Apparatus and method for master election and topology discovery in an Ethernet network

• US 7,675,869 B1
• Filed: 08/27/2004
• Issued: 03/09/2010
• Est. Priority Date: 07/06/2004
• Status: Active Grant

• Current Assignee: Marvell Asia Pte Limited (Marvell Technology Group Limited)
• Original Assignee: Marvell International Limited (Marvell Technology Group Limited)
• Inventors: Anker, Tal, Shevach, Gil, Cohen, Anat, Siso, Gil
• Primary Examiner(s): CHO, HONG SOL
• Application Number:
  US10/926,946
• Time in Patent Office: 2,020 Days
• Field of Search: 370/254, 370/255, 370/258, 370/389, 370/392
• US Class Current: 370/255
• CPC Class Codes: H04L 12/42 Loop networks
• CPC Class Codes: H04L 12/423 with centralised control, e.g. polling
• CPC Class Codes: H04L 41/12 Discovery or management of network topologies
• CPC Class Codes: H04L 49/351 for local area network [LAN], e.g. Ethernet switches

Abstract

An apparatus, method and computer memory for electing a master unit from multiple candidate units on a ring or chain topology network is provided. Master proposal data packets are transmitted onto a plurality of stacking links. At least one message data packet is received on the one candidate unit. A candidate unit is elected as the master unit if it receives message data packets corresponding to the transmitted master proposal data packets.

Claims

1. A method for electing a master unit from a plurality of candidate units on a ring or chain topology network, comprising the steps of:

transmitting from one of the candidate units a plurality of master proposal data packets onto a plurality of stacking links communicatively coupled to the network;

receiving on the one candidate unit at least one message data packet; and

electing the one candidate unit as the master unit if the one candidate unit receives a plurality of message data packets corresponding to the plurality of transmitted master proposal data packets.

2. A method according to claim 1, further comprising the steps of:

extracting from the received message data packet topology information; and

updating a topology database on the one candidate unit with the topology information extracted from the received message data packet.

3. A method according to claim 2, further comprising the steps of:

building an information packet including updated topology information from the one candidate unit'"'"'s updated topology database and an identifier identifying the master unit; and

transmitting the information packet onto the network.

4. A method according to claim 3, wherein the identifier includes at least one arbitrary and/or at least one dynamic variable, wherein the arbitrary variable is static and the dynamic variable changes over time.

5. A method according to claim 3, wherein the identifier identifying the master unit includes the value of a user preference variable, an up time variable, a physical unit identifier and/or a hardware unit identifier stored on the master unit.

6. A method according to claim 1, further comprising the step of:

updating a topology database on the one candidate unit with updated topology information extracted from at least one of the master proposal data packets;

building a master identity packet including the topology information stored in the one candidate unit'"'"'s topology database and an identifier identifying the one candidate unit as the master unit; and

transmitting onto the network the master identity packet.

7. A method according to claim 6, wherein the identifier identifying the one candidate unit includes the value of a user preference variable, an up time variable, a physical unit identifier and/or a hardware unit identifier stored on the one candidate unit.

8. A method according to claim 1, further comprising the steps of:

extracting a unit identifier from the received message data packet; and

discarding the received message data packet if the identifier of the one candidate unit is less than the unit identifier extracted from the received message data packet.

9. A method according to claim 8, wherein the unit identifier includes the value of a user preference variable, an up time variable, a physical unit identifier and/or a hardware unit identifier stored on a unit supplying the message data packet.

10. A method according to claim 9, wherein the identifier of the one candidate unit is less than the unit identifier when:

a user preference variable of the one candidate unit is greater than the user preference variable of the unit identifier.

11. A method according to claim 9, wherein the identifier of the one candidate unit is less than the unit identifier when:

a user preference variable of the one candidate unit is equal to the user preference variable of the unit identifier and an up time variable of the one candidate unit is greater than the up time of the unit identifier.

12. A method according to claim 9, wherein the identifier of the one candidate unit is less than the unit identifier when:

a user preference variable of the one candidate unit is equal to the user preference variable of the unit identifier, an up time variable of the one candidate unit is greater than the up time variable of the unit identifier, and a physical unit identifier of the one candidate unit is less than the physical unit identifier of the unit identifier.

