Dr Fred Zellner fzellner@uh.edu http://www.uh.edu/~fzellner University of Houston Introduction to IP Telephony Datacom II Lecture 13 Dr Fred Zellner fzellner@uh.edu.

Dr Fred Zellner fzellner@uh.edu http://www.uh.edu/~fzellner
University of Houston Introduction to IP Telephony Datacom II Lecture 13 Dr Fred Zellner

Digital Speech Interpolation (DSI)
Voice Activity Detection (VAD) Removal of voice silence Examines voice for power, change of power, frequency and change of frequency All factors must indicate voice “fits into the window” before cells are constructed Automatically disabled for fax/modem Very effective in real-time bandwidth efficiencies VAD removes ~ 60% of cells, renders a full-duplex conversation half-duplex as far as the network is concerned All unused bandwidth is made available to other bursty applications 11/30/2018 Datacom II Spring 2002

Voice Activity Detection
- 31 dbm B/W Saved Voice Activity (Power Level) Hang Timer No Voice Traffic Sent SID Buffer SID - 54 dbm Pink Noise Voice “Spurt” Silence Voice “Spurt” Time 11/30/2018 Datacom II Spring 2002

Bandwidth Requirements
Voice Band Traffic Encoding/ Compression Result Bit Rate G.711 PCM A-Law/µ-Law 64 kbps (DS0) G.726 ADPCM 16, 24, 32, 40 kbps G.729 CS-ACELP 8 kbps G.728 LD-CELP 16 kbps 6.3/5.3 kbps Variable G CELP 11/30/2018 Datacom II Spring 2002

Agenda Basic Analog Telephony Basic Digital Telephony
Voice Coding and Compression Techniques Voice Transport and Delay Supplemental Slides: Digital Voice Signaling Techniques 11/30/2018 Datacom II Spring 2002

Voice Network Transport
Voice network transport is typically TDM circuit-based: T1/E1 DS3/E3 SONET (OC-3, OC-12, etc.) But can also be packet-based: ATM Frame Relay IP 11/30/2018 Datacom II Spring 2002

Data Is Overtaking Voice
Evolution from TDM-based transport to packets/cells or a combination Relative Load 30 Data Is 23x Voice Traffic 25 20 Data 15 10 Data Is 5x Voice Traffic 5 Voice 1990 1995 2000 2005 Year Source: Electronicast 11/30/2018 Datacom II Spring 2002

The Tyranny of the DS0 Switching and transport based on circuits
Rigid structure yields high cost for packet Customer Premise Local CO Interexchange Local CO Customer Premise Class-5 Switch Class-5 Switch Class-4 Switch DS0 DS0 Class-4 Switch DS0 DS0 Switching DS1 DS1 DS1 DS1 DS0 DS0 3/1 DACS Transport 3/1 DACS DS1 DS3 DS3 DS3 DS3 DS3 DS3 DS1 SONET ADM SONET ADM OC-3/12 OC-48 OC-48 OC-48 OC-3/12 11/30/2018 Datacom II Spring 2002

TDM Transport Efficiency
Types of Traffic Voice PBX Wasted Bandwidth Utilization Legacy 50–60% LAN Video Single WAN Link Time Slot Assignments Wasted bandwidth No congestion 11/30/2018 Datacom II Spring 2002

Packet Transport Efficiency
Types of Traffic Voice PBX Q U E U E Utilization Legacy 90–95% LAN Cells/Frames/Packets Video Individual Packets High bandwidth efficiency Congestion management 11/30/2018 Datacom II Spring 2002

Delay A A Sender Receiver Network t End-to-End Delay
PBX PBX Network First Bit Transmitted Last Bit Received A A Network Transit Delay t Processing Delay Processing Delay End-to-End Delay 11/30/2018 Datacom II Spring 2002

Delay Variation—“Jitter”
Sender Receiver Network A B C Sender Transmits t A B C Sink Receives D3 = D2 D1 D2 = D1 t 11/30/2018 Datacom II Spring 2002

Voice Delay Guidelines
One Way Delay (msec) Description 0–150 Acceptable for Most User Applications 150–400 Acceptable Provided That Administrations Are Aware of the Transmission Time Impact on the Transmission Quality of User Applications [CLICK] This table summarizes the ITU’s recommendations for voice delay guidelines. You can see that below 150 msecs is considered acceptable for most applications. Delays ranging from msecs are also acceptable subject to current voice quality. For example, a 200 msec delay from Chicago to NYC is unacceptable, given experiences with public networks. On the other hand, a 200 msec delay from Chicago to Singapore will likely be acceptable given current conditions. Furthermore, higher delays may be acceptable if cost savings are taken into account. 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 11/30/2018 Datacom II Spring 2002

