NETGEAR RT210, RT211 , Connecting to ISDN

Reference Guide for the Model RT210/RT211 ISDN Routers

1-6 Introduction

Using ISDN as the connection medium adds another circuit state to the equation. The connection

can be functioning, but no data or routing updates are being passed because the call is currently

closed. If this state exists longer than the routing protocol time-out (normally 3 minutes), the

routes would decay and be removed from the tables at each end of the link. If this happens, routing

could not take place between the units at either end of the ISDN link.

To overcome this problem, the NETGEAR Model RT210 and Model RT211 ISDN routers

automatically treat routes learned over ISDN as semipermanent. They are not decayed and can be

updated by any received routing protocol updates if any of the hop counts have changed since the

last update.

Another issue concerning passing routing updates across ISDN is whether a call is made or left

connected for the sole purpose of passing routing information. The NETGEAR routers do not

make calls speciﬁcally for passing routing updates. The next user data call includes the routing

update information that was copied to the local routing table when the connection was closed.

Therefore, a call that has been made for data transfer is not kept open by routing updates because

these are not included in the idle calculation for that call.

Connecting to ISDN

When you connect to ISDN, there are several important things you must know in order to make the

correct decisions in placing your order and conﬁguring your router.

When you order the ISDN line from your telephone company, you must know what type of ISDN

service your telephone company provides so that you can conﬁgure your router properly. Your

telephone company might provide you with Service Proﬁle Identiﬁers (SPIDs) along with the

ISDN telephone numbers. You need to know the SPIDs, if you are given them, and the ISDN

telephone number(s) before setting up the router.

In most areas, your ISDN equipment is connected to the telephone company by a four-wire

S/T interface, such as the one provided by the Model RT210 router. The telephone company

provides a network termination device commonly known as an NT1, which converts this four-wire

S/T interface to a two-wire U interface for transmission over long lines to the central switch. In

North America, the customer is expected to provide an NT1. For this reason, the Model RT211

ISDN router integrates the function of the NT1, reducing cost and wiring complexity.

For more information, refer to Appendix C, “Ordering ISDN Lines.”

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