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Computer networking

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lan vs wan, port,dtu, connection, computer networking, osi model v

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Ocampo, Amerita B. ECE-551

ICE- 5203 December 15,2013

1. Carrier Sense Multiple Access With Collision Detection (CSMA/CD) Carrier Sense Multiple Access With Collision Detection (CSMA/CD) is a media access control method used most notably in local area networking using early Ethernet technology. It uses a carrier sensing scheme in which a transmitting data station detects other signals while transmitting a frame, and stops transmitting that frame, transmits a jam signal, and then waits for a random time interval before trying to resend the frame. CSMA/CD is a modification of pure carrier sense multiple access (CSMA). CSMA/CD is used to improve CSMA performance by terminating transmission as soon as a collision is detected, thus shortening the time required before a retry can be attempted.

Simplified Algorithm of CSMA/CD http://en.wikipedia.org/wiki/Carrier_sense_multiple_access_with_collision_detection The terms LAN and WAN are often confusing for people that aren’t that tech savvy. These are both connections that allow users to connect their computer to a network, including the internet. LAN is short for Local Area Network, while WAN is short for Wide Area Network. These two differ from each other in distinct ways. 2. LAN vs WAN

LAN is a computer network that connects computers in small areas such as home, office, school, corporation, etc. using a network media. It is useful for sharing resources such as printers, files, games, etc. A LAN network includes a couple of computer systems connected to each other, with one system connected to a router, modem or an outlet for internet access. The LAN network is built using inexpensive technologies such as Ethernet cables, network adapters and hubs. However, other wireless technologies are also available to connect the computer through a wireless access. In order to configure a LAN network, a person may also require specialized operating system software. The most popular software includes the Microsoft Windows’ Internet Connection Sharing ( ICS), which allows users to create LAN. The first successful LAN network was created by Cambridge University in 1974 known as the Cambridge Ring; however it was not commercialized until 1976 by Datapoint Corporation. Datapoint’s ARCNET was installed at Chase Manhattan Bank in New York in 1977. The main purpose of creating a LAN was to share storage and other technologies such as printers, scanners, etc. The smallest LAN can include two computers, while the largest can, in theory, support 16 million devices according to About.com. Wikipedia states that “the larger LANs are characterized by their use of redundant links with switches using the spanning tree protocol to prevent loops, their ability to manage differing traffic types via quality of service (QoS), and to segregate traffic with VLANs.” The larger LANs also employ other devices such as switches, firewalls, routers, load balancers, and sensors.

WAN is a network that covers a broad area using private or public network transports. The best example of WAN would be the Internet, which can help connect anyone from any area of the world. Many businesses and government use WAN in order to conduct business from anywhere in the world. WANs are also responsible largely for businesses that happen across the world (i.e. a company in UK does business with a company in China). The basic definition of WAN includes a network that can span regions, countries, or even the world. However, in practicality, WAN can be viewed as a network that is used to transmit data over long distances between different LANs, WANs and other networking architectures. WANs allow the computer users to connect and communicate with each other regardless of location. WAN uses technologies such as SONET, Frame Relay, and ATM. WANS allow different LANs to connect to other LANs through technology such as routers, hubs and modems. There are four main options for connecting WANs: Leased line, Circuit switching, Packet switching and Call relay. Leased lines are point-to-point connection between two systems. Circuit switching is a dedicated circuit path between two points. Packet switching includes devices transporting packets via a shared single point-topoint or point-to-multipoint link across a carrier internetwork. Call relay is similar packet switching but uses fixed length cells instead of variable length packets. LANs are become more and more common in many places such as offices, corporations, homes, etc. A main reason for their growing popularity is that they are cheaper to instill and offer higher transfer speeds. LANs offer speeds up to 80 or 90 mbps due to the proximity of the computer systems to each other and lack of congestion in the network. In comparison, WANs can provide a speed of 10 to 20 mbps. Also LANs offer better security compared to WANs, which are more easily accessible with the people that know how to hack systems. WANs and LANs can be secured using firewalls, anti-virus and spyware softwares. http://www.differencebetween.info/difference-between-lan-and-wan 3. TCP/IP Model vs OSI Model A Comparison of Network Models There are two network models that describe how networks 'work'. The OSI Model, the older model, was designed for the OSI protocol stack. While different organizations were

battling over standards, Vint Cerf and Bob Khan worked out the TCP/IP software from which the TCP/IP Model was co-designed. The diagram below shows how the two networking models compare, and how the logical and physical networking protocols relate to the layers in each of the two models. .

