Clicks is a new software architecture for building flexible and configurable routers. A Click router is assembled from packet processing modules called elements. Individual elements implement simple router functions like packet classification, queuing, scheduling, and interfacing with network devices. A router configurable is a directed graph with elements at the vertices; packets flow along the edges of the graph. Several features make individual elements more powerful and complex configurations easier to write, including pull connections, which model packet flow drivn by transmitting hardware devices, and flow-based router context, which helps an element locate other interesting elements. Click configurations are modular and easy to extend. A standards-compliant Click IP router has 16 elements on its forwarding path; some of its elements are also useful in Ethernet switches and IP tunnelling configurations. Extending the IP router to support dropping policies, fairness among flows, or Differentiated Services simply requires adding a couple of element at the right place. On conventional PC hardware, the Click IP router achieves a maximum loss-free forwarding rate of 333,000 64-byte packets per second, demonstrating that Click's modular and flexible architecture is compatible with good performance.

The click modular router

From the Publisher:
The most up-to-date introduction to the field of computer networking, this book's top-down approach starts at the application layer and works down the protocol stack. It also uses the Internet as the main example of networks. This all creates a book relevant to those interested in networking today. By starting at the application-layer and working down the protocol stack, this book provides a relevant introduction of important concepts. Based on the rationale that once a reader understands the applications of networks they can understand the network services needed to support these applications, this book takes a "top-down" approach that exposes readers first to a concrete application and then draws into some of the deeper issues surrounding networking. This book focuses on the Internet as opposed to addressing it as one of many computer network technologies, further motivating the study of the material. This book is designed for programmers who need to learn the fundamentals of computer networking. It also has extensive material making it of great interest to networking professionals.

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Computer Networking: A Top-Down Approach Featuring the Internet

This paper considers the potentially negative impacts of an increasing deployment of non-congestion-controlled best-effort traffic on the Internet. These negative impacts range from extreme unfairness against competing TCP traffic to the potential for congestion collapse. To promote the inclusion of end-to-end congestion control in the design of future protocols using best-effort traffic, we argue that router mechanisms are needed to identify and restrict the bandwidth of selected high-bandwidth best-effort flows in times of congestion. The paper discusses several general approaches for identifying those flows suitable for bandwidth regulation. These approaches are to identify a high-bandwidth flow in times of congestion as unresponsive, "not TCP-friendly", or simply using disproportionate bandwidth. A flow that is not "TCP-friendly" is one whose long-term arrival rate exceeds that of any conformant TCP in the same circumstances. An unresponsive flow is one failing to reduce its offered load at a router in response to an increased packet drop rate, and a disproportionate-bandwidth flow is one that uses considerably more bandwidth than other flows in a time of congestion.

/pdf/promoting-the-use-of-end-to-end-congestion-control-in-the-86ipvhets3.pdf

Promoting the use of end-to-end congestion control in the Internet

Click is a new software architecture for building flexible and configurable routers. A Click router is assembled from packet processing modules called elements. Individual elements implement simple router functions like packet classification, queueing, scheduling, and interfacing with network devices. Complete configurations are built by connecting elements into a graph; packets flow along the graph's edges. Several features make individual elements more powerful and complex configurations easier to write, including pull processing, which models packet flow driven by transmitting interfaces, and flow-based router context, which helps an element locate other interesting elements.We demonstrate several working configurations, including an IP router and an Ethernet bridge. These configurations are modular---the IP router has 16 elements on the forwarding path---and easy to extend by adding additional elements, which we demonstrate with augmented configurations. On commodity PC hardware running Linux, the Click IP router can forward 64-byte packets at 73,000 packets per second, just 10% slower than Linux alone.

