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a variety of NATs and application programs. However, STUN does not allow
incoming UDP packets through symmetric NATs and cannot be used to obtain
an Internet Protocol address (IP address) to communicate with a peer behind the
same NAT.
Switch
A small device for connecting one or more computers to other computers,
networked devices, or to other networks. Compared to a hub (which is also a
connecting type of device), the switch is more intelligent. It is capable of pick-
ing up on traffic patterns and learning where particular addresses are. In this way,
it sends traffic only where it needs to go rather than to every port, making the
network significantly faster. Switches work at the data link layer (layer 2) of the
OSI model.
T1 (also called channelized T1)
A digital carrier modulation method in which a T1 line is divided into 24 chan-
nels, each having a maximum data speed of 64 thousand bits per second (Kbps),
and each capable of supporting a unique application that can run concurrently
with, but independently of, other applications on different channels.
T.38 [RFC 3362]
A protocol that describes how to send a fax over a computer data network. T.38
allows a fax to be converted into an image and then sent to other T.38 fax devic-
es, where it is converted back to an analog fax signal. T.38 is supported by most
VoIP gateways and ATAs.
TCP (Transmission Control Protocol/Internet Protocol) [793]
The communication protocol for the Internet. TCP/IP defines the rules that
computers must follow to communicate with each other over the Internet. It can
also be used as a communications protocol in a private network (either an in-
tranet or an extranet).
TFTP (Trivial File Transfer Protocol) [RFC 1350]
A simple, less-capable form of the File Transfer Protocol (FTP). TFTP uses the
User Datagram Protocol (UDP) and provides no security features, so it is typi-
cally used where user authentication and directory visibility are not required (e.g.,
by servers to boot diskless workstations, X-terminals, and routers).
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