With IPHost Network Monitor you can run simple snmp requests against a Nortel device in your network.
x25DteLcnOutPacketSize
x25 Dte Logical Channel Number Out Packet Size
1.3.6.1.4.1.562.2.4.1.90.4.11.1.2
This attribute indicates the maximum transmit packet size in octets.
Back to Nortel-Magellan-Passport-X25DteMIB MIB page.
IPHost Network monitor allows you to monitor x25DteLcnOutPacketSize on Allied Telesis device via the SNMP protocol. Download IPHost Network Monitor (500 monitors for 30 days, 50 monitors free forever) to start monitoring Nortel switches right now.