Introduction A Communications Model pot

INTRODUCTION INTRODUCTION A Communications Model A Communications Model • Source – generates data to be transmitted • Transmitter – Converts data into transmittable signals • Transmission System – Carries data • Receiver – Converts received signal into data • Destination – Takes incoming data Simplified Communications Simplified Communications Model - Diagram Model - Diagram Simplified Data Simplified Data Communications Model Communications Model Networking Networking • Point to point communication not usually practical – Devices are too far apart – Large set of devices would need impractical number of connections • Solution is a communications network Simplified Network Model Simplified Network Model Wide Area Networks Wide Area Networks • Large geographical area • Crossing public rights of way • Rely in part on common carrier circuits • Alternative technologies – Circuit switching – Packet switching – Frame relay – Asynchronous Transfer Mode (ATM) Network Models Network Models Multi-layer Network Models Multi-layer Network Models • The process of transferring a message between sender and receiver is more easily implemented by breaking it down into simpler components. • Instead of a single layer, a group of layers are used, dividing up the tasks required for network communications. • The two most important such network models are the OSI and Internet models. The OSI Reference Model The OSI Reference Model • Stands for Open Systems Interconnection • Created by the International Standards Organization (ISO) as a framework for computer network standards • Released in 1984, the model has 7 layers [...]... ensure that hardware and software produced by different vendors can work together • The use of standards makes it much easier to develop software and hardware that link different networks because software and hardware can be developed one layer at a time The Standards Making Process Two types of standards: – Formal standards are developed by an official industry or government body – Defacto standards... alternatives 3 Acceptance, the most difficult stage: defining the solution and getting recognized industry leaders to agree on a single, uniform solution Telecommunications Standards Organizations • International Organization for Standards (ISO) – Member of the ITU, makes technical recommendations about data communications interfaces Telecommunications Standards Organizations • International Telecommunications... OSI 7-layer Model Application: provides a set of utilities used by application programs Presentation: formats data for presentation to the user, provides data interfaces, data compression and translation between different data formats Session: responsible for initiating, maintaining and terminating each logical session between sender and receiver Transport: deals with end-to-end issues such as segmenting... envelope and adds addressing information related to that layer • At the receiving end, messages travels up through the network layers, each layer removing the envelopes added when the message was sent Fig 1-4 Message transmission using layers NETWORK STANDARDS The Importance of Standards • Standards are necessary in almost every business and public service entity • The primary reason for standards is... transmitted through the network *same as corresponding layer in OSI model Network Models OSI v TCP/IP Message Transmission Using Layers • Network model layers use protocols, i.e., sets of rules to define how to communicate at each layer and how to interface with adjacent layers • Generally, messages travel down all network layers • When a message is sent to the next layer, that layer places it in an... Telecommunication Standardization Sector (ITU-TSS) – Technical standard setting organization of the UN ITU Formerly called the Consultative Committee on International Telegraph and Telephone (CCITT) – Comprised of representatives of over 150 Postal Telephone and Telegraphs (PTTs), like AT&T, RBOCs, or common carriers TC Standards Organizations – American National Standards Institute (ANSI) – Institute... the marketplace and supported by several vendors, but have no official standing The Standards Making Process Formal standardization process has three stages 1 Specification stage: developing a nomenclature and identifying the problems to be addressed 2 Identification of choices stage: those working on the standard identify the various solutions and choose the optimum solution from among the alternatives... Institute (ANSI) – Institute of Electrical and Electronics Engineers (IEEE) – Electronic Industries Association (EIA) – National Institute of Standards and Technology (NIST) – National Exchange Carriers Association (NECA) – Corporation for Open Systems (COS) – Electronic Data Interchange -(EDI) of Electronic Data Interchange for Administration Commerce and Transport (EDIFACT) ... Internet’s 5-Layer Model Application: used by application program Transport: responsible for establishing end-to-end connections, translates domain names into numeric addresses and segments messages Network*: responsible for end-to-end addressing and routing, determines destination address if unknown Data Link*: deals with message delineation, error control & network access Physical*: defines how information... message for network transport, and maintaining the logical connections between sender and receiver Network: responsible for making routing decisions Data Link: deals with message delineation, error control and network medium access control Physical: defines how individual bits are formatted to be transmitted through the network The OSI Environment OSI as Framework for Standardization Layer Specific Standards . OSI as Framework for OSI as Framework for Standardization Standardization Layer Specific Standards Layer Specific Standards Elements of Standardization Elements of Standardization • Protocol. INTRODUCTION INTRODUCTION A Communications Model A Communications Model • Source – generates data to be transmitted • Transmitter – Converts data into transmittable signals • Transmission. System – Carries data • Receiver – Converts received signal into data • Destination – Takes incoming data Simplified Communications Simplified Communications Model - Diagram Model - Diagram