isdn semester 4, chapter 5. table of contents isdn & the osi model isdn common uses configuring...

ISDNISDN

Semester 4, Chapter 5

Table of ContentsTable of Contents

ISDN & The OSI Model

ISDN Common Uses

Configuring ISDN

Dial-On-Demand Routing

Go There!Go There!

Go There!Go There!

Go There!Go There!

Go There!Go There!

End Slide ShowEnd Slide Show


ISDN & The OSI ModelISDN & The OSI Model

What is ISDN?What is ISDN?

Integrated Services Digital Networks allow digital signals to be transmitted over existing phone lines.

Provides connectivity for remote sites without the added expense of a leased line (e.g. T1)

ISDN has the following benefits: Can carry voice, video, and data on B Channel Faster call setup than modems (sometimes < 1 sec.) using

the out-of-band D (or Delta) channel Offers faster data transfer using the B (or Bearer) channels

at 64kbps (2B+D=144kbps)

BRI versus PRIBRI versus PRI

Basic Rate Interface ISDN uses 2 Bearer channels at 64kbps ea. & a 16 kbps Delta channel for signaling.(2B+D)Users get 128kbps although the link is really 144kbps plusWhen not using voice communications, both B channels are

available for data.

Primary Rate Interface ISDN uses 23 Bearer channels at 64kbps ea. & a 64kbps Delta channel for signalingAlso called a digital T1 because the total bandwidth is 1.544Mbps

Basic ISDN ComponentsBasic ISDN Components

The capabilities of Customer Premise Equipment varies.

Therefore, different types of equipment exist to provide virtually any user the ability to access the ISDN local loop.

Two questions to ask when determining the needed equipment: Does my current equipment support ISDN? Do I need to attach multiple devices to a single ISDN

connection? With those two questions in mind, let’s investigate

the options.


Is device ISDN compatible? “Yes, my device is compatible with ISDN.”

Then you have a Terminal Equipment Type 1 device (TE1)“No, my device is not compatible with ISDN.”

Then you have a Terminal Equipment Type 2 device (TE2) and will require a Terminal Adapter (TA) to convert the electrical signals to ISDN

Connect multiple devices or a single device?“No, I’m only connecting my computer.”

Then you only need a Network Termination 1 (NT1) to convert the 2-wire incoming phone line to 4-wire

“Yes, I’m connecting multiple devices.”Then you also need a Network Termination 2 (NT2) to provide switching functions

before attaching to the NT1.With the answers in mind, let’s look at a graphic.


Notice, we’re using a NT2 to connect all devices to the NT1 The NT1 is used to terminate the BRI local loop at the

customer premise & convert 2-wire to 4-wire. Notice also that the

TE2 must have a TA since it is not compatible with ISDN.

The Reference Points (R,S,T,U) define the interface for connecting between the different devices.

S interface

T interface

BRI Local Loop

ISDN reference pointsISDN reference points

Cisco Cisco InterfacesInterfaces

In the United States, the customer is required to provide the NT1.

In Europe and various other countries, the telephone company provides the NT1 function and presents an S/T interface to the customer.

S/T interface requires an NT1 connection.

BRI S/T Interface – Cisco 2503BRI S/T Interface – Cisco 2503

Configuring ISDN interfaceConfiguring ISDN interfaceRouter(config)#interface bri number

Router(config-if)#

If the router is a TE2 device, which does not have a native BRI, it must use an external ISDN terminal adapter.

On a TE2 router, configure the appropriate serial interface to send the ISDN traffic to the TA.

Terminal Adapter

ISDN Switches & SPIDsISDN Switches & SPIDs

You must configure the router for the switch type your provider is using for ISDN service (Similar to configuring dial-up service for the right modem).

In addition, you must know the Service Profile Identifier (SPID) your ISP is using to identify you and configure your line.

SPIDs vary in length depending on the provider. They are usually some combination of the phone number and optional numbers

For example: Phone Number: (510) 555-1234SPID: 51055512340001

ISDN EncapsulationsISDN Encapsulations

If you do not configure a data link layer encapsulation, ISDN will use the default HDLC.

However, PPP is the preferred method of encapsulating across ISDN links because… PAP/CHAP Authentication Link quality determination through LCPs and other options available through PPP

ISDN Common UsesISDN Common Uses



Common Uses for ISDN: SOHOCommon Uses for ISDN: SOHO

Some of the characteristics of ISDN SOHOs include:Support a limited number of simultaneous usersUse DHCP or NAT so only one outside IP address is neededSave the cost of using dedicate connections such as a T1 by only

using dialup connections.

Configuring ISDNConfiguring ISDN



Summary of Configuration TasksSummary of Configuration Tasks

The following assumes all normal global and interface configuration is complete.

Global: Router(config)# Select your ISP’s switch type Specify traffic to trigger DDR calls (“interesting traffic”)

Interface: Router(config-if)# Select interface specifications Configure ISDN addressing

Optional Configurations

Global: Switch TypeGlobal: Switch Type

Since switch signaling differs across switch types, you must specify the switch type

Our Adtran unit is a “basic-ni” (There are about 10 switch types.)

Use the command isdn switch-type nnnn

Router#config tRouter(config)#isdn switch-type basic-ni!!This command can also be entered on the interface!Router(config)#int bri0Router(config-if)#isdn switch-type basic-ni

Interface: SPIDsInterface: SPIDs

SPIDs allow multiple ISDN devices, such as voice and data, to share the local loop. . SPIDs are obtained from your service provider.

To keep them simple, SPIDs are usually some combination of the phone number plus some optional numbers (and a Local Directory Number [LDN], if necessary)

The SPID commands for each B channel are:Router(config-if)#isdn spid1 spid-number [ldn]

Router(config-if)#isdn spid2 spid-number [ldn]

Router(config)#int bri0Router(config-if)#isdn spid1 51055512340001 5551234Router(config-if)#isdn spid2 51055512350001 5551235

Interface: EncapsulationInterface: Encapsulation

PPP is, by far, the most favored of the encapsulations on ISDN links because of its capabilities.

Since HDLC is on by default, you must configure PPP The configuration steps are the same as we studied in

Ch. 4 – PPP. NOTE: The username name password password

command must be entered in global configuration mode in order to make CHAP authenticate.

Router(config-if)#encap pppRouter(config-if)#ppp authentication chap

Dial-On-Demand RoutingDial-On-Demand Routing



DDR OverviewDDR Overview

A major benefit of using an ISDN link instead of a dedicated link is its significant savings in bandwidth costs.

Connections are initiated by remote offices and telecommuters on an as-needed basis.

Since the call setup time is significantly reduced compared to traditional analog modems, the user rarely experiences a delay.

When services are no longer needed (the user times out), the call is terminated.

However, interesting traffic must be defined and filtered. Otherwise, unexpected protocols (e.g. routing updates) could cause the router to dial continuously even when the network is not in use.

DDR ConfigurationDDR Configuration

Four steps: Define what is “interesting traffic” Assign interesting traffic definition to ISDN Define destination Define call parameters

DDR: Interesting TrafficDDR: Interesting Traffic

Defining “interesting traffic” involves specifying what types of packets will initiate a call.

Use the dialer-list command in global configuration mode.

The command structure, similar to ACLs, is as follows:dialer-list dialer-group-number protocol

protocol-name {permit | deny} For example, you want IP traffic to initiate calls.Router(config)#dialer-list 1 protocol ip permit

DDR: Interesting TrafficDDR: Interesting Traffic

The simple form of the dialer-list command specifies whether a whole protocol suite, such as IP is permitted to trigger a call.

The more complex form of the command references an access list, allowing finer control of the definition of interesting traffic.

When a dialer-list command is used in conjunction with the access list, the access-list command specifies interesting traffic that initiates a DDR call.

By referencing an access list to specify interesting traffic , you have granular control of which protocols, sources, and destinations are worthy of bringing up a link.

DDR: Defining Interesting TrafficDDR: Defining Interesting Traffic

Router(config) dialer-list dialer-group list access-list-number .

The following configuration commands permits a single host to initiate DDR: RTA(config) access-list 24 permit host 192.168.1.2 RTA(config) dialer-list 1 list 24

DDR: Assign Interesting TrafficDDR: Assign Interesting Traffic

Once the dialer-list is created, it needs to be assigned to the interface responsible for initiating the call.

The command structure is:dialer-group dialer-group-number

Router(config)#int bri0Router(config-if)dialer-group 1

DDR: Define DestinationDDR: Define Destination

Now configure the interface with all the parameters necessary to reach the destination

With the dialer-map command, we are “mapping” (or bundling) Layer 3 addressing with Layer 2 addressing.

In our example: Layer 3: IP address Layer 2: LDN

The command structure is:Router(config-if)#dialer map protocol next-hop-address [name hostname] dial-string

dial-string is the ldn of the next hop address [name hostname] is the hostname of the connected router

Router(config-if)dialer map ip 172.16.20.1 name Lab-A 5551234

ISDN And Static RoutesISDN And Static Routes

Multi dialer Maps on a DDR InterfaceMulti dialer Maps on a DDR Interface

Central Office

SOHO1

SOHO2

SOHO3

ISDN Cloud

172.10.10.0/24

172.10.11.0/24

172.10.12.0/24

Ip route 172.10.10.0 255.255.255.0 10.1.1.2 Ip route 172.10.11.0 255.255.255.0 10.1.1.3 Ip route 172.10.12.0 255.255.255.0 10.1.1.4 Dialer map ip 10.1.1.2 name SOHO1 5551212 Dialer map ip 10.1.1.3 name SOHO2 5551213 Dialer map ip 10.1.1.4 name SOHO3 5551214

Setting Default/Static RoutesSetting Default/Static Routes

DDR: Passive Interface/Static RoutesDDR: Passive Interface/Static Routes

When configuring your routing protocol, you want to stop routing updates from going across your ISDN link. Why?

However in order to connect to networks beyond the next hop network, you must enter a static route.

Using ACLs To Prevent RIP From Bringing Using ACLs To Prevent RIP From Bringing Up a DDR InterfaceUp a DDR Interface

The following configuration is done at the Central Router end: (config)# access list 101 deny udp any any eq rip (config)#access list 101 permit ip any any (config) dialer-list 1 list 101 (config)#int bri0 (config-if) dialer group 1

Defining Optional Call ParametersDefining Optional Call Parameters

Dial-up connections are subject to an idle timer, which keeps track of how much time has passed since interesting traffic was routed out the interface. By default, the idle-timeout is set to 120 seconds. Router(config-if)#dialer idle-timeout seconds

When the router is waiting to use a line to make another call, it uses a more aggressive idle timeout called fast-idle. The fast-idle time is the number of seconds that a line can remain idle before the current call is disconnected to allow another call that is waiting to use the line. Router(config-if)#dialer idle-timeout 60

Router(config-if)#dialer fast-idle 15

Defining Optional Call ParametersDefining Optional Call Parameters

The dialer load-threshold command is used to specify the interface load at which the router will initiate another call to the destination. This command is typically used with Multi-link PPP

Multi Link PPPMulti Link PPP

MLP provides the following: load balancing over multiple WAN links Packet fragmentation, proper sequencing Load calculation on both inbound and outbound traffic

Configuring The BRI Interface To Forward Configuring The BRI Interface To Forward Incoming Voice CallsIncoming Voice Calls

(config-if) ISDN incoming-voice modem Switch to dial-peer sub configuration mode:

Dial-peer voice 1 pots (config-dial-peer) port 1 (config-dial-peer) destination-pattern 5551234

Verifying ISDN OperationVerifying ISDN Operation

To confirm ISDN is up and running, use the command show isdn status

To see an ISDN call in progress and the number called…. First, ping the destination to activate the link. Then, use the command show isdn active to see

information about the call

Verifying ISDN OperationVerifying ISDN Operation

#show int bri 0 Spoofing is necessary because the router removes a route from it

routing table if the route points to a "down" interface.

Show ISDN StatusShow ISDN Status Command Command

This command displays ISDN status information for Layer 1, Layer 2, and Layer 3.

Verifying PPP MultilinkVerifying PPP Multilink

As soon as you configure a BRI interface with the ppp multilink command, the router will create a virtual interface called a virtual access interface


The output of this command displays which links are members of the bundle


The debug dialer command indicates whether the multilink is up after authentication, and also indicates when the overload occurs.

The debug ppp multilink command displays packet sequence numbers. It is useful only as a last resort because it does not help troubleshoot when connections are not being bundled.

ISDN Debug CommandsISDN Debug Commands

Identification Identification RequestRequest

Identification Identification AssignmentAssignment

Action Action IndicatorIndicator

Set Asynchronous Set Asynchronous Balanced Mode Balanced Mode

ExtendedExtended

ISDN Debug CommandsISDN Debug Commands

ISDN LabsISDN Labs

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