Configuring T1 and T3 Interfaces
| T1 is the basic physical layer protocol used by the Digital Signal level 1 (DS-1) multiplexing method in North America. A T1 interface operates at a bit rate of 1.544 Mbps and can support 24 DS-0 channels. T3 is the physical layer protocol used by the Digital Signal level 3 (DS-3) multiplexing method in North America. A T3 interface operates at a bit rate of 44.736 Mbps. The JUNOS software supports payload scrambling and subrate operation on each physical T3 interface. DS-1 and DS-3 standards supported include ANSI TI.107, TI.102; GR 499-core, GR 253- core ; Bellcore TR-TSY-000009 (DS-3 only); AT&T Pub 54014; and, ITU G.751, G.703, G823 (DS-3 only). To configure T1-specific physical interface properties, include the t1-options statement: [edit interfaces interface-name ] t1-options { bert-error-rate rate ; bert-period seconds ; buildout (0-133 133-266 266-399 399-532 532- 655); byte-encoding (nx64 nx56); fcs (32 16); framing (sf esf); idle-cycle-flag (flags ones) ; invert-data; line-encoding (ami b8zs); loopback (local remote); start-end-flag (shared filler) ; timeslots time-slot-number ; } To configure T3-specific physical interface properties, include the t3-options statement: [edit interfaces interface-name ] t3-options { bert-algorithm algorithm ; bert-error-rate rate ; bert-period seconds ; (cbit-parity no-cbit-parity); compatibility-mode (digital-link kentrox larscom) <subrate value >; fcs (32 16); (feac-loop-respond no-feac-loop-respond); idle-cycle-flag value ; (long-buildout no-long-buildout); loopback (local remote); (payload-scrambler no-payload-scrambler); start-end-flag value ; } You can configure a T1 or T3 interface to execute a bit error rate test (BERT) when the interface receives a request to run this test. You specify the duration of the test and the error rate to include in the bit stream by including the bert-period and bert-error-rate statements. For T3 interfaces, you specify the pattern to send in the bit stream by including the bert-algorithm statement. [edit interfaces interface-name t1-options] or [edit interfaces interface-name t3-options] bert-algorithm algorithm ; bert-error-rate rate ; bert-period seconds ; For T3 interfaces, algorithm is the pattern to send in the bit stream. The algorithm for the T1 BERT procedure is pseudo-2e15-o151 (pattern is 2 15 “1, as defined in the CCITT/ITU O.151 standard). rate is the bit error rate. This can be an integer in the range 0 through 7, which corresponds to a bit error rate in the range 10 “0 (that is, 0, which corresponds to no errors) to 10 “7 (that is, 1 error per 10 million bits). The default is 0. seconds is the duration of the BERT procedure, in seconds. The test can last from 1 to 240 seconds; the default is 10 seconds. A T1 interface has five possible setting ranges for the T1 line buildout: 0-133, 133-266, 266-399, 399-532, or 532-655 feet. By default, the T1 interface uses the shortest setting (0-133). To have the interface drive a line at one of the longer distance ranges, include the buildout statement: [edit interfaces interface-name t1-options] buildout 532-655; By default, T1 interfaces use a byte encoding of 8 bits per byte ( nx64 ). You can configure an alternative byte encoding of 7 bits per byte ( nx56 ). To have the interface use an encoding of 7 bits per byte, include the byte-encoding statement, specifying the nx56 option: [edit interfaces interface-name t1-options] byte-encoding nx56; To configure a T3 interface so that it is compatible with the channel service unit (CSU) at the remote end of the line, include the compatibility statement: [edit interfaces interface-name t3-options] compatibility-mode (digital-link kentrox larscom) <subrate value >; You can configure the interface to be compatible with a Digital Link, Kentrox, or Larscom CSU. The subrate of a T3 interface must exactly match that of the remote CSU. To specify the subrate, include the subrate option in the compatibility-mode statement:
On T3 interfaces, C-bit parity mode controls the type of framing that is present on the transmitted T3 signal. When C-bit parity mode is enabled, the C-bit positions are used for the FEBE, FEAC, terminal data link, path parity, and mode indicator bits, as defined in ANSI T1.107a-1989. When C-bit parity mode is disabled, the basic T3 framing mode (M13) is used. By default, C-bit parity mode is enabled. To disable C-bit parity mode and use M13 framing for your T3 link, include the no-cbit-parity statement: [edit interfaces interface-name t3-options] no-cbit-parity; The T3 far-end alarm and control (FEAC) signal is used to send alarm or status information from the far-end terminal back to the near-end terminal and to initiate T3 loopbacks at the far-end terminal from the near-end terminal. To allow the remote CSU to place the local router into loopback, you must configure the router to respond to the CSU's FEAC request by including the feac-loop-respond statement: [edit interfaces interface-name