Chapter 2: Background and Literature Review
A Computer Network is a collection of computers interconnected by wires or wireless to the purposes of sharing data and make communication between them. Several devices are used in order to build a computer network, for example Router, Switch, Hub, Modem, etc:There are three types of networks: the Internet, theintranet, and the extranet.
Internet: It is a worldwide system which interconnected computer networks that use the standard Internet Protocol Suite(TCP/IP) to serve billions of users worldwide. The Internet carries a vast informationresources and services, most notably the inter-linked hypertext documents of the World Wide Web(WWW).
Intranet: It is a private computer network that uses Internet Protocol technologies to securely share any part of an organization's information or operational systems within that organization.
Extranet: It is an as an intranet mapped onto the public Internet or some other transmission system not accessible to the general public, but managed by more than one company's administrator(s).
Type of Area Networks
Local area network(LAN), which is usually a small network constrained to a small geographic area. An example of a LAN would be a computer network within a building.
A local area network (LAN) supplies networking connection to a limited area that is computers in close proximity to each other such as in an office building, a home or campus within few kilometres in size. Local area network is useful for exchange resources like files, printers, and other information among personal computers and workstations. There are three main characters which differentiate from other kind of network system.
- Transmission technology
ARCNET, Token Ring, Ethernet and Wi-Fi are the two most common technologies currently in use.
ARCNET used RG-62/U coax cable of 93O impedance and either passive or active hubs in a star-wired bus topology. A layout finally copied by modern twisted pair Ethernet LANs. ARCNET had somewhat lower best-case performance. ARCNET also has the advantage that it achieved its best collective performance under the highest loading, approaching asymptotically its maximum throughput.
Another important difference is that ARCNET provides the sender with a concrete acknowledgment (or not) of successful delivery at the receiving end before the token passes on to the next node, permitting much faster fault recovery within the higher level protocols (rather than having to wait for a timeout on the expected replies). ARCnet doesn't waste network time transmitting to a node not ready to receive the message, since an initial inquiry (done at hardware level) establishes that the recipient is able and ready to receive the larger message before it is sent across the bus.
Token ring local area network technology is a local area network protocol which sits at the data link layer (DLL) of the OSI model. It uses a special three-byte frame a token, which travels around the ring. Token ring frames travel completely around the loop. Physically, a token ring network is wired as a star, with 'hubs' and arms out to each station and the loop going out-and-back through each. Ethernet is an extensively used technology using a bus topology. It is low in cost and simple. In a bus topology a packet travels the length of the bus and is seen by every device attached to the bus. Unfortunately, the biggest problem in bus situation was that of unacceptable segment termination. Bridging and switching can section the network into multiple collision domains. Ethernet remains as a single broadcast domain.
Metropolitan area network (MAN)
This is used for medium size area. For example, city or a state can be considered. It generally interconnects a number of local area networks using a high-capacity basic technology, for example fibre-optical links, and provides up-link services to wide area networks and the Internet.
Wide area network(WAN) is usually a larger network that covers a large geographic area. Normally WANs built with public packet networks, military networks, large corporate networks, banking networks and airline reservation networks. Organisations supporting WANs are using the Internet Protocol which is the Network Service Providers for communication.
Wireless networks (WLAN, WWAN)
Wireless LANs are the wireless equivalent of the LAN and WAN.A wireless local area network links devices via a wireless distribution method and usually provides a connection through an entree point to the wider internet. This gives users the mobility to move around within a local coverage area and still be connected to the network.
Storage Area Network is a network specifically dedicated to the task of transporting data for storage and retrieval. SAN architectures are alternatives to storing data on disks directly attached to servers or storing data on Network Attached Storage (NAS) devices which are connected through general purpose networks.
Controller-area network is a vehicle bus standard designed to allow microcontrollers and devices to communicate with each other within a vehicle exclusive of a host computer. This is a message based protocol, designed specifically for automotive applications but now also used in other areas such as industrial automation and medical equipment.
Personal area network is computers become more ever-present, as more people have them, they become smaller, and computers end up being in small things, such as cell phone and on laptops.
DAN (Desk Area Network) is an interconnection of computer devices around the ATM (Asynchronous Transfer Mode).
