IBM SC30-3681-08 manual Addressing, Oversubscribing and Circuit Contention

Using ISDN

Note: You can assign a destination name to a connection list (add ISDN address) and assign a destination number to each line in the list. When that destination name is called, the numbers in the list are tried one by one until a connection is made or the list is exhausted.

Routable protocols and bridging and routing features cannot communicate directly with an ISDN interface. You need to con®gure these protocols to run on the dial circuits. This implementation supports the following protocols and features for ISDN dial circuits:

v	APPN
v	Banyan VINES
v	DECnet
v	DLSw
v	IP
v	IPX
v	AppleTalk 2
v Bridging (SRB, STP, SR-TB, and SRT)
v	Bandwidth reservation
v	WAN restoral
v	DIALS
Addressing
To place an ISDN call, specify the telephone number of the destination. To identify
yourself to the switch, you need to specify your own telephone number. For ISDN,
telephone numbers are called network dial addresses and, for convenience, they
are given names called network address names that represent the telephone
number.
When you set up an ISDN interface, you add addresses for each potential
destination as well as for your own telephone number, which is called the local
network address. When you con®gure a dial circuit, the local network address is
obtained from the physical interface con®guration and you set a destination
addresses for the circuit.
Oversubscribing and Circuit Contention
An ISDN PRI T1/J1 interface can support a maximum of 23 active calls, and an
ISDN PRI E1 interface can support a maximum of 30 active calls. An ISDN BRI
interface can support a maximum of two active calls. Normally, an ISDN BRI can
have two active calls, except on the 1S4/1S8/1U4/1U8 models when the WAN is
also active.There can be more dial circuits con®gured on an ISDN interface than
active calls supported. This is called oversubscribing. If a dial circuit attempts a call
when the ISDN interface has all calls active, there are two possibilities: 1) If the dial
circuit has a higher priority than a dial circuit with an active call, the active call will
be terminated for the low priority dial circuit and a call will be attempted for the low
priority dial circuit and a call will be attempted for the higher priority dial circuit. 2) If
the dial circuit does not have a higher priority than any dial circuits with active calls,

no call will be made. The router will drop packets sent by protocols on dial circuits that cannot connect to their ISDN destination.

Note: There is no circuit contention when you are running X.25 over the D-channel because the D-channel is always available for the X.25 connection.

Chapter 45. Using the ISDN Interface 613