包转发 Second-level Network Dispatcher (cluster 1) Server 1 (address 1) First-level Second-level User Client Network Dispatcher4LNetwork Dispatcher_7 (IP-SVA) Step 1: Document request (IP-SVA) Server N Step 2: Web-dluster selection Second-level (address N) Step 3: Packet rewriting (IP-SVA->cluster k) Network Dispatcher step 4: Packet routing (cluster m) Step 5: Web Step 6: Packet rewriting (cluster K->IP-SVA) Step 8: Document response(IP-SvA)包转发