Fast Serial Interface Processor

This chapter provides information on the Fast Serial Interface Processor (FSIP). (See Figure 8-1.)

The FSIP provides four or eight channel-independent, synchronous serial ports that support full-duplex operation at T1 (1.544 megabits per second [Mbps]) and E1 (2.048 Mbps) speeds. The FSIP ships as Product Numbers CX-FSIP4(=) and CX-FSIP8(=).

The ports are divided into two 4-port modules, each of which is controlled by a dedicated Motorola MC68040 processor and contains 128 kilobytes (KB) of static random-access memory (SRAM). Each module can support up to four T1 or three E1 interfaces, and an aggregate bandwidth of up to 6.132 Mbps at full-duplex operation.

The FSIP4 has one module for ports 0-3, and the FSIP8 has two modules, one for ports 0-3 and the other for ports 4-7. To provide a high density of ports, the FSIP uses special port adapters and adapter cables. A port adapter is a daughter board that provides the physical interface for two FSIP serial ports. Each FSIP comprises an FSIP board with two or four port adapters. (One module is equivalent to two port adapters.) Additional port adapters are available as spares so that you can replace one that fails; however, you cannot upgrade a 4-port FSIP to an 8-port FSIP by adding port adapters. (The 4-port FSIP is not constructed to support additional ports after it leaves the factory; it contains the circuitry to control only one 4-port module.) An adapter cable provides the network connection for each port and determines the electrical interface type and mode of that interface. (For more information, refer to the section "FSIP Port Adapters, Interface Cables, and Connections" on page 8-5.)

Each serial port on the FSIP4 or FSIP8 can transmit and receive data at the rate of 6.132 Mbps; however, if one or more ports consumes the full 6.132 Mbps bandwidth, then we strongly recommend that the remaining ports be administratively shut down.

For example, you can configure four T1 interfaces on a module (one T1 on each port) such that they do not exceed 6.132 Mbps, or you can configure one port to operate at up to 6.132 Mbps, and leave the remaining three ports shut down. Note that some environments will support four E1 interfaces per module without any problems; however, the type of electrical interface, the amount of traffic processed, and the types of external data service units (DSUs) connected to the ports affect actual rates.

FSIP Interface Types

Each port supports any of the available interface types: Electronics Industries Association/Telecommunications Industries Association (EIA/TIA)-232, EIA/TIA-449, E1-G.703/G.704, V.35, X.21, and EIA-530.

All interface types except EIA-530 can be individually configured for operation with either external (data terminal equipment [DTE] mode) or internal (data communications equipment [DCE] mode) timing signals; EIA-530 operates with external timing only.

In addition, all FSIP interface types support nonreturn to zero (NRZ) and nonreturn to zero inverted (NRZI) format, and both 16-bit and 32-bit cyclic redundancy checks (CRCs). The default configuration is for NRZ format and 16-bit CRC. You can change the default settings with software commands. (See the section "Configuring the FSIP" on page 8-31.)

There is no default mode or clock rate set on the FSIP ports, although an internal clock signal is present on all ports for DCE support. The internal clock also allows you to perform local loopback tests without having to terminate the port or connect a cable. (All interface types except X.21 DTE support loopback.)

To use the port as a DCE interface, you must set the clock rate and connect a DCE adapter cable. To use the port as a DTE interface, you need only connect a DTE adapter cable to the port. Because the serial adapter cables determine the mode and interface type, the FSIP port becomes a DTE when a DTE cable is connected to it.

If a DTE cable is connected to a port with a clock rate set (using the clockrate command), the DTE ignores the clock rate and uses the external clock signal that is sent from the remote DCE. (For a brief description of the clockrate command, refer to the section "Configuring Timing (Clock) Signals" on page 8-34.)

Each E1-G.703/G.704 interface is a 2.048-megabit per second (Mbps), E1 telecommunications interface; all the other available FSIP interfaces are synchronous serial data communications interfaces. G.703 is an International Telecommunication Union Telecommunication Standardization Sector (ITU-T) electrical and mechanical specification for connections between telecommunications interfaces and data communications equipment (DTE).

Typically, G.703 provides a means of connecting standard serial interfaces such as V.35 to telephone lines or Postal Telephone and Telegraph (PTT) networks. The E1-G.703/G.704 port adapter supports point-to-point connections to Cisco 7000 series and Cisco 7500 series routers from 2.048-Mbps, E1 leased-line services, and eliminates the need for a separate, external data termination unit that is typically used to convert standard serial interfaces, such as V.35, to E1-G.703/G.704.

Synchronous Serial Distance Limitations

Serial signals can travel a limited distance at any given bit rate; generally, the slower the baud rate, the greater the distance. All serial signals are subject to distance limits beyond which a signal degrades significantly or is completely lost. Table 8-1 lists the recommended maximum speeds and distances for each FSIP serial interface type.

