Time-Triggered Ethernet (TTEthernet, TTE)
The TTEthernet protocol was developed to enable time-triggered communication over Ethernet. Its services include a clock synchronization service, a startup service, and clique detection and recovery services. TTEthernet is a transparent synchronization protocol, which means that it is able to co-exist with other traffic, potential legacy traffic, on the same physical communication network. It defines basic building blocks that allow to transparently integrate the time-triggered services on top of message-based communication infrastructures such as standard Ethernet. In addition, it is designed to operate for a multitude of cross-industry applications. As such, TTEthernet comprises demanding fault-tolerant capabilities.
TTEthernet specifies services that enable time-triggered communication on top of Ethernet, the TT Services. Messages from higher layer protocols, like IP or UDP, can easily be "made" time-triggered without modifications of the messages' contents itself. This is, because the TTEthernet protocol overhead is transmitted in dedicated messages, called Protocol Control Frames, which are used to establish system-wide clock synchronization. In short, TTEthernet is only concerned with "when" a data message is sent, rather than with specific contents within a data message.
For details about the protocol, please refer to the TTEthernet specification, available from TTTech (email@example.com).
- Any protocol that can be on top of standard Ethernet can also be on top of TTE.
- Usually, UDP/IP is used (see the AFDX standard).
- PCF: The "data payload" of such frames is entirely used by TTEthernet. PCF contain no real payload.
Captured TTE traffic can, for example, look like this:
The recognition of TTE traffic is based on the MAC Destination Constant Field. The TTE dissector actually consists of two dissectors, one for TTE Data Frames (TTE, based on ARINC664 AFDX Frame), and one for TTE Protocol Control Frames (TTE-PCF). The former dissects the destination MAC address and displays the "Constant Field" and the "Critical Traffic Identifier (CT ID)". The latter dissects the contents of a PCF frame, as shown in the above example.
Both dissectors are fully functional and are active by default. They can be disabled independently, using the 'Analyze.Enabled protocols...' menu entry.
Traffic satisfying the equation "Constant Field" & "CT Mask" = "CT Marker" is considered critical traffic and is hence processed by the TTE dissectors.
- Select "TTE" from the available protocols.
- Set "CT Mask" and "CT Marker" according to the above equation.
Example capture file
Note: the MAC Destination Constant Field was set to 3000101 for this example.
all TTEthernet based
all traffic to the Ethernet MAC address 3000101
all with the Critical Traffic Identifier 20
all TTE Protocol Control Frame (PCF) traffic
all TTE PCF traffic within a certain sync domain
ether proto 0x891d
only frames with ethertype 0x891d
ether src 00:08:15:00:08:15
only frames from 00:08:15:00:08:15
ether dst 00:08:15:00:08:15 and ether src 00:08:15:00:08:20
only frames directed to 00:08:15:00:08:15 and coming from 00:08:15:00:08:20
only frames with a size of less than or equal to 100 bytes
Additional examples for capture filters can be found in the tcpdump capture filter expressions at [http://www.tcpdump.org/tcpdump_man.html].
- The TTEthernet specification is available at