Cumulative Transmission Path Delay
Delay in Perspective Cumulative Transmission Path Delay CB Zone Satellite Quality High Quality Fax Relay, Broadcast 100 200 300 400 500 600 700 800 Time (msec) Delay Target 11/30/2018 Datacom II Spring 2002

Fixed Delay Components
Propagation Delay Serialization Delay— Buffer to Serial Link Processing Delay Propagation—six microseconds per kilometer Serialization Processing Coding/compression/decompression/decoding Packetization [CLICK] The delay components on this slide are fixed in nature and add very little to delay variation. [CLICK] First, propagation delay is based on the total distance between source and destination. As a planning number we use 6 microseconds per kilometer. [CLICK] Serialization is the process of placing bits on the circuit. The higher the circuit speed, the less time it takes to place the bits on the circuit. So, the higher the speed, the less serialization delay. For example, it takes 125 microseconds to place one byte on a 64K circuit. The same byte placed on an OC-3 circuit will take half a microsecond. [CLICK] Processing delays can be broken down as follows: Coding, compression, decompression and decoding delay will be based on the algorithm employed. It is important to note that these functions can be performed in either hardware or software. Using specialized hardware such as DSPs will dramatically improve the quality and reduce the delay associated with different voice compression schemes. Current voice over Internet products using software-based compression should not be confused with the practicality of carrying voice over IP. Packetization delay is the process of holding the digital voice samples for placement into the payload until enough samples are collected to fill the packet or cell payload. To reduce excessive packetization delay associated with some compression schemes, partial packets could be sent. A further discussion about fixed delay and its components can be found in the design guide. 11/30/2018 Datacom II Spring 2002

Variable Delay Components
Queuing Delay Queuing Delay Queuing Delay Dejitter Buffer Queuing delay Dejitter buffers Variable packet sizes [CLICK] The delay components depicted on this slide are variable in nature and result in higher delay variation; they are also more controllable. [CLICK] Queuing delay occurs when a packet is waiting for others to be serviced first on the trunk. This waiting time is statistically based on the arrival of traffic; hence, the more inputs, the more likely we will encounter contention for the trunk. It is also based on the size of the packet currently being serviced. [CLICK] Dejitter buffers are used at the receiving end to smooth out delay variability and allow time for decoding and decompression. They also help on the first talk spurt to provide smooth playback of voice traffic. Setting these buffers too low will cause overflows and loss of data while setting them too high will cause excessive delay. In effect, a dejitter buffer reduces or eliminates delay variation by converting it to fixed delay. The next few slides will highlight the process to calculate delay. If you’re so inclined, the details can best be seen in your handout. 11/30/2018 Datacom II Spring 2002

An Example Assumptions: We have eight trunks
We are going to use CS-ACELP that uses 8 Kbps per voice channel Our uplink is 64 Kbps Voice is using a high priority queue and no other traffic is being used 11/30/2018 Datacom II Spring 2002

(Private Line Network) Serialization Delay 3 ms
Delay Calculation Los Angeles Coder Delay 25 ms Queuing Delay 6 ms Dejitter Buffer 50 ms Munich Propagation Delay—32 ms (Private Line Network) Serialization Delay 3 ms Fixed Delay Variable Delay Coder Delay G.729 (5 msec Look Ahead) 5 msec Coder Delay G.729 (10 msec per Frame) 20 msec Packetization Delay—Included in Coder Delay Max Queuing Delay 64 kbps Trunk 21 msec Variable Delay Component Serialization Delay 64 kbps Trunk 3 msec Propagation Delay (Private Lines) 32 msec Network Delay (e.g., Public Frame Relay Svc) Dejitter Buffer 50 msec 11/30/2018 Total Datacom II Spring 2002 110 msec 82

Variable Delay Calculation
We have eight trunks, so in the worst case we will have to wait for seven voice calls prior to ours To put one voice frame out on a 64 Kbps link takes 3 msec 1 byte over a 64 Kbps link takes 125 microseconds. We have a 20 byte Frame Relay frame with 4 bytes of overhead. 125 * 24 = 3000 usecs or 3 msec Does not factor in waiting for a possible data packet or the impact of variable sized frames Assumes voice prioritization of frames 11/30/2018 Datacom II Spring 2002

