 access may or may not be accom- modated. The access method also determines the time a station may have to wait before gaining access to the network. Some access methods like token passing are "deterministic," meaning that the delay time is a predictable fixed function dependent on a particular network spec- ification, such as number of network nodes. Others, are "statisti- cal," meaning that only the odds of gaining access are calculable, not the exact waiting time itself. Deterministic networks are easier to model than statistical networks, when the effect of a change in- NETWORK STRUCTURES 87 volving data rates, message size, or other variables must be deter- mined. The network's ability to recover from the failure of a critical net- work component, such as a node, is also determined by the access protocol. The access method also determines the stability with which the network accommodates exception conditions, such as operating under extreme loads, in terms of maintaining acceptable delay times and fair access. There are nearly as many types of access methods, as there are LAN network offerings. The types can be broken down into two basic classes: centralized access methods, in which a central arbiter controls the user stations' right to access; and distributed access methods, in which the individual user stations control the right to access. 6.2.1 The Ethernet Way Local Area Network interconnection schemes such as the Ethernet provide the framework in which one can construct a system of shar- ing resources in an effective manner. Ethernet uses a broadcast mechanism (coaxial cable) and a distributed access procedure to al- low for sharing of the channel. The procedure is called carrier sense, multiple access with collision detection (CSMA/CD). Nodes on Eth- ernet can sense ongoing transmissions and defer theirs until the chan- nel is idle. They also have the ability to monitor the channel while transmitting to determine if any other stations are also attempting to transmit. Once an idle channel is sensed a st