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ATT DEFINITY Communications System Generic 3 Instructions Manual
ATT DEFINITY Communications System Generic 3 Instructions Manual
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Data Management Issue 3 March 1996 2-15 The EIA RS-232D protocol provides two interface connectors. The female side connector is known as data communications equipment (DCE). The male side connector is known as data terminal equipment (DTE). Data equipment manufacturers design either the DCE or DTE interface into their products. Products such as modems, data service units (DSUs), Digital Terminal Data Modules (DTDMs), and Processor Data Modules (PDMs) have a built-in DCE interface. Products such as some typ es of multiplexers, data terminals, printers, computer ports, and Trunk Data Modules (TDMs) have a built-in DTE interface. Modular Data Modules (MDMs) can be configured as either DCE or DTE. The maximum c a ble length recommended by EIA for the EIA RS-232D protocol is 25 feet (15 meters). However, practical applications have shown that the cable length can be much greater. Factors limiting cable length include transmission speed, cable capacitance, and nearness of noise sources such as fluorescent lights or electric generators. Each a p plication should be considered separately. RS-449 This protocol allows longer c a bles than the EIA RS-232D. Maximum cable lengths for various data speeds are as follows: n19.2 kb ps — 200 feet (61 meters) n9.6 kbps — 400 feet (122 meters) n4.8 kbps — 800 feet (244 meters) n2.4 kbps — 1,600 feet (488 meters) The RS-449 protocol is provided as a communications link interface on the Applications Processor (AP). This standard uses a 37-conductor c a ble. The AP RS-449 interface contains unbalanced driver/receivers that also permit interconnection to the EIA RS-232D interface when used with a 37- to 25-pin cable adapter. Since the AP RS-449 interface is compatible with the EIA RS-232D protocol, it also is limited to the same maximum 19.2 k b ps data rate. RS-366 The RS-366 communications protocol specifies the standards for interfacing computers to ACUs. This permits a computer to originate data calls over a switched telephone network. The AP provides one RS-366 interface for each six EIA RS-232D interface ports. Digital Communications Protocol (DCP) Interface The DCP is used by the system’s d i gital switch, d i gital voice terminals, data modules, the 510D terminal, and the 515 BCT. This protocol permits simultaneous voice and data over the same communications link to the switch. The DCP consists of a 160 k bps, four-wire serial data link that operates full-duplex over standard twisted-pair building cable. For data-only transmission,
Functional Description 2-16Issue 3 March 1996 the maximum cable length is 5,000 feet (1,524 meters). When voice and data transmission is carried over the same data link, as when a 510D terminal, 515 BCT, or a DTDM is used , the cable length is limited by the voice transmission distance. The D CP sends digitized voice and digital d ata in frames. Each frame consists of four fields or channels (see Figure 2-3). The first field is a unique three-bit framing pattern that defines the frame boundary. The second field is a one-bit control or signaling channel between the digital switch and di gital data endpoint. The third and fourth fields are two independent information (I) channels. The information channels are eight bits each and are used to send digitized voice or digital data. Figure 2-3. Digital Communications Protocol Frame Structure There are 8,000 frames per second. Therefore, the bit rate available is eight for the signaling channel and 64 kbps for the information channel. The digital switch routes each information channel independently so that simultaneous voice and data can be completed to different destinations. The full capacity of the information channels (64 kbps) is available for digitized voice. Data terminals typically operate at speeds from below 300 bps up to 19.2 kbps, asynchronous or synchronous. The DCP uses data modules to map the data terminal data into a 64 kb ps information channel. The framing rate of 8,000 per second and eight bits per information channel is consistent with other telecommunication systems such as the DS1/E1 carrier. This minimizes potential conversion problems when interfacing to d ifferent digital facilities. BX.25 Packet Switching Protocol The BX.25 protocol implements the international standard for packet switching. It is a multilayered protocol. [Layering is a structuring of specific p rotocol functions (for example, error detection and correction) that are grouped together as a unique layer or level.] FRAMING FIELDSIGNALINFORMATION #1INFORMATION #2FRAMING FIELD DCP FRAME
