Table of Contents

Line Interface Cards

This chapter describes the hardware and related functions for each circuit line card in the IGX. The description of each card includes:

• Function
  
  
• System interconnect
  
  
• Faceplate indicators
  
  

A brief description of optional peripherals and third-party equipment appears at the end of the chapter. For system specifications, such as protocols and standards, refer to Appendix A.

For all matters relating to installation, troubleshooting, user-commands, and repair and replacement, refer to the IGX  Installation Manual.

Other manuals that relate to IGX operation are:

• The Command Reference and Superuser Command Reference describe standard user commands and superuser commands.
  
  
• The System Manual contains general StrataCom system and network information.
  
  
• The StrataView Plus Operations contains information on StrataCom network management.
  
  

Circuit Line Card Groups

The IGX currently has the following circuit line card groups:

• Channelized Voice Module Card Group
  
  
• Frame Relay Card Group
  
  
• FastPAD Card Group
  
  
• Serial Data Card Group
  
  
• Alarm Interface Card Group
  
  

This chapter introduces each card in the preceding groups.

Card Types

Table 4-1 lists the front cards that can be used in the IGX. Table 4-2 lists the back cards that can operate in an IGX. In addition to the front and back cards, the IGX uses an Adapter Card Module (ACM). These cards attach to existing IPX 16/32 service module cards and perform the adaptation necessary to allow IPX 16/32 front cards to operate in an IGX 8, 16, or 32 system. Note that IPX 8-specific cards do not apply to the upgrade scheme. Beyond this, IPX back cards can operate in an IGX system without modifications.

Common Alarms, Controls, and Indicators

Front cards and back cards have faceplates with indicator LEDs and, on some front cards, push-button controls. In addition, back card faceplates have the cable connectors. In slots where no back card exists, a blank faceplate must reside to contain Electromagnetic Interference (EMI) and Radio Frequency Interference (RFI) and to ensure correct air flow.

The LED indicators are on the front and back card faceplates. Each plug-in card has both a green ACTIVE LED and a red FAIL LED at the bottom of the faceplate. In general, the meaning of each LED is indicated in Table 4-3. Some other cards have additional indicators, connectors, or controls, which the appropriate sections describe.

Adapter Cards

StrataCom can upgrade IPX service/interface cards for use in an IGX. This allows the IGX to provide all the services of the IPX with cards of proven efficiency, functionality, and reliability. The upgrade is available only as a factory upgrade. The factory upgrade consists of an adding one of three possible Adapter Card Modules (ACM) and possible firmware or hardware modifications. Due to the complexity of the ACM, field upgrades of IPX cards are not possible.

Connecting IPX front cards to their corresponding back cards on the IPX requires the use of a utility or local bus. On upgraded IPX cards (IGX cards), the local or utility bus is not necessary.

The following IPX cards can be adapted for use in the IGX:

• NTC
  
  
• AIT
  
  
• CDP
  
  
• FRP
  
  
• FTC
  
  
• SDP
  
  
• LDP
  
  
• ARC
  
  

Channelized Voice Module (CVM)

This section introduces the Channelized Voice Module (CVM) and its related back cards. The subsections within this section are as follows:

• A CVM overview and feature list
  
  
• An introduction to the modes of CVM data and voice processing
  
  
• A brief description of CVM voice processing
  
  
• A brief description of CVM data processing
  
  
• CVM signalling support
  
  
• Loopbacks on the CVM card set
  
  
• Front card and back card faceplate descriptions
  
  
• TDM Transport (support for older TDM equipment)
  
  

For setup instructions, see the IGX Installation Manual and the relevant commands in the Command Reference.

The CVM is a multi-purpose front card. A CVM circuit line can carry the following types of traffic:

• Voice
  
  
• Data
  
  
• A combination of voice and either low-speed or high-speed data
  
  

In addition to other CVMs, a CVM can communicate with a CDP in an IPX. The default mode for a channel on a CVM is voice. Figure 4-1 illustrates different traffic configurations. You can use the CVM in either 24-channel mode (T1) or 30-channel mode (E1). You assign the circuits on a CVM hop on a per-timeslot basis within a T1 or E1 frame.

The CVM resides in any non-reserved front slot in an IGX. It operates with either a BC-T1, BC-E1, or BC-J1 back card. The back card plugs into the P2 connector on the CVM front card. For details on the back cards, refer to the forthcoming sections titled "T1 Interface Back Card (BC-T1) ," "E1 Interface Back Card (BC-E1)," or "BC-J1 Description ."

Figure 4-1: CVM Application Diagram

CVM Features

The following is a list of CVM features.

• Packet assembly/disassembly (PAD) for voice or data connections
  
  
• Software configurable ports on T1, E1, or J1 back cards
  
  
• Support for Dynamic Network Switching (DNS)
  
  
• Local and remote loopbacks for port and circuit testing
  
  
• Self-test of all on-board circuits, including optional echo cancellers
  
  
• Y-cable redundancy
  
  
• Up to 4:1 voice compression using adaptive differential pulse code modulation (ADPCM) with integral voice activity detection (VAD)
  
  
• Integral, per-channel, echo cancelling (requires optional circuits on the front card)
  
  
• A-law or µ-law voice encoding on a per-channel basis
  
  
• Programmable voice circuit gain in the range -8 dB through +6 dB
  
  
• Support for many domestic and international signalling types
  
  
• Flexible signalling-bit conditioning when a circuit alarm occurs
  
  
• Per-channel tone detection to disable compression for modem or FAX circuits
  
  
• Sub-rate, standard rate, and super-rate data connections
  
  
• Support for transparent TDM channels through a network
  
  

Modes of CVM Operation

This section describes the operational parameters you can specify for the CVM card set. Table 4-4 is a list of the types of CVM operation. The sections that follow further describe the listed subjects.

The first two entries in Table 4-4 are the two types of 64-Kbps, clear channel operation. The "p" indicates uncompressed PCM voice. The "t" indicates 64 Kbps clear channel data. The table then shows voice and data modes, transmit/receive rates, and indications of compression and ZCS (zero code suppression). A "c" or an "a" preceding a numerical value indicates compression. A "c" indicates compression with voice activity detection (VAD), so "c" does not apply to data connections. An "a" indicates compression without VAD. The "a" can apply to either voice or data. The numerical value following the "a" or "c" is the bit rate. Table 4-4 also explains the significance of the other characters that may follow the bit rate.

Standard-rate (64 Kbps) voice connections terminate on CVM T1 or E1 lines. You can configure the voice compression, and echo cancelling for each channel, and-when circumstances make it appropriate-A-law or µ-law encoding. You can select voice frequency compression of 64 Kbps (no compression), 32 Kbps (2:1), 24 Kbps (3:1), or 16 Kbps (4:1). The compression ratios approximately double when you also enable the internal VAD.

CVM Voice Operation

The particular voice features are:

• High-speed modem and FAX circuits.
  
  
• Transparent, 64-Kbps transport of CCS signalling.
  
