  We study the higher spin anologs of the six vertex model on the basis of its
symmetry under the quantum affine algebra $U_q(\slth)$. Using the method
developed recently for the XXZ spin chain, we formulate the space of states,
transfer matrix, vacuum, creation/annihilation operators of particles, and
local operators, purely in the language of representation theory. We find that,
regardless of the level of the representation involved, the particles have spin
$1/2$, and that the $n$-particle space has an RSOS-type structure rather than a
simple tensor product of the $1$-particle space. This agrees with the picture
proposed earlier by Reshetikhin.
