ISDN

1
ISDN

• Semester 4, Chapter 5

When you know what you want, and want it bad
enough, youll find a way to get it!
-Jim Rohn
2
ISDN

• There are several WAN technologies used to
  provide network access from remote locations. One
  of these technologies is ISDN. ISDN can be used
  as a solution to the low bandwidth problems that
  small offices or dial-in users have with
  traditional telephone dial-in services.

3
Purpose if ISDN

• Telephone companies developed ISDN with the
  intention of creating a totally digital network.
  ISDN allows digital signals to be transmitted
  over existing telephone wiring. This became
  possible when the telephone company switches were
  upgraded to handle digital signals. ISDN is
  generally used for telecommuting and networking
  small and remote offices into the corporate LAN.

4
What is ISDN?

• Integrated Services Digital Network (ISDN) is a
  set of communications protocols to allow digital
  signals (voice data) to be transmitted over
  existing phone lines.
• Provides connectivity for remote sites without
  the added expense of a leased line (e.g. T1/Frame
  Relay)
• 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)

5
Table of Contents
Go There!
ISDN Common Uses
Go There!
ISDN The OSI Model
Go There!
Configuring ISDN
Go There!
Dial-On-Demand Routing
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ISDN Common Uses
Table of Contents
End Slide Show
7
Dedicated Telecommuter / Teleworker

• Workers that work out of the home
• Increased from 5 million in 1990 to 44 million in
  1995
• Need to access the networks for longer periods of
  time
• Power users
• Connection needs to be reliable and available

8
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.

• Comprised of multiple users
• Require reliable and available connections

9
Dial-up Connections

• Least expensive and widely available methods
• Low speeds

10
ISDN The OSI Model
Table of Contents
End Slide Show
11
Signaling

• When a TCP connection is established, there is an
  exchange of information called the connection
  setup. This information is exchanged over the
  path on which the data will eventually be
  transmitted. Both the control information and the
  data share the same pathway. This is called
  in-band signaling. ISDN however, uses a separate
  channel for control information, the D channel.
  This is called out-of-band signaling.

12
Basic Rate Interface (BRI)

• Operates over most copper twisted-pair telephone
  wiring
• Total bandwidth of 144 kbps in three separate
  channels
• Two 64 kbps B (bearer) channels carry voice or
  data traffic
• One 16 kbps D (data) channel provides
  instructions that tell the telephone network how
  to handle each of the B channels
• Often referred to as 2BD

13
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
• In Europe, PRI uses 30 B channels for a total of
  2.048 Mbps

14
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.

15
ISDN Terminology

• Terminal Equipment 1 (TE1) - Designates a device
  that is compatible with the ISDN network. A TE1
  connects to a Network Termination of either Type
  1 or Type 2.
• Terminal Equipment 2 (TE2) Designates a device
  that is not compatible with ISDN and requires a
  Terminal Adapter.

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ISDN Terminology

• Terminal Adapter (TA) Converts standard
  electrical signals into the form used by ISDN so
  that non-ISDN devices can connect to the ISDN
  network.
• Network Termination Type 1 (NT1) Connects 4-wire
  ISDN subscriber wiring to the conventional 2-wire
  local loop facility.

17
ISDN Terminology

• Network Termination Type 2 (NT2) Directs traffic
  to and from different subscriber devices and the
  NT1. The NT2 is an intelligent device that
  performs switching and concentrating.

18
ISDN Reference Points

• R point that is between a non-ISDN compatible
  device and a terminal adapter
• S point that connects into the NT2. Enables
  calls between the different CPE
• T electrically identical to the S interface, it
  references the outbound connection from the NT2
  to the ISDN network.
• U the the connection between the NT1 and the
  ISDN network owned by the phone company

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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.

21
ISDN SWITCHING

• ISDN is considered a circuit-switched connection.
  The B channel is the elemental circuit-switching
  unit

22
ISDN Switch Types

• Several different types of ISDN switches used by
  carriers
• Must know the switch type used by your CO
• Also need to know the Service Profile Identifier
  (SPID)
• SPID area a series of characters that identify
  you to the switch at the CO

23
Switch Configurations

• Services offered by ISDN carriers vary
  considerably from country to country or region to
  region. Like modems, each switch type operates
  slightly differently, and has a specific set of
  call setup requirements. Before the router can be
  connected to an ISDN service, it must be
  configured for the switch type used at the CO.
  This information must be specified during router
  configuration so the router can communicate with
  the switch, place ISDN network level calls, and
  send data.

