Level 2 Development Training Level 2 Development Training Level 2 Development Training Technical Overview
Contents 1 Introduction... 3 Overview... 3 2 Glossary... 4 3 Network Technology... 5 Fundamentals... 5 IP Addresses... 5 Subnet Masks... 6 Data Transfer... 7 4 Conclusion... 8
1 Introduction Overview This document is intended to be a self-study guide to be used to prepare the reader for the subsequent Level 2 Instructor-Led Training (ILT) courses on the RealPresence Platform. Level 1 introduced three distinct learning paths which all converge when discussing the RealPresence Platform. They are Polycom terminology for features and functions, technical video terminology which is used to detail how those features and functions work, and also the actual solutions themselves. We will develop each of these three paths further through each training level, but first we will cover some more commonly used terms to assist with the other Level 2 Development modules and help lay a foundation moving forward into Level 2 and beyond.
2 Glossary There are a number of terms which may or may not be familiar but will be used consistently throughout this training. Dial plan every conferencing or telephony network needs a numbering scheme which defines how many digits must be dialed per extension, and which exact numbers will be utilized, to take into account current and future requirements. This is known as a dial plan. E.164 a standard which defines the format of extensions in a public telecommunications network. Where an endpoint is registered to a gatekeeper, the extension it is given is known as an E.164 alias (an alias literally means an alternate name, such as an alternative to dialing an IP address) GUI Graphical User Interface; a term often given to a browser interface or program which is used to control a device such as an endpoint, see also UI Hertz (abbreviated to Hz) the name for the measure of how many times something happens per second (also known as frequency). If a TV refreshes the screen 50 times per second, so this rate is 50Hz Kilo the standard unit for a thousand, for example a kilometer is a thousand meters Kilohertz - (abbreviated to KHz) another measurement of frequency, where kilo means a thousand, so 50Khz refers to something happening 50,000 times per second. When referring to KHz in terms of audio, the higher the frequency, the higher the sound, the lower the frequency, the lower the sound Mega the standard unit for a million Multicast sending the same messages to multiple network destinations simultaneously Transcode to convert from one signal to another. In terms of videoconferencing, this usually refers to the ability of a bridge to take a number of different protocols and resolutions and convert them all to provide a signal back to each in the correct protocol and resolution UI User Interface; a term often given to a browser interface or program which is used to control a device such as an endpoint, see also GUI Unicast sending messages to a single network destination using a single unique address Wideband operating at a wide range of frequencies; commonly used when discussing audio in a Polycom environment. HDAudio is an example of wideband audio; where a standard telephone cuts audio frequencies down to a range only 3.5kHz, HDAudio transmits a frequency range of up to 22kHz, which is approximately the same as the hearing of a normal person.
3 Network Technology Fundamentals To understand the concept of sending information (including video traffic) over a network it is necessary first to take a step back and make sure some other concepts are clear first. Let s look at some mathematics. Our standard decimal numbering system (using 1, 2, 3, 4, 5, 6, 7, 8, 9 and 0) is called Base10 or denary (from the Latin meaning containing ten ). All numbers can be made using these ten digits. In networking, computing and digital technologies, a numbering system called binary is used. Also called Base2, it only uses two digits, 0 and 1. All numbers can also be made using only these two digits. Instead of numbers increasing by the power of 10 as they move to the left they are doubled. In decimal 111 = 100+10+1 while in binary 111 = 4+2+1. You will no doubt have heard of bits and bytes well, bit is actually short for binary digit, and literally means either a 1 or a 0. A byte is a group of eight bits, which forms one piece of data. An example of a piece of data formed using a byte would be the letter A. More complex characters such as those used in the Chinese language may require two bytes and are know as double byte characters. Data transfer is always measured in bits while data storage is measured in bytes. As bits and bytes start with the same letter the abbreviation b is used for bit and B for byte. You may see examples of this as 512kb for data transfer speed and 15kB for a file size. IP Addresses An IP address is a really good example of how this all fits in together. As any of you who have studied IP networking will know IP addressing and subnetting is a very complex subject. This is a deliberately simplified view that is appropriate for the needs of this training. We would normally look at an IP address in decimal format, for example 192.168.1.1. Each one of these numbers will fit into one byte by using the following table (note there are eight numbers, one for each bit) simply put, if there is a 1 in a box, you count that number; if there is a 0 in the box, you don t. You can then add up then columns with all the 1s and you have both the binary and decimal version of that number, for example: 128 64 32 16 8 4 2 1 converts to 0 0 0 0 0 0 0 1 1 0 0 0 0 0 1 0 0 4 0 0 0 0 0 1 0 1 5 You can work out the binary version of a denary number by putting a 1 in the largest box which will fit, then putting a 1 in the largest box which will fit the remainder, then repeating the process until you have matched the entire number; if done correctly there is only one sequence for each one. You can also use the Windows calculator to convert for you. Select Programmer from the View menu and you have the option to switch the display between decimal and binary.
