multimedia transmission

Multimedia Transmission

Permission granted to reproduce for educational use only.

© Goodheart-Willcox Co., Inc.

Voice and Audio Signals

Voice and other audio signals are analog Must be converted to digital signals to transfer

over the network At the destination, digitized voice and audio

signals must be converted to analog



Analog-to-Digital Conversion

Done by taking samples of the analog signal's amplitude at specific times

The higher the sampling rate and bit rate, the better the sound quality

Typical voice sampling frequency is about 11 kHz Sampling frequency of music is about 44 kHz



Jitter

High sampling rate requires high bandwidth If sampling rate is too high, some packets will be

dropped to accommodate inefficient bandwidth Caused by missing packets and latency



Latency

Can be caused by bottlenecks and inefficient equipment

Minimal latency can be tolerated for telephone conversation

Listener will notice but tolerate a break in data flow of about 250 milliseconds

500 milliseconds is unacceptable to listener



Acoustical Echo

Commonly encountered in VoIP when using a laptop and audio headset with a microphone

Can be prevented by decreasing the level of amplification

Single participant experiencing acoustical echo in a conference call can affect all participants



Simplified Example of ADC and DAC

Uses Analog-to-Digital Converter (ADC) and Digital-to-Analog Converter (DAC)



Voice over IP (VoIP)

Relies on TCP/IP technology Requires inexpensive equipment Less expensive for long-distance phone calls Also known as Internet telephony



VoIP Transmission Model

Uses UDP packets to send voice data Uses TCP protocol for video or audio streaming Can communicate from PC to PC using TCP/IP Can be used by mixing TCP/IP with modern

phone technologies such as ISDN (Integrated Services for Digital Network, or older systems such as Public Switched Telephone Network (PSTN) (old twisted pair phone network)



Bandwidth-Shaping Techniques

Relied on by VoIP to ensure quality of service A bandwidth shaper uses technique that can:

Prioritize network packets by protocol or assigned switch port or port number

Delay the delivery of low-priority packets Bandwidth rate for switch port can be manually

set Bandwidth can be limited for particular IP

addresses, type of protocol, or particular application



Telephone Gateway and H.323

Telephone gateway connects a packet-style network communications system to a telephone system Uses the H.323 protocol

H.323 protocol controls processes such as: Name to telephone number conversion Call forwarding Caller ID Call blocking Conversion from TCP/IP to wireless Conversion to European telephone systems



Telephone Gateway Configuration



Quality of Service (QoS)

Developed to minimize latency Windows operating systems later than Windows

XP install QoS Packet Scheduler by default Works for wired and wireless networks



Session Initiation Protocol (SIP)

Does not carry data Rather it uses call signaling, which controls

session until session is terminated Skype software is example of SIP application Skype supports telephone communications

across Internet using a;

soft phone ( a virtual telphonic service)

or

hard phone ( a physical telphonic service)



Skype Soft Phone Example



Real-Time Transport Protocol (RTP)

Uses UDP to deliver packets as fast as possible Does not guarantee packet delivery Used in video conferencing and gaming Used with Real-time Transport Control Protocol

(RTCP), which: Ensures quality of service Monitors performance

Can also be used with SIP, H.255, and H.245



VoIP Troubleshooting

Procedure for troubleshooting depends on: Type of system installed Topology Symptoms of the problem

Questions to ask Is problem performance related (quality of VoIP

service)? Is problem due to a complete failure of the system

(connection failure between destination and source)?



Protocol Analyzer

A protocol analyzer can be used to: Verify a complete network path Detect latency Detect missing packets



Improving VoIP Quality

Routers, switches, and gateways allow for QoS configuration

QoS can be configured to give priority to the packets of a specific application, such as the following Skype Online gaming MSN Messenger Yahoo! Messenger



Firewall and Blocked VoIP Packets

One of most common sources of VoIP problems is computer firewall blocking the packets

Check if firewall is configured to allow the port assignments associated with the VoIP software application



Audio Device Configuration

Failure can be due to the microphone, speaker, or headset

Ensure they are turned on Speaker and microphone configuration and

testing can be completed through Windows Control Panel/Hardware and Sound



Impedance Mismatch

For example, connecting a two-wire local loop telephone circuit to a four-wire telephone circuit

One of the most common causes of VoIP echo Also occurs when VoIP technology uses

telephone transmission cables for part of the circuit



Windows 7 Hardware and Sound Menu



You’ve installed a VoIP application on a networked computer. The VoIP application can successfully make calls, but it cannot receive incoming calls. What might be the problem, and how would you fix it?

