In October of '86, the Internet had the first of what became a series of 'congestion collapses'. During this period, the data throughput from LBL to UC Berkeley (sites separated by 400 yards and three IMP hops) dropped from 32 Kbps to 40 bps. Mike Karels1 and I were fascinated by this sudden factor-of-thousand drop in bandwidth and embarked on an investigation of why things had gotten so bad. We wondered, in particular, if the 4.3BSD (Berkeley UNIX) TCP was mis-behaving or if it could be tuned to work better under abysmal network conditions. The answer to both of these questions was “yes”.Since that time, we have put seven new algorithms into the 4BSD TCP: round-trip-time variance estimationexponential retransmit timer backoffslow-startmore aggressive receiver ack policydynamic window sizing on congestionKarn's clamped retransmit backofffast retransmit Our measurements and the reports of beta testers suggest that the final product is fairly good at dealing with congested conditions on the Internet.This paper is a brief description of (i) - (v) and the rationale behind them. (vi) is an algorithm recently developed by Phil Karn of Bell Communications Research, described in [KP87]. (viii) is described in a soon-to-be-published RFC.Algorithms (i) - (v) spring from one observation: The flow on a TCP connection (or ISO TP-4 or Xerox NS SPP connection) should obey a 'conservation of packets' principle. And, if this principle were obeyed, congestion collapse would become the exception rather than the rule. Thus congestion control involves finding places that violate conservation and fixing them.By 'conservation of packets' I mean that for a connection 'in equilibrium', i.e., running stably with a full window of data in transit, the packet flow is what a physicist would call 'conservative': A new packet isn't put into the network until an old packet leaves. The physics of flow predicts that systems with this property should be robust in the face of congestion. Observation of the Internet suggests that it was not particularly robust. Why the discrepancy?There are only three ways for packet conservation to fail: The connection doesn't get to equilibrium, orA sender injects a new packet before an old packet has exited, orThe equilibrium can't be reached because of resource limits along the path. In the following sections, we treat each of these in turn.

/pdf/congestion-avoidance-and-control-5b0pxljiwg.pdf

Congestion avoidance and control

Despite the apparent randomness of the Internet, we discover some surprisingly simple power-laws of the Internet topology. These power-laws hold for three snapshots of the Internet, between November 1997 and December 1998, despite a 45% growth of its size during that period. We show that our power-laws fit the real data very well resulting in correlation coefficients of 96% or higher.Our observations provide a novel perspective of the structure of the Internet. The power-laws describe concisely skewed distributions of graph properties such as the node outdegree. In addition, these power-laws can be used to estimate important parameters such as the average neighborhood size, and facilitate the design and the performance analysis of protocols. Furthermore, we can use them to generate and select realistic topologies for simulation purposes.

/pdf/on-power-law-relationships-of-the-internet-topology-19fp34v7ee.pdf

On power-law relationships of the Internet topology

The Internet has led to the creation of a digital society, where (almost) everything is connected and is accessible from anywhere. However, despite their widespread adoption, traditional IP networks are complex and very hard to manage. It is both difficult to configure the network according to predefined policies, and to reconfigure it to respond to faults, load, and changes. To make matters even more difficult, current networks are also vertically integrated: the control and data planes are bundled together. Software-defined networking (SDN) is an emerging paradigm that promises to change this state of affairs, by breaking vertical integration, separating the network's control logic from the underlying routers and switches, promoting (logical) centralization of network control, and introducing the ability to program the network. The separation of concerns, introduced between the definition of network policies, their implementation in switching hardware, and the forwarding of traffic, is key to the desired flexibility: by breaking the network control problem into tractable pieces, SDN makes it easier to create and introduce new abstractions in networking, simplifying network management and facilitating network evolution. In this paper, we present a comprehensive survey on SDN. We start by introducing the motivation for SDN, explain its main concepts and how it differs from traditional networking, its roots, and the standardization activities regarding this novel paradigm. Next, we present the key building blocks of an SDN infrastructure using a bottom-up, layered approach. We provide an in-depth analysis of the hardware infrastructure, southbound and northbound application programming interfaces (APIs), network virtualization layers, network operating systems (SDN controllers), network programming languages, and network applications. We also look at cross-layer problems such as debugging and troubleshooting. In an effort to anticipate the future evolution of this new paradigm, we discuss the main ongoing research efforts and challenges of SDN. In particular, we address the design of switches and control platforms—with a focus on aspects such as resiliency, scalability, performance, security, and dependability—as well as new opportunities for carrier transport networks and cloud providers. Last but not least, we analyze the position of SDN as a key enabler of a software-defined environment.

