Table of Contents

AT3-6ME (T3 to T2) Interface Adapter

AT3-6ME (T3 to T2) Interface Adapter

This chapter describes the AT3-6ME Interface Adapter, sometimes referred to as the T3-T2 Interface Adapter. It is used with the BPX switch to provide a 6 Mbps ATM network interface to T2 transmission facilities.

Application

The AT3-6ME Interface Adapter is used with the BPX Broadband ATM Switch in applications where it is required to interface a 6 Mbps T2 digital network facility to the 45 Mbps T3 ATM port on the BPX or IGX node.

Applications include networks where T2 transmission facilities are available. Users with ATM networks who require somewhat more bandwidth than is provided by the T1 or E1 ATM network connections but do not need the full T3 bandwidth provided by the BPX ATM network ports can also benefit from using the AT3-6ME Interface Adapter. See Figure 33-1 for a typical application.

General Description

The AT3-6ME Interface Adapter is a bi-directional device that provides a conversion between transmission systems of different transmission rates:

• the North American T3 (44.736 Mbps)
  
  
• the Japanese 6M (T2).
  
  

The AT3-6ME Interface Adapter is used only in ATM networks. The adapter is transparent to both users and the network.

The T3 interface operates at 44.736 Mbps with the B-ISDN Physical Layer Convergence Protocol (PLCP) and meets the ATM Forum standards. The T2 interface operates at 6 Mbps according to the Japanese Nippon Telephone & Telegraph (NTT) User-Network Interface (UNI) specifications.

ATM cells from one interface are mapped to the other interface enabling users with ATM node equipment with North American T3 ATM ports to operate in a T2 network. The ATM cell throughput on a T2 digital trunk using this adapter is limited to 14,490 cells per second.

The cell transfer rate for T2 is greatly reduced from the T3 cell rate from a BPX port. It is very important to restrict the cell rate from the node when using a T2 trunk. Cell rate adaptation is done via software trunk configuration at the T3 ATM interface, where the non null cell throughput is limited to the T2 capacity. In the T2 to the T3 direction, the T3 ATM interface has more than enough capacity to accommodate the T2 cell rate.

The Interface Adapter can buffer a 70-cell burst at the T3 rate before the T2 interface will begin to drop cells. Cells will continue to be dropped until the T3 interface returns to a rate that complies with the bandwidth of the T2 interface.

All alarms and line errors are passed through the Interface Adapter unchanged. Any existing network management system has an instant view of the actual network transmission system. Errors at the ATM layer propagate through from one interface to the other, thus you have complete knowledge and statistical information regarding the network status at all times. Therefore a special network management interface is not required.

Because the T3 interface is asynchronous and the T2 is synchronous, you can configure the AT3-6ME to carry the synchronization information through from one interface to the other. The synchronization is carried through the T3 interface using the PLCP-embedded 8 KHz. The T2 interface clock may be generated locally or it may be slaved to the public network.

Equipment Description

The AT3-6ME is fully contained in a metallic housing designed to be mounted in a 19" equipment rack. It occupies only one rack mounting space and is powered from normal AC line powering. The power supply accommodates an input voltage over the range 90 to 240 VAC, 50 or 60 Hz.

Interface Connectors

The interface connectors are located on the rear panel (see Table 33-1 and Figure 33-2). These connectors include:

• Two T3 BNC connectors, XMT and RCV.
  
  
• Two 6M BNC connectors, XMT and RCV.
  
  
• A single RS-232 male, subminiature 9-pin control terminal interface.
  
  
• AC input connector with integral fuse.
  
  

The control terminal is a standard RS-232 interface DTE interface. No hardware handshake is required for the interface. The diagnostic display comes up immediately. It operates at 9.6 Kbps with any ASCII terminal.

Front Panel Indicators

The front panel of the system provides LED indicators for the alarm status of the transmit and the receive T3 and the T2 interfaces (refer to Table 33-2 and Figure 33-2). Also on the front panel are indications for power and for operating status (Fail/Active).

The Overflow LED indicates that the cell rate coming from the T3 interface exceeds the bandwidth of the T2 facility and that the Interface Adapter buffer has overflowed.

DIP Switches

The adapter has two front panel DIP switches:

• a two-position (SW-1)
  This controls the configurations that may interrupt operation and should be done through a two-step operation.
  
