Semester 6 – Chapter 4

ISDN

ISDN Uses

• Used primarily as a WAN backup technology

• to provide remote access to telecommuters and small offices

• to support large numbers of POTS (analog modem) and/or ISDN Basic Rate Interface (BRI) calls.

DSL vs ISDN

• offers much higher throughput at a lower cost.• However, ISDN still used because

– ISDN is more widely available than DSL or cable. – Many companies and service providers have made a

significant investment in ISDN equipment and training, and plan to continue leveraging that investment.

– Remote offices using ISDN can connect to central offices directly, without traversing the public Internet. Most DSL and cable implementations require the remote host communicate with the central site using a VPN over the Internet.

ISDN Advantages Over Analog (Asychronous)

• Higher Speed

• Faster Call Setup

• Cheaper than leased lines

• Can run voice and data simultaneously

BRI Characteristics

• Two 64-kbps bearer channels • One 16-kbps delta channel • 48 kbps of framing and synchronization

information • Total speed of 192 kbps • Although not commonly done, you may

reference the total bandwidth of an ISDN BRI, including framing and synchronization, which is 192 kbps.

PRI over T1

• 23 64-kbps bearer channels

• One 64-kbps D channel, carried in timeslot 24

• 8 kbps of framing and synchronization information

• Total speed of 1.544 Mbps

PRI Over E1

• 30 64-kbps bearer channels

• One 64-kbps D channel, carried in timeslot 16

• 64 kbps of framing and synchronization information

• Total speed of 2.048 Mbps

ISDN Call Processing

• Signaling System 7 (SS7) protocols used to set up a path inside the public switched telephone network (PSTN)

• 931.q is used between end user and ISDN switch

• D channel is used for signaling

Designations

• E Telephone network standards

• I Concepts, terminology, and methods

• Q Signaling and switching

PRI

• a channel service unit/data service unit (CSU/DSU) is required to connect a router (the TE) to the carrier network. Internal CSU/DSUs are common among modular routers.

• PRI's primary application is modem aggregation – not point-to-point connectivity

• Can provide both analog and digital dial solutions

ISDN and OSI Model

• Operates at layers 1 2, and 3• Layer 1

– .430 for BRI, .431 For PRI, ANSI T1.601 for BRI

• Layer 2– As specified by Q.921, the D channel typically

frames data using Link Access Protocol on the D channel (LAPD)

• Layer 3– the B channel can carry datagrams using a variety of

Layer 3 protocols, including IP, IPX, and AppleTalk.

TE1 Addresses

• 0-63 for non-automatic TEI assignment • 64-126 for automatic TEI assignment • 127 for group assignment, or broadcast • TEI works together with the service access

point identifier (SAPI) to complete the Layer 2 address– SAPI is a 6-bit number used to identify and manage – TEI represents the specific ISDN device, while the

SAPI represents the specific process running on that device

ISDN Call Termination

• disconnect • release • release complete

– It issues a disconnect message to the calling party. – It starts a timer to ensure receipt of a released

message. – It disconnects the switched path. – When a released message is received from the

preceding exchange, it returns a release complete message to the preceding exchange.

ISDN Addressing Tasks

• Assign the IP address• Assign dialer group (for DDR), • Assign ISDN service profile statements (SPID

numbers• Include a dialer map command that

associates a statically mapped destination to a destination IP address, hostname, and ISDN dial number.

• ISDN switch type can be set in global mode or assigned to individual interfaces

BRI Interface Commands

• RTA(config)#interface bri 0RTA(config-if)#isdn switch-type basic-5ess

• Router(config-if)#encapsulation ppp

• Router(config-if)#ppp authentication chap

• Other encapsulations– encapsulation [ppp | labp | hdlc | x25 | cpp]

DDR Configuration

• 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, and• telephone number to dial by using the dialer• map command. • 4.(Optional) Define call parameters by using other• dialer commands such as dialer idle-timeout, dialer

fast-idle, and dialer load-threshold.

Dial-on-Demand Commands

• Router(config)#dialer-list dialer-group-number protocol protocol-name {permit | deny}

• RTA(config)#dialer-list 1• Router(config)#access-list access-list-number

[permit |deny] {protocol | protocol- keyword}{source source-wildcard | any}{destination destination-wildcard | any}[protocol-specific-options] [log]protocol ip permit

Attach Dialer List to Interface

• Router(config)#dialer-list 1 protocol ip permit

• Router(config)#interface bri0• Router(config-if)#dialer-group 1

• Note: For a given protocol and a given dialer group, only one access-list can be specified in the dialer-list command.

Dialer Map Command

• Identifies destination router information, such as the phone number to dial: – Router(config-if)#dialer map protocol next-hop-

address [name hostname] [broadcast] dial-string

• Cisco IOS commands often contain the word "map," which is used to statically map Layer 2 addresses to Layer 3 addresses

• Dialer maps for inbound calls are maps between protocol addresses and authenticated user names

Call Parameters

• Router(config-if)#dialer idle-timeout seconds• Router(config-if)#dialer fast-idle seconds• Router(config-if)#dialer load-threshold load

[outbound | inbound | • To manually set the idle timeout value, use the

dialer idle-timeout command– By default, the idle-timeout is set to 120 seconds either]

• The dialer load-threshold command is used to specify the interface load at which the router will initiate another call to the destination

DDR Environment

• In a DDR environment, dynamic routing can be a source of problems.