Balanced drivers allow EIA/TIA-449 signals to travel greater distances than EIA/TIA-232. The recommended distance limits for EIA/TIA-449 shown in Table 8-1 are also valid for V.35, X.21, and EIA-530. However, you can get good results at distances and rates far greater than these. While EIA/TIA-449 and EIA-530 support 2-Mbps rates, and V.35 supports 4-Mbps rates without any problems, we do not recommend exceeding published specifications for transmission speed versus distance; do so at your own risk.

E1-G.703/G.704 Distance Limitations

Unbalanced G.703 interfaces allow for a longer maximum cable length than those specified for balanced circuits. Table 8-2 lists the maximum cable lengths for each FSIP E1-G.703/G.704 cable type by the connector used at the network (non-FSIP) end.

FSIP Port Adapters, Interface Cables, and Connections

The universal port adapters and adapter cables allow eight interface ports on an FSIP, regardless of the size of the connectors typically used with each electrical interface type. (See Figure 8-2.)

Port adapters are field-replaceable daughter boards mounted to the FSIP, and each provides two high-density connectors for two FSIP ports.

All FSIP port adapters use an identical 60-pin, D-shell receptacle that supports all interface types: EIA/TIA-232, V.35, EIA/TIA-449, X.21, and EIA-530. An exception to this is the E1-G.703/G.704 port adapter, which uses a 15-pin, D-shell receptacle.

FSIP Interface Cables

Each port requires a serial interface adapter cable that provides the interface between the high-density FSIP port and the standard connectors that are commonly used for each electrical interface type. Rate of data transmission depends on the type of electrical interface: EIA/TIA-232 for speeds of 64 kilobits per second (kbps) and below; X.21, EIA/TIA-449, V.35, or EIA-530 for higher speeds.

The router (FSIP) end of all adapter cables is a 60-pin, D-shell plug that connects to the 60-pin port on the FSIP. The network end of the cable is an industry-standard connector for the type of electrical interface that the cable supports. For most interface types, the adapter cable for DTE mode uses a plug at the network end, and the cable for DCE mode uses a receptacle at the network end. Exceptions are V.35 adapter cables, which are available with either a V.35 plug or a receptacle for either mode, and the EIA-530 adapter cable, which is available only in DTE mode with a DB-25 plug at the network end.

The mode (DCE or DTE) is labeled on the molded plastic connector shell at the ends of all cables except V.35 (which uses the standard Winchester block-type connector instead of a molded plastic D-shell).

Following are the available port adapter and cable options for the mode and network-end connectors for each synchronous serial cable listed by product number:

• PA-7KF-SPA(=)--Universal synchronous serial port adapter

• CAB-232MT(=)--EIA/TIA-232 DTE mode cable with a DB-25 plug

• CAB-232FC(=)--EIA/TIA-232 DCE mode cable with a DB-25 receptacle

• CAB-449MT(=)--EIA/TIA-449 DTE mode cable with a 37-pin D-shell plug

• CAB-449FC(=)--EIA/TIA-449 DCE mode cable with a 37-pin D-shell receptacle

• CAB-V35MT(=)--V.35 DTE mode cable or DCE mode (CAB-V35MC=) with a 34-pin Winchester-type V.35 plug

• CAB-V35FT(=)--V.35 DTE mode cable or DCE mode (CAB-V35FC=) with a 34-pin Winchester-type V.35 receptacle

• CAB-X21MT(=)--X.21 DTE mode cable with a DB-15 plug

• CAB-X21FC(=)--X.21 DCE mode with a DB-25 receptacle

• CAB-530MT(=)--EIA-530 DTE mode cable with a DB-25 plug

Following are the available port adapter and cable options for the E1-G.703/G.704 interface:

• PA-7KF-E1/120(=)--Dual-port E1-G.703/G.704, 120 ohm, balanced port adapter

• PA-7KF-E1/75(=)--Dual-port E1-G.703/G.704, 75 ohm, unbalanced port adapter

• CAB-E1-TWINAX(=)--E1 cable, TWINAX, 120 ohm, balanced, 5 meters

• CAB-E1-DB15(=)--E1 cable, DB-15, 120 ohm, balanced, 5 meters

• CAB-E1-BNC(=)--E1 cable, BNC, 75 ohm, unbalanced, 5 meters

All cables and port adapters are available as spare parts (=).

For replacement instructions, refer to the configuration note that shipped with your replacement port adapter. For cable pinouts, refer to the section "FSIP Port Adapter Interface and Cable Pinouts" on page 8-10.

Figure 8-3 shows the synchronous serial port adapter cables for connection from the FSIP port adapters to your network.