  
• CAS, by transporting signalling transitions across the network in packets.
  
  
• Optional circuit for the CVM is the on-board Integrated Echo Canceller (IEC): the two models of the IEC are the 24-channel (T1) and the 31-channel (E1) versions.
  
  
• Selectable A-law or µ-law encoding when the circumstances require it. (Normally, T1 automatically uses just µ-law and E1 just A-law.)
  
  

In addition to the preceding, the CVM can set, invert, and clear AB or ABAB bits (T1) or ABCD bits (E1) to accommodate some signalling conversions.

CVM Data Operation

A CVM can provide data connections to the network. Data connections that originate on a CVM can terminate on either a CVM, HDM, or LDM card set on another node.

Two categories of data connections exist on the CVM. The categories are super-rate and subrate. A super-rate connection is an aggregate of channels that functions as a single, logical connection. A super-rate connection can consist of any combination of 56 or 64 Kbps-connections up to a maximum of 8 connections totalling 512 Kbps. The DS0 timeslots must be contiguous or alternating (not random). All 56-Kbps data channels are bit-stuffed up to 64 Kbps on a circuit line. The CVM removes the bits prior to packetization. Note that super-rate connections carry no supervisory bits.

A subrate data connection has a rate less than 64 Kbps and exists within a DS0. The supported rates are 2.4, 4.8, 9.6, and 56 Kbps. The type of subrate data connection that StrataCom supports is DS0A.

In-band DS0A link codes are translated into EIA control lead states for CVM-to-HDM or LDM connections, but fast EIA, DFM, and isochronous clocking are not available.

Signalling on the CVM

The CVM extracts information from the signalling bits in the E1 or T1 frame. When a signalling bit changes state, the CVM generates signalling packets to the CVM at the other end of the connection. DPNSS and ISDN signalling are supported through a clear channel (transparent mode). The supported combinations of signalling and line configurations are as follows:

• T1 uses ABAB or ABCD signalling bits when the line framing is ESF.
  
  
• T1 uses AB signalling bits when the line framing is D4.
  
  
• T1 can use CCS in timeslot 24 on applicable PBXs if your application requires CAS to be off.
  
  
• E1 uses either CCS or, if you selected CAS, ABCD signalling bits. For CCS, you configure channel 16 as a t-type connection to carry the signalling, making a possible total of 31 channels.
  
  

Up to 23 voice interface types, such as 2-W E&M, FXO/FXS, or DPO/DPS, can be selected from a template to condition the VF signalling. You can also specify customized signal conditioning. Voice channel signalling is programmable for any of the following:

• Robbed bit (either D4 or ESF frame format)—for T1 lines
  
  
• Channel Associated Signalling (CAS)—for E1 lines
  
  
• Transparent CCS (ISDN & DPNSS)—for T1 or E1 lines
  
  
• E&M-to-DC5A and DC5A-to-E&M conversion—for international applications
  
  

Line Statistics

The CVM card set monitors and reports statistics on the following input line conditions:

• Loss of signal
  
  
• Frame sync loss
  
  
• Multi-frame sync loss
  
  
• CRC errors (for E1 only)
  
  
• Frame bit errors
  
  
• Frame slips
  
  
• Bipolar violations
  
  
• Frame bit errors
  
  
• AIS, all-1's in channel 16 (CAS mode)
  
  
• Remote (yellow) alarm
  
  

Loopbacks on the CVM Card Set

You can set up local and remote loopbacks to check CVM-terminated connections. A local loopback functions at the system bus interface. It returns data and supervision back to the local facility to test the local CVM card set and the customer connection. Remote loopbacks extend to the CVM card at the other end and check both transmission directions and much of the far-end CVM.

CVM Faceplate Description

The CVM faceplate has four LED indicators: ACTIVE, FAIL, MAJOR, and MINOR (see Table 4-5). The label on the faceplate also shows the type of CVM card.

T1 Interface Back Card (BC-T1)

The BC-T1 back card provides a T1 circuit line interface for a CVM card. The BC-T1 plugs into the P2 connector on the CVM front card. The card set can reside in any non-reserved slot. The BC-T1 provides the following features:

• Trunk line interfaces to T1 trunks at 1.544 Mbps
  
  
• Software selectable AMI or B8ZS (bipolar 8 zero suppress) line code
  
  
• Software selectable D4 or ESF (extended super-frame) framing format
  
  
• Configuration as either full or fractional T1 service
  
  
• Extraction of receive-timing from the input signal for use as the node timing
  
  
• Software selectable line buildout for cable lengths up to 655 feet
  
  
• Passes T1 line event information to the front card (events include Frame loss, Loss of signal, bi-polar violations, and frame errors)
  
  

B8ZS supports clear channel operation because B8ZS eliminates the possibility of a long string of 0s. B8ZS is preferable whenever available, especially on trunks.

The BC-T1 supports two clock modes. The clock modes are normal clocking and loop timing. You select the mode through software control. With normal clocking, the node uses the receive clock from the network for the incoming data and supplies the transmit clock for outgoing data. The node can use the receive clock to synchronize itself with the network.

With loop timing, the node uses the receive clock from the network for the incoming data and redirects this receive clock to time the transmit data.

BC-T1 Faceplate Description

Figure 4-2 and Table 4-6 provide information on the faceplate of the BC-T1. When you correlate the descriptions in the table with the callouts in the figure, read from the top of the table to the bottom. The standard port connector is a female DB15.

Figure 4-2: BC-T1 Faceplate

Table 4-6: BC-T1 Connections and Status LEDs

E1 Interface Back Card (BC-E1)

The BC-E1 back card provides an E1 circuit line interface for a CVM card. The BC-E1 back card plugs into the P2 connector on the CVM front card. The card set can reside in any non-reserved slot. The BC-E1 provides the following features:

• Interfaces to CEPT E1 lines (CCITT G.703 specification)
  
  
• Support for both Channel Associated Signalling and Common Channel Signalling
  
  
• Support for 30-channel (1.920 Mbps) operation
  
  
• CRC-4 error checking
  
  
• Support for HDB3 (clear channel operation on E1 lines) or AMI
  
  
• Passes E1 line events to the front card (events include Frame loss, Loss of signal, BPV, frame errors, CRC errors, and CRC synchronization loss)
  
  
• Detection of loss of packet sync when used with the CVM
  
  
• 120-ohm balanced or 75-ohm balanced or unbalanced physical interfaces
  
  

The BC-E1 supports two clock modes. The clock modes are normal clocking and loop timing. You select the mode through software control. With normal clocking, the node uses the receive clock from the network for the incoming data and supplies the transmit clock for outgoing data. The node can use the receive clock to synchronize itself with the network.

With loop timing, the node uses the receive clock from the network for the incoming data and redirects this receive clock to time the transmit data.

