The EMM generates packets on the network (channel) in the following three instances:
❑When establishing and maintaining a remote login session (RCP or Telnet session).
❑When resolving a name tag (or IP Address) to a network address (TAG, ARP).
❑When the EMM is configured to support SNMP, and send Alert messages.
In all other cases, the EMM does not generate any network activity. Traffic statistics are collected by operating in promiscuous mode, that is, listening to each packet on the network. Management of the other modules in the concentrator is accomplished by utilizing a separate control bus on the ONline backplane.
Note that when the EMM is isolated from the backplane, it cannot generate, nor receive, any Ethernet traffic.
3Com Protocols
In order to support the remote login mechanism, 3Com has defined a thin protocol layer called RCP (Remote Character Protocol). This protocol uses the IEEE 802.2 link control layer protocol. This implies that remote login sessions can exist across bridges, but not across a router.
Also, 3Com has defined a support protocol similar to ARP that resolves names to addresses. This “tag resolution” occurs when a user initiates the REMOTE_LOGIN or PING command, using the EMM name.
The entire 3Com protocol packet is structured as follows:
802.3 Header
802.2 Header
3Com Protocol Header
Data
4 - 8 ONline Ethernet Management Module Installation and Operation Guide
