Switching Systems
Private telephone switching systems are network devices that are small versions of telephone switching systems. Early key telephone switches used mechanical levers (crossbars) to interconnect lines. These were called key service units (KSUs). PBX systems use a time slot interchange (TSI) memory matrix to dynamically connect different communications paths through software control. Computer telephony and LAN telephony systems use packet switching systems to interconnect one of more telephone station with each other.
For large private telephone systems, some of the switching functions may be distributed to remote points. An example of distributed switching is the Nortel RPE that allows the Meridian PBX to remote a portion of its station interface to a remote site via a pair T1’s or E1’s.
Numbering Plan
Each extension in a private telephone system has a unique extension number. The station numbering plan for private telephone systems is controlled by the owner of the private telephone system. Many private systems have a limited range for extension numbers (e.g., 1000 -1999. This extension range is restricted due to hardware configurations.
When private telephone systems are interconnected to the public telephone network, the CCITT world numbering plan (E.164) and national numbering plans are used. PBX call processing systems are able to filter numbers to enable least cost routing (LCR). LCR is a telephone system feature that routes the connection of a call over the least expensive route available at the time the call is originated.
To allow automatic routing of incoming calls, direct inward dialing (DID), or higher-level trunk lines (e.g., T1 or E1) with advanced signaling may be used. DID connections are 2-wire trunk-side (network side) EO connections that provide additional information to the PBX to allow the automatic routing of calls within the PBX system. Although network signaling on incoming 2-wire circuits is primarily limited to one-way, incoming service, DID connections employ different supervision and address pulsing signals than dial lines. Typically, DID connections use a form of loop supervision called reverse battery, which is common for one-way trunk-side connections. Until recently, most DID trunks were equipped with either Dial Pulse (DP) or dual tone multifrequency (DTMF) address pulsing. While many carriers would have preferred to use multifrequency (MF) address pulsing, a number of LEC’s prohibited the use of MF on DID trunks.
Showing posts with label Private Telephone Networks. Show all posts
Showing posts with label Private Telephone Networks. Show all posts
Private Telephone Networks : Telephone Stations, Local Wiring
Telephone Stations
Telephone stations are telephone instruments that are connected to a telephone network for the purpose of telephony. When these telephone stations are used as part of the private network, they are often identified by the type of system they are connected with. For example, telephone stations that are connected to key systems are called key telephones.
Telephone stations can vary from simple POTS telephones (sometimes called 2500 telephones) to complex Internet telephones (IP Telephones). Telephone stations usually receive their power from the telephone line (loop current) but may receive it from an external source (such as the PBX switching system).
Figure 1 shows a typical telephone station that is used in a PBX system. This diagram shows the difference between standard analog telephone stations and more advanced PBX stations. This diagram shows that analog telephones receive their power directly from the telephone line and digital PBX telephones require a control section that gets its power from the PBX system. Analog telephones also use in-band signaling to sense commands (e.g., ring signals) and to send commands (e.g., send dialed digits). Digital telephones use out-of-band signaling on separate communication lines to transfer their control information (e.g., calling number identification).
Figure 1: Analog and Digital Telephone Stations
Local Wiring
The local wiring for private telephone systems includes the lines between the telephone stations and switching assemblies or interconnection equipment. Local wiring systems may include interconnection points or wiring rooms. Incoming trunks enter the building in a main distribution frame (MDF). Trunks between multiple floors or other buildings are called intermediate distribution frames (IDFs). These IDF areas are often referred to as “wiring closets” because in the past telecommunications wiring was seldom considered when designing a building and the space available for terminating cables was usually in utility closets.
Private telephone system wiring is usually connected through unshielded twisted pair (UTP) wire. There are exceptions where shielded cable, coaxial cable, or fiber is used. Shielded cable is used in areas the may cause or be sensitive to electromagnetic interference (EMI) such as hospital radiology areas or near high voltage equipment in manufacturing plants. Coaxial cable and fiber is used for high-speed data inter-connection trunks or for LAN backbone systems that are part of the private telephone system.
Figure 2 shows the typical wiring systems that are used for private telephone systems. Key systems required many pairs (12 or 25 pairs typical) of lines for each telephone. These telephones were wired to a punch block (splice point) near the telephones. The punch block was connected to the key service unit (KSU). Analog PBX systems usually required 4 wire connections from extension telephones to the PBX switching unit. Two wires were used for audio and two (or more) wires for status or special feature lines. Digital PBX systems connect to each extension using 4 wires. Two wires are used for audio (analog or digital) and two are used for external power. This diagram shows that some digital PBX systems may use multiplexed digital lines to allow multiple phones to share a single line (e.g., a line between building). When this occurs, it is called a remote peripheral equipment (RPE). The RPE separates (demultiplexes) the digital line from the PBX to multiple digital stations.