Figure 8-4, Figure 8-5, and Figure 8-6 show the unbalanced and balanced cables used for connection between the E1-G.703/G.704 port adapter and your network. The port-adapter end of each cable has a DB-15 connector.

Caution It is a requirement of the statutory approval of the E1-G.703/G.704 interface that the jackscrews of the connector backshell be securely screwed down while the FSIP is operating.

Metric (M3) thumbscrews are included with each port adapter cable to allow connections to devices that use metric hardware. Because the FSIP uses a special, high-density port that requires special adapter cables for each electrical interface type, we recommend that you obtain serial interface cables from the factory.

FSIP Port Adapter Interface and Cable Pinouts

The FSIP supports EIA/TIA-232, EIA/TIA-449, X.21, V.35, and EIA-530 serial interfaces and the E1-G.703/G.704 interface. All FSIP ports use a universal port adapter, which is a 60-pin receptacle that supports all available interface types. A special synchronous serial adapter cable, which is required for each synchronous port, determines the electrical interface type and mode of the synchronous serial interface. The router (FSIP) end of all of the adapter cables is a 60-pin plug; the connectors at the network end are the standard connectors used for the respective interfaces. An exception to this is the E1-G.703/G.704 port adapter, which uses a 15-pin, D-shell receptacle.

All synchronous serial interface types except EIA-530 are available in DTE or DCE format: DTE with a plug connector at the network end and DCE with a receptacle at the network end. V.35 is available in either mode with either gender at the network end. EIA-530 is available in DTE only.

The tables that follow list the signal pinouts for both the DTE and DCE mode serial port adapter cables for each FSIP interface types:

• Table 8-3, on page 8-11, lists the EIA/TIA-232 pinouts

• Table 8-4, on page 8-12, lists the EIA/TIA-449 pinouts

• Table 8-5, on page 8-14, lists the X.21 pinouts

• Table 8-6, page 8-15, lists the V.35 pinouts

• Table 8-7, on page 8-17, lists the EIA-530 pinouts

• Table 8-8, on page 8-18, lists the E1-G.703/G.704 pinouts

FSIP Cable Connections

This section provides information on the synchronous serial interface connectors used on the FSIP synchronous serial cables.

Use the information in the following sections for your serial connections:

• EIA/TIA-232 Connections, page 19

• EIA/TIA-449 Connections, page 20

• V.35 Connections, page 21

• X.21 Connections, page 22

• EIA-530 Connections, page 23

• Metric Thumbscrews, page 24

EIA/TIA-232 Connections

EIA/TIA-232 supports unbalanced circuits at signal speeds up to 64 kbps. The router (FSIP) end of all EIA/TIA-232 adapter cables is a high-density 60-pin plug. The opposite (network) end of the adapter cable is a standard 25-pin D-shell connector (known as a DB-25) that is commonly used for EIA/TIA-232 connections. Figure 8-7 shows the connectors at the network end of the adapter cable.

EIA/TIA-449 Connections

EIA/TIA-449, which supports balanced (EIA/TIA-422) and unbalanced (EIA/TIA-423) transmissions, is a faster (up to 2 Mbps) version of EIA/TIA-232, which provides more functions and supports transmissions over greater distances. The EIA/TIA-449 standard was intended to replace EIA/TIA-232, but it was not widely adopted. The resistance to convert to EIA/TIA-449 was due primarily to the large installed base of DB-25 hardware and to the larger size of the 37-pin EIA/TIA-449 connectors, which limited the number of connections possible (fewer than is possible with the smaller, 25-pin EIA/TIA-232 connector).

The router (FSIP) end of all EIA/TIA-449 adapter cables is a high-density 60-pin plug. The opposite (network) end of the adapter cable provides a standard 37-pin D-shell connector, which is commonly used for EIA/TIA-449 connections.

Figure 8-8 shows the connectors at the network end of the adapter cable.

V.35 Connections

The V.35 interface is recommended for speeds up to 48 kbps (although in practice it is used successfully at up to 4 Mbps).

The router (FSIP) end of all V.35 adapter cables is a high-density 60-pin plug. The opposite (network) end of the adapter cable provides a standard, 34-pin Winchester-type connector commonly used for V.35 connections.

Figure 8-9 shows the connectors at the network end of the V.35 adapter cable.

X.21 Connections

The X.21 interface uses a 15-pin connection for balanced circuits and is commonly used in the United Kingdom to connect public data networks. The X.21 interface relocates some of the logic functions to the DTE and DCE interfaces and, as a result, requires fewer circuits and a smaller connector than EIA/TIA-232.

The router (FSIP) end of all X.21 adapter cables is a high-density 60-pin plug. The opposite (network) end of the adapter cable is a standard DB-15 connector.

Figure 8-10 shows the connectors at the network end of the X.21 adapter cable.

