To specify a HSSI and enter interface configuration mode, use one of the following commands in global configuration mode:

The HSSI supports the serial encapsulation methods, except for X.25-based encapsulations. The default method is HDLC. You can define the encapsulation method by using the following command in interface configuration mode:

If you have an ATM DSU, you can invoke ATM over a HSSI line. You do so by mapping an ATM virtual path identifier (VPI) and virtual channel identifier (VCI) to a DXI frame address. ATM-DXI encapsulation defines a data exchange interface that allows data terminal equipment (DTE; such as a router) and data circuit-terminating equipment (DCE; such as an ATM DSU) to cooperate to provide a User-Network Interface (UNI) for ATM networks.

To invoke ATM over a serial line, use the following commands in interface configuration mode:

You can also configure the dxi map command on a serial interface.

The HSSI network module provides full-duplex connectivity at SONET OC-1/STS-1 (51.840 Mhz), T3 (44.736 MHz), and E3 (34.368 MHz) rates in conformance with the EIA/TIA-612 and EIA/TIA-613 specifications. The actual rate of the interface depends on the external DSU and the type of service to which it is connected. You can convert the HSSI interface into a clock master by using the following command in interface configuration mode:

Disabling fair queuing will dramatically improve fast switching rates over the HSSI. To disable fair queuing, use the following command in interface configuration mode:

To specify a synchronous serial interface and enter interface configuration mode, use one of the following commands in global configuration mode:

By default, synchronous serial lines use the HDLC serial encapsulation method, which provides the synchronous framing and error detection functions of HDLC without windowing or retransmission. The synchronous serial interfaces support the following serial encapsulation methods:

You can define the encapsulation method by using the following command in interface configuration mode:

Encapsulation methods are set according to the type of protocol or application you configure in the Cisco IOS software. ATM-DXI is described in this chapter in the section "Configuring the CRC." Serial encapsulation methods are also discussed in Chapter 4, "Configuring Interface Commands," under the encapsulation command.

By default, synchronous interfaces operate in full-duplex mode. To configure an SDLC interface for half-duplex mode, use the following command in interface configuration mode:

BSC is a half-duplex protocol. Each block of transmission is acknowledged explicitly. To avoid the problem associated with simultaneous transmission, there is an implicit role of primary and secondary station. The primary re-sends the last block if there is no response from the secondary within the period of block receive timeout.

To configure the serial interface for full-duplex mode, use the following command in interface configuration mode:

The JT2 6.3-MHz serial port adapter (PA-2JT2) is available on a second-generation Versatile Interface Processor (VIP2) in Cisco 7500 series routers and in Cisco 7000 series routers with the RSP7000 and RSP7000CI.

The PA-2JT2 port adapter provides two DTE interfaces with coaxial BNC connectors—one for transmit (TX) and one for receive (RX). This port adapter is compatible with G.703a allowing communication over a high-speed digital 6.3-MHz (HSD 6.3) leased line service specified in ITU Recommendation G.704. The PA-2JT2 port adapter provides the following features and capabilities:

To configure a PA-2JT2 port adapter, see the section "Specifying a Synchronous Serial Interface" in this chapter.

The synchronous serial port adapters (PA-8T-V35, PA-8T-X21, PA-8T-232, and PA-4T+) on Cisco 7200 series routers support half-duplex and binary synchronouscommunications (Bisync). Bisync is a character-oriented data-link layer protocol for half-duplex applications. In half-duplex mode, data is sent one direction at a time. Direction is controlled by handshaking the RST and CTS control lines.

The SA-Comp/1 and SA-Comp/4 data compression service adapters (CSAs) are available on Cisco 7200 series routers and on VIP2s in Cisco 7500 series routers. (CSAs require VIP2 model VIP2-40.)

The SA-Comp/1 supports up to 64 WAN interfaces, and the SA-Comp/4 supports up to 256 WAN interfaces.

On the Cisco 7200 series routers you can optionally specify which CSA the interface uses to perform hardware compression.

You can configure point-to-point compression on serial interfaces that use PPP encapsulation. Compression reduces the size of a PPP frame via lossless data compression. PPP encapsulations support both predictor and Stacker compression algorithms.

