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<sect><heading>ISDN<label id="isdn"></heading>

<p><em>Last modified by &a.wlloyd;</em>.

<p>A good resource for information on ISDN technology and hardware is
<url url="http://alumni.caltech.edu/~dank/isdn/" name="Dan Kegel's
ISDN Page">.

A quick simple roadmap to ISDN follows:
<itemize>
<item>If you live in Europe I suggest you investigate the ISDN card
section.

<item>If you are planning to use ISDN primarily to connect to the
Internet with an Internet Provider on a dialup non-dedicated basis, I
suggest you look into Terminal Adapters.  This will give you the most
flexibility, with the fewest problems, if you change providers.

<item>If you are connecting two lans together, or connecting to the
Internet with a dedicated ISDN connection, I suggest you consider the
stand alone router/bridge option.
</itemize>

<p>Cost is a significant factor in determining what solution you will
choose.  The following options are listed from least expensive to most
expensive.

<sect1><heading>ISDN Cards</heading>

<p><em>Original Contribution by &a.hm;.</em>

<p>This section is really only relevant to European ISDN users.  The
cards supported are not yet(?) available for North American ISDN
standards.

<p>You should be aware that this code is largely under development.
Specifically, drivers have only been written for two manufacturers
cards.
  
<p>PC ISDN cards support the full bandwidth of ISDN, 128Kbs.  These
cards are often the least expensive type of ISDN equipment.  

<p>Under FreeBSD 2.1.0 and 2.1.5, there is early unfinished ISDN code
under /usr/src/gnu/isdn.  This code is out of date and should not be
used.  If you want to go this route, get the bisdn stuff.  This code
has been removed from the main source tree starting with FreeBSD 2.2.

<p>There is the bisdn ISDN package available from 
<url url="ftp://ftp.muc.ditec.de/isdn" name="ftp.muc.ditec.de">
supporting FreeBSD 2.1R, FreeBSD-current and NetBSD.
The latest source can be found on the above mentioned ftp server under
directory isdn as file bisdn-097.tar.gz.

There are drivers for the following cards:
<itemize>
<item>Currently all (passive) Teles cards and their clones are supported
for the EuroISDN (DSS1) and 1TR6 protocols.
<item>Dr. Neuhaus - Niccy 1016
</itemize>

There are several limitations with the bisdn stuff. Specifically the
following features usually associated with ISDN are not supported.

<itemize>
<item>No PPP support, only raw hdlc.  This means you cannot connect to most
standalone routers.
<item>Bridging Control Protocol not supported.
<item>Multiple cards are not supported.
<item>No bandwidth on demand.
<item>No channel bundling.
</itemize>

A majordomo maintained mailing list is available, to subscribe, send the
usual majordomo requests to 
<htmlurl url="mailto:isdn-request@muc.ditec.de"
name="isdn-request@muc.ditec.de">.

<sect1><heading>ISDN Terminal Adapters</heading>

<p>Terminal adapters(TA), are to ISDN what modems are to regular phone
lines.
<p>Most TA's use the standard hayes modem AT command set, and can be
used as a drop in replacement for a modem.

A TA will operate basically the same as a modem except connection and
throughput speeds will be much faster than your old modem.  You will
need to configure <ref id="ppp" name="PPP"> exactly the same as for a
modem setup.  Make sure you set your serial speed as high as possible.

The main advantage of using a TA to connect to an Internet Provider is
that you can do Dynamic PPP.  As IP address space becomes more and more
scarce, most providers are not willing to provide you with a static IP
anymore.  Most standalone routers are not able to accommodate dynamic IP
allocation.

TA's completely rely on the PPP daemon that you are running for their
features and stability of connection.  This allows you to upgrade easily
from using a modem to ISDN on a FreeBSD machine, if you already have PPP
setup.  However, at the same time any problems you experienced with the
PPP program and are going to persist.

If you want maximum stability, use the kernel  <ref id="ppp" name="PPP">
option, not the user-land <ref id="userppp" name="iijPPP">.  
<p>The following TA's are know to work with FreeBSD.

