4B: ISDN

1
4B ISDN

• Integrated Services Digital Network

2
What is ISDN?

• WAN service over existing telephone lines
• Typically a low bandwidth link for remote
  locations, dial-in users, or as a backup to other
  WAN services.
• Digital service in a circuit-switched environment
• Choice of two types of service Basic Rate ISDN
  (BRI) and Primary Rate ISDN (PRI). BRI can
  transmit up to 128 kbps. PRI (which is
  transmitted over a T1 line) can transmit up to
  1.536 Mbps.
• Supports voice, data, and video applications.
• Connection is established when the user places a
  call to another party. The WAN link is brought
  up for the duration of the call and is taken down
  when the call is completed. Pricing is usage
  based.

3
Why is ISDN Important?

• Its an available WAN option in most communities.
• Shorter installation time since it runs over
  existing phone lines.
• Cost effective. Avoids the cost of full-time
  data services.
• CCNA certification exam topics deal with ISDN.
• ISDN is a required part of the TCS design.

4
Design Issues of ISDN

• Security Issues because network devices can be
  connected over the PSTN, a robust security model
  is needed to protect the network.
• Cost Containment Issues periodic evaluation
  of data traffic and monitoring of ISDN usage
  patterns necessary to ensure WAN costs are
  controlled.

5
Basic ISDN Components
Connects to the ISDN Network through a 4-wire,
twisted pair, digital link
Predates ISDN standards
Can be either a standalone device or built-in
Usually integrated in the CPE device and provided
by carrier
Typically found in digital PBXs
6
ISDN Reference Points

• Reference points are a series of specifications
  that define the connection between specific ISDN
  devices.
• A CPE device (router) may support different
  reference points
• The reference points supported will determine
  what specific equipment is required

7
ISDN Reference Points
S interface

• R connection between a non ISDN-compatible
  device to a TA

• S connections into the NT2
• T outbound connection from the NT2 to the
  ISDN network or an NT1

• U connection between the NT1 to phone
  companys ISDN network

8
ISDN Switches

• ISDN providers can use various types of switches
  that connect you to their central office.
• The correct switch type must be configured on the
  ISDN device for proper operation.
• Most common switch types
• U.S. ATTs 5ESS, Nortels DMS-100
• Japan NTT
• U.K. Net3 and Net5

9
More Stuff to KnowSPIDs

• SPIDS are Service Profile Identifiers
• SPIDs identify the line configuration of the ISDN
  service.
• SPIDs allow multiple ISDN devices (voice data
  devices) to share the local loop.
• The SPID number is generally 10 digits long and
  includes the customers seven digit ISDN phone
  number.
• The source of the SPID number is the ISDN service
  provider

10
ISDN Protocols/Standards

• Protocols beginning with
• Q - deal with signaling and switching
• I - deal with terminology concepts
• E - recommend telephone network standards for
  ISDN
• Examples Q.921, Q.931, etc

11
ISDN Physical Layer

• ISDN physical layer frame is 48 bits long (36
  data)
• Two 24 bit frames (two 8-bit B Channels and a
  2-bit D Channel 6 bits of framing information)
• 8000 ISDN BRI frames are sent per second
• 8000 24 192 kbps
• Effective rate is 8000 18 144 kbps

12
ISDN Data Link Layer D Channel

• LAPD is the ISDN Layer 2 signaling protocol on
  the D Channel
• LAPD ensures that control signaling information
  flows and is received properly

13
ISDN Data Link Layer B Channel

• PPP HDLC are the most common Layer 2
  encapsulation types on ISDN B Channels
• ISDN defaults to HDLC
• LAPB (Link Access Procedure Balanced) can also be
  used
• Most networking designs use PPP encapsulation
  (more robust, authentication)
• PPP uses LCP to establish and configure the link
• PPP uses PAP CHAP for security

14
ISDN Uses Remote Access

• Remote Access (through analog dial-up from
  telecommuters home, mobile users hotel room,
  small remote office)
• Most common use of ISDN
• Remote access links generally represent the
  lowest-speed link in the enterprise.

15
ISDN Uses Remote Nodes

• Remote Nodes connects a single user who appears
  to be a network node.

