ISDN

1
ISDN
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I. ISDN Concepts

• General concepts
• DDR
• Routing with ISDN
• PRI

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ISDN

• ISDN - Integrated Services Digital Network
  Unlike POTS, ISDN is digital from end to end.
• Voice, Data and Video

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ISDN Advantages

• Faster than POTS (typically 128 Kbps vs. 53 Kbps)
• Cheaper than leased lines

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ISDN Disadvantages

• BRI is slower than DSL and cable
• More expensive than DSL and cable
• Bottom line ISDN, in its current form, is no
  longer a first-choice technology.

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BRI and PRI

• ISDN is widely available in two flavors
• BRI Basic Rate Interface
• 2 64 Kbps Bearer Channels,16 Kbps Delta Channel
  (for control information), 48 Kbps for framing
  and synchronization
• 2B 1D
• 192 Kbps 1281648
• PRI Primary Rate Interface
• 23B 1D (T1), the D channel is 64-kbps
• 30B 1D (E1), European E1
• 1.544 Mbps (North America) or 2.048 Mbps (E1)

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ISDN Call Setup
4 B Channel
4 B Channel
4 B Channel
1 D Channel
3 D Channel
2 SS7
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ISDN Call Setup (Q.931)

• 1. When the call is initiated, the D channel
  comes up. The called number is sent to the local
  ISDN switch.
• 2. The local switch uses the Signaling System 7
  (SS7) signaling protocols to set up a path and
  pass the called number to the terminating ISDN
  switch.

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ISDN Call Setup

• 3. The far-end switch brings up the D channel
  to the destination. The D channel is used for
  call setup, signaling, and call termination,
  which are the call-control functions.
• 4. When the terminating end answers, the B
  channel is connected end to end. The B channel
  carries the conversation or data. Both B channels
  can be used simultaneously to the same or
  different destinations.

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ISDN Protocols - D Channel
LAPD (Link Access Procedure on the D channel) is
the framing protocol for the D channel
data. Q.931 of the DSS1 (Digital Subscriber Layer
1) protocol suite is the layer 3 protocol for the
D channel. The D channel is governed by DDR, the
mechanism for building connections over an analog
or ISDN connection.
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LAPD - SAPI and TEI
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LAPD - SAPI and TEI
Layer 2 The first address field byte contains the
service access point identifier (SAPI), which
identifies the type of service provided to Layer
3 (6 bits) (example Call-control, L2
management...) The terminal endpoint identifier
(TEI) field identifies either a single terminal
or multiple terminals. You can have up to 8
ISDN terminals on an S/T bus, which are
differentiated from each other through TEIs and
SAPIs. Switch assigns you a dynamic TEI and you
will communicate over the switch using the
signaling that uses a SAPI A TEI of all ones
indicates a broadcast.
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ISDN Protocols - B Channel
HDLC, PPP, Frame Relay, or LAPB (Link Access
Procedure, Balanced) can be used as the layer 2
protocol for the B Channel. IP or IPX can be
used as the layer 3 protocol for the B Channel.
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show isdn status - problem
phoenixshow isdn status The current ISDN
Switchtype basic-ni1 ISDN BRI0 interface
Layer 1 Status DEACTIVATED Layer 2
Status Layer 2 NOT Activated Layer 3
Status No Active Layer 3 Call(s)
Activated dsl 0 CCBs 0 Total Allocated ISDN
CCBs 0
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show isdn status - working
phoenixshow isdn status Global ISDN Switchtype
basic-ni ISDN BRI0 interface dsl 0,
interface ISDN Switchtype basic-ni Layer 1
Status ACTIVE Layer 2 Status
TEI 64, Ces 1, SAPI 0, State
MULTIPLE_FRAME_ESTABLISHED TEI 65, Ces
2, SAPI 0, State MULTIPLE_FRAME_ESTABLISHED
Spid Status TEI 64, ces 1, state
5(init) spid1 configured, spid1 sent,
spid1 valid TEI 65, ces 2, state 5(init)
spid2 configured, spid2 sent, spid2
valid Layer 3 Status 1 Active Layer 3
Call(s)
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II. ISDN and DDR

