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..[ Phrack Magazine ]..
.:: An Introduction to Packet Switched Networks ::.

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Current issue : #18 | Release date : 1988-07-06 | Editor : Crimson Death
Index of Phrack 18Crimson Death
Pro-Phile XI on Ax MurdererCrimson Death
An Introduction to Packet Switched NetworksEpsilon
Primos: Primenet, RJE, DPTXMagic Hasan
Hacking CDC's CyberPhrozen Ghost
Unix for the ModerateUrvile
Unix System Security IssuesJester Sluggo
Loop Maintenance Operating SystemControl C
A Few Things About NetworksPrime Suspect
Phrack World News XVIII Part IEpsilon
Phrack World News XVIII Part IIEpsilon
Title : An Introduction to Packet Switched Networks
Author : Epsilon
                               ==Phrack Inc.==

                     Volume Two, Issue 18, Phile #3 of 11

         _ _ _ _ _____________________________________________ _ _ _ _
         _-_-_-_-                                             -_-_-_-_
         _-_-_-_-             An Introduction To              -_-_-_-_
         _-_-_-_-                                             -_-_-_-_
         _-_-_-_-          Packet Switched Networks           -_-_-_-_
         _-_-_-_-                                             -_-_-_-_
         _-_-_-_-                                             -_-_-_-_
         _-_-_-_-                                             -_-_-_-_
         _-_-_-_-  Written By -                   Revised -   -_-_-_-_
         _-_-_-_-                                             -_-_-_-_
         _-_-_-_-  Epsilon                        05/3/88     -_-_-_-_
         _-_-_-_-_____________________________________________-_-_-_-_


Preface -

   In the past few years, Packet Switched Networks have become a prominent
feature in the world of telecommunications.  These networks have provided ways
of communicating with virtually error-free data, over very large distances.
These networks have become an imperative to many a corporation in the business
world.  In this file we will review some of the basic aspects of Packet
Switched Networks.

Advantages -

   The Packet Switched Network has many advantages to the common user, and
even more to the hacker, which will be reviewed in the next topic.

   The basis of a Packet Switched Network is the Packet Switch.  This network
enables the service user to connect to any number of hosts via a local POTS
dial-up/port. The various hosts pay to be connected to this type of network,
and that's why there is often a surcharge for connection to larger public
services like Compuserve or The Source.

   A Packet Switched Network provides efficient data transfer and lower rates
than normal circuit switched calls, which can be a great convenience if you
are planning to do a lot of transferring of files between you and the host.

   Not only is the communication efficient, it is virtually error free.
Whereas in normal circuit switched calls, there could be a drastic increase in
errors, thus creating a bad transfer of data.

   When using a Packet Switched Network, it is not important that you
communicate at the same baud rate as your host.  A special device regulates
the speed so that the individual packets are sped up or slowed down, according
to your equipment.  Such a device is called a PAD (Packet Assembler
Disassembler).

   A PSN also provides access to a variety of information and news retrieval
services.  The user pays nothing for these calls, because the connections  are
collect. Although the user may have to subscribe to the service to take
advantage of it's services, the connection is usually free, except for a
surcharge on some of the larger subscription services.

Advantages To Hackers -

   Packet Switched Networks, to me, are the best thing to come along since the
phone system.  I'm sure many other hackers feel the same way.  One of the
reasons for this opinion is that when hacking a system, you need not dial out
of your LATA, using codes or otherwise.

   Now, the hacker no longer has to figure out what parameters he has to set
his equipment to, to communicate with a target computer effectively.  All
PSSes use the same protocol, set by international standards.  This protocol is
called X.25.  This protocol is used on every network-to-network call in the
world.

   When operating on a packet switch, you are not only limited to your own
network (As if that wasn't enough already).  You can access other PSSes or
private data networks through gateways which are implemented in your PSN.
There are gateways to virtually every network, from virtually every other
network, except for extremely sensitive or private networks, in which case
would probably be completely isolated from remote access.

   Another advantage with PSNs is that almost everyone has a local port, which
means if you have an outdial (Next paragraph), you can access regular circuit
switched hosts via your local Packet Switched Network port.  Since the ports
are local, you can spend as much time as you want on it for absolutely no
cost.  So think about it.  Access to any feasible network, including overseas
PSNs and packet switches, access to almost any host, access to normal circuit
switched telephone-reachable hosts via an outdial, and with an NUI (Network
User Identity - Login and password entered at the @ prompt on Telenet),
unlimited access to any NUA, reverse-charged or not.