To use the IP address given above as an example, converting 192, 168, 1 and 1 into binary gives us: 128 64 32 16 8 4 2 1 converts to 1 1 0 0 0 0 0 0 192 1 0 1 0 1 0 0 0 168 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 1 1 We use the decimal version of the IP address, which is easy for us to read, while the computer would use binary internally and when sending data across a network. This binary IP address becomes 11000000.10101000.00000001.00000001, which is made up of 32 bits or 4 bytes. To move a little deeper into this, if we add up all the numbers across the top of the table, we get 255. So IP addresses can be anything from 0.0.0.0 to 255.255.255.255, right? Well, no, but nearly! We will now look at the subnet mask to learn more about how IP addresses and why some numbers are reserved. Subnet Masks We briefly looked at subnets in Level 1 and talked about using these to split the network up so that the devices could decide which IP addresses are part of the (sub) network and which aren t. To define the subnet, we use a subnet mask, which uses 1s to mask the parts of the IP address which are the same for all devices in the subnet. A subnet mask is also based on a series of binary digits. Some common subnet masks are shown in the table below. Decimal Binary Number of Bits 255.0.0.0 11111111.00000000.00000000.00000000 8 255.255.0.0 11111111.11111111.00000000.00000000 16 255.255.255.0 11111111.11111111.11111111.00000000 24 For example, with a subnet mask of 255.255.255.0 only the last 8 bits can change the first 24 remain the same. The part of the IP address that is covered by the 1s in the subnet mask is referred to as the network address and the part covered by 0s is referred to as the host address. So as an example we have a network address 192.168.1.0 with a subnet mask of 11111111.11111111.11111111.0, otherwise seen as 255.255.255.0. This can also be described as a /24 network because there are 24 masked bits. When communicating with other devices the computer will compare the source and destination IP address and use its own subnet mask to decide whether they are on the same network. If the part of
the address covered by 1s in the subnet mask does not match, the packet will be sent to the default gateway (router) to be forwarded to the correct network. As mentioned above, some IP addresses are reserved. In our example above it appears that the IP addresses could range from 192.168.1.0 to 192.168.1.255 but all networks require two addresses to be reserved. The Network Address is the part of the IP address that is covered by the 1s of the subnet mask with all remaining bits set to 0. In our example this gives 192.168.1.0. The Broadcast Adress is determined by setting all the host bits of the IP address to 1s. In our example this is 192.168.1.255. This address is used to send (broadcast) a message to all devices on the network. The last element needed is the Default Gateway address. This can be any IP address that is on the same network. The convention is to use a high or a low number such as 192.168.1.1 or 192.168.1.254. Data Transfer Bits are also used when discussing call speeds for example, a call at 720p will require a minimum call speed of 512kbps, or kilobits per second. The image shows the relationship between video quality and the bandwidth required.
4 Conclusion This guide has provided a further foundation to the fundamentals covered in the Level 1 Infrastructure Overview Course.. Level 2 Development Training 2011 Polycom, Inc. All rights reserved. POLYCOM, the Polycom Triangles logo and the names and marks associated with Polycom s products are trademarks and/or service marks of Polycom, Inc. and are registered and/or common law marks in the United States and various other countries. All other trademarks are property of their respective owners. No portion hereof may be reproduced or transmitted in any form or by any means, for any purpose other than the recipient s personal use, without the express written permission of Polycom. 3222_0611