Delay Calculation Site B Site A Site C Private Line Network
Fixed Delay Variable Delay Delay #1 DELAY #1 Coder Delay G msec Packetization Delay (Included in Coder Delay) Max Queuing Delay 64 kbps Trunk 21 msec Serialization Delay 64 kbps Trunk 3 msec Propagation Delay (Private Lines) 32 msec Dejitter Buffer 50 msec Tandem Switch — Delay #1 Total 110 msec Private Line Network Delay #2 Site C 11/30/2018 Datacom II Spring 2002

Delay Calculation Site B Site A Site C Private Line Network
Fixed Delay Variable Delay Delay #1 DELAY #1 Total 110 msec DELAY #2 Coder Delay G msec Packetization Delay (Included in Coder Delay) Max Queuing Delay 2 Mbps Trunk .7 msec Serialization Delay 2 Mbps Trunk 0.1 msec Propagation Delay (Private Lines) 5 msec Dejitter Buffer 50 msec Delay #2 Total 80 msec Total Delay 190 msec Private Line Network Delay #2 Site C 11/30/2018 Datacom II Spring 2002

Other Useful Voice QoS Schemes in IP
Custom queuing, priority queuing and Weighted Fair Queuing (WFQ) Resource Reservation Protocol (RSVP) IP precedence bit setting in the ToS field of the IP Header Compressed Real-Time Protocol (CRTP) 11/30/2018 Datacom II Spring 2002

Summary Voice traffic engineering principles still apply
Packet-based voice trunks can provide efficiency with high quality if properly engineered The biggest impact on voice quality over a data network will be as a result of the delay and delay variation 11/30/2018 Datacom II Spring 2002

Repeat: Voice Is Not a Network
Voice is an application Complete understanding of voice application fundamentals helps us to design and build better networks 11/30/2018 Datacom II Spring 2002

Agenda Basic Analog Telephony Basic Digital Telephony
Voice Coding and Compression Techniques Voice Transport and Delay Supplemental Slides: Digital Voice Signaling Techniques 11/30/2018 Datacom II Spring 2002

Digital Voice Signaling Techniques
ISDN Q.930/Q.931 Signaling System 7 Voice addressing 11/30/2018 Datacom II Spring 2002

ISDN Integrated Services Digital Network Standards-based
Part of a network architecture Definition for the access to the network Allows access to multiple services through a single access Standards-based ITU recommendations Proprietary implementations 11/30/2018 Datacom II Spring 2002

Network Access Traditional Access ISDN Access
Public Packet-Switched Network Customer Equipment (PBX) PSTN (CO Lines) 800 Tie Trunks FX Private Lne Data ISDN Access Public Packet-Switched Network PSTN (CO Lines) Customer Equipment (PBX) Telephone Switch 800 Tie Trunks FX Private Line Data 11/30/2018 Datacom II Spring 2002

Terminology B channel “bearer channel” 64 kbps
Carries information (voice, data, video, etc.) DS-0 11/30/2018 Datacom II Spring 2002

Terminology (Cont.) D channel “signaling channel” 16 Kbps or 64 Kbps
Carries instructions between customer equipment and network Carries information Can also carry packet switch data (X.25) for the public packet switched network 11/30/2018 Datacom II Spring 2002

Terminology (Cont.) BRA/BRI (Basic Rate Access/ Basic Rate Interface)
2 B + D 2 x 64 Kbps + 16 Kbps = 144 Kbps (not including overhead) Designed to operate using the average local copper pair 11/30/2018 Datacom II Spring 2002

Terminology (Cont.) PRA/PRI (Primary Rate Access/ Primary Rate Interface) 23 B + D 23 x 64 Kbps + 64 Kbps (D Channel) + 8 Kbps (Frame Alignment bit) = Mbps Designed to operate using T1/E1 In E1 environments: 30 B + D 11/30/2018 Datacom II Spring 2002

ISDN Reference Points . . . . . . . . . Carrier Customer Premises
TE1 . . NT1 BRA TE1 S/T U . TE2 TA R Carrier . TE1 S NT2 (PBX) . . . PRA NT1 TE2 T U R . . TE2 TA R S Customer Premises Local Loop 11/30/2018 Datacom II Spring 2002