Topology is the way in which the elements of network are interconnected. Topology can be imagined as a virtual shape of a network. This shape really does not match to the concrete physical design of the devices on the network. The computers on a home network can be arranged in a circle shape but it does not automatically mean that it gives a ring topology. There are four important topologies are: Bus topology, Star topology, Ring topology and Tree topology.
Bus topology is used in local area networks; each machine is connected to a single cable through some kind of connector. A signal from the source computer travels in both directions to all computers connected on the bus cable until it finds the MAC address or IP address on the network that is the planned recipient. If the machine address does not match the planned address for the data, the machines disregard the data. If the data does match the machine address, the data is accepted by the receiver. Bus topology consists of only one wire, so it is inexpensive to implement when compared to other topologies, but, it is high in cost on managing the network. Because a single point of failure can break the entire network.
This network topology consists of one central switch, hub or computer in its network, which acts as a channel to transmit messages. The originating node must be able to bear the response with an echo of its own transmission delayed by the two derection transmission time plus any delay produced in the central node if the central node is passive. An active star network topology has an active central node that frequently has the resources to keep away from echo-related problems.
The star topology will reduce the possibility of network failure by connecting all of the systems to a central node. A bus based network this particular central hub rebroadcasts all transmissions received from any minor node to all peripheral nodes on the network, sometimes it send signals including the originating node.
A star topology has many advantages such as;
- Better performance: The star topology prevents the sending of data packets during an unnecessary number of nodes. However this topology places a massive overhead on the central hub, with sufficient capacity, the hub can hold very high utilization by one device without affecting others.
- Isolation of devices: Each device is as expected could be isolated by the link that connects it to the hub. These create the separation of individual devices basic and amounts to disconnecting all devices from the others. This isolation protects any non centralized crash from upsetting the network.
- Benefits from centralization: As the central hub is the traffic jam, increasing its capacity, or connecting additional devices to it, amplify the size of the network extremely easily. Centralization also allows the examination of traffic through the network. These may make possible analysis of the traffic and discovery of doubtful behaviour.
- Simplicity: This is easy to recognize, set up, and find the way.
The main drawback of a star topology is the high reliance of the system on the performance of the central hub. The breakdown of the central hub renders the network crash, immediately separating all other nodes. The presentation and scalability of the network depend on the potential of the hub. Network size is restricted by the number of connections which can be made to the hub. Performance for the entire network is limited by its throughput.
In a ring topology every node connects to precisely two other nodes, making a single continuous path for signals through each node - a ring. Data travels from node to node, with each node along the way handling every packet. Very well arranged network where every device has access to the token and the opportunity to transmit. The performance of ring topology is better than a star topology under heavy network load. This does not require network server to manage the connectivity between the computers. A node failure or cable break might isolate every node attached to the ring. Moving, adding and changing of devices can affect the network. Network adapter cards and MAU's are much more expensive than Ethernet cards and hubs.
A tree topology is also known as a hierarchical network. In this topology a central root node connected to more than one nodes that are one level lower in the with a point-to-point link. In this network each and every node having a defined fixed number of nodes connected to it at the next lower level in the hierarchy. The number is known as 'branching factor'. A network that is based on the physical hierarchical topology should have at least three levels. The physical linear topology is topology with a branching factor of 1. Branching factor is not depending on total number of nodes in the network. The total number of links in a network will be one less than the total number of nodes. If the nodes in a network are essential to perform any processing on the data that is transmitted between nodes, the nodes that are at higher levels in the hierarchy required to perform additional processing operations on behalf of nodes that are lower level.
Network Hardware Devices
A network switch is a specialized device that connects multiple network segments. It's a more modern and efficient form of the present network hub. Each node on a network has a unique hardware address which is the MAC address. A switch-based network is one that utilizes switches instead of hubs. Instead of sending all network data to each and every network node, the switch will analyze the MAC address and determine where to send the data. So the network bandwidth is not wasted by sending every frame to every port. So when a switch receives data for a file, if it was addressed to one computer it will only be sent there.
A hub joins multiple computers or other network devices together to form a single network division. A hub includes a series of ports that each accepts a network cable. Hubs classify as physical layer devices in the OSI model. Hubs do not read any of the data passing through them and are not aware of their source or destination, they simply receives incoming packets, possibly amplifies the electrical signal, and broadcasts these packets out to all devices on the network. There are three different types of hubs exist: passive, active and intelligent. Passive hubs do not amplify the electrical signal of incoming packets before broadcasting them out to the network. Active hubs, on the other hand, do execute the amplification, as does a different type of devoted network device called a repeater. Intelligent hubs add extra features to an active hub that are of particular importance to businesses. An intelligent hub built in such a way that multiple units can be placed one on top of the other to conserve space.
