P4/P2 - Secure & Transparent Transmission over Copper - technical brief

A lot has been stated about the inherent security features of these products.
Here we reproduce a succict white paper on the subject.

Symmetric High Speed Digital Subscriber Line (SHDSL) technology and its particular product implementation represents a highly secure transmission platform over copper in the tactical environment.

In simple and unambiguous terms: P4/P2 data transmission can be equated to a ‘one time pad’. 
It can not be detected due to low signbal strength and amplitude that is driven directly in to copper wire. If the cable is damaged, the transmission stops. The only device that can detect and unscramble the signal is another P4/P2.

Transmission security is implemented in multiple layers during extensive signals processing (line set up) and further masked by the proprietary management protocol. For clarity this is not a government accredited security protocol i.e. no encryption processing is involved. Rather, it is the nature of the signal modulation that makes the transmission highly secure. This inherent security is further enhanced with engineered and integrated network protocols including: MAC filtering, SSH, Radius and SNMPv3 protocols – as standard.


How this is achieved - in more detail:

DSL Initialisation Process & Data Scrambling
Digital signal modulation scrambles data transmission across multiple (up to 300) frequency carriers within a 1.2MHz spectrum (for SHDSL), that in turn represent maximum possible bandwidth. At the time of initialisation each of the frequency carriers is tested for its signal-to-noise ratio and bit-error-rate. The length and physical condition of the copper cable will have impact on these parameters. Once the process is complete, only those carriers that passed the initialisation test will be activated. Data packets are then scrambled across active carriers.
In P4/P2 products multiple data modulation modes are implemented. These are called TC-PAM 8, 16, 32, 64 & 128. TC-PAM is a ’Trellis Coded Pulse Amplitude Modulation’. It enables efficient and interference-free transmission of data within a limited frequency spectrum (of 1.2MHz).  Although TC-PAM is defined by the standard (ITU-T G991.2), its implementation is proprietary to chipset manufacturers.
The next security layer is proprietary handshake signals that automatically set up a data link. Called ‘Zero Mode’, it is a manufacturer proprietary feature that is available only on P4/P2 equipment. The process represents a significant layer of transmission security.  By introducing these additional bits to the transmission, the data cannot be deciphered by any other equipment.
Finally, there is distribution or further scrambling of user data across multiple transmission channels. Known as Auto Bandwidth Aggregation, it provides three effective functions: transmission redundancy, increased bandwidth and security i.e. the greater the number of data users, the greater the scrambling effect, the more indecipherable the transmission on any given D10 link.

Electronic signature: the maximum transmission energy of SHDSL is under 1W per channel.  The effective energy level drops with shorter cable distance i.e. lower attenuation.  It is important to note that the energy is driven directly into the copper, making its electronic signature extremely small.Any signal leakage or energy that is not driven directly into the copper cable is eliminated during the initialisation i.e. each frequency carrier that did not pass the bit-error-test is deactivated. It is impossible to ‘listen’ to the transmission as any transmission parameters variation will cause the link to shut down. Similarly, when the copper cable is cut or damaged, the transmission stops.

Transmission Security Summary
The inherent features of SHDSL and P4/P2 specific product design provide extremely effective transmission security.  In order to establish ‘government level’ security, a certified encryption device could be used – making a P4/P2 transmission link a transparent entity.