Data Management Issue 3 March 1996 2-17 The BX.25 protocol is similar to the ITU-T X .2 5 protocol and, from a user perspective, is compatible with the standard . The BX.25 protocol has three layers that are not specified for the X.25 protocol. These layers are Application, Presentation, and Session. The A pp lication and Presentation layers are defined in the Transa ction-Oriente d Protocol (TOP) of the BX.25. The TOP is a high-level protocol, intended to standardize communications between transaction-oriente d systems. Transaction-oriented communications involve communication of small messages or requests describing a single unit of work that may result in a reply being sent b ack to the originating system. The Session layer is intended to establish, manage, and terminate sessions for use by higher-level protocols or, in some cases, by user applications directly. Other differences between X.25 and BX.25 are as follows: nThe X.25 protocol specifies network standards only; the BX.25 protocol places requirements on the user interface as well. nThe X.25 protocol p rovides for d atagram services while the BX.25 p rotocol does not. Datagram service has not been implemented within the continental United States. nThe X.25 protocol leaves the users in a point-to-point environment to develop their own solutions to the following areas of potential conflict, while the BX.25 protocol provides solutions: — Link layer a d dressing — Logical channel selection — Call collision Basic elements of the Application and Presentation layers must be user defined under both protocols. The following figures shows the relationship and similarity between the BX.25 and X.25 protocols. The BX.25 protocol is used in the system to provide communications between the switch and the switch-related features. The BX.25 p rotocol is also used in the system to provide communications between the switch and the AUDIX and to provide communication between DCS switches
Functional Description 2-18Issue 3 March 1996 Figure 2-4. BX.25 Packet-Switching Protocol USER APPLICATION LAYER PRESENTATION LAYER SESSION LAYER NETWORK LAYER DATA L IN K LAYER PHYSICAL LAYER TRANSPORT LAYER ------ ------ --- BX.25 Protocol LayersUSER PACKET LAYER LINK LAYER PHYSICAL LAYER SESSION LAYER T O P*
Data Management Issue 3 March 1996 2-19 Figure 2-5. X.25 Packet-Switching Protocol USER PACKET LAYER LINK LAYER PHYSICAL LAYERNot Specified by ProtocolUSER APPLICATION LAYER PRESENTATION LAYER SESSION LAYER NETWORK LAYER DATA LI N K LAYER PHYSICAL LAYER TRANSPORT LAYER ------ ------ --- X.25 Protocol Layers
Functional Description 2-20Issue 3 March 1996 International Telecommunications Union - Telecommunications, Specifications Sector (ITU-T) Interface X.25 Packet-Switching Protocol The ITU-T (formerly CCITT) i s one of three divisions of the International Telecommunications Union, an agency of the United Nations. The standards set by the ITU-T generally deal with public networks. Two series of standards or recommendations specifically deal with data transmission: nThe V-series p rovides recommendations for d ata transmission over analog or voice telephone networks. nThe X-series provides recommendations for data transmission over digital networks. The V-series includes the V.10, V.11, V.24, V.28, and V.35. Also, V.26, V.27, and V.28 are mo dem recommendations for 2400, 4800, and 9600 bps, respectively. V.10 and V.11 are the equivalent to the EIA RS-423 and RS-422. V.24 provides definitions for all interchange circuits crossing the DTE/DCE interface. V.28 defines a set of electrical characteristics comp atible with EIA RS-232D. V.35 provides the constant current interface for 48 kbps operation. The X.25 protocol is the ITU-T recommendation for imp lementing International Standards Organizations Reference Model of Open Systems Interc onnection. This is the international model for packet-switching networks and is a bit-oriente d, layered-type p rotocol. The transport, network, data link, and physical layers (levels) are defined functionally by the ITU-T. The X.25 protocol specifies network requirements and procedures to provide the user interface for a packet-switching network. Typically, users generate low-speed asynchronous data. The X.25 software segments this data into packets, adds framing and routing information, and queues the packets into a buffer memory. User data p ackets, along with the added framing bits, are then transmitted over high-sp eed carriers. This permits efficient and dynamic sharing of these high-speed data links. The X.25 protocol provides the communications links between multiple APs.
