The WISI Inca Networks GT 21 W module is part of the Tangram product portfolio. The GT 21 W module allows you to add up to 6 services in PAL /SECAM or NTSC format per module to your network. Tangram is a very high density and highly flexible solution for all kinds of networks. The WISI Tangram chassis uses a fully redundant concept (n+1, 1+1).