HP 600 Series, Services And Applications

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Selecting Sync Pass-Through Station
Addresses
To configure sync pass-through, a station address must be selected for each
sync pass-through port. Care must be taken to avoid selecting a station
address already in use on the extended LAN. Fortunately, the Ethernet/IEEE
802.3 standards provide a handy mechanism to accomplish this. Figure 4
shows the structure of a station address.
48-BIT ADDRESS FORMAT
I/G U/L 46-BIT ADDRESS
I/G 0 INDIVIDUAL ADDRESS
I/G 1 GROUP ADDRESS
U/L 0 GLOBALLY ADMINISTERED ADDRESS
U/L 1 LOCALLY ADMINISTERED ADDRESS
Figure 4. Station Address Structure
Recall that station addresses are 48 bits in length. They are usually presented
in a form such as XX-xx-xx-xx-xx-xx. Each “xx” indicates a single byte repre-
sented by two hexadecimal digits. “XX” indicates the most significant byte of
the station address. The least significant bit of the most significant byte is
the I/G bit. This specifies whether the address is an individual (I) or group
(G) address. The I/G bit is the first address bit transmitted (although it is not
the most significant bit), as shown in figure 4. The address selected for sync
pass-through must be an individual address (I/G bit = 0).
The next bit (U/L bit) specifies whether the address is globally administered
(U for universal) or locally (L) administered. This is the “handy mechanism”
referred to above. Computer manufacturers always ship LAN networking
products with globally administered (unique) addresses. The station address
selected for use with sync pass-through should, therefore, be locally adminis-
tered (U/L bit = 1). This should avoid any conflicts with any installed LAN
equipment. The value of the most significant byte of the station address is,
therefore, 02 hex (assuming I/G = 0, U/L = 1, all other bits = 0). Using the
value 02 hex as the most-significant byte of the station address will avoid
duplicating a station address used elsewhere in an extended LAN. 02-11-22-
33-44-55 is an example of an individual, locally administered LAN address.
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Using Synchronous Pass-Through to Consolidate Synchronous Traffic
Selecting Sync Pass-Through Station Addresses
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