Multiplex communications – Network configuration determination – Using a particular learning algorithm or technique
Reexamination Certificate
2000-10-26
2004-10-26
Cangialosi, Salvatore (Department: 2661)
Multiplex communications
Network configuration determination
Using a particular learning algorithm or technique
C370S242000
Reexamination Certificate
active
06810021
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a frame relay apparatus and method for relaying frames, arranged in a network, and more particularly, to a frame relay apparatus for relaying frames so as to obviate an infinite loop of frames which may occur in a looped transmission path.
2. Description of the Relates Art
A typical relay apparatus arranged on an IP network such as Internet or Intranet has hitherto been provided with a function to relay frames depending on MAC addresses that provide the second layer (L2). This frame relay function is called an L2 switching function or simply an L2 switch. The LAN protocols advance toward the integration with the IP protocols. In the network consisting of LAN apparatuses, when a part of the network is cut off, communication may be interrupted and its reliability may be impaired. For the purpose of improving the network reliability, a looped transmission path based redundant structure is built up so as not to interrupt the communication in spite of any possible partial cutoff of the network.
In case of provision of the looped transmission path based redundant structure, there may occur an infinite loop that causes the iteration of the frame transmission in the loop passing through specific L2 switches although the network reliability can be improved. Occurrence of the frame infinite loop may possibly result in a risk of the entire LAN going down. The standardized and prevailing spanning tree is a conventional method for obviating the occurrence of the infinite loop of frames in the LAN. The spanning tree is a technique allowing all the L2 switches to fully post on their own existence periodically and to grasp the loop structure, leaving only one port not dealing in frame sending and reception in the looped LAN.
Referring to
FIG. 1A
is shown a LAN spanning tree composed of the L2 switches by way of example. This spanning tree includes four personal computers
100
-
1
to
100
-
4
acting as nodes which are looped by use of four L2 switches
102
-
1
to
102
-
4
, with a path extending between the switches
102
-
1
and
102
-
3
being severed to allow therein the formation of only one port not dealing in the frame sending and reception. In such a spanning tree, when a cutoff
104
occurs between the L2 switches
102
-
1
and
102
-
3
as in
FIG. 1B
for example, the L2 switch
102
-
1
judges the cutoff
104
of the network from the absence of information from the L2 switches
102
-
3
and
102
-
4
to be sent periodically. When the L2 switch detects the cutoff, the sending and reception by the port for the L2 switch
102
-
2
, that has hitherto been idle, commence to obviate the entire communication break. However, since the spanning tree judges the cutoff of the network from the absence of the information from the L2 switches, if a communication break is erroneously recognized owing to e.g., the loads in the L2 switches or in the transmission path or to the bug of the L2 switches, the looped transfer path is formed as in
FIG. 1C
, which may eventually cause an infinite loop in the network.
SUMMARY OF THE INVENTION
According to the present invention there is provided a frame relay apparatus and method for judging and obviating the occurrence of a frame infinite loop through analysis of a received frame without relying on the other apparatuses.
According to the present invention there is provided a frame relay apparatus and method for obviating the occurrence of a frame infinite loop in a network which relays frames in conformity with MAC addresses (layer 2 addresses).
The present invention is directed to a frame relay apparatus for relaying frames, arranged in a network including a looped transmission path. The frame relay apparatus of the present invention comprises a frame reception unit for receiving a frame; a frame sending unit for sending a frame; an entry processing unit for entering into a table the frame information and the reception time received by the frame reception unit; a loop judgment unit for referring to the table upon the receipt of a frame by the frame reception unit, to detect a second receipt of the same frame to judge the occurrence of a loop; and a frame processing unit for allowing a received frame to be sent from the frame sending unit when no loop occurrence is judged, but discarding the received frame without sending the same when a loop occurrence is judged. In this manner, without relying on the other apparatuses as in the conventional spanning tree, the frame relay apparatus of the present invention analyzes the received frames by itself to judge the occurrence of an infinite loop to thereby discard the received frames in order to securely obviate the occurrence of the infinite loop, thus building up a highly reliable LAN.
The entry processing unit enters the frame information together with the reception time into the table, the frame information including a source address of an IP frame received by a second layer IP protocol, an ID indicative of a packet sending sequence, and a fragment offset indicative of a segmented position when the ID has the same value. In such an event, the loop judgment unit, in case the received IP frame source address has already been entered in the table, judges whether a received ID is equal to an entered ID, the loop judgment unit when the received ID is not equal to the entered ID, judging that a loop has occurred if a predetermined conditional expression is satisfied, the loop judgment unit when the received ID is equal to the entered ID, judging that a loop has occurred if a received fragment offset is equal to an entered fragment offset.
The conditional expression for the frame processing unit is used to judge that a loop has occurred if a predetermined maximum packet transfer speed is exceeded by a calculated packet transfer speed PPS of a received frame and an entered frame. More specifically, the conditional expression for the frame processing unit is given, when ID (n)>ID (n−1), as
{
ID
(
n
)−
ID
(
n
−1)}/{
T
(
n
)−
T
(
n
−1)}>MAXPPS
where ID (n) is the value of a received ID, ID (n−1) is the value of an entered ID, IDMAX is the maximum value of the ID, T (n) is the reception time, T (n−1) is the entered reception time, and MAXPPS is the predetermined maximum packet transfer speed, and if the conditional expression is satisfied, then judgment is made that a loop has occurred. The conditional expression for the frame processing unit is given, when ID (n)≦ID (n−1), as
{
ID
MAX+
ID
(
n
)−
ID
(
n
−1)}/{
T
(
n
)−
T
(
n
−1)}>MAXPPS
and, if the conditional expression is satisfied, then judgment is made that a loop has occurred. The frame processing unit when judging that a loop has occurred, discards only a received frame of which second receipt has been detected. The frame processing unit when judging that a loop has occurred, suspends the frame relay for a constant period of time, after the discard of a received frame of which second receipt has been detected.
To obviate the occurrence of the infinite loop, the frame relay apparatus of the present invention is arranged on a looped transmission path formed by L3 switches disposed at the boundary of a virtual local area network (hereinafter, referred to as VLAN) which limits the broadcast frame transfer to the interior of the group. In case of provision of the frame relay apparatus of the present invention at the boundary of the LVAN, the entry processing unit enters frame information together with the reception time into the table, the frame information including a source address of an IP frame received by a third layer IP protocol, an ID indicative of a packet sending sequence, and a fragment offset indicative of positions segmented when the ID has the same value, the entry processing unit further entering into the table a virtual LAN tagged frame identifier VID received by the second layer protocol. Similar to the case of the ordinary VL
Cangialosi Salvatore
Fujitsu Limited
Staas & Halsey , LLP
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