TWAMP C++ Implementation

TWAMP is a Two-Way Active Measurement Protocol designed to measuring metrics between two network devices.

Simple Logic Diagram:

 +----------------+               +-------------------+
 | Session-Sender |<-TWAMP-Test-->| Session-Reflector |
 +----------------+               +-------------------+
   ^                                     ^
   |                                     |
   |                                     |
   |                                     |
   |  +----------------+<----------------+
   |  |     Utils     |
   |  +----------------+
   |    ^
   |    |
   | TWAMP-Control
   |    |
   v    v
 +----------------+
 | Control-Client |
 +----------------+

Overview:

Modus Operadis

Following Chapter 5 (two-host implementation) from RFC 5357 will be the Controller(Client) and the Responder(Server), which will implement Session-Sender and Session Reflector respectively.

• TWAMP-Control:
  • Connection Setup
  • Integrity Protection (Probably will not be implemented) (Implement later with shared-secrets)
  • TWAMP-Control Commands
  • Create Test Sessions
  • Send Schedules
  • Start Test Sessions
  • Stop Test Sessions
  • Fetch Session
• TWAMP-Test
  • Sender Behaviour
    • Packet Timings
    • Packet Format and Content
  • Reflector Behaviour
    • TWAMP-Test Packet Format and Content

Connection Setup:

Same as OWAMP, network byte order.

Packet:

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                                                               |
|                      Unused (12 octets)                       |
|                                                               |
|+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                            Modes                              |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                                                               |
|                     Challenge (16 octets)                     |
|                                                               |
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                                                               |
|                        Salt (16 octets)                       |
|                                                               |
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                        Count (4 octets)                       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                                                               |
|                        MBZ (12 octets)                        |
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Timestamp:

The format of the timestamp is the same as in [RFC1305] and is as follows: the first 32 bits represent the unsigned integer number of seconds elapsed since 0h on 1 January 1900; the next 32 bits represent the fractional part of a second that has elapsed since then.

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                   Integer part of seconds                     |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                 Fractional part of seconds                    |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

After connections is established, client can send the following commands: Request-Session, Start-Sessions, Stop-Sessions and Fetch-Session (in TWAMP Fetch-Sessions does not exists).

Creating Test Session

The client sends a Request-TW-Session message the same format as described in Section 3.5 of OWAMP, but without the Schedule Slot Descriptions field(s) and uses only one HMAC, so the fields MBZ. The description of the Request-TW-Session format follows.

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|   1 [Command] |  MBZ  | IPVN  |  Conf-Sender  | Conf-Receiver |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                  Number of Schedule Slots                     |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                      Number of Packets                        |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|          Sender Port          |         Receiver Port         |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                        Sender Address                         |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                                                               |
|           Sender Address (cont.) or MBZ (12 octets)           |
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                        Receiver Address                       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                                                               |
|           Receiver Address (cont.) or MBZ (12 octets)         |
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                                                               |
|                        SID (16 octets)                        |
|                                                               |
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                         Padding Length                        |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                           Start Time                          |
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                       Timeout, (8 octets)                     |
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                       Type-P Descriptor                       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                         MBZ (8 octets)                        |
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                                                               |
|                       HMAC (16 octets)                        |
|                                                               |
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

5 in command is the Request-TW-Session, the two-way test session using the TWAMP-Test protocol.

Both the Conf-Sender field and Conf-Receiver field MUST be set to 0 since the Session-Reflector will both receive and send packets, and the roles are established according to which host initiates the TCP connection for control. If not, the server MUST send Accept-Session with accept = 3.

If the IP's of both the Session-Sender and Session-Reflector is the same as the Control-Client and Server respectively, SenderAddress and ReceiverAddress are set to 0.

The server also creates a SID for this client that will be used for client identity.

The timeout here is to wait for packages that are yet to come after a Stop-Session is sent. The server MUST not reflect any packet sent after TIMEOUT.

Accept-Session message:

Test Session

Session-Sender first sending and then receiving test packets.

About Floating Point Numbers

The developer had to implement own float IEEE 754 parser to get integral and fractional part of timestamp.

Dependencies

1. spdlog
   1. pacman -S spdlog
   2. sudo apt install libspdlog-dev

References

1. RFC 5357
2. Understand Two-Way Active Measurement Protocol
3. Beej's Guide to Network Programming
4. Socket Disconnected
5. Double Precision Float
6. Modf

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