ISDN

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ISDN

• Semester 4, Chapter 5

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Table of Contents
Go There!
ISDN The OSI Model
Go There!
ISDN Common Uses
Go There!
Configuring ISDN
Go There!
Dial-On-Demand Routing
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ISDN The OSI Model
Table of Contents
End Slide Show
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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 lt 1
  sec.) using the out-of-band D (or Delta) channel
• Offers faster data transfer using the B (or
  Bearer) channels at 64kbps (2BD144kbps)

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BRI versus PRI

• Basic Rate Interface ISDN uses 2 Bearer channels
  at 64kbps ea. a 16 kbps Delta channel for
  signaling.(2BD)
• Users get 128kbps although the link is really
  144kbps plus
• When 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 signaling
• Also called a digital T1 because the total
  bandwidth is 1.544Mbps

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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, lets
  investigate the options.

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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, Im 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, Im 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, lets look at a graphic.

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Basic ISDN Components

• Notice, were 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.

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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 [phone]
• SPID 51055512340001

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ISDN Protocol Lyers
Signaling between the ISDN Switch and the router
TEI, Layer 2 Address (Dynamically assigned by the
switch)
I.430 T I.431 PRI ANSI T1.601 U
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ISDNs Q Protocols by the International
Communication Union (ITU)

• The Q.931 protocol is used to govern signaling
  between the TE and the ISDN switch in the CO.
• Because various ISDN switches implement the Q.931
  protocol differently, you must configure the
  switch type before any D-channel communication
  can occur.

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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

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ISDN Common Uses
Table of Contents
End Slide Show
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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.

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Configuring ISDN
Table of Contents
End Slide Show
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Summary of Configuration Tasks

• The following assumes all normal global and
  interface configuration is complete.
• Global Router(config)
• Select your ISPs switch type
• Specify traffic to trigger DDR calls
  (interesting traffic)
• Interface Router(config-if)
• Select interface specifications
• Configure ISDN addressing
• Optional Configurations

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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

Routerconfig 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
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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)isd
n spid2 51055512350001 5551235
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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
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Dial-On-Demand Routing
Table of Contents
End Slide Show
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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.

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DDR Configuration

• Four steps
• Define what is interesting traffic
• Assign interesting traffic definition to ISDN
• Define destination
• Define call parameters

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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
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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.

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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

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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-gr
oup 1
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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
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ISDN And Static Routes
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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

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Setting Default/Static Routes
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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.

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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

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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
  60Router(config-if)dialer fast-idle 15

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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

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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

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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

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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

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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.

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Show ISDN Status Command

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

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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

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Verifying PPP Multilink

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

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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.

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ISDN Debug Commands
Identification Assignment
Identification Request
Action Indicator
Set Asynchronous Balanced Mode Extended
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ISDN Debug Commands
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ISDN Labs