ISDN Reference Points NT1 Terminates local loop
Coding and transmission conversion Maintenance and performance monitoring Functions as a CSU 11/30/2018 Datacom II Spring 2002

ISDN Reference Points (Cont.)
TE1 ISDN compatible equipment TE2 Non-ISDN compatible equipment Requires TA TA Interfaces available for different TE2 E.g. RS-232, X.21, V.35, PC-Bus, video, etc. 11/30/2018 Datacom II Spring 2002

ISDN Reference Points (Cont.)
Typically a PBX Provides switching functions Handles Layer 2 and Layer 3 protocols 11/30/2018 Datacom II Spring 2002

Access to ISDN At the S-reference point:
RJ-45 (receive and transmit pair) Optional power can be provided for TE devices Distance: 1 Km (1 x TE only), 200 m (8 x TE), 500 m (4 x TE) When more than one TE, wires act as a bus CSMA/CD Limitation: cannot have an extension phone 11/30/2018 Datacom II Spring 2002

Access to ISDN At the U-Reference point (BRA)
Standards differ NA, France, UK vs. Germany vs. Japan In North America, designed to use as much of existing copper plant available Two wire, unloaded local loops are 99% of total Up to 5.5 Km loop length At the U-Reference point (PRA) T1/E1 standard 11/30/2018 Datacom II Spring 2002

D Channel ISDN Access Protocols are carried in the D channel
Layer 2 and Layer 3 protocol specifications Protocol specifications are identical for BRA and PRA Layer 2, Q.920/921, LAP-D Supports the communications for Layer 3 Maintains the connections between devices Layer 3, Q.930/931 Call setup, call supervision, call tear down, and supplementary services Uses standard set of messages to communicate 11/30/2018 Datacom II Spring 2002

D-Channel Encapsulation
Layer 3 Protocol Discriminator Length of Call Reference Call Reference Message Type Information Elements Layer 2 Flag Address Control Information CRC Flag Layer 1 D Channel (16 Kbps or 64 Kbps) 11/30/2018 Datacom II Spring 2002

ISDN CCS (Q.930/931) Messages Call Establishment Call Information
Alerting Call proceeding Connect Connect ack Progress Setup Setup ack Call Information Hold Hold ack Hold reject Resume Resume ack Resume reject Retrieve Retrieve ack Retrieve reject Suspend Suspend ack Suspend reject User information Call Clearing Disconnect Release Release complete Restart Restart ack Miscellaneous Congestion control Facility Information Notify Register Status Status inquiry 11/30/2018 Datacom II Spring 2002

Public ISDN and Signaling System 7
Signaling Network BRI BRI Transmission Network Switch Switch PBX1 PRI PRI PBX2 DSS1 Signaling System 7 DSS1 DSS1 Is a Public ISDN Protocol 11/30/2018 Datacom II Spring 2002

ISDN and SS7 “The Bridge Between the Islands”
Voice Transmission STP Switch Switch SSP SSP SS7 Signaling Network SCP Voice Transmission Voice and Signaling STP STP ISDN— PRI STP STP Switch PBX1 SSP STP SCP 11/30/2018 Datacom II Spring 2002

SS7 Components Network 1 Network 2 STP STP SSP STP STP SSP SSP SSP SCP
Voice Trunk SSP: Signal Switching Point STP: Signal Transfer Point SCP: Signal Control Point Signaling Link 11/30/2018 Datacom II Spring 2002

Network Addressing LEC IXC LEC PSTN E.164 Addressing PBX PBX WAN
PSTN E.164 Addressing Dials: PBX PBX 1234 Dials: 1234 VCI/VPI VCI/VPI WAN 11/30/2018 Datacom II Spring 2002

End of Part #1 Introduction to IP Telephony
11/30/2018 Datacom II Spring 2002

Dr Fred Zellner fzellner@uh.edu http://www.uh.edu/~fzellner University of Houston Introduction to IP Telephony Datacom II Lecture 13 Dr Fred Zellner fzellner@uh.edu.

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Dr Fred Zellner fzellner@uh.edu http://www.uh.edu/~fzellner University of Houston Introduction to IP Telephony Datacom II Lecture 13 Dr Fred Zellner fzellner@uh.edu.

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Presentation on theme: "Dr Fred Zellner fzellner@uh.edu http://www.uh.edu/~fzellner University of Houston Introduction to IP Telephony Datacom II Lecture 13 Dr Fred Zellner fzellner@uh.edu."— Presentation transcript:

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