The congestion problem cannot resolved hav-ing multiple incoming and outgoing ports

364 ◾ Networking for Big Data

•� QoS technology both in individual switches (CoS/QoS) as well as e2e [6], where AF [23] and EF [24] modes of packet forwarding are specifically important and are well defined both at Layer 2 (CoS header) and Layer 3 (DSCP header) [25]; note that penetration rate of these standards in practical use is fairly low, which results in poor overall e2e QoS support in networks today [6,26–28].

•� Practical DC-specific technology applied to both intra- and inter-DC networking [9], which today mostly ignores the above two topics and mostly focuses on FCoE [21,22].

Switch		Switch

Qualitatively
identical

FIgURE 17.1 A simple way to visualize switches in respect to the congestion problem. The right side can be generalized as several overlayed many-to-one switches (left).