Internet-Draft SOLEC May 2026
bt Expires 2 December 2026 [Page]
Workgroup:
SOLEC Working Group
Internet-Draft:
SOLEC
Published:
Intended Status:
Experimental
Expires:
Author:
bt, Ed.
RCTT.net

System of Lightweight Electronic Communication

Abstract

This document describes working principles, features and network protocol of SOLEC system.

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at https://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."

This Internet-Draft will expire on 2 December 2026.

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Table of Contents

1. Introduction

SOLEC is currently under development for PWR group project and as part of my engineering thesis.

System of Lightweight Electronic Communication or SOLEC is a system for decentralised communication designed for low-speed networks. It uses binary protocol to keep required bandwidth as low as possible.

Current implementation works on top of TCP/IP stack. In future, SOLEC will be adapted to work over LoRa.

1.1. Decentralisation

Recurring problem with modern day instant messaging is its centralisation. SOLEC solves is it in similar fashion to XMPP or SMTP. SOLEC servers exchange messages between each other so the users using server A can reach out users using server B.

1.2. User to user communication

User can exchange messages with other users of the network if they are both in their contacts group. Messages from untrusted users are not forwarded by the server. If users are using different servers chat history is stored on both.

1.3. Channels

Message can be send to a group of users called channel. Channels settings and history is stored on a specific server. Users can access channels from servers other than their own. To receive channel messages user have to join specific channel.

2. Network protocol

In current version session is provided by TCP connection. Security of client-server connection can be achieved using TLS.

2.1. Protocol Data Unit Structure

SOLEC is using Type Length Value (TLV) structure for data exchange.

  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |    Type       |             Length            |   Payload   ...
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure: SOLEC PDU Layout

  • Type (8): Payload type is indicated by 1 octet which gives 256 types that can be represented.

  • Length (16): Payload length is 2 octets. It indicates length of the payload field. The length does not include type and length fields.

  • Payload (variable): Payload stores set of fields determined by its type.

2.2. Payload structure

Payload usually consist of one or more data fields but it is possible for payload to be empty. Some payload types are used only to signal some event and does not carry any data.

2.3. Data types

Data types are basic types that are used in construction of more complex payload types.

2.3.1. Numeric types

Numeric types are Big-Endian. Numeric types names are taken from Go language spec. Following types are in use:

Number in numeric type name is number of bits used to encode this type.

2.3.2. Timestamp

Uint64 containing Unix timestamp in UTC timezone.

  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                          Timestamp                            |
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

2.3.3. String

String is prefixed with two octets indicating number of bytes that it occupies. Text is encoded using UTF-8.

  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |             Length            |         UTF-8 string        ...
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure: String Layout

2.4. Payload types

Payload type attributes describes following characteristics:

  • R - Reserved: implementation should ignore payloads of this type
  • S - Server: can be send only by a server
  • C - Client: can be send only by a client
  • E - Empty: signals an event but does not carry any data
Table 1
Type Name Attributes
0x00 R
0x01 Success SCE
0x02 Error S
0x03 Handshake SC
0x04 UserAuth C
0x05 Message SC
0x06 ServerAuth S
0x07 UserMode C
0x08 History. C
0xFF Test R

2.4.1. Success

Payload is always empty for this type.

2.4.2. Error

Table 2
Type Name
uint8 error_type
2.4.2.1. Error types
Table 3
Type Description
0x01 Client auth failed. Invalid username or password.
0x02 Not found. User or channel cannot access user or channel.
0x03 Unauthorized.

2.4.3. Handshake

Table 4
Type Name
uint8 ver_major
uint8 ver_minor
uint8 conn_type
2.4.3.1. Connection types

conn_type specifies type of the connection. User connecting to server should use 0x01. If connection is initialize between two servers to exchange message connection type should be 0x02. Depending on connection type different auth method will be used.

Table 5
Type Connection type
0x01 User -> Server
0x02 Server -> Server

2.4.4. UserAuth

Table 6
Type Name
string user_address
string password

2.4.5. ServerAuth

Table 7
Type Name
string name

2.4.6. Message

Table 8
Type Name
string source_address
string target_address
timestamp send_time
string message_content

2.4.7. Usermode

Usermode payload is used for changing user settings related to channels. For example: joining, leaving or setting privilages.

Table 9
Type Name
string user_address
string channel_address
uint8 mode
2.4.7.1. Modes
Table 10
Type Name
0x00 none
0x01 in_channel

2.4.8. History

Read messages previously send to a specific channel. User has to member of the channel to perform this action. since field specifies start of time range for which history should be retrieved. count specifes how many messages should be returned in a single response. GetHistory is a locking sequence and it cannot be cancelled while in progress so count should be set relatively low. To get more messages use multiple requests with incremented offset.

Response is just a sequence of Message. Client should use Timestamp field of a Message to show them in corrent order.

Table 11
Type Name
string channel_address
timestamp since
int64 count
int64 offset

2.4.9. Test

Test payload is used for encoder and decoders testing. Clients and servers should ignore this kind of payload.

Table 12
Type Name
uint8 num1
timestamp time1
string str1
uint16 num2
string str2
uint32 num3
string str3
uint64 num4

2.5. Sequential operations

Some operations require multiple rounds of communication. In this case payloads are send in a sequence. Payload that is not part of this specific operation (for example incoming message) cannot interrupt this process.

2.6. Client-Server connection initialisation 

+--------+                   +--------+
| Client |                   | Server |
+----+---+                   +----+---+
     |                            |
     | Initialise TCP connection  |
     +--------------------------->|
     |                            |
     | Send [Handshake]           |
     +--------------------------->|
     |                            |
     |                            +- If [ver_major] does not match
     |                            |  server protocol version close
     |                            |  the connection.
     |                            |
     | Send [UserAuth]            |
     +--------------------------->|
     |                            |
     | Send [Error 0x01]          |
     |<---------------------------+- If [username] or [password]
     |                            |  does not match and close
     |                            |  the connection.
     |                            |
     | Send [Sucesss]             |
     |<---------------------------+

2.7. Exchanging messages between servers

Exchanging messages between SOLEC servers is a core concept behind the project. Sending message to user residing on a different server require estabilishing a connection between both servers.

2.7.1. Authentication

Server authentication is crucial to prevent message spoofing and other forms of abuse. Server cannot use same auth process as clients because that would require creating account for each server on any other server which is impossible. Possible solution are TLS or other public key based protocol.

As for now the issue remains open and server authorization uses mock [ServerAuth] payload which specifies just the connecting server name. This is obviously insecure.

2.7.2. Server-Server connection initialisation 

+--------+                   +--------+
| Server |                   | Server |
+----+---+                   +----+---+
     |                            |
     | Initialise TCP connection  |
     +--------------------------->|
     |                            |
     | Send [Handshake]           |
     +--------------------------->|
     |                            |
     |                            +- If [ver_major] does not match
     |                            |  server protocol version close
     |                            |  the connection.
     |                            |
     | Send [ServerAuth]          |
     +--------------------------->|
     |                            |
     | Send [Sucesss]             |
     |<---------------------------+

3. Addresses

Message can be addressed to a single user or a channel.