When you configure Stacker compression on Cisco 7200 series and Cisco 7500 series routers, there are three methods of compression: hardware compression, distributed compression, and software compression. Specifying the compress stac command with no options causes the router to use the fastest available compression method, as described here:

Using hardware compression in the CSA frees the router's main processor for other tasks. You can also configure the router to use the VIP2 to perform compression by using the distributed option, or to use the router's main processor by using the software option. If the VIP2 is not available, compression is performed in the router's main processor.

When compression is performed in software installed in the router's main processor, it might significantly affect system performance. You should disable compression in the router's main processor if the router CPU load exceeds 40 percent. To display the CPU load, use the show process cpu EXEC command.

You can configure point-to-point software compression on serial interfaces that use HDLC encapsulation. Compression reduces the size of an HDLC frame via lossless data compression. The compression algorithm used is a Stacker (LZS) algorithm.

Compression is performed in software and might significantly affect system performance. Cisco recommends that you disable compression if CPU load exceeds 65 percent. To display the CPU load, use the show process cpu EXEC command.

If the majority of your traffic is already compressed files, you should not use compression.

To configure compression over HDLC, use the following commands in interface configuration mode:

Real-time Transport Protocol (RTP) is a protocol used for carrying packetized audio and video traffic over an IP network. RTP is described in RFC 1889. RTP is not intended for data traffic, which uses TCP or UDP. RTP provides end-to-end network transport functions intended for applications with real-time requirements, such as audio, video, or simulation data over multicast or unicast network services.

The cyclic redundancy check (CRC) on a serial interface defaults to a length of 16 bits. To change the length of the CRC to 32 bits on an Fast Serial Interface Processor (FSIP) or HIP of the Cisco 7500 series only, use the following command in interface configuration mode:

All FSIP interface types on the Cisco 7500 series routers and the PA-8T and PA-4T+ synchronous serial port adapters on the Cisco 7000 series routers with RSP7000, Cisco 7200 series routers, and Cisco 7500 series routers support nonreturn-to-zero (NRZ) and nonreturn-to-zero inverted (NRZI) format. This is a line-coding format that is required for serial connections in some environments. NRZ encoding is most common. NRZI encoding is used primarily with EIA/TIA-232 connections in IBM environments.

The default configuration for all serial interfaces is NRZ format. The default is no nrzi-encoding.

To enable NRZI format, use one of the following commands in interface configuration mode:

When a DTE does not return a transmit clock, use the following interface configuration command on the Cisco 7000 series to enable the internally generated clock on a serial interface:

If the interface on the PA-8T and PA-4T+ synchronous serial port adapters is used to drive a dedicated T1 line that does not have B8ZS encoding, you must invert the data stream on the connecting CSU/DSU or on the interface. Be careful not to invert data on both the CSU/DSU and the interface because two data inversions will cancel each other out.

If the T1 channel on the CT3IP is using alternate mark inversion (AMI) line coding, you must invert the data. For more information, see the t1 linecode controller command. For more information on the CT3IP, refer to the "Configuring a Channelized T3 Interface Processor" section in this chapter.

To invert the data stream, use the following command in interface configuration mode:

Systems that use long cables or cables that are not transmitting the TxC signal (transmit echoed clock line, also known as TXCE or SCTE clock) can experience high error rates when operating at the higher transmission speeds. For example, if the interface on the PA-8T and PA-4T+ synchronous serial port adapters is reporting a high number of error packets, a phase shift might be the problem. Inverting the clock signal can correct this shift. To invert the clock signal, use the following command in interface configuration mode:

It is possible to send back-to-back data packets over serial interfaces faster than some hosts can receive them. You can specify a minimum dead time after transmitting a packet to alleviate this condition. This setting is available for serial interfaces on the MCI and SCI interface cards and for the HSSI or MultiChannel Interface Processor (MIP). Use one of the following commands, as appropriate for your system, in interface configuration mode:

You can configure pulsing DTR signals on all serial interfaces. When the serial line protocol goes down (for example, because of loss of synchronization), the interface hardware is reset and the DTR signal is held inactive for at least the specified interval. This function is useful for handling encrypting or other similar devices that use the toggling of the DTR signal to resynchronize. To configure DTR signal pulsing, use the following command in interface configuration mode:

This task applies to Quad Serial NIM interfaces on the Cisco 4000 series and Hitachi-based serial interfaces on the Cisco 2500 series and Cisco 3000 series.

