US 5,903,559 AGranted

Method for internet protocol switching over fast ATM cell transport

AssigneeNEC USA, Inc.

InventorsArup Acharya, Rajiv Dighe

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Abstract

A method for transporting Internet Protocols (IP's) over an Asynchronous Transfer Mode (ATM) network that exhibits the strengths of ATM, namely packet interleaving (using cell-based transport) with Quality of Service support for connection-oriented traffic (such as multiclass native ATM traffic and flows-based IP traffic using RSVP), while optimizing the connectionless requirements of existing IP traffic. Advantageously, both the IP protocol stack and ATM protocol stack operate as peers over ATM cell transport hardware. The method exploits an "implicit" signaling/control phase characteristic of IP traffic/protocols thereby minimizing setup. The implicit signaling phase is used to map a flow from a routed path to a switched path immediately upon transmission of a first packet. Similarly, particular packets may be immediately transported over the routed path even after establishment of the switched path. This mapping from the routed path to the switched path and vice versa is based upon the structure/semantics of the protocol driving the flow and not just the duration of the flow as done with prior-art methods. Consequently, while prior-art methods require cell-level counters to monitor activity (or lack thereof) for switching state, the method uses explicit control messages and soft-state at the IP level (as opposed to the cell level) to do the same. Advantageously, the method imposes no switching overhead as there is no coordination between neighboring nodes when a flow is moved from the routed path to the switched path.

A method for transmitting connectionless packet data between a source and destination over an ATM network comprising one or more nodes wherein each one of said nodes includes an ATM switch connected to a packet router, wherein each ATM switch contains one or more routing tables identifying a plurality of VC's and each packet router contains one or more lookup tables, each one of said tables identifying a plurality of ports, said method comprising the steps of:

a) initializing, in each one of said ATM switches, said routing tables such that an inbound VC points to the packet router connected to the switch;
b) transmitting, on a first unused VC, a connectionless packet from said source to a first one of said ATM switches such that said packet is forwarded to the router connected to the ATM switch as directed by the routing table within said ATM switch;
c) identifying, by said router, an outbound port on said ATM switch according to said connectionless packet and the lookup table in the router;
d) identifying, a first unused VP/VC associated with said outbound port;
e) establishing, at said ATM switch, a switched path to a downstream ATM switch by mapping the inbound VC to the outbound port;
f) forwarding, simultaneously with establishing step e, said connectionless packet through said outbound port to the downstream ATM switch such that said packet is forwarded to the router connected to the downstream ATM switch as directed by the routing table within said downstream ATM switch;
g) repeating the above steps c-f in an uncoordinated, hop-by-hop manner until a switched path is established from the source to the destination such that a persistent routed control path and a switched data path are simultaneously established between said source and said destination and that all subsequent connectionless packets transmitted from source to destination traverse either the routed control path or the switched data path as indicated within each of said subsequent connectionless packets.

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Abstract

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