13. A method according to claim 9, wherein the identifier of the one candidate unit is less than the unit identifier when:

a user preference variable of the one candidate unit is equal to the user preference variable of the unit identifier, an up time variable of the one candidate unit is greater than the up time variable of the unit identifier, a physical unit identifier of the one candidate unit is equal to the physical unit identifier of the unit identifier, and a hardware unit identifier of the one candidate unit is equal to the hardware unit identifier of the unit identifier.

14. A method according to claim 1, further comprising the steps of:

extracting a message sequence number from the received message data packet;

comparing a message sequence number stored on the one candidate unit to the message sequence number; and

discarding the received message data packet if the one candidate unit'"'"'s stored message sequence number is greater than or less than the message sequence number.

15. A method according to claim 1, further comprising the steps of:

extracting a message sequence number from the received message data packet;

comparing a message sequence number stored on the one candidate unit to the extracted message sequence number;

incrementing a counter if the one candidate'"'"'s stored message sequence number is equal to the extracted message sequence number;

updating a topology database on the one candidate unit with updated topology information extracted from the master proposal data packet if the value of the counter equals the number of master proposal data packets transmitted onto the network by the one candidate;

building a master identity packet including the topology information stored in the one candidate unit'"'"'s topology database and an identifier identifying one candidate unit as the master unit; and

transmitting onto the network the master identity packet.

16. A method according to claim 1 wherein the transmitting step is triggered by a change in a topology of the network.

17. A method according to claim 1 further comprising the steps of:

receiving a request to initiate a master election process message; and

wherein the transmitting step is triggered upon receiving the request to initiate a master election process message.

18. A method according to claim 1, further comprising the steps of:

including marking information in the plurality of transmitted master proposal data packets; and

preventing one of the transmitted plurality of master proposal data packets from endlessly looping within the network by recognizing the marking information and discarding at least one of the transmitted packets.

19. A method according to claim 1, further comprising the steps of:

including a time to live field in the plurality of master proposal data packets;

initializing the time to live field with a predetermined value; and

decrementing the time to live field; and

preventing one of the master proposal data packets from endlessly looping within the network by discarding the packet when the time to live field is lower than another predetermined value.

20. A network device on a ring or chain topology network, comprising:

a packet processor adapted to transmit a plurality of master proposal data packets onto a plurality of stacking links communicatively coupled to the network and to receive at least one message data packet; and

a control unit adapted to control the packet processor and to elect the device as a master unit if the packet processor receives a plurality of message data packets corresponding to the plurality of transmitted master proposal data packets.

21. A network device according to claim 20, further comprising:

a topology database adapted to store topology information;

wherein the control unit is further adapted to extract from the message data packet topology information and update the topology database with the topology information extracted from the message data packet.

22. A network device according to claim 21, wherein the control unit is further adapted to build an information packet including updated topology information from the topology database and an identifier identifying the network device as a master unit, and wherein the packet processor is further adapted to transmit the information packet onto the network.

23. A network device according to claim 22, wherein the identifier includes at least one arbitrary and/or at least one dynamic variable, wherein the arbitrary variable is static and the dynamic variable changes over time.

24. A network device according to claim 22, wherein the identifier includes the value of a user preference variable, an up time variable, a physical unit identifier and/or a hardware unit identifier stored on the master unit.

25. A network device according to claim 20, further comprising:

a topology database adapted to store topology information, and

wherein the control unit is further adapted to update the topology database with updated topology information extracted from at least one of the master proposal data packets and build a master identity packet including the topology information stored in the topology database and a master unit identifier identifying the network device as the master unit, and

wherein the packet processor is further adapted to transmit onto the network the master identity packet.

26. A network device according to claim 25, wherein the identifier includes the value of a user preference variable, an up time variable, a physical unit identifier and/or a hardware unit identifier stored on the one candidate unit.

27. A network device according to claim 20, further comprising:

a memory adapted to store an identifier of the network device, and

wherein the control unit is further adapted to extract a unit identifier from the received message data packet, and discard the received message data packet if the identifier stored in the memory is less than the unit identifier extracted from the received message.

28. A network device according to claim 27, wherein the unit identifier includes the value of a user preference variable, an up time variable, a physical unit identifier and/or a hardware unit identifier stored on a unit supplying the message data packet.

29. A network device according to claim 28, wherein the identifier of the device is less than the unit identifier when:

a user preference variable stored in the memory is greater than the user preference variable of the unit identifier from the received message data packet.

