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TUCoPS :: Phreaking Technical System Info :: 9x_dcom.txt

Digital Telecomms




STATION ID - 7047/3.12

9x Datakit Network
FOR OFFICIAL USE ONLY

This is a 9x system, restricted to authorized persons and for
official 9x business only. Anyone using this system, network or data
is subject to being monitored at any time for system administration and
for identifying unauthorized users or system misuse. Anyone using this
system expressly consents to such monitoring and is advised that any
evidence of criminal activity revealed through such monitoring may be
provided to law enforcement for prosecution.



1 0                1   1        0         0        1  0         1       0   1
101  1   1       001 1 0 0    1 1   0     1 0  1 1 0 11       001     0100 10
010 12  010 1 1  01001 11 1   1 00 11   1 110  0 0 0 1100 1 0 1010   00011 11
1010011 11010 0  11110101010  0101 011 0001100 11100 0001 110 000011 00001101
10100010101001010101000101010100101010101001010101110010010100100010100101010
10100101010100010101000100101001001011001010001001001010101010100100100101010
101000101010100101010101010 US Switching Hierarchies 110101001101010010101000
10101010101010101010101010101101100011010101010101010101010011100101010101010
101010101000111010001010010101 DiGiTaL Telcomms 01010001010100010101010100101
10101001010100100101010101010101010100010101010100100101010101010101010100101
10101001010101010100101010101010  By Hybrid  01010101010110101010100101010001
                       written for 9x sometime in 1998

Index:
~~~~~~
        1. Intro
        2. Switching Hierarchy
        3. North American Digital Hierarchies
        4. The Local Subscriber Loop
       
       
1. Intro:
~~~~~~~~~
thanx for reading my 4th file for 9x, Bascially its just a few things I
think have never covered before. I have to say at this point that you may
want to get a cup of coffee (or somthing else) to keep you awake, as some
of the subjects covered in this t-file may be less appealing to some people.

        If you don't want to know about any of the things listed above in
the index, then hang up now. OK, lets get started. Most of my
9x files have been UK specific, this file is for you US dudes, hopefully you
can make some use of it. All of the information in this article comes from
various sources, such as telco books, and technical manuals. I have taken the
time to write all of this, so I hope you can find the time to read it all!
Please excuse my crude looking diagrams, I hope you can all make sence of
them, I have designed this article so it is easy to read... So of the other
files I have read on Switching Systems etc, just look like massive essays,
and you end up skipping through the whole thing. I have tried to make this as
interesting as possible... Enjoy.