A bridge device filters data traffic at a network boundary. Bridges reduce the amount of traffic on a LAN by dividing it into two segments. Bridges operate at the data link layer (Layer 2) of the OSI model. Bridges inspect incoming traffic and decide whether to forward or discard it. Bridges serve a similar function as switches that also operate at data link layer. Traditional bridges, though, support one network boundary, whereas switches usually offer four or more hardware ports. Switches are sometimes called "multi-port bridges" for this reason.
Networking Cables are used to connect to one or more devices such as share printer, scanner etc. Different types of network cables such as Optical fibre cable, Coaxial cable, Twisted Pair cables are used depending on the network's topology, protocol and size.
Twisted pair cabling is a form of wiring in which two conductors (the forward and return conductors of a single circuit) are twisted together for the purposes of cancelling out electromagnetic interference (EMI) from external sources.
Coaxial lines confine the electromagnetic wave to the area inside the cable, between the centre conductor and the shield. The transmission of energy in the line occurs totally through the dielectric inside the cable between the conductors. Coaxial lines can therefore be bent and twisted (subject to limits) without negative effects, and they can be strapped to conductive supports without inducing unwanted currents in them. The most common use for coaxial cables is for television and other signals with bandwidth of multiple megahertz.
A patch cable is an electrical or optical cable, which used to connect electronic or optical device to another for the purpose of signal routing. Devices of different types such as a switch, or router are connected with patch cords. It is a very fast in connection speed.
Ethernet crossover cable
An Ethernet crossover cable is a verity of Ethernet cable which used to connect computing devices together directly. Normally it would be connected via a network switch, hub or router, for example directly connecting two personal computers via their network adapters.
While switches connect multiple computers, a router is required to connect multiple networks, like your LAN to the Internet. Routers work by storing large tables of networks and addresses, then using algorithms to determine the shortest routes to individual addresses within those networks. In this way efficient routers not only facilitate intra-network communications, but also play a role in overall network performance delivering the information faster.
Network repeaters used to regenerate the incoming electrical, wireless or optical signals. With physical media like Ethernet, the data transmissions can only cross a limited distance before the qualities of the signal corrupt. Repeaters attempt to protect signal integrity and extend the distance over where data can safely travel.
TCP: TCP (Transmission Control Protocol) is a set of rules (protocol) used along with the Internet Protocol (IP) to send data in the form of message units between computers over the Internet. TCP make sure of keeping track of the individual units of data (called packets) that a message is divided into for efficient routing through the Internet. When an HTML file is sent to you from a Web server, the Transmission Control Protocol (TCP) program layer in that server divides the file into one or more packets, numbers the packets, and then forwards them individually to the IP program layer. Although each packet has the same destination IP address, it may get routed differently through the network. At the client computer TCP reassembles the individual packets and waits until they have arrived to forward them to you as a single file.
TCP is known as a connection-oriented protocol, which means that a connection is established and maintained until such time as the message or messages to be exchanged by the application programs at each end have been exchanged. TCP is responsible for ensuring that a message is divided into the packets that IP manages and for reassembling the packets back into the complete message at the other end. In the Open Systems Interconnection (OSI) communication model, TCP is in the Transport Layer.
IP: Internet Protocol is the main network protocol used on the Internet. It is developed in the 1970s. IP is often used together with the Transport Control Protocol (TCP) on the Internet and many other networks. IP supports on unique addressing of computers on a network. Most networks use the Internet Protocol version 4 (IPv4). It has the standards features of IP addresses four bytes (32 bits) in length. The newer Internet Protocol version 6 (IPv6) has standard features addresses 16 bytes (128 bits) in length.