30. A network device according to claim 28, wherein the identifier of the one candidate unit is less than the unit identifier when:

a user preference variable of the network device is equal to the user preference variable of the extracted unit identifier and an up time variable of the network device is greater than the up time of the extracted unit identifier.

31. A network device according to claim 28, wherein the identifier of the network device is less than the unit identifier when:

a user preference variable of the network device is equal to the user preference variable of the extracted unit identifier, an up time variable of the network device is greater than the up time variable of the extracted unit identifier, and a physical unit identifier of the network device is less than the physical unit identifier of the extracted unit identifier.

32. A network device according to claim 28, wherein the identifier of the network device is less than the unit identifier when:

a user preference variable of the network device is equal to the user preference variable of the extracted unit identifier, an up time variable of the network device is greater than the up time variable of the extracted unit identifier, a physical unit identifier of the network device is equal to the physical unit identifier of the extracted unit identifier, and a hardware unit identifier of the network device is equal to the hardware unit identifier of the extracted unit identifier.

33. A network device according to claim 20, further comprising:

wherein the control unit is further adapted to extract a message sequence number from the received message data packet, compare a message sequence number of the transmitted plurality of master proposal packets to the extracted message sequence number, and discard the received message data packet if the message sequence number of the transmitted plurality of master proposal packets is greater than or less than the extracted message sequence number.

34. A network device according to claim 20, further comprising:

a topology database adapted to store topology information,

wherein the control unit is further adapted to extract a message sequence number from the message data packet, compare a message sequence number of the transmitted plurality of master proposal packets to the extracted message sequence number, increment a counter if the message sequence number of the transmitted plurality of master proposal packets is equal to the extracted message sequence number, update the topology database with updated topology information extracted from the master proposal data packet if the value of the counter equals the number of master proposal data packets transmitted onto the network by the packet processor, build a master identity packet including the topology information stored in the topology database and an identifier identifying the network device as the master unit, and

wherein the packet processor is further adapted to transmit onto the network the master identity packet.

35. A network device according to claim 20, wherein the control unit is further adapted to trigger the packet processor to transmit the plurality of master proposal data packets upon detecting a change in a topology of the network.

36. A network device according to claim 20, wherein the packet processor is further adapted to receive a request to initiate a master election process message and to transmit upon receiving the request to initiate a master election process message.

37. A network device according to claim 20, wherein the packet processor is further adapted to mark the plurality of transmitted master proposal data packets and prevent one of the transmitted plurality of master proposal data packets from endlessly looping within the network by recognizing the mark and discarding at least one of the transmitted packets.

38. A network device according to claim 20, wherein the packet processor is further adapted to include a time to live field in the plurality of master proposal data packets, initialize the time to live field with a predetermined value, decrement the time to live field, and prevent one of the master proposal data packets from endlessly looping within the network by discarding the packet when the time to live field is lower than another predetermined value.

39. An apparatus for electing a master unit from a plurality of candidate units on a ring or chain topology network, comprising:

means for transmitting from one of the candidate units a plurality of master proposal data packets onto a plurality of stacking links communicatively coupled to the network;

means for receiving on the one candidate unit at least one message data packet; and

means for electing the one candidate unit as the master unit if the one candidate unit receives a plurality of message data packets corresponding to the plurality of transmitted master proposal data packets.

40. An apparatus according to claim 39, further comprising:

means for extracting from the received message data packet topology information; and

means for updating a topology database on the one candidate unit with the topology information extracted from the received message data packet.

41. An apparatus according to claim 40, further comprising:

means for building an information packet including updated topology information from the one candidate unit'"'"'s updated topology database and an identifier identifying the master unit; and

means for transmitting the information packet onto the network.

42. An apparatus according to claim 41, wherein the identifier includes at least one arbitrary and/or at least one dynamic variable, wherein the arbitrary variable is static and the dynamic variable changes over time.

43. An apparatus according to claim 41, wherein the identifier identifying the master unit comprises the value of a user preference variable, an up time variable, a physical unit identifier and/or a hardware unit identifier stored on the master unit.

44. An apparatus according to claim 39, further comprising:

means for updating a topology database on the one candidate unit with updated topology information extracted from at least one of the master proposal data packets;

means for building a master identity packet including the topology information stored in the one candidate unit'"'"'s topology database and an identifier identifying the one candidate unit as the master unit; and

means for transmitting onto the network the master identity packet.