Figure 2: PBX Local Wiring
Telephone stations are telephone instruments that are connected to a telephone network for the purpose of telephony. When these telephone stations are used as part of the private network, they are often identified by the type of system they are connected with. For example, telephone stations that are connected to key systems are called key telephones.
Telephone stations can vary from simple POTS telephones (sometimes called 2500 telephones) to complex Internet telephones (IP Telephones). Telephone stations usually receive their power from the telephone line (loop current) but may receive it from an external source (such as the PBX switching system).
Figure 1 shows a typical telephone station that is used in a PBX system. This diagram shows the difference between standard analog telephone stations and more advanced PBX stations. This diagram shows that analog telephones receive their power directly from the telephone line and digital PBX telephones require a control section that gets its power from the PBX system. Analog telephones also use in-band signaling to sense commands (e.g., ring signals) and to send commands (e.g., send dialed digits). Digital telephones use out-of-band signaling on separate communication lines to transfer their control information (e.g., calling number identification).
Local Wiring
The local wiring for private telephone systems includes the lines between the telephone stations and switching assemblies or interconnection equipment. Local wiring systems may include interconnection points or wiring rooms. Incoming trunks enter the building in a main distribution frame (MDF). Trunks between multiple floors or other buildings are called intermediate distribution frames (IDFs). These IDF areas are often referred to as “wiring closets” because in the past telecommunications wiring was seldom considered when designing a building and the space available for terminating cables was usually in utility closets.
Private telephone system wiring is usually connected through unshielded twisted pair (UTP) wire. There are exceptions where shielded cable, coaxial cable, or fiber is used. Shielded cable is used in areas the may cause or be sensitive to electromagnetic interference (EMI) such as hospital radiology areas or near high voltage equipment in manufacturing plants. Coaxial cable and fiber is used for high-speed data inter-connection trunks or for LAN backbone systems that are part of the private telephone system.
Figure 2 shows the typical wiring systems that are used for private telephone systems. Key systems required many pairs (12 or 25 pairs typical) of lines for each telephone. These telephones were wired to a punch block (splice point) near the telephones. The punch block was connected to the key service unit (KSU). Analog PBX systems usually required 4 wire connections from extension telephones to the PBX switching unit. Two wires were used for audio and two (or more) wires for status or special feature lines. Digital PBX systems connect to each extension using 4 wires. Two wires are used for audio (analog or digital) and two are used for external power. This diagram shows that some digital PBX systems may use multiplexed digital lines to allow multiple phones to share a single line (e.g., a line between building). When this occurs, it is called a remote peripheral equipment (RPE). The RPE separates (demultiplexes) the digital line from the PBX to multiple digital stations.
Private Telephone Networks : Overview
Private Telephone Networks
Private telephone networks are communication systems that are owned, leased or operated by the companies that use these systems. These telephone systems include key systems, private branch exchange (PBX) systems, computer telephony, and local area network (LAN) telephones. Private telephone systems that are owned or operated by a company or private individual are called customer premises equipment (CPE).
Private telephone systems primarily allow the interconnection of multiple telephones within the private network with each other and provide for the sharing of telephone lines from a public telephone network. Private telephone systems can vary from simple multi-line telephones (key systems) to integrated voice and data service LAN telephone networks.
The first private telephone systems were key telephone systems. These systems used multi-line telephones to provide access to outside lines and used intercom features to allow inter-station connections.
As switching technology improved, small switching systems were installed to provide private branch exchange (PBX) systems. PBX systems provide switching between incoming trunk lines (multiple channel lines) and provide for advanced inter-system calling features.
To offer similar services as PBX systems, central exchange (Centrex) services were developed for end office (EO) switches. Centrex software allows local telephone companies to provide similar features as private telephone systems. These features include 3 or 4 digit abbreviated dialing, automated attendant (call transfer), least cost routing (LCR), and other local switching functions.
CTI systems integrate computer networks and telephony systems. CTI allows PBX technology to provide for voice mail, interactive voice response (IVR), and automatic call distribution (ACD) functions.
The combining of LAN systems with telephone systems is called LAN telephony. LAN telephony allows the sharing of equipment data network cost with telephone system cost.
