A method of characterizing the delay through an overlay network, wherein the overlay network operates on top of the internet, comprising: transmitting a specially marked packet from a sending node to a receiving node through the overlay network, comprising a plurality of overlay nodes (110a-g) connected by a plurality of links (120a-c), wherein the packet is marked as a retransmission probe and is first transmitted to a first overlay node; receiving the specially marked packet at a second overlay node from the first overlay node in the overlay network; forwarding the specially marked packet from the second overlay node and requesting retransmission of the specially marked packet to the second overlay node from the first overlay node; receiving the retransmitted packet sent from the first overlay node at the second overlay node, wherein the first overlay node modifies the retransmitted packet to include an indication of the link that is being retried and removes the special marking from the packet prior to retransmission; forwarding the retransmitted packet from the second overlay node; receiving a predetermined number of packets including the specially marked packet and the retransmitted packet at the receiving node, wherein the predetermined number is one more than the number of links between the sending node and the receiving node; determining, at the receiving node, a difference between a smoothed time in network and a time in network of the retransmitted packet, wherein the smoothed time in network is a measure of the average time in network; and calculating the delay associated with each link, wherein the delay is based on the difference between the smoothed time in network and the time in network of the retransmitted packet. transmitting a specially marked packet from a sending node to a receiving node through the overlay network, comprising a plurality of overlay nodes (110a-g) connected by a plurality of links (120a-c), wherein the packet is marked as a retransmission probe and is first transmitted to a first overlay node; receiving the specially marked packet at a second overlay node from the first overlay node in the overlay network; forwarding the specially marked packet from the second overlay node and requesting retransmission of the specially marked packet to the second overlay node from the first overlay node; receiving the retransmitted packet sent from the first overlay node at the second overlay node, wherein the first overlay node modifies the retransmitted packet to include an indication of the link that is being retried and removes the special marking from the packet prior to retransmission; forwarding the retransmitted packet from the second overlay node; receiving a predetermined number of packets including the specially marked packet and the retransmitted packet at the receiving node, wherein the predetermined number is one more than the number of links between the sending node and the receiving node; determining, at the receiving node, a difference between a smoothed time in network and a time in network of the retransmitted packet, wherein the smoothed time in network is a measure of the average time in network; and calculating the delay associated with each link, wherein the delay is based on the difference between the smoothed time in network and the time in network of the retransmitted packet.