This is quite a rabbit-hole that started when a message ended up getting lost, and I wondered why that tends to happen with text messages and not apps like messenger. TLDR: the difference is that text messages (SMS/MMS/RCS) are only forwarded from one phone to another, while apps like messenger centrally stores the data in a server.

Below is an overview of the main messaging service types: SMS/MMS, RCS, and Messaging Apps.

SMS (Short Message Service)

• Widely supported
• Must use mobile networks
• Not encrypted
• Limited to 160 characters (extended with MMS)
• Messages are deleted from SMSC (Short Message Service Center) after forwarding
• Messages may be lost if the receiver is unavailable
• Receiver is responsible for backing up messages, if desired

RCS (Rich Communication Services)

• Can use any data connection
• Can be encrypted, if the provider supports it
• Supported by major providers
• Designed to integrate with SMS/MMS
• Supports longer messages and larger media than SMS/MMS
• Messages are deleted from provider after forwarding
• Receiver is responsible for backing up messages

Typical Messaging Apps

Just to simplify things, I'll split this into only 2 categories

Central Storage

• Can use any data connection
• Can be encrypted, if the app supports it
• Messages are stored on central servers
• Messages can be edited/deleted since the history is centrally stored
• Examples: Messenger, Discord

Local Storage

• Can use any data connection
• Can be encrypted, if the app supports it
• Similar to SMS/RCS, messages are forwarded, then deleted from the provider
• Messages typically can't be edited/deleted since the history is local
• Receiver is responsible for backing up messages
• Examples: WhatsApp, Signal

Encoding

The way I described SMS above makes it look kind of useless, honestly, but that’s just because it was created for a different era, where networks had very limited bandwidth. The SMS protocol was originally developed in 1986, around the same time that the first cellular network was being adopted (retroactively named 1G), with speeds around 2.4Kpbs. Compare that to 5G at 20Gbps, 10 million times faster.

Practically speaking, the constraints put on SMS at the time is why each message has a max of 160 characters. Going even deeper, the encoding of each character (using 7-bit GSM) was designed to support only what seemed necessary to convey most information. Because of the limitations of using only 7 bits, it really only works for certain languages like the latin languages where there are a limited number of distinct characters.

For the rest of the messaging options mentioned (and most of the modern web for that matter), UTF-8 encoding is used, which supports almost all languages.

Encryption

I mentioned encryption without really going into detail because there are many ways it could be done, and you really need to look into each provider to see how/if encryption is used and whether that meets your needs.

• SMS for example, has no encryption, meaning someone could technically intercept your message and read it in plain text, but there is a shorter window of time before the message is deleted from the central storage.
• Discord is not encrypted either, but since it is typically used for groups, the company uses automated systems to moderate harmful content, which would be much more difficult if the messages were encrypted.
• WhatsApp offers end-to-end encryption, which means messages are encrypted before being sent to the temporary provider storage, so no one should be able to intercept and read the messages, not even WhatsApp. This doesn’t stop the receiver from storing the messages in plain text, though.

Why Does it Matter?

This article formed out of curiosity to learn a little bit more about how the world works. I don’t claim to know everything about messaging protocols, I’m just learning about it myself, but hopefully this was an interesting look behind something we use every day.

The diagrams were created with D2.