Applied Networking



Your VoIP application successfully connects. However, you can hear the person you called but that person cannot hear you. What might be the problem with your VoIP connection?

Applied Networking



An analog signal is converted into digital code by taking samples of the analog signal’s amplitude. The number of times the sample is taken during a specific period is referred to as the _____.

A. bit rate

B. sampling frequency

C. sampling rate

C. sampling rate

Review



An analog signal is converted into digital code by taking samples of the analog signal’s amplitude. How often the amplitude is measured per second is referred to as the _____.

A. bit rate


C. sampling rate


Review



The number of bits used to represent the amplitude of the analog signal is referred to as _____.

A. bit rate


C. sampling rate

A. bit rate

Review



The small staggers or hesitations in the delivery sequence of audio or video data is referred to as _____.

jitter

Review



Jitter is caused by _____ or missing packets.

latency

Review



The delay of data as it travels to its destination is called _____.

latency

Review



When a microphone and speaker are in close proximity or the audio is improperly adjusted, _____ occurs.

acoustical echo

Review



The _____ standard compresses video by predicting which areas of the next frame will change and which areas will not. Areas that do not change are not transmitted or stored.

A. ADC

B. DAC

C. video resolution

D. MPEG

D. MPEG

Review



A(n) _____ can be software, hardware, or both that compresses and decompresses video and audio.

codec

Review



The _____ protocol uses analog signals to transmit data at a maximum rate of 56 kbps.

A. ATM

B. Frame Relay

C. VoIP

D. X.25

D. X.25

Review



The _____ protocol is a packet switching protocol that has a maximum data rate of 1.544 Mbps.

A. ATM

B. Frame Relay

C. VoIP

D. X.25

B. Frame Relay

Review



The _____ protocol divides text and audio/video into cells of 53 bytes each. The cells are placed in sequence, giving higher priority to audio/video cells.

A. ATM

B. Frame Relay

C. VoIP

D. X.25

A. ATM

Review



The ATM protocol uses _____ Bit Rate for applications such as video conferencing and telephone communications.

Constant

Review



The maximum size of an ATM cell is 53 bytes, with a maximum payload of _____ bytes.

48

Review



VoIP uses _____ packets for voice data and _____ packets for video and audio.

UDP, TCP

Review



The _____ protocol relies on existing TCP/IP technology and network equipment to deliver voice, audio, video, and multimedia.

A. ATM

B. Frame Relay

C. VoIP

D. X.25

C. VoIP

Review



A(n) _____ is a technique that prioritizes network packets by protocol or assigned switch port or port number and delays the delivery of low-priority packets.

bandwidth shaper

Review



A(n) _____ connects a packet-style network communications system to a telephone system using the H.323 protocol.

A. telephone gateway

B. bandwidth shaper

C. ATM switch

D. PSTN

A. telephone gateway

Review



The _____ protocol gives time-sensitive packets a higher priority than data packets.

A. H.323

B. SIP

C. RTP

D. QoS

D. QoS

Review



The _____ protocol is used to stream voice and video in real time.

A. H.323

B. SIP

C. RTP

D. QoS

C. RTP

Review



The _____ protocol is used for initiating, maintaining, and terminating the exchange of voice, multimedia, gaming, and chat.

A. H.323

B. SIP

C. RTP

D. QoS

B. SIP

Review



The _____ protocol controls processes such as name to telephone number conversion, call forwarding, caller ID, call blocking, conversion from TCP/IP to wireless, and conversion to European telephone systems.A. H.323B. SIPC. RTPD. QoS

A. H.323

Review



The Skype software program is an example of a(n) _____ application.

A. H.323

B. SIP

C. RTP

D. QoS

B. SIP

Review



What is one of the most common sources of VoIP problems?

A. Incomplete path between source and destination

B. Latency

C. Computer firewall blocking the packets

D. Jitter

C. Computer firewall blocking the packets

Review



A(n) _____ can be used to verify a complete network path, detect latency, and detect missing packets.

protocol analyzer

Review


© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.


