# US 8,787,217 B2 · Method, apparatus and computer program product for fast retransmission of proposal messages

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- Number: US 8,787,217 B2
- Document ID: US8787217B2
- Status: Granted
- Kind: B2
- Application number: 13/007,917
- Filed: 2011-01-17
- Published: 2012-07-19
- Granted: 2014-07-22
- Earliest claimed: 2011-01-17
- Assignees: Telefonaktiebolaget L M Ericsson (publ)
- Applicants: Amarender Musku; Simranjit Singh Chadha
- Inventors: Amarender Musku; Simranjit Singh Chadha
- Web page: https://patentgrep.com/patent/US8787217B2

## CPC

- H04L 45/028: Dynamic adaptation of the update intervals, e.g. event-triggered updates
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)

## Abstract

In one aspect, the invention provides a layer 2 network device that implements a fast retransmission method that causes the layer 2 network device to transmit proposal messages more frequently than defined in the RSTP standard. By transmitting proposal messages (e.g., proposal RST BPDUs) more frequently, the network device can significantly reduce the duration of a network traffic outage caused by a lost proposal message or a lost agreement message.

## Claims

### Claim 1

A layer 2 network device configured for fast retransmission of proposal messages, comprising:
a first port;
a second port;
a data storage system for storing (i) a data structure for mapping each one of a set of one or more layer 2 addresses to a port of the network device and (ii) an hello-timer value (ht) that defines the interval between periodic transmissions of configuration messages; and
a data processing system coupled to the data storage system and the ports, wherein the layer 2 network device is configured such that, after a port of the layer 2 network device is activated, the layer 2 network device:
(1) transmits onto a local area network (LAN) to which the port is connected a proposal message, the transmission of said proposal message occurring at time Ts; and
(2) transmits another proposal message onto the LAN at time T1 if by that time the network device has not received, from a second layer 2 network device, a response to said proposal message, wherein T1−Ts<ht.

### Claim 2 (depends on 1)

The layer 2 network device of claim 1, wherein
the data storage system stores a function f(i),
f(i)<ht for i=0 . . . M, M being greater than or equal to zero, and
T1=(Ts+f(i=x)), x being greater than or equal to zero but less than or equal to M.

### Claim 3 (depends on 2)

The layer 2 network device of claim 2, wherein the layer 2 network device is configured such that, after time T1, the layer 2 network device transmits at time T2 said proposal message if by that time the layer 2 network device has not received, from a second layer 2 network device, a response to said proposal message, wherein T2=(Ts+f(i=y)), wherein f(i=y)>=f(i=x).

### Claim 4 (depends on 3)

The layer 2 network device of claim 3, wherein f(i=y) is less than ht.

### Claim 5 (depends on 4)

The layer 2 network device of claim 4, wherein f(i=x)=(2x)(c)+d and f(i=y)=(2y)(c)+d, wherein x>=0, y>x, c>0, and d>=0.

### Claim 6 (depends on 4)

The layer 2 network device of claim 4, wherein the proposal message is a Rapid Spanning Tree (RST) Bridge Protocol Data Unit (BPDU) in which the proposal flag is set.

### Claim 7 (depends on 4)

The layer 2 network device of claim 4, wherein the layer 2 network device is configured such that, after time T2, the layer 2 network device transmits at time T3 said proposal message if by that time the layer 2 network device has not received, from a second layer 2 network device, a response to said proposal message, wherein T3=(Ts+f(i=z)), wherein f(i=z)>f(i=y), f(i=z) is less than ht.

### Claim 8 (depends on 7)

The layer 2 network device of claim 7, wherein (T3−T2)>(T2−T1).

### Claim 9 (depends on 8)

The layer 2 network device of claim 8, wherein (T2−T1)=(T1−Ts).

### Claim 10 (depends on 7)

The layer 2 network device of claim 7, wherein (T3−T2)=(T2−T1).

### Claim 11 (depends on 1)

The layer 2 network device of claim 1, wherein the layer 2 network device is configured such that, in response to the port of the layer 2 network device being activated, the layer 2 network device:
(1) puts the port in a discarding state with a role of designated;
(2) generates said proposal message;
(3) transmits onto the LAN to which the port is connected said proposal message, the transmission of said proposal message occurring at time Ts; and
(4) transmits said proposal message onto the LAN at time T1 if by that time the layer 2 network device has not received, from a second layer 2 network device, a response to said proposal message, wherein T1 minus Ts is less than ht.

