ISDN

ISDN allows multiple digital channels to be operated simultaneously through the same regular phone wiring. The same physical wiring can be used, but a digital signal, instead of an analog signal, is transmitted across the line.

Terminals - Functional Groups

• Terminal Equipment (Type 1) - end-user devices that are ISDN-ready
• Terminal Equipment (Type 2) - end-user devices that are not ISDN-ready
• Terminal Adapter (for type 2 endpoints) - allows a non-ISDN device to communicate with the network.
• Network Termination Point NT2 - customer site switching, multiplexing and/or concentration.
• Network Termination Point NT1 - termination of the physical connection between the customer site and LE.
• Local Exchange (LE) - provides ISDN services

Reference Points (I.411)

• R - Regular - between endpoint and terminal adapter
• S - Special - between endpoint / terminal adapter and NT2
• T - Termination - between NT2 and NT1
• U - unpowered - between NT1 and Telco

S and T are electrically the same

ISDN Channels

In ISDN and other Digital TDM environments, a channel generally refers to a time slot on a transmission facility and is full-duplex (bi-directional).

• D - signaling, 16Kbps (BRI) or 64 Kbps (PRI)
• B - bearer, clear channel only data, 64 Kbps

Basic Rate Interface

2B + D

144Kbps = 64 + 64 + 16

Service Profile ID (SPID) is required in NA, serves as a password, numerical string assigned by the telco to each B channel

10 digit phone number + 2 digit sharing terminal ID (01-32) + 2 digit terminal ID (01-08)

Primary Rate Interface

• NA: 23B + D (T1)
• EU: 30 B + D (E1)

Dial On Demand Routing (DDR)

ISDN Switch-Type can be set globally or per interface.

int bri 0
	ip address 172.20.1.1.2 255.255.255.252
	isdn switch-type basic-net3
	isdn spid1 111
	dialer-group 1
	encapsulation ppp
	ppp multilink
	dialer load-threshold 1 either
	dialer map ip 172.20.1.1 broadcast 4802222222
	dialer idle-timeout 120
	no shut
	
dialer-list 1 protocol ip permit

show isdn status

show dialer

debug dialer

Floating static route option

ip route 192.168.2.0 255.255.255.0 172.20.1.1 250

Backup Interface option

router ospf 1
	network 172.20.1.2 0.0.0.0 area 0
	
int s0
	backup interface bri 0
	backup delay 3 15

OSPF disable hello packets option

Does not work if any ASBR in OSPF network, will need to put ISDN in its own Stub area

router ospf 1
	network 172.20.1.2 0.0.0.0 area 0
	
int bri 0
	ip ospf demand-circuit

Dialer watch option

Needs exact match, can’t use summary

dialer watch-list 1 ip 172.16.4.0 255.255.255.0

int bri 0
	dialer watch-group 1
	dialer map ip 172.16.4.0 4802222222