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Glossary of Terms
SMTP (Simple Mail Transfer Protocol) - SMTP is used for
sending and receiving e-mail. However, as it is ‘simple,’ it is
limited in its ability to queue messages at the receiving end,
and is usually used with one of two other protocols, POP3 or
IMAP. These other protocols allow the user to save messages in
a server mailbox and download them periodically from the
server.
SMTP authentication is an extension of SMTP, whereby the
client is required to log into the mail server before or during the
sending of email. It can be used to allow legitimate users to
send email while denying the service to unauthorized users,
such as spammers.
SNMP (Simple Network Management Protocol) - SNMP
forms part of the Internet Protocol suite, as defined by the
Internet Engineering Task Force. The protocol can support
monitoring of network-attached devices for any conditions
that warrant administrative attention.
Sockets - Sockets are a method for communication between a
client program and a server program over a network. A socket is
defined as ‘the endpoint in a connection.’ Sockets are created
and used with a set of programming requests or ‘function calls’
sometimes called the sockets application programming
interface (API).
SSL/TSL (Secure Socket Layer/Transport Layer Security)
These two protocols (SSL is succeeded by TSL) are cryptographic
protocols that provide secure communication on a network. SSL
is commonly used over HTTP to form HTTPS, as used e.g. on the
Internet for electronic financial transactions. SSL uses public
key certificates to verify the identity of the server.
Subnet/subnet mask - A subnet is an identifiably separate
part of an organization's network. Typically, a subnet may
represent all the machines at one geographic location, in one
building, or on the same local area network (LAN). Having an
organization's network divided into subnets allows it to be
connected to the Internet with a single shared network address.
The subnet mask is the part of the IP address that tells a
network router how to find the subnet that the data packet
should be delivered to. Using a subnet mask saves the router
having to handle the entire 32-bit IP address; it simply looks at
the bits selected by the mask.
SVGA - Super VGA, is a set of graphics standards designed to
offer greater resolution than VGA. SVGA supports 800 x 600
resolution, or 480,000 pixels.
Switch - A switch is a network device that connects network
segments together, and which selects a path for sending a unit
of data to its next destination. In general, a switch is a simpler
and faster mechanism than a router, which requires knowledge
about the network and how to determine the route. Some
switches include the router function. See also Router.
TCP (Transmission Control Protocol) - TCP is used along with
the Internet Protocol (IP) to transmit data as packets between
computers over the network. While IP takes care of the actual
packet delivery, TCP keeps track of the individual packets that
the communication (e.g. requested a web page file) is divided
into, and, when all packets have arrived at their destination, it
reassembles them to re-form the complete file.
TCP is a connection-oriented protocol, which means that a
connection is established between the two end-points and is
maintained until the data has been successfully exchanged
between the communicating applications.
Telnet - Telnet is a simple method with which to access
another network device, e.g. a computer. The HTTP protocol and
the FTP protocols allow you to request specific files from
remote computers, but do not allow you logon as a user of that
computer. With Telnet, you log on as a regular user with
whatever privileges you may have been granted for specific
applications and data residing on that computer.
UDP (User Datagram Protocol) - UDP is a communications
protocol that offers limited service for exchanging data in a
network that uses the Internet Protocol (IP). UDP is an
alternative to the Transmission Control Protocol (TCP). The
advantage of UDP is that it is not required to deliver all data
and may drop network packets when there is e.g. network
congestion. This is suitable for live video, as there is no point in
re-transmitting old information that will not be displayed
anyway.
Unicast - Communication between a single sender and a single
receiver over a network. A new connection is established for
each new user.
URL (Uniform Resource Locator) - An "address" on the
network.
Varifocal lens - A varifocal lens provides a wide range of focal
lengths, as opposed to a lens with a fixed focal length, which
only provides one.
VGA - Video Graphics Array is a graphics display system for
PCs developed by IBM. In graphics mode, the resolution is
either 640 by 480 (with 16 colors) or 320 by 200 (with 256
colors).
VPN (Virtual Private Network) - This creates a secure
"tunnel" between the points within the VPN. Only devices with
the correct "key" will be able to work within the VPN. The VPN
network can be within a company LAN (Local Area Network),
but different sites can also be connected over the Internet in a
secure way. One common use for VPN is for connecting a
remote computer to the corporate network, via e.g. a direct
phone line or via the Internet.
VOP (Video Object Plane) - A VOP is an image frame in an
H.264 video stream. There are several types of VOP:
- An I-VOP is complete image frame.
- A P-VOP codes the differences between images, as long as it
is more efficient to do so. Otherwise it codes the whole image,
which may also be a completely new image.
WAN (Wide-Area-Network) - Similar to a LAN, but on a
larger geographical scale.
W-LAN (Wireless LAN) - A wireless LAN is a wireless local
area network that uses radio waves as its carrier: where the
network connections for end-users are wireless. The main
network structure usually uses cables.
Web server - A web server is a program, which allows web
browsers to retrieve files from computers connected to the
Internet. The web server listens for requests from web browsers
and upon receiving a request for a file sends it back to the