US5991300A
Expired / Lapsed
US
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Technique for efficiently performing optional TTL propagation during label imposition
Assignee: Cisco Technology Inc
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Filing: 1998-09-08
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Granted: 1999-11-23
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Expires: 2018-09-08
Abstract
Abstract A router (10) in a packet-based telecommunications system assembles an outgoing packet by inserting between an incoming packet's link-layer and network-layer headers a shim header containing a label that the next-hop router will use as an index into its forwarding table. The shim header also includes a time-to-live field, and the router determines on a case-by-case basis whether to propagate into that field the value from a corresponding time-to-live field in the incoming packet's network-layer header. Specifically, the router computes the output packet's shim-header time-to-live value by decrementing the result of a bitwise OR operation in which the operands are the network-layer time-to-live value and a switch value that the router fetches from its forwarding-table entry for the incoming packet's destination. This propagates the incoming network-layer time-to-live information into the shim header if the switch value's bits are all logical zeros but not if they are all logical ones.
Inventors
- 👤 Daniel C. Tappan
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-03 13:07
CPC Classifications
H; H04; H04L; H04L45/00; H04L45/50
Claims Analysis
Total Claims: 13
Claim 1
Independent Claim
184 words
A label-switching router including: A) reception circuitry that receives electrical signals representing incoming packets of which each includes at least one time-to-live field in a structure that includes a network-layer datagram and an outer header that includes a link-layer header; B) time-to-live circuitry that determines, for each of a plurality of the incoming packets, an output time-to-live value by a process that includes performing a bitwise OR operation between a switch operand and an input operand whose value is determined in accordance with the value in one said time-to-live field in that incoming packet; C) packet-assembly circuitry for constructing, for each of the plurality of the incoming packets, a respective output packet associated therewith whose outer header includes a shim header, located between the link-layer header and the network-layer datagram, that includes a stack-entry sequence comprising at least one more shim-header stack entry than the incoming packet with which it is associated, at least the top shim-header stack entry including a time-to-live field containing the output time-to-live value determined by the time-to-live circuitry; and D) output circuitry for transmitting the outgoing packets thus constructed.
Claim 2
Dependent Claim
184 words
A label-switching router including: A) reception circuitry that receives electrical signals representing incoming packets of which each includes at least one time-to-live field in a structure that includes a network-layer datagram and an outer header that includes a link-layer header; B) time-to-live circuitry that determines, for each of a plurality of the incoming packets, an output time-to-live value by a process that includes performing a bitwise OR operation between a switch operand and an input operand whose value is determined in accordance with the value in one said time-to-live field in that incoming packet; C) packet-assembly circuitry for constructing, for each of the plurality of the incoming packets, a respective output packet associated therewith whose outer header includes a shim header, located between the link-layer header and the network-layer datagram, that includes a stack-entry sequence comprising at least one more shim-header stack entry than the incoming packet with which it is associated, at least the top shim-header stack entry including a time-to-live field containing the output time-to-live value determined by the time-to-live circuitry; and D) output circuitry for transmitting the outgoing packets thus constructed.
Claim 3
Dependent Claim
73 words
A router as defined in claim 1 wherein: A) the router further includes storage circuitry for maintaining a forwarding information base containing a plurality of forwarding entries, each of which is associated with a respective destination, each of at least some of the forwarding entries including a switch value; and B) the time-to-live circuitry fetches the switch value from one said forwarding entry and employs it as the value of the switch operand.
Claim 4
Dependent Claim
52 words
A router as defined in claim 2 wherein: A) each incoming packet's network-layer datagram includes a destination-address field; and B) the forwarding entry from which the time-to-live circuitry fetches the switch value for a given output packet contains a destination-prefix field with which the contents of the incoming packet's destination-address field begin.
Claim 5
Dependent Claim
25 words
A router as defined in claim 3 wherein the input packet's network-layer datagram includes said one time-to-live value from which the input operand is determined.
