Modems

Modems in a Mobile Environment

This chapter describes roaming with external wireless modems.

Roaming with External Wireless Modems

General Packed Radio Service/Code Division Multiplex Access (GPRS/CDMA) modems provide the mobile access router with a Layer 2 roaming interface. The Mobile IP stack allows layer 3 roaming IP connectivity for the mobile access router. External modems are connected to a serial interface of the mobile access router. The serial interface should be running in asynchronous mode. Figure 13-1 shows a sample scenario in which the serial port of the mobile access router is connected to a CDMA modem.

Figure 13-1 Modem to Mobile Access Router Connection

The mobile access router supports the following modems:

•Airlink Raven

•AnyDATA I-Port

•Wavecom

Configuration Example

The example configurations shown in Figure 13-2 and Figure 13-3 demonstrate the router's ability to roam back and forth between 802.11b and Cellular technologies. The browser-based applications and video move dynamically to and from the different technologies. The 1X technology provides approximately 60 Kbps. The Nextel provides approximately 20 Kbps, but the network provides for static IP addresses and private links back to the headquarters. Implementing IPsec VPN in the mobile access router provides a secure connection back to the headquarters through 802.11b technology.

Figure 13-2 IPsec VPN Connection

Figure 13-3 Wireless Internet Connection

Example of a Mobile Access Router with Dialer Interface and GRE Mobile IP Tunneling

chat-script airlink-cdma "" "AT&C1&D2" TIMEOUT 30 OK "ATDT#19788" TIMEOUT 30 CONNECT

interface Loopback0

 ip address 15.4.1.2 255.255.255.0

interface FastEthernet0/0

 ip address 10.20.1.1 255.255.255.0

interface Serial1/0

 physical-layer async

 no ip address

 encapsulation ppp

 dialer in-band

 dialer pool-member 1

 dialer-group 1

interface Dialer0

 ip address negotiated

 ip nat outside

 ip mobile router-service roam

 ip mobile router-service collocated

 encapsulation ppp

 dialer pool 1

 dialer idle-timeout 0

 dialer string 1

 dialer persistent

 dialer-group 1

ip mobile secure home-agent 64.161.107.162 spi 100 key hex 
12345678123456781234567812345678 algorithm md5 mode prefix-suffix

ip mobile router

 address 15.4.1.2 255.255.255.0

 home-agent 64.161.107.162

 reverse-tunnel

 tunnel  mode  gre

line 1

 exec-timeout 0 5

 flush-at-activation

 script dialer airlink-cdma

 modem InOut

 no exec

 transport input all

 stopbits 1

 speed 115200

 flowcontrol hardware

line aux 0

 exec-timeout 0 0

 speed 115200

line vty 0 4

 exec-timeout 0 0

 password cisco

 logging synchronous

 login

Example of a Mobile Access Router Without Dialer Interface

hostname 3200

chat-script airlink-cdma "" "AT&C1&D0" TIMEOUT 30 OK "ATDT#19788" TIMEOUT 30 CONNECT

interface Loopback0

 ip address 15.4.1.2 255.255.255.0

interface Serial1/0

 physical-layer async

 mtu 1450

 bandwidth 115200

 ip address negotiated

 ip mobile router-service roam

 ip mobile router-service collocated

 encapsulation ppp

 keepalive 900

 dialer in-band

 dialer idle-timeout 0

 dialer string airlink-cdma

 dialer-group 1

 async default routing

 async mode interactive

 no peer default ip address

 no fair-queue

 no ppp lcp fast-start

router mobile

ip mobile secure home-agent 64.161.107.162 spi 100 key hex 
12345678123456781234567812345678 algorithm md5 mode prefix-suffix

ip mobile router

 address 15.4.1.2 255.255.255.0

 home-agent 64.161.107.162

dialer-list 1 protocol ip permit

line con 0

 exec-timeout 0 0

 logging synchronous

 stopbits 1

line 1

 exec-timeout 0 0

 flush-at-activation

 script dialer airlink-cdma

 login

 modem InOut

 no exec

 transport input all

 autoselect during-login

 autoselect ppp

 stopbits 1

 speed 115200

 flowcontrol hardware

line aux 0

 exec-timeout 0 0

 speed 115200

line vty 0 4

 exec-timeout 0 0

 password cisco

 logging synchronous

 login

Example of a Mobile Access Router with Multiple Wireless Connections

ip dhcp excluded-address 10.10.10.1

ip dhcp pool testpool

   import all

   network 10.10.10.0 255.255.255.0

   default-router 10.10.10.1 255.255.255.0

   dns-server 204.117.214.10

ip cef

chat-script airlink-cdma2 "" "ATDT#19788" TIMEOUT 60 "CONNECT"

chat-script tmobile "" "AT" TIMEOUT 5 OK "ATE0V1" TIMEOUT 5 OK "ATS0=0" TIMEOUT 5 OK 
"AT+CGATT=1" TIMEOUT 5 OK "AT+CGACT=1,1" TIMEOUT 5 OK "ATD*99***1#" TIMEOUT  10 CONNECT