UDP: User Datagram Protocol is a simple OSI transport layer protocol for client and server network applications based on Internet Protocol. This is the main alternative to TCP and one of the oldest protocols present and it is introduced in 1980. This is often used in video conferencing applications specially made for real-time performance. In order to achieve higher performance, the protocol allows individual packets to be dropped and packets to be received in a different order than they were sent as dictated by the application. The network traffic is prepared in the shape of datagram. A datagram contains one message unit. The first eight bytes of a datagram enclose header information and the remaining bytes have message data. A datagram header consists of four fields of two bytes each destination port number, source port number, datagram size and checksum. This port numbers allow different applications to maintain their own channels for data similar to Transmission Control Protocol. The port headers are two bytes long; as a result, valid port numbers range from 0 to 65535. The size of datagram depending on the operating environment but has a maximum of 65535 bytes. It checksums protect message data from tampering. The checksum value represents .an encoding of the datagram data calculated first by the sender and later on by the receiver.
FTP: FTP technology allows you to transfer files between two computers over the Internet. FTP is a simple network protocol based on IP and also the name people use when referring to the process of file transfer.
HTTP: Hyper Text Transfer Protocol, the underlying protocol used by the World Wide Web. HTTP defines how messages are formatted and transmitted, and what actions Web servers and browsers should take in response to various commands.
SMTP: Simple Mail Transfer Protocol is a protocol for sending email messages across the Internet. It is used in conjunction with both POP3 and IMAP, protocols that enable you to download messages from a mail server to your computer. SMTP is used for outgoing mail while POP3 and IMAP are used for incoming mail.
TELNET: (TErminaL NETwork) is a network protocol used on the Internet or local area networks to provide a bidirectional interactive text-oriented communications facility via a virtual terminal connection.
Network architecture model
Open Systems Interconnection (OSI) model is a reference model developed by ISO (International Organization for Standardization) in 1984, as a conceptual framework of standards for communication in the network across different equipment and applications by different merchants. It is now considered the primary architectural model for inter-computing and internetworking communications. The OSI model describes the communications process into 7 layers, which splits the tasks involved with moving information between networked computers into seven smaller, more manageable task groups. The OSI 7 layers model has clear features.
It provides services for an application program. It is to make sure whether effective communication with another application program in a network is possible. The application makes sure that the other party is identified and can be reached. And whether the other party is appropriate, authenticates either the message sender or receiver or both. This layer ensures agreement at both ends about error recovery procedures, data integrity, and privacy. The user interface protocols like FTP,Telnet,SMTP are used in this layer . The application layer protocols often contain of the session and presentation layer functions.
This is sixth layer of the OSI model of networking. This Layer is responsible for the delivery and formatting of information to the application layer for further processing or display. It relieves the application layer of concern regarding syntactical differences in data representation within the end-user systems. Some other function of this layer is decompressing, compressing, encrypting and decrypting the data send by application layer.
The Session Layer is fifth layer of the OSI model. The Session Layer provides the methods for managing a session between end-user application processes. Communication sessions consist of requests and responses that occur between applications. Session Layer services are commonly used in application environments that make use of remote procedure calls. Session layer does synchronization between transactions. Think the problems that may occur when trying to do a transfer between two machines on a network with a stand for time among crashes. After every transfer was ended, the whole transfer would have to start over again, and may be failing again with the next crash. To eliminate this problem, the session layer provides a way to insert checkpoints into the data stream, so that after a crash, only the data after the last checkpoint has to be repeated. AppleTalk Data Stream Protocol, AppleTalk Session Protocol, Call Control Protocol for Multimedia Communication, OSI Session Layer ,Real-time Transport Control Protocol, Short Message Peer-to-Peer, Secure Copy Protocol, Secure Shell, ZIP( Zone Information Protocol) and SDP( Sockets Direct Protocol) are protocols of session layer.
The Transport Layer is a collection of methods and protocols within a covered structural design of network components. It is accountable for covering the application data blocks into data units appropriate for transfer to the network communications for transmission to the destination host, or managing the reverse transaction by abstracting network datagram and delivering their payload to an application. This layer has connection oriented and connectionless protocols.
A connection-oriented protocol is where the two communicating system exchange message to establish a connection before they transmit any application data. This makes sure that the systems both are active and ready to exchange message. For example, TCP is a connection-oriented protocol when users use a web browser to connect to an internet server, the browser and the server first carry out what is known as three-way handshake to set up the connection. Then only it does the browser transmit the address of the required web page to the server. The systems perform a same handshake to break down connection when the data transmission is ended. It also gives additional services such as data segmentation, packet acknowledgment, flow control, and end-to-end error detection and correction.
