3Com 10014299 manual Configure X.25

Configure X.25 215

which guarantees no occurrence of link overload when an address is accessed by a large number of subscribers.

X.25 load balancing is provided by DCEs. In order to implement the load balancing in X.25 networks, a group of DTE/DCE interfaces (synchronous serial interfaces or XOT Tunnels) need to be configured at the remote DCE on the network as a hunt group. And it is necessary to allocate an X.121 address to such hunt group. When other equipment in the network accesses the DTE inside the hunt group, they need to call the hunt group address. After receiving the call request packets, the remote DCE will, according to diverse channel selection policies (round-robin or vc-number), select a line in the hunt group and send the incoming call packets. Different calls will be allocated to the lines in the hunt group, thus achieving load balancing.

It should be noted that X.25 hunt group can dynamically select different transmission lines only in the process of the establishment of virtual circuit call. Once the whole virtual circuit is established and enters into the stage of data transmission, hunt group will be ineffective and data transmission will be processed in accordance with the normal virtual circuit. After being established, PVC stays at the data transmission stage without the process of call establishment and call deletion, therefore X.25 load balancing is ineffective on PVC and functions only on SVC.

Within a single X.25 hunt group, all DTEs hold identical status and have the same X.121 addresses. The DTEs in a hunt group can call other DTEs outside the hunt group in a normal mode. When equipment outside the hunt group access the hunt group, they cannot know which equipment they will access, because the line selection is controlled by the DCEs configured with hunt group.

DTE addresses in a hunt group may be identical or different to the hunt group addresses. X.25 hunt group supports the substitutions of source address and destination address. The function of destination address substitution enables us to hide the addresses of DTEs inside the hunt group, thus external DTEs only know the hunt group address, which enforces the security of the internal network of hunt group. The function of source address substitution can hide the addresses of DTEs outside a hunt group, therefore internal DTEs can only know the substituted source address instead of the source address a call is connected to, which protects subscribers' privacy.