VPDN uses the following tunneling protocols:
- Point-to-Point Tunneling Protocol (PPTP)
- Layer 2 Forwarding (L2F)
- Layer 2 Tunneling Protocol (L2TP)
The AR supports L2TP, but does not support PPTP or L2F. However, it can forward PPTP and L2F packets.
L2TP has advantages of both PPTP and L2F and is widely used. It is used when a single or a few terminals remotely connect to an intranet through a public network.
When the radio chip sends data in OFDM modulation mode, it divides a frame into different data blocks to send. To ensure data transmission reliability, the guard interval (GI) is used between the data blocks to ensure that the receive end correctly parses each data block. During spatial propagation, the delay will occur on wireless signals at the receive end because of multipath. If subsequent data blocks are transmitted fast, these data blocks will interfere with the original data block. The GI is used to avoid such interference. The common GI is 800 ns, whereas the short GI defined in the 802.11n standard is 400 ns, which increases the physical connection rate by 11%.
