* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Communication systems
Survey
Document related concepts
Cracking of wireless networks wikipedia , lookup
Wake-on-LAN wikipedia , lookup
Airborne Networking wikipedia , lookup
Low-voltage differential signaling wikipedia , lookup
Computer network wikipedia , lookup
Zero-configuration networking wikipedia , lookup
Deep packet inspection wikipedia , lookup
Routing in delay-tolerant networking wikipedia , lookup
Communication protocol wikipedia , lookup
Recursive InterNetwork Architecture (RINA) wikipedia , lookup
Transcript
Communication systems Communication systems enable people and systems to share and exchange data and information electronically. This communication occurs between transmitting and receiving hardware and software over a network- each device on a network is called a node. Diagram: Communication system framework from NSW Board of Studies IPT syllabus (modified). Protocols- set of rules that components agree on for the communication to be successful. Protocols are classified according to the level or layer in which they operate. Handshaking- establishing and agreeing on which set of protocols will be used and the specific detail of each protocol must occur before any data can be transmitted or received. 7. Application Presentation 6. Presentation 5. Session 4. Transport Communication and control 3. Network 2. Data link 1. Physical Transmission Diagram: Comparison of the seven layers of the OSI model with the three levels used in IPT. Characteristics of communication system Overview of protocol levels Software used to control and direct the operation of hardware. The transmitter and the receiver must agree on how the hardware will be used to transfer messages. A large variety of applications transfer data sing a wide variety of operating systems, protocols, devices and transmission media. IPT presentation level 7. OSI application layer- the actual data to be transmitted is created by a software application, this data is organized in a format understood by the application that will receive the data. 6. OSI presentation layer - the data is reorganized into a form suitable for subsequent transmission. IPT communication control and addressing level 5. OSI session layer - this is where communication with the network is established, commences and is maintained. It determines when a communication session is started with a remote computer and also when it ends. 4. OSI transport layer - the transport layer manages the correct transmission of each packet of data. This layer ensure that packets failing to reach their destination are retransmitted. IPT transmission level 2. OSI data link layer - this layer defines how the transmission media is actually shared. Device drivers that control the physical transmission hardware operate at this layer. 1. OSI Physical layer – this layer performs the actual physical transfer, hence it is composed solely of hardware. It converts the bits in each message into the signals that are transmitted down the transmission media. Mac Address – Media Access Controller. Address hardwired into each device. A hardware address that uniquely identifies each node on a network. Overview of how messages are passed between source and destination 1. Message creation – The message is compiled at the source in preparation for sending, using some type of software application, and perhaps collection of message data from one of the system’s users or participants. 2. Organisation of packets at the interface between source and transmitter – message descends the stack of protocols from the application level down to where t is ready for physical transmission by the hardware operating at the transmission level. Each protocol wraps the data packet from the layer above with its own header and trailer. 3. Signal generation by the transmitter – physical hardware that generate or encodes the data onto the medium creating a signal. In most cases transmitters and receivers decode the signal on the medium. This hardware is controlled by protocols operating at the transmission level. 4. transmission – as the signal travels or propagates through the medium. Each bit or often pattern of bits moves from transmitter to receiver as a particular waveform. 5. Synchronizing the exchange – to accurately decode the signal requires the receiver to sample the incoming signal using precisely the same timing used by the transmitter during encoding. This ensures each symbol or waveform is detected by the receiver. 6. Addressing and routing – during transmission data packets may ass through many different and varied links - particularly when the communication is over the internet. Furthermore it is likely that packets forming part of a single file will travel over quite different paths from the transmitter to the receiver. Each new communication link will have its own protocol or set of protocols and hence each packet must ascent the protocol stack unitil it reaches the addressing or routing protocol and then descent the protocol stack as it is prepared for transmission down the next path. Ethernet and other transmission level protocols use the receiver’s MAC address to determine the path leading to the receiver. 7. Error detection and correction – as message descent the stack prior to transmission many protocols calculate checksums or CRC (cyclic Redundancy check) values and include the within their headers or footers. 8. Security and management – Many protocols restrict messages based on usernames and passwords, and other go a step further by encrypting messages during transmission Protocols A formal set of rules and procedures that must be observed for two devices to transfer data efficiently and successfully. POP - (Post office protocol), application layer internet standard protocol used by the local email clients to retrieve email from a remote server over a TCP/IP connection. TCP/IP – (transmission control protocol/internet protocol) SMTP – (simple mail transfer protocol) is an Internet standard for electronic mail (e-mail) transmission across Internet Protocol (IP) networks. MIME – (multipurpose internet mail extension) is an internet standard that extends the format of email to support; text in characters sets other than ASCII, non-text attachments, message bodies with multiple parts, header information in non-ASCII character sets. HTTP – (Hypertext transfer protocol) is an application layer protocol for distributed, collaborative, hypermedia information systems. FTP – (file transfer protocol) is a standard network protocol used to copy a file from one host to another over a TCP/IP – based network, such as the internet. SSL (secure socket layer) are cryptographic protocols that provide security for communications over networks such as the internet. Ethernet – operates at the IPT transmission level including OSI data link layer 2 and also at the OSI physical layer 1. Using Ethernet it is possible for two nodes to transmit a frame at the same time. If these nodes share the same physical transmission line then a data collision will occur and both frames will be corrupter. Ethernet uses a system called carrier sense multiple access with collision detection (CSMA/CD) to deal with such collisions. Modern Ethernet networks prevent collisions altogether through the use of switches where just two nodes (including switches) exist on each segment.