ZyXEL Communications PLA-470 V2 - V3.0.5 Guía de instalación descargar pdf (Pagina 121)

The 48-bit address consists of the four following parts:

•

Individual/Group (I/G). The first bit indicates whether the address is an indi-

vidual (1) or group (0) address.

•

Universal/Local (U/L). The second bit indicates whether the address is a local

(1) or universal (0) address. If this is a local address, the following 46 bits are

locally defined.

•

Organizationally unique identifier. The number assigned by IEEE correspond-

ing to the 22 bits following the I/G and U/L bits.

•

Serial number. The last three bytes, i.e., 24 bits, correspond to the serial num-

ber generally defined by the manufacturer.

Hexadecimal Format

The hexadecimal writing, or base 16 numbering system, of the MAC address is generally

preferred to binary writing.

The MAC addresses consist of two distinct address families: individual addresses

addressing a single station on the network, and group addresses addressing several sta-

tions on the network. In the latter case, the MAC address represents a group of stations.

There are two types of group addresses:

•

Broadcast address. This address is associated with a group of stations consist-

ing of all the network stations. Information can be sent to all the network sta-

tions using a broadcast address. A broadcast address always has a 48-bit

format; all the bits are set to 1.

•

Multicast address. Like for the broadcast address, this address is associated

with a group of stations but in finite number. This type of address always

begins with the first 24 bits of the MAC 48-bit address equal to 01:00:5E (hex-

adecimal).

A MAC 802.3 frame like that used in HomePlug contains the two following

address fields:

•

DA (destination address). The address to which the frame or segment is trans-

mitted. The DA address can be an individual or group address.

•

SA (source address). The address that has transmitted the frame or the seg-

ment. The SA address is always an individual address.

Format of an Encrypted MAC Frame

The IEEE 802.3 standard enables the encryption of a frame to go across the power

line medium so that no user can decrypt the information.

In practice, as illustrated in Figure 5.17, a frame is only partially encrypted. The

frame is encrypted using the two following fields:

102 Frames

1 2 ... 116 117 118 119 120 121 122 123 124 125 126 ... 348 349

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ZyXEL Communications PLA-470 V2 - V3.0.5 Guía de instalación Pagina 121

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