
Configuring Dial Services
1-10
308621-14.00 Rev 00
Demand Circuit Protocols
The protocol for a demand circuit can be either PPP or frame relay. A frame relay
demand circuit can have any number of service records and PVCs. Typically,
frame relay connections are used with ISDN lines. PPP and frame relay circuits
can use the same demand pool.
Figure 1-3
on page 1-9 shows an example of a PPP demand circuit over modem
lines; Figure 1-4
shows a frame relay demand circuit over ISDN lines.
Figure 1-4. Dial-on-Demand Connection over a Frame Relay Network
In Figure 1-4, remote routers A, B, and C are connecting to the central router D
through a frame relay network, dialing into the network across ISDN lines. Router
D connects to the network across a leased line.
The permanent virtual circuits (PVCs) in this network can be either fully meshed
or non-fully meshed, allowing routers A, B, C, and D to connect to one another.
With the dial connection between the routers and the frame relay network, each
router can dial into the network and communicate with another router, provided
that the PVCs are set up properly and that the physical and logical connections are
active. Frame relay demand circuits cannot answer incoming calls. They can only
dial into a frame relay network, that is, they can place outbound calls.
Router A
Router B
Router C
DS0033A
Router D
Frame relay network
Frame
relay
switch
Frame
relay
switch
Frame
relay
switch
Frame
relay
switch
T1/HSSI/SYNC
BRI
PRI
Raise DTR/V.25bis
MODEM
Key
Leased line
Dial-up line
Kommentare zu diesen Handbüchern