• Configuring Basic ISDN
• B Channel Aggregation BOD and MP
• Optional Dialer Commands
• Nice link for command reference
  http//www.cisco.com/warp/public/779/smbiz/service
  /configs/isdn/isdn_glossary.htm

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Using DDR with ISDN
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ISDN Configuration Tasks
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Configuring Basic ISDN BRI
Step 1 IP Addresses and Encapsulation Step 2
Selecting the ISDN Switch Type Step 3
(Optional) Setting SPIDs Step 4 DDR -
Initiating the call Other B Channel Aggregation
and Optional Dialer commands
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Step 1 IP Addressing Encapsulation

• Router(config) interface bri interface
• Router(config-if) encapsulation layer-2
• Layer 2 B Channel options
• HDLC (default)
• PPP (Options CHAP or PAP authentication)
• Other LAPB, X.25, Frame Relay
• Layer 2 D Channel options
• LAPD

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EXAMPLE IP and Encapsulation/Authentication

• Gateway
• Gateway(config) username ISP password class
• Gateway(config) interface bri 0
• Gateway(config-if)
• ip add 10.0.0.3 255.0.0.0
• Gateway(config-if)
• encapsulation ppp
• Gateway(config-if) ppp authen chap

ISP ISP(config) username Gateway password class
ISP(config) interface bri 0 ISP(config-if) ip
add 10.0.0.4 255.0.0.0 ISP(config-if)
encapsulation ppp ISP(config-if) ppp authen chap
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• Syntax
• Router (config) isdn switch-type switch-type
• Variety of switch types vary.
• If you are connecting to a Northern DMS-100
  switch or a National ISDN-1 switch, you will also
  need to configure the SPID on your router. (next
  section)
• Can be configured at interface level or global
  level.

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EXAMPLE Switch Type

• Gateway
• Gateway(config) username ISP password class
• Gateway(config)
• isdn switch-type basic-dms100
• Gateway(config) interface bri 0
• Gateway(config-if) ip add 10.0.0.3 255.0.0.0
• Gateway(config-if) encapsulation ppp
• Gateway(config-if) ppp authen chap

ISP ISP(config) username Gateway password
class ISP(config) isdn switch-type
basic-5ess ISP(config) interface bri
0 ISP(config-if) ip add 10.0.0.4
255.0.0.0 ISP(config-if) encapsulation
ppp ISP(config-if) ppp authen chap
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EXAMPLE 1

• Gateway
• Gway(config) username ISP password class
• Gway(config) isdn switch-type basic-dms100
• Gway(config) interface bri 0
• Gway(config-if) isdn spid1 51055512340001
  5551234
• Gway(config-if) isdn spid2 51055512350001
  5551235
• Gway(config-if) encapsulation ppp
• Gway(config-if) ppp authen chap
• Gway(config-if) ip add 10.0.0.3 255.0.0.0

ISP ISP(config) username Gateway password
class ISP(config) isdn switch-type
basic-5ess ISP(config) interface bri
0 ISP(config-if) encapsulation
ppp ISP(config-if) ppp authen chap ISP(config-if
) ip add 10.0.0.4 255.0.0.0
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Step 4 DDR Configuration
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DDR Configuration Steps

• 1. Define what constitutes interesting traffic
  by using the dialer-list command.
• 2. Assign this traffic definition to an
  interface by using the dialer-group command.
• 3. Define the destination address, hostname,
  telephone number to dial, and optional call
  parameters by using the dialer map command or a
  dialer string command.
• 4. Define call parameters by using commands
  such as dialer idle-timeout, dialer fast-idle,
  and dialer load-threshold.

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Dialer Map Command

• dialer map protocol next-hop-address name
  hostname speed 56 64 broadcast
  dial-stringisdn-subaddress
• speed option - Used for ISDN rate adaption for
  links with only 56 Kbps bandwidth. 64 Kbps is
  the default.
• Must use authentication when using dialer maps -
  bug.

