  To better understand the wireless network design with a large number of hops,
we investigate a line network formed by general discrete memoryless channels
(DMCs), which may not be identical. Our focus lies on Generalized Batched
Network Coding (GBNC) that encompasses most existing schemes as special cases
and achieves the min-cut upper bounds as the parameters batch size and inner
block length tend to infinity. The inner blocklength of GBNC provides upper
bounds on the required latency and buffer size at intermediate network nodes.
By employing a bottleneck status technique, we derive new upper bounds on the
achievable rates of GBNCs These bounds surpass the min-cut bound for large
network lengths when the inner blocklength and batch size are small. For line
networks of canonical channels, certain upper bounds hold even with relaxed
inner blocklength constraints. Additionally, we employ a channel reduction
technique to generalize the existing achievability results for line networks
with identical DMCs to networks with non-identical DMCs. For line networks with
packet erasure channels, we make refinement in both the upper bound and the
coding scheme, and showcase their proximity through numerical evaluations.
