3com Corporation

Annette E Sohor

Daniel M O'Keeffe

Justin A Drummond-Murray

Neil J Clifford

Eoin O'Brien

Derry M O'Donoghue

Paul Flood

A network unit includes a forwarding database which includes entries relating packet addresses to forwarding data and is operative to form linked chains of entries wherein the entries in a chain represent different packet addresses which are reduced by hashing to the same pointer for the database. A seed for a hashing algorithm is provided by a combination, such as an exclusive-OR combination, of part of an input address word and a selected word. Hashing is preferably performed in at least two cycles, wherein in one cycle a hash function is applied to a portion of the input address not including the part which is combined with the selected word to constitute a hash seed and in another (preceding) cycle a further part of the address and the aforementioned hash seed are subject the hash function. The selected word may be a software programmable mask and it is possible thereby to ensure a high degree of randomness in the hash seed and to reduce the incidence of convergence of different addresses to a common pointer.

Network unit including address hashing

A multi-port data communication device includes a common central memory through which all data packets must pass. Packet data is written to and read from the common memory space in bursts in response to receive write requests and transmit read requests. A transmit read request for a first burst of data in a packet has in a central arbiter a relatively low priority and transmit read requests for a second and any subsequent burst of data in a packet have in the central arbiter a relatively high priority. Preferably the receive write requests have in said central arbiter a priority intermediate said relatively low priority and said relatively high priority. The priority system reduces the likelihood of underrun and overrun particularly when the burst size is generally smaller than the packet size.

Inhibition of underrun in network switches and the like for packet-based communication systems

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Dublin, Ireland

Annette E Sohor