A. Glossary
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Subnet Mask.
A number that, when applied to an IP address, can identify the subnetwork where
the address resides. For example, within a class B network, a subnet mask of 255.255.255.0
specifies that the first two portions of the decimal dot format are the network number, while the
third portion is a subnet number. The fourth portion is the host number. A subnet mask of
255.255.0.0 species a class B network that does not have a subnet.
Switch.
A network device that selects a path or circuit for sending a unit of data to its next
destination. A switch may also include the function of the router. A switch is generally a simpler
and faster mechanism than a router, which requires knowledge about the network and how to
determine the route. A switch is usually associated with layer 2 of the OSI communications
model.
Transmission Control Protocol (TCP).
A set of communications protocols that, when used with
Internet Protocol (IP), support peer-to-peer connectivity functions for both local and wide area
networks. TCP/IP is a communications protocol which allows computers with different operating
systems to communicate with each other and controls how data is transferred between
computers on the Internet.While IP handles the actual delivery of data, TCP tracks the data
packets into which a message is divided for efficient routing through the internet. The ZIP 4x4
phone supports TCP as described by RFC 793.
Trivial File Transfer Protocol (TFTP).
An Internet software utility for transferring files that, while
simpler to use than FTP, provides fewer features. TFTP is used where user authentication and
directory visibility are not required. The ZIP 4x4 phone uses TFTP to download configuration files
and software updates from the TFTP Server, as described in RFC 1350.
Trunk Port.
A device that allows a switch to bundle traffic from several VLANs through a single
physical port, sorting the various packets by the VLAN identifier (VID) in their frame headers.
Trusted Network.
Networks inside your network security perimeter. Only known and approved
sources are allowed access to a trusted network.
Tunnelling.
The transmission of data intended for use only within a private network through a
public network in such a way that the routing nodes in the public network are unaware that the
transmission is part of a private network. Tunneling is generally done by encapsulating the
private network data and protocol information within the public network transmission units so
that the private network protocol information appears to the public network as data. Tunneling
allows the use of the Internet, which is a public network, to convey data on behalf of a private
network.
Universal Resource Locator (URL).
A standard method of specifying the location of an internet
resource. Also referred to as a location or address, URLs specify the location of files on servers. A
general URL has the syntax protocol://address. For example, http://www.Zed-3.com/index.htm
specifies that the protocol is http and the address is www.Zed-3.com/ index.htm.
Unshielded Twisted Pair (UTP).
Also known as 10BaseT. This is the standard cabling used for
telephone lines. It is also used for Ethernet connections.
Untrusted Network.
Networks that are outside of your security perimeter. Private and shared
networks over which you have no control over the administration or security policies. Firewalls
deal with the problem of communicating with these networks while protecting your trusted
network.
User Agent.
A SIP logical entity that can act as both a user agent client (UAC) and user agent server
(UAS). The role of UAC and UAS, as well as proxy and redirect servers, are defined on a
transaction-by-transaction basis. For example, the user agent initiating a call acts as a UAC when