TTL is reduced by 1 with each hop. If a data packet has not yet
reached its destination when its TTL expires, it is discarded.
Twofish
Twofish is an encryption method (see Cipher). Twofish uses a fixed
block length of 128 bits. The key length is 128, 192 or 256 bits.
U-ADSL
Universal Asymmetric Digital Subscriber Line (UADSL) is a DSL
variant. It was developed as ANSI T1.413 and standardised as
G.992.2. U-ADSL enables different communication technologies to
be used in parallel, e. g. ISDN and POTS, and does not require a
splitter.
UDP
The User Datagram Protocol (UDP) is a connectionless protocol. It
works on the transport layer of the OSI model. With a connection-
less protocol, no control is integrated for delivering the packet. The
control must take place in the application layer. Conversely, UDP is
faster than connection-oriented protocols.
ULA
Unique Local Addresses (ULA) are IPv6 addresses that are not
routed. They can be used in private networks (e. g. a LAN). ULAs
begin with the prefix fd.
UMTS
The Universal Mobile Telecommunications System (UMTS), also
known as 3G, is a mobile communications standard with a specified
max. data transmission rate of 384 kbit/s and 21 Mbit/s in associ-
ation with HSPA+.
Unicast
With Unicast, data packets are transmitted from a sender to a single
recipient.
UP0
The UP0 connection is an interface for the ISDN Basic Rate Inter-
face, and links one ISDN terminal to the NTBA. The connection is
implemented via a two-wire circuit, and offers a greater range than
the S0 bus.
UPnP
Universal Plug and Play (UPnP) is used to control devices (audio
devices, routers, printers, etc.) from any manufacturer via an IP-
based network.
Upstream
The gateway forwards the data from its own network.
URL
A Uniform Resource Locator (URL) identifies a file's storage loca-
tion. Example: http://www.example.org/index.htp (Internet website)
UUS
With User to User Signalling (USS), text messages can be ex-
changed with other subscribers.
Glossary
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