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8 Cards in this Set
- Front
- Back
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The Internet: * Communication b/w the browser and web server is done through the HTTP protocol * But connecting the browser and a web server on the internet is done through the TCP/IP protocol * Internet is a network of networks, and it uses the TCP/IP protocol * TCP/IP lets these networks connected by a number of routers to be thought of as a large network |
Basics: * A network is the connection between a number of computer to exchange information * Computers, routers, switches, hubs, cables, and the implementation of the protocols are needed to create a network. * Data is sent through the network in small chunks also knows as packet. * Each packet contains the data, but also the information used for delivery of the data * The network architecture is the design of the communication network |
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The role of the router: * Networks are connected with routers * They contain at least 2 network interface layers (link layers), because it connects two networks and forwards data between them two. It can have two or more network interface layers depending on how many networks there are Network hub: * A device for connecting multiple ethernet devices together and making them act as a single network segment Switches: * A device which connects devices together on a computer network by using packet switching to send, receive, and process data to the another device. |
Role of TCP/IP: * All computers that communicate on the internet use TCP/IP to send and recieve packets. * TCP/IP basically tells you: - The mechanism that computers use to find each other - The method of creating and destroying a connection between the computers - The mechanism for making sure the data exchange is error-free and that the packets were received in the correct order *TCP/IP does not bother with contents of data, only that the data is sent error-free and the destination has received it |
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TCP/IP * is a four layer protocol suite Application layer - what we need to send (HTTP, email) Transport layer - ways to send the data (TCP, UDP) Network layer - Figure out where to send the data (IP, ICMP, IGMP) Link (datalink) layer - how to send the data from your computer to the nearest (Ethernet, radio, mobile)
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Data communicated (how is exchanged between two computers on a network) : * Data is created by application. So as it travels down the TCP/IP protocol, the relevant protocol attaches information in form of a header * When data arrives at the destination, reverse happens. Data travels up the layers each protocol strips off and reads the corresponding header. * This way relevant layer communicate with the relevant layer. This is called peer to peer communications. |
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TCP/IP Layers in detail: Link layer (How to communicate the data with the other computer) : * Link layers is a combination of both datalink layer and the physical layer * On a network, computer communicate directly using the datalink layer. For this to happen, computers use an addressing mechanism, known as MAC (Media access control). This is a unique number that identifies a computer on the network * User communication occurs between two points, and can be through a media such as a physical line such as copper wire. * The factors that results in burstiness of an internet connection is the number of hops between you and the device you're communicating with. Delays occurs if theres terminators between you and the destination, different link level protocols etc. *Traceroute - traceroute sends out packets to the destination with a "time to live" counter starting at 1. It keeps increasing until the destination is reached. Each router decrements the TTL counter. When the counter gets to 0, the router sends back a ICMP error identifying itself and its time and date. |
Network layer: (Where to send the info) * is the layer at which the IP exists * Provides for the flow of data between two hots connected to the internet * IP has a number of features : - It provides an addressing scheme - It routes packets through the network - Its connectionless * Every interface on the internet has an unique 32 bit IP Address. It provides 2 pieces of information about a host. It tells us which network the host is located at and specifies which host it is on that network. * To do this: IP address contains a network portion and a host portion. * Netmask : is the traditional way to specify the network prefix. * Domain name services (DNS) - names are mapped to numbers using domain name services ( a searchable database of domain names and IP addresses) |
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ICMP/IGMP * IP by nature is unreliable. It offers the service but does not guarantee delivery. If doesn't tell the sender that the packet is lost. * Internet control messages protocol (ICMP) - - its a protocol built on top of IP - it can report simple errors (such as network being down, destination host being unknown) - It does not report lost packets or other failures, but it does stop the sender from keep sending when there is no success. *Internet group management protocol(IGMP) - This operates at the network layer and allows multiple devices to single IP address for broadcasts |
Transport layer (Ways to get the information there): * the flow of data is transparent to the method of transfer * The reliability of the data flow can be controlled by error-control, state control and flow control. * state information can be communicated through using networks * sessions can be created as using 'connections' |
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Transport layer: * Transmission control protocol (TCP) is a transport layer protocol * TCP is built on top of IP. Its more reliable. It parses data into packets , numbers each segment, and passes these to the network layer When a packet of data is sent from the sender, the destination must acknowledge each segment it receives. If the sender does not receive the acknowledgement it sends the segment again. It will keep sending copies of the segment if the acknowledgement takes longer than the timeout. If the segments traverse through different paths, they may be received out of order. This way TCP adds reliability over IP |
User datagram protocol (UDP) * Is also a transport layer protocol * TCP is robust - it guarantees delivery, but for many systems reliability is just an overhead. Meaning sometimes you don't really need that guarantee. * For these situations UDP is used. It does not guarantee delivery (just like IP), but it still does provide packet based service like TCP, providing a consistent interface to application software. * UDP is used when large amounts of data are sent, but reliability is not important, eg: streaming audio most likely uses UDP. Its used when lightweight connections are required. Printers also use it. |
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comparison b/w tcp and udp |
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Application layer (What to do with the information) : * What we do with the data depends on the application * Applications are defined as ports * Users can define their own ports * Ability to allocate temporary ports * Each application uses a port to identify itself. * TCP store in the header the port number that identifies an application, and also the service associated with that port. * As a system can support many application using many ports. Most applications spend most of their simply suspended waiting for requests on different ports. This is waste of resources. Instead a daemon, inetd, is used to listen to many ports and execute the application when the request arrives. |
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