1. A network controller to communicate with a link partner, the network controller comprising: data frame circuitry to generate a data frame, the data frame including a user priority field to represent at least one traffic class; media access control (MAC) circuitry to generate a MAC credit flow control frame to be exchanged with the link partner to monitor and track available credit, wherein the MAC credit flow control frame includes: at least one field for specifying credit for the at least one traffic class wherein the credit is based on available space in a receive buffer associated with the at least one traffic class; an opcode field to identify the MAC credit flow control frame as a credit-based flow control frame; and a credit enable vector field to indicate if a credit vector is valid for a traffic class; transmit scheduler circuitry to send data packets to the link partner based on the credit, the data packets associated with the at least one traffic class; and credit management circuitry to: increment at least one counter corresponding to a traffic class for which a received credit was specified; and decrement the at least one counter when at least one data packet corresponding to the at least one traffic class is sent to the link partner.