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|
SOLEC Working Group bt, Ed.
Internet-Draft RCTT.net
Intended status: Experimental 14 April 2026
Expires: 16 October 2026
System of Lightweight Electronic Communication
SOLEC
Abstract
This document describes working principles, features and network
protocol of SOLEC system.
Table of Contents
1. Introduction
1.1. Decentralisation
1.2. User to user communication
1.3. Channels
2. Network protocol
2.1. Protocol Data Unit Structure
2.2. Payload structure
2.3. Data types
2.3.1. Numeric types
2.3.2. Timestamp
2.3.3. String
2.4. Payload types
2.4.1. Success
2.4.2. Error
2.4.3. Handshake
2.4.4. Auth
2.4.5. Message
2.4.6. Test
2.5. Sequential operations
2.5.1. Connection initialisation
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 (https://go.dev/ref/spec#Numeric_types). Following
types are in use:
* uint8
* uint16
* uint32
* uint64
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
+======+===========+============+
| Type | Name | Attributes |
+======+===========+============+
| 0x00 | | R |
+------+-----------+------------+
| 0x01 | Success | SCE |
+------+-----------+------------+
| 0x02 | Error | S |
+------+-----------+------------+
| 0x03 | Handshake | SC |
+------+-----------+------------+
| 0x04 | Auth | C |
+------+-----------+------------+
| 0x05 | Message | SC |
+------+-----------+------------+
| 0xFF | Test | R |
+------+-----------+------------+
Table 1
2.4.1. Success
Payload is always empty for this type.
2.4.2. Error
+=======+============+
| Type | Name |
+=======+============+
| uint8 | error_type |
+-------+------------+
Table 2
2.4.2.1. Error types
+======+============================================================+
| Type | Description |
+======+============================================================+
| 0x01 | Auth failed. Invalid username or password. |
+------+------------------------------------------------------------+
| 0x02 | Not found. User or channel cannot access |
| | user or channel. |
+------+------------------------------------------------------------+
Table 3
2.4.3. Handshake
+=======+===========+
| Type | Name |
+=======+===========+
| uint8 | ver_major |
+-------+-----------+
| uint8 | ver_minor |
+-------+-----------+
| uint8 | conn_type |
+-------+-----------+
Table 4
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.
+======+==================+
| Type | Connection type |
+======+==================+
| 0x01 | User -> Server |
+------+------------------+
| 0x02 | Server -> Server |
+------+------------------+
Table 5
2.4.4. Auth
+========+==========+
| Type | Name |
+========+==========+
| string | username |
+--------+----------+
| string | password |
+--------+----------+
Table 6
2.4.5. Message
+===========+=================+
| Type | Name |
+===========+=================+
| string | source_address |
+-----------+-----------------+
| string | target_address |
+-----------+-----------------+
| timestamp | send_time |
+-----------+-----------------+
| string | message_content |
+-----------+-----------------+
Table 7
2.4.6. Test
Test payload is used for encoder and decoders testing. Clients and
servers should ignore this kind of payload.
+===========+=======+
| Type | Name |
+===========+=======+
| uint8 | num1 |
+-----------+-------+
| timestamp | time1 |
+-----------+-------+
| string | str1 |
+-----------+-------+
| uint16 | num2 |
+-----------+-------+
| string | str2 |
+-----------+-------+
| uint32 | num3 |
+-----------+-------+
| string | str3 |
+-----------+-------+
| uint64 | num4 |
+-----------+-------+
Table 8
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.
2.5.1. Connection initialisation
+--------+ +--------+
| Client | | Server |
+----+---+ +----+---+
| |
| Initialise TCP connection |
+--------------------------->|
| |
| Send [Handshake] |
+--------------------------->|
| |
| +- If [ver_major] does not match server
| | protocol version close the connection
| |
| Send [Auth] |
+--------------------------->|
| |
| Send [Error 0x01] |
|<---------------------------+- If [username] or [password] does not match
| | and close the connection
| |
| Send [Sucesss] |
|<---------------------------+
|
