As we know, Huawei SFD64 is updated version of SLD64, for its transmission distance is further than SLD64.
Technically, in Huawei SDH transmission boards, SFD64 can transit longer than SLD64 in normal condition, but when you use DWDM color interface into SLD64, it can transit longer than SFD64. For when SFD64 with SFP or XFP, it can transit 40km, but when SLD64 equiped with DWDM color interface module, it has two options, 40km and 80km, which based on your maximum demand.
