An apparatus, comprising: a receive port; a transmit port; and a receive buffer, having buffer space partitioned into a plurality of buffers; the apparatus being configured to: receive data defining an initial receive buffer configuration of a receive port of a peer apparatus to which the apparatus is configured to be linked in communication, the receive buffer configuration comprising an overall buffer space partitioned into a plurality of buffers including a plurality of virtual lane buffers, each allocated for a respective VL, the data including an initial allocation of credits for the VL buffers; send first credit organization information for the receive buffer of the apparatus to the peer apparatus from which a size of a first variable-size allocation unit (vAU) can be determined and from which a first variable-size credit return ACKnowledgement unit (vCU) defining a number of receiver vAU represented by each credit returned to the peer apparatus via credit return ACKs can be determined, wherein the first vAU corresponds to a minimum block size used for buffer allocation in the receive buffer of the apparatus; receive second credit organization information for the receive buffer of the peer apparatus from the peer apparatus, the second credit organization information including a second vAU and a second vCU, wherein the second vAU corresponds to a minimum block size used for buffer allocation in the receive buffer of the peer apparatus; employ a first AU and a first CU corresponding to the first vAU and first vCU for determining credit ACKs to be transmitted to the peer apparatus in response to buffer space being freed in the receive buffer of the apparatus; and employ a second AU and second CU corresponding to the second vAU and second vCU to manage and track credits for the receive buffer in the peer apparatus, wherein the first AU and second AU are different, and wherein the first CU and second CU are different. a receive port; a transmit port; and a receive buffer, having buffer space partitioned into a plurality of buffers; the apparatus being configured to: receive data defining an initial receive buffer configuration of a receive port of a peer apparatus to which the apparatus is configured to be linked in communication, the receive buffer configuration comprising an overall buffer space partitioned into a plurality of buffers including a plurality of virtual lane buffers, each allocated for a respective VL, the data including an initial allocation of credits for the VL buffers; send first credit organization information for the receive buffer of the apparatus to the peer apparatus from which a size of a first variable-size allocation unit (vAU) can be determined and from which a first variable-size credit return ACKnowledgement unit (vCU) defining a number of receiver vAU represented by each credit returned to the peer apparatus via credit return ACKs can be determined, wherein the first vAU corresponds to a minimum block size used for buffer allocation in the receive buffer of the apparatus; receive second credit organization information for the receive buffer of the peer apparatus from the peer apparatus, the second credit organization information including a second vAU and a second vCU, wherein the second vAU corresponds to a minimum block size used for buffer allocation in the receive buffer of the peer apparatus; employ a first AU and a first CU corresponding to the first vAU and first vCU for determining credit ACKs to be transmitted to the peer apparatus in response to buffer space being freed in the receive buffer of the apparatus; and employ a second AU and second CU corresponding to the second vAU and second vCU to manage and track credits for the receive buffer in the peer apparatus, receive data defining an initial receive buffer configuration of a receive port of a peer apparatus to which the apparatus is configured to be linked in communication, the receive buffer configuration comprising an overall buffer space partitioned into a plurality of buffers including a plurality of virtual lane buffers, each allocated for a respective VL, the data including an initial allocation of credits for the VL buffers; send first credit organization information for the receive buffer of the apparatus to the peer apparatus from which a size of a first variable-size allocation unit (vAU) can be determined and from which a first variable-size credit return ACKnowledgement unit (vCU) defining a number of receiver vAU represented by each credit returned to the peer apparatus via credit return ACKs can be determined, wherein the first vAU corresponds to a minimum block size used for buffer allocation in the receive buffer of the apparatus; receive second credit organization information for the receive buffer of the peer apparatus from the peer apparatus, the second credit organization information including a second vAU and a second vCU, wherein the second vAU corresponds to a minimum block size used for buffer allocation in the receive buffer of the peer apparatus; employ a first AU and a first CU corresponding to the first vAU and first vCU for determining credit ACKs to be transmitted to the peer apparatus in response to buffer space being freed in the receive buffer of the apparatus; and employ a second AU and second CU corresponding to the second vAU and second vCU to manage and track credits for the receive buffer in the peer apparatus, wherein the first AU and second AU are different, and wherein the first CU and second CU are different.