24
Global Switch Type (options)
Note Locality drives switch type. Why?
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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

26
ISDNs Q Protocols

• ITU-T administers the protocols used in ISDN
  communications.
• The protocols are grouped in three categories
• E Telephone standards over ISDN networks
• I Concepts, terminologies, and general methods
• Q Switching and signaling protocols
• 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.

27
ISDN Physical Layer

• The physical layer frame format is 48 bits of
  which 36 bits is data.
• The bits of an ISDN physical-layer frame are used
  as follows
• F---Provides synchronization
• L---Adjusts the average bit value
• E---Ensures contention resolution when several
  terminals on a passive bus contend for a channel
• A---Activates devices
• S---Unassigned
• B1, B2, and D---Handles user data

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ISDN Data Link Layer

• Link Access Procedure on the D Channel (LAPD)
• error-correction and link establishment protocol
  used across the D channel to ensure proper flow
  control and signaling information
• Similar to HDLCs implementation of LAPB
  (Balanced)

29
ISDN Network Layer

• The D channel uses Q.931 to setup the call and
  establish circuit switched connections.
• The Q.931 process is illustrated below

30
Encapsulation

• Each ISDN B channel can make a separate serial
  connection to any other site in the ISDN network.
  Since PPP operates over both synchronous and
  asynchronous serial links, ISDN lines can be used
  in conjunction with PPP encapsulation.

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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

NOTE Only one encapsulation type on an ISDN
interface may be used
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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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Configuring ISDN
Table of Contents
End Slide Show
34
ISDN Configuration

• Must specify global and interface parameters
• Global select the switch type, and establish
  the criteria for interesting traffic
• Interface Assign an IP address and subnet mask
  to the interface, assign DDR information, and ID
  assigned by the service provider.

35
Configuration Tasks

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

36
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 (if needed)

• Once in interface configuration mode, you must
  specify the SPID each B channel will use. 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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Configuration Sample
39
Verifying ISDN Operation
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Verifying ISDN Operation
41
Dial-On-Demand Routing
Table of Contents
End Slide Show
42
DDR

• Dial-on-demand routing (DDR) is triggered when
  traffic that matches a predefined set of criteria
  is queued to be sent out a DDR-enabled interface.
  The traffic that causes a DDR call to be placed
  is referred to as interesting traffic. Once the
  router has transmitted the interesting traffic,
  the call is terminated.

43
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.

44
Dialer-list

• The key to efficient DDR operation is in the
  definition of interesting traffic. Interesting
  traffic is defined with the dialer-list command.
  Dialer lists can allow all traffic from a
  specific protocol to bring up a DDR link, or they
  can query an access list to see what specific
  types of traffic should bring up the link. Dialer
  lists do not filter traffic on an interface. Even
  traffic that is not interesting will be forwarded
  if the connection to the destination is active.

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DDR Configuration

• Four steps
• Define what is interesting traffic
• Assign interesting traffic definition to ISDN
• Define destination
• Define call parameters (optional will not be
  covered)

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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.
• Bonus Question
• What would a dialer-list denying RIP updates look
  like?

Router(config)dialer-list 1 protocol ip permit
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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 SPIDs
• 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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Timeout

• The dialer idle-timeout seconds command may be
  used to specify the number of idle seconds before
  a call is disconnected. The seconds represent
  the number of seconds until a call is
  disconnected after the last interesting packet is
  sent. The default is 120.

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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.
• However in order to connect to networks beyond
  the next hop network, you must enter a static
  route.
• For example, you share an ISDN link with another
  router whose address is 10.1.1.3
• The other router also has a LAN 192.168.3.0/24
• Set a passive interface to stop routing updates
  and then configure a static route

Router(config)router igrp 100 Router(config-route
r)passive-interface bri0 ! !continue configuring
networks, then set static route ! Router(config)i
p route 192.168.3.0 255.255.255.0 10.1.1.3
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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 the activate the
  link.
• Then, use the command show isdn active to see
  information about the call

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Table of Contents
End Slide Show