# Overview of Twisted Spread

Perspective Broker (affectionately known as “PB” ) is an asynchronous, symmetric [1] network protocol for secure, remote method calls and transferring of objects. PB is “translucent, not transparent” , meaning that it is very visible and obvious to see the difference between local method calls and potentially remote method calls, but remote method calls are still extremely convenient to make, and it is easy to emulate them to have objects which work both locally and remotely.

PB supports user-defined serialized data in return values, which can be either copied each time the value is returned, or “cached” : only copied once and updated by notifications.

PB gets its name from the fact that access to objects is through a “perspective” . This means that when you are responding to a remote method call, you can establish who is making the call.

## Rationale

No other currently existing protocols have all the properties of PB at the same time. The particularly interesting combination of attributes, though, is that PB is flexible and lightweight, allowing for rapid development, while still powerful enough to do two-way method calls and user-defined data types.

It is important to have these attributes in order to allow for a protocol which is extensible. One of the facets of this flexibility is that PB can integrate an arbitrary number of services could be aggregated over a single connection, as well as publish and call new methods on existing objects without restarting the server or client.

Footnotes

[1]

There is a negotiation phase for the `banana` serialization protocol with particular roles for listener and initiator, so it’s not completely symmetric, but after the connection is fully established, the protocol is completely symmetrical.