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.
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.
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.
Branch office or Home network
Network is 10 Base T Ethernet. Connect router to network cable with AUI/10BT transceiver, if necessary.
---Sun workstation | ---FreeBSD box | ---Windows 95 (Do not admit to owning it) | Standalone router | ISDN BRI lineIf your home/branch office is only one computer you can use a twisted pair crossover cable to connect to the standalone router directly.
Head office or other lan
Network is Twisted Pair Ethernet.
-------Novell Server
| H |
| ---Sun
| |
| U ---FreeBSD
| |
| ---Windows 95
| B |
|___---Standalone router
|
ISDN BRI line
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.
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.