2. Switching Hierarchy
~~~~~~~~~~~~~~~~~~~~~~

Ok, let's start with the basics. Before anyone can understand the US switch
system, they need to understand how it has evolved to be what it is today.
Early phone customers where linked by point-to-point lines as shown in the
following shit looking diagram:



                                     (1)
                                    /   \
                                  /       \
                                /           \
                              /               \   Point-to-Point Connections
                            /                   \
                          /                       \
                        /                           \
                      /                               \
                    /                                   \
                  /                                       \
                /                                           \
              /                                               \
            (2)------------------------------------------------(3)
                                      


This kind of connection seems like a simple system (it is), However, as the
number of customers increaseases, the number of lines incrteases even faster.
There are over 165 million phone customers in the US and Canada, it would be
imposible to connect everyones phones with this simple form of point-to-point
connection.

The first phone eXchanges were manual and all of the calls were handled by
operators (probably as dumb as the 555-1212 operators). This is not posible
today as there are so many phone subscribers, and most of the world uses
automatic switching sytems, either employing electromechanical realys or the
latest computer controled electronic machines, (I'll discues this later).

A central switching point allows the connection of customers in a single
'star' fashion, as shown in the following diagram, pheer my ascii:


                                     (1)
                        (6)           |           (2)
                           \          |          /
                             \        |        /
                               \/~~~~~~~~~~~\/
                               |   Central   | 
   Central Switching           |    Switch   |
      Point                    /\___________/\
                             /        |        \
                           /          |          \
                         (5)          |            (3)
                                     (4)




In this diagram ALL calls are switched through the central switching point,
dramatically reducing the number of lines required in the previous diagram.

As phone usage grew, network switching evolved into a hierarchy that
consisted of the 5 levels shown in the next diagram:



  Class 1          Class 2         Class 3         Class 4       Class 5

  /~~~~~~\          _____           _____           _____           
 |        |________|     |_________|     |_________|     |_________/~~\
 |        |   a    |     |         |     |         |     |         \__/
  \______/          ~~\~~           ~~~~~           ~~|~~            
     |                  \                             |
     |                    \                           |
     |                      \ b                       | b
     |                        \                       |
     |                          \                     |
  /~~~~~~\    a     _____         \ _____           __|__           
 |        |________|     |_________|     |_________|     |_________/~~\
 |        |        |     |         |     |         |     |         \__/
  \______/          ~~~~~           ~~~~~           ~~~~~            

  Regional         Sectional        Primary          Toll           End
   Center           Center           Center         Center         Office


     a: Final Trunks
     b: High-Usage Trunks


Upon divestiture of the RBOC's from AT&T, the access by long distance
companies to local networks changed, and for practical purposes eliminated
the traditional switching hierarchy in the US. Just before divestiture at the
lowest level there where some 20,000 Class (5) Switching centers called End-
Offices, which interface directly with the customer equipment via the LOCAL
LOOP. At the next level there where 1,300 or more Toll-centers (Class 4),
they where called this because their usage implies higher rates. Then came
265 Primary Centers (Class 3) and 75 Sectional Centers (Class 2). At the top
of the hierarchy where Regional Centers (Class 1), which numbered only 12
(10 in the US and 2 in Canada). Traffic is always routed through the lowest
available level in the hierarchy; if that level is BUSY, higher levels are
selected.

It was not necessary that Class 4 or 3 offices always home on the next higher
ranking office. Possible homing arrangemnts for each class of switching
office are shown in the following table:


 ___________________________________________________________________________
                     |                     |
 Rank                |  Class of office    |   May home on
 ~~~~~~~~~~~~~~~~~~~~|~~~~~~~~~~~~~~~~~~~~~|~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 End office          |       5             |   class 4, 3, 2, or 1
 ~~~~~~~~~~~~~~~~~~~~|~~~~~~~~~~~~~~~~~~~~~|~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 Toll center         |       4             |   class 3, 2, or 1
 ~~~~~~~~~~~~~~~~~~~~|~~~~~~~~~~~~~~~~~~~~~|~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 Primary center      |       3             |   class 2 or 1
 ~~~~~~~~~~~~~~~~~~~~|~~~~~~~~~~~~~~~~~~~~~|~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 Sectional center    |       2             |   class 1
 ~~~~~~~~~~~~~~~~~~~~|~~~~~~~~~~~~~~~~~~~~~|~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 Regional center     |       1             |   All regional centers 
                     |                     |   interconnected
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


In the US, the divestiture has created the ACCESS TANDEM. This is the gateway
between the intereXchange carrier's (For example AT&T, Sprint and MCI) point
of presence (POP) and the exchange carrier's end office. End offices and
tandems may be served directly from any interexchange carrier location.

Routing rules between switching centers determine the selection of fixed set
of alternate routes using final or high-usage trunks. There are some
limitations to the efficency gains achivable with hierarchical alternate
routing. A number of dynamic routing concepts are being used in the North
American Toll-Network. Dynamic nonhierarchical routing (DNHR) is AT&T's
version of circuit-switched dynamic routing. DNHR is a centralized time-
dependant routing scheme that is supposed to increrase network efficiency by
taking adavantage of the noncoincidence of busy hours in the North American
Toll-Network. Common Channel Interoffice Signaling (CCIS) is used for
signaling between phone exchanges in the call path. CCIS is a system for
eXchanging signaling information between eXchanges via a network of signaling
links instead of the individual voice circuits. Another routing scheme called
dynamically controled routing (DCR) is a centralized adaptive routing system
developed by Northern Telecom. The DCR concept makes efficient use of the
network resources.

Basically phones are connected to each other via a hieratchy of switching
centers. The lowest level switching center is called the end office.
Customers can access other customers connected to other end offices toll free
within the local eXchange area.