EIA-530 Connections

The EIA-530 interface, which supports balanced transmission, provides the increased functionality, speed, and distance of EIA/TIA-449 on the smaller, DB-25 connector used for EIA/TIA-232. The EIA-530 interface is used primarily in the United States. The EIA-530 standard was created to support the more sophisticated circuitry of EIA/TIA-449 on the large number of existing EIA/TIA-232 (DB-25) hardware instead of the larger, 37-pin connectors used for EIA/TIA-449. Like EIA/TIA-449, EIA-530 refers to the electrical specifications of EIA/TIA-422 and EIA/TIA-423. Although the specification recommends a maximum speed of 2 Mbps, EIA-530 is used successfully at 4 Mbps and at even faster speeds over short distances.

The router (FSIP) end of the EIA-530 adapter cable is a high-density 60-pin plug. The opposite (network) end of the adapter cable is a standard DB-25 plug commonly used for EIA/TIA-232 connections.

Figure 8-11 shows the DB-25 connector at the network end of the adapter cable.

Metric Thumbscrews

A pair of metric thumbscrews is included with each port adapter cable except V.35. If you plan to connect serial cables to a remote device that uses metric hardware, replace the standard 4-40 thumbscrews at the network end of the cable with the metric, M3 thumbscrews.

To remove thumbscrews, use the flat side of a large (1/4-inch) flat-blade screwdriver to push the tip of the screw into the connector housing and out the other side. (See Figure 8-12.) If the screw resists, use pliers to pull it out. Insert the new thumbscrew and push it into the connector housing until it pops into place.

Cable Connection Precautions

The router (port adapter) end of the FSIP serial interface cables must be connected to the 60-pin receptacles on the port adapter as shown at the top of Figure 8-13. Although the 60-pin plug on each cable is keyed for proper insertion, it can be forced onto the port adapter's receptacle if you are not careful. Also, older serial cables, with fewer pins, cannot be used for the 60-pin receptacle on the port adapter.

Attaching Network Interface Cables to the FSIP

All FSIP ports support any available synchronous serial interface type and mode. The serial adapter cable determines the electrical interface type and mode of the port to which it is connected. E1-G.703/G.704, EIA/TIA-232, EIA/TIA-449, V.35, and X.21 interfaces are available in DTE mode with a plug at the network end and in DCE mode with a receptacle at the network end. EIA-530 is available only in DTE mode with a plug. Connect the FSIP serial cables as shown in Figure 8-14; however, observe the connection precautions indicated in the section "Cable Connection Precautions" on page 8-25.

When you connect serial devices, consider the adapter cables as an extension of the router for external connections. Therefore, use DTE cables to connect the router to remote DCE devices such as modems or DSUs, and use DCE cables to connect the router to remote DTE devices such as a host server, PC, or another router.

Using LEDs to Check FSIP Status

The FSIP has several status LEDs on its faceplate, next to each port, which indicate conditions on that port. (See Figure 8-15.)

The four LEDs adjacent to each port indicate the state of that interface. The labels on each LED indicate the signal state when the FSIP port is in DTE mode. When the FSIP port is in DCE mode, the direction of the signals is reversed.

For example, a DCE device usually generates a clock signal, which it sends to the DTE device. Therefore, when the FSIP port is a DTE port, the Receive Clock (RxC) LED indicates that the DTE is receiving the clock signal from the remote DCE device. However, when the FSIP is operating as a DCE, the RxC LED indicates that the DCE is sending a clock signal to the remote DTE device. Only DTE mode states are labeled on each port because of limited space on the FSIP faceplate.

Figure 8-16 shows the signal flow between DTE and DCE devices and the LEDs that correspond to signals for each mode.

Table 8-9 lists the LED states for ports in DTE and DCE mode; a more complete explanation follows.

Step 2 When the reinitialization is complete, verify that the enabled LED on the FSIP is on and remains on. If the LED does stay on, proceed to Step 5. If the enabled LED does not stay on, proceed to the next step.

Step 3 If the enabled LED on the FSIP fails to go on, suspect that the FSIP board connector is not fully seated in the backplane. Loosen the captive installation screws, then firmly push the ejector levers until both are parallel to the FSIP faceplate. Tighten the captive installation screws. After the system reinitializes the interfaces, the enabled LED on the FSIP should go on. If the enabled LED goes on, proceed to Step 5. If the enabled LED does not go on, proceed to the next step.

Step 4 If the enabled LED still fails to go on, remove the FSIP and try installing it in another available interface processor slot.

• If the enabled LED goes on when the FSIP is installed in the new slot, suspect a failed backplane port in the original interface processor slot.

• If the enabled LED still fails to go on, but other LEDs on the FSIP go on to indicate activity, proceed to Step 5 to resume the installation checkout and suspect that the enabled LED on the FSIP has failed.

