TCP/IP Protocol Suite 1 Chapter 25 Upon completion you will be able to: Multimedia Know the...

TCP/IP Protocol Suite 1

Chapter 25Chapter 25

Upon completion you will be able to:

MultimediaMultimedia

• Know the characteristics of the 3 types of services• Understand the methods of digitizing and compressing.• Understand jitter, translation, and mixing in real-time traffic• Understand the role of RTP and RTCP in real-time traffic• Understand how the Internet can be used as a telephone network

Objectives


Figure 25.1 Internet audio/video


Streaming stored audio/video refers to on-demand requests for compressed

audio/video files.

Note:Note:


Streaming live audio/video refers to the broadcasting of radio and TV programs through the Internet.

Note:Note:


Interactive audio/video refers to the use of the Internet for interactive

audio/video applications.

Note:Note:


What is Sound

Sound is a wave that involves a molecules of air being compressed and expanded under the action of a physical device.

Without air there is no sound Sound is a pressure wave that has continuous

values Sound is measured by measuring the wave

pressure at any point. Trnsducer (a device that transforms one type of

energy into another) converts pressure to voltage level

Voltages’ amplitude change over time (pressure increases or decreases)


Digitization

The voltage levels (amplitude) are represented by a continues signal (analog) that varies over time (two dimensions: amplitude and time)

To digitize an analog signal (Convert it into a digital signal) we sample in each dimension

The rate at which we sample is referred to as sampling frequency


Digitization

Audio sampling rate (8 kHz to 48 kHz) Human ear hear between 20 Hz to 20 kHz Ultrasound > 20 kHz Human voice can reach approximately 4 kHz Sampling in the amplitude dimension is called quantization Typical uniform quantization rate is 8-bit and 16-bit 8-bit quantization divides the vertical axis into 256 (28)

levels, and 16-bit divides it into (216) 65,536 levels Voice is sampled at 8000 samples per second (8 kHz) with 8

bits per sample, this results in a digital signal of 64 kbps. Music is sampled at 44,100 samples per second (44.1 kHz)

with 16 bits per sample, this results in a digital signal of 705.6 kbps for monaural and 1.411 Mbps for stereo.


25.1 DIGITIZING AUDIO AND VIDEO

Before audio or video signals can be sent on the Internet, they need to be Before audio or video signals can be sent on the Internet, they need to be digitized. We discuss audio and video separately.digitized. We discuss audio and video separately.

The topics discussed in this section include:The topics discussed in this section include:

Digitizing Audio Digitizing Audio Digitizing Video Digitizing Video


Compression is needed to send video over the Internet.

Note:Note:


25.2 AUDIO AND VIDEO COMPRESSION

To send audio or video over the Internet requires compression. To send audio or video over the Internet requires compression.


Audio Compression Audio Compression Video Compression Video Compression


Figure 25.2 JPEG gray scale


Figure 25.3 JPEG process


Figure 25.4 Case 1: uniform gray scale


Figure 25.5 Case 2: two sections


Figure 25.6 Case 3: gradient gray scale


Figure 25.7 Reading the table


Figure 25.8 MPEG frames


Figure 25.9 MPEG frame construction


25.3 STREAMING STORED AUDIO/VIDEO

We turn our attention to a specific applications called streaming stored We turn our attention to a specific applications called streaming stored audio and video. We use four approaches to show how a file can be audio and video. We use four approaches to show how a file can be downloaded, each with a different complexity.downloaded, each with a different complexity.


First Approach: Using a Web Server First Approach: Using a Web Server Second Approach: Using a Web Server with Metafile Second Approach: Using a Web Server with Metafile Third Approach: Using a Media Server Third Approach: Using a Media Server Fourth Approach: Using a Media Server and RTSP Fourth Approach: Using a Media Server and RTSP


Figure 25.10 Using a Web server


Figure 25.11 Using a Web server with a metafile


Figure 25.12 Using a media server


Figure 25.13 Using a media server and RTSP


25.4 STREAMING LIVE AUDIO/VIDEO

In streaming live audio/video the stations broadcast through the In streaming live audio/video the stations broadcast through the Internet. Communication is multicast and live. Live streaming is better Internet. Communication is multicast and live. Live streaming is better suited to the multicast services of IP and the use of protocols such as suited to the multicast services of IP and the use of protocols such as UDP and RTP.UDP and RTP.


25.5 REAL-TIME INTERACTIVE AUDIO/VIDEO

In real-time interactive audio/video, people communicate visually and In real-time interactive audio/video, people communicate visually and orally with one another in real time. Examples include video orally with one another in real time. Examples include video conferencing and the Internet phone or voice over IP. conferencing and the Internet phone or voice over IP.


Characteristics Characteristics


Figure 25.14 Time relationship


Jitter is introduced in real-time data by the delay between packets.

Note:Note:


Figure 25.15 Jitter


Figure 25.16 Timestamp


To prevent jitter, we can timestamp the packets and separate the arrival time

from the playback time.

Note:Note:


Figure 25.17 Playback buffer


A playback buffer is required forreal-time traffic.

Note:Note:


A sequence number on each packet is required for real-time traffic.

Note:Note:


Real-time traffic needs the support of multicasting.

Note:Note:


Translation means changing the encoding of a payload to a lower quality to match the bandwidth

of the receiving network.

Note:Note:


Mixing means combining several streams of traffic into one stream.

Note:Note:


TCP, with all its sophistication, is not suitable for interactive multimedia

traffic because we cannot allow retransmission of packets.

Note:Note:


UDP is more suitable than TCP for interactive traffic. However, we need

the services of RTP, another transport layer protocol, to make up for the

deficiencies of UDP.

Note:Note:


25.6 RTP

Real-time Transport Protocol (RTP) is the protocol designed to handle Real-time Transport Protocol (RTP) is the protocol designed to handle real-time traffic on the Internet. RTP does not have a delivery real-time traffic on the Internet. RTP does not have a delivery mechanism; it must be used with UDP.mechanism; it must be used with UDP.


RTP Packet Format RTP Packet Format UDP Port UDP Port


Figure 25.18 RTP


Figure 25.19 RTP packet header format


Table 25.1 Table 25.1 Payload typesPayload types


RTP uses a temporary even-numbered UDP port.

Note:Note:


25.7 RTCP

Real-time Transport Control Protocol (RTCP) is a protocol that allows Real-time Transport Control Protocol (RTCP) is a protocol that allows messages that control the flow and quality of data. RTCP has five types messages that control the flow and quality of data. RTCP has five types of messages.of messages.


Sender Report Sender Report Receiver Report Receiver Report Source Description Message Source Description Message Bye Message Bye Message Application Specific Message Application Specific Message UDP Port UDP Port


Figure 25.20 RTCP message types


RTCP uses an odd-numbered UDP port number that follows the port

number selected for RTP.

Note:Note:


25.8 VOICE OVER IP

Voice over IP, or Internet telephony is an application that allows Voice over IP, or Internet telephony is an application that allows communication between two parties over the packet-switched Internet. communication between two parties over the packet-switched Internet. Two protocols have been designed to handle this type of communication: Two protocols have been designed to handle this type of communication: SIP and H.323. SIP and H.323.


SIP SIP H.323 H.323


Figure 25.21 SIP messages


Figure 25.22 SIP formats


Figure 25.23 SIP simple session


Figure 25.24 Tracking the callee


Figure 25.25 H.323 architecture


Figure 25.26 H.323 protocols


Figure 25.27 H.323 example

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TCP/IP Protocol Suite 1 Chapter 25 Upon completion you will be able to: Multimedia Know the...

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