CN1588827A - Self adaptive channel reservation and searching method in light burst exchange - Google Patents

Abstract

An adaptive channel reservation and search method in optical burst switching adopts the principle of differentiated processing, and adaptively performs channel reservation and search according to different service levels, input flow characteristics, network performance and channel configuration of output ports. Different classes of services have different maximum number of channels that can be reserved. Only when the number of channels reserved by a class of business is less than the maximum number of channels that can be reserved can channels be reserved for burst data packets of this class. Different levels of services have different maximum channel search times in a time slot, and the channel search times of a certain level of service in a time slot cannot exceed the maximum channel search times of this level. The present invention adaptively adjusts the reservation and search parameters according to the actual network input and operation effect, can significantly improve the unfairness of channel allocation caused by the large-scale changes in the length of data packets of different levels in optical burst switching, and improve the performance and performance of the network. Utilization of bandwidth resources.

Description

Adaptive Channel Reservation and Search Method in Optical Burst Switching

technical field

The invention relates to a channel scheduling method in an optical burst switching (OBS) network, in particular to an adaptive channel reservation and search method in the optical burst switching, and belongs to the technical field of optical fiber communication.

Background technique

Stimulated by the development of optical communication technologies such as data services and wavelength division multiplexing (WDM), traditional optical networks are developing towards a new generation of optical networks that are highly flexible, highly reliable, and low-cost for IP services. Among the currently proposed switching technology solutions for realizing IP over WDM, optical burst switching is an ideal optical switching method. Its characteristic is that control packets and data packets are separated in transmission channel and time. The control packet is transmitted in a dedicated dense wavelength division multiplexing channel before the data packet, and an all-optical path is reserved for the corresponding data packet at the passing intermediate node. After a period of delay, the data packets are directly transmitted transparently in the pre-set all-optical channel. The one-way reservation scheme that does not require confirmation reduces the delay and wait time for channel establishment and improves bandwidth utilization; the medium-grained data packets reduce the overhead of control packets and improve utilization. The separation of data packets and control packets, suitable granularity and non-slot switching methods can reduce the requirements for photonic devices and the complexity of intermediate switching nodes, and can give full play to the advantages of existing photonic and electronic technologies.

Channel reservation and search is one of the core issues in optical burst switching networks. Currently, two methods have been proposed, namely the nearest schedulable channel (LAUC) and the last available channel with filling (LAUC-VF). The paper "Control Structure of Optical Burst Switching Wavelength Division Multiplexing Network (IEEE Journal on Selected Areas in Communication, Vol.18, No.10, pp.1838-1851, 2000)" by Yi jun Xiong et al. elaborates on LAUC in detail. and LAUC-VF algorithm. LAUC is a relatively simple scheduling algorithm without padding, which is easy to implement, but has low bandwidth utilization. The LAUC-VF algorithm minimizes the gap between data packets by selecting the nearest "unused" channel, which improves bandwidth utilization, but is more complicated. When the LAUC or LAUC-VF algorithm is used, large-scale changes in the length of packets of different levels will lead to unfair channel allocation, increase the delay of services with high delay requirements, and result in the loss of services with high delay requirements. Deterioration of packet and output channel utilization.

Contents of the invention

The purpose of the present invention is to address the deficiencies in the prior art, to provide an adaptive channel reservation and search method in optical burst switching, to improve the unfairness of channel allocation caused by the large-scale changes in the lengths of data packets of different levels, Improve network performance.

In order to achieve such a purpose, the self-adaptive channel reservation and search method proposed by the present invention adopts the principle of differentiated processing, and adaptively performs channel reservation according to different service levels, input traffic characteristics, network performance and channel configuration of output ports and search. Different classes of services have different maximum number of reservable channels. In the process of channel reservation and search, only when the number of reserved channels of a certain class of business is less than the maximum number of channels that can be reserved, the channel can be reserved for the burst data packet of this class. Businesses of different classes have different maximum times of channel searches in one time slot. The number of channel searches for a service of a certain level within a time slot cannot exceed the maximum number of channel searches for this level. The maximum number of reservable channels and the maximum number of channel searches of different grades are dynamically adjusted according to changes in service grades, input traffic characteristics, network performance, and channel configuration of output ports.

