Coresma NeMo CMTS, User Manual, Page: 83 / 93

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PPENDIX
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M u l t i p l e M A C M o d e m s
Preface
The new NeMo (NeMo-E_imp) can support up to 4 PCs (or any other IP devices e.g. IP
telephone etc.). The PCs and the modem are all connected to a HUB (The modem should
use a crossed cable). Communication between the PCs is done through the HUB with no
disruption to the communication to the outside world. The PCs can use a static IP or
DHCP. To the outside world it appears as if one computer has (up to) four IP numbers
over one Ethernet interface. The maximum number of devices attached to the modem is
set at the CMTS and sent to the modems in the UCD message.
Note:
Only IP protocols supported.
Multiple MAC Detailed Description
Modem Identification
The modem is identified using its Serial-MAC Address. This address is guaranteed to be
unique in the LAN using the Serial Allocation Mechanism. All the Ethernet frames
transmitted from the modem on the up stream carries this Serial-MAC as the Ethernet
Source Address (the original MAC address is replaced with the Serial-MAC). Every
modem has a burned in serial number. This number is to be used for authentication
instead of the PC MAC Address.
Modem Ethernet Operation Mode
The CMTS reports to all modems about the CMTS Gateway MAC Address.
The modem programs it’s Ethernet hardware filter to the Gateway MAC Address (Non
Promiscuous Mode). This prevents all internal traffic (between PCs on the HUB) from
going out to the RF network (actually the modem software will not receive this traffic at
all).