I read a article that describes the caracteristics of anonymous communication protocols.

One of their is the synchronization. A protocoles can be asynchronous or synchronous.

This is the definitions on the paper:

A connection is asynchronous if the establish- ment of connections and relaying of messages is initiated by a user without any timing coordination with other participants.

Connections are synchronous if they begin and end at specific timings and messages are also re- layed at specific moments in time, based on some timing coordination between network entities.

Authors claims that TOR is asynchronous but I don't understand why?

TOR is a anonymous network for application in real time like browsing or IRC.It can not be asynchronous for this reason.

Unless I misunderstood the definition of asynchronous?

The article is available here.

1 Answer 1


Some anonymity networks send messages on in "lock-step" (they follow a predetermined schedule and exchange messages at the same time), especially high latency anonymity networks.

In this way, Tor is "asynchronous". Clients can send cells at any time and the relay sends them on as they're received, not on a predetermined schedule.

Because of this Tor is a low-latency anonymity network, which is exactly why it can be used for HTTP or IRC or XMPP and isn't only useful messaging like email.

  • Can you talk about flushing algorithm? TOR can not use a flushing algorithm because it is low-latency. From what I understand, a low-latency anonymity networks is automatically asynchronous? For example, JAP is considered synchronous on the paper.
    – salt
    Commented Aug 24, 2017 at 19:59

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