• If no LEDs on the FSIP go on, suspect that the FSIP is faulty.

• If the enabled LED still does not go on, do not proceed with the installation. Contact a service representative to report the faulty equipment and obtain further instructions.

Step 5 Use the show interfaces or show controllers cbus command to verify the status of the FSIP interfaces. (If the FSIP interfaces are not configured, configure them using the procedures in the section "Configuring the FSIP.")

If an error message displays on the console terminal, refer to the appropriate reference publication for error message definitions. If you experience other problems that you are unable to solve, contact a service representative for assistance.

Configuring the FSIP

If you want to change the configuration of an existing interface, you must enter configuration mode to configure the interface. If you replaced an FSIP that was previously configured, the system will recognize the new FSIP interfaces and bring each of them up in their existing configuration.

After you verify that the new FSIP is installed correctly (the enabled LED goes on), use the privileged-level configure command to configure the new interfaces. Be prepared with the information you will need, such as the following:

• Protocols you plan to route on each new interface

• Internet protocol (IP) addresses if you will configure the interfaces for IP routing

• Whether or not the new interfaces will use bridging

• Timing source for each new interface and clock speeds for external timing

For complete descriptions of configuration subcommands and the configuration options available for serial interfaces, refer to the appropriate software documentation listed in the section "If You Need More Information" in the chapter "Using Interface Processors."

Configuring the FSIP first requires privileged-level access to the EXEC command interpreter. (Refer to the section "Using the EXEC Command Interpreter" in the chapter "Using Interface Processors.") Also, privileged-level access usually requires a password. (Contact your system administrator, if necessary, to obtain privileged-level access.)

Interface Port Numbering for the FSIP Serial Interfaces

Cisco 7000 series and Cisco 7500 series routers identify an interface address by its interface processor slot number and port number in the format slot/port. Each FSIP contains either four or eight serial interfaces. Ports are numbered sequentially beginning with interface 0. For example, the slot/port address of the first interface on an FSIP installed in interface processor slot 0 is 0/0, and the adjacent port on the same FSIP is 0/1.

Configuring the Interfaces

The following instructions are provided for performing a basic configuration: enabling an interface, specifying IP routing, and setting up external timing on a DCE interface. You might also need to enter other configuration subcommands, depending on the requirements for your system configuration and the protocols you plan to route on the interface.

In the following procedure, press the Return key after each step unless otherwise noted.

Step 1 At the privileged-level prompt, enter configuration mode and specify that the console terminal will be the source of the configuration subcommands, as follows:

Router# configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Router(config)#

Step 2 At the prompt, specify the first interface to configure by entering the subcommand interface, followed by the type (serial) and slot/port (interface processor slot number/0). The example that follows is for the first port on an FSIP in interface processor slot 0:

Router(config)# interface serial 0/0

Step 3 If IP routing is enabled on the system, you can assign an IP address and subnet mask to the interface with the ip address configuration subcommand, as in the following example:

Router(config-if)# ip address 1.1.1.67 255.255.255.0

Step 4 Add any additional configuration subcommands required to enable routing protocols and adjust the interface characteristics.

Step 5 If you are configuring a DTE interface, proceed to Step 7. If you are configuring a DCE interface, you also need to configure the external clock signal, as described in the next step.

Step 6 Set the clock rate with the clockrate command. (For a description of the clockrate command, refer to the section "Configuring Timing (Clock) Signals" which follows.)

Router(config-if)# clockrate 72000

Step 7 Change the shutdown state to up and enable the interface as follows:

Configuring Timing (Clock) Signals

All interfaces support both DTE and DCE mode (except the EIA-530 interface, which is DTE only). The mode of the interface cable attached to the port. To use a port as a DTE interface, you must connect a DTE adapter cable to the port. When the system detects the DTE mode cable, it automatically uses the external timing signal.

To use a port in DCE mode, you must connect a DCE interface cable and set the clock speed with the clockrate configuration command. You must also set the clock rate to perform a loopback test.

This section describes how to set the clock rate on a DCE port and, if necessary, how to invert the clock to correct a phase shift between the data and clock signals.

Setting the Clock Rate

All DCE interfaces require a noninverted internal transmit clock signal, which is generated by the FSIP. The default operation on an FSIP DCE interface is for the DCE device (FSIP) to generate its own Transmit Clock (TxC) signal and send it to the remote DTE. The remote DTE device returns the clock signal to the DCE (FSIP port). The clockrate command specifies the rate as a bits-per-second value.

In the following example, the clock rate for the first serial interface on an FSIP in interface processor slot 0 (0/0) is defined as 72 kbps:

Router(config)# interface serial 0/0
Router(config-if)# clockrate 72000

Use the no clockrate command to remove the clock rate.

