VoIP: The components 

VoIP: The components
The voice from the PCM interface (that is, the input device) goes to the Echo Canceller. You need an echo canceller to cut out the feedback of your own voice in the earphone/headset. A VAD (Voice Activity Detector) monitors the input device for voice so that the process of sending it over the network occurs only in case of voice activity at the mouthpiece. This can be compared to something called VOX used in lots of handheld tape recorders. A Tone/DTMF Receiver at the user's end checks if the ‘connection’ is alive. The generator for these signals lies at the receiver end. If the connection is alive, the voice signal from the PCM interface is encoded by the Voice Encoder and sent over to the host interface that is the gateway to the carrier like TCP/IP. The Voice Decoder will decode this signal at the receiver end. Now comes an interesting part. When we talk, about 60 percent of the time we are silent. This refers to the breath pauses that we have between speaking words. So if we went about encoding, both voice and silence, we would waste enormous bandwidth. Here comes in the Comfort Noise Encoder. The device at the user’s end detects these pauses and ‘tells’ the Comfort Noise Generator at the receiver's end to generate 'noise'. This gives the feeling of the conversation being 'live'. If you are using the same setup for fax also, a Classifier comes into the picture, which separates voice and fax signals for further processing at the sender's end. An optional component called the modem/ fax demodulator and remodulator is also added to the setup to process fax data. Ashish Sharma

muLinux

A fully-configurable, application-centric and tiny

distribution

muLinux installs on the Windows or DOS partition and requires

a minimum of a 386 processor with 8 MB of RAM. It bundles many packages

including those for console, networking, and X-Window.

Let’s get straight into setting it up. Copy the directory

mulinux from the /os directory on the CD to C:\. Unzip ‘DOS TOOLS.ZIP’ in

the same directory. Now restart the computer in full DOS mode. Change to the

directory C:\MULINUX and type ‘INSTALL’. In the first screen, select the

second option, which would install muLinux in the directory C:\LINUX. The

compressed archive is uncompressed and then the system reboots. After the

reboot, go to full-DOS by using the F8 key. Change to the directory C:\LINUX and

type ‘LINUX’. This will start up an interactive setup where you’ll go

through a massive (but very helpful because the configuration files need not be

edited later) question and answer session that covers the entire range from

setting up your keyboard to setting up networking.

You are asked to create a swap space, which can be skipped if

you have enough RAM say more than 128 MB. Otherwise leave swap file name as

/SWAP/LINUX.SWP. The swap file size can be selected to 64 MB.

You are asked to configure keyboard and also some add-ons

including X-Windows. Select Skip when you are asked to upgrade, as these add-ons

have already been setup. Specify the serial and parallel ports to which your

mouse, modem, and printer are connected. Remember ttys0 is COM1 and lp0 is LPT1.

Let mouse protocol be the default.

For networking, you are asked for the model of your Ethernet

card and only six network card models of EtherLink, Intel, RealTek, and AMD are

supported. Then though a series of questions, which are well explained, you can

configure your network, NFS services for Linux–Linux sharing and SAMBA for

Windows-Linux sharing. If you choose to have PPP support, you can configure your

dial-up connection. Subsequently you can configure Fetchmail for retrieving mail

from a POP3 account. muLinux auto detects your IDE CD-ROM drive. Finally you can

decide what daemons or background processes you need to run at startup.

You are now given the login prompt. Login, start up X-Windows

using the startx command and you are ready to swing!

FreeDOS BETA5 ("LARA")

Full distributionIf you are a DOS lover, you’ll love this

This is a free and fully MS-DOS compatible OS. System

requirements are minimal and it installs on a x486 with as little as 8 MB RAM.

The distribution on the CD has zipped files and you need ‘UNZIP’

(included) to extract the installation disks. Keep a pack of formatted 3½"

floppies at hand. Through the DOS prompt, Unzip ‘BASE1. ZIP’ using the

command UNZIP BASE1. ZIP —d A: (note the lowercase -d). This is the only

floppy you need for the Mini FreeDOS distribution. For the full version, repeat

the unzip process with rest of the install disks. Now you need to install the

Boot floppy image. Use ‘RAWRITE’ (included in the package). Run RAWRITE from

DOS prompt, read the .BIN image file (MINI.BIN for Mini version and FULL.BIN for

Full version) and write to a preformatted floppy in A: drive. Now you are ready

to install FreeDOS.

Reboot and start your PC with the boot floppy you created.

You are left at the DOS prompt. You can install FreeDOS in a folder in the

existing partition or work purely on FreeDOS. Use FDISK and FOR MAT at the

prompt in the latter case. Then run INSTALL at the prompt. Give the location

from where you’ll install as A: and the destination can be C:\FDOS. Pop in the

install floppies you created one after the other. The process is a bit slow due

to slow FDD access. Alternatively you can install from the hard disk directly.

Note, however, that in this case you’ll have to unzip all the install floppies

in one single directory say C:\FDINSTALL and give the source path accordingly

after booting up.

The package also includes the Seal GUI for FreeDOS.

MINIX

A small, free UNIX clone for those who want to peep into Unix

Unlike Linux which requires at least a 386 processor to run,

Minix can be run even on an 8088 or 80286. Basic memory requirements are as low

as 3 MB.

On our CD we have the 386 precompiled binaries (i386.tar).

The procedure for Minix installation is outlined in readme.txt and install.txt.

Unzip the i386.tar using Winzip to get the three files Root, Usr, and Usr.taz.

Then you create the Minix bootable floppies using FDVOL utility. This is also

included on the CD. These floppies are then used to boot the machine and install

the OS. We have also included zipped files for the compiler, debugger,

networking utilities, etc, in the package. DOSUTILS come in handy to prepare

your hard disk for the installation.

Shekhar Govindarajan and Ashish Sharma