AT3-6ME (T3 to T2) Interface Adapter

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 32-1 for a typical application.

Figure 32-1: Network 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 32-1 and Figure 32-2). 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.

Table 32-1: Rear Panel Connectors

Connector	Type	Description
T3 RX	BNC	Receive T3 input from BPX or IGX ATM port.
T3 TX	BNC	Transmit T3 output to BPX or IGX ATM port.
T2 RX	BNC	Receive 6 MB input from T2 facility.
T2 TX	BNC	Transmit 6 MB input to T2 facility.
RS-232	DB9	Control terminal connection.
Primary Power	IEC	AC power input with fuse.

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 32-2 and Figure 32-2). 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.

Table 32-2: Front Panel Indicators

Indicator	Color	Description
T3 Receive Status—AIS	Green	Alarm Indication signal detected on the RCV T3 line.
T3 Receive Status—RAI	Yellow	Remote Alarm Indication signal detected on the receive T3 line.
T3 Receive Status—LOS	Red	Loss of receive T3 signal.
T3 Receive—LOF	Red	Loss of frame on receive T3 signal.
T3 Transmit Status—AIS	Green	Alarm Indication signal detected on the transmit T3 line.
T3 Transmit Status—RAI	Yellow	Remote Alarm Indication signal detected on the transmit T3 line.
T3 Transmit Status—LOS	Red	Loss of transmit T3 signal.
T2 Receive Status—AIS	Green	Alarm Indication signal detected on the RCV T2 line.
T2 Receive Status—RAI	Yellow	Remote Alarm Indication signal detected on the receive T2 line.
T2 Receive Status—LOS	Red	Loss of receive T2 signal.
T2 Receive—LOF	Red	Loss of frame on receive T2 signal.
T2 Transmit Status—AIS	Green	Remote Alarm Indication signal detected on the transmit T2 line.
T2 Transmit Status—RAI	Yellow	Loss of transmit T2 signal.
T2 Transmit Status—LOS	Red	Loss of frame on transmit signal.
Overflow	Red	T3 receive cell rate exceeds the T2 line capacity.
FT2	Red	Fractional T2 indication for future use.
T3/T2 loop	Red	Indicates the unit is in loop back mode, external toward the T3 and T2 line interfaces.
Active/Fail	Green/Red	Upon power up the system will go through extensive self tests. If self-test passes, the Active/Fail LED will be green; if self-test fails the LED will be RED.
Power	Green	Power ON indication.

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.

Figure 32-2: Front and Rear Panel Features

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 1 For use with BPX switch, connect one cable between one of the three TX connectors on a selected BPX LM-3T3 card and the T3-RX connector on the AT3-6ME back panel.

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 setting 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 32-3 and Table 32-4. Set the appropriate DIP switches with the power off.

Table 32-3: DIP Switch SW-1 Selection Guide

Switch	Position	Function
1	Down	Enable configuration via the TTY.
1	Up	Disable configuration via the TTY (default).
2	Down	Enable front panel loop push button.
2	Up	Disable front panel loop push button (default).

Table 32-4: DIP Switch SW-2 Selection Guide

Switches	Position	Function
1 2	Up Up	Internal synchronization source for the T2 transmitter
1 2	Up Down	Slave T2 transmitter to T3 line
1 2	Down Down	Slave T2 transmitter to T2 receiver
3 4	Up Up	Long length T3 cable
3 4	Up Down	Medium length T3 cable
3 4	Down Down	Short length T3 cable; system is co located to IGX or BPX¹ (default)
5, 6	don't care	Unused
7	Up	ATM converter mode
7	Down	Test Mode
8	Up	Enable BPV relay from T2 to T3
8	Down	Disable PV relay from T2 to T3
9	Up	Long length T2 cable
9	Down	Short length T2 cable (default)¹
10, 11, 12	Don't care	Unused

¹T2 and T3 cable length should be set to "short" upon power-up for self-test.
Upon LOS, defaults to "internal synchronization."

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 1 Telnet to the first node equipped with an AT3-6ME.

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 32-5.

Table 32-5: Alarm Handling

Alarms Passed Thru (both directions)	Errors Relayed Thru (both directions)
AIS	HEC Error—both directions.
RAI	BPV (up to 10-5 rate)—6M to T3 only.
LOS
LOF

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 1 Enable the proper DIP switch on SW-1.

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:

Electrical Interface:	RS232
DTE/DCE:	DCE
Speed:	9.6 Kbps
Handshake:	NON
Connector:	Male DB9

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 32-6).
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.

Table 32-6: DIP Switch Settings

1	2	3	4	5	6	7	8	9	10	11	12	1	2
0/1	0/1	0/1	0/1	0/1	0/1	0/1	0/1	0/1	0/1	0/1	0/1	0/1	0/1

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 32-7 lists available commands for use with the AT3-6ME terminal interface while Table 32-8 indicates the display format.

Table 32-7: Command Summary

Command	Parameters	Meaning
?		Help Menu.
dspstat		Display status.
dspstat clear		Clears the status display.
Override dipsw	0 1	Disable TTY configuration entry. Enable TTY configuration entry. Operates only when DIP switch 1-1 is down.
Sync source	0 1 2	System is slaved to the 6M line. System is slaved to the T3 line. System runs of its internal clock.
Remote loop	No of seconds stop	Enable remote loop back operation. Cancel the loop back operation.

Table 32-8: Status Display

Status	T3¹	T2¹
BPV	NNN	NNN
Parity Errors	NNN	X
Framing Errors	NNN	NNN
PLCP Framing Errors	NNN	X
HEC Errors	NNN	NNN
RX Cells	NNN	NNN
TX Cells	NNN	NNN
AIS	1/0	1/0
1/0	1/0	1/0
LOF	1/0	1/0
Overflow	X	1/0

¹X = not available

Specifications

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

Table 32-9: T3 Interface

Line rate:	44.736 Mbps ±20 ppm
Framing format:	C-bit parity
Line code:	B3ZS
Physical layer:	PLCP format
ATM layer:	UNI per the ATM Forum UNI 3.0 specification
Cell Rate:	Up to 96,000 cells/sec.
Connector:	75 ohm BNC

Table 32-10: T2 Interface

Line rate:	6.312 Mbps
Line code:	B8ZS
Synchronization:	Internal 6.312 Mbps ±30 ppm or Slave to the incoming 6 Mbps line or Slave to the T3 PLCP frame
Framing format:	ITU-T G.703
ATM Layer:	Per NTT UNI specification dated 1993
Queue:	75 cell FIFO
Cell Rate:	Up to 14,490 cells/sec.
Connector:	75 ohm BNC

Table 32-11: Power

Input Power:	90 VAC to 250 VAC, 50/60 Hz
Power consumption:	30 watts
Input Power Connector:	Universal power entry module with fuse
Fuse size:	1/2A 250 VAC

Table 32-12: Mechanical

Rack Mounting Space:	1 rack mount space, 19" rack
Size:	19" x 1.75" x 8.5"

Table 32-13: Terminal Interface

Speed:	9.6 Kbps
Type:	DTE
Handshake:	NONE
Connector:	DB9

Table of Contents

AT3-6ME (T3 to T2) Interface Adapter