All long distance calls are routed through the interExchange carrier
switching offices. The hierarchical system which consisted of the toll center,
sectioned center and finally the regional center hage been largely replaced
by less compartmentalized system in which dynamic routing concepts are
applied on a network basis. The continuing intoduction of new technology in
the North American toll network will see a wider application of dynamic
routing concepts in the near future.




3. North American Digital Hierarchies.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The design of the North American Digital Network has evolved around a series
of hierarchical levels based on the DS-1 (1.544 Mb/s) Primary rate. The DS-1
rate was established by the bell Labs as the transmission rate for the first
commercial pulse code modulation (PCM) cable carrier system back in 1962.
This rate was chosen as an optimum rate for transmission over existing 6,000
foot spans of 22-gauge eXchange grade cable. At has since been accepted as
the basic building block for the North American digital hierarchy. The
magority of transmission systems and multiplexers in use in North America
today are electrically compatable at this rate, although signaling formats
may vary.

The DS-1C (3.152 Mb/s) rate was derived by combining 2 DS-1 inputs and adding
housekeeping pulses for frame allignment and synchronisation.

The DS-2 (6.312 Mb/s) rate was derived by combining 4 DS-1 inputs and adding
housekeeping pulses for frame allignment and synchronization.

The DS-3 (44.736 Mb/s) rate was derived by combining 7 DS-2 inputs and adding
pulses for frame allignment and synchronization, as shown in my following
crude looking diagram:


                          DS-1              DS-2            DS-3
                          1.544 Mb/s        6.312 Mb/s      44.736 Mb/s
                          ~~~~~~~~~~        ~~~~~~~~~~      ~~~~~~~~~~~
                  
 A Phone!          _______                   Digital Signal Hierarchy
 /~/~~~~\~\       |  PCM  |         _______
 ~~|::::|~~      1|Channel|        | M-12  |         _______
   |____|=========| Bank  |       1| Multi |        | M-23  |
                 =|       |========|plexer |       1| Multi |
                 =|       |     ___|       |========|plexer |
                 =| 24*   |     ___|       |     ___|       |==========|>>
                 =|Channels     ___| 96*   |     ___|       |
                24|       |       4|Channels     ___| 672*  |
                   ~~~~~~~         |_______|     ___|Channels      
                                                   7|_______|

        * Assumes 64 Kb/s Encoding Rate


The next step up in the digital hierarchy is the DS-4 (274.176 Mb/s) rate,
which has always been the highest level in the North American
telecommunications hierarchy. However, all of the new lightawve systems
(which I will explain later in this file) go beyond this rate due to the
rapid development in this new technology. There transmission rates are all
multiples of DS-3 streams. The current rates are 565 Mb/s (12 DS-3s), 1.2
gigabits per second (Gb/s) (24DS-3s), and 2.4 Gb/s (48 Ds-3s). Lightwave
systems associated with the SONET use different rates, which will be discused
later.

All of these digital bit streams use the same TDM techniques. For instance,
the DS-3 bit stream is made up in an M-23 Multiplexer by taking 1 but at a
time from each of the 7 DS-2 inputs and then interleaving them to form a
single bit stream. Housekeeping bits are added at difinate intervals carrying
control information. The DS-3 signal, along with 5 other DS-3 signals, can
then be connected to an M-34 multiplexer, where the proccess is reapeated
again to to create a DS-4 signal. The only digital cable carrier that used
thid bit rate (274.176 Mb/s) was the T4M system, which operated over coaxial
cable and provided 4,032 voice circuits.

Various multiplexing schemes can be used to achieve conversaiton between the
levels of hierarchy. The following dialgram shows commonly accepted
relationships as well as the names of the digital signal cross-connects used
at each level:

DiGiTaL Sigmal Building blocks:

