The RCube Router

ASIM team
LIP6 Laboratory
Paris, France

Next: SmartHSL Features Up: Introduction to the IEEE 1355 Previous: The Serialization/Deserialization Operator

The RCube Router

The hardware architecture department of the LIP6 laboratory has developed a VLSI packet router between 8 HS-Links. This router called RCube [2] is a 208 pin, 3.3 V integrated circuit.

The IEEE 1355 standard defines the packet format as shown on the figure 5. A 1 or 2 byte long header specifies the destination of the packet in the network, and the following bytes constitute the pay-load. The packet length is unlimited and is closed by a special EP (End of Packet) character.

**Figure 5:** IEEE 1355 Packet Format
$\begin{figure} \center \leavevmode \epsfysize=3cm \epsfbox{pack.eps}\end{figure}$

An interval routing technique is used, which authorizes a compact representation of the routing tables.

In order to reduce latency, the router uses a wormhole strategy. The header of a packet is reemitted before the tail is received. The inherent latency of the router ( without contention ) is 150 ns. The flow control uses a credit strategy: router emits to a neighbour, only if it is granted that the receiver can accept 32 bytes of data. This authorization is carried by special FCC (Flow Control Characters) multiplexed in the opposite flow. This technique introduces a 3 % penalty on the bandwidth and prevents any data loss.

If a packet requests a busy output port, it can be redirected to an other output. This capacity is called adaptivity. If all the potential out ports are busy, the packet is blocked waiting.

**Figure 6:** RCube router diagram
$\begin{figure} \center \leavevmode \epsfysize=5cm \epsfbox{rcube.eps}\end{figure}$

Next: SmartHSL Features Up: Introduction to the IEEE 1355 Previous: The Serialization/Deserialization Operator