Macroblock
The fundamental unit used during image compression.
Mailbox
Allows contacts to have individual mailboxes (accessible by a PIN) which can receive individual messages (fax or voice, dependent on product).
MAN
Metropolitan Area Network. A data communication network that connects local area networks located in the same urban zone.
MTU
Maximum Transfer Unit. The largest size packet or frame that can be sent in a packet- or frame-based network such as the Internet. If the MTU size is too large, the packet may encounter a router that can't handle the packet, resulting in retransmission. Too small an MTU size means relatively more header overhead and more acknowledgements that have to be sent and handled.
MC
Multipoint Controller. An H.323 entity on a network which provides for the control of three or more terminals participating in a multipoint conference. Often contained within an MCU.
MCU
Multipoint Control Unit. Allows three or more endpoints to engage in a multipoint conference call. Consists of an MC and an optional MP.
MEGACO
MEdia GAteway COntrol. IP telephony protocol derived from MGCP.
Metalfile
A single computer file that contains more than one kind of information. For example, text and graphics.
MGCP
Media Gateway Control Protocol. IP telephony protocol defined by the IETF.
Micropayments
Allow you to purchase low-cost, pay-per-use services over the Internet.
MIMD
Multiple Instruction Multiple Data. Computer architecture using multiple processors.
MJPEG
Motion JPEG. See MPEG.
MMI
Man Machine Interface. See GUI.
MMS
Mail Management System or Messaging Management System or Multimedia Messaging Service (Nokia).
Mobile Node
A node that can change its point of attachment from one link to another, while still being reachable via its home address.
Modem
MOdulator DEModulator. A device which converts digital signals to a form suitable for transmission over an analogue network.
Modem speed
The maximum modem speed expressed in kbps.
Motion estimation / compensation
Method used by video compression algorithms to predict the future positions of objects in an image by examining the data contained in previous video frames. Used in H.26x codecs.
MP
Multipoint Processor. H.323 entity on a network that performs centralised processing of audio, video, and/or data streams in a multipoint conference. The MP allows mixing, switching, or other processing of media streams under the control of an MC.
MPEG
Motion Picture Experts Group. Defines the MPEG-x standards for compressed video transmission.
MPEG-1
DCT based lossy compression intended for broadcast quality applications.
MPEG-2
Evolution of MPEG-1 also intended for broadcast quality applications, though not as good at MPEG-1. Allows finer control over image quality then MPEG-1.
MPEG-3
Intended as an ultra-high quality compression method but was abandoned during development.
MPEG-4
All things to all people compression mechanism that is expected to replace MPEG-2 for broadcast quality applications as it is approximately twice as efficient. Also suitable for streaming and multimedia applications.
MSN
Multiple Subscriber Number. Allows several pieces of equipment to share a single ISDN line. The line is assigned a block of numbers, and each piece of equipment connected to it is allocated one or more of these numbers. When an incoming call arrives on the line, only the equipment whose allocated number matches the number that was dialled will respond.
Multimedia
Generic term for a system which utilises a variety of audio and visual resources.
Multiplexor
It is a device that merges several low-speed transmissions into one high-speed transmission and vice versa.
MBCP+
Multi-Protocol Border Gateway Protocol Plus. MBGP+ enhances BGP to support more types of advertised routes, including IPv6 routes.
Music on hold
Callers are entertained with music whilst being put on hold, reassuring them that they have not been cut off.
MVIP
Multi-Vendor Integration Protocol. A bus and switching protocol allowing digital voice and video data to be multiplexed and transmitted between cards in a PC.