45. An apparatus according to claim 44, wherein the identifier identifying the one candidate unit comprises the value of a user preference variable, an up time variable, a physical unit identifier and/or a hardware unit identifier stored on the one candidate unit.

46. An apparatus according to claim 39, further comprising:

means for extracting a unit identifier from the received message data packet; and

means for discarding the received message data packet if the identifier of the one candidate unit is less than the unit identifier.

47. An apparatus according to claim 46, wherein the unit identifier includes the value of a user preference variable, an up time variable, a physical unit identifier and/or a hardware unit identifier stored on a unit supplying the message data packet.

48. An apparatus according to claim 47, wherein the identifier of the one candidate unit is less than the unit identifier when:

a user preference variable of the one candidate unit is greater than the user preference variable of the unit identifier.

49. An apparatus according to claim 47, wherein the identifier of the one candidate unit is less than the unit identifier when:

a user preference variable of the one candidate unit is equal to the user preference variable of the unit identifier and an up time variable of the one candidate unit is greater than the up time of the unit identifier.

50. An apparatus according to claim 47, wherein the identifier of the one candidate unit is less than the unit identifier when:

a user preference variable of the one candidate unit is equal to the user preference variable of the unit identifier, an up time variable of the one candidate unit is greater than the up time variable of the unit identifier, and a physical unit identifier of the one candidate unit is less than the physical unit identifier of the unit identifier.

51. An apparatus according to claim 47, wherein the identifier of the one candidate unit is less than the unit identifier when:

a user preference variable of the one candidate unit is equal to the user preference variable of the unit identifier, an up time variable of the one candidate unit is greater than the up time variable of the unit identifier, a physical unit identifier of the one candidate unit is equal to the physical unit identifier of the unit identifier, and a hardware unit identifier of the one candidate unit is equal to the hardware unit identifier of the unit identifier.

52. An apparatus according to claim 39, further comprising:

means for extracting a message sequence number from the received message data packet;

means for comparing a message sequence number stored on the one candidate unit to the extracted message sequence number; and

means for discarding the received message data packet if the one candidate unit'"'"'s stored message sequence number is greater than or less than the extracted message sequence number.

53. An apparatus according to claim 39, further comprising:

means for extracting a message sequence number from the received message data packet;

means for comparing a message sequence number stored on the one candidate unit to the extracted message sequence number;

means for incrementing a counter if the one candidate'"'"'s stored message sequence number is equal to the extracted message sequence number;

means for updating a topology database on the one candidate unit with updated topology information extracted from the master proposal data packet if the value of the counter equals the number of master proposal data packets transmitted onto the network by the one candidate;

means for building a master identity packet including the topology information stored in the one candidate unit'"'"'s topology database and an identifier identifying one candidate unit as the master unit; and

means for transmitting onto the network the master identity packet.

54. An apparatus according to claim 39, further comprising:

means for triggering the means for transmitting by a change in the topology of the network.

55. An apparatus according to claim 39 further comprising:

means for receiving a request to initiate a master election process message; and

wherein the means for transmitting is triggered upon receiving the request to initiate a master election process message.

56. An apparatus according to claim 39, further comprising:

means for including marking information in the plurality of transmitted master proposal data packets; and

means for preventing one of the transmitted plurality of master proposal data packets from endlessly looping within the network by recognizing the marking information and discarding at least one of the transmitted packets.

57. An apparatus according to claim 39, further comprising:

means for including a time to live field in the plurality of master proposal data packets;

means for initializing the time to live field with a predetermined value; and

means for decrementing the time to live field; and

means for preventing one of the master proposal data packets from endlessly looping within the network by discarding the packet when the time to live field is lower than another predetermined value.

58. An apparatus for initiating a process for electing a master unit from a plurality of candidate units on a ring or chain topology network, comprising:

means for receiving on one of the candidate units a message data packet;

means for extracting a unit identifier from the message data packet;

means for discarding the message data packet if the unit identifier is not equal to an identifier stored on the one candidate unit;

means for building a plurality of master proposal data packets including topology information from the one candidate unit and an identifier identifying the one candidate; and

means for transmitting onto the network the plurality of master proposal data packets.

