WO2000072532A1

WO2000072532A1 - System and method for network packet reduction

Info

Publication number: WO2000072532A1
Application number: PCT/US2000/014381
Authority: WO
Inventors: B.R. Badrinath; Predeep Sudame
Original assignee: Rutgers, The State University Of New Jersey
Priority date: 1999-05-24
Filing date: 2000-05-24
Publication date: 2000-11-30
Also published as: WO2000072532A9; AU5288700A

Abstract

A system of and method for reducing network packet traffic is described. Embodiments of the present invention combine small packets with the same destination into a larger packet, thereby reducing the number of packets flowing in the network. Small packets dominate Internet traffic patterns today. The overhead due to queuing, processing, routing, differential treatment, and delivery is the same irrespective of the size of the packet. Hence, small packets impose a relatively higher overhead on the network. The domination of small packet traffic is expected to get only worse with the ever increasing web applications and the introduction of new applications such as Voiceover IP.

Description

System and Method for Network Packet Reduction

Field of the Invention

The present invention relates generally to computer networks and more specifically to reducing packets on a network.

Copyright Notice/Permission A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever. The following notice applies to the software and data as described below and in the drawings hereto: Copyright © 2000 Rutgers,

The State University of New Jersey, All Rights Reserved. Background of the Invention Data communication in a computer network involves the exchange of data between two or more entities interconnected by communication links and subnetworks. These entities are typically software programs executing on hardware computer platforms, such as end stations and intermediate stations. Examples of an intermediate station may be a router or switch which interconnects the communication links and subnetworks to enable transmission of data between the end stations. A local area network (LAN) is an example of a subnetwork that provides relatively short distance communication among the interconnected stations; in contrast, a wide area network (WAN) enables long distance communication over links provided by public or private telecommunications facilities. Communication software executing on the end stations correlates and manages data communication with other end stations. The stations typically communicate by exchanging discrete packets or frames of data according to predefined protocols. Collectively, these hardware and software components comprise a communications network. Small packets (less than the default link MTU of 512 bytes) dominate Internet traffic patterns today. Wide-area Internet traffic measurements show that as many as sixty percent (60%) of the packets transmitted over the Internet backbone are less than 44 bytes. Web servers, for example, are a leading generator of small packets. All of the TCP ACKs generated by the clients have the same destination (the web server). These ACKs are just 40 bytes in size. Another example of small packet traffic is ICP

(Internet Cache Protocol) queries generated among web proxies. ICP queries are about 60 bytes in size. This domination of small packets in Internet traffic patterns is expected to get only worse with the ever increasing web traffic and with introduction of new applications such as VoIP (Voiceover-IP applications generate small audio samples, about 40 to 60 byte packets every 40 ms). The network overhead cost due to queuing, processing, routing, differential treatment and delivery is the same irrespective of the size of the packet. Hence, small packets impose a relatively higher overhead on the network. Therefore, in order to improve overall network performance, there is a need to reduce the number of packets in the network.

Summary of the Invention A system of and method for reducing network packet traffic is described. Embodiments of the present invention combine small packets with the same destination into a larger packet, thereby reducing the number of packets flowing in the network. Small packets dominate Internet traffic patterns today. The overhead due to queuing, processing, routing, differential treatment, and delivery is the same irrespective of the size of the packet. Hence, small packets impose a relatively higher overhead on the network. The domination of small packet traffic is expected to get only worse with the ever increasing web applications and the introduction of new applications such as Voiceover IP. To mitigate the impact of small packets, a novel approach of combining multiple small packets going towards the same destination is provided. One aspect of the invention is a computerized method of reducing packets on a network. The method comprises combining multiple packets for a destination into an aggregated packet, and separating the aggregated packet into the multiple packets at the destination.

Still other and further embodiments, aspects and advantages of the invention will become apparent by reference to the drawings and by reading the following detailed description.

Brief Description of the Drawings Figure 1 is a block diagram of a traditional communication network. Figure 2 is a block diagram of a communication network according to an example embodiment of the invention. Figure 3 A is a block diagram of a traditional router.

Figure 3B is a block diagram of an aggregator, such as the aggregator shown in Figure 2, according to an example embodiment of the present invention. Figure 4 is a block diagram of a splitter, such as the splitter shown in Figure 2, according to an example embodiment of the present invention.