                                           
  Digital                                  Bit Rate               Cross-
  signal                                   No. of                 Connect
  Level                                    Voicegrade             Jumper
  ~~~~~~~                                  Channels               Type
                                           ~~~~~~~~~~             ~~~~~~~


                                           274.176
                                           Mb/s
                                           4,032
                                           Channels
  DS-4 ====================================================================
           |
           |
         |~~~~~~|                          44.736
         | M34  |                          Mb/s
         | MUX  |                          672                    DSX-3
         |______|                          Channels               Coax
           |
  DS-3 ====================================================================
              |                   |                                     
              |                   |
         |~~~~~~|              |~~~~~~|    6.312
         | M23  |              | M13  |    Mb/s
         | MUX  |              | MUX  |    96                      DSX-2
         |______|              |______|    Channels                STP
              |                   |
  DS-2 ===========================|========================================
                  |               |
                  |               |
               |~~~~~~|           |
               | M12  |           |
               | MUX  |           |        3.152                   
               |______|           |        Mb/s                    DSX-1C
                  |               |        48                      UTP
                  |               |        Channels
  DS-1C ==========|===============|========================================
           |      |      |        |
           |      | |~~~~~~~~~~|  |             
           |      | | Channel  |  |
         |~~~~~~| | |  Bank    |  |
         | M1C  | | |__________|  |         1.544
         | MUX  | |      |        |         Mb/s                   DSX-1
         |______| |      |        |         24                     UTP
           |      |      |        |         Channels
           |      |      |        |
  DS-1 ==================|=================================================
              |          |
              |          |
         |~~~~~~|        |
         |Channel        |                  64 kb/s                DSX-0
         |Bank  |        |                  1                      UTP
         |______|        |                  Channel                (or DCS)
              |          |
              |          |
  DS-0 ====================================================================
            |
            |                        M- Nultiplexer
         |~~~~~~|                    STP- Shielded Twisted Pair
         |Codec |                    UTP- Unshielded Twisted Pair
         |______|
            |
            |
   Analog ======================================== 3.1 kHz Voicegrade Channel


1 of the 1st applications of digital signal processing (DSP) in the phone
network was the installation of pulse code modulation (PSM_ carrier systems
back in the 1960s. This was the introduction of PCM carrier systems and the
acceptance of 64 kb/s as the standard for coding voice in the emerging
digital network. While 64 kb/s PCM provides good transmission quality, it has
been realised for some time that that it is realatively inifficiant in it's
use of transmission facility bandwith. Essentially, there are 2 basic
techniques which would be applied to increase the circuit capacity: digital
signal interpolation (DSI) and low-bit-rate encoding (LBRE).

DSI is a proccess which time-shares a fixed number of digital voice channels
between a larger number of talkers. Since the average speech activty in a 2-
way voice converstation is typically on the order of 30% to 40% in each
direction, it is possible to fill in speech gaps in 1 converstaion with talk
spurts from another conversation. Practical systems which provide a 2:1
concentration ratio (a doubleing of transmission capacity) are caommercialy
available. Higher concentration ratios are realizable when the network
carries a high proportion of voice traffic. Lower concentration ratios are
neccesary with data traffic because data signals normally operate
continuously on a given call.

LBRE is a technique which uses advanced signal-proccessing techniques to
reduce the number of bits required to encode the voice signal. The most
'prommising' technique is to exploit the correlation between succesive speech
samples. The difference between the actual voice sample and an estimated (or
predicted) value based on the immediate precceding voice samples is encoded
or transmited. This is refeard to as adaptive differntial pulse code
modulation (ADPCM).

PCM carrier systems employing this technique with an effective encoding rate
of 32 kb/s are used in many digital transmission systems. These LBRE systems
initially were used to provide private line voice service but are now widely
deployed throughout the public network. The 32 kb/s ADPCM has many advantages
over DSI systems but does not provide as much potential efficiancy and it
does not provide good performance with voice band data applications.

Also under development are 16 kb/s and 8 kb/s schemes. Subject to further
studies, it is expected that these techniques will find additional
apllications within the toll-network over the next few years because they
have the potential to greatly increase the capacity of existing lightwave,
digital radio and satelite systems.




4. The Local Subscriber Loop.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


        |~~~~~~~~~~~~|        Feeder             |~~~~~~~~~~~~~~~~~~|
        |    End     |___________________________|  Servicing Area  |
        |   Office   |                           |     Interface    |
        |____________|                           |  (Cross-Connect) |
                                                  ~~~~~~~~~|~~~~~~~~
                                                           |
                                                           |
                               /~~~~~~~~~~\                | Distribution
 A diagram of the basic       |  Pedestal  |_______________/   
 Structure of the             |            |
 Local Subscriber              \__________/
 Loop.                         / |      | \
                             /   |      |   \
                           /     |      |     \    Drop 
                         /       |      |       \    (Service Wire)
                       /         |      |         \
                     /          /        \          \
                   /          /            \          \
                 /^\        /^\            /^\        /^\
               /_____\    /_____\        /_____\    /_____\
               |     |    |     |        |     |    |     |
