updated hw.tex for hw4

git-svn-id: svn://anubis/gvsu@236 45c1a28c-8058-47b2-ae61-ca45b979098e

cs677/hw4/hw.tex

@@ -21,6 +21,16 @@
 \noindent
 \begin{enumerate}
 \item[1.]{
+    In store-and-forward communication, the communication cost is given by
+    $$T_{\mathrm{comm}} = t_s + (t_h + mt_w)\ell = t_s + \ell t_h + \ell mt_w$$
+    In cut-through routing, the communication cost is given by
+    $$T_{\mathrm{comm}} = t_s + \ell t_h + mt_w$$
+    Since the ``header'' is the only part of the communication that is
+    encountering overhead for the $\ell$ links in the communication network,
+    cut-through routing can save communication time on the order of
+    $(\ell - 1) mt_w$.
+    Obviously, this makes cut-through routing only advantageous on
+    architectures with $\ell > 1$, meaning non-fully-connected networks.
 }
 
 \vskip 1em