In a tunneled environment such as DS-Lite, a fragmented packet must be reassembled in the end node before it is decapsulated. DS-Lite reassembly is implemented in-line, which means that the reassembly function runs in the same MS-ISA where native DS-Lite processing occurs. The presence of the Fragment Extension header in the IPv6 header signals the need for reassembly for all traffic destined for the AFTR in the upstream direction.
Fragments of a frame can be buffered for up to two seconds in an MS-ISA to wait for all the fragments of the original frame to arrive can be reassembled.
DS-Lite reassembly is performed only in the upstream direction.