  
• a 12-position (SW-2) switch
  This enables all other configuration parameters.
  
  

Installation

Install the AT3-6ME in a rack adjacent to the BPX enclosure (allowing room for any AC Power Supply Assembly that you might need to mount) wherever there is space for the AT3-6ME adapter.

System Connections

Two short BNC-BNC cables are required to connect the AT3-6ME to the BPX node.

Step 2   Connect the other cable between the associated RX connector on the BPX LM-3T3 or ATMT card and the T3-TX connector on the AT3-6ME back panel.

Step 3   Connect the cable coming from the 6 Mbps facility to the T2-RX connector on the AT3-6ME.

Step 4   Connect the cable going to the 6 Mbps facility to the T2-TX connector on the AT3-6ME.

Step 5   Connect the AC power cord to the IEC connector on the rear of the AT3-6ME.

AT3-6ME Configuration

You configure the adapter by seting a group of DIP switches located on the front panel. There are two sets of switches:

• a 12-position switch
  
  
• a two position switch.
  This switch enables the configuration change via the terminal and enable/disable the loop push button located in the front panel (to secure against accidental operation).
  
  

Review both Table 33-3 and Table 33-4. Set the appropriate DIP switches with the power off.

BPX or IGX Port Configuration

You configure the trunk on the BPX or IGX node by using Cisco WAN Manager network management workstation or a local control terminal.

Step 2   Use the Configure Trunk (cnftrk) command to select T2 for the Tx Trunk Rate.

Step 3   Set the RCV Trunk Rate to 28980 cps.

Step 4   Repeat steps 1 through 3 for all other nodes using the AT3-6ME.

Operation

This section describes the operating modes for the AT3-6ME. The unit is designed for unattended operation. Any failures in the unit or any line alarms or errors will be propagated.

Power-Up Sequence

During the system power-up, the unit goes through a self test procedure:

• The Power LED turns green.
  
  
• The Active/ Fail LED stays off until the self test sequence is completed. Through the self test, all LEDs light up.
  
  
• At the end of the self test the loop LED comes on for about 5 seconds.
  
  
• When the test is completed successfully the Active/Fail LED turns green.
  
  

If the system fails self test, it will repeat the self-test twice more. If it continues to fail, the Active/Fail LED turns red.

Normal Operation

In standard operation, the AT3-6ME system relays ATM cells from the T2 6M to the T3 interface. To accommodate for the difference in the transmission rate, the AT3-6ME removes all null cells from the T3 interface. The T3 sources connected to the AT3-6ME must regulate their ATM Cell rate not to exceed the T2 6M cell rate. The AT3-6ME can absorb up to 70 cells in a single burst.

The AT3-6ME Interface Adapter can interface to any ATM UNI or NNI line at the T2 or T3 rate. The AT3-6ME Relays alarms and errors from one interface to the other. It relays the alarm and error conditions as indicated in Table 33-5.

Remote Loop Operation

The AT3-6ME can create a remote loop on both the T3 and the T2 sides for test purposes. You can manually activate the loop by pressing a front-panel switch or through the control terminal. The loopbacks are through looping relays at the two interfaces and they operate simultaneously.

To activate the loop from the front panel:

Step 2   Press and hold the front panel push button for one second. This is to prevent accidental operation of the loop.

Once the loop is set, you can remove it by operating the loop switch a second time. Otherwise it will automatically remove itself after one hour.

Terminal Operation

The system is designed to operate without a terminal. The terminal interface is designed for diagnostics and maintenance purpose only. The terminal interface is always active and continuously displays the user prompt. The terminal interface operating parameters are:

Upon power up:

• The system goes through power up diagnostics:
  
  
• The terminal displays the diagnostics sequence.
  
  
• Upon successful self test the unit is available for operation.
  
  
• The terminal displays the actual set up of the system represented by the DIP switches (see Table 33-6).
  
  
• If the configuration was overwritten through the TTY, the terminal will display the actual set up that could be different then the dip switch setting.
  
  

Commands

You enter commands after the user prompt to:

• Display the various error counters and alarms associated with the T2 line and the T3 port interface
  
  
• Select the source of timing for the DSU
  
  
• Enable and remove the remote loop
  
  

Table 33-7 lists available commands for use with the AT3-6ME terminal interface while Table 33-8 indicates the display format.

Specifications

These are the specifications for the AT3-6ME Interface Adapter: