3Com 10014299 manual List of Configuration Tasks of X.25 Load Balancing

216CHAPTER 16: CONFIGURING LAPB AND X.25

Figure 65 Diagram of X.25 network load balancing

Hunt group HG1

		8888
		Remote
User terminal	X.25	DCE
		Server A
	packet		9999
User terminal	switching
	network	RouterAQuidwayA
User terminal		Server B	9999

As shown in the above figure, Server A and Server B concurrently provide subscribers with identical services. They are configured as a hunt group named hg1. Server A and Server B have the same address of 9999 and the hunt group address is 8888. Enable the function of destination address substitution on Router RouterA for changing calls connected to address 8888 to calls connected to address 9999. When a subscriber processes a service, the subscriber terminal will send a call to the destination address 8888. The calls from various terminals will be substituted on the router RouterA with the calls to 9999 and transmitted to Server A and Server B respectively. Thus load balancing is realized between Server A and Server B, and the pressure on a single server is decreased.

X.25 hunt group supports two types of call channel selection policies: round-robin mode and vc-number mode, but a hunt group can only utilize one type of channel selection policy.

■In round-robin mode, cyclic selection method is adopted to select the next interface or the XOT Tunnel for every call request. For example, as shown in Figure1-1, if hunt group hg1 adopts rotary mode, calls will be sent to Server A and Server B by turns.

■vc-number mode selects the interfaces with the free logical channels in a hunt group for every call request. For example, as shown in the above Figure1-1, if hunt group hg1 adopts vc-number mode, there will be 500 residual logical channels in the lines between Server A and DCE and 300 residual logical channels in the lines between Server B and DCE. Thus all the first 200 calls will be sent to Server A, and the calls following the first 200 ones will be sent to Server A and Server B by turns.

X.25 hunt group supports synchronous serial interfaces and XOT Tunnels. It can indiscriminately select the available lines between synchronous serial interfaces and XOT Tunnels. But XOT Tunnels cannot calculate the number of logical channels, therefore it cannot be added into a hunt group adopting vc-number selection policy.

List of Configuration Tasks of X.25 Load Balancing

The load balancing of X.25 networks is configured on DCE equipment. The 3Com Router is generally utilized as a DTE equipment in X.25 networks. If load balancing is provided by ISPs on packet switching exchanges, routers need no special configuration. The specific configuration procedure can be seen in the previous chapters. If the 3Com Router is used as an X.25 switching exchange (it serves as a