Statistics are kept on most line errors and fault conditions, including the following:

• Loss of signal
  
  
• Frame sync loss
  
  
• Multi-frame sync loss
  
  
• CRC errors
  
  
• Frame slips
  
  
• Bipolar violations
  
  
• Frame bit errors
  
  
• AIS, all-1's in channel 16 (CAS mode)
  
  

Figure 4-3 shows and Table 4-7 lists status LEDs and connections on the BC-E1 faceplate. When you correlate the table and figure items, read from the top to the bottom.

Figure 4-3: BC-E1 Faceplate

Table 4-7: BC-E1 Connections and Status LEDs

BC-J1 Description

The BC-J1 back card provides a Japanese J1 circuit line interface for a CVM card. The BC-J1 back card plugs into the P2 connector on the CVM front card. The card set can reside in any non-reserved slot. The BC-J1 provides the following features:

• Provides interfaces for Japanese TTC (J1) lines specified by JJ-20-10, JJ-20-11, and JJ-20-12
  
  
• Supports Channel Associated Signalling (CAS) and Common Channel Signalling (CCS)
  
  
• Supports 30-channel, 2.048 Mbps operation
  
  
• Uses Coded Mark Inversion (CMI) line coding
  
  
• Automatically starts local loopback tests in response to certain line alarms
  
  
• Passes J1 line event information to the front card (events include frame loss, loss of signal, bi-polar violations, and frame errors)
  
  

The BC-J1 supports two clock modes. The modes are normal clocking and loop timing. You select the mode through software control. With normal clocking, the node uses the receive clock from the network for the incoming data and supplies the transmit clock for outgoing data. The node can use the receive clock to synchronize itself with the network. With loop timing, the node uses the receive clock from the network for incoming data and redirects the receive clock to time the transmit data.

Figure 4-4 shows a BC-J1 faceplate. Table 4-8 lists BC-J1 connections and status LEDs.

Figure 4-4: BC-J1 Faceplate
 
Table 4-8: BC-J1 Connections and Status LEDs

The TDM Transport Feature

This section applies only to CVMs (and CDPs in the IPX) that have Rev. C firmware. Rev. C provides a service called Time Division Multiplexing Transport (TDM Transport). TDM Transport bundles DS0s to form a single, transparent connection through the network. TDM Transport is most valuable for transporting TDM data from trunks in older, non-StrataCom WANs. For setup instructions, see the IGX Installation Manual and the relevant commands in the Command Reference.

Rev. C Features

The Rev. C firmware features are as follows:

• A collection of properly configured data connections behaves as a single, transparent connection. A single connection can be from 1 to 8 DS0s (64 to 512 Kbps).
  
  
• TDM Transport supports inverse multiplexing support.
  
  
• The maximum rate is 2 Mbps.
  
  
• The supported line coding is 8/8 on the circuit and trunk interfaces.
  
  
• TDM Transport service preserves DS0 alignment within frames.
  
  

Rev. C Limitations

The limitations on TDM Transport within Rev. C firmware are as follows:

• TDM Transport supports bundled data connections only—no voice or DS0A.
  
  
• Circuit timing cannot come from user equipment.
  
  
• Pleisochronous clocking is not allowed.
  
  
• Super-frame alignment is not preserved.
  
  
• Framing bits are not transported.
  
  
• Rev. C does not support 7/8 line encoding on circuit lines or packet lines.
  
  
• A CDP or CVM with Rev. C firmware is compatible only with other CDPs or CVMs that have Rev. C firmware.
  
  
• Connections on any CVM or CDP with Rev. C firmware must terminate on only one other CVM or CDP.
  
  
• The parameter "Max. Network Delay of CDP-CDP High Speed Data Connections" must not exceed 45 ms.
  
  
• The difference in delay due to propagation and maximum trunk queuing cannot exceed 25 ms. For example, one connection taking one hop and another taking six hops is not allowed. Likewise, a connection over a satellite link and another over a terrestrial link is not allowed.
  
  
• For loopbacks on a CDP or CVM with Rev. C firmware, the card must have only one connection.
  
  

Inverse Multiplexing

To achieve full T1 and E1 rates on a single CVM or CDP, TDM Transport supports inverse multiplexing. Figure 4-5 shows a simple example. In this example, the three, bundled 512-Kbps data connections symbolized by the arrows add up to a T1 connection.

Figure 4-5: Inverse Multiplexing

Achieving Optimal Performance for TDM Transport

Because a single bit error can cause the entire group of connections to lose synchronization temporarily, trunks and nodes that carry the traffic should have a low bit error rate. To minimize the recovery time after a loss of synchronization, configure the least possible number of connections to carry the bandwidth. In specifying a transparent T1, for example, 3 8x64 connections is much better than 24 1x64 connections.

Frame Relay Cards

This section describes the frame relay service cards. The frame relay cards consist of the UFM (Universal Frame Module) family of front and back cards and the FRM (Frame Relay Module) family of front and back cards. The first part of this section contains information that applies to UFM and FRM cards. Subsequent sections contain information that is particular to individual front and back cards. The frame relay and individual card topics are:

• Introduction to frame relay on IGX
  
  
• UFM front cards
  
  
• UFI back cards, which provide interfaces for T1 and E1 lines
  
  
• FRM front cards
  
  
• FRI back cards, which provide interfaces for T1, E1, V.35, and X.21 lines
  
  
• FRM-2 front card and FRI-2 back card, which support the Port Concentrator Shelf (PCS)
  
  
• Frame relay port redundancy
  
  
• Card self-test
  
  
• Port Testing
  
  

Refer to the IGX Installation Manual for installation instructions. For technical details on the line types that individual back cards support, refer to the appendix titled "System Specifications." For a description of the frame relay services that the FastPAD provides, refer to the section titled "FastPAD Trunk Module" later in this chapter.

Introduction

This section lists information that applies to frame relay service. The first list describes functions at the node-level and the network interface. The second list contains card-specific information.

An IGX frame relay network features the following:

• A Permanent Virtual Circuit (PVC) service.
  
  
• Three Local Management Interface (LMI) protocols: ANSI Annex D, the ITU-T (CCITT) Annex A, and a StrataCom LMI. LMI protocols operate between the user device and the network. LMI is the only supervisory signalling on a logical port.
  
  
• A frame-forwarding service. This service forwards all valid HDLC frames from one port to a single port in the network without frame relay header processing or LMI control. For example, a workstation that transmits HDLC frames can connect to a single frame relay port on an FRM. To use this feature, the entire physical port must be dedicated to that workstation.
  
  
• Bundled connections.
  
  
• Explicit congestion notification.
  
  

The FRM and UFM front cards perform the following functions:

• Packetize and depacketize frame relay data frames.
  
  
• Provide frame multiplexing and demultiplexing using the DLCI field.
  
  
• Regulate the flow of data frames into the network to prevent congestion.
  
  
• Inspect frames to ensure they are within size limits and consist of an integer number of octets.
  
  
• Perform CRC check to detect transmission errors.
  
  
• Support intelligent communication with user devices to share information on addition, deletion, congestion, and alarms of the multiple PVCs on each port.
  