Acoustical echo A condition that takes place when a microphone and

a speaker are in close proximity or the audio is improperly adjusted, causing feedback.

Analog-to-Digital Converter (ADC) A computer chip designed to change an analog

signal to a digital signal. Asynchronous Transfer Mode (ATM)

A protocol designed especially for transmitting data, voice, and video.

Glossary




Available Bit Rate (ABR) An ATM data transfer classification most appropriate

for file transfer. It uses the available bit rate associated with the networking medium. The speed of a file transfer using the ABR classification is affected by the amount of traffic on the network system.

Bandwidth shaper A technique implemented in a network by hardware

or software to control the bandwidth through a particular device such as a gateway, shared Internet connection, network switch, or router.

Glossary




Bit rate The number of bits used to represent the amplitude

of an analog signal. Codec (compressor/decompressor)

Software, hardware, or combination of software and hardware that compress and decompress video and audio information.

Committed Information Rate (CIR) A guaranteed bandwidth a commercial carrier will

provide a subscriber with.

Glossary




Constant Bit Rate (CBR) An ATM data transfer classification in which a steady

stream of ATM cells move at a predictable rate. Digital-to-Analog Converter (DAC)

A computer chip designed to change a digital signal to an analog signal.

Frame Relay A packet switching protocol that typically uses leased

lines such as T1 to carry data over long distances.

Glossary




H.323 A telecommunications standard and protocol used

for audio, video, and data communications using IP or packet-type networks defined by the International Telecommunication Union (ITU).

Hard phone A physical telephonic device.

Impedance mismatch The effect of connecting two different electronic

audio systems that have different electronic characteristics.

Glossary




Jitter The small staggers or hesitations in the delivery

sequence of audio or video data caused by latency or missing packets.

Latency The amount of time it takes a signal to travel from its

source to its destination. MPEG (Moving Picture Experts Group)

An industry standard that ensures compatibility between different cameras, displays, and other multimedia equipment.

Glossary




Permanent virtual circuit (PVC) A type of connection that behaves as if it were a

hard-wired connection between the destination and source.

Public Switched Telephone Network (PSTN) The older telephone system that uses twisted pair

cabling and analog signals rather than digital. Quality of Service (QoS)

A protocol that gives time-sensitive packets, such as those carrying telephone conversations, a higher priority than data packets.

Glossary




Real-time Transport Protocol (RTP) A standard and a protocol used to stream voice and

video in real time. Sampling frequency

The number of times per second that a sample of a signal’s amplitude is taken.

Sampling rate The number of times during a specific period that a

sample of a signal’s amplitude is taken.

Glossary




Session Initiation Protocol (SIP) A standard and a protocol for initiating, maintaining,

and terminating the exchange of voice, multimedia, gaming, chat, and more.

Soft phone A virtual telephonic device.

Telephone gateway A specialized piece of equipment that connects a

packet-style network communications system to a telephone system using the H.323 protocol.

Glossary




Unspecified Bit Rate (UBR) An ATM data transfer classification that does not

guarantee any speed or meet requirements of any special application such as multimedia or telephony. This classification is typically applied inside TCP/IP frames.

Glossary




Variable Bit Rate (VBR) An ATM data transfer classification in which the ATM

cell rate automatically adjusts to support time-sensitive data. It uses multiplexing techniques to provide a minimum Constant Bit Rate for time-sensitive audio and video transmissions while controlling the data rate of not time-sensitive data, such as text or plain e-mail.

Glossary




Variable Bit Rate-Non Real Time (VBR-NRT) An ATM data transfer classification that allows cells

to move at a variable rate. The rate of movement depends on the type of data contained in each cell.

Variable Bit Rate-Real Time (VBR-RT) An ATM data transfer classification that allows cells

to move at a variable rate depending on the cell’s contents to support real-time audio and video transfers.

Glossary




Voice over IP (VoIP) An Internet telephony protocol designed for high-

performance data delivery and quality of service. It relies on existing TCP/IP technology and existing TCP/IP networking equipment.

X.25 A protocol that uses analog signals to transmit data

across long distances.

Glossary

multimedia transmission

Documents

educational use

video signals

digital signals

analog signals amplitude

transfer of audio

jitterhigh sampling

high bandwidthif sampling

rate faster