Glossary-4
Media Access Control
Address (MAC)
The hardware address usually “burned in” on a ROM for any device connected
to the network. Ethernet cards in the subscriber PC have a MAC address. The
cable modem and the network interface card on a CMTS have MAC addresses.
The MAC address is used by the link layer protocol to forward packets “one
hop at a time” between the host and the first router and between the first router
and the next router and so on through the network until the packet arrives at its
final destination. In contrast, an IP address is a “source” to “destination”
address. It does not include all the intermediate hops.
Media Access Control
(MAC) sublayer
The part of the data link layer that supports topology-dependent functions and
uses the services of the physical layer to provide services to the logical link
control (LLC) sublayer.
MHz
Mega Hertz. A measure of radio frequency - millions of cycles per second.
modem registration
The process by which a cable modem makes itself known to a CMTS. The
modem configuration and authorization are verified and the COS is negotiated.
network driver
A file packaged with the Ethernet card that connects the card to the PC
communications software.
network layer
Layer 3 in the Open System Interconnection (OSI) architecture. This layer
provides services to establish a path between open systems.
packet data
Each IP datagram consists of one or more packets. A packet has a header that
contains the source address and a destination address for routing (and other
housekeeping information). Since both the header and the data area can vary in
length, an IP datagram itself is variable in length.
PING
A program that tests host reachability by using the Internet Control Message
Protocol (ICMP) echo request and waiting for a reply. It is initiated and
verified from an IP device.
physical layer (PHY)
Layer 1 in the Open System Interconnection (OSI) architecture. It is the layer
that provides services to transmit bits or groups of bits over a transmission link
between open systems. It includes the electrical, mechanical, and handshaking
procedures.
Physical Media
Dependent (PMD)
Sublayer
A sublayer of the physical layer that transmits bits or groups of bits over
particular types of transmission links between open systems. It entails the
electrical, mechanical, and handshaking procedures.
piggybacking
A process that occurs when a modem transmits data and requests additional
bandwidth at the same time.
Quadrature Amplitude
Modulation (QAM)
Modulation scheme that uses both amplitude and phase modulation to encode
multiple bits of data in one signaling element, thus achieving higher data
transfer rates than just amplitude or phase modulation alone.
However, the signal is more prone to errors caused by noise and so requires a
better quality transmission circuit than QPSK (lower noise and therefore higher
Carrier to Noise Ratio (CNR) value).
Summary of Contents for AL 200
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