Quick Reference

Sunday, July 1, 2007

Quick Notes - ISDN

In ISDN, what do E-series protocols specify?
E-series protocols specify telephone network standards for ISDN. Examples include International ISDN addressing and the International Telephone plan.

What do protocols that begin with I deal with?
I-series protocols deal with concepts, terminology, and general methods of ISDN, such as service aspects, user network interfaces, and network aspects.

What do ISDN protocols that begin with Q specify?
Q-series protocols specify how switching and signaling (call setup) should operate. For example, ISDN protocol Q.921 is used for LAPD on the D channel, and protocol Q.931 is used for the ISDN network layer between the terminal and switch.

What is the data transfer speed for ISDN BRI?
The data transfer rate for ISDN BRI is 128 Kbps. The total transfer rate for ISDN BRI is 144 Kbps. This consists of two 64 Kbps (128 Kbps) Bearer (B) channels plus one 16 Kbps Delta (D) channel. The B channels can be used for data transfer and voice transmission. The D channel carries control and signaling information for fast call setup and operates at the first three layers of the OSI model.

What is the total rate in Mbps for ISDN PRI?
The total rate for ISDN PRI in the U.S. and Japan is 1.544 Mbps. PRI consists of 23 64 Kbps B channels and one 64 Kbps D channel. In Europe, PRI consists of 30 B channels and one D channel for a total rate of 2.048 Mbps.
In ISDN, the D channel appears to always be up and is what makes the call to the ISDN switch.

What signaling protocol does the ISDN switch use to set up a path and pass the called number to the terminating ISDN switch?
The ISDN local switch uses the SS7 protocol to set up a path and pass the called number to the terminating ISDN switch.

Devices connecting to an ISDN network are known as terminal equipment (TE) and network termination (NT) equipment. What do the TE1 and TE2 equipment types refer to?
TE1 refers to a device that has a native ISDN interface. That is, it can plug directly into an ISDN network. TE2 refers to equipment that does not have an ISDN interface and that requires a terminal adapter (TA) to plug into an ISDN network.

To what do ISDN NT1 and NT2 termination types refer?
Network Terminal 1 converts BRI signals into a form used by the ISDN line. It implements the physical layer specifications and connects the devices to the ISDN network. NT2 is the point where all ISDN lines are aggregated and switched using a customer-switching device.

What is the function of the TA?
The terminal adapter converts non-ISDN signals into ISDN signals. Devices that are not native to ISDN connect to a TA to access the ISDN network.

What does the ISDN R reference point define?
The R reference point defines the point between a non-ISDN-compatible device and a TA.

What does the ISDN S point reference?
The S point references the points or customer equipment that connects to the NT2 or customer-switching device.

What does the ISDN T reference point define?
ISDN T reference points refer to the point between NT1 and NT2 devices. T and S reference points are electronically the same and reference the outbound connection from the NT2 to the ISDN network.

What is the ISDN U reference point?
The U reference point is the point between the NT1 and the ISDN network.

What happens when you connect a router with a U interface into an NT1?
If you connect a router with a U interface into an NT1, you will damage the interface. This is because the U interface on a Cisco router already has a built-in NT1.

What are SPIDs?
Service provider or profile identifiers (SPIDs) are used to identify your router to the switch at the central office (the ISP). They are a series of characters that look like phone numbers and are not always required.

How do you enable ISDN on a Cisco router?
To enable ISDN on a Cisco router, first you need to define the switch type your router will be connecting to. The switch type is the type of switch used by your service provider. To define the ISDN switch type, enter the isdn switch-type switch-type global or interface command. Specifying the isdn switch-type global command specifies the ISDN switch type for the entire router. The second step is to enter the SPIDs provided by your service provider by entering the isdn spid1 spid-number and isdn spid2 spid-number interface commands. The following example enables ISDN on a router, specifying AT&T basic-rate switches as the switch type:

RouterA(config-if)#isdn switch-type basic-5ess

RouterA(config-if)#isdn spid1 123456789123

RouterA(config-if)#isdn spid2 123456789124

If you have DDR enabled on your router, when does the router decide when to bring up the ISDN line and send traffic?
If DDR is enabled on your router, it brings up the ISDN line when it sees "interesting traffic".

How do you enable DDR on a Cisco router?
To enable DDR on a Cisco router, you first need to define static routes with the ip route command. Next, specify interesting traffic, and finally, configure the dialer information.

How do you specify interesting traffic?
As an administrator, you define that interesting traffic can be based on protocol type or addresses for source or destination hosts. To define interesting traffic, use the following command: dialer-list dialer-group protocol protocol-name {permit deny list access-list-number}
dialer-group is the number that identifies the dialer list. protocol-name can be IP, IPX, AppleTalk, DECnet, or Vines.

RouterA(config)#dialer-list 10 protocol ip list 100

RouterA(config)#access-list 100 permit tcy any any eq www

RouterA(config)#access-list 100 permit tcy any any eq smtp

RouterA(config)#access-list 100 permit tcy any any eq dns

The last step in configuring DDR on a Cisco router is to configure the dialer information. How do you do this?
Do the following to configure the dialer information:
Step 1. Choose the interface.
Step 2. Configure an IP address on the interface.
Step 3. Configure the encapsulation type.
Step 4. Bind interesting traffic to the interface by using the dialer-group group-number interface command.

What command can you use to view the call in progress?
The show isdn active command shows the call in progress and the number dialed:

show isdn st

RouterA#Global ISDN Switchtype = basic-5ess

ISDN BRI0 interface dsl 0, interface ISDN Switchtype = basic-5ess

Layer 1 Status:


Layer 2 Status: TEI = 64, Ces = 1, SAPI = 0, State =


Layer 3 Status: 0 Active Layer 3 Call(s) Activated dsl 0 CCBs = 0

The Free Channel Mask: 0x80000003

Total Allocated ISDN CCBs = 0

How can you view the number of times the dial string has been successfully reached on a Cisco router?

The show dialer command displays information about the interface configured for DDR, the number of times the dialer string has been successfully reached, and the fast and idle timer values for each B channel.



doron said...

i checkout on the cisco site and did not see that isdn is included in the exam .
am i right ?


a3tips said...

Hi Doron,

Yes ISDN not part of 640-802 exam.. this was part of old exam. for info its on the blog.