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EXAMPLE Without access lists, IP or IPX traffic
will initiate the link

• Gateway
• Gateway(config) username ISP pass class
• Gateway(config) isdn switch-type basic-dms100
• Gateway(config) dialer-list 1 protocol ip permit
• Gateway(config) dialer-list 1 protocol ipx
  permit

Gateway(config) interface bri 0 Gateway(config-if
) ip add 10.0.0.3 255.0.0.0 Gateway(config-if)
encapsulation ppp Gateway(config-if) ppp authen
chap Gateway(config-if) dialer-group
1 Gateway(config-if) dialer map ip 10.0.0.4 name
ISP 5554000 Gateway(config-if) isdn spid1
51055512340001 5551234 Gateway(config-if) isdn
spid2 51055512350001 5551234
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EXAMPLE With access lists. EIGRP traffic will
not trigger the link. All other IP traffic will
initiate the link.
Gateway(config) interface bri 0 Gateway(config-if
) ip add 10.0.0.3 255.0.0.0 Gateway(config-if)
encapsulation ppp Gateway(config-if) ppp authen
chap Gateway(config-if) dialer-group
1 Gateway(config-if) dialer map ip 10.0.0.4 name
ISP 5554000 Gateway(config-if) isdn spid1
51055512340001 5551234 Gateway(config-if) isdn
spid2 51055512350001 5551234

• Gateway
• Gateway(config) username ISP pass class
• Gateway(config) isdn switch-type basic-dms100
• Gateway(config) dialer-list 1 protocol ip list
  101
• Gateway(config) access-list 101 deny eigrp any
  any
• Gateway(config) access-list 101 permit ip any
  any

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• NOTE If using dialer map statements with ppp,
  you must use PPP with authentication for router
  to accept the call.
• Problem Connecting two routers via an
  asynchronous connection, modems, using PPP
  encapsulation, no authentication, and with dialer
  map statements at both ends. The router (with a
  dialer map statement) will dial out, but the
  remote router (also with a dialer map statement)
  will not create a connection. The answering
  modem does answer, but after a few seconds the
  line is deactivated. By removing the
  dialer-group from the interface of the remote
  router, the router will accept the call, but
  cannot be the one to initiate a call.
• Environment IOS 12.05(T), Routers 1720 and
  2621, Modems Hayes Accura V.90
• Solution You must add PPP with authentication
  for this to work! Used PPP with CHAP and life
  was good again! Also works with PAP. If dialer
  map statements are used at both ends, and you
  want either router to initiate the call, (and of
  course the remote router to answer), you must use
  PPP with authentication. Both routers can now
  initiate and answer calls from the other router.
  Other workaround If you want the routers to
  dial each other without mapping ip address to
  phone numbers and chat-scripts, you can use the
  dialer string command.
• Notes
• There are weird combinations that I did get to
  work, with a dialer map at one end and a dialer
  string at the other, but at some point I need to
  get a life.
• This is also true when using ISDN with dialer map
  statements.

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B Channel Aggregation
B Channel Aggregation - Mechanism for combining
two or more B channels into a single ISDN pipe
for the equivalent of 128 Kbps or greater
bandwidth, with bandwidth-on-demand.
Bandwidth-on-demand (BOD) provides a dynamic
method of enabling you to use only the
communications bandwidth that is required to do
the job. Cisco offers two methods to obtain
BOD 1. Generic Cisco proprietary BOD 2.
Multilink PPP
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-
B Channel Aggregation - BOD
Cisco Proprietary BOD Triggered by outbound
traffic only. Router(config-if) dialer
load-threshold load The load is the calculated
weighted average load value for the interface,
where 1 is unloaded and 255 is fully loaded.
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-
Multilink PPP (MP or MLP) If you want both
inbound and outbound traffic to be used in load
calculation, you must use MP. dialer
load-threshold load inboundoutboundeither
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-
B Channel Aggregation - MP
Example Gateway(config)int bri
0 Gateway(config-if) dialer load-threshold 128
either Gateway(config-if) ppp multilink Note
Be sure to use a dialer map for each B channel.
It is the only way I got it to work. -
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DDR Optional Commands
-