The concrete steps of the inventive method are as follows:

1. Set the maximum number of reservable channels for all classes of services to the maximum number of data channels of the output port, and set the maximum number of searches for all classes of services to 1. Initialize the input traffic and performance monitoring parameters, and start the adjustment timer for the number of reserved channels and searchable times, and enter an adjustment cycle.

2. During an adjustment period, real-time monitoring and statistics at the input port of the characteristics of the input traffic of different levels of business during the network operation within the adjustment period, including load and traffic distribution. At the same time, according to the current maximum number of reservable channels and the maximum number of searchable times of services of different grades, channels are reserved and searched for burst packets to be sent in order of grades from high to low.

If the waiting time of the burst packet has exceeded its maximum waiting delay, discard the burst packet and count the number of lost packets of this level; otherwise, judge whether the number of reserved channels of the level corresponding to the data packet has exceeded The current maximum number of channels that can be reserved, if so, delay the burst packet and process the next level, and the delayed burst packet will not be processed until a burst data packet of the same level releases a channel; if it has been reserved If the number of channels does not exceed its current maximum number of reservable channels, it will enter the channel search process.

3. In the channel search process, first initialize the search times to zero. Determine the sending start time of the burst control packet and the burst data packet. Then, search the channel multiple times by changing the start time of sending the burst packet and/or the offset time (offset time) until an available channel is found or the number of channel searches reaches the current maximum channel of this level The number of searches or the start of burst sending is greater than the maximum delay. Among them, if an available channel is found, the LAUC-VF algorithm is used to select an available channel to reserve for the data packet, the number of reserved channels of this level is increased by 1, and the delay characteristics of this level are counted; if the burst packet is sent If the start time is greater than the maximum delay, discard the packet and increase the number of lost packets of this level; if the number of channel searches has reached the maximum number of channel searches of this level in this scheduling cycle, then this packet will be reserved for the next burst deal with.

4. When the timer for adjusting the number of reserved channels and searchable times arrives:

First, according to the monitoring results of input traffic and network performance parameters, calculate the load of input traffic of different levels of business in this period, the average packet length and average arrival interval of burst packets, and its packet loss rate and delay, using exponential smoothing Add variance estimation techniques to predict the input rate for the next cycle at different levels.

Then update the maximum number of reservable channels and the maximum number of searches for services of different grades in descending order of grades.

If the packet loss rate of a certain level is lower than its maximum allowable packet loss rate, the new maximum number of reservable channels is the original maximum number of reservable channels plus the change (increase or decrease) of its input rate and the single output channel Rate ratio (rounded up). Its maximum number of searches remains unchanged.

Otherwise, it is judged whether the maximum number of searchable times of this level does not cause the data packets of this level to exceed the maximum delay, and if so, the maximum number of searchable times of this level is increased. Otherwise, add 1 to the maximum number of reservable channels for services of this level. At the same time, calculate the ratio of the actual packet loss rate of each level to the maximum allowable packet loss rate, multiply each ratio by the number of levels and round it up to find out For the level corresponding to the minimum value, subtract 1 from the maximum number of reservable channels of this level. If the predicted input rate of this level increases, the maximum number of reservable channels plus the ratio of the increase in input rate to the rate of a single output channel will be rounded up, otherwise no adjustment will be made.

After the adjustment is completed, the timer for adjusting the number of reserved channels and the number of searchable times is restarted to enter a new adjustment period.

The present invention adopts the principle of differentiated processing, and adaptively adjusts the reservation and search parameters according to the actual network input and operation effect, which can significantly improve the unfairness of channel allocation caused by the large-scale changes in the length of data packets of different levels in optical burst switching. performance, improve network performance and utilization of bandwidth resources.

Description of drawings

Figure 1 Channel reservation and search process in a single cycle.

Fig. 2 is a schematic diagram of multiple channel search processes.