Figure 5 is a block diagram showing how metadata is stored when two small packets are combined at a router according to an example embodiment of the invention.

Description of the Embodiments In the following detailed description of the embodiments, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. It is to be understood that other embodiments may be utilized and that structural, logical and electrical changes may be made without departing from the scope of the present inventions. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present inventions is defined only by the appended claims. A system of and method for reducing network packet traffic is described below. Embodiments of the present invention combine small packets with the same destination into a larger packet, thereby reducing the number of packets flowing in the network.

Figure 1 is a block diagram of a traditional communication network 100. As shown in Figure 1, the traditional communication network 100 comprises a plurality of end stations 102 and a plurality of intermediate stations 104 interconnected by communications links. In the example shown in Figure 1, the intermediate links are routers 104.

Figure 2 is a block diagram of a communication network 200 according to an example embodiment of the present invention. As shown in Figure 2, the communication network 200 comprises a plurality of end stations 202 and a plurality of intermediate stations 204. The intermediate stations 204 include an aggregator and a splitter which are further described below. The aggregator and the splitter function to reduce the packets on the communications link between them. The aggregator combines a small packets into a larger packet so that the routers see a smaller number of packets. The splitter separates these packets so that the subsequent stations in the network are unaware of the packet aggregation. Aggregators, as well as splitters, can be placed at intermediate stations or at end stations in the network. The placement of aggregators and splitters may be varied depending on traffic patterns, level of congestion and software application needs.

In one embodiment, the aggregators as well as the splitters can be the end stations in the network. In an alternate embodiment, the aggregators and splitters are placed at ingress and egress routers in the network. The placement of aggregators and splitters may be manually configured or may be dynamically assigned according to a signaling mechanism of the present invention which is further described below. In another embodiment, the aggregated packets on the communications links between the aggregator and the splitter are treated as a special class of traffic to further enhance network performance. The number of packets in the network are reduced by combining small packets multiple times at various points in the network.

In one embodiment, the placement of the aggregator in the network is based on the application and is dynamically determined by the receiver of the packets. A signaling mechanism of the present invention allows the receiver of the packets to place aggregators at points in the network where packets can be combined. If the aggregation at that location in the network is ineffective, the aggregators can be dynamically or manually removed and, if desired, repositioned at another point in the network. In other words, if the application ceases to need aggregation, the network can remove the aggregators without affecting the normal network routing. Thus, the signalling mechanism allows the aggregation of packets to be initiated and stopped dynamically. In an alternate embodiment, the signaling mechanism can be initiated and stopped by manual configure according to a user. Figure 3 A is a block diagram of a traditional router 300. As shown in

Figure 3A, three packets 302 are received by router 300. The router 300 performs a routing table 304 lookup to determine the output queue 306 for each one of the packets. All three packets 302 leave router 300 and are transmitted across a communication link. Figure 3B is a block diagram of an aggregator such as the aggregator shown in Figure 2. As used herein, an aggregator refers to any end station or intermediate station capable of combining multiple small packets to the same destination and sending them as one packet. For example, an aggregator may be implemented as a hardware module or a software module in a router. As shown in Figure 3B, three packets 312 are received by router 310. The router 310 performs a routing table 304 lookup to determine the destination of the packets 302. However, unlike the traditional router shown in Figure 3 A, the router 310 comprises an aggregation module 315. In this example, the three packets 302 have the same destination. The aggregation module 315 combines the three packets 312 into a single packet 318 referred to herein as an "aggregated packet." The aggregated packet 318 is placed in the output queue 316 for the destination and unlike the traditional router, only the single aggregated packet leaves the router 310 and is transmitted across the communication link.

Once such an aggregated packet reaches the destination, all the original packets can be regenerated. The node that separates aggregated packets is referred to herein as a "splitter." Figure 4 is a block diagram of a splitter 400. As used herein, a splitter refers to any end station or intermediate station capable of separating an aggregated packets into the original multiple packets. For example, a splitter may be implemented as a hardware module or a software module in a router. As shown in Figure 4, an aggregated packet 402 is received by router 400. The router 400 performs a routing table 404 lookup to determine the destination of the packet 402. However, unlike the traditional router shown in Figure 3 A, the router 400 comprises a splitter module 406. The splitter module 400 separates the aggregated packet 406 into the original multiple packets 408. In one embodiment, the multiple packets 408 are placed in the output queue 410 for router 400.

