fundamentals transcript7v2

7/29/2019 Fundamentals Transcript7v2

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Polycom, Inc. All rights reserved.

Fundamentals SeriesNetwork Communication I


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Polycom, Inc. All rights reserved. 2

Fundamentals Series

Signals

Analog vs. Digital

Defining Quality

Standards

H.323

SIP

Network

Communication I

Network

Communication II

Welcome to Network Communication part 1, the seventh module in the Polycom Fundamentalsseries. This module is approximately 5 minutes long.

It is recommended that if you are not already familiar with the OSI model that you consider Network+or similar training to become so prior to proceeding on the path to the Polycom CVE certification.


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Introduction

In order to understand how videoconferencing works its important to understand the underlyingtechnologies at work behind the scenes. In this short module we will talk about the OSI model andhow it fits in with sending real-time media across a network.

We will begin with a recap of the familiar OSI 7-layer model.


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OSI 7-layer model

And here it is. If you are working on your computer, the data you enter in your applicationmoves down into each layer, being encapsulated in each as it goes. As the data isencapsulated in each layer, specific information is added which enables the data to beunpacked at the receiving end. Finally, when the data hits the physical layer, the 0s and 1stravel across the network, and the data is unpacked, removing each level of encapsulationand moving up each layer until it appears in the application as the original data which wassent.


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OSI 7-layer model

To recap, each layer has a specific function. The Physical layer is responsible for the binarydata transmission by defining the relationship between the a device and the transmissionmedium. The Data Link layer provides structure and reliability for data between connectedsystems. Data from the Physical layer is put into the frame we mentioned in the last moduleat this point, and is addressed using a MAC address. The Network layer adds IP addressingto allow the data to be transmitted between networks. The Transport layer adds somereliability measures, including the ability to re-transmit damaged data. The Session layerdefines the relationship between the source and destination computer such as handshakingprotocols. The Presentation layer defines the format for data, compression and encryption,and, finally, the Application layer defines the type of data are you navigating a web page,

or sending an email?


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TCP/IP Model

Moving on from here, the TCP/IP model is a more compact and specific version whichdirectly relates to TCP and IP data transmission and is usually described using a diagramsimilar to the one seen here.

Each of the four TCP/IP model layers more or less correlate to one or more OSI modellayers; there are specific IETF protocols which slot into each of the TCP/IP model layers, butdue to the mechanisms required for them to do their work they dont always fit neatly into

just one layer.

This diagram can also sometimes be seen as a five layer model with the Link, or Network

Access, layer depicted separately.


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TCP/IP Model

Here are some the protocols and how they fit into the TCP/IP model. With the knowledgeyou have it should be fairly clear why they sit in the layers they do. The connectionsbetween Ethernet and the Link layer, IP and the Internet layer, TCP, UDP and the Transportlayer and so on.


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H.323 Protocol Stack

So, how does this all relate to making a video call? Well, rest assured that it does, of course.This is a diagram of the protocol stack for H.323. Here you can see IP inside the Internetlayer, then UDP and TCP and RTP inside the Transport layer, each aspect of our video callsits atop either TCP for call control and signaling, and UDP for audio, video, content and far-end camera control.


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SIP Protocol Stack

And here is the protocol stack for SIP. Although it is similar, you can see here an example ofhow SIP differs from H.323; it is able to use TCP or UDP, depending on how it is configured.

Because SIP covers both control and signaling, it replaces H.225 and H.245, though audioand video are separate like H.323; remember that SIP does not determine which video andaudio codecs to use.

fundamentals transcript7v2

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