A Bounded-Hop-Count Deflection Scheme for Manhattan-Street Networks

We present a new deeection method suitable for Manhattan-street networks (MSN), which, without dropping packets, limits the number of hops travelled by a packet on its way from source to destination. This allows the destination to bound the size of the reassembly buuer needed to reconstruct the original order of packets that may arrive out of sequence. The proposed routing scheme is intended for bidirectional networks|with four incoming and four outgoing links per switch. In terms of average performance measures, our method performs not worse than the best local routing schemes when the ooered load is light or moderate. In particular, when there is no contention, packets move along the shortest routes to their destinations. Routing decisions are made based on locally-available information: the coordinates of the routing switch are compared with the coordinates of the packet's destination. Unlike other deeection schemes proposed for MSN, our method is inherently asynchronous. Every incoming packet is processed independently of other packets that may arrive at (approximately) the same time. This means that packets arriving from diierent input links don't have to be aligned at the switch. This approach reduces the complexity of the routing algorithm and simpliies the switch design. The network doesn't have to compensate for the slight discrepancies in the transmission rates of diierent switches. This is the most painful implementation problem with the original synchronous approach and its becomes more severe for larger and/or faster networks.