59. A system of stacked units on a ring or chain topology network, comprising:

a candidate unit adapted to transmit a plurality of master proposal data packets onto a plurality of stacking links communicatively coupled to the network and to receive at least one message data packet, and

wherein the candidate unit elects itself as a master unit if it receives a plurality of message data packets corresponding to the plurality of transmitted master proposal data packets.

60. A system according to claim 59, wherein the candidate unit is further adapted to extract from the received message data packet topology information, and update a topology database on the candidate unit with the topology information extracted from the received message data packet.

61. A system according to claim 60, where the candidate unit is further adapted to build an information packet including updated topology information from the candidate unit'"'"'s updated topology database and an identifier identifying a master unit, and transmit the information packet onto the network.

62. A system according to claim 61, wherein the identifier includes at least one arbitrary and/or at least one dynamic variable, wherein the arbitrary variable is static and the dynamic variable changes over time.

63. A system according to claim 61, wherein the identifier identifying the master unit includes the value of a user preference variable, an up time variable, a physical unit identifier and/or a hardware unit identifier stored on the master unit.

64. A system according to claim 59, wherein the candidate unit is further adapted to update a topology database on the candidate unit with updated topology information extracted from at least one of the master proposal data packets, build a master identity packet including the topology information stored in the candidate unit'"'"'s topology database and an identifier identifying the candidate unit as the master unit, and transmit onto the network the master identity packet.

65. A system according to claim 64, wherein the identifier identifying the candidate unit includes the value of a user preference variable, an up time variable, a physical unit identifier and/or a hardware unit identifier stored on the candidate unit.

66. A system according to claim 59, wherein the candidate unit is further adapted to extract a unit identifier from the received message data packet and discard the received message data packet if the identifier of the candidate unit is less than the unit identifier extracted from the received message data packet.

67. A system according to claim 66, wherein the unit identifier includes the value of a user preference variable, an up time variable, a physical unit identifier and/or a hardware unit identifier stored on a unit supplying the message data packet.

68. A system according to claim 67, wherein the identifier of the candidate unit is less than the unit identifier of a second candidate unit when:

a user preference variable of the candidate unit is greater than the user preference variable of the unit identifier of the second candidate unit.

69. A system according to claim 67, wherein the identifier of the candidate unit is less than the unit identifier of a second candidate unit when:

a user preference variable of the candidate unit is equal to the user preference variable of the unit identifier of the second candidate unit and an up time variable of the candidate unit is greater than the up time of the unit identifier of the second candidate unit.

70. A system according to claim 67, wherein the identifier of the candidate unit is less than the unit identifier of a second candidate unit when:

a user preference variable of the candidate unit is equal to the user preference variable of the unit identifier of the second candidate unit, an up time variable of the candidate unit is greater than the up time variable of the unit identifier of the second candidate unit, and a physical unit identifier of the candidate unit is less than the physical unit identifier of the unit identifier of the second candidate unit.

71. A system according to claim 67, wherein the identifier of the candidate unit is less than the unit identifier of a second candidate unit when:

a user preference variable of the candidate unit is equal to the user preference variable of the unit identifier of the second candidate unit, an up time variable of the candidate unit is greater than the up time variable of the unit identifier of the second candidate unit, a physical unit identifier of the candidate unit is equal to the physical unit identifier of the unit identifier of the second candidate unit, and a hardware unit identifier of the candidate unit is equal to the hardware unit identifier of the unit identifier of the second candidate unit.

72. A system according to claim 59, wherein the candidate unit is further adapted to extract a message sequence number from the received message data packet, compare a message sequence number stored on the unit to the extracted message sequence number, and discard the received message data packet if the candidate unit'"'"'s stored message sequence number is greater than or less than the extracted message sequence number.

73. A system according to claim 59, wherein the candidate unit is further adapted to extract a message sequence number from the received message data packet, compare a message sequence number stored on the candidate unit to the extracted message sequence number, increment a counter if the one candidate'"'"'s stored message sequence number is equal to the extracted message sequence number, update a topology database on the candidate unit with updated topology information extracted from the master proposal data packet if the value of the counter equals the number of master proposal data packets transmitted onto the network by the candidate, build a master identity packet including the topology information stored in the candidate unit'"'"'s topology database and an identifier identifying the candidate unit as the master unit, and transmit onto the network the master identity packet.

74. A system according to claim 59, wherein the candidate unit is further adapted to detect a change in a topology of the network.