               |_____|    |_____|        |_____|    |_____|
                                            .
                              Your house.../


Some words from the 1st Phreak...

        'Cables of telephone wires could be laid underground or
         suspended overhead, communicating by branch wires
         with private dwellings, counrty houses, shops,
         manufactories, etc., etc., unitting them through the
         main cable with a central office where the wires could
         be connected as desired, establishing direct communications
         between two places in the city.'

                -Alexander Graham Bell

This description by Mr Bell himself, describes the basic structure of the
customer loop as we know it today. Today telcos have spent over $50 billion,
with the anual telco expenditure of $5 billion on the growth and maintance of
loops.

The phone set is supplied with direct current (DC) from a 48-volt batery
supply in the end office over a pair of twisted copper wires. The 2 wires
form a loop from the phone to the telepohne office, that's why it is called
'The Local Loop.'

The bateries are backed up by a diesel generator at the local office, so if
there is an electrical problem the system can still operate.

The local loop provides you with access to the telecommunications network
through the end office. In the US, the end office connects with the
intereXchange carrier's point of presence (POP) either directly or through
the phone company's access tandem.

The local loop consists of a pair of insulated wires twisted together and
combined with 100's of other twisted pairs in a single cable. These cables
can be strung on poles, buried underground or installed in underground
conduit. The diamater of the wire varies from 0.016 inch (26 gauge) to 0.036
inch (19 gauge): the thiner the wire, the higher the loss.

In the late 70s and early 80s, digital subscriber carrier systems came into
general use. The primary objectives of using digital carrier systems were to
reduce the number of copper pairs required in the feeder portion of the
customer loop and to limit the length of the distrobution portion of the loop
to 12,000 feet or less. Providing a remote terminal at the end of the feeder
section, operating over a digital carrier system, reduces the amount of
twisted pair cable required and eliminates the need for reinforcing feeder
routes to accomodate customer growth.

DLC Remote Terminal or Remote Switching Terminal:


        24-2,000                                    1.544 Mb/s Repeated
        Customer Lines                              T-1 Span Lines
        \ \ \ / / / /                                    |
        | | | | | | |                                   /
        | | | | | | |                          _______/
        | | | | | | |                        /      
        | | | | | | |                      /
        | | | | | | |        |~~~~~|     \|/   |~~~~~|
      |~~~~~~~~~~~~~~~|______|__>__|___________|__>__|______|~~~~~~~~~~~~~|
      |Remote Terminal|______|_____|___________|_____|______| CO Terminal |
      |_______________|      |  <  |           |  <  |      |_____________|
        |   |      |         |_____|           |_____|
        |   |      |
        |   |      |
       /    |    Phone           Example:
     Phone   \
              Phone              * Concentrates 128 customer lines
                                   to 32 trunks between terminals

                                 * Each digital signal cariies 24
                                  conversations on 2 cable pairs.


Digital carriers systems allow 64-kb/s or higher-rate digital services to be
provided on even the longest loops.

Telcos are planning to provide fiber to home (FTTH), or fiber to curb (FTTC)
in order to enter the video dostrobution market, this subject will be
discussed later in the file in more detail.

However, in order to squeeze the maximum bandwith out of the existing copper
pair loop, a number of new technologies have emerged. Asymmetric digital
subscriber lines (ADSL), in combinitation with the latest advances in digital
video compresion, is now making it possible to transmit a digitaly encoded
video channel over the existing twisted pair loop.

Telco's are exploring several ASDL options called ADSL-1, 2 and 3. ADSL-1
will operate over nonloaded loop plant which extends to 18,000 feet. It will
operate at 1.5 Mb/s and deliever a single channel of encpded video. The
quality level will be equivalent to a VHS tape. ADSL-2, operating at 3 Mb/s,
will extend to 12,000 feet. ADSL-3, operating at 6 Mb/s, has been proposed
for loops upto 8,000 feet:

Asymetric Digital Subscriber Line:



        Central Office            Remote Terminal           House


       |~~~~~~~~~~~~~|  Fiber     |~~~~~~~~~~|            |~~~~~~~~~~~~~~~|
       |   ADSL-2    |____________| ADSL-2   |____________| ADSL-2 3 Mb/s |
   T   |             |            |          |  Copper    |_______________|
   o   |             |            |__________|                |      |
 <=========>         |                 |                      |      |
   N   |             |                 |                      |      |
   e   |             |                 |                      TV     Phone
   t   |             |                 | Fiber
   w   |   ADSL-3    |                 |
   o   |_____________|                 |
   r         |                     |~~~~~~~~~~|           |~~~~~~~~~~~~~~~|
   k         |                     | ADSL-3   |___________| ADSL-3 6 Mb/s |
             |                     |          |  Copper   |_______________|
             |                     |__________|               |      |
             |                                                |      |
             |                                                |      |
             |                                                |      |
             |________________________|~~~~~~~~~~~~|          TV     Phone
                  Copper              | ADSL-1 1.5 |
                                      |____________|
                                         |     |
                                         |     |
                                         |     |
                                         |     |
                                         TV    Phone


The existing local loops support switched and dedicated digital services at
speeds up to 64 kb/s. The loop also supports the ISDN digital subscriber line
(DSL), which provides 2 64 kb/s 'beaver' channels (circuit switched). The DSL
can extend up to 18,000 feet from the central office or a digital loop
carrier remote terminal on nonloaded cable. A number of commercially
available pair gain devices use DSL technology to double or quadruple the
capacity of a given twisted pair in the loop. These pair gain devices use 64-
kb/s or 32-kb/s encoding to achieve the pair gain.

The high bit rate digital subcriber line (HDSL) is being widely used in the
local loop environment, and is probably in use in your area. The HDSL
provides a standard DS-1 rate signal up to 12,000 feet from the serving
central office using 2 cable pairs and no repeaters.

Shouts:
~~~~~~~

