Krishan Sabnani

• Johns Hopkins University

A network architecture includes one or more feature servers and control servers in a control plane that is logically separate from a data plane that includes forwarding elements. Feature servers facilitate adding network-based functionality in a centralized way that is has better scalability than the traditional router architecture. Some examples o...

The rapid growth in multimedia traffic is straining mobile networks thus necessitating the need for efficient content delivery mechanisms. In this paper we present the design and analysis of a scheme for streaming non-live, pre-recorded content (e.g. Video on Demand) that opportunistically takes advantage of the “slow fading” variations in the wire...

The invention includes a method and apparatus for providing multimedia content to a plurality of wireless terminals. The method includes transcoding an original media stream to form at least one companion media stream, each media stream having a different data rate, and advertising each media stream to each of the plurality of wireless terminals, e...

Multicast is an efficient means of transmitting the same content to multiple receivers while minimizing network resource usage. Applications that can benefit from multicast such as multimedia streaming and download, are now being deployed over 3G wireless data networks. Existing multicast schemes transmit data at a fixed rate that can accommodate t...

The telecom industry has an aspiration of moving to an Internet core for all of its services. Even cellular networks, with billions of end points, are moving to an Internet core. This poses a number of challenges, especially with ever-increasing content traffic. This talk will present these challenges and some efforts at Bell Labs to deal with them...

Multicast is an efficient means of transmitting the same content to multiple receivers while minimizing network resource usage. Applications that can benefit from multicast such as multimedia streaming and download, are now being deployed over 3G wireless data networks. Existing multicast schemes transmit data at a fixed rate that can accommodate t...

Control software in routers has gotten increasingly complex today. Further, since the control software runs in every router, managing a large network of routers is complex and expensive. In this paper, we propose that the control software be hosted in a few control element servers remotely from the forwarding elements (routers). This reduces the so...

Border gateway protocol (BGP) is the de facto standard used for interdomain routing. Since packet forwarding may not be possible until stable routes are learned, it is not only critical for BGP to converge but it is important that the convergence be rapid. The distributed and asynchronous nature of BGP in conjunction with local policies makes it di...

We consider a variation of a constrained Steiner minimal tree problem that is applicable for multicast conferencing. We assume a network having a cost and delay values associated with each edge. Then, we find an optimal shared tree with minimal cost subject to the constraint that the delay between any two nodes of the tree must be bounded by some m...

The aim of passive testing is to detect faults in a system while observing the system during normal operation, that is, without forcing the system to specialized inputs explicitly for the purposes of testing. We formulate some general correctness requirements on any passive-testing algorithm which we term soundness and completeness. With respect to...

This paper presents the design and implementation of call processing and mobility management software created for wireless networks using an asynchronous transfer mode (ATM) backbone. It describes the motivation for the work, reviews the system design and research results, and discusses the implementation of the system. It also presents ongoing wor...

Mobile communications is now so pervasive that, in some countries, mobile phones outnumber landline phones. Penetration rates of over 50% have been reached in many markets. This paper is focused on the standards, network platforms, and applications that are driving this phenomenon in terms of how these elements are providing new capabilities and se...

Mobile phones are quickly becoming one of the most ubiquitous wireless consumer devices. Separately, Internet services are growing by leaps and bounds. Thus, an interesting area of research is to see if and how the two can be married together to provide wireless ubiquitous access to the ever-growing Internet services. In this paper, we highlight t...

Wireless data services are poised for trememdous growth, accelerated by both the Internet and the rapid build-out of the necessary infrastructure. To support this growth, it is critical to design applications, protocols and system architecture that are adapted for a wireless operating environment. In this paper, we identify the key issues and chall...

We study congestion control for one-to-many multicast applications in the Internet and establish a three-way relationship between the choice of regulation parameter (i.e., rate or window size), the requirement to estimate receiver round trip times, and the type of fairness that may be accomplished. In particular, we show that in order to provide TC...

We present an efficient procedure that computes protocol converters from formal specifications. This procedure has a polynomial number of computation steps; on the other hand, all other procedures reported in the literature require an exponential number of computation steps. A major step in our procedure is the computation of the largest common sub...

