Relay encapsulation
• Service interworking compatible FRF.8 Carrier compatible 403 0916_04F9_c3
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VoATM—Summary • ATM reference model • Fixed size cells—Delay • Service category—CBR, VBR, ABR • Service criteria for QoS, SCR, CDVT • Chose service for requirements— Circuit emulation (AAL1) voice over AAL5 • Combined networks 403 0916_04F9_c3
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References ATM Forum af-phy-0016.000
DS1 Physical Layer Specification
ATM Forum af-phy-0064.000
E-1 Physical Layer Specification
ATM Forum af-saa-0032.000
Circuit Emulation
ATM Forum af-uni-0010.002
UNI Signaling 3.1
IETF RFC1483
Multiprotocol Over ATM
IETF RFC1577
IP Over ATM
IETF RFC1695
AToM MIB
ANSI T1.630—ITU T1.630 ITU I.363—I.363. I.363 I.363.
ATM AAL 1 (Constant Bit Rate)
ANSI T1.635—ITU T1.635 ITU I.363.5
ATM AAL 5 (Variable Bit Rate)
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Web Sites
• Cisco http://www.cisco.com
• ATM Forum http://www.atmforum.com/
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Please Complete Your Evaluation Form Session 403
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