By default, when the serial interface is operating in DTE mode, it monitors the Data Carrier Detect (DCD) signal as the line up/down indicator. By default, the attached DCE device sends the DCD signal. When the DTE interface detects the DCD signal, it changes the state of the interface to up.

In some configurations, such as an SDLC multidrop environment, the DCE device sends the data set ready (DSR) signal instead of the DCD signal, which prevents the interface from coming up. To tell the interface to monitor the DSR signal instead of the DCD signal as the line up/down indicator, use the following command in interface configuration mode:

On Cisco 4000 series routers, you can specify the serial Network Interface Module timing signal configuration. When the board is operating as a DCE and the DTE provides terminal timing (SCTE or TT), you can configure the DCE to use SCTE from the DTE. When running the line at high speeds and long distances, this strategy prevents phase shifting of the data with respect to the clock.

To configure the DCE to use SCTE from the DTE, use the following command in interface configuration mode:

When the board is operating as a DTE, you can invert the TXC clock signal it gets from the DCE that the DTE uses to transmit data. Invert the clock signal if the DCE cannot receive SCTE from the DTE, the data is running at high speeds, and the transmission line is long. Again, this prevents phase shifting of the data with respect to the clock.

To configure the interface so that the router inverts the TXC clock signal, use the following command in interface configuration mode:

This section describes the optional tasks for configuring a G.703 serial interface (a serial interface that meets the G.703 electrical and mechanical specifications and operates at E1 data rates). G.703 interfaces are available on port adapters for the FSIP on a Cisco 4000 series or Cisco 7500 series router.

The E1-G.703/G.704 serial port adapters (PA-4E1G-120 and PA-4E1G-75) are available on Cisco 7500 series routers, Cisco 7200 series routers, and Cisco 7000 series routers with the RSP7000 and RSP7000CI. These port adapters provide up to four E1 synchronous serial interfaces, which are compatible with and specified by G.703/G.704. The PA-4E1G-120 supports balanced operation and the PA-4E1G-75 supports unbalanced operation with 15-pin, D-shell (DB-15) receptacles on the port adapters. Both port adapters operate in full-duplex mode at the E1 speed of 2.048-Mbps.

Configuration tasks are described in these sections:

If you do not modify the configuration of the CT3IP, the configuration defaults shown in Table 2-1 are used.

If you must change any of the default configuration attributes, use the first command in global configuration mode followed by any of the optional commands in controller configuration mode:

You must configure the timeslots used by each T1 channel on the CT3IP. Optionally, you can specify the speed, framing format, and clock source used by each T1 channel. If you do not specify the speed, framing format, and clock source used by each T1 channel, the configuration defaults shown in Table 2-2 are used.

To specify the timeslots used by each T1 channel, use the following commands beginning in global configuration mode:

If you need to change any of the default configuration attributes, use the first command in global configuration mode, followed by any of the optional commands in controller configuration mode:

After you configure the T1 channels on the CT3IP, you can continue configuring it as you would a normal serial interface. All serial interface commands might not be applicable to the T1 channel. For more information, refer to the section "Configuring a Synchronous Serial Interface" in this chapter.

To enter interface configuration mode and configure the serial interface that corresponds to a T1 channel, use the following command in global configuration mode:

In addition to the commands in the "Configuring a Synchronous Serial Interface" section, the invertdata interface command can be used to configure the T1 channels on the CT3IP. If the T1 channel on the CT3IP is using AMI line coding, you must invert the data. For information on the invertdata interface command, refer to the section "Inverting the Data" later in this chapter. For more information, see the t1 linecode controller command.

The first three T1 channels (1, 2, and 3) of the CT3IP can be broken out to the DSUP-15 connectors so the T1 channel can be further demultiplexed by the MIP on the same router, another router, or other multiplexing equipment.

To configure a T1 channel as an external port, use the following commands beginning in EXEC mode:

After you configure the external T1 channel, you can continue configuring it as a channelized T1 from the MIP. All channelized T1 commands might not be applicable to the T1 interface. To define the T1 controller and enter controller configuration mode, use the following command in global configuration mode:

After you configure the channelized T1 on the MIP, you can continue configuring it as you would a normal serial interface. All serial interface commands might not be applicable to the T1 interface. To enter interface configuration mode and configure the serial interface that corresponds to a T1 channel group, use the following command in global configuration mode:

For more information, refer to the section "Configuring Each T1 Channel" in this chapter. For an example of configuring an external T1 channel, see the "Channelized T3 Interface Processor Configuration Examples" section in this chapter.

