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  1. ISDN Semester 4, Chapter 5

  2. Table of Contents Go There! ISDN & The OSI Model Go There! ISDN Common Uses Go There! Configuring ISDN Go There! Dial-On-Demand Routing

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

  4. 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.) usingthe out-of-band D (or Delta) channel • Offers faster data transfer using the B (or Bearer) channels at 64kbps (2B+D=144kbps)

  5. 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

  6. 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.

  7. 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.

  8. T interface BRI Local Loop S interface 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.

  9. ISDN reference points

  10. S/T interface requires an NT1 connection. Cisco Interfaces • In the United States, the customer is required to provide the NT1. • In Europe and various other countries, the telephone company provides the NT1 function and presents an S/T interface to the customer.

  11. BRI S/T Interface – Cisco 2503

  12. Configuring ISDN interface Router(config)#interface bri number Router(config-if)# If the router is a TE2 device, which does not have a native BRI, it must use an external ISDN terminal adapter. On a TE2 router, configure the appropriate serial interface to send the ISDN traffic to the TA. Terminal Adapter

  13. 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) 555-1234 • SPID: 51055512340001

  14. 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

  15. ISDN Common Uses Table of Contents End Slide Show

  16. 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.

  17. Configuring ISDN Table of Contents End Slide Show

  18. 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

  19. 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

  20. 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)#isdn spid2 51055512350001 5551235

  21. 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

  22. Dial-On-Demand Routing Table of Contents End Slide Show

  23. 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.

  24. DDR Configuration • Four steps: • Define what is “interesting traffic” • Assign interesting traffic definition to ISDN • Define destination • Define call parameters

  25. 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

  26. 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.

  27. DDR: Defining Interesting Traffic • Router(config) dialer-listdialer-grouplistaccess-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

  28. 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

  29. 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 5551234

  30. ISDN And Static Routes

  31. Multi dialer Maps on a DDR Interface • Ip route • Ip route • Ip route • Dialer map ip name SOHO1 5551212 • Dialer map ip name SOHO2 5551213 • Dialer map ip name SOHO3 5551214

  32. Setting Default/Static Routes

  33. 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.

  34. 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

  35. 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-timeoutseconds • 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

  36. 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

  37. 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

  38. 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

  39. 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

  40. 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.

  41. Show ISDN Status Command • This command displays ISDN status information for Layer 1, Layer 2, and Layer 3.

  42. 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

  43. Verifying PPP Multilink The output of this command displays which links are members of the bundle

  44. 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.

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

  46. ISDN Debug Commands

  47. ISDN Labs