When you have multiple lines and only one phone number for incoming calls, you need to use a roll-over or hunt group. This concept is the same one a lot of companies use for customer service. Call one number and the next available person picks up the phone. We use the same concept here except for data calls. You can use this technique if you have a lot of people calling from outside your organization, for example, if you are with an Internet service provider (ISP). Give your customers one number that can reach a large number of modems, and the next available one answers. You can also use rotary groups for outgoing calls, but they have largely been replaced by dialer profiles, which provide greater flexibility. With incoming calls, however, we have a little more predictability because most low-speed traffic comes across analog lines and we can often dictate settings to the people calling in.
Configuring Rotary GroupsWhen configuring a rotary group, we need to specify a dialer interface and tell the router which physical interfaces will participate in the hunt group. We do so with the interface dialer number command and the dialer rotary-group number commands shown in Table 8.3.
When configuring a rotary group for outgoing calls, you need to configure dialer strings on the dialer interface. Don't forget to put the dialer inband command on interfaces with modems to turn on DDR. |