5. Intrinsic limitations of SSL VPNs

SSL VPNs can provide services equivalent to IPsec using a fat client. However, the SSL protocol, based on TCP, cannot lose packets. At first glance, this may appear to be an advantage, but some real-time applications such as voice are designed to be able to lose packets in order to limit latency (network transmission delay) and jitter (latency variation). SSL therefore poses quality of service problems for certain applications.

To circumvent this problem, some gateways incorporate a mechanism that attempts to set up an IPsec tunnel and then falls back on an SSL tunnel in the event of failure. Another alternative could be the DTLS protocol , which is...