Aggregation as well as splitting can be performed either at layer 2 (MPLS) or at layer 3 (network layer) of the protocol stack. Aggregators at layer 2 require a hardware implementation. In an example embodiment, aggregators and splitters are implemented using transformer tunnels. Transformer tunnels are described in more detail in Predeep Sudame and B. R. Bardinath, "Transformer tunnels: A framework for providing route-specific adaptions," in Proceedings of the USENIX Annual Technical Conference, June 1998, pp. 191-200, which is herein incorporated by reference. However, embodiments of the present invention are not limited to being implemented with transformer tunnels and alternate embodiments are contemplated. To control the number of routing table entries at an aggregator node, the splitter can be a node other than the final destination. This way, packets belonging to multiple destinations (for example, a subnet) can be combined using a single tunnel. Aggregators may also be dynamically placed in the network so that the bottleneck links lie between the splitters and the aggregators. A computerized method of reducing packets on a network according an example embodiment of the invention comprises combining multiple packets for a destination into an aggregated packet, transmitting the single packet to the destination, and separating the aggregated packet into the multiple packets at the destination. In one embodiment, an aggregation function combines the multiple packets for a destination into an aggregated packet using a mechanism similar to TCP delayed ACKs. Every small packet is delayed by a small amount of time. The process of combining small packets continues until either m (a parameter to the aggregation function described below) packets have been combined, or a timeout occurs. If no other small packets arrive before the timeout, the delayed packet is sent as is. This aggregation mechanism is different from IP reassembly (performed after IP fragmentation). An aggregation function combines small packets, along with their IP headers, to get a larger packet. The receiver regenerates all the original packets when it receives such an aggregated packet. Thus, this mechanism can be used even for protocols that honor message boundaries (e.g., UDP).

In one embodiment, for the receiver to be able to regenerate the original packets, some information is added (metadata) to the aggregated packet. Figure 5 is a block diagram showing how metadata is stored when two small packets are combined at a router. The generated larger packet has a new protocol number (77) in the IP header. (The original protocol therefore has to be stored as part of the metadata, along with the original destination of the packet, if it is different than the address of the splitter node.) The receiver of this packet handles the packet to the protocol handler for this new protocol. This handler is responsible for removing all the metadata and restoring the packets. As small packets are delayed for some time in the hope that they can be combined with other small packets, the delayed packets see increased latency. The latency depends on the packet inter-arrival rate, and the timeout set by the applications. In the best case, when m packets are combined, the timeout does not come into picture, because the buffers are flushed immediately when the packets are combined. An example embodiment of an aggregation function as described above is provided below. The aggregation function is provided for illustrative purposes only.

Parameters: timeout, m: max packets to be combined

Initialization code: delayed_packet = null; aggregate (p) { if (p is large) { cancel timer; send delayed_packet; delayed_packet=«M/7;

} send p; return PACKET_SENT;

} if (delayed_packet exists) { if (p and delayed_packet can be combined) { delayed_packet = combine (delayed_packet, p); if (m packets have been combined) { cancel timer; send delayed_packet; delayed_packet = null;

} return PACKET_SENT; } else { cancel timer; send delayed_packet; set timer; delayed_packet = p; return PACKET_SENT;

} } else { set timer; delayed_packet = p; return PACKET SENT;

Timer expires: send delayed_packet; delayed_packet = null; Given that there is sufficient evidence of small packet traffic in the Internet, there are a number of benefits to be obtained by packet-level aggregation. First, most router implementations (such as FreeBSD, Linux, and many Cisco routers) are packet limited rather than byte limited. They place a limit on the number of packets that the router can queue irrespective of the size of each packet. For reasons of efficiency, routers store packet headers (whose sizes are independent of the packet sizes) in fast memory, and the packet payload in slow memory. The fast memory being expensive decides the queue size. Every packet, irrespective of the size, consumes one slot in the queue. Combining small packets into a larger packet reduces the number of packets seen at routers, and hence helps absorb bursts (reduce losses) for a given level of congestion.