Claim 6
Dependent Claim
153 words
A router as defined in claim 4 wherein: A) each of a second plurality of the incoming packets includes a shim header, located between the link-layer header and the network-layer datagram, that includes a stack-entry sequence comprising at least one shim-header stack entry containing a shim input time-to-live field; B) the network-layer datagram in each of the second plurality of incoming packets includes a datagram input time-to-live field; C) the time-to-live circuitry determines an output time-to-live value for the second plurality of the incoming packets from the smaller of the contents of the shim and data input time-to-live fields; and D) the packet-assembly circuitry constructs, for each of the second plurality of the incoming packets, a respective output packet associated therewith whose outer header includes no shim header between its link-layer header and its network-layer datagram and whose datagram includes a time-to-live field containing the output time-to-live value determined by the time-to-live circuitry.
Claim 7
Dependent Claim
25 words
A router as defined in claim 2 wherein the input packet's network-layer datagram includes said one time-to-live value from which the input operand is determined.
Claim 8
Dependent Claim
153 words
A router as defined in claim 6 wherein: A) each of a second plurality of the incoming packets includes a shim header, located between the link-layer header and the network-layer datagram, that includes a stack-entry sequence comprising at least one shim-header stack entry containing a shim input time-to-live field; B) the network-layer datagram in each of the second plurality of incoming packets includes a datagram input time-to-live field; C) the time-to-live circuitry determines an output time-to-live value for the second plurality of the incoming packets from the smaller of the contents of the shim and data input time-to-live fields; and D) the packet-assembly circuitry constructs, for each of the second plurality of the incoming packets, a respective output packet associated therewith whose outer header includes no shim header between its link-layer header and its network-layer datagram and whose datagram includes a time-to-live field containing the output time-to-live value determined by the time-to-live circuitry.
Claim 9
Dependent Claim
49 words
A router as defined in claim 1 wherein: A) the value of the input operand equals the value in said one time-to-live field in the incoming packet; and B) the output time-to-live value determined by the time-to-live circuitry is one less than the result of the bitwise OR operation.
Claim 10
Dependent Claim
49 words
A router as defined in claim 1 wherein: A) the value of the input operand is one less than the value in said one time-to-live field in the incoming packet; and B) the output time-to-live value determined by the time-to-live circuitry is the result of the bitwise OR operation.
Claim 11
Dependent Claim
25 words
A router as defined in claim 1 wherein the input packet's network-layer datagram includes said one time-to-live value from which the input operand is determined.
Claim 12
Dependent Claim
153 words
A router as defined in claim 10 wherein: A) each of a second plurality of the incoming packets includes a shim header, located between the link-layer header and the network-layer datagram, that includes a stack-entry sequence comprising at least one shim-header stack entry containing a shim input time-to-live field; B) the network-layer datagram in each of the second plurality of incoming packets includes a datagram input time-to-live field; C) the time-to-live circuitry determines an output time-to-live value for the second plurality of the incoming packets from the smaller of the contents of the shim and data input time-to-live fields; and D) the packet-assembly circuitry constructs, for each of the second plurality of the incoming packets, a respective output packet associated therewith whose outer header includes no shim header between its link-layer header and its network-layer datagram and whose datagram includes a time-to-live field containing the output time-to-live value determined by the time-to-live circuitry.
Claim 13
Dependent Claim
153 words
A router as defined in claim 1 wherein: A) each of a second plurality of the incoming packets includes a shim header, located between the link-layer header and the network-layer datagram, that includes a stack-entry sequence comprising at least one shim-header stack entry containing a shim input time-to-live field; B) the network-layer datagram in each of the second plurality of incoming packets includes a datagram input time-to-live field; C) the time-to-live circuitry determines an output time-to-live value for the second plurality of the incoming packets from the smaller of the contents of the shim and data input time-to-live fields; and D) the packet-assembly circuitry constructs, for each of the second plurality of the incoming packets, a respective output packet associated therewith whose outer header includes no shim header between its link-layer header and its network-layer datagram and whose datagram includes a time-to-live field containing the output time-to-live value determined by the time-to-live circuitry.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 2002-11-22 | 2003-05-24 | 2003-11-23 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 2006-11-22 | 2007-05-24 | 2007-11-23 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2010-11-22 | 2011-05-24 | 2011-11-23 | $7700.00 | Window Closed / Lapsed |