Performance Enhancement Proxy
A Performance Enhancement Proxy-Server or Performance Enhancing Proxy ( PEP ), in German about proxy server to increase performance , is a proxy server that accelerates TCP on the transport level when internet services are mediated via satellite connections.
TCP is designed for interference immunity and connection-oriented . The sending and size of the data packets depend on the recipient's reaction. It is unsuitable for switching over satellite radio links. The signal propagation times cause long latency times until there is feedback from the receiver. On the other hand, the line quality is so good that confirmation from the recipient is not necessary.
A PEP sends replies to the sender that could have come from the recipient. It intervenes in TCP and changes the headers accordingly. At the same time, it signals high performance quality in order to request larger data packets. The replies cause the sender to send further data packets even though the recipient has not responded. Together with the second server on the opposite side of the satellite, the PEP take over the data throughput over the radio link and ensure that the connection appears as a normal TCP / IP connection for the sender and receiver.
Encrypted data such as IPsec - VPN , which also extend to the TCP header, cannot accelerate a PEP. One way out is to limit the encryption to the user data and not to include the TCP / IP header ( SLE Selective Layer Encryption / Application Layer Security ). Another solution relocates the PEP in front of the VPN server, but the PEP-VPN connection could be exposed to attacks. The procedures are not standardized and are partially protected by patents.
For DVB-S protocols come Unidirectional Lightweight Encapsulation (ULE) and Generic Stream Encapsulation (GSE) is used to access the switch plane IP data packets to encapsulate and thereby reduce the data header.