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G
Gateway
Gateway is used in two different ways within networking. A gateway is a
device that routes datagrams and/or packets from one network to another.
For instance an Internet gateway is a router which routes packets to and
from the Internet and a private network. The term gateway is also
synonymous with protocol converter. A protocol converter is a device that
converts information from one networking architecture (such as TCP/IP) to
another (such as SNA). An example of a gateway is an IBM 3172 LAN gateway
used to convert Token Ring and Ethernet LAN frames to 3270 data streams.
Geostationary
Satellite
communications systems transmit signals from earth stations to satellites
located in space. Antennas located on the earth are pointed at the
geostationary satellite (also called geosynchronous) and microwave signals
are sent up to the satellite (uplink) where the satellite repeats the
signal and sends it down (downlink) to a remote receiving antenna. There
are three frequency ranges that satellite systems use, C band (4GHz
downlink, 6GHz uplink), KU band (11GHz downlink, 14GHz uplink) and KA band
(20GHz downlink, 30GHz uplink).
Geosynchronous
See geostationary
above.
Gigabits
Gigabits means
1,000,000,000 bits or one thousand million bits or one billion bits. Giga
is the prefix meaning one billion. A gigabyte would be one thousand million
bytes or 8,000,000,000 bits.
GRE
The Generic Routing Encapsulation (GRE) protocol
provides a mechanism for encapsulating arbitrary packets within an
arbitrary transport protocol. In the most general case, a system has a
packet that needs to be encapsulated and routed (the payload packet). The
payload is first encapsulated in a GRE packet, which possibly also includes
a route. The resulting GRE packet is then encapsulated in some other
protocol and forwarded (the delivery protocol). GRE is also used with IP,
using IP as the delivery protocol or the payload protocol. The GRE header
used in PPTP is enhanced slightly from that specified in the current GRE
protocol specification.
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