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 o...

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 Network configuration There are two types of network configuration, peer-to-peer networks and client/server networks. Client/server networks are more suitable for larger networks. A central computer, or 'server', acts as the storage location for files and applications shared on the network. In which many less powerful computers or workstations (clients) are connected. The server also controls the network access of the other computers which are referred to as the 'client' computers. The clients run programs and access data that are stored on the server. Only the network administrator will have access rights to the server. Peer-to-peer networks are more commonly implemented where less than ten computers are involved and where strict security is not necessary. It is created when two or more PCs are connected and share resources without going through a separate server computer. All computers have the same operational status/capacity, hence the term 'peer', and they communicate with each other on an equal footing. Files, such as word processing or spreadsheet documents, can be shared across the network and all the computers on the network can share devices, such as printers or scanners, which are connected to any one computer. Peer-to-peer networks have no centralized control. Types of Networks There are three (3) major types of network; Local area network (LAN), Wide area network (WAN), LOCAL AREA NETWORK (LAN) LAN (local area network): this is a network that interconnects users with computer resources within a particular building together. They are widely used to connect personal computers and workstations in company offices and factories to share resources (e.g., printers) and exchange information. Most local area networks are built with relatively inexpensive hardware such as Ethernet cables, network adapters, and hubs. Wireless LAN options also exist. Traditional LANs run at speeds of 10 Mbps to 100 Mbps, have low delay (microseconds or nanoseconds), and make very few errors and they operate within the distance of 100m. WLANs are generally composed of two basic elements: access points and other wireless-enabled client devices, such as laptop computers Access points are physically wired to a conventional network and provide a means for wireless devices to connect to them. There are THREE main ways in which LAN can be broadcasted; we have the ring topology, bus topology and star topology. A Network Topology is a way of “laying out” the network. Topologies can be either physical or logical. Physical topologies describe how the cables are run, while Logical topologies describe how the network messages travel between different components. i. Ring Topology creates a network by arranging 2 or more hosts in a circle. Data is passed between hosts through a 'token.' This token moves rapidly at all times throughout the ring in one direction. Ring topology In a Token Ring network, empty information frames are continuously circulated around the ring as shown in Figure below. In this figure, when one device wants to send data to another device, it grabs an empty frame and inserts both the packet data and destination address. The frame is then examined by each successive device, and if the frame address matches a given device, it takes a copy of the data and sets the token to 0. The frame is then sent back around the ring to the sending device as an acknowledgment, which then clears the frame. ii. Bus Topology uses a common backbone to connect all devices. A single cable which is the backbone functions as a shared communication medium that devices attach or tap into with an interface connector. Bus topology iii. Star or Mesh Topology is one of the most common network setups where each of the devices and computers on a network connect to a central hub. A major disadvantage of this network topology is that if the central hub fails, all computers connected to that hub would lose connectivity. Star topology Wide Area Network (WAN), spans a large geographical area, often a country or continent. WANs utilize public communication links. The largest and most well-known example of a WAN is the Internet. WANs often connect multiple smaller networks such as LANs or MANs. A WAN can have a distance of 100 to 10,000 km around a continent, transmission rates are typically 2 Mbps, 34 Mbps or more.. WAN network topology Fiber Optic Technology Fiber optic cable uses optical fibers that carry digital signal in form of modulated pulses of light. It consists of an extremely thin cylinder of glass called the core surrounded by a concentric layer of glass called the ‘cladding’. There are two fibers in each cable, one for transmitting and the other for receiving data. To reduce signal loss, the core can also be an optical-quality clear plastic, and the cladding can be made up of gel that reflects signals back into the fiber. Fiber-optic cables have signal strength over long distances and are highly secure from outside interference and electrical noise. However, they are too expensive. There are two types of fiber-optic cables: Single-mode fiber (SMF) Multi-mode fiber (MMF) Single-mode uses a single ray of light known as mode to carry transmission over long distances of about 2km, while Multi-mode uses multiple ray of light simultaneously to carry transmission over short distances. Hub and Switch and Router ROUTERS: A router is a networking device that forwards data packets between computer networks. Routers perform traffic directing functions on the internet. A data packet is typically forwarded from one router to another through the networks that constitute the internet until it reaches the destination node. SWITCHES: In networks, a device that filters and forwards packets between LAN segments is termed switch. LANs that use switch to join segments are called switched LANs. HUBS: A common connection point for devices in a network is termed a Hub. Hubs are commonly used to connect segments of a LAN. A Hub contains multiple ports and it floods the host system. It doesn’t filter messages rather it floods the different host on the network with the message and the one who owns the message regards it while the others disregard it. A HUB AND A SWITCH Network interface Card (NIC) A NIC (pronounced 'nick') is also known as a network card. It connects the computer to the cabling, which in turn links all of the computers on the network together. Each computer on a network must have a network card. Most modern network cards are 10/100 NICs and can operate at either 10Mbps or 100Mbps. Only NICs supporting a minimum of 100 Mbps should be used in new installations students. Computers with a wireless connection to a network also use a network card. NIC CARD OPEN SYSTEM INTERCONNECTION LAYER (OSI LAYERS) The OSI model defines internetworking in terms of a vertical stack of seven layers. The upper 3 layers of the OSI model represent software that implements network services like encryption and connection management. The lower 4 layers of the OSI model implement more primitive, hardware-oriented functions like routing, addressing, and flow control. Internet protocol address The Internet Protocol (IP) is the method or protocol by which data is sent from one computer to another on the Internet. Each computer (known as a host) on the Internet has at least one IP address that uniquely identifies it from all other computers on the Internet. An Internet Protocol address (IP address) is a numerical label assigned to each device (e.g., computer, printer) participating in a computer network that uses the internet protocol for communication. An IP address serves two principal functions: host or network interface identification and location addressing. The designers of the Internet Protocol defined an IP address as a 32-bit number and this system, known as internet protocol version 4 (IPv4), is still in use today. However, because of the growth of the internet and the predicted depletion of the address, a new version of IP, IPv6 using 128 bits for the address, was developed in 1995.