L7- Building Telecommunication System (Part 2) Flashcards
Most of the lines in the telephone systems of the world at present are _______. Signals are transmitted as continuous waves. This is a satisfactory way to transmit voice.
Analog
The conversion of data from digital form into analog for transmission and then back into digital at the receiving end is done by a pair of interface devices
called
modems (modulator-demodulator)
Modem-based telecommunications have created a significant bottleneck in an environment where computer and peripheral speeds have increased dramatically. The solution is end-to-end __________ communications, in which signals are sent as streams of on/off pulses.
digital
Digital lines are capable of much faster communication and ______________ is now cheaper than analog. All the new equipment now installed in telephone networks is indeed digital.
digital circuitry
Trend: There is a shift toward digital telecommunications is taking place throughout the world. A digital system for telecommunications, called _____________, is in wide use in parts of the telephone network.
TI carrier
Future: ________________ - a completely digital telecommunications network standardized by an international committee.
Integrated Services Digital Network (ISDN)
With the geographical distribution of information systems, increased volumes of transmission, and the move to multimedia, the costs of telecommunications are a significant business concern. Two principal
methods of reducing these costs are:
- Multiplexing - the sharing of a high-capacity link by a number of transmissions
- Signal Compression - using the link more efficiently by removing redundancies from the signal.
Many individual transmissions can share a physical channel through a variety of techniques collectively called ______________. It combines several lower-capacity transmissions into a single transmission, which is split at the receiving end.
Multiplexing
It is the reduction of the need for channel capacity by
removing redundancies from the signal.
Signal compression
________________ differ in scope from relatively slow wide area networks, employed to transmit messages across vast geographic distances, to very fast local area networks that may connect computers located in the same building.
Computer networks
Computers, switches, and terminals interconnected by network links are collectively called _____
nodes
The purpose of network control is to provide a connection between nodes that need to communicate. The arrangement of nodes and links in a network is called a ______
topology
The following network topologies are the most widely used:
- Hierarchical Network
- Star Network
- Ring Network
- Bus Network
This topology matches the organizational structure of
many firms and is still frequently used in WANs. The user workstations may be, in turn, interconnected
using one of the LAN topologies.
Hierarchical Network
In this topology, a hub computer or switch (such as a PBX) interconnects a number of workstations. . The computer at the hub acts as the network server, providing access to the shared database and software. All communications between the workstations must go through this central mode.
Star Network
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.
Ring Network
The nodes 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.
Bus Network
Principal techniques for switching include:
- Circuit Switching
- Packet Switching
- Fast Packet Switching
It is a technique employed in a telephone network. Communication links are connected to switching centers, which connect to one node to another on demand. It is suitable for file transfers and similar longer transmissions.
Circuit switching
It 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.
It offers flexibility in connecting to a network. It is
used by most of the public data networks provided by value-added carriers.
Packet switching
In packet switching, messages are divided at the source into fixed-length chunks, called ___________, that also include bits identifying the receiver. Typically, a packet contains 128 bytes of data.
packets
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.
Fast Packet Switching
There are two fast packet-switching technologies being
introduced:
- Frame Relay
- Cell Relay (asynchronous transfer mode, or ATM)
Fast packet switching that checks a packet for errors only at the entry and exit nodes of the telecommunications network, thus reducing transmission delay.
Frame Relay
Fast packet switching that transfers very short
fixed-length packets, called cells, over fast LANs or WANs.
Cell Relay
Communication rules, called _______________, enable dissimilar hardware and software to communicate over a single network. All the nodes in the network must follow a set of rules.
protocols
International Standards Organization (ISO) has developed the OSI model in order to organizing protocols. The _______________ 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.
open system approach
OSI Layer and Function:
1. _____________ provides access to the telecommunications medium and ensures transmission of the bit stream over it.
Physical
OSI Layer and Function:
2. ____________ ensures error-free transmission of frames (blocks) of data over a network link.
Data Link
OSI Layer and Function:
3. ____________ routes messages (or packets) from source to destination by selecting connecting links.
Network
OSI Layer and Function:
4. ____________ provides reliable end-to-end connection between two communicating nodes. When packet switching is used this layer breaks a message into packets.
Transport
OSI Layer and Function:
5. ______________ 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.
Session
OSI Layer and Function:
6. _____________ provides any necessary conversions of the character being sent (encryption/decryption, compression/decompression, or character code conversions). Issue requests for establishing and
terminating a session to the session layer.
Presentation
OSI Layer and Function:
7. ____________ provides services to communicating application programs; examples include file transfer, running a remote program, allocating a remote peripheral, and ensuring integrity of remote databases.
Application
Two protocol sets have gained importance:
- SNA - IBM’s Systems Network Architecture
- its functions are broken down into five layers, basically performing the functions of the five middle OSI levels. - TCP/IP - Transmission Control Protocol/Internet Protocol
- its functions are broken down into five layers. 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
Interconnection between two networks of the same type is accomplished by a relatively simple ________, implemented in hardware and software.
bridge
Interconnection between dissimilar networks, for example, a LAN and a WAN, is achieved through a more complex _________. It is 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.
router
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
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).
A company with a large number of telephones (from 50 to over 10,000) often elects to own a computer-based ____________, an electronic switchboard that interconnects its telephones and provides
connections to the public network.
private branch exchange (PBX)