t3-options] feac-loop-respond; By default, the router does not respond to FEAC requests . If you have configured remote or local loopback with the T3 loopback statement, the router does not respond to FEAC requests from the CSU even if you have included the feac-loop-respond statement in the configuration. To have the router respond, you must delete the loopback statement from the configuration. By default, T1 and T3 interfaces use a 16-bit frame checksum. You can configure a 32-bit checksum, which provides more reliable packet verification. However, some older equipment might not support 32-bit checksums. To configure a 32-bit checksum, include the fcs 32 statement: [edit interfaces interface-name t1-options] or [edit interfaces interface-name t3-options] fcs 32; By default, T1 interfaces use extended super frame (ESF) framing format. You can configure SF (super frame) as an alternative. To have the interface use the SF framing format, include the framing statement, specifying the sf option: [edit interfaces interface-name t1-options] framing sf; By default, data inversion is disabled on T1 interfaces. To enable data inversion at the HDLC level, include the invert-data statement. When you enable data inversion, all data bits in the data stream are transmitted inverted; that is, zeros are transmitted as ones and ones as zeroes. Data inversion is normally used only in AMI mode to guarantee ones' density in the transmitted stream. [edit interfaces interface-name t1-options] invert-data; A T3 interface has two settings for the T3 line buildout: a short setting, which is less than 225 feet (about 68 meters ), and a long setting, which is greater than 225 feet. By default, the interface uses the short setting. The long-buildout and no-long-buildout statements apply only to copper -cable “based T3 interfaces. You cannot configure a line buildout for a DS-3 channel on a Channelized OC-12 interface, which runs over fiber- optic cable. If you configure this statement on a Channelized OC-12 interface, it is ignored. To have the interface drive a line that is longer than 255 feet, include the long-buildout statement: [edit interfaces interface-name t3-options] long-buildout; By default, T1 interfaces use B8ZS line encoding. To configure AMI line encoding, include the line-encoding statement, specifying the ami option: [edit interfaces interface-name t1-options] line-encoding ami; When setting the line encoding parameter, you must set the same value for paired ports. Ports 0 and 1 must share the same value, and likewise ports 2 and 3 must share the same value, but ports 0 and 1 can have a different value from that of ports 2 and 3. You can configure loopback capability between the local T1 or T3 interface and the remote channel service unit (CSU), as shown in Figure 6.5. You can configure the loopback to be local or remote. With local loopback, the T1 or T3 interface can transmit packets to the CSU, but receives its own transmission back again and ignores data from the CSU. With remote loopback, packets sent from the CSU are received by the T1 or T3 interface but also are immediately retransmitted to the CSU. Figure 6.5. Remote and Local T1 Loopback To configure loopback capability on a T1 or T3 interface, include the loopback statement: [edit interfaces interface-name t1-options] or [edit interfaces interface-name t3-options] loopback (local remote); Packets can be looped on either the local router or the remote CSU. To turn off loopback, remove the loopback statement from the configuration. T3 HDLC payload scrambling, which is disabled by default, provides better link stability. Both sides of a connection must either use or not use scrambling. On a Channelized OC-12 interface, the SONET payload-scrambler statement is ignored. To configure scrambling on the DS-3 channels on the interface, you can include the t3-options payload-scrambler statement: [edit interfaces interface-name t3-options] payload-scrambler; By default, a T1 or T3 interface transmits the value 0x7E in the idle cycles. To have the interface transmit the value 0xFF (all ones) instead, include the idle-cycle-flag statement, specifying the ones option: [edit interfaces interface-name t1-options] or [edit interfaces interface-name t3-options] idle-cycle-flag ones; By default, a T1 or T3 interface waits two idle cycles between sending start and end flags. To configure the interface to share the transmission of start and end flags, include the start-end-flag statement, specifying the shared option: [edit interfaces interface-name t1-options] start-end-flag shared; To configure the number of time slots allocated to a T1 interface, include the timeslots statement. The slot number can be in the range 1 through 24 for T1 interfaces. There are 24 time slots on a T1 interface. You can designate any combination of time slots for usage. [edit interfaces interface-name t1-options] timeslots timeslot-number ;  |
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