You can use the following methods to troubleshoot the CT3IP using Cisco IOS software:

You can perform the following types of loopbacks on a T1 channel:

To enable loopbacks on a T1 channel, use the first command in global configuration mode, followed by any one of the following commands:

Figure 2-1 shows an example of a local loopback in which the loopback occurs in the T1 framer.

Figure 2-2 shows an example of a network line loopback in which just the data is looped back toward the network (before the T1 framer).

Figure 2-3 shows an example of a network payload loopback in which just the payload data is looped back toward the network at the T1 framer.

Figure 2-4 shows an example of a remote inband loopback in which the network line enters a line loopback.

You can put the entire T3 line into loopback mode (that is, all T1 channels are looped) by using the following types of loopbacks:

To enable loopbacks on the T3 (and all T1 channels), use the first command in global configuration mode followed by any one of the following commands:

After configuring the new interface, you can monitor the status and maintain the CT3IP in the Cisco 7000 series routers with an RSP7000 or in the Cisco 7500 series routers by using the show commands. To display the status of any interface, use one of the following commands in EXEC mode:

The CT3IP can be configured to send a Maintenance Data Link (MDL) message as defined in the ANSI T1.107a-1990 specification. To specify the transmission of the MDL messages, use the following commands beginning in global configuration mode:

Use the show controllers t3 command to display MDL information (received strings). MDL information is displayed only when framing is set to C-bit.

The CT3IP supports performance reports via the Facility Data Link (FDL) per ANSI T1.403. By default, performance reports are disabled. To enable FDL performance reports, use the following commands beginning in global configuration mode:

To display the remote performance report information, use the following command in EXEC command mode:

To enable and disable generation of a BERT test pattern for a specified interval for a specific T1 channel, use the following commands beginning in global configuration mode:

The BERT test patterns from the CT3IP are framed test patterns (that is, the test patterns are inserted into the payload of the framed T1 signal).

To view the BERT results, use the show controller t3 or show controller t3 brief EXEC command. The BERT results include the following information:

When the T1 channel has a BERT test running, the line state is DOWN. Also, when the BERT test is running and the Status field is Not Sync, the information in the total bit errors field is not valid. When the BERT test is done, the Status field is not relevant.

The t1 bert pattern command is not written to NVRAM because it is used only for testing the T1 channel for a short predefined interval and for avoiding accidentally saving the command, which could cause the interface not to come up the next time the router reboots.

You can perform the following types of remote Facility Data Link (FDL) loopbacks on a T1 channel:

To enable loopbacks on a T1 channel, use the following commands beginning in global configuration mode:

The commands listed in Table 2-3 have been added to support the PA-E3 interface configuration. If you do not modify the configuration of the PA-E3, the configuration defaults shown in Table 2-3 are used.

If you need to change any of the default configuration attributes, use the first command in global configuration mode, followed by any of the optional commands in interface configuration mode:

To set the following loopbacks to troubleshoot the PA-E3 port adapter using Cisco IOS software, use the first command in global configuration mode, followed by any of the other commands, depending on your needs:

These loopback commands loop all packets from the E3 interface back to the interface and direct the packets to the network.

After configuring the new interface, you can display its status. To show current status of the E3 interface on the PA-E3 port adapter, use any of the following commands in EXEC mode:

The commands listed in Table 2-4 have been added to support the PA-T3 interface configuration. If you do not modify the configuration of the PA-T3, the configuration defaults shown in Table 2-4 are used.

If you need to change any of the default configuration attributes, use the first command in global configuration mode, followed by any of the optional commands in interface configuration mode:

To set the following loopbacks to troubleshoot the PA-T3 port adapter using Cisco IOS software, use the first command in global configuration mode, followed by any of the other commands depending on your needs:

These loopback commands loop all packets from the T3 interface either back to the interface or direct packets from the network back out toward the network.