Following are the acceptable clockrate settings:

1200, 2400, 4800, 9600, 19200
38400 , 56000 , 64000 , 72000 , 125000
148000 , 500000, 800000, 1000000, 1300000
2000000 , 4000000 , 8000000

Speeds above 64 kbps (64000) are not appropriate for EIA/TIA-232. On all interface types, faster speeds might not work if your cable is too long.

Inverting the Clock Signal

Systems that use long cables can experience high error rates when operating at higher transmission speeds. Slight variances in cable construction, temperature, and other factors can cause the clock and data signals to shift out of phase. If an FSIP DCE port is reporting a high number of error packets, a phase shift might be the problem. Inverting the clock can often correct this shift.

When a port is operating in DCE mode, the default operation is for the attached DTE device to return the Synchronous Clock Transmit Enable (SCTE) signal to the DCE (FSIP port). The DCE sends the Synchronous Clock Transmit (SCT) and Synchronous Clock Receive (SCR) signals to the DTE, and the DTE returns an SCTE signal to the DCE. If the DTE does not return the SCTE signal, you must use the command transmit-clock-internal to configure the DCE port to use its own clock signal in place of the SCTE signal that would normally be returned.

To configure an interface to accept the internal clock generated by the FSIP in place of the SCTE signal that is normally returned by the DTE device, specify the slot and port address of the interface followed by the command transmit-clock-internal.

In the example that follows, the first serial port on an FSIP in interface processor slot 0 is configured to accept the internal clock signal:

Router(config)# interface serial 0/0
Router(config-if)# transmit-clock-internal

When the FSIP port is a DTE, the invert-transmit-clock command inverts the TxC signal it receives from the remote DCE. When the FSIP port is a DCE, this command inverts the clock signal to the remote DTE port. Use the no invert-transmit-clock command to change the clock signal back to its original phase.

Configuring NRZI Format

All interfaces support both NRZ and NRZI formats. Both formats use two different voltage levels for transmission. NRZ signals maintain constant voltage levels with no signal transitions (no return to a zero voltage level) during a bit interval and are decoded using absolute values (0 and 1). NRZI uses the same constant signal levels, but interprets the presence of data at the beginning of a bit interval as a signal transition and the absence of data as no transition. NRZI uses differential encoding to decode signals rather than determining absolute values.

NRZ format, the factory default on all interfaces, is most common. NRZI format, which is configured with a software command, is commonly used with EIA/TIA-232 connections in IBM environments. To enable NRZI encoding on any interface, specify the slot and port address of the interface followed by the command nrzi-encoding. Enter Ctrl-Z when you have finished with the configuration change. In the example that follows, the first serial port on an FSIP in interface processor slot 0 is configured for NRZI encoding:

Router# configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
Router(config)# interface serial 0/0
Router(config-if)# nrzi-encoding 
Router(config-if)# ^Z

To disable NRZI encoding on a port, specify the slot and port address and use the no nrzi-encoding command.

Configuring CRCs

The cyclic redundancy check (CRC) is an error-checking technique that uses a calculated numeric value to detect errors in transmitted data. All interfaces use a 16-bit CRC by default, but also support a 32-bit CRC. The sender of a data frame divides the bits in the frame message by a predetermined number to calculate a remainder or frame check sequence (FCS). Before it sends the frame, the sender appends the FCS value to the message so that the frame contents are exactly divisible by the predetermined number. The receiver divides the frame contents by the same predetermined number that the sender used to calculate the FCS. If the result is not 0, the receiver assumes that a transmission error occurred and sends a request to the sender to resend the frame.

The designators 16 and 32 indicate the number of check digits per frame that are used to calculate the FCS. CRC-16, which transmits streams of 8-bit characters, generates a 16-bit FCS. CRC-32, which transmits streams of 16-bit characters, generates a 32-bit FCS. CRC-32 transmits longer streams at faster rates; therefore, it provides better ongoing error correction with fewer retransmissions. Both the sender and the receiver must use the same setting.

To enable 32-bit CRC on an interface, specify the slot and port address of the interface followed by the command crc32. In the example that follows, the first serial port on an FSIP in interface processor slot 0 is configured for 32-bit CRC:

Router# configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
Router(config)# interface serial 0/0
Router(config-if)# crc32 
Ctrl-Z

To disable CRC-32 and return to the default CRC-16 setting, specify the slot and port address and use the no crc32 command.

For additional command descriptions and examples, refer to the related software configuration documentation listed in the section "If You Need More Information" in the chapter "Using Interface Processors."

Configuring E1-G.703/G.704 Balanced and Unbalanced Modes

The E1-G.703/G.704 interface is available in either balanced or unbalanced mode. A unique port adapter supports each type. Neither the modes nor the cables are interchangeable; you cannot configure a balanced port to support an unbalanced line, nor can you attach an interface cable intended for a balanced port to an unbalanced port.