9x, Substance, gr1p, DarkCYDE, Extreem, Chimmy, ELF, DownTime, ZerOnine
Essance, Dialt0ne and finally PF BBS in London, Darkcyde (the person)


Notice:
~~~~~~~

Sorry about the shortness of this file, I am in the middle of another file,
which will contain the following:

       Switching Systems
       Public Packet Switched Networks PPSN
       The IRIDIUM Network
       PCS Personal Communications Services
       U.S. National and Regional Lightwave Networks
       SONET Synchronous Optical Network
       Protection Switching
       Phiber to Home
       Phreaking the Military, Secrets of 71o 
       The Old AUTOVON Network
       Prefix assignments



                                -+ Hybrid +-

hybrid_blue@hotmail.com


        'Technology has turned reallity into a paradox.
         Forms are not always as they seem.

         The strugle for non conformity
         has become even more complicated.
         Technology has learned to duplicate, rebuild,
         and remanufacture reality and humanity.
         The ability to take a template and replicate it
         is not a fantasy anymore, it is a threat.
         The strugle against conformity has become a
         comprehensive investigation into technology
         that works against the principle of individuality
         and non conformity.

         Humanity has become a relative term in the search for truth;
         A search for clues.
         A search for variables in life and mutation in a genus.

                                -Fear Factory.

                    
                9x - spReading hP iN thE nEw mIllen1um        
                          1998 (c) 9x Production, all rights lost

                    ___ ___ _____.___.____________________  ____________
hybrid@b4b0.org    /   |   \\__  |   |\______   \______   \/_   \______ \
hybrid@ninex.com  /    ~    \/   |   | |    |  _/|       _/ |   ||    |  \
hybrid.dtmf.org   \    Y    /\____   | |    |   \|    |   \ |   ||    `   \
----------------   \___|_  / / ______| |______  /|____|_  / |___/_______  /
                         \/  \/               \/        \/              \/



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