The PDU used for ETH-BN information is called the Bandwidth Notification Message (BNM).
The BNM PDU format consists of the following fields:
MEG level – carries the MEG level of the client MEP (0 to 7); this field can be any value
Version – current version is 0
OpCode – value for this PDU type is GMN (32)
Flags – contains one information element:
period – bits 3 to 1 indicate how often BN messages are transmitted; currently, the only valid values are 100 (1 frame/s), 101 (1 frame/10 s), and 110 (1 frame/min)
TLV Offset – set to 13
Sub-OpCode – value for this PDU type is BNM (1)
Nominal Bandwidth – the nominal full bandwidth of the link, in Mb/s; this information is ignored by the 7705 SAR
Current Bandwidth – the current bandwidth of the link, in Mb/s
Port ID – a non-zero unique identifier for the port associated with the ETH-BN information, or zero if not used; this information is ignored by the 7705 SAR
End TLV – all zeros octet value
Typical behavior for ETH-BN is that if no BNM frames are received within an interval of 3.5 times the BNM transmission period indicated in the last BNM frame received, the MEP signals to the management system that it no longer has any bandwidth information (for example, because the full bandwidth has been restored). For the 7705 SAR implementation, no action is taken if no BNM frame arrives within 3.5 periods.
Upon startup or restart of the system, the configured egress rate is used until a BNM arrives on the port with a new bandwidth request from the ETH-BN server MEP.
Event logs are generated each time the egress bandwidth is changed based on reception of a BNM. If a BNM is received that does not result in a bandwidth change, no event log is generated.
BN messages are transmitted with a source MAC address that cannot be a multicast address or have a value of 0. The destination MAC address can be a Class 1 multicast address (that is, 01-80-C2-00-0x) or the MAC address of the configured port. If these conditions are not satisfied, the message is discarded. The packets are rate-limited to the CSM as are all OAM packets.
BN messages with zero, one, or two VLAN tags are supported.