Balanced interfaces typically use three conductors and three signal states: high, low, and ground. The high and low signals mirror each other. Unbalanced interfaces use only two signals: signal and ground. You can determine the mode of each interface in two ways: check the agency approval label on each FSIP port or use the show controller cbus command. Following is an example of the latter:

Router# show controllers cbus
(additional displayed text omitted from this example)
 FSIP 0, hardware version 1.0, microcode version 1.0
  Interface 8 - Serial0/0, electrical interface is E1-G.703, balanced
  Interface 9 - Serial0/1, electrical interface is E1-G.703, balanced
(additional displayed text omitted from this example)

Configuring E1-G.703/G.704 Framed and Unframed Operation

The E-G.703 interface is divided into 32 time slots, or frames. (See Figure 8-17.) Each of the 32 time slots is an 8-bit frame that transmits data at 64 kbps. Each of these time slots can be configured to carry data or to remain empty. (The E1-G.703/G.704 port adapter inserts an idle pattern into empty time slots.)

[no] timeslot 0/start-slot-31/stop_slot 

Router# timeslot 1-13

Configuring E1-G.703/G.704 CRC-4

Framed mode supports a 4-bit CRC, which you enable with a software command. CRC-4 is a 4-bit error checking technique that uses a calculated numeric value to perform an ongoing data integrity check and detect errors in transmitted data. The E1-G.703/G.704 interface supports CRC in framed mode only. By default, CRC-4 is not enabled. To enable CRC-4 on the E1 interface, specify the slot and port address of the interface followed by the command crc4. Press Ctrl-Z after altering the configuration and before exiting configuration mode.

In the example that follows, the first port on an FSIP in interface processor slot 0 is configured for CRC-4:

Router# configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
Router(config)# interface serial 0/0
Router(config-if)# crc4 
Ctrl-Z

To disable CRC and return an interface to the default of no CRC error checking, specify the interface and use the no crc4 command.

Configuring E1-G.703/G.704 Clock Source

The E1-G.703/G.704 interface does not operate in the DTE and data communications equipment (DCE) modes that are typical of data communications interfaces. The E1-G.703/G.704 interface operates with either a line-recovered or an internal clock signal. The default is for a line clock signal that the interface recovers from the received data stream. The interface can also operate with an internal clock signal. The E1-G.703/G.704 port adapter generates the internal clock signal; the interface does not use the FSIP clock.

We recommend that you leave one port on each module shut down to avoid exceeding the 6.132 Mbps maximum for each module because the E1-G.703/G.704 interfaces operate at a default clock rate of 2.048 Mbps (E1 speed).

To specify the clock source, use the clock source {line | internal} command. To change the default and use the internal clock, use the clock source internal command. To return the interface to the default state, use the clock source line command. (The no clock source internal command also returns the interface to the default state.)

Interpreting E1-G.703/G.704 Alarms

Following are definitions and descriptions of the five alarms used with the E1-G.703/G.704 interface:

• AIS--The alarm indication signal occurs and a failure is declared (for E1 links) when 64 consecutive ones occur on the Receive Data (RD) line between the applique and the FSIP.

• RAI--The remote alarm indication (also called the far end alarm and distant alarm for E1 links) is sent by the remote end of the link to indicate failure at the remote end. This failure is declared (for E1 links) when 32 contiguous pulse positions have no pulses of either positive or negative polarity.

• LOS--The loss of signal alarm occurs and a failure is declared (for E1 links) when more than ten consecutive zeroes are detected.

• LOF--The loss of frame alarm occurs and a failure is declared (for E1 links) when an out-of-frame (OOF) defect has persisted for T seconds, where 2 < T < 10. This failure is cleared when there have been no OOF defects during a period T seconds, where 0 < T < 20.

• SQ--The signal quality alarm occurs and a failure is declared (for E1 links) when the bit error rate (BER) is greater than 10^-3 on the RD line between the applique and the FSIP.

Configuring E1-G.703/G.704 Loopback

The E1-G.703/G.704 interface supports the same local loopback test as the other (data communications) FSIP interfaces. Loopback functions enable you to check the integrity of the physical data path between the FSIP and the E1 port adapter with the loopback command. The no loopback command disables all loopback tests on the interface.

You do not have to configure a clock signal on the interface before performing a loopback test because the E1-G.703/G.704 interface uses a default clock rate of 2.048 Mbps.

The loopback command tests the path between the FSIP and the interface port (without leaving the FSIP and port adapter). On the E1 port adapter, the loopback signal follows this path regardless of whether or not a cable is attached to the port.

