At the top level, Verse data is always associated with with a session. Session is a name for the connection between two applications that talk using the Verse protocol. Typically, in such a situation, one end is called the host and the other is the client.
Hosts are mainly passive, acting as containers of data made available to clients. Clients do all the work by connecting to a host and manipulating (reading, writing, creating, editing, and generally using) the data held by it. Several clients can connect to the same host simultaneously, and will then be given individual views of the data contained on the server. Typically, much data will be shared, so that they both get the sensation of being in the same world and so that data modified by one client is visible to all other clients.
At the user level, hosts are perceived as "containing" a world, and making it available to clients through the Verse protocol. In this regard, Verse hosts are very similar to the server in any common client-server system, such as a web server for instance. It stores content, and makes it available to clients through a well-defined communications protocol.
Many operations in Verse are independent of time, they happen now, which is as soon as the data arrives, it is assumed to be valid immediately upon receipt. Some operations, however, do not make sense without a concept of time. As we'll see later, it is possible for a client to read out the current time, and receive a value which is (more or less) in sync with the host's idea of what time it is.
Time is counted in seconds, with a precision of 64 bits. Of these, 32 bits are the number of whole seconds since some unspecified previous event (such as the starting of the host), while the remaining 32 bits are fractions. Fractions are used so that times less than one second can be expressed. So, time is a pair of unsigned 32-bit integers, one called time_s (the whole seconds) and the other time_f (the fractional part).
The time_f fractional part is in units of 1/4,294,967,296:th of a second. This means that the time "four and a half seconds" is expressed as the pair of values (time_s=4, time_f=2,147,483,648).