The Network Layer is third layer of the OSI model. The Network Layer is in charge for end to end packet deliverance jointly with routing through among hosts. The Data Link Layer is in charge for node to node frame delivery on the similar link. This Layer provides the functional and technical resources of transferring variable length data sequences from a source to a destination host. And it sent through one or more networks at the same time as maintaining the quality of service and error control functions.
Data link Layer
This is the second layer of the OSI model. This layer is the protocol layer which transfers data between neighbouring network nodes in a wide area network or between nodes on the same local area network. The Data Link Layer provides the functional and technical way to transfer data between network entities. Examples of data link protocols are Ethernet for local area networks, the Point-to-Point Protocol (PPP), HDLC (High-Level Data Link Control) and ADCCP (Advanced Data Communication Control Procedures) for point-to-point (dual-node) connections.
This layer has the crucial hardware transmission technologies of network. It is an essential layer fundamentally the logical data structures of the superior level functions in a network. It makes sure bit synchronisation and places the binary pattern that it receives into a receive buffer. When it decodes the bit stream, then the physical layer notifies the data link layer that a frame has been received and sends it up.
TCP/IP model is Internet reference model and also referred as DoD (Department of Defense) or ARPANET reference model. This has 4 layers.
The Application Layer is the first layer of TCP/ IP model. This consist the protocols such as File Transfer Protocol, it used for transferring big files between remote machines. Simple Mail Transfer Protocol is used by mail servers to exchange mail. Simple Network Management Protocol is used by network monitoring machines to determine the health and status of the network. Telnet is used by machine to connect to a remote host.
Transport Layer where the connection protocols such as TCP, exist. Some transport Layer Protocols are UDP (User Datagram Protocol), DCCP (Datagram Congestion Control Protocol), SCTP (Stream Control Transmission Protocol), etc. This layer facilitates opening and maintaining connections as well as ensures that the message packets are received properly.
The Internet Layer which defines IP address system and the routing schemes for navigating packets from one IP address to another. There are three basic functions on this later. Select the "next hop" host (gateway) and transmit the packet to this host by passing it to the appropriate Link Layer implementation for an outgoing packet. Capture packets and pass the packet payload up to the appropriate Transport Layer protocol for incoming packets, if appropriate. And it provides error detection and problem-solving capability.
The Link Layer is the lowest layer in the Internet Protocol Suite, the networking architecture of the Internet (RFC 1122, RFC 1123). The link is the physical and logical network components used to interconnect hosts or nodes in the network and a link protocol is a suite of methods and standards that operate only between neighbouring network nodes of a Local area network segment or a wide area network connection.
The core protocols of this layer are the Address Resolution Protocol (ARP), the Reverse Address Resolution Protocol (RARP), and the Neighbour Discovery Protocol (NDP).
FDDI (Fiber Distributed Data Interface) is a set of ANSI (American National Standards Institute) and ISO standards for data transmission on fiber optic lines in a local area network (LAN) that can extend in range up to 200 km (124 miles). The FDDI protocol is based on the Token Ring protocol. In addition to being large geographically, an FDDI local area network can support thousands of users.
The Point-to-Point Protocol is a data link protocol. It normally used to set up a direct connection between two networking nodes. It provides connection authentication, transmission encryption privacy, and compression. It is used in many types of physical networks including serial cable, phone line, trunk line, cellular telephone, specialized radio links, and fiber optic links such as SONET. The phases of the Point to Point Protocol according to RFC 1661 are described as followings;
Link Dead: This occurs when the link fails or can occur when one side has been told not to connect.
Link Establishment Phase: This occurs when Link Control Protocol negotiation is attempted.
Authentication Phase: It permits the both sides to authenticate each other before a connection is established.
Network-Layer Protocol Phase: This occurs when each desired protocols' Network Control Protocols are invoked.
Link Termination Phase: This occurs when closes down of a connection made. This may happen if there is an authentication breakdown.
Multiple accesses protocols and LANs
Addressing and ARP
The Address Resolution Protocol (ARP) is a computer networking protocol for determining a network host's link layer or hardware address when only it's Internet Layer (IP) or Network Layer address is known. The term address resolution refers to the process of finding an address of a computer in a network. The address is "resolved" using a protocol in which a piece of information is sent by a client process executing on the local computer to a server process executing on a remote computer. The information received by the server allows the server to uniquely identify the network system for which the address was required and therefore to provide the required address. The address resolution procedure is completed when the client receives a response from the server containing the required address.There are four types of ARP messages that may be sent by the ARP protocol. These are identified by four values in the "operation" field of an ARP message. The types of message are: ARP request, ARP reply, RARP request, and RARP reply.