International Telecommunications Union - Telecommunications, Specifications Sector (ITU-T) Interface Issue 3 March 1996 2-21 Wideband Switching Wideband Switching provides a range of data transmission sp eeds (from 128 to 1984 k b ps for E1 services, 128 to 1536 kbps for T1 services). The higher transmission rates are needed for applications such as video conferencing, data backup, scheduled batch processing, and primary data connectivity.
Functional Description 2-22Issue 3 March 1996 Data Management Features The following features are associated with Data Management: nAdministered Connections nAlphanumeric Dialing nData Call Setup [including Default Dialing and Alphanumeric Dialing] nData Hot Line nData-Only Off-Premises Extensions nData Privacy nData Restriction nDefault Dialing nDigital Multiplexed Interface nDS1/E1 Tie Trunk Servic e nEIA Interface nInformation System Network (ISN) Interface nModem Poolin g nPC Interface nPC/PBX Connection nUniform Call Distribution (See Direct Department Dialing [a VOICE Management Feature]) nWideband Switching nWorld Class Core BRI
Network Services Issue 3 March 1996 2-23 Network Services Network Services allows a group of switches (consisting of DEFINITY Generic 1, Generic 2, Generic 3, System 75 and System 85, and/or other systems) to be configured to meet the communications needs of a medium- to larg e-size corporation. Possible arrangements include an Electronic Tandem Network (ETN), Distributed Communications System (DCS), and Main/Satellite/Tributary. Each is briefly described in this chapter. Do not assume that the system has any c a pabilities other than those explicitly stated herein. Refer to the System 75/85 AT&T Network and Data Services Reference manual, 555-025-201, for differences between this system and other AT&T systems. Network Services Features The following features are associated with Network Services: nAAR/ARS Partitioning nARS to AAR Conversion nAutomatic Alternate Routing nAutomatic Circuit Assurance nAutomatic Route Selection nDCS Alphanumeric Display for Terminals nDCS Attendant Control of Trunk Group Ac cess nDCS Attendant Direct Trunk Group Selection nDCS Attendant Display nDCS Automatic Callback nDCS Automatic Circuit Assuranc e nDCS Busy Verification of Terminals and Trunks nDCS Call Coverage nDCS Call Forward ing All Calls nDCS Call Waiting nDCS Distinctive Ringing nDCS Leave Word Calling nDCS Multi-Appearance Conference/Transfer nDCS Trunk Group Busy/Warning Indication nNon-Facility Associated Signaling and D-channel Backup (G3i) nFacility Restriction Levels and Traveling Class Marks
Functional Description 2-24Issue 3 March 1996 nForced Entry of CDR Ac count Codes nGeneralized Route Selection nIntegrated Services Digital Network — Primary Rate Interface nNetwork Access — Private nNetwork Access — Public nOff-Premises Station nQSIG Global Networking nRestriction — Toll nSubnet Trunkin g nTime of Day Routing nUniform Dial Plan Private Network Configurations A p rivate network is a configuration of trunk and switching facilities d e dicated to the use of a b usiness or organization. It may have as few as two switches or it may have hundreds of switches located throughout the world. Although they normally serve moderate to heavy calling between locations, the following configurations make it p ossible for organizations of all sizes to realize the benefits of a private network. nElectronic Tandem Network (ETN) — Serves the needs of customers with many locations in a large g eographic area. This configuration p rovides for calling between locations without accessing toll facilities. nDistributed Communications System (DCS) — Serves the needs of customers with several locations in a small or large geographic area. A Distributed Communications System (DCS) a p pears as a single switch with respect to certain features. nMain/Satellite/Tributary — Serves the needs of customers with a few locations in a small geographic area. The system also can b e used within a Tandem Tie Trunk Network (TTTN). A TTTN is a nonhierarchical network of tie trunks interconnecting three or more switches. User dialing into each switch in the call’s p ath is required. That is, the user at one switch dials the trunk access code for a tie trunk group to another switch, receives dial tone from that switch, and then dials another trunk access code to reach another switch. When dial tone is received from the final (d esired) switch, the user dials the desired extension number.