  
• Perform — and report the results of — loopback tests for internal, local external, and remote external tests to modems or NTUs. (Loopback tests do not apply to T1 or E1 lines.)
  
  

On the receiving end, the UFM, FRM, or FRM-2 card set checks arriving frames against the embedded Frame Check Sequence (FCS) code and discards any non-compliant frames. The frame relay card places frame relay data into FastPackets. Frame relay flag bytes and bit-stuffing provide frame delimiting and transparency. If a user data byte has a value of hexadecimal 7E, the frame relay card changes it by using 0-bit insertion, so that the card does not process the byte as a flag byte. (The frame relay card uses flag bytes to fill partial FastPackets.)

Frame Relay Over T1 and E1 Lines

On an IGX, frame relay over a T1 or E1 line requires:

• FRM front card with an FRI-T1 or FRI-E1 back
  
  
• UFM-4C or UFM-8C front card with a UFI-8T1-DB15, UFI-8E1-DB15, or UFI-8E1-BNC back card
  
  

A Frame Relay T1/E1 connection can terminate on any Frame Relay Interface—V.35, X.21, T1 or E1.

Frame relay over a T1 or E1 interface supports groups of DS0 timeslots in a logical port. A logical port is a single DS0 or a group of contiguous DS0s. Logical ports consisting of multiple DS0s operate at the full rate of 64 Kbps per timeslot. If a logical port consists of a single DS0, you can configure either 56 Kbps or 64 Kbps. See Figure 4-6.

If the rate on a logical port is 56 Kbps, the frame relay interface strips the least significant (signalling) bit from the incoming octet and puts a 1 in the least significant bit of the outgoing octet. The 56-Kbps rate typically applies to a groomed DDS circuit that uses a T1/E1 line.

Figure 4-6: Multiple and Single DS0s Forming a Logical Port

Frame Relay Card Redundancy

Frame relay card redundancy can be provided through a second card set in adjacent slots and a Y-cable between each port that connects to the user-equipment. See Figure 4-7 for an illustration. The hardware kits for this feature contain a second frame relay card set, a set of Y-cables to interconnect the two card sets, and any other pieces that apply to the card types. Y-cable redundancy is not possible using back cards with different interfaces, such as an FRI T1 and FRI V.35.

Figure 4-7: Frame Relay Port Redundancy

UFM Front Cards

The channelized Universal Frame Model (UFM-C) supports either 4 or 8 T1 or E1 lines per back card. The UFM-4C supports 4 lines regardless of the presence of the 8 lines on the UFI back card. The UFM-8C supports all 8 lines. Both models of the UFM-C support 1 to 24 or 1 to 31 DS0s per physical line.

The UFM-C can also operate unchannelized for E1 only, with 32 DS0s constituting one unchannelized E1. In the unchannelized mode, one logical E1 port maps to one E1 line.

Table 4-9 shows the front and back cards described in this and subsequent sections.

The features and functions of the UFM-C are as follows:

• Up to 1000 logical channels per card. All 1000 logical channels can be on a single physical line or configured across multiple lines.
  
  
• Maximum total throughput of 16 Mbps — 2.048 Mbps per port
  
  
• Up to 250 logical ports, which map in any contiguous manner to the physical lines
  
  
• Front card support for either four or eight T1 or E1 lines on the eight-line back card.
  
  
• Each T1 (DS1) is configurable for 1 to 24 (T1) or 31 (E1) frame relay data streams.
  
  
• The rate of each data stream is configurable as 56 Kbps or n x 64 Kbps (where 1 <= n <= 24 for T1 and 1 <= n <= 32 for E1). If a data stream occupies more than one timeslot, the timeslots must be contiguous. The total for all rates is no more than 1.536 Mbps for T1 (56 Kbps occupy 64 Kbps channels for the calculation of this limit).
  
  
• Maps, segments, and reassembles frame relay frames to and from FastPackets.
  
  
• Each stream meets ANSI T1.618 using two-octet header.
  
  
• Interfaces configurable as a frame relay UNI or a frame relay NNI.
  
  
• Generates CLLM messages for congestion notification across NNIs.
  
  
• Supports CCITT Q.933 Annex A, ANSI T1.617 Annex D, and StrataCom LMI local management for Semi-Permanent Virtual Circuits.
  
  
• With back card, consumes up to 60 Watts at -48 VDC.
  
  
• Usage Parameter Control (UPC) in accordance with ITU-T recommendation I.370.
  
  

Figure 4-8: UFM Faceplate



Table 4-10: UFM Faceplate Indicators

UFI-8T1 Back Card

The Universal Frame Interface 8T1 (UFI-8T1-DB15) back card has 8, bi-directional, DB15 connectors. See Figure 4-9. For each port, one tri-color LED displays the status, as the emphasized area of Figure 4-9 shows. The line is inactive if the LED is off. See Table 4-11 .

Figure 4-9: UFI-8T1-DB15 Faceplate

Table 4-11: UFI 8T1 Port LED Indicators

UFI-8E1 Back Cards

Universal Frame Interface 8E1 cards have connectors for 8 E1 lines. The UFI-8E1-DB15 has 8 bi-directional DB15 connectors. The UFI-8E1-BNC has 16 BNC connectors (2 per line). See Figure 4-10. Each port has a tri-color LED for status display. See Table 4-12 . Note that the line is inactive if the LED is off.

Figure 4-10: UFI-8E1-DB15 and UFI-8E1-BNC Faceplates

Frame Relay Module (FRM)

The Frame Relay Module (FRM) front card supports 1 to 4 data ports and, in single-port mode, operates at up to 2.048 Mbps.

FRM Features and Functions

The FRM supports a maximum port speed of 2.048 Mbps plus the following features:

• Bundled connections
  
  
• Frame forwarding
  
  
• GMT request/response
  
  
• Explicit Congestion Notification (ECN)
  
  
• Multicast services
  
  
• ForeSight dynamic congestion avoidance
  
  
• AIP applications
  
  
• Enhanced V.35 loopback test
  
  
• T1 and E1 frame relay port interfaces
  
  
• Network-to-Network Interface (NNI) ports for V.35 and X.21 frame relay connections that extend across a StrataCom network to a foreign network
  
  
• Network-to-Network Interface (NNI) ports for T1 and E1 frame relay connections
  
  

The FRM can support a maximum of 252 virtual circuits (PVCs). PVC distribution can cross all four ports if they do not exceed the 252 PVC limit and the limit of 2.048 Mbps per FRM.

Bundled and grouped connections are software groupings of multiple virtual circuits within a single routing connection. Grouping allows a node to support up to 1024 virtual circuits, which is the logical equivalent of four FRMs.

Frame Relay Interface (FRI) V.35 Card

The Frame Relay Interface V.35 (FRI-V.35) is a four-port back card to the FRM card. Two models of the FRI-V.35 can support the FRM:

• FRI-V.35 Model A—supports composite data rates up to 1.024 Mbps and provides a CCITT V.35 interface for each port.
  