A virtual LAN is a group of hosts with a common set of requirements that communicate as if they were attached to the same broadcast domain, regardless of their physical location. There are two types of VLAN, cell-based VLANs and frame-based VLANs. Cell-based VLANs are used in ATM switched networks with LAN Emulation. LANE is used to allow hosts on legacy LAN segments to communicate using ATM networks without having to use special hardware or software modification. Frame-based VLANs are used in ethernet networks with frame tagging.
Quality of Services (QoS)
The objective of QoS is to provide assurance on the capability of a network to transport expected results. QoS is considered on Throughput, Dropped packets, Delay, Jitter and error. Throughput: this can be affected by users sharing than LAN where it reaches the maximum bit rate it can handle. Dropped packets: The routers might fail to deliver some packets. It will delay the overall transmission and affects the Qos. Delay: Some packets long time to reach its destination may be because it gets held up in long queues, or takes a less direct route to avoid congestion. Jitter: Packets from the source will reach the destination with changed delays. This difference in delay is known as jitter. And it can seriously change the quality of streaming audio or video. Error: Sometimes packets are missed, or combined together, or corrupted, while routing. The receiver has to detect this and, if the packet was dropped, it will ask the sender to repeat it.
The Institute of Electrical and Electronics Engineers is an international non-profit, professional organization for the advancement of technology related to electricity. The IEEE helps the development of standards for maintaining a world class standard. It controls standards development and publishing. Developing value-added product and services for users is one of the key features of IEEE.
Factors effecting network performance
There are few factors that affect the performance of a network. Those factors will reduce the quality of service of the network. The major factors are Latency, Packet loss, Retransmission, Throughput, queuing delay.
Latency is the kinds of delays typically incurred in processing of network data. A low latency network connection is one that generally experiences small delay times, while a high latency connection generally suffers from long delays.
Although the peak bandwidth of a network connection is fixed according to the technology used, but the actual bandwidth which is obtained change over time and is affected by high latencies. Excessive latency creates bottlenecks that prevent data from filling the network pipe, thus decreasing effective bandwidth. The result of latency on network bandwidth can be temporary which may lasts for a few seconds or constantly depends on the source of the delays.
To measure the Network Latency tools like ping tests and trace-route are used. The measuring is done by determining the time it takes a given network packet to travel from source to destination and back, and this the so-called round-trip time. Round-trip time is not the only way to specify latency, but it is the most common.
Packet loss is the failure of one or more transmitted packets to arrive at their destination. There are various reasons for packet loss. Sometimes the signal may degrade over time. Sometimes hardware problems could originate packet loss. Networks that have too much demand and corrupted packets also might be a reason for packet loss.
If packet loss occurs, computers may try to recover that information. Once a packet is received, that computer sends a signal to the sending computer that it has been received. It will resend any packets for which it does not receive a signal if the sending computer does not receive a signal for every packet sent.
Commonly, it is not an issue to resend the packets, but sometimes there are some applications where resending packets is not possible. Resending a packet of lost information in such a case is not realistic. It also is true for voice communication applications. To some extent, it can be prevented by prioritizing the type of packets that are to be sent. Generally, there is not much the average computer user can do to avoid packet loss issues. If it is happening always on a local area network, such as in a business environment network's IT professional may offer some relief. By making sure the hardware is in proper working state can avoid the packet lost.
It means resending of packets which have been either damaged or lost. Retransmission is basic mechanisms which used by protocols operating on a packet switched computer network to provide consistent communication. Networks are usually varying, no guarantee for no delay or no damage, no packets lost and no unordered delivery will occur. Protocols which provide reliable communication on such networks use a combination of sending acknowledgments, retransmission of missing or damaged packets and checksums to make sure the reliability.
There are several forms of acknowledgments can be used in networking protocols. Positive Acknowledgement is one of the forms of sending acknowledgement. The receiver clearly notifies the sender which packets, messages, segments were received correctly. In the mean time it absolutely informs the sender which packets were not received even though they were sent and therefore may need to be retransmitted. Positive Acknowledgment with Retransmission is a method used by TCP to confirm receipt of transmitted data. This operates by re-transmitting data at well-known period of time until the receiving host acknowledges response of the data.
