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For any $q \geq 2$, let $\Sigma_{q}=\{0,\ldots,q\!-\!1\}$, and fix a string $A$ over $\Sigma_{q}$. The $A$-free strings of length $n$ are the strings in $\Sigma_{q}^n$ which do not contain $A$ as a contiguous substring. In this paper, we investigate the possibility of listing the $A$-free strings of length $n$ so that successive strings differ in only one position, and by $\pm 1$ in that position. Such a listing is a Gray code for the $A$-free strings of length $n$. We identify those $q$ and $A$ such that, for infinitely many $n \geq 0$, a Gray code for the $A$-free strings of length $n$ is prohibited by a parity problem. Our parity argument uses techniques similar to those of Guibas and Odlyzko (Journal of Combinatorial Theory A 30 (1981) pp. 183–208) who enumerated the $A$-free strings of length $n$. When $q$ is even, we also give the complementary positive result: for those $A$ for which an infinite number of parity problems do not exist, we construct a Gray code for the $A$-free strings of length $n$ for all $n \geq 0$.

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The ATM Forum's LAN Emulation (LANE) Specification has now been available for more than two years, and LANE products have matured sufficiently that enterprises have deployed production LAN Emulation networks. However, the scaleability of LANE is still frequently debated, as is its applicability in Wide-Area Networks (WANs). This paper examines design features and supporting applications that can enhance the scaleability and manageability of LAN Emulation networks. The design features include techniques for distributing the LANE Services to provide load balancing and robustness, mechanisms for managing broadcast and multicast traffic (which have been a classical problem with large LAN networks), approaches for controlling signalling rates during power-up and failover situations, and extensions that exploit the distributed routing capabilities provided by the Next Hop Resolution Protocol (NHRP). Issues associated with WAN deployment of LAN Emulation are also explored, including requirements for canier-based service environments, where conservation of network resources, security capabilities, and monitoring applications are especially important. The paper is concluded with an assessment of LANE's status/prospects as a technology for building large-scale networks.