  
• FRI-V.35 Model B—supports composite data rates to 2.048 Mbps with V.35 interface.
  
  

The FRI-V.35 has the following functions and features:

• Interfaces 1 to 4 frame relay ports via 34-pin MRAC connector (Winchester, female)
  
  
• RTS, CTS, DSR, DTR, DCD, LLB, RLB, and TM control leads supported
  
  
• Handles up to 252 virtual circuits per card
  
  
• Hardware jumpers to configure the interface as DCE or DTE
  
  
• Supports normal and looped clocking
  
  

Figure 4-11: Frame Relay V.35 Connectors and Indicator
s

Table 4-14 shows the relationship between the number of ports used on the FRI and maximum operating speed for each port. Model A FRM and FRI cards are included for early users who may not have updated the cards. Note that the port numbers start at the top on the FRI faceplate.

Frame Relay V.35 Port Numbering

Each frame relay logical channel has a number in the form:

  SLOT.PORT.DLCI

where

• SLOT is the number of the front and back slots where the FRM and FRI-V.35 reside.
  
  
• PORT is the back card port number in the range 1 to 4.
  
  
• DLCI is the identification number for the PVC. The usable range of DLCIs is 16 to 1007. The reserved DLCIs are 0 through 15 and 1008 through1023.
  
  

FRI-V.35 Data Clocking

The two clocking modes that the FRI supports are normal and looped. Figure 4-12 illustrates the two modes. Note that the direction for the clock and data is reversed for the two FRI mode configurations (DCE or DTE), as follows:

• If the FRI is DCE with normal clocking, it provides both transmit and receive clock to the user device.
  
  
• If the FRI is DTE with normal timing, the user device provides both the transmit and the receive clock.
  
  
• If the FRI is a DCE with looped timing, the user device provides the transmit clock on the EXT XMT CLK line, and the FRI provides the receive clock to the user device.
  
  
• If the FRI is DTE with looped timing, it provides the transmit clock on the EXT XMT CLK line, and the user device provides the receive clock.
  
  

Figure 4-12: Frame Relay Data Clocking Modes

Figure 4-13 illustrates the FRI-T1 and FRI-E1 back cards.

Figure 4-13: Frame Relay T1/E1 Back Cards

Loopbacks

The IGX does not support port loopbacks (tstport and addextlp command) towards the IGX. In contrast, for V.35 and X.21 interfaces only, you can set up connection loopbacks towards the facility by using the addloclp and addrmtlp commands.

FRM-FRI Compatibility

The firmware on the front card must match the type of interface on the back card. Rev D firmware on the FRM supports X.21 and V.35 protocols. Rev E firmware on the FRM supports T1 and E1 protocols. The Display Card (dspcd) command indicates the type of back card that the FRM firmware supports and reports any mismatch.

Frame Relay Interface for X.21

The FRI-X.21 back card provides an X.21 interface to the user equipment. The two model D FRI cards are the FRI-V.35 and FRI-X.21. They differ only in the physical connectors (see Table 4-15). The operating rates of each port and the composite data rate supported by the FRI-X.21 card is the same as the FRI-V.35. You can configure each port as either a DCE or a DTE. Another FRI card is the FRI-2-X.21. This is the back card that provides the interface between the Port Concentrator Shelf (PCS) and the FRM-2. See the section titled "FRM-2 Interface to the Port Concentrator Shelf ."

The FRI-X.21 uses leased line service for international networks. The V.35 version is for domestic (U.S.) use and also uses a leased line service for its connections. The FRI-X.21 back card features:

• Four frame relay data ports with CCITT X.21 interface through DB15 connectors.
  
  
• Support for all standard X.21 data rates up to 2.048 Mbps.
  
  
• Support for C (control) and I (indication) control leads.
  
  
• Daughter board used to configure FRI as DCE or DTE.
  
  
• Card redundancy option provided by Y-cable and standby card pair.
  
  

FRI configuration supports one to four ports. The configuration depends on the maximum speed requirement (the card itself has a maximum composite speed). Figure 4-14 shows the FRI faceplate. Table 4-16 lists the available port operating speeds.

Any one port can operate at 2048 Kbps. Any combination of ports can equal 2048 Kbps. If a port is operating at 2048 Kbps, it must be port 1, and no other port can be active. Numbering of the 4 DB15 connectors starts at the top of the faceplate. Table 4-17 lists the cable and pinouts for an X.21 port.

Figure 4-14: Frame Relay X.21 Connectors and Indicators

X.21 Data Clocking

The FRI-X.21 supports only normal clock mode. The direction of the clock and data lines is reversed if the FRI is configured as a DCE or as a DTE as follows (see Figure 4-15):

• If the FRI is configured as a DCE, it provides a clock signal to the user device (DTE) on the S (clock) lead. This clock is synchronous with the node timing.
  
  
• If the FRI is configured as a DTE, the FRI-X.21 receives clock from the user device (DCE) on the S (clock) lead.
  
  

Figure 4-15: Frame Relay Data Clocking Modes

Y-Cable Redundancy and Port Modes

The Y-cable redundancy kits for the FRI-X.21 and FRI-V.35 contain four extra daughter cards for specifying individual ports as either DCE or DTE. The extra daughter cards are 200-Ohm versions for the FRI already installed. The higher impedance cards are necessary because of circuit behavior at higher speeds when the two interfaces are in parallel (by way of the Y-cable).

Card Self Test

As with all IGX cards, the FRI-X.21 includes internal diagnostic routines that periodically test the card's performance. These self-test diagnostics automatically start and run in background. They do not disrupt normal traffic. If a failure is detected during the self test, the faceplate red FAIL LED is turned on. The operator can also view the status at the control terminal by executing the Display Card (dspcd) command.

A report of a card failure remains until cleared. A card failure is cleared by the Reset Card (resetcd) command. The two types of reset that resetcd can do are hardware and failure. The failure reset clears the event log of any failure detected by the card self-test but does not disrupt operation of the card. A reset of the card firmware is done by specifying a hardware reset. This reboots the firmware and momentarily disables the card. If a redundant card is available, the hardware reset causes a switch over to the standby card.

Port Testing (X.21)

The X.21 frame relay ports and any associated external modems, CSUs, or NTUs can be tested using data loopback points in the circuit path. The three possible loopbacks for X.21 frame relay ports are:

• An internal loopback of the port
  
  
• A loopback of the near end (local) modem
  
  
• A loopback of the other end (remote) modem
  
  

The modems must be compatible with the StrataCom loopback protocol. For information on supported modems and protocols, refer to the appendix titled "Peripherals Specifications" in the IGX Installation Manual. Also, refer to the Command Reference for protocol requirements for the addextlp, addloclp, and addrmtlp commands. For information that applies to loopbacks on the FRM-2/FRI-2 and PCS, see the descriptions of these loopback commands in the Command Reference. If these sources fail to clarify a particular situation, contact Cisco Customer Service.

