In present paper the Equal Channel Angular Extrusion (ECAE) through a rectangular die was firstly physically simulated using plasticine and then theoretically analyzed by upper bound method. Physical simulation was used to identify the deformation zone and as a background for the following theoretical ECAE analysis by rigid block model. The plane strain deformation mode and ideal plasticity of an extruded material were assumed. The dependencies of ECAE pressure, accumulated shear and dimension of a "dead zone" upon friction factor were analytically determined. The rise in ECAE pressure, accumulated shear and size of a "dead zone" with the increase in friction was predicted. The obtained results were compared with the slip line based solution and a good agreement between them was found. Finally the results of upper bound analysis were discussed together with the results of experimental investigations and finite element analysis of ECAE mechanics published elsewhere.