Why is Tor so Slow?


A number of users accessing the deep web must have known about the Tor software. The Tor software enables the users to browse and communicate through the internet privately. It was initially started as a software project with the name – ‘The Onion Router’. It directs the internet traffic through a free worldwide overlay network consisting of thousands of relays, thereby helping the users to hide their location and usage from anyone conducting the traffic analysis or surveillance.

Onion routing is implemented simply by encrypting the communication protocol stack in the application layer. As the layers are nested, the connection speed is a bit slow. Here, we will discuss the reasons why is tor so slow.

But before we move forward, let us learn who use Tor. Tor is generally used to browse the web anonymously and can be used for both licit and illicit purposes. A number of users around the globe use Tor while accessing the deep web.

Why is Tor so slow?

There are several reasons for why is tor so slow. Firstly, with the increase of awareness of the users, the tor network had grown rapidly. The sudden increase in its user base has impacted the network performance. We can categorize the reasons for why is tor so slow for six major reasons. They are:

Tor’s Congestion control doesn’t work well

One of the tor’s major critical performance issues is due to how it combines its high-volume streams with its low volume streams. To overcome the issue, we need to come up with ways to let the quiet streams like web browsing to co-exist better with the loud streams.

  1. TCP back-off slow down every circuit at once: Tor basically combines all the circuits into a single TCP connection. This is a good idea which helps to prevent the anonymity of the users but research has shown it has a negative impact on its performance.
  2. Choosing Tor’s congestion control window sizes wrong: Tor generally maintains a per-circuit maximum of unacknowledged cells. In case if this value exceeds, then it is assumed to have a congested circuit and the originator refuses to send it.Generally, the best-defined circuit window-size is 512kb and the per stream size of the window is 256kb.

Some users add way too much load

A major challenge to tor is sometimes the users add way too much load than the network can handle. So, whenever there is too much load, in the first-place tor cannot handle it and therefore makes the system slow. Also, bittorrent traffic is another major reason for tor’s network load which reduces it speed.

Tor’s network doesn’t have enough capacity

This is another major reason why is tor so slow. Tor network lacks the ability to handle the large user base or the total number of users handling tor at that instant of time. Now when we think we can solve the problem just by adding the capacity, that’s not the case. If they add more capacity without solving the high-volume streams issues, then these high volumes would expand up to eat up even the newly added capacity. This would indeed just add to cost of tor and make no actual benefit to it.

Tor client’s chose the path incorrectly

Why is tor slow, this question would still rise even if tor solves the congestion controlling problems, then too the problem of users who abuse the network with too much traffic would still give rise to the speed issue with tor. This problem rises due to several algorithm problems which lies within tor. These includes problem like they don’t balance traffic over their bandwidth numbers correctly.

  • The Bandwidth estimates they calculate aren’t much accurate. Also, to tackle this issue, they use bandwidth metric while it might be quite possible that bandwidth might not be the right metric to measure and resolve this issue.
  • The exit policy for relay selection is also not robust which ends up providing relays with permissive exit policies to be candidates for more circuits leading to more heavily loaded when compared to relays with restrictive policies.
  • Another major algorithm issue is that the older entry guards are overloaded which means that tor selects a small number of entry guards which leads to a large number of clients accumulating at the entry point.

Clients need to handle latency and failures better

The clients accessing tor network are not good at handling high or variable latency and connection failures. Currently, the lack of ways to smoothen out the latency which clients see and poor heuristics which doesn’t allow clients to move out of bad circuits leads to the slowdown of the tor network.

The Final Words

There are several minor reasons why is tor so slow, and the tor team is working on it to improve the algorithms and technology to provide better user experience and performance of the tor network. But with the current state, there are several steps which one can get online if implemented and flowed which enables the user to overcome the performance issue and get a better network to work with.

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