Negative Acknowledgment is another form of acknowledgment. The receiver clearly notifies the sender which packets, messages, or segments were received wrongly and therefore which may need to be retransmitted.
A Selective Acknowledgment (SACK) is the form which sends receiver clearly lists which packets, messages, or segments in a stream are acknowledged where negatively or positively.
A Cumulative Acknowledgment is another form which sends the receiver acknowledges that it correctly received a packet in a stream which absolutely informs the sender that the previous packets were received correctly.
Throughput is the rate at which a computer or network sends or receives data. It is a good measure of the channel capacity of a communications link, and connections to the internet are usually rated in terms of how many bits they pass per second (bit/s). When the number of buffers that the redirector reserves for network performance is increased it increases network throughput.
The queuing delay is the time a work waits in a queue awaiting it can be executed. It is a key component of network delay. This is the delay stuck between the point of entrance of a packet in the transmit line up to the real point of transmission of the message. This delay depends on the weight on the communication link. Queues may be caused by delays at the originating switch, intermediate switches, or the call receiver servicing switch. Queuing delay is increases if the buffer size increases. The longer the average waiting time is taken for the longer the line of packets. This is much preferable to a shorter buffer, which would result in ignored packets in turn it would result in much longer overall transmission times.
Network utilization is the ratio of current network traffic to the maximum traffic that the port can handle. It represents the bandwidth use in the network. So high network utilization means the network is busy, low network utilization means the network is idle. When network utilization exceeds the threshold limit it will slow down the transmission speed, intermittence, and request delay and so on. The challenge is to make sure there is no packet loss when network utilization reaches a certain value.
Importants and effects of network utilization
When the network unitilization is high users will exprience a slow down in response time. It will delay all the responses and may cause various issues like packet loss, incomplete transactions. This may result big business losts, for example banking transactions , bidding sysytem, etc.
Investigation of utilization
It is important to investigate the factors that can cause high network, and then those factors can be considered for managing such high performance networks.
The first factor that can cause high network unitization is the infrastructure of the network. Infrastructure is the plan of the internal network and the devices attached to it impact network performance. The response time of a request depend on response of all the components which are interconnected in a network for that operation.
As per Rule of thumb response time will be slow down when a component of the network is more than 70% utilized. The second factor that causes high network unitization is Internal Usage of a network. Some internal processes need a considerable amount of bandwidth under normal conditions such as teleconferences, data backups, VOIP phones, and even virus.
The third factor is the non-business related actions such as Internet radio streaming, informal web surfing, and viruses that have spoiled machines will cause high network utilization.
Experiments for utilization
Experiment the network unitization is an important aspect when we want to maintain a good bandwidth. There are much network utilization monitoring softwares available but we need to think about several issues that the network utilization tool may case. For example the tool could include delay on the network, inconsistent network availability, and possible virus. It should be make sure the product will support future plans, such as additional users, network changes and so on.
When experimenting about the network utilization, the information that should be collected from top sites users visit, information on the top users, optionally block certain sites, filters, alerts, catch and examine packets off the line (wireshark), Network sniffing and so on
OPNET Modeller 15.0
OPNET modeller is a comprehensive network developer tool, Graphical User Interface (GUI), Object oriented modelling, Integrated data analysis, More scalable and efficient simulation engine .
It is virtual network environment including routers, switches, servers, workstation, protocols and links. May analyse realistic network standard and to the future development.
OPNET workflows, create network model, choose individual statistic, run simulation, view results and analyse.
Mainly three editors in OPNET
Network editor, Topology of the network contains switches, routers, servers and links to simulate OPNET.
Node editor, internal infrastructure of the node where we can edit functional attribute of the node.
Process editor, each node generates process during the simulation behaviour and functionality described in process editor.
OPNET Modeller used in research and development process for analyzing and designing communication networks, devices, protocols, and applications. Modeller incorporates a broad suite of protocols and technologies, and includes a development environment to enable modelling of all network types and technologies including: VoIP (voice over internet protocol), TCP (transmission control protocol), OSPFv3 (Open Shortest Path First), MPLS (Multi-Protocol Label Switching), IPv6 (internet protocol), and others.