   Due to the recent abuse of long distance companies, the use of codes when
making free calls is getting to be more and more  hazardous.  You may ask, 'Is
there any resort to making free calls without using codes, and without using a
blue  box?'  The answer is yes, but only when using data.  With an outdial,
accessible from your local PSN port, you can make data calls with a remote
modem, almost always connected directly to a server, or a port selector. This
method of communicating is more efficient, safer, and more reliable than using
any code.  Besides, with the implementation of equal access,  and the
elimination of 950 ports, what choice will you have?

Some Important Networks -

   As aforementioned, PSNs are not only used in the United States.  They are
all over the place.  In Europe, Asia, Canada, Africa, etc.  This is a small
summary of some of the more popular PSNs around the world.

         Country          Network Name          *DNIC
         ~~~~~~~          ~~~~~~~ ~~~~           ~~~~
         Germany          Datex-P                2624
         Canada           Datapac                3020
         Italy            Datex-P                0222
         South Africa     Saponet                0655
         Japan            Venus-P                4408
         England          Janet/PSS              2342
         USA              Tymnet                 3106
         USA              Telenet                3110
         USA              Autonet                3126
         USA              RCA                    3113
         Australia        Austpac                0505
         Ireland          Irepac                 2724
         Luxembourg       Luxpac                 2704
         Singapore        Telepac                5252
         France           Transpac               2080
         Switzerland      Telepac                2284
         Sweden           Telepac                2405
         Israel           Isranet                4251
         ~~~~~~~~~        ~~~~~~~                ~~~~
         * - DNIC (Data Network Identification Code)
             Precede DNIC and logical address with a
             '0' when using Telenet.
______________________________________________________________________________

Notes On Above Networks -

   Some countries may have more than one Packet Switching Network.  The ones
listed are the more significant networks for each country.  For example, the
United States has eleven public Packet Switching Networks, but the four I
listed are the major ones.

   Several countries may also share one network, as shown above.  Each country
will have equal access to the network using the basic POTS dial-up ports.

Focus On Telenet -

   Since Telenet is one of the most famous, and highly used PSNs in the United
States, I thought that informing you of some of the more interesting aspects
of this network would be beneficial.

Interconnections With Other Network Types -

   Packet Switched Networks are not the only type of networks which connect a
large capacity of hosts together.  There are also Wide Area Networks, which
operate on a continuous link basis, rather than a packet switched basis.
These networks do not use the standardized X.25 protocol, and can only be
reached by direct dial-ups, or by connecting to a host which has network
access permissions.  The point is, that if you wanted to reach, say, Arpanet
from Telenet, you would have to have access to a host which is connected to
both networks.  This way, you can connect to the target host computer via
Telenet, and use the WAN via the target host.

   WANs aren't the only other networks you can access.  Also, connections to
other small, private, interoffice LANs are quite common and quite feasible.

Connections To International NUAs via NUIs -

   When using an NUI, at the prompt, type 0+DNIC+NUA.  After your connection
is established, proceed to use the system you've reached.

Private Data Networks -

   Within the large Packet Switched Networks that are accessible to us there
are also smaller private networks.  These networks can sometimes be very
interesting as they may contain many different systems.  A way to identify a
private network is by looking at the three digit prefix.  Most prefixes
accessible by Telenet are based on area codes.  Private networks often have a
prefix that has nothing to do with any area code. (Ex. 322, 421, 224, 144)
Those prefixes are not real networks, just examples.

   Inside these private networks, there are often  smaller networks which are
connected with some type of host selector or gateway server.  If you find
something like this, there may be hosts that can be accessed only by this port
selector/server, and not by the normal prefix.  It is best to find out what
these other addresses translate to, in case you are not able to access the
server for some reason.  That way, you always have a backup method of reaching
the target system (Usually the addresses that are accessed by a gateway
server/port selector translate to normal NUAs accessible from your Telenet
port).

   When exploring a private network, keep in mind that since these networks
are smaller, they would most likely be watched more closely during business
hours then say Telenet or Tymnet.  Try to keep your scanning and tinkering
down to a minimum on business hours to avoid any unnecessary trouble.
Remember, things tend to last longer if you don't abuse the hell out of them.

Summary -

   I hope this file helped you out a bit, and at least gave you a general idea
of what PSNs are used for, and some of the advantages of using these networks.
If you can find something interesting during your explorations of PSNs, or
Private Data Networks, share it, and spread the knowledge around.  Definitely
exploit what you've found, and use it to your advantage, but don't abuse it.

If you have any questions or comments, you reach me on -

             The FreeWorld II/Central Office/Forgotten Realm/TOP.

   I hope you enjoyed my file.  Thanks for your time.  I should be writing a
follow up article to this one as soon as I can.  Stay safe..

         - Epsilon
______________________________________________________________________________

                                - Thanks To -

         Prime Suspect/Sir Qix/The Technic/Empty Promise/The Leftist
______________________________________________________________________________
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