There are seven layers in the OSI Model, only four in the TCP/IP model. This is because TCP/IP assumes that applications will take care of everything beyond the Transport layer. The TCP/IP model also squashes the OSI's Physical and Data Link layers together into the Network Access Layer. Internet Protocol really doesn't (and shouldn't) care about the hardware underneath, so long as the computer can run the network device and send IP packets over the connection http://www.inetdaemon.com/tutorials/basic_concepts/network_models/comparison.shtml

4. PDU In telecommunications, the term protocol data unit (PDU) has the following meanings: 1. Information that is delivered as a unit among peer entities of a network and that may contain control information, such as address information, or user data.

2. In a layered system, a unit of data which is specified in a protocol of a given layer and which consists of protocol-control information and possibly user data of that layer. For example: Bridge [1] PDU or iSCSI PDU PDUs are relevant in relation to each of the first 4 layers of the OSI model as follows:
[2]

1. The Layer 1 (Physical Layer) PDU is the bit or, more generally, symbol (can also be seen as "stream") 2. The Layer 2 (Data Link Layer) PDU is the frame 3. The Layer 3 (Network Layer) PDU is the packet 4. The Layer 4 (Transport Layer) PDU is the segment for TCP, or the datagram for UDP Given a context pertaining to a specific OSI layer, PDU is sometimes used as a synonym for its representation at that layer. http://en.wikipedia.org/wiki/Protocol_data_unit

5.Port In computer networking, a port is an application-specific or process-specific software construct serving as a communications endpoint in a computer's host operating system. A port is associated with an IP address of the host, as well as the type of protocol used for communication. The purpose of ports is to uniquely identify different applications or processes running on a single computer and thereby enable them to share a single physical connection to a packet-switched network like the Internet. The protocols that primarily use ports are the Transport Layer protocols, such as the Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP) of the Internet Protocol Suite. A port is identified for each address and protocol by a 16-bit number, commonly known as the port number. The port number, added to a computer's IP address, completes the destination address for a communications session. That is, data packets are routed across the network to a specific destination IP address, and then, upon reaching the destination computer, are further routed to the specific process bound to the destination port number. Note that it is the combination of IP address and port number together that must be globally unique. Thus, different IP addresses or protocols may use the same port number for communication; e.g., on a given host or interface UDP and TCP may use the same port number, or on a host with two interfaces, both addresses may be associated with a port having the same number. Of the thousands of enumerated ports, about 250 well-known ports are reserved by convention to identify specific service types on a host. In the client-server model of application architecture, ports are used to provide a multiplexing service on each server-side port number that network clients connect to for service initiation, after which communication can be reestablished on other connection-specific port numbers. http://en.wikipedia.org/wiki/Port_(computer_networking) 6. Decoded AppData AppData helps developers and financial firms analyze mobile apps across the Facebook, Apple iOS, and Google Play platforms. Our research services offer Facebook MAU/DAU estimates, iOS revenue & download estimates, and Google Play app rankings.

Package appdata implements a HTTP Handler that rewrites the request based on the presense of a signed_request containing app_data. This allows for Page Tabs on facebook.com to dispatch to standard URLs using base64 URL encoded app_data. https://godoc.org/github.com/daaku/go.signedrequest/appdata 7. Why networking models are used?

