ISDN

1. ISDN Semester 4, Chapter 5 Allan Johnson

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

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 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

10. ISDN’s 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.

11. ISDN Layers • The basic difference between ISDN call setup and regular phone service is that ISDN uses digital signaling. • A suite of standards had to be specified to implement ISDN.

12. 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

13. 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 HDLC’s implementation of LAPB (Balanced)

14. 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

15. 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

16. ISDN Common Uses Table of Contents End Slide Show

17. Common Uses for ISDN • There are many uses for ISDN. We’ll look at three: • Remote access • Remote nodes • Small Office/Home Office (SOHO)

18. Remote Access • The most common use for ISDN is remote access through dial-up connections. • These links are typically the slowest links in the enterprise. • Users dial into a bank of modems that provide them with connectivity

19. Remote Node • Slightly different than Remote Access, users log into an access server. • The user appears to be part of the network with access to all LAN services. • Ideal for the power user, road warrior.

20. 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.

21. Configuring ISDN Table of Contents End Slide Show

22. Summary of Configuration Tasks • The following assumes all normal global and interface configuration is complete. • Global: Router(config)# • Select your ISP’s 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

23. 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

24. Interface: SPIDs • 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)#isdn spid2 51055512350001 5551235

25. 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

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

27. 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.

28. 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)

29. 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

30. 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

31. 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

32. 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. • 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-router)#passive-interface bri0 ! !continue configuring networks, then set static route ! Router(config)#ip route 192.168.3.0 255.255.255.0 10.1.1.3

33. 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

34. Table of Contents End Slide Show