The SSAVI Cable Scrambling System by Mad Phone-man
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Short of the D.E.S. based Video Cypher system, one of the most sophisticated
and versitile video/audio scrambling systems is the S.S.A.V.I. system. The
acronym is the "Suppressed Sync Active Video Inversion". Zenith has exploited
this system for years and later enhanced versions, known as Z-Tac and A-Tac
have SSAVI at their roots.
SSAVI was sucessfully marketed to numerous over-the-air subscription services,
most of which are defunct now. In the wake of these services, however are
thousands of SSAVI decoder units being sold by a variety of companies and
individuals for use on CATV systems.
There is an inherent problem in this re-marketing of STV units in that the
Zenith tuner has been stripped of its VHF capability. The STV services were
UHF systems. The STV SSAVI units, therefore, had no need for VHF tuning
capabilitys.
There are, on the other hand, SSAVI units whose initial purpose was CATV based
and which do have VHF tuning capability. The average consumer, however is hard
pressed to know just what he might receive when ordering a SSAVI unit.
companies employ a variety of techniques to modify the STV (UHF) units for VHF
reception. There are also numerous revisions of the SSAVI units, all from
Zenith, that date back to the pre-VLSI era. Most units which the author has
dealt with do employ VLSI technology and therefore are minus an entire PCB
which earlier models had mounted in their top shells and accomidated discreet
circutry, later replaced by a single VLSI device (GATEARRAY).
The old discreet versions are the most versitile in terms of modifying, but
least available in numbers. Schematic diagrams for the discreet SSAVI devices
are available from Shojiki Electronics, (716) 284-2163
This article, therefore will deal with the SSAVI units at a more superficial
level. There are 4-modes of operation obtained from 3 variables available to
the SSAVI operator. These variables are:
1) Normal/ Suppressed sync
2) Normal/ Inverted video
3) Normal/ Suppressed audio
The 4 video modes of operation thus yield:
1) Normal video/ Normal sync
2) Normal video/ suppressed sync
3) Inverted video/ Normal sync
4) Inverted video/ suppressed sync
The first of these modes is "clear" transmission or "non-scrambled". The
remaining three are designed to foil reception by standard TV receivers. In the
case of mode 2, thw sync pulses are offset from their normal "Blacker-than
black" position such that the front and back porch of the sync pedistal are at
+80 IRE units. This action prevents the sync-seperator in a standard TV from
stripping off the sync pulses. The result is that horizontal sync is lost and
the picture tends to "tear" or roll horizontaly. In addition, the AGC circutry
is confused and tends to DC clamp the blackest portion of the video to the
sync level.
The level used in maximum security is mode 4. In this mode, the video is
inverted between each horizontal sync pulse from line 25 to line 260 of the
active scan lines. The sync pulses are suppressed as described earlier, but
NOT inverted. This is a clever technique to foil pirate decoders. This is
because if one simply inverts the composite video, one also inverts the sync
pedestal, thus inverting the chroma burst on the sync back porch. Thus the
video chroma (color) will be incorrect. The successful decoder must, therefore
invert the video ONLY between horizontal sync pulses, and provide an offset
pulse gated to shift the sync pulses back to their normal level.
To further compicate matters, modes 1-4 may be switched between at random,
under command of the head end, to foil simple static decoders which cannot
automaticly track these mode switches.
Audio in the SSAVI system may also be displaced, preventing reception on a
standard TV receiver. It, when desired can be shifted, SCA style, to a
subcarrier. One can see that the SSAVI system provides a fairly high degree
of security.
The availability of SSAVI units and their employment by unauthorized persons
caused some inital grief for CATV operators. To render the SSAVI units non-
usable, Zenith changed the video inversion key employed by the CATV-SSAVI units
to differ from the STV SSAVI units.
The SSAVI units key on the binary level transmitted during the second half of
line 20 during the vertical blanking interval. When this level is high, the
comming frame is to be inverted. When this level is low, the comming frame is
to be normal (non-inverted).
SSAVI cable systems, therefore, employ a couple of techniques to foil STV units
which are keying on line 20. One technique involvs maintaining the video in the
inverted state, but transmitting a "bogus" line 20 ke to cause the STV SSAVI
units to switch states at a random, frequent rate. This results in "flashing".
The picture switches between normal and inverted at a high rate producing an
annoying FLASH syndrome.
Another technique used by CATV-SSAVI systems is to transmit the bogus line 20
signal as described, but to transmit the key on line 21 which then allows the
video to become dynamically switched from normal to inverted once again.
Shojiki sells a manual on a circut called Z-trap. This circut foils the first
of these techniques by returning control of the line 20 key to the user. The
circut provides the user with a switch which selects between high and low for
insertion during line 20. The circut stops the flashing.
The more state-of-the-art systems like Z-tac use a still different inversion
key. The sync suppression technique is never-the-less, identical to the SSAVI
system.
It is an easy mater enough to use a STV-SSAVI unit for CATV reception. One
need only to employ a "block converter" ahead of the SSAVI unit. The STV-SSAVI
units can be tuned through the upper 2/3 of the UHF spectrum by means of a
multi-turn pot inside the unit. The block converter will up-convert CATV
frequencys into this same band of freqs. The block converters are available
from Radio Shack and the likes.