<itemize>
<item>Motorola BitSurfer and Bitsurfer Pro
<item>Adtran
</itemize>

Most other TA's will probably work as well, TA vendors try to make sure
their product can accept most of the standard modem AT command set.

The real problem with external TA's is like modems you need a good
serial card in your computer.  

You should read the <ref id="uart" name="serial ports"> section in the
handbook for a detailed understanding of serial devices, and the
differences between asynchronous and synchronous serial ports.

A TA running off a standard PC serial port (asynchronous) limits you to
115.2Kbs, even though you have a 128Kbs connection.  To fully utilize
the 128Kbs that ISDN is capable of, you must move the TA to a
synchronous serial card. 

Do not be fooled into buying an internal TA and thinking you have
avoided the synchronous/asynchronous issue.  Internal TA's simply have a
standard PC serial port chip built into them.  All this will do, is save
you having to buy another serial cable, and find another empty
electrical socket.

A synchronous card with a TA is at least as fast as a standalone router,
and with a simple 386 FreeBSD box driving it, probably more flexible.

The choice of sync/TA vs standalone router is largely a religious
issue.  There has been some discussion of this in the mailing lists.  I
suggest you search the <url url="http://www.freebsd.org/search.html"
name="archives"> for the complete discussion.

<sect1><heading>Standalone ISDN Bridges/Routers</heading>

<p>ISDN bridges or routers are not at all specific to FreeBSD or any
other operating system.  For a more complete description of routing and
bridging technology, please refer to a Networking reference book.

In the context of this page, I will use router and bridge
interchangeably.

<p>As the cost of low end ISDN routers/bridges comes down, it will
likely become a more and more popular choice.  An ISDN router is a small
box that plugs directly into your local Ethernet network(or card), and
manages its own connection to the other bridge/router.  It has all the
software to do PPP and other protocols built in.

A router will allow you much faster throughput that a standard TA, since
it will be using a full synchronous ISDN connection.

The main problem with ISDN routers and bridges is that interoperability
between manufacturers can still be a problem.  If you are planning to
connect to an Internet provider, I recommend that you discuss your needs
with them.

<p>If you are planning to connect two lan segments together, ie: home
lan to the office lan, this is the simplest lowest maintenance
solution.  Since you are buying the equipment for both sides of the
connection you can be assured that the link will work.

For example to connect a home computer or branch office network to a
head office network the following setup could be used.

<em>Branch office or Home network</em>

Network is 10 Base T Ethernet.  Connect router to network cable with
AUI/10BT transceiver, if necessary.

<verb>
---Sun workstation     
|
---FreeBSD box
|
---Windows 95 (Do not admit to owning it)
|
Standalone router
   |
ISDN BRI line
</verb>
If your home/branch office is only one computer you can use a twisted
pair crossover cable to connect to the standalone router directly.

<em>Head office or other lan</em> 

Network is Twisted Pair Ethernet.
<verb>
    -------Novell Server
    | H	|
    |	---Sun      
    |	|
    | U	---FreeBSD
    |	|
    |	---Windows 95
    | B	|
    |___---Standalone router
		|
       	ISDN BRI line
</verb> 

One large advantage of most routers/bridges is that they allow you to
have 2 SEPARATE INDEPENDENT PPP connections to 2 separate sites at the
SAME time.  This is not supported on most TA's, except for
specific(expensive) models that have two serial ports.  Do not confuse
this with channel bonding, MPP etc.

This can be very useful feature, for example if you have an dedicated
internet ISDN connection at your office and would like to tap into it,
but don't want to get another ISDN line at work.  A router at the office
location can manage a dedicated B channel connection (64Kbs) to the
internet, as well as a use the other B channel for a separate data connection.
The second B channel can be used for dialin, dialout or dynamically
bond(MPP etc.) with the first B channel for more bandwidth.

<p>An Ethernet bridge will also allow you to transmit more than just
IP traffic, you can also send IPX/SPX or whatever other protocols you
use.</p>