All three loopbacks are set up using the tstport command. Only one port at a time can be in loopback mode for testing.

The internal loopback point is established inside the FRI card. Figure 4-16 illustrates the setup. The FRM generates a test pattern, sends it out on the transmit circuitry, and detects this pattern on the receive circuitry. This test takes several seconds and momentarily interrupts traffic on the port. The test runs on a port that is in either DCE or DTE mode.

Figure 4-16: Frame Relay Loopback Modes

For ports configured for DTE, the two additional tests (local loopback and remote loopback) are available. For these ports there are two methods of loopback testing:

• A loopback data pattern (Test Mode) is transmitted to initiate a loopback. The modems or NTUs may or may not recognize these codes to perform the loopback. The FRI does not care and waits a programmable period (default = 10 seconds) of time to send the test pattern. After the test is completed, transmission of the codes is terminated and the circuit returns to normal operation. A Model D FRM is required for this testing. The test result is displayed on the IGX control terminal tstport screen.
  
  
• Some external equipment supports loopback testing but does not recognize the test pattern (Test Mode) in the data stream. In these cases, the FRM/FRI toggles the V.35 LLB (local loopback) and the RLB (remote loopback) leads then runs the test pattern. The FRM/FRI still waits the user-programmable time period (default = 10 secs) before running the data test pattern. A Model D FRM is required for this testing. The test result is displayed on the IGX control terminal tstport screen.
  
  

Unit Replacement

FRI card replacement is the same as other back card replacement. For back card replacement procedures, refer to the IGX Installation Manual.

FRM-2 Interface to the Port Concentrator Shelf

This section introduces the Port Concentrator Shelf (PCS) for frame relay traffic. The PCS is an external device that expands the capacity of a Frame Relay Module (FRM) to 44 low-speed ports. This ability to increase the port density of an IGX switch supports more efficient usage for the common switch equipment. The port parameters are as follows:

• The per-port range is 9.6 Kbps through 384 Kbps.
  
  
• The typical configured rate is 64 Kbps per port or less.
  
  
• The maximum total throughput for the 44 ports is 1792 Kbps.
  
  

The PCS requires a version of the FRM/FRI card set that is exclusively dedicated to the PCS. The front card is the FRM-2. The back card that interfaces the FRM-2 to the PCS is the FRI-2-X.21. Figure 4-17 illustrates the relation ship between the FRM/FRI card set and the PCS. It provides one or more X.21 links. Each X.21 link is called a concentrated link. In a full configuration, each concentrated link services one of four 11-port modules in the PCS. This makes a total of 44 ports on the FRM-2.

For more detailed information on the PCS, refer to the section on the Port Concentrator Shelf in the System Manual. For detailed installation instructions, refer to the Port Concentrator Installation document that comes with each unit. Cabling information for the PCS appears in the cabling appendix and in the Port Concentrator Installation document.

Figure 4-17: Port Concentrator Shelf Components

Terminology

The following terms are used to identify PCS components:

• "FRC" (Frame Relay Concentrator) ports—FRM-2-X.21 ports connected to the PCS, used in commands such as dspfrcport. These are also known as PCS "physical" ports.
  
  
• Frame relay logical ports—each of the 44 PCS ports, from the perspective of the IGX interface, is a logical port. This distinguishes it from a physical frame relay port.
  
  

Operation and User Interface

Other than front panel LEDs, the PCS has no user interface because the PCS functions as an extension of the FRM-2. PCS ports are operated and maintained from the IGX user interface.

The PCS operates within the IGX environment as a frame relay card with 44 ports. Existing frame relay commands (cnffrport, upfrport, dnfrport, addcon, delcon, etc.) are the same in syntax and function. The difference is that a range of 44 ports can be specified instead of 4. The configuration of each of the PCS logical ports is similar to that of non-PCS frame relay ports. A frame relay card connected to a PCS notifies the system database and permits the additional ports to be specified.

PCS-to-IGX Interface

Compatibility

The PCS requires the following:

• System software version 8.1 or later
  
  
• FRM-2 front card and FRI-2-X.21 back card
  
  

Concentrated Link

The concentrated link refers to the connection between port concentrator and frame relay card. Each module supporting 11 external ports is connected to 1 of the 4 ports on the FRI-2-X.21 back card.

Configuration

Each of the four composite links between PCS and IGX has a fixed configuration of:

• Speed: 512 Kbps
  
  
• FRM-2 physical port: FRI-2-X.21 DCE
  
  
• PCS composite port: X.24/V.11 DTE
  
  

The PCS Concentrated Link cable is illustrated in the cabling appendix. Its maximum length is 25 feet. You cannot use a modem to extend this distance.

Activation

FRM-2 firmware interacts with the PCS over composite links only if the FRM-2 is active. The FRM-2 changes from standby to active state when its first logical port is activated.

upfrport Command

A PCS logical port associated with an FRM-2 card is activated with the upfrport command. The upfrport command requires the slot number of the FRM-2 to which the PCS is connected. Enter the slot number and a logical port in the range of 1-44 (assuming a connection exists for all 4 composites between the PCS and IGX).

  Example: upfrport 4.1

This example indicates that the FRM-2 in slot 4 and concentrated link 1 are connected.

Entering the upfrport command for one port activates all four ports. The following events are generated by successful activation of four concentrated links. The display is from the example "upfrport 4.1:"

  "Info FRM 4 Activated"
"Info FRM Port 4.1 Activated
"Info FRM Concentrated Link 4.1 Failure Cleared"
"Info FRM Concentrated Link 4.2 Failure Cleared"
"Info FRM Concentrated Link 4.3 Failure Cleared"
"Info FRM Concentrated Link 4.4 Failure Cleared"

A noticeable delay occurs after upfrport begins executing on the first port. During initial upfrport execution, the FRM-2 performs first-time configuration, diagnostic, and up/download functions.

If a concentrated link is not connected or fails to come up, the logical port remains in a failed state until either the link comes up or the port is deactivated with the dnfrport command.

De-activation: the dnfrport Command

The FRM-2 card set returns to the standby state after you de-activate all 44 logical ports by executing the dnfrport command.

PCS Port Configuration

When the frame relay ports are activated, the IGX recognizes them as PCS-connected ports. Subsequently, all applicable frame relay port management commands accept logical port numbers in the form slot.port. The range for port is 1 to 44. Table 4-18 shows the logical ports the PCS supports. In Table 4-18 , slot is the IGX slot in which the FRM-2 resides.

Interface Hardware Configuration

The interface and clocking characteristics for each PCS port is independently configured to be V.11 (X.21), V.35, or V.28 by inserting the required interface card (or "ICARD") into the associated slot in the PCS. For detailed information on PCS hardware interfaces, refer to the Port Concentrator Installation document. This document comes in the PCS shipping container.

The IGX does not have the capacity to read the type of interface present for the PCS port. The values you enter under Interface Type with the cnffrport command appear in the display only and cannot be checked against the hardware.

