Reliability

So let's talk about reliability. This is a very important concept which could be at first sight difficult but which will be very handy later on.

As you know we have two opposites, TCP on one hand and UDP on the other. TCP has a lot of feature UDP does not have, like shown below.

TCP

  • Guarantee of delivery.
  • Guarantee for order.
  • Packets will not be dropped.
  • Duplication not possible.
  • Automatic fragmentation.

UDP

  • Unreliable.
  • No guarantee for delivery.
  • No guarantee for order.
  • No way of getting the dropped packet.
  • Duplication possible.
  • No fragmentation.

It would be useful if we could somehow specify the features we want on top of UDP. Like that you say: I want the guarantee for my packets to arrive, however they don't need to be in order. Or, I don't care if my packet arrives but I do want to receive only new ones.

Before continuing, it would be helpful to understand the difference between ordering and sequencing: ordering documentation

The 5 Reliability Guarantees

Laminar provides 5 different ways for you to send your data:

Reliability Type Packet Drop Packet Duplication Packet Order Packet Fragmentation Packet Delivery
Unreliable Unordered Any Yes No No No
Unreliable Sequenced Any + old No Sequenced No No
Reliable Unordered No No No Yes Yes
Reliable Ordered No No Ordered Yes Yes
Reliable Sequenced Only old No Sequenced Yes Only newest

Unreliable

Unreliable: Packets can be dropped, duplicated or arrive in any order.

Details

Packet Drop Packet Duplication Packet Order Packet Fragmentation Packet Delivery
Any Yes No No No

Basically just bare UDP. The packet may or may not be delivered.

Unreliable Sequenced

Unreliable Sequenced: Packets can be dropped, but could not be duplicated and arrive in sequence.

Details

Packet Drop Packet Duplication Packet Order Packet Fragmentation Packet Delivery
Any + old No Sequenced No No

Basically just bare UDP, free to be dropped, but has some sequencing to it so that only the newest packets are kept.

Reliable Unordered

Reliable UnOrder: All packets will be sent and received, but without order.

Details

Packet Drop Packet Duplication Packet Order Packet Fragmentation Packet Delivery
No No No Yes Yes

Basically, this is almost TCP without ordering of packets.

Reliable Ordered

Reliable Unordered: All packets will be sent and received, but in the order in which they arrived.

Details

Packet Drop Packet Duplication Packet Order Packet Fragmentation Packet Delivery
No No Ordered Yes Yes

Basically this is almost like TCP.

Reliable Sequenced

Reliable; All packets will be sent and received but arranged in sequence. Which means that only the newest packets will be let through, older packets will be received but they won't get to the user.

Details

Packet Drop Packet Duplication Packet Order Packet Fragmentation Packet Delivery
Only old No Sequenced Yes Only newest

Basically this is almost TCP-like but then sequencing instead of ordering.

Example

 

# #![allow(unused_variables)]
#fn main() {
use laminar::Packet;

// You can create packets with different reliabilities
let unreliable = Packet::unreliable(destination, bytes);
let reliable = Packet::reliable_unordered(destination, bytes);

// We can specify on which stream and how to order our packets, checkout our book and documentation for more information
let unreliable = Packet::unreliable_sequenced(destination, bytes, Some(1));
let reliable_sequenced = Packet::reliable_sequenced(destination, bytes, Some(2));
let reliable_ordered = Packet::reliable_ordered(destination, bytes, Some(3));
#}

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