Cisco Systems DNC-305 manual Setting Up an Offload Server, DNC-318

Telco and ISP Dial Scenarios and Configurations

Large-Scale POPs

Because device #1 is the first access server to receive a packet and establish a link, this access server creates a virtual interface and becomes the bundle master. The bundle master takes ownership of the MLP session with the remote device. The Multichassis Multilink PPP (MMP) protocol forwards the second link from device #2 to the bundlemaster, which in turn bundles the two B channels together and provides 128 kbps to the end user. Layer 2 Forwarding (L2F) is the mechanism that device #2 uses to forward all packet fragments received from the terminal adapter to device #1. In this way, all packets and calls virtually appear to terminate at device #1.

Figure 55 A Stack Group of Access Servers Using MMP Without an Offload Processor

Stack of two Cisco AS5200 access servers used in one service provider network

		Hunt
		group
		555-1001
Dial-in session #2			#1
	Terminal	C	A
		ISDN network
PC	adapter	D
		Analog network	#2
			B
		Modem
		PC

D C B A

Remote security

server

Internet access

S6751

Setting Up an Offload Server

Because MMP is a processor-intensive application, you might need to offload the processing or segmentation and reassembly from the Cisco AS5200 access servers to a router with a higher CPU, such as the Cisco 4700-M or Cisco 7206. We recommend that you include an offload server for dial-in solutions that support more than 50 percent ISDN calls or more than ten multilink sessions per Cisco AS5200 access server. (Refer to Figure 56.)

Cisco IOS Dial Services Configuration Guide: Network Services

DNC-318