Ethernet flow control is a mechanism for temporarily stopping the transmission of data on Ethernet family computer networks. The goal of this mechanism is to avoid packet loss in the presence of network congestion. The first flow control mechanism, the pause frame, was defined by the IEEE 802.3x standard. The follow-on priority-based flow control, as defined in the IEEE 802.1Qbb standard, provides a link-level flow control mechanism that can be controlled independently for each class of service (CoS), as defined by IEEE P802.1p and is applicable to data center bridging (DCB) networks, and to allow for prioritization of voice over IP (VoIP), video over IP, and database synchronization traffic over default data traffic and bulk file transfers. Description A sending station (computer or network switch) may be transmitting data faster than the other end of the link can accept it. Using flow control, the receiving station can signal the sender requesting suspension of transmissions until the receiver catches up. Flow control on Ethernet can be implemented at the data link layer. The first flow control mechanism, the pause frame, was defined by the Institute of Electrical and Electronics Engineers (IEEE) task force that defined full duplex Ethernet link segments. The IEEE standard 802.3x was issued in 1997. Pause frame An overwhelmed network node can send a pause frame, which halts the transmission of the sender for a specified period of time. A media access control (MAC) frame (EtherType 0x8808) is used to carry the pause command, with the Control opcode set to 0x0001 (hexadecimal). Only stations configured for full-duplex operation may send PAUSE frames. When a station wishes to pause the other end of a link, it sends a pause frame to either the unique 48-bit destination address of this link or to the 48-bit reserved multicast address of . The use of a well-known address makes it unnecessary for a station to discover and store the address of the station at the other end of the link. Another advantage of using this multicast address arises from the use of flow control between network switches. The particular multicast address used is selected from a range of address which have been reserved by the IEEE 802.1D standard which specifies the operation of switches used for bridging. Normally, a frame with a multicast destination sent to a switch will be forwarded out to all other ports of the switch. However, this range