Cisco CCNA - ISDN - Integrated Services Digital Network

ISDN - Integrated Services Digital Network

Carries a variety of traffic. Video, Circuit Switched Data And Telephone Services using normal phone network.
Call set up and data rates faster than modem.
Operates at layer 1 to 3.
ISDN uses SS7 signalling to set up a path with a remote switch.

ISDN Physical layer

ISDN frames differ depending on inbound (network to terminal NT format) or outbound (terminal to network TE format).
ISDN frames are 24 bits long.
ISDN BRI service offers 2 B channels operating at 64kbps which can be used independently from one another for user data or voice traffic.

2*(2*8B + 2D + 6F) sent in pairs

ISDN BRI sent at 8000/sec

(1*8B + 2D + 6F) = 24*8000 = 192kbps

but effective data rate = 2*8B = 16*8000 = 128kbps

ISDN Data link layer

ISDN datalink layer is LAPD - Link Access Procedure D channel - ensures control and signalling information flows properly.
D channel operates at 16kbps and is used to carry control and signalling information.
Terminals cannot transmit into D channel unless they first detect a specific number of ones (indicating no signal). If the TE detects a bit in the echo (E) channel that is different from it's D bits then it stops transmitting immediately.

ISDN SPIDs - Service Profile Identifiers

You also need to know your assigned SPID to identify your configuration at the CO.

SPIDs allow multiple ISDN devices to share local loop.
SPIDs are processed during each call set up.
SPIDs assigned by your service provider.
A SPID is required for each B channel.

ISDN Devices

TE1 - Device compatible with ISDN network, connects to NT1 or NT2
TE2 - Device not compatible with ISDN requires TA
TA - (terminal Adapter) Converts signals so non-ISDN devices can use ISDN
NT1 - Connects 4-wire ISDN to 2-wire local loop
NT2 - Directs traffic to and from different subscriber devices and NT1

ISDN Reference Points

R - References points between non-ISDN device and TA
S - References points that connect into NT2 (Inbound)
T - References Outbound connections from NT2 into ISDN network or NT1
U - References connection between NT1 and ISDN network (North America only)

ISDN Protocols

E - Telephone network standards
I - Concepts, terminology, general methods
Q - How switching should operate

Dial on Demand Routing - DDR

Before setting up a dial on demand connection you must consider what kind of traffic will initiate the dial up connection, consider the following points:

You must first establish how ISDN connections will be initiated, established and maintained.
You must establish which sites are involved, who can initiate and terminate connections.
Applications supported over DDR, which applications can initiate a connection.
What unexpected protocols could cause a connection to be made.

ISDN switch types

For proper ISDN configuration you have to configure the correct switch type. Most common type in US is At&T's 5ESS and Nortel DMS-100. In UK it's Net3 and Net5.

Next set of revision notes: Novell IPX revision notes