• dialer idle-timeout
• dialer fast-idle

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III. Routing and ISDN

• Static Routes and Default Routes
• Dynamic Routing
• Dialer Maps and ISDN
• Router Spoofing
• Snapshot Routing

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-
172.16.0.0/24
Static Routes and Default Routes Static routes
and default routes eliminate the need to send
routing updates over the ISDN link which will
trigger a DDR call. ISP(config) ip route
172.16.0.0 255.255.0.0 10.0.0.3
OR ISP(config) ip route 172.16.0.0 255.255.0.0
BRI0
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-
172.16.1.0/24
172.16.4.0/24
172.16.2.0/24
172.16.3.0/24
Dynamic Routing If your DDR interface is on the
same network in which you are running dynamic
routing protocol, and you do not want your
routing updates to be sent over your DDR link,
then use the passive-interface command
. ISP(config) router igrp 100 ISP(config-router)
network 172.16.0.0 ISP(config-router)
passive-interface bri0
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Router Spoofing

• DDR interfaces must spoof, that is, pretend to
  be up and up, so that they stay in the routing
  table.
• By default, a router removes any routes that
  points to down interfaces from its routing table
• phoenixshow inter bri 0
• BRI0 is up, line protocol is up (spoofing)
• Hardware is PQUICC BRI with U interface
• Internet address is 10.1.1.2/24
• MTU 1500 bytes, BW 64 Kbit, DLY 20000 usec,
• reliability 255/255, txload 1/255, rxload
  1/255
• Encapsulation PPP, loopback not set. Etc.

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Snapshot routing
-

• Snapshot Routing provides an efficient and
  cost-effective routing for DDR environments.
• Snapshot Routing is a routing update mechanism
  that
• 1. It eliminates the need for configuring
  and maintaining large static tables
• (dynamic routing protocols can now be
  used on DDR lines).
• 2. It cuts down the overhead of these
  routing updates.

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Snapshot routing
-

• Concept
• During a specified active time interval, snapshot
  clients initiate an ISDN connection to exchange
  routing information with a snapshot server.
• Operation
• Snapshot routing uses the client-server design
  model.
• When snapshot routing is configured, one router
  is designated as the snapshot server and one or
  more routers are designated as snapshot clients.
• The server and clients exchange routing
  information during an active period.

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Snapshot routing
-

• At the end of the quiet period, another active
  period begins, and the client router dials the
  server router to obtain the latest routing
  information.
• The client router determines the frequency at
  which it calls the server router.
• The quiet period can be as long as 100,000
  minutes (approximately 69 days).

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Snapshot routing
-

• Server
• RTA(config)int bri0/0
• RTA(config-if)snapshot server 5
• Client
• RTB(config)int bri0/0
• RTB(config-if)dialer map snapshot 1 name RTA
  broadcast 5551234
• RTB(config-if)snapshot client 5 10
  suppress-statechange-update dialer

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Snapshot routing
-
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IV. PRI

• PRI configuration tasks are as follows
• 1. Specify the correct PRI switch type that the
  router interfaces with at the providers CO.
• 2a. Specify the T1/E1 controller, framing type,
  line coding, and clocking for the providers
  facility.
• 2b. Set a PRI group timeslot for the T1/E1
  facility and indicate the speed used.
• 3. Identify the interface that you will configure
  to act with DDR.

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PRI Concepts

• ISDN PRI (Primary Rate Interface) - ISDN
  interface to primary rate access.
• Primary rate access consists of a single 64 Kbps
  D channel, plus 23 (T1) or 30 (E1) B channels for
  voice of data.
• T-1 is a digital communications service that
  operates at 1.544 Mbps in a full-duplex,
  time-division-multiplexing (TDM) mode.
• ISDN PRI maps nicely onto the 1.544 Mbps T1
  circuit.
• See T1 article on web site. If you are not
  familiar with T1, PCM, line coding, framing, DS0
  hierarchy, and TDM, then it is important that
  you read this article.

