  Recovery of data packets from packet erasures in a timely manner is critical
for many streaming applications. An early paper by Martinian and Sundberg
introduced a framework for streaming codes and designed rate-optimal codes that
permit delay-constrained recovery from an erasure burst of length up to $B$. A
recent work by Badr et al. extended this result and introduced a sliding-window
channel model $\mathcal{C}(N,B,W)$. Under this model, in a sliding-window of
width $W$, one of the following erasure patterns are possible (i) a burst of
length at most $B$ or (ii) at most $N$ (possibly non-contiguous) arbitrary
erasures. Badr et al. obtained a rate upper bound for streaming codes that can
recover with a time delay $T$, from any erasure patterns permissible under the
$\mathcal{C}(N,B,W)$ model. However, constructions matching the bound were
absent, except for a few parameter sets. In this paper, we present an explicit
family of codes that achieves the rate upper bound for all feasible parameters
$N$, $B$, $W$ and $T$.