The cnffrport Command

You configure a PCS with the cnffrport command. With the following limitations, all parameters for the cnffrport command are supported:

Port Statistics

All frame relay summary and interval statistics are kept for PCS ports. The PCS and FRM-2 share responsibility for statistics collection on PCS ports. The PCS maintain counters for:

• CRC errors on received frames
  
  
• Aborted/underrun received frames
  
  
• Transmit Frames Discards
  
  
• Transmit Bytes Discards
  
  

All remaining statistics counters are collected by the FRM-2. Although the IGX supports ForeSight for PCS connections, CLLM (ForeSight) statistics are not available in Release 8.1. These fields are present but not valid.

PCS Monitoring Functions

Monitoring functions generally apply to the PCS except that you can specify up to 44 logical ports for a FRM-2 slot. For descriptions of the monitoring commands, refer to the "Troubleshooting" chapter of the Command Reference. Note that commands dspchcnf, dspchstats, dspportstats, and dspbob fail when the required concentrated link is down. Trying to execute one of these commands on a concentrated link that is down causes an error message to appear.

Collecting the Monitoring Information

Logical Port Speed

The PCS measures the speed of receive data on logical ports if the port is configured as a DTE interface. To see the measured speed, use the dspbob command. The PCS measures port speed after any of the following occurs:

• When the PCS is first powered up.
  
  
• When a port is configured with the cnffrport command. After the port is reconfigured, speed of incoming data is measured.
  
  
• When signals are displayed for the port with the dspbob command, you are given the option of measuring port speed at that time.
  
  
• When the PCS is reset or power is interrupted for any reason.
  
  

The process of measuring port speed sends out two 1-byte frames with no CRC on the port.

Physical Port Speed

The IGX measures the physical port speed for FRI-2-X.21 ports once per minute. The current measured speed is displayed with the dspfrcport command and should always read 512 Kbps when the port is active.

PCS Front Panel LEDs

Card Insertion and Removal

If the FRM-2 or FRI-2.X21 card is removed for any reason, be sure to maintain card compatibility upon card replacement: the FRM-2 card is compatible with only the FRI-2-X.21 back card. The IGX declares a mismatch state for any other back card inserted into an active FRM-2 slot. Inserting compatible hardware is the only way to clear the mismatch. Similarly, once an IGX slot is active with an FRM-2, a mismatch is declared if any other front card is inserted into this slot. Before the slot can be used for any other type of card, the slot must be de-activated as a PCS-capable frame relay card.

PCS Command Summary

The commands in the list that follows apply to PCS frame relay ports. Most commands have the syntax described in the Command Reference with the exception that system software recognizes 44 ports per FRM-2 instead of 4. Some commands are PCS-specific.

PCS Port Failures

A PCS logical port failure is defined as a minor alarm. The FTC/FRP Port Comm Failure icon appears in the dspalms screen. Any connection that terminates on a failed port is also failed. Three causes of a port failure are defined, as described under Alarms and Events.

Conditioning

A failed connection on a PCS logical port is conditioned in the same manner as a failed connection on a non-PCS FRP port. Only the active control template is supported on PCS ports. The "conditioned" control template should not be used for PCS logical ports.

PCS General Operation

Firmware Download

When it detects a Port Concentrator on one of its links, the FRM-2 checks for a compatible firmware revision on the Port Concentrator. If the FRM8-2 detects that the firmware on the Port Concentrator is incompatible, the FRM8-2 downloads the current firmware to the Port Concentrator. This download operation takes about two minutes. An event is logged when a firmware download has either started or failed.

Operating software on the Port Concentrator is stored in Flash memory. Download should be required only if the PCS is connected to an FRM-2 with newer firmware or a PCS module is replaced and a software version difference exists.

Automatic Diagnostics—FRM-2 and FRI-2-X.21 Cards

The FRM-2 card runs a self-test diagnostic when it is in the standby state. The system software uses a reserved channel on the FRM-2 card to perform background loopback tests that include both the FRM-2 and FRI-2-X.21. This test verifies that all components up to the FRI-2-X.21 physical port are functioning. These diagnostics do not test the PCS.

StrataView Plus Interface

Information about PCS logical ports and frame relay connections is automatically reported to StrataView Plus, just as they are for FRP ports and connections.

Connection Management and other FRM-2 port functions may also be handled for PCS ports from StrataView Plus.

SNMP Manager

The SNMP agent supports Port Concentrator logical ports. This includes configuring PCS port parameters, adding, or deleting frame relay connections, and retrieving statistics.

The SNMP agent also supports provisioning for 44 frame relay ports for FRM-2; the existing MIB variables are extended to the expanded number of logical ports. SNMP management functions are not supported for the Port Concentrator concentrated links.

User Interface

Interaction between the FRM-2 and PCS automatically updates the database to display the number of connected logical FRM-2 ports at the PCS. As a result, both the IGX user interface and the StrataView Plus interface automatically display the additional capacity of 44 ports for the FRM-2.

Concentrated Link Failure

If, during normal operation, communication stops between FRM-2 and PCS over a concentrated link, a concentrated link failure alarm is generated.

In addition, during start-up, a concentrated link is failed for any of the following reasons:

• Port Concentrator is not present.
  
  
• Code download from FRM-2 to Port Concentrator fails.
  
  
• Port Concentrator self-test fails.
  
  
• Cable is unplugged or bad.
  
  

FastPAD Trunk Module

The IGX supports FastPAD devices. The interface cards for FastPADs are the FTM front card and FPC back card. The back card provides either a T1, E1, V.35, or X.21 interface. Each FPC V.35 and FPC X.21 provides four ports. Each port can support one FastPAD either locally or remotely (via modem). The T1 card has a DB15 for RX/TX and an alternate pair of RX/TX BNC connectors. The E1 connections are the same except for additional RX/TX-monitoring BNC connectors. Y-cable redundancy is also supported. Figure 4-18 shows the FTM front card and the FPC-V.35.

Commands you enter manage the FTM/FPC, the FastPAD, and their ports and connections. Statistics that relate to cards, ports, and the FastPAD are collected for StrataView Plus. Card management of the FTM/FPC card set includes detection of when you install or remove a card, accidentally mis-match back cards, or set up Y-cable redundancy.

Figure 4-18: FastPAD Cards: FTM and FPC (V.35)

Port management includes EIA signalling, LMI alarms, upping and downing of ports and the collection of port statistics available to StrataView Plus.

FastPAD management permits the management of cards and ports on the FastPAD device from the IGX. This management includes card and card removal detection, card mismatch, uploads and downloads between the FastPAD and the IGX node.

Connection management involves mapping FastPAD connection to Frame Relay-type virtual circuits (VCs). Connections that originate at a FastPAD must terminate at another FastPAD. Each FTM/FPC card set supports up to 252 connections. The card set collects statistics on these connections and provides them to StrataView Plus.

For descriptions of the FastPAD commands and detailed information on the FastPAD, refer to the FastPAD User's Guide. Refer also to the StrataView FastPAD User's Guide.

