RS-232 interface. Due to the low bandwidths involved it is extremely slow to browse the web with such a connection, but useful for sending email, Secure Shell data and using other low-bandwidth protocols. Since satellite phones tend to have omnidirectional antennas no alignment is required as long as there is a line of sight between the phone and the satellite. One-way receive, with terrestrial transmit One-way terrestrial return satellite Internet systems are used with conventional dial-up Internet access, with outbound (upstream) data traveling through a telephone modem, but downstream data sent via satellite at a higher rate. In the U.S., an FCC license is required for the uplink station only; no license is required for the users. Another type of 1-way satellite Internet system uses General Packet Radio Service (GPRS) for the back-channel. Using standard GPRS or Enhanced Data Rates for GSM Evolution (EDGE), costs are reduced for higher effective rates if the upload volume is very low, and also because this service is not per-time charged, but charged by volume uploaded. GPRS as return improves mobility when the service is provided by a satellite that transmits in the field of 100-200 kW. Using a 33 cm wide satellite dish, a notebook and a normal GPRS equipped GSM phone, users can get mobile satellite broadband. System components The transmitting station has two components, consisting of a high speed Internet connection to serve many customers at once, and the satellite uplink to broadcast requested data to the customers. The ISP's routers connect to proxy servers which can enforce quality of service (QoS) bandwidth limits and guarantees for each customer's traffic. Often, nonstandard IP stacks are used to address the latency and asymmetry problems of the satellite connection. As with one-way receive systems, data sent over the satellite link is generally also encrypted, as otherwise it would be accessible to anyone with a satellite receiver. Many IP-over-satellite implementations use paired proxy servers at both endpoints so that certain communications between clients and servers need not to accept the latency inherent in a satellite connection. For similar reasons, there exist special Virtual private network (VPN) implementations designed for use over satellite links because standard VPN software cannot handle the long packet travel times. Upload speeds are limited by the user's dial-up modem, while download speeds can be very fast compared to dial-up, using the modem only as the control channel for packet acknowledgement.