This scenario enables IPComp compression between roadwarrior carol and gateway moon. Two IPv6 ICMP requests from carol to alice check the established tunnel with compression. The packet sizes are different because the kernel does not compress small packets.
Note: The kernel applies IPComp after fragmenting the original packet according to the MTU. Also, because alice does not know about the IPsec tunnel between moon and carol the response to the first ICMP request is fragmented in too large fragments and moon sends back ICMPs with type 2 to notify alice about this (Path MTU Discovery). The second ping is then answered successfully.