This feature is only supported on the 7210 SAS-Mxp, 7210 SAS-R6, and 7210 SAS-R12.
The Ethernet Bandwidth Notification (ETH-BN) function is used by a server MEP to signal link bandwidth changes to a client MEP.
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) to continue transmitting.
This change in bandwidth is communicated from the server MEP on the radio, using an Ethernet Bandwidth Notification Message (ETH-BNM), to the client MEP on the connected router. The server MEP transmits periodic frames with ETH-BN information, including the interval, the nominal and currently available bandwidth. A port MEP with the ETH-BN feature enabled will process the information contained in the CFM PDU and appropriately adjust the rate of traffic sent to the radio.
A port MEP that is not a LAG member port supports the client side reception and processing of the ETH-BN CFM PDU sent by the server MEP. By default, processing is disabled. The config>port>ethernet>eth-cfm>mep eth-bn>receive CLI command sets the ETH-BN processing state on the port MEP. A port MEP supports untagged packet processing of ETH-CFM PDUs at domain levels 0 and 1 only. The port client MEP sends the ETH-BN rate information received to be applied to the port egress rate in a QoS update. A pacing mechanism limits the number of QoS updates sent. The config>port>ethernet>eth-cfm>mep>eth-bn>rx-update-pacing CLI command allows the updates to be paced using a configurable range of 1 to 600 seconds (the default is 5 seconds). The pacing timer begins to count down following the most recent QoS update sent to the system for processing. When the timer expires, the most recent update that arrived from the server MEP is compared to the most recent value sent for system processing. If the value of the current bandwidth is different from the previously processed value, the update is sent and the process begins again. Updates with a different current bandwidth that arrive when the pacing timer has already expired are not subject to a timer delay. See the 7210 SAS-Mxp, R6, R12, S, Sx, T Interface Configuration Guide for more information about these CLI commands.
A complimentary QoS configuration is required to allow the system to process current bandwidth updates from the CFM engine. The config>port>ethernet>eth-bn-egress-rate-changes CLI command is required to enable the QoS function to update the port egress rates based on the current available bandwidth updates from the CFM engine. By default, the function is disabled.
Both the CFM and QoS functions must be enabled for the changes in current bandwidth to dynamically update the egress rate.
When the MEP enters a state that prevents it from receiving the ETH-BNM, the current bandwidth last sent for processing is cleared and the egress rate reverts to the configured rate. Under these conditions, the last update cannot be guaranteed as current. Explicit notification is required to dynamically update the port egress rate. The following types of conditions lead to ambiguity:
administrative MEP shut down
port admin down
port link down
eth-bn no receive transitioning the ETH-BN function to disable
If the eth-bn-egress-rate-changes command is disabled using the no option, CFM continues to send updates, but the updates are held without affecting the port egress rate.
The ports supporting ETH-BN MEPs can be configured for the network, access, hybrid, and access-uplink modes. When ETH-BN is enabled on a port MEP and the config>port>ethernet>eth-cfm>mep>eth-bn>receive and the QoS config>port>ethernet>eth-bn-egress-rate-changes contexts are configured, the egress rate is dynamically changed based on the current available bandwidth indicated by the ETH-BN server.
For SAPs configured on an access port or hybrid port, changes in port bandwidth on reception of ETH-BNM messages will result in changes to the port egress rate, but the SAP egress aggregate shaper rate and queue egress shaper rate provisioned by the user are unchanged, which may result in an oversubscription of the committed bandwidth. Consequently, Nokia recommends that the user should change the SAP egress aggregate shaper rate and queue egress shaper rate for all SAPs configured on the port from an external management station after egress rate changes are detected on the port.
The port egress rate is capped by the minimum of the configured egress-rate, and the maximum port rate. The minimum egress rate using ETH-BN is 1024 kb/s. If a current bandwidth of zero is received, it does not affect the egress port rate and the previously processed current bandwidth will continue to be used.
The client MEP requires explicit notification of changes to update the port egress rate. The system does not timeout any previously processed current bandwidth rates using a timeout condition. The specification does allow a timeout of the current bandwidth if a frame has not been received in 3.5 times the ETH-BNM interval. However, the implicit approach can lead to misrepresented conditions and has not been implemented.
When you start or restart the system, the configured egress rate is used until an ETH-BNM arrives on the port with a new bandwidth request from the ETH-BN server MEP.
An event log is generated each time the egress rate 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.
The destination MAC address can be a Class 1 multicast MAC address (that is, 01-80-C2-00-0x) or the MAC address of the port MEP configured. Standard CFM validation and identification must be successful to process CFM PDUs.
For information about the eth-bn-egress-rate-changes command, see the 7210 SAS-Mxp, R6, R12, S, Sx, T Interface Configuration Guide.
The Bandwidth Notification Message (BNM) PDU used for ETH-BN information is a sub-OpCode within the Ethernet Generic Notification Message (ETH-GNM).
The following table shows the BNM PDU format fields.
| Label | Description |
|---|---|
MEG Level |
Carries the MEG level of the client MEP (0 to 7). This field must be set to either 0 or 1 to be recognized as a port MEP. |
Version |
The current version is 0 |
OpCode |
The value for this PDU type is GNM (32) |
Flags |
Contains one information element: Period (3 bits), which indicates how often ETH-BN messages are transmitted by the server MEP. The following are the valid values:
|
TLV Offset |
This value is set to 13 |
Sub-OpCode |
The value for this PDU type is BNM (1) |
Nominal Bandwidth |
The nominal full bandwidth of the link, in Mb/s. This information is reported in the display but not used to influence QoS egress rates. |
Current Bandwidth |
The current bandwidth of the link in Mb/s. The value is used to influence the egress rate. |
Port ID |
A non-zero unique identifier for the port associated with the ETH-BN information, or zero if not used. This information is reported in the display, but is not used to influence QoS egress rates. |
End TLV |
An all zeros octet value On the 7210 SAS, port-level MEPs with level 0 or 1 should be implemented to support this application. A port-level MEP must support CCM, LBM, LTM, RDI, and ETH-BN, but can be used for ETH-BN only. |
The show eth-cfm mep eth-bandwidth-notification display output includes the ETH-BN values received and extracted from the PDU, including a last reported value and the pacing timer. If the n/a value appears in the field, it indicates that field has not been processed.
The base show eth-cfm mep output is expanded to include the disposition of the ETH-BN receive function and the configured pacing timer.
The show port port-id detail is expanded to include an Ethernet Bandwidth Notification Message Information section. This section includes the ETH-BN Egress Rate disposition and the current Egress BN rate being used.