/pdf/the-click-modular-router-1nn6g98t3q.pdf

The Click modular router

Fair queuing is a technique that allows each flow passing through a network device to have a fair share of network resources. Previous schemes for fair queuing that achieved nearly perfect fairness were expensive to implement; specifically, the work required to process a packet in these schemes was O(log(n)), where n is the number of active flows. This is expensive at high speeds. On the other hand, cheaper approximations of fair queuing reported in the literature exhibit unfair behavior. In this paper, we describe a new approximation of fair queuing, that we call deficit round-robin. Our scheme achieves nearly perfect fairness in terms of throughput, requires only O(1) work to process a packet, and is simple enough to implement in hardware. Deficit round-robin is also applicable to other scheduling problems where servicing cannot be broken up into smaller units (such as load balancing) and to distributed queues.

Efficient fair queueing using deficit round-robin

Synchronization overhead, contention, and deadlock can pose severe challenges to designers and implementers of parallel programs Therefore, many researchers have proposed update disciplines that solve these problems in restricted but commonly occurring situations However, these proposals rely either on garbage collectors [7, 8], termination of all processes currently using the data structure [10], or expensive explicit tracking of all processes accessing the data structure [5, 15] These mechanisms are inappropriate in many cases, such as within many operating-system kernels and server applications This paper proposes a novel and extremely efficient mechanism, called read-copy update, and compares its performance to that of conventional locking primitives

/pdf/read-copy-update-using-execution-history-to-solve-51yefq77bd.pdf

Read-copy update: using execution history to solve concurrency problems

A class of algorithms called stochastic fairness queuing is presented. The algorithms are probabilistic variants of fairness queuing. They do not require an exact mapping and thus are suitable for high-speed software or firmware implementation. The algorithms span a broad range of CPU, memory, and fairness tradeoffs. It is shown that the worst-case execution-speed stochastic fairness queuing is faster than the best-case execution speed of all of the implementations of fair queuing presented. This advantage is larger for protocols with longer addresses, e.g. the ISO protocol suite. >

Stochastic fairness queueing

A technique for fiber-optic networks based on forward-error correction (FEC) that allows the destination to reconstruct missing data packets by using redundant parity packets that the source adds to each block of data packets is presented. Methods for generating several types of parity packets are described, along with decoding techniques and their implementations. Algorithms are presented for packet interleaving and selective rejection of packets from node buffers, both of which disperse missing packets among many blocks, thereby reducing the required coding complexity. Performance evaluation, by both analytic and simulation models, shows that this technique can result in a reduction of up to three orders of magnitude in the packet loss rate. >

Packet recovery in high-speed networks using coding and buffer management

A substantially zero overhead mutual-exclusion apparatus and method (90, 120) is provided that allows concurrent reading and updating data while maintaining data coherency. That is, a data reading process executes the same sequence of instructions that would be executed if the data were never updated. Rather than depending exclusively on overhead-imposing locks, this mutual-exclusion mechanism tracks an execution history (138) of a thread (16, 112) to determine safe times for processing a current generation (108, 130, 131) of data updates while a next generation (110, 132, 133) of data updates is concurrently being saved. A thread is any locus of control, such as a processor. A summary of thread activity (106, 122) tracks which threads have passed through a quiescent state after the current generation of updates was started. When the last thread related to the current generation passes through a quiescent state, the summary of thread activity signals a callback processor (104, 124) that it is safe to end the current generation of updates. The callback processor then processes and erases all updates in the current generation. The next generation of updates then becomes the current generation of updates. The callback processor restarts the summary of thread activity and initiates a new next generation of updates. All data-updating threads pass through a quiescent state between the time they attempt to update data and the time the data are actually updated.

Apparatus and method for achieving reduced overhead mutual exclusion and maintaining coherency in a multiprocessor system utilizing execution history and thread monitoring

http://csng.cs.toronto.edu/publication_files/0000/0159/jpdc07.pdf

Paul E. McKenney

Papers

Read-copy update: using execution history to solve concurrency problems

Stochastic fairness queueing

Packet recovery in high-speed networks using coding and buffer management

Apparatus and method for achieving reduced overhead mutual exclusion and maintaining coherency in a multiprocessor system utilizing execution history and thread monitoring

Performance of memory reclamation for lockless synchronization