Local and Wide Area Network - Essay Example

COMPUTER NETWORKS Student’s Name Class Instructor Institution of Affiliation City Date Networks There are two main types of networks illustrated in the illustration and they are LAN and WAN. LAN (Local Area Network) is a simple network that interconnects computers in a small area or distance usually one or a small number of buildings and is controlled by one network administrator. The network do not rely on the internet for it to function. The Local area Network illustrated uses Ethernet technology and the switch to interconnect devices on the network to facilitate communication through forwarding of data. The network qualifies as a LAN because of the switch which acts as a server to the clients, and the router which is connected to another network usually through the internet. The LAN uses star topology where the clients are connected to a central node (switch) with a point-point connection. The point-to-point topology is achieved because the clients are indirectly connected to each other by the switch. This is because the client is connected to a central hub which in this case is the switch and all the traffic flows through it before reaching the clients. The WAN (Wide Area Network), on the other hand interconnects multiple Local Area Networks over large geographical areas to each other using a router for a quick and secure data transfer. A router and two switches that are interconnected form a WAN. In case of sending a large file to another network, devices on two separate LANS can communicate with each other over the internet and send the file over WAN. In the illustration given, the WAN is identified through the router that interconnects the two LAN together which is in turn connected to the two switches. All this can be achieved through the use of a router. The WAN topology adapted by this illustration is a star topology where the router is used as the central hub of connecting the two LANs together. The router in this case is referred to as the concentrator router which provides a disadvantage of a single failure point. TCP/IP Layers Client The application layer is found on the client. This is because the application layer provides an interface for the user to interact with the server or access a network service such as web chat, web surfing, file transfer and network data sharing (application program). The client on the other hand, is a computer software or hardware that enables a user to access services provided by a server. Switch The internet layer if found on the switch. The internet layer function is to accept packets and deliver them for the network. It involves Address Resolution Protocol (ARP), ICMP (Internet Control Message Protocol) protocol and IP (Internet Protocol). Just like the network or internet layer, the main role of a switch is receiving incoming packets and forwarding them through another link, a function known as switching and forwarding. The physical layer is also found on switches in terms of RJ-45 connectors Router The router acts as an interconnection device where it establishes and terminates connections physically. Therefore it contains the physical layer. The internet layer is also found on the router and is used to forward datagrams across networks and among hosts and also IP datagrams routing (Harvard, 2002, 180). Server The physical layer is found on the server through the network interface ports that connect the server to other devices and vice versa. Physical layer The physical layer main role is to define electrical and physical specifications of all the devices that are used to connect to a network. It offers a way of transmitting raw bits between devices for synchronized communication through establishing and terminating of connections to an optic or twisted pair cable (communication medium). It is interconnected with other layers through the data link layer. Every network device has a physical layer. In the given scenario, the physical layer facilitates communication through the routers, cables, connectors and switches (port connectors) operate at the physical layer. Signal Transmission Data represented by telecommunication devices and computers using signals is transmitted as electromagnetic energy from one node to another. These electromagnetic signals can be transmitted through other transmission mediums, air or vacuum. There are several factors that can influence signal delay in the transmission process and they include: Network media which can be explained as the actual path through which the signals travel, bandwidth (Kbps, Mbps or Gbps) and transmission type (serial or parallel). In network media, it can be wireless media, wired media, physical wires or radio signals. The types of wired media include fiber-optic, twisted-pair and coaxial cable. When transmitting signals using wired media, the most appropriate media to use is fibre-optic cable which offers high speed data transmission over other wired media. Wired media compared to wireless media has high data transmission speed and are reliable. Wireless media on the other hand, use radio signals in data transmission through air. However, even though wired media provides flexibility, accessibility and space, it is much slower in data transmission, unreliable and less secure than wired media. Latency Propagation time Propagation time is the time a signal takes to travel from one point to another over a medium. It is the main cause of latency in networks. In order to reduce signal propagation time, the network administrator can change the DNS time to live settings, change the domains names registry and changing the networking media. Transmission time The main causes of a lag in transmission time are poor network connections, packet size and the bit rate. In order to increase transmission time, the network administrator can decrease the amount of packet size that can be transmitted in the network to avoid traffic or contact the Internet service providers. Queuing time Queuing in a network can be caused by delays at intermediate switches, routers, and call receiver servicing switch or the originating switch. In order to reduce queuing time, the network administrator can configure the router to discard excess packets, reboot the