https://publications.uni.lu/bitstream/10993/20596/1/survey_on_SDN.pdf

Software-Defined Networking: A Comprehensive Survey

This paper describes a new replication algorithm that is able to tolerate Byzantine faults. We believe that Byzantinefault-tolerant algorithms will be increasingly important in the future because malicious attacks and software errors are increasingly common and can cause faulty nodes to exhibit arbitrary behavior. Whereas previous algorithms assumed a synchronous system or were too slow to be used in practice, the algorithm described in this paper is practical: it works in asynchronous environments like the Internet and incorporates several important optimizations that improve the response time of previous algorithms by more than an order of magnitude. We implemented a Byzantine-fault-tolerant NFS service using our algorithm and measured its performance. The results show that our service is only 3% slower than a standard unreplicated NFS.

/pdf/practical-byzantine-fault-tolerance-58gb0de0hd.pdf

Practical Byzantine fault tolerance

This memo discusses a proposed extension to the Internet architecture and protocols to provide integrated services, i.e., to support real- time as well as the current non-real-time service of IP. This extension is necessary to meet the growing need for real-time service for a variety of new applications, including teleconferencing, remote seminars, telescience, and distributed simulation.

Integrated Services in the Internet Architecture: an Overview

ASN .1 is the OSI standard for describing and encoding data which is to be transferre d between two systems via a data network. Independent of its role in OSI, ASN .1 is widel y considered an important data communications standard and is used in some non-OSI protocols. This book is a tutorial on ASN .1, written by one of the members of the standards committee s that designed it. ASN .1 is actually divided into two parts : a data description language and a set of encoding rules which are used to transmit the data described by the language over a network. Th e language and encoding rules are theoretically distinct ; in practice they are almost distinct — th e language clearly reflects the expectation that an encoding scheme like the one defined fo r ASN .l will be used. The book begins with two short introductory chapters which outline the history of ASN. I and describe the basic idea of an abstract syntax. The next three chapters describe the ASN. I language in detail. The sixth chapter explains the encoding rules, with many useful examples. The final three chapters present ASN .1's role in OSI, very very briefly discuss implementatio n issues, and mention some changes that are being considered in the standards bodies. The boo k concludes with a variety of useful appendicies including syntax diagrams and lists of ASN. I keywords. Overall, the book is impressive. The examples arc clear and usually well-chosen. Th e text is informative. The author's occasional explanations of standards debates which led t o particular design choices are quite useful. The only serious complaint that can be made about the book is that its discussion o f implementation concerns, and in particular, of the implementation issues surrounding th e encoding rules, is inadequate. The original work on which the encoding rules are based [I ] was an attempt to define a regular encoding scheme (in which all values are represented in a consistent form) that minimized the size of the encoding. As a result, encoding and decodin g ASN .1 is often reported to be more than a factor of ten more expensive than other encodin g schemes and has led some researchers to propose alternative encoding schemes [2]. The boo k does not seriously address this implementation problem .

Book Review: Abstract Syntax Notation One (ASN .1): The Tutorial and Reference by Douglas Steedman (Technology Appraisals Ltd. ISBN 1-871802-06-7)

About ten years ago, Bob Lucky asked me for a list of open research questions in networking. I didn't have a ready list and reacted it would be good to have one. This essay is my (long- belated) reply.

/pdf/forty-data-communications-research-questions-4yar3lmzh3.pdf

Forty data communications research questions

Technologies are available to unlock radio spectrum as consumers need it.

Realizing the future of wireless data communications

A pair of IP options that can be used to learn the minimum MTU of a
path through an internet is described, along with its possible uses.
This is a proposal for an Experimental protocol.

IP MTU discovery options

Embodiments of the invention reduce the probability of success of a DOS attack on a node receiving packets by decreasing the probability of random collisions of packets sent by a malicious user with those sent by honest users. The probability of random collisions may be reduced in one class of embodiments of the invention by supplementing the identification field of the IP header of each transmitted packet with at least one bit from another field of the header. The probability of random collisions may be reduced in another class of embodiments of the invention by ensuring that packets sent from a transmitting IPsec node to a receiving IPsec node are not fragmented.

Craig Partridge

Papers

Book Review: Abstract Syntax Notation One (ASN .1): The Tutorial and Reference by Douglas Steedman (Technology Appraisals Ltd. ISBN 1-871802-06-7)

Forty data communications research questions

Realizing the future of wireless data communications

IP MTU discovery options

Means of mitigating denial of service attacks on IP fragmentation in high performance IPsec gateways