Data Cards

A data circuit has a direct interface to the IGX through either a High-speed Data Module (HDM) or Low-speed Data Module (LDM) card set. The HDM set consists of an HDM front card and a Synchronous Data Interface (SDI) back card. The LDM set consists of an LDM front card and a Low-speed Data Interface (LDI) back card. The back cards match the circuit type to the front card. Synchronous data card sets are listed in Table 4-20. An IGX 32 node can have up to 25 HDM/LDM sets in a non-redundant system, for support of up to 200 full-duplex data connections.

The synchronous data cards support the ability to configure and monitor EIA leads; the ability to configure each channel for clocking, data rate, and DTE or DCE interface type; and complete loopback testing capability. Data channels can support null modem emulation as well as constant-carrier and switched-carrier operation. Data interfaces are transparent with respect to protocol. Asynchronous, binary synchronous, and bit synchronous protocols are supported with no impact on host or terminal software.

High-speed Data Module (HDM)

The HDM front card in an IGX is a programmable communications processor that can support one to four high speed, synchronous data channels. It operates at speeds from 1.2 Kbps up to 1344 Kbps on all four ports while performing link error monitoring.

The HDM front data card:

• Performs cell adaptation
  
  
• Supports normal, looped, and split clocking
  
  
• Provides isochronous clocking circuitry
  
  
• Packetizes and depacketizes EIA lead sampling information
  
  
• Provides loopback capabilities, testing, and diagnostics
  
  

An internal baud rate generator provides transmit and receive data clocks to the SDI card at the selected rate. The HDM can accept data from an external data device with a non network synchronized clock (isochronous clock) up to 112 Kbps. With isochronous clocking, the HDM sends a clock control signal to the other end of the circuit to synchronize the far end HDM receive clock to the isochronous clock received at the near end.

Unless specified, a packet of data for EIA control lead information is built only at a very low rate or when a change of state is detected on one or more of the control leads. The data rate is specified as either "fast" or "not fast" (the default) by the addcon command for data connections. A fast EIA lead transmission can be specified in the software to send EIA control lead information in every FastPacket (interleaved EIA mode). This tightly couples the EIA lead states with the transmitted data but reduces the bandwidth efficiency.

The HDM card is installed in a front slot. An SDI back card plugs directly into the P2 connector of the front card. The SDI back card provides the proper data channel interface.

The faceplate of the HDM has message lights and buttons for loopback control and signal monitoring. The buttons relate to loopback testing or scrolling through the FastPacket data ports for a snapshot of selected data port conditions (indicated by PORT, PORT UNDER TEST, loopback, and communication line state lights). Figure 4-19 illustrates and Table 4-21 lists the controls and indicators. When correlating the figure to the table, read from the top down.

Figure 4-19: HDM Controls and Indicators

Table 4-21: HDM Controls and Indicators

Redundancy for HDM data cards can be provided with a second front and back card set and a Y-cable connection on each port to the customer equipment. See Figure 4-20.

Figure 4-20: HDM Data Port Redundancy

Synchronous Data Interface Card (SDI)

The SDI card is a synchronous data interface back card that directly connects to a front HDM card. Each SDI card has four connectors and provides the physical and electrical connection interface to four data ports. Each port is independently configurable for DTE or DCE mode, baud rate, and so on. One for one port redundancy is provided with a second card set and a standard Y-cable arrangement.

The SDI card:

• Provides four ports for interfacing to the data equipment.
  
  
• Provides EIA control circuitry and samples EIA lead information.
  
  
• Performs serial to parallel conversion of data.
  
  
• Provides a jumper strap for configuring the ports as DTE or DCE.
  
  

Four types of SDI back cards can provide an interface between an HDM front card and the customer data equipment. Table 4-22 distinguishes each type of SDI card.

Three clocking modes are available on the SDI for clocking in transmit data and clocking out receive data. In addition, the SDI can operate as either a DCE or DTE, which makes possible six combinations of clocking. (See Figure 4-21 and Figure 4-22 .) With loop clocking, the user device must loop the RxC to the XTC for clocking out the transmit data.

When the SDI is configured as DTE, the user device is the source of clock timing and is generally not synchronous with the network (IGX) timing. This is isochronous clocking. Isochronous clocking allows the customer data sets at each end of a circuit to operate at slightly different rates (non-synchronously) with minimum delay and loss of data. This feature limits the amount of data allowed to accumulate in the HDM receive buffers and forces a re-synchronization before the delay reaches an unacceptable level.

Figure 4-21: Clocking Modes for SDI in DCE Mode

Figure 4-22: Clocking Modes for SDI in DTE Mode

Isochronous clocking involves a mechanism that lets a node at the far end compensate for an unstable clock in the user device at the near end. Data transmission in an isochronous network is reliable up to 112 Kbps. You can use isochronous clocking on only one input at a time per port. The SDI does not support two isochronous clock inputs in the same direction as required by some modems that generate the TxC and RxC clocks independent of each other.

Split clocking uses the user-device timing for timing data transmission in one direction and the IGX timing for the other direction.

Low Speed Data Module (LDM)

The LDM front card supports up to 8 synchronous or asynchronous data ports. Each port is independently configurable for DTE or DCE mode, baud rate, and so on. The LDM card is a low speed data module for use on RS-232C ports with data rates up to 19.2 Kbps, where the higher speed capabilities of an HDM are unnecessary. An LDM can provide 56 Kbps Digital Data Service interfaces to the IGX when it operates with an LDI4/DDS.

The LDM can process either synchronous or non-synchronous input data. With non-synchronous inputs, the data is over-sampled at a rate determined by how much jitter your equipment can tolerate. Using an external device is also possible for synchronizing the asynchronous data before the data enters the IGX.

The LDM front data card:

• Performs cell adaptation of customer data and EIA control leads.
  
  
• Supports normal and looped clocking.
  
  
• Provides loopback capabilities, testing and diagnostics.
  
  

Additional features, such as embedded (fast) EIA, sixth EIA lead support, and pleisochronous clocking, are also supported. The fast EIA control lead lets the user include the RTS/CTS EIA control leads in the same FastPacket as customer data. The EIA control lead status is encoded as the eighth data bit in each data byte. This provides a quick EIA response without significantly affecting bandwidth requirements. It is limited to data rates of 19.2 Kbps and below.

The LDM can reside in any empty front slot and requires an LDI back card. The LDI card plugs directly into the P2 connector of the LDM card.

The faceplate of the LDM has message lights and buttons for loopback control and signal monitoring. Figure 4-23 shows and Table 4-23 lists these indicators and buttons. When correlating the figure to the table, read from the top down. The buttons are for loopback testing and scrolling through the FastPacket data ports to obtain a snapshot of selected port conditions (indicated by PORT, PORT UNDER TEST, loopback, and communication line status lights).

Figure 4-23: LDM Connections and Indicators

Table 4-23: LDM Connections and Indicators