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PRI Concepts

• The T-1 circuit is just a carrier and not a type
  of encapsulation.
• Just about any layer 2 serial encapsulation can
  be used on a T-1 line including
• HDLC
• PPP
• Frame Relay
• ISDN
• Other X.25, etc.
• We will focus only on ISDN PRI

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PRI Configuration - Switch

• 1. Specify the correct PRI switch type that the
  router interfaces with at the providers CO.
• Note This must be done first.
• Router(config)isdn switch-type switch type
• primary-net5 European, New Zealand and Asia ISDN
  PRI switches
• primary-ntt Japanese ISDN PRI switches
• primary-4ess ATT 4ESS switch type for the U.S.
• primary-5ess ATT 5ESS switch type for the U.S.
• primary-dms100 NT DMS-100 switch type for the
  U.S.
• primary-ni ATT National ISDN switch type
• primary-ts014 Australia PRI switches

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PRI Configuration-Controller

• 2a. Specify the T1/E1 controller, framing type,
  line coding, and clocking for the providers
  facility.
• Controller
• Router(config)controller t1e1 slot/portunit
  num
• Framing
• Router(config-controller)framing
  sfesfcrc4no-crc4
• Line coding
• Router(config-controller)linecode
  amib8zshdb3
• Clocking
• Router(config-controller)clock source line
  primary secondary internal

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PRI Configuration-Controller

• 2b. Set a PRI group timeslot for the T1/E1
  facility and indicate the speed used.
• The pri-group command configures the specified
  interface for PRI operation and the number of
  fixed timeslots that are allocated on the
  provider's digital facility.
• T1 timeslots 1 to 24
• E1 timeslots 1 to 31
• Router(config-controller)pri-group timeslots
  range
• When this is completed, the serial interface and
  its timeslots as subinterfaces will be created.

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PRI Configuration-D Channel

• 3. Identify the interface which will be the D
  Channel
• The interface serial command specifies an
  interface for PRI D-channel operation.
• The interface is a serial interface to a T1/E1 on
  the router or access server
• Router(config)interface serial slot/port
  unit23 15
• Note Within an E1 or T1 facility, the channels
  start numbering at 1 (1 to 31 for E1 and 1 to 24
  for T1). Serial interfaces in the Cisco router
  start numbering at 0. Therefore, channel 16, the
  E1 signaling channel, is serial port subinterface
  15. Channel 24, the T1 signaling channel, becomes
  serial subinterface 23.

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PRI Configuration-D Channel

• 3. Identify the interface which will be the D
  Channel
• Router(config)interface serial slot/port
  unit23 15
• When you configure the D channel, its
  configuration is applied to all the individual B
  channels, such as IP address, encapsulation, etc.

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PRI Configuration - Config.

• controller T1 1/0
• framing esf
• linecode b8zs
• pri-group timeslots 1-24
• - Creates subinterfaces on Serial 1
• Serial 1/00 to Serial 1/023
• - 1-23 or Serial1/00 - Serial 1/022 are
  
• the B channels
• - Last slot (24 023) is the D channel
• interface serial 1/023 (23 D Channel of 0 -
  23)
• ip address 10.0.0.3 255.0.0.0
• encap ppp
• dialer map ip 10.0.0.4 name ISP 5554000
• dialer-group 1
• isdn switch-type primary-5ess
• ppp authen chap

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• Other debug commands
• debug isdn active - Displays the status of the
  ISDN connection while the call is in progress.
• debug dialer - Displays the configuration and
  operation of the dialer.

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debug isdn q921

• debug isdn q921 EXEC command to display data link
  layer (Layer 2) access procedures that are taking
  place at the access router on the D channel
  (LAPD) of its ISDN interface.
• debug isdn q921 command output is limited to the
  commands and responses exchanged during
  peer-to-peer communication carried over the D
  channel.

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debug isdn q931

• debug isdn q931 EXEC command to display
  information about call set up and teardown of
  ISDN network connections (Layer 3) between the
  local router (user side) and the network.
• the debug isdn q931 command output is limited to
  the commands and responses exchanged during
  peer-to-peer communication carried over the D
  channel.