75. A system according to claim 59, wherein the candidate unit is further adapted to receive a request to initiate a master election process message and transmit a plurality of master proposal data packets upon receiving the request to initiate a master election process message.

76. A system according to claim 59, wherein the candidate unit is further adapted to include marking information in the plurality of transmitted master proposal data packets, and wherein another unit prevents the transmitted plurality of master proposal data packets from endlessly looping within the network by recognizing the marking information and discarding at least one of the transmitted packets.

77. A system according to claim 59, wherein the candidate unit is further adapted to include a time to live field in the plurality of master proposal data packets, wherein the time to live field is initialized with a predetermined value, and wherein at least one of the stacked units in the network is adapted to decrement the time to live field, and prevent one of the master proposal data packets from endlessly looping within the network by discarding the packet when the time to live field is lower than another predetermined value.

78. A system of stacked units on a ring or chain topology network, comprising:

means for transmitting a plurality of master proposal data packets onto a plurality of stacking links communicatively coupled to the network;

means for receiving at least one message data packet; and

means for electing a master unit if the means for transmitting receives a plurality of message data packets corresponding to the plurality of transmitted master proposal data packets.

79. A system according to claim 78, further comprising:

means for extracting from the received message data packet topology information; and

means for updating a topology database with the topology information extracted from the received message data packet.

80. A system according to claim 79, further comprising:

means for building an information packet including updated topology information from the updated topology database and an identifier identifying a master unit; and

means for transmitting the information packet onto the network.

81. A system according to claim 80, wherein the identifier includes at least one arbitrary and/or at least one dynamic variable, wherein the arbitrary variable is static and the dynamic variable changes over time.

82. A system according to claim 80, wherein the identifier includes the value of a user preference variable, an up time variable, a physical unit identifier and/or a hardware unit identifier stored on the master unit.

83. A system according to claim 78, further comprising:

means for updating a topology database with updated topology information extracted from at least one of the master proposal data packets;

means for building a master identity packet including the topology information stored in the topology database and an identifier identifying the master unit; and

means for transmitting onto the network the master identity packet.

84. A system according to claim 83, wherein the identifier includes the value of a user preference variable, an up time variable, a physical unit identifier and/or a hardware unit identifier.

85. A system according to claim 78, further comprising:

means for extracting a unit identifier from the received message data packet; and

means for discarding the received message data packet if the identifier of a candidate unit is less than the identifier extracted from the received message data packet.

86. A system according to claim 85, wherein the identifier includes the value of a user preference variable, an up time variable, a physical unit identifier and/or a hardware unit identifier stored on a unit supplying the message data packet.

87. A system according to claim 78, further comprising:

means for extracting a message sequence number from the received message data packet;

means for comparing a stored message sequence number to the extracted message sequence number; and

means for discarding the received message data packet if the stored message sequence number is greater than or less than the extracted message sequence number.

88. A system according to claim 78, further comprising:

means for extracting a message sequence number from the received message data packet;

means for comparing a stored message sequence number to the extracted message sequence number;

means for incrementing a counter if the stored message sequence number is equal to the extracted message sequence number;

means for updating a topology database with updated topology information extracted from the master proposal data packet if the value of the counter equals the number of master proposal data packets transmitted onto the network;

means for building a master identity packet including the topology information stored in the topology database and an identifier identifying the master unit; and

means for transmitting onto the network the master identity packet.

89. A system according to claim 78, further comprising:

means for detecting a change in a topology of the network.

90. A system according to claim 78, further comprising:

means for receiving a request to initiate a master election process message; and

means for transmitting a plurality of master proposal data packets upon receiving the request to initiate a master election process message.

91. A system according to claim 78, further comprising:

means for including marking information in the plurality of transmitted master proposal data packets; and

means for preventing the transmitted plurality of master proposal data packets from endlessly looping within the network by recognizing the marking information and discarding at least one of the transmitted packets.

92. A system according to claim 78, further comprising:

means for including a time to live field in the plurality of master proposal data packets;

means for initializing the time to live field with a predetermined value;

means for decrementing the time to live field; and

means for preventing one of the master proposal data packets from endlessly looping within the network by discarding the packet when the time to live field is lower than another predetermined value.

93. A system according to claim 78, further comprising:

means for determining an identifier of a first candidate unit is less than a unit identifier of a second candidate.