Rays Systems

INTRODUCTION TO VIRTUAL PRIVATE NETWORKS VPN:Definition n Virtual Private Network is a private network that uses a public network (usually the Internet) to connect remote sites or users together. Instead of using a dedicated connection such as leased line, a VPN uses “virtual” connections routed though the internet.It works like a point-to-point private link. Traditional Corporate WAN n Traditional corporate WANs are built using private lines or private Frame Relay/ATM n The remote access needs are accommodated by remote access servers and modems. The users dial in through the public switched telephone network. n Main advantages of Traditional WAN q Predictable bandwidth q Security and privacy n Main disadvantages Traditional WAN: q High telecommunication costs q Not easily scalable Virtual Private Network n Definition - A VPN is a private network constructed within the public Internet n Goals q Connect private networks u

Wireless Communication Communication n Is the exchange of information n This exchange achieved through signals n Verbal and non verbal Signals n A signal is a set of information or data n May be electrical, electromagnetic, acoustic optical and so many others. n A communication is termed as accordingly n Communication by electromagnetic signals is termed as radio communication n Analog signal - signal intensity varies in a smooth fashion over time • No breaks or discontinuities in the signal n Digital signal - signal intensity maintains a constant level for some period of time and then changes to another constant level n Periodic signal - analog or digital signal pattern that repeats over time • s(t +T ) = s(t ) where T is the period of the signal n A common signal (Sinusoidal or Sine wave) General Sine wave is represented by

DOS Configuration Files 1.In the MS-DOS operating system, there are two special configuration files, called CONFIG.SYS and AUTOEXEC.BAT. 2.These important files can be included in the DOS boot up process. 3.These two files play a crucial role in optimizing the system for operations in particular functions or with different options. 4.Both the AUTOEXEC.BAT and CONFIG.SYS files can play significant roles in optimizing the system memory and disk-drive usage.

The BIOS loads the Boot Code. The Boot Code then looks for the three OS files IO.SYS MSDOS.SYS COMMAND.COM 1.The Boot Code loads the IO.SYS 2.The IO.SYS loads the MSDOS.SYS 3.MSDOS.SYS loads the COMMAND.COM 4.COMMAND.COM looks for the configuration files CONFIG.SYS and AUTOEXEC.BAT if found, it loads them, if not it goes to the command prompt. ( C:\ )

Transmission standards. It indicates the behavior of cable pairs with electrical signal which traverses through it . Transmission standards of cable consists of standard insulation of cable pairs, loop resistance, line loss, resistance unbalanced etc. etc. Drop of Signal from Exchange to sub-office. Maximum permissible transmission losses from MDF to DPs is = 8dbs Insulation P,S & Junction S Cable > 5000 M ohms/Km P Cable > 1000 M ohms/Km Jn Cable > 2000 M ohms/Km Loop Resistance P,S & Jn cable Cond dia Rs/Km 0.4 mm 300 ohms 0.5 mm 185 ohms 0.6 mm 127 ohms Resistance un-balance P,S & Jn cable Resistance measured b/w two conductor of any pair & unbalanced %tage shall be calculated. Cond dia Ave Rs/Km 0.4 mm 1.5% 300 ohms 0.5 mm 1.5% 185 ohms 0.6 mm 1.5% 127 ohms Line Loss P,S & Jn cable Measure with a Transmission Measuring

1. FUNDAMENTALS OF PCM 1.1 INTRODUCTION This chapter is intended as an introduction to pulse code modulation (PCM), Time-Division multiplexing (TDM). Explanations have been limited to the most important principles and concepts. In order to keep this general survey brief and readily understandable circuitry is not dealt with in any great detail. In the case of TDM the transmitted telephone signals are separated in a time period of 125 Micro second containing 32 time slot (see fig.1). One time slot in each of the consecutive period is allocated to each telephone signal. 1.2 PULSE AMPLITUDE SIGNAL: It is sufficient to sample the waveform at regular intervals and to only transmit these samples (see fig.2). When a waveform is sampled, a train of short pulses is produced. The amplitude of each pulse represents the amplitude of the waveform at the specific sampling instants. This conversion is known as pulse amplitude modulation (PAM) .The envelope of the PAM signal reflects the original form

Alias Addresses •H.323 offers a number of alias address types –dialedDigits (formerly called e164) –h323-ID –url-ID –transportID –email-ID –partyNumber –mobileUIM •Of these, dialedDigits is the most widely used for placing calls (as users today generally still use telephone numbers) •h323-IDs are of local significance and are usually just used between an endpoint and its Gatekeeper •url-ID (including the H.323 URL and “tel” URL) and e-mail addresses are becoming more popular

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