Cisco Systems DNC-305 manual How Stacking Works, Typical Multilink PPP Session, DNC-317

Telco and ISP Dial Scenarios and Configurations

Large-Scale POPs

How Stacking Works

Before you install and configure a stack of access servers, you should understand the basic concepts described in the following sections, and how they work together in a large-scale dial-in solution:

•A Typical Multilink PPP Session

•Using Multichassis Multilink PPP

•Setting Up an Offload Server

•Using the Stack Group Bidding Protocol

•Using L2F

A Typical Multilink PPP Session

A basic multilink session is an ISDN connection between two routing devices, such as a Cisco 766 router and a Cisco AS5200 access server. Figure 54 shows a remote PC connecting to a Cisco 766 ISDN router, which in turn opens two B-channel connections at 128 kbps across an ISDN network. The Multilink PPP (MLP) session is brought up. The Cisco 766 router sends four packets across the network to the Cisco AS5200, which in turn reassembles the packets back into the correct order and sends them out the LAN port to the Internet.

Figure 54 A Typical Multilink PPP Session

Dial-in session #1

PC running

Windows 95

			Service provider network
		Hunt
		group
		555-1001
	3		1
	4	2	4	3	2	1
Cisco 766	ISDN network		Cisco AS5200			Internet access

S6752

Using Multichassis Multilink PPP

The dial solution becomes more complex when the scenario is scaled to include multiple multilink calls connecting across multiple chassis. Figure 55 shows a terminal adapter making a call in to the

Cisco AS5200, labeled #1. However, only one of the access server’s 48 B channels is available to accept the call. The other channels are busy with calls. As a result, one of the terminal adapter’s two B channels is redirected to device #2. At this point, a multilink multichassis session is shared between two Cisco AS5200s that belong to the same stack group. Packet fragments A and C go to device #1. Packet fragments B and D go to device #2.

Cisco IOS Dial Services Configuration Guide: Network Services

DNC-317