Brocade Network OS Administrator’s Guide v4.1.1 - Manual (Page 451)

‐ MAC/PHY configuration/status TLV — Indicates duplex and bit rate capabilities and the
current duplex and bit rate settings of the local interface. It also indicates whether the
current settings were configured through auto-negotiation or through manual configuration.
‐ Power through media dependent interface (MDI) TLV — Indicates the power capabilities of
the LAN device.
‐ Link aggregation TLV — Indicates whether the link (associated with the port on which the
LLDPDU is transmitted) can be aggregated. It also indicates whether the link is currently
aggregated and provides the aggregated port identifier if the link is aggregated.
‐ Maximum Ethernet frame size TLV — Indicates the maximum frame size capability of the
device’s MAC and PHY implementation.
DCBX
Storage traffic requires a lossless communication which is provided by DCB. The Data Center Bridging
(DCB) Capability Exchange Protocol (DCBX) is used to exchange DCB-related parameters with
neighbors to achieve more efficient scheduling and a priority-based flow control for link traffic.
DCBX uses LLDP to exchange parameters between two link peers; DCBX is built on the LLDP
infrastructure for the exchange of information. DCBX-exchanged parameters are packaged into
organizationally specific TLVs. The DCBX protocol requires an acknowledgment from the other side of
the link, therefore LLDP is turned on in both transmit and receive directions. DCBX requires version
number checking for both control TLVs and feature TLVs.
DCBX interacts with other protocols and features as follows:
• LLDP — LLDP is run in parallel with other Layer 2 protocols such as RSTP and LACP. DCBX is built
on the LLDP infrastructure to communicate capabilities supported between link partners. The DCBX
protocol and feature TLVs are treated as a superset of the LLDP standard.
• QoS management — DCBX capabilities exchanged with a link partner are passed down to the QoS
management entity to set up the Brocade VDX hardware to control the scheduling and priority-based
flow control in the hardware.
The DCBX QoS standard is subdivided into two features sets, discussed below:
• Enhanced Transmission Selection on page 451
• Priority Flow Control on page 452
Enhanced Transmission Selection
In a converged network, different traffic types affect the network bandwidth differently. The purpose of
Enhanced Transmission Selection (ETS) is to allocate bandwidth based on the different priority settings
of the converged traffic. For example, Inter-process communications (IPC) traffic can use as much
bandwidth as needed and there is no bandwidth check; LAN and SAN traffic share the remaining
bandwidth. The table below displays three traffic groups: IPC, LAN, and SAN. ETS allocates the
bandwidth based on traffic type and also assigns a priority to the three traffic types as follows: Priority 7
traffic is mapped to priority group 0 which does not get a bandwidth check, priority 2 and priority 3 are
mapped to priority group 1, priorities 6, 5, 4, 1 and 0 are mapped to priority group 2.
The priority settings shown in the following table are translated to priority groups in the Brocade VDX
hardware.
ETS priority grouping of IPC, LAN, and SAN traffic TABLE 73
Priority Priority group Bandwidth check
7 0 No
DCBX
Network OS Administrator’s Guide 451
53-1003225-04