### Claim 12 (depends on 1)

The layer 2 network device of claim 1, wherein T1−Ts<0.5 seconds.

### Claim 13

A method for fast retransmission of proposal messages, said message being performed by a layer 2 network device having a port, the method comprising:
storing one or more configuration parameters, the one or more configuration parameters including an hello-timer value (ht) that defines the interval between periodic transmissions of configuration messages;
placing the port in a discarding state;
generating a proposal message;
transmitting, at time Ts, said proposal message onto a local area network (LAN) to which the port is connected;
transmitting another proposal message onto the LAN at time T1 if by that time the network device has not received a response to said proposal message, wherein (T1−Ts)<ht.

### Claim 14 (depends on 13)

The method of claim 13, further comprising storing a function f(i), wherein
f(i)<ht for i=0 . . . M, M being greater than or equal to zero, and
T1=(Ts+f(i=x)), x being greater than or equal to zero but less than or equal to M.

### Claim 15 (depends on 14)

The method of claim 14, further comprising:
transmitting at time T2 said proposal message if by that time the layer 2 network device has not received a response to said proposal message, wherein T2=(TS+f(i=y)), wherein f(i=y)>=f(i=x), and T2−Ts<ht.

### Claim 16 (depends on 15)

The method of claim 15, wherein f(i=x)=(2x)(c)+d and f(i=y)=(2y)(c)+d, wherein x>=0, y>x, c>0, and d>=0.

### Claim 17 (depends on 13)

The method of claim 13, further comprising:
placing the port in a discarding state; and
changing the state of the port from the discarding state to a forwarding state in response to receiving an agreement message that was sent in response to the proposal message.

### Claim 18 (depends on 13)

The method of claim 13, wherein
the proposal message is a Rapid Spanning Tree (RST) Bridge Protocol Data Unit (BPDU) in which the proposal flag is set; and
(T1−Ts)<0.5 seconds.

### Claim 19 (depends on 13)

The method of claim 13, further comprising transmitting said proposal message onto the LAN at time T2 if by that time the network device has not received a response to said proposal message, wherein (T2−Ts)<ht.

### Claim 20 (depends on 19)

The method of claim 19, wherein (T2−T1)=(T1−Ts).

### Claim 21

A computer program product for fast retransmission of proposal messages, the computer program product comprising a non-transitory computer readable medium storing computer readable program code, said computer readable program code comprising:
a set of instructions for generating a proposal message;
a set of instructions for transmitting said proposal message;
a set of instructions for keeping a count (c) of the number of times said proposal message or another proposal message has been transmitted;
a set of instructions for activating a timer when said proposal message is transmitted, said instructions being configured to configure the timer such that the timer will expire at time Ts+f(i), where Ts is the time at which said proposal message was first transmitted, and i is a function of c and wherein f(i)<a hello-timer value (ht) for i=0 . . . M;
a set of instructions for transmitting said another proposal message in response to the timer expiring; and
a set of instructions for deactivating the timer in response to receipt of a response to said proposal message or said another proposal message so that said proposal message or said another proposal message will not be transmitted again in the event a response is received.

### Claim 22 (depends on 21)

The computer program product of claim 21, wherein f(i) is one of a exponential function, linear function or constant function, for i=0 . . . M.

### Claim 23 (depends on 21)

The computer program product of claim 21, wherein f(i) equals ht for i=M+1 . . . N.

### Claim 24 (depends on 21)

The computer program product of claim 21, wherein said computer readable program code further comprises instructions for activating a second timer when the proposal message is transmitted the first time, the second timer being configured such that the timer will expire at time Ts+ht.

### Claim 25 (depends on 21)

The computer program product of claim 21, wherein said computer readable program code further comprises instructions for generating a configuration message and for transmitting the configuration message in response to the second timer expiring.

### Claim 26 (depends on 21)

The computer program product of claim 21, wherein the proposal message is a Rapid Spanning Tree (RST) Bridge Protocol Data Unit (BPDU) in which the proposal flag is set.