However, if this is to be done, we must have a way of ensuring that these various pieces can interoperate; that is, each must know what is expected of it, and also what it can expect from the other pieces. This is one of the important roles of networking models. They split the multitude of tasks required to implement modern networks, into smaller chunks that can be more easily managed. Just as importantly, they establish “walls” between those pieces, and rules for passing information over those walls. A good analogy of a networking model is to that of an assembly line at a manufacturer. No company attempts to have one person build an entire car; even if they did, they wouldn't expect that individual to be able to learn how to do it all at once. The division of labor offers several advantages to a company that builds a complex product, such as an automobile. Generally speaking, these include the following: o Training and Documentation: It is easier to explain how to build a complex system by breaking the process into smaller parts. Training can be done for a specific job without everyone needing to know how everything else works. Specialization: If everyone is responsible for doing every job, nobody gets enough experience to become an expert at anything. Through specialization, certain individuals develop expertise at particular jobs. Easier Design Modification and Enhancement: Separating the automobile into systems, and particular jobs required to build those systems, makes it easier to make changes in the future. Without such divisions, it would be much more difficult to determine what the impact might be of a change, which would serve as a disincentive for innovation. Modularity: This is related to each of the items above. If the automobile's systems and manufacturing steps are broken down according to a sensible architecture or model, it becomes easier to interchange parts and procedures between vehicles. This saves time and money.

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Networking models yield very similar benefits to the networking world. They represent a framework for dividing up the tasks needed to implement a network, by splitting the work into different levels, or layers. Hardware and software running at each layer is responsible for interacting with its corresponding hardware and software running on other devices at the same layer. The responsibilities of each hardware or software element are defined in part by specifically delineating lines that exist between the layers. The result is that you get all of the benefits listed in the bullet points above: easier training, specialized capabilities at each layer, improved capabilities for modification, and modularity. Modularity is particularly important, as it allows you to interchange technologies that run at different layers. While nobody would try to build a vehicle that is partly a compact sedan, partly an SUV and partly a motorcycle, there are situations in networking where you may want to do something surprisingly similar to this. Networking models help make this possible. http://www.tcpipguide.com/free/t_TheBenefitsofNetworkingModels.htm

8. Explain the postal network, metaphor for decapsulation? The picture below shows how postal network works. The network is composed of different bodies and components. The bodies have coordination and communicate with one another in able to send a mail from one point to another.

The same story applies for any data which needs to be sent from one computer to another. The OSI model which was created by the IEEE committee is to ensure that everyone follows these guidelines (just like the production line above) and therefore each computer will be able to communicate with every other computer, regardless of whether one computer is a Macintosh and the other is a PC. One important piece of information to keep in mind is that data flows 2 ways in the OSI model, DOWN (data encapsulation) and UP (data decapsulation).

The receiving computer will firstly synchronize with the digital signal by reading the few extra 1's and 0's as mentioned above. Once the synchonization is complete and it receives the whole frame and passes it to the layer above it which is the Datalink layer. The Datalink layer will do a Cyclic Redundancy Check (CRC) on the frame. This is a computation which the comupter does and if the result it gets matches the value in the FCS field, then it assumes that the frame has been received without any errors. Once that's out of the way, the Datalink layer will strip off any information or header which was put on by the remote system's Datalink layer and pass the rest (now we are moving from the Datalink layer to the Network layer, so we call the data a packet) to the above layer which is the Network layer. At the Network layer the IP address is checked and if it matches (with the machine's own IP address) then the Network layer header, or IP header if you like, is stripped off from the packet and the rest is passed to the above layer which is the Transport layer. Here the rest of the data is now called a segment. The segment is processed at the Transport layer, which rebuilds the data stream (at this level on the sender's computer it was actually split into pieces so they can be transferred) and acknowledges to the transmitting computer that it received each piece. It is obvious that since we are sending an ACK back to the sender from this layer that we are using TCP and not UDP. Please refer to the Protocols section for more clarification. After all that, it then happily hands the data stream to the upper-layer application. You will find that when analysing the way data travels from one computer to another most people never analyse in detail any layers above the Transport layer. This is because the whole process of getting data from one computer to another involves usually layers 1 to 4 (Physical to Transport) or layer 5 (Session) at the most, depending on the type of data.

http://visual.merriam-webster.com/communications/communications/public-postal-network/public-postalnetwork.php http://www.firewall.cx/networking-topics/the-osi-model/179-osi-data-encapsulation.html

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