What is the “Differential Delay” on IMA cards, and when do I need to change it?
A. The differential-delay-maximum command sets the maximum delay allowed between the reception of packets from adjacent IMA links on the receiving end. The IMA protocol sends cells in a “round robin” fashion on the ATM T1 lines which make up the IMA group. These cells should be received within the specified maximum delay period. When this delay is exceeded, the data stream cannot be reconstructed correctly. If a particular T1 line coming into a router (or ATM switch) has delays greater than the specified IMA maximum, this T1 will be brought down and will not participate in the IMA group. The example below shows the maximum differential delay being set to 75 milliseconds: R1 (config)# interface atm 1/ima1 R1(config-if)# ima differential-delay-maximum 75 The configurable delay period ranges from 25-250 milliseconds. Configuring too high a value permits too much delay tolerance, and this may affect certain network applications or cause retransmission. While the maximum delay differential