Figure 8-18 shows the path of the loopback function.

Replacing Port Adapter Cables and Changing Interface Modes

The port adapter cable connected to each port determines the electrical interface type and mode of the port. The default mode of the ports is DCE, which allows you to perform a loopback test on any port without having to attach a port adapter cable. Although DCE is the default, there is no default clock rate set on the interfaces. When there is no cable attached to a port, the software actually identifies the port as Universal, Cable Unattached rather than either a DTE or DCE interface.

Following is an example of the show controller cxbus command, which shows the first serial port on an FSIP in interface processor slot 0 (0/0) that has an EIA/TIA-232 DTE cable attached, and a second serial port (0/1) with no cable attached:

Router# show controller cxbus
(additional displayed text omitted from this example)
FSIP 0, hardware version 3, microcode version 1.0
Interface 16- Serial0/0, electrical interface is RS-232 DTE
31 buffer RX queue threshold, 101 buffer TX queue limit, buffer size 1520
    Transmitter delay is 0 microseconds
Interface 17- Serial0/1, electrical interface is Universal (cable unattached)
31 buffer RX queue threshold, 101 buffer TX queue limit, buffer size 1520
(additional displayed text omitted from this example)

To change the electrical interface type or mode of a port online, you must replace the serial adapter cable and use software commands to restart the interface and, if necessary, reconfigure the port for the new interface.

At system startup or restart, the FSIP polls the interfaces and determines the electrical interface type of each port (according to the type of port adapter cable attached). However, it does not necessarily repoll an interface when you change the adapter cable online. To ensure that the system recognizes the new interface type, shut down and reenable the interface after changing the cable.

Perform the following steps to change the mode (DTE or DCE) or interface type (EIA/TIA-232, and forth) of a port by replacing the adapter cable. First replace the cable, then shut down and bring up the interface with the new cable attached so that the system recognizes the new interface. If you are replacing a cable with one of the same interface type and mode, these steps are not necessary (simply replace the cable without interrupting operation).

Step 1 Locate and remove the adapter cable to be replaced.

Step 2 Connect the new cable between the FSIP port and the network connection. Tighten the thumbscrews at both ends of the cable to secure it in the ports.

Step 3 At the privileged level of the EXEC command interpreter, specify the port address, shut down the interface, and write the configuration to nonvolatile random-access memory (NVRAM). Add additional configuration commands as needed. Then exit from configuration mode by entering Ctrl-Z.

Router# configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Router(config)# int serial 0/1
Router(config-if)# shutdown
Ctrl-Z

Router# copy running-config startup-config

Step 4 Enter configuration mode again and bring the port back up:

Router# configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Router(config)# int serial 0/1
Router(config-if)# no shutdown
Router(config-if)# ^Z

These steps prompt the system to poll the interface and recognize the new interface immediately. (For a complete description of the shutdown procedure, refer to the section "Shutting Down an Interface" in the chapter "Using Interface Processors.")

When you configure a port for a DCE interface for the first time, or when you set up a loopback test, you must set the clock rate for the port. When you connect a DCE cable to a port, the interface will remain down, the clock LEDs will remain off, and the interface will not function until you set a clock rate (regardless of the DCE mode default).

If you are changing the mode of the interface from DCE to DTE, you do not need to change the clock rate for the port. After you replace the DCE cable with a DTE cable and the system recognizes the interface as a DTE, it will use the external clock signal from the remote DCE device and ignore the internal clock signal that the DCE interface normally uses. Therefore, once you configure the clock rate on a port for either a DCE interface or loopback, you can leave the clock rate configured and still use that port as a DTE interface.

For additional descriptions of software configuration commands, refer to the appropriate publications listed in the section "If You Need More Information" in the chapter "Using Interface Processors."

Using Show Commands to Check the Configuration

The following summary describes how to use the show commands to verify that the new interfaces are configured correctly:

Step 1 Use the show version command to display the system hardware configuration. Ensure that the list includes the new interfaces.

Step 2 Display all the current interface processors and their interfaces with the show controllers cbus command. Verify that the new FSIP appears in the correct slot.

Step 3 Specify one of the new interfaces with the show interfaces serial slot/port command and verify that the first line of the display specifies the interface with the correct slot number. Also verify that the interface and line protocol are in the correct state: up or down.

Step 4 Display the protocols configured for the entire system and specific interfaces with the command show protocols. If necessary, return to configuration mode to add or remove protocol routing on the system or specific interfaces.

Step 5 Display the entire system configuration file with the show running-config command. Verify that the configuration is accurate for the system and each interface.

If an interface is down and you configured it as up, or if the displays indicate that the hardware is not functioning properly, ensure that the network interface is properly connected and terminated. If you still have problems, contact a service representative for assistance.

This completes the FSIP configuration procedure.