Second, every packet at a router requires a routing table lookup and incurs the same performance cost irrespective of the size of the packet. Combining small packets at a router reduces the number of packets seen by all the subsequent routers. Moreover, to implement a specific per-hop behavior (as in differential services), routers have to give preferential treatment to every packet of a particular class. By combining small packets belonging to the same class, these overheads can be reduced. Third, every packet requires a link-layer header. For example, every ethernet packet has 18 bytes overhead (2 bytes for type, 6 bytes for source address, 6 bytes for destination address, 4 bytes for CRC). Moreover, an ethernet frame also has 12 bytes of frame spacing and 8 bytes of preamble. Also, packets smaller than 46 bytes have to be padded with additional bytes to make the frame size 64 bytes. Therefore, by combining two 40 bytes packets into a larger packet, 44 bytes are saved. The gains increase further if more than two packets are combined into a larger packet.

For gigabit ethernet, the minimum frame size is 512 bytes, and hence even bigger savings are obtained by combining multiple small packets into a single larger packet. Packet bursting technique reduces the padding overheads by sending back-to-back frames, however, the first frame still incurs the padding overhead and two consecutive frames must have the required inter- frame spacing.

Fourth, on links such as Ethernets and wireless LANs, terminals need to contend for the channel prior to sending a packet. Reducing the number of packets reduces the contention cost and increases channel utilization.

Finally, aggregation reduces interrupt overheads. Incoming packets generate an interrupt at the receiver. On a modern RISC processor, each interrupt breaks the CPU pipeline, interferes with the cache, requires a change to the memory management context, and forces a substantial number of CPU registers to be saved. An /.-fold reduction in packets thus reduces the interrupt and packet overhead by a factor of n.

It is to be understood that the above description is intended to be illustrative, and not restrictive. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.

Claims

What is claimed is:

1. A computerized method of reducing packets on a network, the method comprising: combining multiple packets for a destination into an aggregated packet; transmitting the single packet to the destination; separating the aggregated packet into the multiple packets at the destination.

2. The method of claim 1 , wherein a predetermined number of the multiple packets are combined into the aggregated packet.

3. The method of claim 1 , wherein the multiple packets received over a predetermined period of time are combined into the aggregated packet.

4. The method of claim 1 wherein the combining and splitting is implemented in hardware.

5. The method of claim 1 wherein the combining and splitting is implement in software.

6. The method of claim 1 wherein the destination is an end station.

7. The method of claim 1 wherein the destination is an intermediate station.

8. The method of claim 1 wherein the combining is performed at a dynamically designated network station.

9. The method of claim 1 wherein the combining is performed at a user-designated network station.

10. A network router comprising: a routing table to identify a destination for a plurality of packets; and an aggregator module to combine at least two of the packets with a same destination into an aggregate packet.

11. The network router of claim 10, wherein a predetermined number of the multiple packets are combined into the aggregated packet.

12. The network router of claim 10, wherein the multiple packets received over a predetermined period of time are combined into the aggregated packet.

13. The network router of claim 10 wherein the aggregator module is a hardware module.

14. The network router of claim 10 wherein the aggregator module is a software module.

15. A network router comprising : a routing table to identify a destination for an aggregated packet; and a splitter module to regenerate a plurality of original packets from a second aggregated packet.

16. The network router of claim 15 wherein the splitter module is a hardware module.

17. The network router of claim 15 wherein the splitter module is a software module.

18. A computerized system comprising: an aggregator module to combine multiple packets with a same destination into a first aggregate packet; and a splitter module to regenerate a plurality of original packets from a second aggregated packet.

19. The computerized system of claim 18, further comprising a signaling mechanism to dynamically establish an aggregator module.

20. A computer readable medium containing executable program instructions combining network packets, the executable instructions comprising program instructions for: combining small packets for a same destination into a single larger packet; adding meta data to the aggregated packet; and sending the aggregated packet to a receiver.

21. The computer readable medium of claim 20 wherein the combining of small packets into a single larger packet continues until a predetermined number of small packets have been combined into the larger packet.

22. The computer readable medium of claim 20 wherein the combining of small packets continues until a predetermined period of time expires.