Figure 1 shows the different types of private telephone systems. This diagram shows the first telephone systems were multiple line key telephone systems. This changed to private branch exchange (PBX) systems. Computer telephony (CT) systems are communication networks that merge computer intelligence with telecommunications devices and technologies. Local access network (LAN) telephony (sometimes called TeLANophy) use LAN systems to transport voice communications.
Figure 1: Private Telephone Systems
Overview
Private telephone systems are composed primarily of telephones (called “stations”), local wiring, and switching systems. Telephone stations are the interface between the user and the telephone network. Wiring connects telephone stations to switching systems or distribution points. Local wiring in private systems varies from shared lines (key systems) to individual lines (digital stations). Switching systems interconnect stations to each other or to outside telephone lines or interoffice trunks.
Companies purchase or lease private telephone system and have one or more of their personnel trained to handle day-to-day administrative functions of the system. Practically all PBX’s and key systems today are computer-based and thus allow for soft changes to be made through an administration terminal or PC. Unless the business has a need for technical telecommunications personnel on staff for other reasons, the business will normally contract with their vendor for routine adds, moves, and changes of telephone equipment.
PBX systems are often equipped with key assemblies and systems including voice mail, call accounting, a local maintenance terminal, and a dial-in modem. The voice mail system is controlled by the PBX only receiving calls when the PBX software determines a message can be left or retrieved. The call accounting system receives system message details on all call activities that occur within the PBX. The local terminal provides onsite access to the PBX for maintenance activities. The dial-in capability also provides access to the PBX for maintenance activities.
Private telephone networks are communication systems that are owned, leased or operated by the companies that use these systems. These telephone systems include key systems, private branch exchange (PBX) systems, computer telephony, and local area network (LAN) telephones. Private telephone systems that are owned or operated by a company or private individual are called customer premises equipment (CPE).
Private telephone systems primarily allow the interconnection of multiple telephones within the private network with each other and provide for the sharing of telephone lines from a public telephone network. Private telephone systems can vary from simple multi-line telephones (key systems) to integrated voice and data service LAN telephone networks.
The first private telephone systems were key telephone systems. These systems used multi-line telephones to provide access to outside lines and used intercom features to allow inter-station connections.
As switching technology improved, small switching systems were installed to provide private branch exchange (PBX) systems. PBX systems provide switching between incoming trunk lines (multiple channel lines) and provide for advanced inter-system calling features.
To offer similar services as PBX systems, central exchange (Centrex) services were developed for end office (EO) switches. Centrex software allows local telephone companies to provide similar features as private telephone systems. These features include 3 or 4 digit abbreviated dialing, automated attendant (call transfer), least cost routing (LCR), and other local switching functions.
CTI systems integrate computer networks and telephony systems. CTI allows PBX technology to provide for voice mail, interactive voice response (IVR), and automatic call distribution (ACD) functions.
The combining of LAN systems with telephone systems is called LAN telephony. LAN telephony allows the sharing of equipment data network cost with telephone system cost.
Figure 1 shows the different types of private telephone systems. This diagram shows the first telephone systems were multiple line key telephone systems. This changed to private branch exchange (PBX) systems. Computer telephony (CT) systems are communication networks that merge computer intelligence with telecommunications devices and technologies. Local access network (LAN) telephony (sometimes called TeLANophy) use LAN systems to transport voice communications.
Overview
Private telephone systems are composed primarily of telephones (called “stations”), local wiring, and switching systems. Telephone stations are the interface between the user and the telephone network. Wiring connects telephone stations to switching systems or distribution points. Local wiring in private systems varies from shared lines (key systems) to individual lines (digital stations). Switching systems interconnect stations to each other or to outside telephone lines or interoffice trunks.
Companies purchase or lease private telephone system and have one or more of their personnel trained to handle day-to-day administrative functions of the system. Practically all PBX’s and key systems today are computer-based and thus allow for soft changes to be made through an administration terminal or PC. Unless the business has a need for technical telecommunications personnel on staff for other reasons, the business will normally contract with their vendor for routine adds, moves, and changes of telephone equipment.
PBX systems are often equipped with key assemblies and systems including voice mail, call accounting, a local maintenance terminal, and a dial-in modem. The voice mail system is controlled by the PBX only receiving calls when the PBX software determines a message can be left or retrieved. The call accounting system receives system message details on all call activities that occur within the PBX. The local terminal provides onsite access to the PBX for maintenance activities. The dial-in capability also provides access to the PBX for maintenance activities.
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