Hello Subhojit,
an etherchannel using LACP is the recommended solution.
This solution can be used if the two links are between the same two devices.
note:
on cisco side you can consider like a single box a stack of 3750 / 3560 or a VSS pair of two C6500
example config (cisco side)
interface gi0/x
switchport
shut
switchport trunk enc dot1q
swichport mode trunk
switchport trunk allowed vlan X,Y,Z
channel-group 5 active
interface gi0/y
switchport
shut
switchport trunk enc dot1q
swichport mode trunk
switchport trunk allowed vlan X,Y,Z
channel-group 5 active
later you can enable both at the same time using
interface range giga 0/x - y
no sh
!
similar configuration has to be done on nortel side
X.Y,Z are just example of vlans to be permitted on the trunk
I' ve used channel-group 5 but it is just an example
you can use
sh etherchannel summary
to find what bundles are active on your system you need to use an unused group number
at the end the same show can tell you if the new bundle is fine
Hope to help
Giuseppe
