2_Lecture 2.docx

Modem (MOdulation + DEModulation) converts the analogue signal back into a digital signal. Codec (Coder+DECoder): compression & decompression for a particular audio / video / data. Rules (Refer to Tutorial) Rule 1: Rule 2: Rule 3: Rule 4: Digital Signals Computers see everything in terms of...

Modem (MOdulation + DEModulation) converts the analogue signal back into a digital signal. Codec (Coder+DECoder): compression & decompression for a particular audio / video / data. Rules (Refer to Tutorial) Rule 1: Rule 2: Rule 3: Rule 4: Digital Signals Computers see everything in terms of binary. In binary systems, everything is described using two values or states: on or off, true or false, yes or no, 1 or 0. A light switch could be regarded as a binary system, since it is always either on or off. Each of the switches in a computer is called a bit, short for binary digit. By arranging bits in groups, the computer is able to describe more complex ideas than just on or off. The most common arrangement of bits in a group is called a byte, which is a group of eight bits. Binary Arithmetic In binary arithmetic, each bit within a group represents a power of two. The following table represents the value for each bit in a byte (remember, a byte is 8 bits). In binary math, the values for the bits ascend from right to left, just as in the decimal system: To calculate the value for each bit in a byte is simply a matter of turning on certain bits and then adding together the values of those bits. For example, what does an 8-bit binary number like 01101110 represent? The following table dissects this number. Remember, a computer uses 1 to signify "on" and 0 to signify "off" In the table above, you can see that the bits with the values 64, 32, 8, 4 and 2 are all turned on. So for the binary value in the table, 01101110, we add together 64+32+8+4+2 to get the number 110. A digital signal can have more than two levels. In this case, we can send more than 1 bit for each level. Figure below shows two signals, one with two levels and the other with four. We send 1 bit per level in part a of the figure and 2 bits per level in part b of the figure. In general, if a signal has L levels, each level needs log2L bits. Example A digital signal has eight levels. How many bits are needed per level? We calculate the number of bits from the formula Number of bits per level =log2 8 =3 Each signal level is represented by 3 bits. Internet Protocol (IP) address IP address is a 32-bit logical address for a host on a TCP/IP network (IPv4) or 128-bit (IPv6). Each host on a TCP/IP network needs a unique IP address for communication to take place reliably on the network. Note: TCP/IP stands for Transmission Control Protocol/Internet Protocol. TCP/IP is a set of standardized rules that allow computers to communicate on a network such as the internet. IPv4 = Internet Protocol version 4 IPv6 = Internet Protocol version 6 An IPv4 address has the following format: x . x . x . x where x is called an octet and must be a decimal value between 0 and 255. Octets are separated by periods. An IPv4 address must contain three periods and four octets. The following examples are valid IPv4 addresses: 1.2.3.4 01 . 102 . 103 . 104 IPv4 IP address are 32 bit numbers. In the above binary format, there are total of 32 binary numbers. Each and every binary number that are separated by the dot is converted to its corresponding binary number. There are total of 4 bytes here. Each and every octet can have a value from 0 to 255. Since there are 4 octets in an ip-address, the total possible combination of unique ipv4 ip addresses are 4,294,967,296. Online calculator: (convert decimal to binary) https://www.cs.princeton.edu/courses/archive/fall07/cos109/bc.html IPv6 ip address has 128 bits. This is a huge improvement from the 32 bit ipv4 ip address. While lot of networks are getting configured for both IPv4 and IPv6, there is still a huge number of networks and systems in the internet that works only for IPv4. But eventually all these systems might go towards the IPv6 route. Note: End users really don't need to understand the binary representation of an IP. In fact, we purposely write IPs in decimal so that it is easier for humans to understand and remember them. However, network administrators must know technically what's going on in order to implement anything but the simplest network (creating TCP/IP networks, the subnet). You will find that being able to look at IP addresses the way your computer does will help you do a better job as a network administrator