chat-script anydata "" "AT&C1&D0" TIMEOUT 30 OK "ATDT#777" TIMEOUT 30 CONNECT

interface FastEthernet0/0

 ip address 10.10.10.1 255.255.255.0

interface Serial2/0

 physical-layer async

 no ip address

 encapsulation ppp

 dialer in-band

 dialer pool-member 1

 dialer-group 1

 no keepalive

interface Serial2/1

 physical-layer async

 no ip address

 encapsulation ppp

 shutdown

 dialer in-band

 dialer pool-member 2

 no keepalive

interface Dialer0

 ip address negotiated

 ip mobile router-service roam priority 130

 ip mobile router-service collocated registration retry 3

 ip mobile router-service collocated

 encapsulation ppp

 dialer pool 1

 dialer idle-timeout 0

 dialer string 1

 dialer persistent

 dialer-group 1

 ppp authentication pap callin optional

interface Dialer1

 ip address negotiated

 ip mobile router-service roam

 ip mobile router-service collocated registration retry 3

 ip mobile router-service collocated

 encapsulation ppp

 dialer pool 2

 dialer idle-timeout 0

 dialer string 2

 dialer persistent

 dialer-group 2

 ppp chap hostname 4082029572

 ppp chap password 0 vzw

ip mobile secure home-agent 64.161.107.162 spi 100 key ascii hello algorithm md5 mode 
prefix-suffix

ip mobile router

 address 20.20.20.1 255.255.255.0

 collocated single-tunnel

 home-agent 64.161.107.162

 mobile-network FastEthernet0/0

 reverse-tunnel

 tunnel mode gre

line 5

 exec-timeout 0 5

 flush-at-activation

 script dialer airlink-cdma2

 modem InOut

 no exec

 transport input all

 stopbits 1

 speed 115200

 flowcontrol hardware

line 6

 exec-timeout 0 5

 flush-at-activation

 script dialer anydata

 modem InOut

 no exec

 transport input all

 stopbits 1

 speed 115200

 flowcontrol hardware

Example of a Home Agent Configuration

hostname HomeAgent

ip subnet-zero

no ip domain-lookup

ip audit notify log

ip audit po max-events 100

fax interface-type fax-mail

mta receive maximum-recipients 0

interface Loopback0

 ip address 10.10.100.1 255.255.255.0

interface FastEthernet0/0

 ip address 64.161.107.162 255.255.255.248

 duplex auto

 speed auto

ip classless

ip route 0.0.0.0 0.0.0.0 64.161.107.161

ip http server

ip pim bidir-enable

ip mobile home-agent

ip mobile virtual-network 15.4.0.0 255.255.0.0

ip mobile host 15.4.1.2 virtual-network 15.4.0.0 255.255.0.0

ip mobile secure host 15.4.1.2 spi 100 key hex 12345678123456781234567812345678

line con 0

 exec-timeout 0 0

 logging synchronous

line aux 0

line vty 0 4

 exec-timeout 0 0

 password cisco

 logging synchronous

 login

end

Initialization Strings

Recommended initialization strings for some common modems are provided in Table 13-1, but be aware that Cisco does not warrant that they are suitable or current. When in doubt, refer to the modem vendor's documentation or technical support.

Table 13-1 Modem Chat Scripts
Modem	Network	Script
Airlink Raven	Sprint	chat-script airlink-cdma "" "ATDT#19788" TIMEOUT 60 "CONNECT"
Airlink Raven	Verizon	chat-script airlink-cdma "" "ATDT#19788" TIMEOUT 60 "CONNECT"
AnyDATA I-Port EMIII	Verizon	chat-script anydata "" "AT&C1&D0" TIMEOUT 30 OK "ATDT#777" TIMEOUT 30 CONNECT
Sony/Ericsson T68i Handset	AT&T	chat-script ericsson-gprs "" "AT" TIMEOUT 30 OK "ATE0Q0&C1&D2V1" TIMEOUT 60 OK "AT" TIMEOUT 30 OK "ATS0=0" TIMEOUT 30 OK "AT" TIMEOUT 30 OK "ATE0Q0&C1&D2V1" TIMEOUT 60 OK "AT" TIMEOUT 30 OK "ATDT99**1#" TIMEOUT 30 CONNECT
Wavecom	T-Mobile or AT&T	chat-script tmobile "" "AT" TIMEOUT 5 OK "ATE0V1" TIMEOUT 5 OK "ATS0=0" TIMEOUT 5 OK "AT+CGATT=1" TIMEOUT 5 OK "AT+CGACT=1,1" TIMEOUT 5 OK "ATD99**1#" TIMEOUT 10 CONNECT
Motorola i90c	Nextel	chat-script ModemTech "" "ATZ2" OK "AT&C1&D2" OK "ATDT" TIMEOUT 60 CONNECT

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