• Routing protocols such as RIP and OSPF rely on regular communication between link partners.

• If routers are connected via a dial-up link, active connections are usually intermittent.

Routing Solutions

• WAN core and remote sites run different protocols, route redistribution may be necessary to "share" routing information between the different protocols.

• use static and default routing to address the challenge of routing in a DDR network

• use dynamic routing, including route redistribution, to propagate routes– Use snapshot routing for serial connections

• Static routes are entered manually – no need for routing tables– Central(config)#ip route 172.24.2.0

255.255.255.010.2.3.2

• At least one static route pointing to the next-hop IP address is necessary for DDR to work– Router(config)#ip route 0.0.0.0 0.0.0.0 {next-

hop-address | exit-interface}

Redistributing EIGRP/Static

• RTA(config)#ip route 123.22.1.1 255.255.255.0 bri0

• RTA(config)#router eigrp 100

• RTA (config-router)# redistribute static

Passive Interface

• R(config)#IP route 10.0.0.1 255.255.0.0 192.16.3.0

• R(config)#router rip• R(config)#version 2• R(config)#network 10.0.0.0• R(config)#redistribute static• R(config)#passive-interface bri0/0

– To avoid routing updates initiating a call

Snapshot Routing

• RIP for IP, IGRP for IP, Novell RIP and SAP for Novell IPX, Routing Table Maintenance Protocol (RTMP) for AppleTalk, Routing Table Protocol (RTP) for Banyan VINES– When distance vector router updates are not considered

interesting traffic, router drops call and route will drop from table

– The hellos from OSPF will keep initiating calls

• Redistribute routes and using RIP between serial connections

Snapshot Routing

• Uses the client-server design model– one router is designated as the snapshot server and one

or more routers are designated as snapshot clients

• At the end of the active period, the router takes a snapshot of the entries in its routing table. These entries remain frozen during what is called the quiet period– client router determines the frequency at which it calls

the server router. The quiet period can be as long as 100,000 minutes (over 69 days)

Snapshot Commands

• Router(config-if)#snapshot server active-time [dialer]

• Router(config-if)#snapshot client active-time quiet-time [suppress-statechange-updates] [dialer]

• Router(config-if)#dialer map snapshot sequence-number dial-string– The value of the active-time argument must be the same

for the client and server routers– make sure your active time is long enough to allow any

routing updates to be sent

Suppress-Statechange

• suppress-statechange-update option disables the exchange of routing updates each time the line protocol goes from "down" to "up"or from "dialer spoofing" to "fully up.

• The dialer map snapshot command specifies which router to call as the snapshot server.spoofing" to "fully up.

Aggregation

• Cisco Proprietary BOD– triggered by outgoing traffic levels only– load value is a number from 1 to 255

• 1 IS 0%; 255 IS 100%

• Multilink PPP (MLP) – Triggers by outgoing or incoming traffic– Both of these methods require the dialer load-threshold

command• Router(config-if)#dialer load-threshold [inbound | outbound |

either ] • only one end of a link should be configured with the dialer load-

threshold command.

Use PPP Multilink

• Asynchronous serial interfaces in dialer rotary groups

• Synchronous serial BRI

• Multiple BRIs in dialer rotary groups

• Multiple BRIs using dialer profiles

• PRI B channels in dialer rotary groups

Accepting Calls

• You can ensure that only a single device answers an incoming call by verifying the number or subaddress in the incoming call against the device configured number, subaddress, or both.

• ISDN routers can be configured to screen incoming calls by using calling line identification (CLID)– Router(config-if)#isdn caller phone-number

ISDN Rate Adaptation

• Router(config-if)#dialer map protocol next-hop-address [name name] [speed speed] [broadcast] dial-string – Assigned on per destination basis– Lower speed is accepted

Debugging Commands

• Show ip int bri0/0• Show ip int brief• Show isdn status• Show isdn history• Show dialer• Show ppp multilink• Debug dialer• Debug ppp multilink• Debug isdn events• Debug ppp authentication | negotiation

D Channel Debugging

• debug isdn q921 at Layer 2• debug isdn q931 at Layer 3.

– display information about call setup and teardown of ISDN network connections at Layer 3 on the D channel.

• includes a call setup message, indicated by "SETUP" in the first line.

• In the second line, the Bearer Capability value of 0x8890 indicates that the coding standard used is ITU-T and the circuit mode is 64kbps.

PRI Configuration

• .Specify the correct PRI switch type that the router interfaces with at the provider's Central Office (CO).

• Specify the T1/E1 controller, framing type, and line coding for the provider's facility.

• Set a PRI group timeslot for the T1/E1 facility and indicate the speed used.

• Identify the interface that you will configure to act with DDR.

T1/E1 Configuration

• Router(config)#controller {t1 | e1}{slot/port | unit number}

• Router(config)#controller t1• Router(config-controller)#framing {sf | esf}• Router(config-controller)#framing{crc4 | no-crc4}

[australia]• Router(config)#controller e1• Router(config-controller)#framing crc4• Router(config-controller)#linecode hdb3