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Glossary
B frame (bi-directional predicted frame)
A frame compressed by inter-frame prediction of
video image compression technology. Prediction
using anteroposterior frames is conducted.
Without both anteroposterior frames, this frame
image can't be played. The B frame referred from
adjacent B frames is particularly called the Br
frame.
CBR (constant bit rate)
Fixed bit rate. A system to maintain a certain bit
rate by dynamically changing the compression
ratio of image when compressing a video image.
Depending on the input image, the image quality
changes.
Gateway
A device to convert communication protocol
among multiple computer networks. A router is a
gateway which doesn't convert protocol.
GOP (group of pictures)
A group to control frames when compressing
video images. Utilized in image output of
fast-forward and fast-rewind. For example, if the
GOP size = 15, it processes 15 frames as a group.
One GOP is composed of at least one frame and
multiple B frames, and multiple P frames. For
example, if GOP is "IP", the I and P frames are
distributed alternately (do not confuse with "IP"
which means Internet protocol).
H.264/MPEG-4 AVC
One of the video image compression
specifications. Although H. 264 and MPEG-4 AVC
are technically the same, as the groups who
formulated them are different (although jointly
formulated), the two names are often put down
together. Baseline profiles are available for I and P
frames. Main and high profiles are available for I,
P and B frames. High profiles are, in addition to
the main profile, available for more advanced
compression algorithms (for that, a compression
process is loaded).
HTTP (hyper text transfer protocol)
Hyper text transfer protocol. Specified in RFC
2616. Normally port No. 80 is used. Used for
transmitting and receiving HTML and so on
between web server and web browser.
IPv4 (internet protocol version 4)
Internet Protocols, Edition 4. The IP addresses of
the IPv4 are expressed in values of 32 bits. At
present, this is most widely used but call has been
made regarding the problem of depletion of global
addresses (no problem at present if used locally).
IPv6(internet protocol version 6)
Internet Protocols, Edition 6. The IP addresses of
the IPv6 are expressed in values of 128 bits.
Possibility of convertibility from IPv4 IP address to
IPv6 IP address. For example, if the v4 address is
[192.168.1.100], the v6 address is expressed as
[::192.168.1.100]. To use the v6 address, all
network environments must be compatible with
IPv6, such as router, etc. At present, IPv6 is
spreading in use.
I frame (intra-coded frame)
Frame compressed without inter-frame prediction
in video image compression technology. The I
frame can play 1 image frame with this frame.
JPEG (joint photographic experts group)
One of the still image compression specifications.
In Motion JPEG, JPEG images are continuously
displayed like animation to make video images.
MAC address (media access control address)
Also known as the physical address. The address
length is 48 bits. The basis for network devices
around the world is the value of 48 bits. This is
assigned uniquely. The upper 24 bits are known
as the OUI (organization unique identifier). The
values that differ according to maker are assigned
by the IEEE and registered. The OUI of this
company is 00-05-2A.
Multicast
A system to send the same data simultaneously
to multiple specified receiving terminals. Specified
in RFC 1112. Compared to when sending to
multiple receiving terminals simultaneously with
Unicast, the load on the sending server and
Network can be eased. As it uses UDP, it is not
suitable for transmission which requires reliability.
A multicast IP address is assigned to a group of
receiving terminals and receiving terminals in the
same group are all assigned the same multicast
IP address (One receiving terminal has 2 types of
addresses, namely a normal IP address and a
multicast IP address). The multicast IPv4 address
is selected in a range of 224.0.0.0/4 (the upper 4
