Feature Interactions in Telecommunications and Software Systems VII
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Distributed Feature Composition DFC is a modular architecture for telecommunication services, designed to provide structured feature composition and easy management of feature interactions. Zave holds 30 patents in the telecommunications area. Zave's work on finding bugs in the Chord protocol  and proving a modified version correct  has been credited by engineers in Amazon Web Services for convincing them to start using formal methods on real distributed systems.
From Wikipedia, the free encyclopedia. Mills Award , retrieved Namespaces Article Talk. The nodes are usually close to one another; this topology is frequently used in LANs. When one node sends a message to another, the message passes through each intermediate node, which restores the signal, as signals deteriorate in transmission.
If a node fails, the ring is out of service, unless the ring contains two channels transmitting in opposite directions. Bus Network : [Figure 7. The nodes on a bus network are connected to a common link such as coaxial cable. This arrangement is used in LANs.
A failing device does not affect the rest of the network; failure of the bus itself, of course, brings the network down. Switching in Networks. Many users can be connected at the same time to a network of communication channels. Switching devices establish connections between nodes that need to communicate over a network. Principal techniques for switching include:. Fast Packet Switching. The circuit switching technique is employed in a telephone network.
Communication links are connected to switching centers, which connect to one node to another on demand. The circuit is established for the entire duration of the communication. Circuit switching is suitable for file transfers and similar longer transmissions. Packet Switching: [Figure 7. Packet switching is of particular importance for data communication owing to its speed and its superior utilization of communication links when handling Abursty, intermittent, traffic. Indeed, data transmission involves short bursts of activity by a computer or a terminal when the data are sent, followed by long periods when there is no transmission.
Packet switching offers flexibility in connecting to a network. It is used by most of the public data networks provided by value-added carriers. In packet switching, messages are divided at the source into fixed-length chunks, called packets , that also include bits identifying the receiver. Typically, a packet contains bytes of data. Each packet, can be transmitted independently, with routing determined at each node the packet passes through as opposed to circuit switching, where the route is predetermined.
Fast Packet Switching :. Traditional packet switching checks each packet for errors at every node the packet passes through. Modern telecommunications equipment is far more noise-free than that for which packet switching was originally designed. To take advantage of this, two fast packet-switching technologies are being introduced:. Frame Relay : Fast packet switching that checks a packet for errors only at the entry and exit nodes of the telecommunications network, thus reducing transmission delay.
Communication rules, called protocols , enable dissimilar hardware and software to communicate over a single network. Network Protocols [Figure 7. Computer networks exist to provide connectivity among a variety of computers and access devices. To ensure orderly communication over a network, all the nodes in the network must follow a set of rules called protocols. These rules are complex. They extend from the electric connection to the network and the format of the message, all the way to the interaction between application programs that run on different nodes. Explain to students that with the globalization of telecommunications, the International Standards Organization ISO has developed the OSI model in order to organizing protocols.
The open system approach opens the field to a broad array of competing vendors, a situation that benefits users to ensure that they are not locked into a closed, proprietary protocol structure of a specific manufacturer. Gives both users and vendors flexibility in conforming to a standard. Users can select a protocol for any layer of the model, as long as the protocol performs the necessary services and provides the same interface to the adjacent layers.
If a layer has to be changed, only the hardware or software implementing that layer need be modified. A protocol layer in one node interacts with the corresponding layer in another one. Table 7. Layer and its Function. Physical Provides access to the telecommunications medium and ensures transmission of the bit stream over it. Data Link Ensures error-free transmission of frames blocks of data over a network link.
Network Routes messages or packets from source to destination by selecting connecting links. Transport Provides reliable end-to-end connection between two communicating nodes. When packet switching is used this layer breaks a message into packets. Session Establishes, maintains, and terminates a connection session between two applications running on communicating nodes. A session lasts, for example, from a long-on to a specific application to a log-off.
Issue requests for establishing and terminating a session to the session layer. Application Provides services to communicating application programs; examples include file transfer, running a remote program, allocating a remote peripheral, and ensuring integrity of remote databases. Two protocol sets have gained importance:. TCP provides the higher-level services in connecting the communicating applications, while IP ensures the lower-level functions of routing and addressing, guiding the packets over the Internet. Interconnections among Networks. As communication needs increase, network connectivity becomes a major issue as users want to access a remote computer.
Gateways such as routers and bridges help solve the problem. Interconnection between two networks of the same type is accomplished by a relatively simple bridge , implemented in hardware and software. A router is a device that accepts messages in the format produced by one of the networks and translates them into the format used by the other. Organizations small and large use fast local area networks LANs to interconnect personal computers, and thus make a basic workgroup tool. Local Area Network: Workplace for a Workgroup.
A LAN interconnects computers within a single site, such as an office building, a manufacturing plan, or a corporate or university campus. Characteristics of a LAN include:. Its scope is commonly measured in feet. Communication speeds are very high. Used as a local means of computing and communication among users in larger firms. Are owned by the organization.
Afford a sense of control and the flexibility to meet the demands of the end users. A LAN gives its users the following capabilities:. Users can share resources, such as a fast printer or a database. Users can collaborate by communicating over their LAN. This collaboration may be facilitated by groupware that runs on a LAN.
Users can access other networks within a firm or outside of it via bridges and routers. There are two principal LAN designs :. Peer-to-peer - peripherals are located at terminals and system administration is largely left up to the users. Server-based networks - shared resources are placed a dedicated server that manage a given resource on behalf of user workstations sharing the resource file server, printer server, gateway, optical disk server. Most of the servers are dedicated to their task; using them as workstations degrades the performance of the net. A company with a large number of telephones from 50 to over 10, often elects to own a computer-based private branch exchange PBX , an electronic switchboard that interconnects its telephones and provides connections to the public network.
Characteristics of a PBX:. Gives a company control over the usage of its telephone system and offers a variety of features, such as call forwarding or voice messaging. Maybe employed as a switch for data communications. Many newer PBXs use digital technology, eliminating the need for modems, and perform conversions needed to ensure connectivity between various equipment and telecommunications links.
Easy to connect a new workstation to the net. Speeds of PBX-based networks are limited. An important current development in organizational computing is downsizing - moving from platforms based on mainframes and minicomputers to a microcomputing environment. The processing of a given application is split up among a number of clients - serving individual users - and one or more servers - providing access to databases and doing most of the computing. Main objective of a client is to provide a graphical user interface to a user. Main objective of a server is to provide shared services to clients.
Two-Tier Architecture. Three-Tier Architecture. Characteristics of Two-Tier Architecture: [Figure 7. Client performs presentation services. It displays the GUI and runs the program that determines what happens when the user selects a menu option. Server manages the accesses to the database. Clients send remote procedure calls to activate specific applications logic on a server.
Characteristics of Three-Tier Architecture: [Figure 7. An application server runs most of the application logic, with the user workstation responsible for the display at the front end and the database server providing database servers at the back end. Objective is to distribute application so as to reduce the overall hardware costs while minimizing the network traffic.
Is attractive in terms of their acquisition price as related to their performance. Is moving computing control out of the data centers and into the end-user areas. Software is complex, and is expensive to maintain. Generate significant traffic on the firm's backbone network that connects clients and servers. Wide area networks are the fundamental infrastructure of organizational computing. These long-distance telecommunications networks employ a variety of equipment so that the expensive links may be used effectively.
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Feature Interactions in Telecommunications and Software Systems
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