16
ISDN Uses - SOHO

• SOHO (Small Office/Home Office) offers
  connectivity to the corporate site or Internet at
  much higher speeds than available over phone
  lines and modems.
• SOHO designs typically involve dialup only
  (SOHO-initiated connections)

17
Basic Rate ISDN (BRI) Services

• Divides a standard telephone line into three
  digital channels capable of simultaneous voice
  and data transmission.
• The three channels are comprised of two bearer
  (B) channels at 64 kbps each and a data (D)
  channel at 16 kbps.
• BRI is also known as 2BD and equals 144 kbps
• BRI B Channels
• carries voice, video, and data to the customers
  site.
• BRI D Channel
• carries all signaling associated with connection
  control as well as supplementary services.

18
Primary Rate ISDN (PRI) Services

• Is still using two twisted pair copper telephone
  wire that is multiplexed into 24 channels, each
  64 kbps. PRI is transmitted over a 1.544 T1
  line.
• Twenty-three 64 kbps bearer (B) channels.
• B channels carry data, voice and video traffic.
• One 64 kbps signaling (D) channel
• The D channel is used to set up calls on the B
  channels.
• PRI is also know as 23BD which equals
  1.544 mbps
• In Europe elsewhere, PRI E1 provides 2.048 mbps

19
Establishing BRI Connectivity with the 2504
Router
20
ISDN Configuration Tasks

• Global Configuration
• Select ISDN providers CO switch type
• Create static routes to destinations
• Specify interesting traffic to initiate an ISDN
  call to the appropriate destination DDR
• Interface Configuration
• Specify interface for ISDN BRI port
• Configure ISDN addressing and DDR dialer
• Specify SPIDs
• Configure interface for PPP encapsulation and
  CHAP authentication
• Enter dialer map and dialer-group
• Enter dialer list
• Optional Configurations (on interface)
• Wait and idle times before router times out or
  drops a call

21
ISDN Global Configurations

• router(config) isdn switch-type basic-5ESS
• (selects switch type)
• router(config) ip route 172.16.29.0
  255.255.255.0 172.16.126.2
• (static route to destination)
• router(config) dialer-list 1 protocol ip permit
• (associates permitted IP traffic with dial group
  1)

22
ISDN Interface Configurations

• router(config) interface bri 0
• (selects an ISDN enabled interface on the router)
• router(config-if) ip address 172.16.126.1
  255.255.255.0
• (configures IP Address)
• router(config-if) dialer-list 1 protocol ip
  permit
• (associated permitted IP traffic with dials group
  1)
• router(config-if) dialer-group 1
• (identifies interesting traffic)
• router(config-if) isdn spid1 0145678912
• (sets up the 1st B Channel SPID)
• router(config-if) isdn spid2 0145678914
• (sets up the 2nd B Channel SPID)
• router(config-if) dialer map ip 172.16.126.2
  name cisco-b 445

23
ISDN Optional Interface Configurations

• router(config-if) dialer wait-for-carrier-time
  15
• (specifies 15 seconds maximum before provider
  responds to call)
• router(config-if) dialer idle-timeout 300
• (specifies number of seconds before the router
  drops a call)

24
Confirming ISDN Operations
25
DDR Considerations

• DDR creates connectivity between ISDN sites by
  establishing and releasing circuit-switched
  connections as needed by networking traffic.
• For total control over initial DDR connections,
  consider
• Which sites can initiate connections based on
  traffic?
• Is dial-out required to SOHO sites?
• How are directory services and routing tables
  supported across an idle connection?
• What applications need to be supported over DDR
  connections? For how many users do they need to
  be supported?
• What unexpected protocols might cause DDR
  connections? (these will cause the router to
  continually initiate a call)

26
Verifying DDR Operations
27
Troubleshooting DDR Operations
28
Checking the Status of an ISDN Line
29
Need more information on ISDN?

• Follow the links in the on-line chapter.
• Ciscos web site www.cisco.com has product and
  reference guides, internetworking technology
  overviews and other technical references.
• Check out www.adtran.com gt training gt technology
  overview for straight forward, easy to understand
  explanations of WAN technologies.

30
THE END

• CCNA 4 ISDN Chapter