The limitation in the block converter technique is that hyper-band and a large
portion of the super-band signals fall above UHF channel 83 and above the
SSAVI's tuning range. For systems where all premium channels are in the
mid-band, however, this technique works well.
If one has need of access to super/hyper band channels a converter-to-block
converter to SSAVI hook-up works equaly well with an important caveat. The
converter must NOT re-modulate the video. Converters which provide mute/volume
control capability are therefore not acceptable. The reason for this follows.
The hook-up then, looks like this:
CATV-> Converter -->ch 3 --> Block conv --> ch 34-36 -->SSVI -->ch 3 --> TV
down out up tunable
The SSAVI decoder relies on a 504khz syncronizing signal derived from the
carrier itself. Therefore, down converters which re-modulate destroy this
reference and cause the SSAVI to malfunction. Simple hetrodyning down-
converters allow the SSAVI unit access to the actual carrier of the
transmitted video.
To circumvent all these frequency conversions, many resellers install small
VHF tuners into the SSAVI units. Depending on the quality of the tuner, the
reception may be better or worse than the multi-conversion system.
SSAVI units may also be modified to "skew" their internal timing so as to key
off of line 21 so as to be compatable with systems whose real inversion key
resides on line 21 as described earlier. The older discreet IC SSAVI units lend
themselves to this most readily. The VLSI equipped units, never the less can
also be modified to be one scan line shifted, by interuption of the 504khz
reference for 32 cycles. [0m
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Showing posts with label Network-Tips. Show all posts
Showing posts with label Network-Tips. Show all posts
Sunday, September 2, 2012
The SSAVI Cable Scrambling System
Labels:
Network-Tips,
Security-Tips
TELENET SCANNING
**********************************************************************
* *
* TELENET SCANNING *
* *
* written by Doc Telecom on July 11, 1988 *
* *
**********************************************************************
Telenet is the largest Packet Switching network, that I know of at this
present time, I could waste valuable buffer space explaining what packet
switching is and what its uses are ect...so for more information read
"Packet Switching (tomorrow's communications today) by Roy D. Rosner. It
is quite indepth and one of the books I cherish in my "legal" Telecomm
library.
DEFINITION of GTE TELENET : The packet switching subsidiary of General
Telephone and Electronics. It provides nationwide common user data
communications via packet switching
Information on GTE TELENET :
----------------------------
The GTE Telenet commercial packet switched network was developed as a
commercial venture of many of the same principals who developed ARPANET.
GTE Telenet first became in 1979.
OPERATION :
------------
Telenets network operation and internal protocals evolved from the ARPANET
experience , with additional cababilitys built into each of the switching nods.
The network is mostly a ciruit bases packet switching protocol, that does meet
the requirments of the CCITT X.25 protocol at the user interface. In addition,
Telenet also provides customized user interfaces to meet the need of the
individual users. It also provides emulation interfaces.
USER ACCESS :
-------------
User access to the network is through one of the three clases of telenet
central offices, such as the one in San Fran, support user access speeds up to
56k bps is a Class I. Class II offices, such as the one in Spokane,Wa provide
connection speeds up to 9600 bps. Class III offices support rates up to 1200
bps, such as the one in tucson,arizona. User access can be made to Public
Dialin ports, private dial in ports, or fixed ports dedicated full time for a
single user. Users can implement X.25 compatable software in there host computer
or they can just use the T-net provided interface processors to provide network
service. Terminal Clusters can be accessed to the network very effciently by use
of Telenet access controllers placed at the customers residece or business,
ect..
Telenet Dialups
---------------
To find the local Telenet dialup for your area just call WATS to 800-TEL-ENET
and ask them for it but remember to watch out "Every thing you do on telenet is
saved on Mega tape for up to 5 years, and they have installed number
identification since December 1987,
WATS TELENET DIALUPS....
(800) 424-9494 300/1200 BPS
(800) 238-0631 2400 & MPE
These wats will change in aug. 88 so if you would like the new ones leave my
E-Mail on Lunitics Labs (415) 278-7421
What to do one you have your POTS dialup:
-----------------------------------------
Remember to do any scanning on telenet you need a POTS dialup not a WATS, the
WATS dialup is mainly used for Telemail or GTE MAIL., or SPRINT HP's
Call your local dial up and you should see something that says TELENET
617 18m, or whatevr...just hit a few times. and you should see something
that looks like this.
@
at the "@" prompt type in NPA XXX..for now just use your area code...
like this....( this is a Network User Address or NUA)
@ 415 333
it will then either connect you, or say "Collect Connection Refused",
because you have not used an NUI, more on NUI's later...
you will see one of the following :
1) call connected ....
2) Remote Procedure Error 11 b6
3) Remote Procedure Error 11 e2
4) Not Reachable 05 e6
5) not reachable 05 db
6) Not operating ....
7) illegal address 03 80
8) Busy 01 00 .....
9) enhanced network services unavalible at this time please try again 05 d8
10) illegal address 03 ba
11) rejecting 00 7e
12) illegal address 03 42
13) remote procedure error 11 31
14) Refused collect connection 19 00 .....
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Network-Tips,
Security-Tips,
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