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! Go There! Go There! Go There! Go There!

End Slide Show End Slide Show Table of Contents Table of Contents ISDN & The OSI Model

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 < 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  Basic Rate Interface 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.  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

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 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) SPID:

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

ISDN’s 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.

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 End Slide Show Table of Contents 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 End Slide Show Table of Contents 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 spid Router(config-if)#isdn spid

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 End Slide Show Table of Contents 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  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 name Lab-A

ISDN And Static Routes

Multi dialer Maps on a DDR Interface  Ip route  Ip route  Ip route  Dialer map ip name SOHO  Dialer map ip name SOHO  Dialer map ip name SOHO

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

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