ISDN - General Description
ISDN is a dial-up technology. It has to establish, maintain and terminate the circuit via a “Delta” channel. It transmits and receives data via “Bearer” channels. This can be done “in-band” or “out-of-band” depending on standards and equipment.
ISDN Technologies are broken down into BRI and PRI.
Bearer channels carry the data.
Delta channels are for call management.
BRI = 2 x 64kbps bearer channels + one 64kbps delta channel + 48kpbs of framing and synchronization. BRIs are generally used to place calls from point A to point B.
PRI (T1) = 23 x 64kbps bearer channels + one 64kbps delta channel + 8kbps of framing and synchronization.
PRI (E1) = 30 x 64kbps bearer channels + one 64kbps delta channel + 64kbps of framing and synchronization.
PRIs are generally used to connect to an ISPs access server for general Internet access.
Out-of-band signaling is done on a channel that is dedicated for the purpose and on a separate channel than the data communication. This is the standard for Signaling System 7 (SS7).
V.25bis is the serial protocol running between the NT1 and the modem.
PPP
PPP Architecture
PPP allows other protocols to run over PPP, this is an advantage over SLIP.
| OSI Layer | |
| 3 | Upper-layer protocols (IP, IPX, AppleTalk) |
| 2 |
Network Control Protocol (NCP) Link Control Protocol (LCP) High-level Data Link Control (HDLC) |
| 1 | Physical Layer (such as EIA/TIA-232, v.24, V.35, ISDN) |
On your callback you can setup your access server at the central site, so the modem can authenticate, then hang-up and call you back. This allows for a little more security, but more to save long-distance toll charges. “The Call Back Feature”
- Multiplexing
- When a router sets up, monitors and tears down multiple layer 3 protocols over a single data line.
Asynchronous PPP and Async Interface Commands
Router(config-if)#encapsulation {ppp | slip}
Router(config-if)#async mode dedicated
Router(config-if)#async mode interactive
Asynchronous Interface Commands for Addressing
Router(config-if)#peer default ip address {address | pool pool-name | dhcp}
Router(config-if)#async dynamic address
Router(config-if)#ip unnumbered {type} {number}
Asynchronous Callback Global Commands
Router(config)#username username password {password} callback-dialstring {phone-number} callback-line {line-number} callback-rotary {rotary-group-number}
Asynchronous Callback Line / Interface Commands
Router(config-if)#ppp callback accept
Router(config-if)#ppp callback initiate
Router(config)#line {line-number}
Router(config-line)#callback forced-wait {seconds}
Router(config-line)#script callback {script-name}
Configuring a PPP Callback Server
To do this, you have two routers (DTE) server/client.
Router(config)#interface s0/2
Router(config-if)#ip address 10.0.1.7 255.255.255.0
Router(config-if)#encapsulation ppp
Router(config-if)#dialer callback-secure
Router(config-if)#dialer map ip 10.0.1.8 255.255.255.0
Router(config-if)#dialer-group1
Router(config-if)#ppp callback accept
Router(config-if)#authentication chap
Router(config-if)#exit
Router(config)#map-class dialer dial1
Router(config-map-class)#dialer callback-server {username}
Router(config-map-class)#dialer hold-queue timeout 60
Configuring a PPP Callback Client
RouterClient(config)#interface s0/0
RouterClient(config-if)#ip address 10.0.1.8 255.255.255.0
RouterClient(config-if)#encapsulation ppp
RouterClient(config-if)#dialer map ip 10.0.1.7 name {server router name} {phone number}
RouterClient(config-if)#dialer-group 1
RouterClient(config-if)#ppp callback request
RouterClient(config-if)#ppp authentication chap
Configuring an asynchronous dialup connection on Cisco Routers
Objective
The objective here is to configure two Cisco routers to connect to each other using PPP. The routers will also be configured to provide in-band connections through the serial interfaces. Then configure the asynchronous connections to support PPP and Dial-On-Demand Routing (DDR).
Inventory
- ROUTER 1 Fa0/0 192.168.0.1/24, S0/1 192.168.8.1/24
- MODEM 1
- HOST 1 192.168.0.2/24 GW 192.168.0.1
- ————————————
- ROUTER 2
- MODEM 2
- HOST 1
Steps
Step 1
Make sure your router configuration is cleared or will provide for all the following settings.
Step 2
Configure the serial interface on ROUTER 2 as follows.
ROUTER2(config)#interface serial 0/1
ROUTER2(config-if)#physical-layer async
ROUTER2(config-if)#ip address 192.168.8.3 /24
ROUTER2(config-if)#encapsulation ppp
ROUTER2(config-if)#async mode dedicated
ROUTER2(config-if)#no cdp enable
ROUTER2(config-if)#dialer in-band
ROUTER2(config-if)#dialer idle-timeout 300
ROUTER2(config-if)#dialer wait-for-carrier-time 60
ROUTER2(config-if)#dialer hold-queue 50
ROUTER2(config-if)#dialer-group 1
ROUTER2(config-if)#dialer map ip 192.168.8.1 name ROUTER1 modem-script hayes56k broadcast 5556666
###
#Note hayes56k is the script name and 5556666 is your telephone number
###
ROUTER2(config-if)#exit
ROUTER2(config)chat-script hayes56k ABORT ERROR "" "AT Z" OK "ATDT \T" TIMEOUT 30 CONNECT \c
ROUTER2(config)line 2
ROUTER2(config-line)#speed 115200
ROUTER2(config-line)#flowcontrol hardware
ROUTER2(config-line)#modem inout
ROUTER2(config-line)#transport input all
ROUTER2(config-line)#stopbits 1
ROUTER2(config-line)#exit
ROUTER2(config)#dialer list 1 protocol ip permit
ROUTER2(config)#ip router 0.0.0.0 0.0.0.0 192.168.8.1
ROUTER2(config)#exit
Step 3
Configure the serial interface on ROUTER 1 as follows.
ROUTER1(config)#interface s0/1
ROUTER1(config-if)#physical-layer async
ROUTER1(config-if)#ip address 192.168.8.1 255.255.255.0
ROUTER1(config-if)#encapsulation ppp
ROUTER1(config-if)#async mode dedicated
ROUTER1(config-if)#no cdp enable
ROUTER1(config-if)exit
ROUTER1(config)#line 2
ROUTER1(config-line)#115200
ROUTER1(config-line)#flowcontrol hardware
ROUTER1(config-line)#modem inout
ROUTER1(config-line)#transport input all
ROUTER1(config-line)#stopbits 1
ROUTER1(config-line)#modem autoconfigure discovery
ROUTER1(config-line)#exit
ROUTER1(config)#ip route 192.168.216.0 255.255.255.0 192.168.8.3
ROUTER1(config)#exit
Step 4
Use show dialer to review the output….