Detailed ways

The self-adaptive channel reservation and search method proposed by the invention can be used for scheduling modules of edge nodes and core nodes of optical burst switching. The specific implementation steps of the adaptive channel reservation and search method proposed by the present invention are described below in conjunction with the accompanying drawings:

1. Initialize, set the maximum number of reservable channels for all levels of services to the maximum number of data channels of the output port, and set the maximum number of searches for all levels of services to 1. Simultaneously initialize the input traffic and performance monitoring parameters; start the number of reserved channels and the number of searchable times to adjust the timer.

2. During an adjustment period, monitor the load and flow distribution characteristics of the input traffic of different levels of services during network operation in the adjustment period at the input port in real time. At the same time, according to the maximum number of reservable channels and the maximum search times of different grades of services in this period, the channels are reserved and searched for burst packets to be sent in order of grades from high to low.

The process of channel reservation and search in a single cycle is shown in Figure 1. First, select the class to be processed according to the order of service class from high to low, if there is no burst packet to be processed in a certain class, then process the next class. In the level to be processed, if the waiting time to process the burst packet has exceeded its maximum waiting delay, then discard the burst packet and count the number of lost packets of this level; otherwise, judge that the level corresponding to the data packet has exceeded Whether the number of reserved channels has exceeded its current maximum number of reservable channels, if so, delay the burst packet and process the next level, and the delayed burst packet will release a channel until a burst data packet of the same level Will deal with later. If the number of reserved channels does not exceed the current maximum number of reservable channels, enter the channel search process.

3. In the channel search process, first initialize the search times to zero. Use the LAUC algorithm to determine the sending control channel and sending start time of the burst control packet. The start time of sending the burst data packet is set as the start time of sending the burst control packet plus the offset time. Then, search for available data channels. If the search is successful and an available data channel is found, then use the LAUC-VF algorithm to select an available channel to reserve for the data packet, add 1 to the number of reserved channels of this level, count the delay characteristics of this level, and end the search. If the search does not find an available data channel, the number of channel searches is increased by 1. If the number of searches for burst packets is greater than the maximum number of searches for this level of service, the search ends and the burst packets are left for next processing. Otherwise, select the next new available burst control packet transmission channel backward (that is, change the burst packet transmission start time) or keep the burst control packet transmission time unchanged to increase the offset time, and thus determine a new burst The start time of packet sending. If the start time of burst packet transmission is greater than the maximum delay, end the search, discard the burst packet, and count the number of lost packets at this level; otherwise, start the next search with the new burst packet transmission start time.

Figure 2 is a schematic diagram of the process of performing multiple channel searches by changing the start time of burst packet transmission while keeping the offset time constant. The two dashed lines on the right side of the figure correspond to the first search. There are no available channels for all data channels at this time. Therefore, the sending time of the burst control packet and the data packet is shifted backward, and a second search is performed, and the solid line corresponds to the second search. It can be seen that there is an available channel on channel 1 for the second time. The leftmost dotted line in the figure is the maximum delay allowed by the package.

4. When the number of reserved channels and searchable times adjustment timer arrives, according to the monitoring results of input traffic and network performance parameters, calculate the load of input traffic of different levels of business, the average packet length and average arrival interval of burst packets , and its packet loss rate and delay; using exponential smoothing plus variance estimation technology, the input rate of the next cycle of different levels can be predicted from the input loads of different levels obtained from the previous statistics. Then, the maximum number of reservable channels and the maximum number of searches for services of different grades are updated in descending order of grades.

If the packet loss rate of a certain level is lower than its maximum allowable packet loss rate, then:

The maximum number of reservable channels of this level in the next cycle = the maximum number of reservable channels in the previous cycle

The number of reserved channels + [the change in its input rate / the rate of a single output channel + a].

in,[ ] indicates rounding, 0≤a≤0.5, which can be optimized according to actual conditions. Its maximum number of searches remains unchanged.

