The Ethernet Bandwidth Notification (ETH-BN) function, as defined in ITU-T Rec. G.8013/Y.1731, is used by a server MEP to signal changes in link bandwidth to a client MEP.
One of the best applications of this functionality is for point-to-point microwave radios. When a microwave radio uses adaptive modulation, the capacity of the radio can change based on the condition of the microwave link. For example, in adverse weather conditions that cause link degradation, the radio can change its modulation scheme to a more robust one (which will reduce the link bandwidth) in order to continue transmitting.
This change in bandwidth is communicated from the server MEP on the radio, using ETH-BNM (Ethernet Bandwidth Notification Message), to the client MEP on the connected router. The router responds to this information by adjusting the rate of traffic being sent to the radio. The server MEP continues to transmit periodic frames with ETH-BN information with the currently available bandwidth. When full bandwidth is restored, the ETH-BNM will start indicating the full bandwidth.
When the 7705 SAR is interoperating with 9500 MPR-e radios, ETH-BN functionality is supported with 9500 MPR-e radios in standalone mode or in MWA mode.
The 7705 SAR supports the client side of ETH-BN, receiving and acting on the ETH-BN information sent by the server MEP.
ETH-BN is supported on Ethernet ports on the following adapter cards, modules, and platforms:
8-port Gigabit Ethernet Adapter card
10-port 1GigE/1-port 10GigE X-Adapter card
Packet Microwave Adapter card
6-port Ethernet 10Gbps Adapter card
2-port 10GigE (Ethernet) Adapter card (v-port)
2-port 10GigE (Ethernet) module (v-port)
6-port SAR-M Ethernet module
all fixed platforms, with the exception of Fast Ethernet ports on the 7705 SAR-A (ports 9 to 12)
The ports can be configured for network, access, or hybrid mode. When ETH-BN is enabled on a port with the egress-rate sub-rate allow-eth-bn-rate-changes command, the egress rate, which was configured as a fixed bandwidth, can be dynamically changed based on the available bandwidth indicated by the ETH-BN server.
The maximum egress rate that the port can be set to is the native port rate (for example, 1 Gb/s), and the minimum egress rate is 1 kb/s. If a rate request is outside that range, including 0, it cannot be implemented, and the egress rate is set as close as possible to the requested rate. Any request for a change less than 1% is ignored.
To reduce the number of bandwidth changes (each change incurs a small data hit), a hold timer can be configured. The range is 1 to 600 s with a default of 5 s. Any ETH-BN message received before the hold timer expires, after the last bandwidth change, is ignored.
The bandwidth indicated by the ETH-BN server includes the FCS; therefore, the include-fcs option must also be selected in the egress-rate command or the bandwidth will not match the intended rate.
For information on the egress-rate command, refer to the ‟Ethernet Commands” section in the 7705 SAR Interface Configuration Guide, ‟Configuration Command Reference” chapter.