After configuring the new interface, you can display its status. To show current status of the T3 interface on the PA-T3 port adapter, use any of the following commands in EXEC mode:

The Packet OC-3 interface is referred to as pos in the configuration commands. An interface is created for each POS found in the system at reset time.

If you need to change any of the default configuration attributes or otherwise reconfigure the Packet OC-3 interface, use one the following commands in global configuration mode:

To set the MTU size for the interface, use the following command in interface configuration mode:

The value of the bytes argument is in the range 64 to 4470 bytes; the default is 4470 bytes. (4470bytes exactly matches FDDI and HSSI interfaces for autonomous switching.) The no form of the command restores the default.

To configure framing on the Packet OC-3 interface, use one of the following commands in interface configuration mode:

With the loopback internal command, packets from the router are looped back in the framer. Outgoing data gets looped back to the receiver without actually being transmitted. With the loopback line command, the RX fiber is logically connected to the TX so that packets from the remote router are looped back to it. Incoming data gets looped around and retransmitted without actually being received.

To enable or disable internal loopback on the interface, use one of the following commands in interface configuration mode:

Local loopback is useful for checking that the POS is working. Packets from the router are looped back in the framer.

Line loopback is used primarily for debugging purposes.

To enable or disable an interface for line loopback, use one of the following commands in interface configuration mode:

The RX is logically connected to the TX so that packets from the remote router are looped back to it.

By default, the Packet OC-3 interface uses the recovered receive clock to provide transmit clocking. To change the transmit clock source, use one of the following commands in interface configurationmode:

SONET payload scrambling applies a self-synchronous scrambler (x^43+1) to the Synchronous Payload Envelope (SPE) of the interface to ensure sufficient bit transition density. Both ends of the connection must use the same scrambling algorithm. When enabling POS scrambling on a VIP2 POS on the Cisco 7500 series that has a hardware revision of 1.5 or higher, you can specify CRC 16 only (that is, CRC 32 is currently not supported).

To enable SONET payload scrambling on a POS interface, use the following command in interface configuration mode.

To configure line alarm indication signals when the POS interface is placed in any administrative shut down state, use the following command in interface configuration mode:

This section describes how to configure a working and protect interface. The commands listed in this section are required. Configure the working interface before configuring the protect interface to avoid the protect interface from becoming the active circuit and disabling the working circuit when it is finally discovered.

To configure the working interface, use the following commands beginning in global configuration mode:

To configure the protect interface, use the following commands beginning in global configuration mode:

To configure the other APS options, use any of the following commands in interface configuration mode. The commands listed in this section are optional.

To provide information about system processes, the Cisco IOS software includes an extensive list of EXEC commands that begin with the word show. When executed, these commands display detailed tables of system information. The following is a list of some of the common show commands for the APS feature. Use these commands in privileged EXEC mode to display the information described:

To configure the thresholds and the type of SONET alarms that are reported, use any of the following commands in interface configuration mode. The commands listed in this section are optional. The default settings are adequate for most POS installations.

To display the current BER threshold setting or to view the reporting of the SONET alarms, use the show controllers pos EXEC command.

Line alarm indication signal can be used to force a protection switch in an APS environment. To force an APS switch when the interface is placed in administrative shut down state, use the following command in interface configuration mode:

To specify the clock source for the FT1/T1 CSU/DSU module, use the following command in interface configuration mode:

Data inversion is used to guarantee the ones density requirement on an AMI line when using bit-oriented protocols such as HDLC, PPP, X.25, and Frame Relay.

To guarantee the ones density requirement on an AMI line using the FT1/T1 CSU/DSU module, use the following command in interface configuration mode:

If the timeslot speed is set to 56 kbps, this command is rejected because line density is guaranteed when transmitting at 56 kbps. Use this command with the 64-kbps line speed. If you transmit inverted bit codes, both CSU/DSUs must have this command configured for successful communication.

To enable normal data transmission on an FT1/T1 network, use the following command in interface configuration mode:

To specify the frame type for a line using the FT1/T1 CSU/DSU module, use the following command in interface configuration mode:

In most cases, the service provider determines which framing type, either esf or sf, is required for your circuit.

To decrease the outgoing signal strength to an optimum value for the telecommunication carrier network, use the following command on the FT1/T1 CSU/DSU module in interface configuration mode: