ISDN & DDR

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30 Οκτ 2013 (πριν από 3 χρόνια και 9 μήνες)

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ISDN

Semester 4, Chapter 5

Table of Contents

ISDN & The OSI Model

ISDN Common Uses

Configuring ISDN

Dial
-
On
-
Demand Routing

Go There!

Go There!

Go There!

Go There!

End Slide Show

Table of Contents

ISDN & The OSI Model

What is ISDN?


I
ntegrated
S
ervices
D
igital
N
etworks 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 PRI


B
asic
R
ate
I
nterface 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 plus


When not using voice communications, both B channels are
available for data.



P
rimary
R
ate
I
nterface ISDN uses 23 Bearer channels at
64kbps ea. & a 64kbps Delta channel for signaling


Also called a
digital T1

because the total bandwidth is 1.544Mbps

Basic 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.

Basic ISDN Components


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.

Basic ISDN Components


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 points

Cisco
Interfaces


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 2503

Configuring ISDN interface

Router(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 & 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
-
1234


SPID: 51055512340001

ISDN 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 Uses

End Slide Show

Table of Contents

Common Uses for ISDN: SOHO


Some of the characteristics of ISDN SOHOs include:


Support a
limited number

of simultaneous users


Use DHCP or NAT so
only one outside IP address

is needed


Save the cost of using dedicate connections

such as a T1 by only
using dialup connections.

Configuring ISDN

End Slide Show

Table of Contents

Summary 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 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 t

Router(config)#isdn switch
-
type basic
-
ni

!

!This command can also be entered on the interface

!

Router(config)#int bri0

Router(config
-
if)#isdn switch
-
type basic
-
ni

Interface: 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 bri0

Router(config
-
if)#isdn spid1 51055512340001 5551234

Router(config
-
if)#isdn spid2 51055512350001 5551235

Interface: 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 ppp

Router(config
-
if)#ppp authentication chap

Dial
-
On
-
Demand Routing

End Slide Show

Table of Contents

DDR 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 Configuration


Four steps:


Define what is “interesting traffic”


Assign interesting traffic definition to ISDN


Define destination


Define call parameters

DDR: 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 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 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 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 bri0

Router(config
-
if)dialer
-
group 1

DDR: 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 Routes

Multi dialer Maps on a DDR Interface


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 Routes

DDR: 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 Up 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 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 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 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 Incoming 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 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 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 Status

Command


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

Verifying 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

Verifying PPP Multilink

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

Verifying PPP Multilink


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 Commands

Identification
Request

Identification
Assignment

Action
Indicator

Set Asynchronous
Balanced Mode Extended

ISDN Debug Commands

ISDN Labs