servers or switch of the switches temporarily. Processing delay This is a major cause of latency in networks. The main causes of processing delay include routers performing complex algorithms, network address translation and checks for packet bit-level errors. If this is the case, the network administrator should upgrade to a high speed router, schedule tasks that need to use the router or reboot the rooter to cancel its current processes. Digital signalling Increasing voltage number levels turns an infinite number of analog devices states into only two digital signal states through the creation of voltage logic levels. A standardized voltage level constitutes logic low or logic high. All the circuits of the logic family have the same characteristics and are compatible with circuits from that same family. The voltage levels enable an accurate device communication and data transmission through integrated circuits with Transistor-transistor logic. The potential problems encountered include lack of device compatibility, incorrect data bits and too much voltage to the CMOS can destroy the chip (Mitra and Kuo, 2006, 46). Manchester and Differential Manchester encoding schemes Self-synchronization Manchester encoding combines the RZ and NRZ-L schemes while differential Manchester encoding combines RZ and NRZ-I schemes. The RZ Return to Zero) uses +, 0, -, values with every symbol having a transition in the middle either from low to zero or from high to zero. The two schemes achieve self-synchronization at this transition. DC components and baseline wandering Both Baseline wandering and DC components are problems that a digital signal encounters when it is being transmitted and decoded in that DC components are frequencies around zero that are created by the spectrum when the digital signal voltage level is constant for a while Baseline wandering is a long string of ones and zeros that causes a drift in the received signal power running average. The Manchester scheme addresses NRZ-L problems and differential Manchester addresses NRZ-I problems in that in both there is no DC components (this is due to the fact that every bit has a voltage contribution of negative and positive) and baseline wandering. TDM and FDM Time-division multiplexing and frequency-division multiplexing techniques are both used in tandem in creating more channels within a provided frequency range. The channels are divided using FDM in order to have a dedicated channel with a frequency range that is small. Then, each FDM channel obtained is then filled by multiple channels multiplexed using the TDM technique. Telecoms employ these two techniques in order to allow a certain frequency to be used by a large number of users. Datagram Network Advantages In datagram network, sharing of bandwidth is possible that is when there is no transmission done by the primary user, a number of arbitrary transmitters can share a link bandwidth. Another advantage of datagram network is that because data is transmitted in terms of packets, this enables easy error detection and also at times supports error correction (good for File Transmission Protocol (FTP) network application which do not tolerate errors). Datagram Network Disadvantages Datagram networks experience high end-to-end delays because in every intermediate switch routing is needed. The second disadvantage of datagram networks is since the transmission of data is done in form of a collection of packets, overhead transmission occurs a lot (for example, the routing information in the header of the packet). Virtual-circuit networks Advantages In Virtual-circuit networks sharing of bandwidth is possible that is when there is no transmission done by the primary user, a number of arbitrary transmitters can share a link bandwidth. Secondly, Virtual-circuit networks in relation to Datagram networks have a lower end-to-end delay. Virtual-circuit networks Disadvantages Virtual-circuit networks experience a path setup delay. Secondly, since the transmission of data in Virtual-circuit networks is done in form of a collection of packets, there is more overhead transmission compared to circuit switching networks. However, because there is no individual packet routing, the switching delay when compared to the switching delay of datagram networks is still less. Reasons for ARP Response Failure Return of the wrong MAC address by the routers proxy ARP request. A router in a network makes ARP requests on its internal subnets on behalf of the computers IP address. In this case, the routers proxy ARP requests can be returning a MAC address that is wrong to the computer, due to this, the computer therefore sends its ARP requests to a wrong MAC address. To solve this problem the proxy ARP is disabled. ARP flooding attack. In this case the computer or device receiving or sending the ARP requests can be affected by a malware programme. This causes the device to send ARP replies to all computers and devices connected to the network leading to ARP cache incorrect entries. Due to this, the device is unable to resolve MAC and IP addresses and therefore fails to connect to the computer in the network. The solution to this problem is running an antivirus software. ARP flux problem. When a Linux box is added to a network segment having multiple network cards, a problem can occur with the link layer where a device responds to ARP requests from the two Ethernet interfaces. These multiple answers may cause the computer to be confused or cause an ARP cache non-deterministic population (ARP flux). This causes the IP to non-deterministically migrate from one link layer address to another. CRC Code generation 11101 Divisor 1011 11001101 1011 1111 1011 1001 1011 0100 0000 1001 1011 010 Remainder Internet checksum calculation 1100 1100 1100 1100 first 16 bit value + 0101 1100 0101 1100 second 16 bit value 0010 1001 0010 1000 produced a carry-out + 1 0010 1001 0010 1001 + 0001 0001 0001 0001 third 16 bit value 0011 1011 0011 1010 One’s compliment 1100 0100 1100 0101 References Harvard Hunt, C., 2002. TCP/IP network administration (Vol. 2). " O'Reilly Media, Inc.". Mitra, S.K. and Kuo, Y., 2006. Digital signal processing: a computer-based approach (Vol. 2). 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