If the packet loss rate of a certain level is greater than or equal to its maximum allowable packet loss rate, then judge whether the maximum number of searches for this level does not cause the data packets of this level to exceed the maximum delay, and if so, increase the maximum number of searches for this level. Otherwise, add 1 to the maximum number of reservable channels for services of this level. At the same time, calculate the ratio of the actual packet loss rate of each level to the maximum allowable packet loss rate, multiply each ratio by the number of levels and round to find out For the level corresponding to the minimum value, the maximum number of reservable channels of this level is reduced by 1.

If the packet loss rate of a class is greater than or equal to its maximum allowable packet loss rate, and the predicted input rate of this class increases, then:

The maximum number of reservable channels of this level in the next cycle = the adjusted maximum reservable channels

number + [change in its input rate/rate of a single output channel + a].

Among them, 0.5≤a≤1. If the predicted input rate for that class is not increasing or decreasing, then no adjustment is made.

After the adjustment is completed, the timer for adjusting the number of reserved channels and the number of searchable times is restarted to enter a new adjustment period.

Claims (1)

1, an adaptive channel reservation and search method in optical burst switching, is characterized in that specifically comprising the steps: 1) Set the maximum number of reservable channels for all levels of business to the maximum number of data channels of the output port, set the maximum number of searches for all levels of business to 1, initialize the input traffic and performance monitoring parameters, and start the reserved channel number and searchable times to adjust the timer, and enter an adjustment period; 2) In an adjustment period, real-time monitoring and statistics of the characteristics of the input traffic of different levels of business in the network operation process in the adjustment period at the input port; at the same time, according to the current maximum number of reservable channels for different levels of business and The maximum number of searchable times is to reserve and search channels for burst packets to be sent in order of rank from high to low. If the burst packet waiting time has exceeded its maximum waiting delay, the burst packet will be discarded and the level will be increased. Otherwise, judge whether the number of channels reserved for the class corresponding to the data packet has exceeded the current maximum number of reserved channels, if so, delay the burst packet, process the next class, and be delayed The burst packet will not be processed until a burst data packet of the same level releases a channel, otherwise it will enter the channel search process; 3) In the channel search process, first initialize the number of searches to zero, determine the start time of sending the burst control packet and the burst data packet, and then search the channel multiple times by changing the start time and/or offset time of the burst packet , until an available channel is searched or the number of channel searches reaches this level. The current maximum number of channel searches or the start moment of burst packet transmission is greater than the maximum delay. Among them, if an available channel is found, an available channel is selected to be reserved for For this data packet, add 1 to the number of reserved channels of this level, and count the delay characteristics of this level; if the start time of burst packet transmission is greater than the maximum delay, discard the packet and increase the number of lost packets of this level; if the channel If the number of searches has reached the maximum number of channel searches of this level in this scheduling period, then the packet is reserved for the burst packet for the next processing; 4) When the number of reserved channels and the number of searchable times adjustment timer arrives, according to the monitoring results of input traffic and network performance parameters, calculate the load of input traffic of different levels of business in this period, the average packet length of burst packets and The average arrival interval, its packet loss rate and delay, using exponential smoothing plus variance estimation technology, predicts the input rate of the next period of different levels; updates the maximum reservable channels of different levels of business in order of levels from high to low number and the maximum number of searches, if the packet loss rate of a certain level is lower than its maximum allowable packet loss rate, the new maximum number of reservable channels is the original maximum number of reservable channels plus the change of its input rate and a single The rounded value of the ratio of the output channel rate, the maximum number of searches remains unchanged; otherwise, determine whether the maximum number of searches for this level does not cause the data packets of this level to exceed the maximum delay, and if so, increase the maximum number of searches for this level. Otherwise, add 1 to the maximum number of reservable channels for services of this level. At the same time, calculate the ratio of the actual packet loss rate of each level to the maximum allowable packet loss rate, multiply each ratio by the number of levels and round it up. Find the level corresponding to the minimum value, and subtract 1 from the maximum number of reservable channels of this level. If the predicted input rate of this level increases, further add the maximum number of reservable channels to its input rate. It is the upward rounded value of the ratio of the increase amount to the rate of a single output channel, otherwise no adjustment is made; after the adjustment is completed, the timer for adjusting the number of reserved channels and the number of searchable times is restarted to enter a new adjustment period.