Mobile phones are quickly becoming one of the most ubiquitous wireless consumer devices. Separately, Internet services are growing by leaps and bounds. Thus, an interesting area of research is to see if and how the two can be married together to provide wireless ubiquitous access to the ever-growing Internet services. We highlight the challenges an...

Wireless networks are characterized by simple end devices and limited bandwidth. One solution to address these and other limitations of the wireless mobile environment that has been widely pursued is the placement of proxies, or agents, inside the network to assist with application processing that would normally take place on end devices. These age...

This paper presents the design, implementation, and performance of a reliable multicast transport protocol (RMTP). The RMTP is based on a hierarchical structure in which receivers are grouped into local regions or domains and in each domain there is a special receiver called a designated receiver (DR) which is responsible for sending acknowledgment...

An important aspect of network management is fault management-determining, locating, isolating and correcting faults in the network. The paper deals with the algorithms for detecting faults, i.e., behavior of the network different from specifications. It is important for communication networks to detect faults “in-process” i.e., while the network i...

Wireless messaging, in the form of two-way paging, is an integral part of universal Personal Communications Services (PCS). Basic wireless messaging services include providing reliable (acknowledged) message delivery, reply capabilities, and message origination from a messaging device. Many more advanced services can also be envisioned. Wireless ne...

A new class of wireless messaging service, called two-way paging, is emerging. Current research on wireless messaging has mostly been concerned with low-level physical layer transmission issues, e.g., modulation and access. Few efforts have addressed high-level issues such as new messaging functionalities, high layer protocols, and overall system d...

We present a new approach for conformance testing of protocols specified as a collection of communicating finite state machines (FSMs). Our approach uses a guided random walk procedure. This procedure attempts to cover all transitions in the component FSMs. We also introduce the concept of observers that check some aspect of protocol behavior. We p...

In this paper, we present several challenges and innovative approaches to support nomadic computing. The nomadic computing environment is characterized by mobile users that may be connected to the network via wired or wireless means, many of whom will maintain only intermittent connectivity with the network. Furthermore, those accessing the network...

A communication system uses a precise set of rules called a protocol, to define interactions among its entities. With advancing computer transmission and switching technology, communication systems are providing sophisticated services demanded by users over a wide area. Protocol standards include a very, large number of options to take care of diff...

This paper describes the design and performance of a link-layer protocol for indoor and outdoor wireless networks. The protocol is asymmetric to reduce the processing load at the mobile, reliability is established by a combination of automatic repeat request and forward error correction, and link-layer packets are transferred appropriately during h...

Describes the design, validation, implementation and performance of an asymmetric link-layer protocol for a wireless link. The motivation for designing a new link-layer protocol is to obtain better performance in terms of end-to-end throughput and latency by correcting errors in an unreliable wireless link in addition to end-to-end correction rathe...

This paper presents the design and analysis of three reliable multicast transport protocols for high speed networks. The novelty of these protocols lies in the technique used in combining the acknowledgments of individual destinations along the underlying multicast tree to prevent acknowledgement implosion and in the technique used in preventing un...

The protocol VLSI engine (PROVE) is programmable VLSI chipset which can be used to implement several standard communication protocols. The protocol to be implemented is described in a formal specification language called the augmented protocol specification language (APSL). From these formal descriptions, a compiler generates microcode for PROVE. P...

The authors study the problem of locating the differences between a protocol specification and its implementation. They give an exact procedure for solving this problem. If there is only one difference between the implementation and the specification, then the algorithm will locate the difference and therefore identify the implementation machine. O...

The performance of the SNR protocol of A. N. Netravali et al. (1990) is studied when it is implemented for end-to-end flow and error control. Using a combination of analysis and simulation, the efficiency with which this protocol uses the network bandwidth and its achievable throughput is evaluated as a function of certain network and protocol para...

A systematic procedure that takes exponential time to synthesize protocol converters from formal specifications is presented. The algorithm proceeds in two steps: compute the largest common subset of services provided by the two mismatched protocols, and reduce the converter, retaining common services, without traversing the entire machine that rep...

An approach for conformance testing of protocols specified as a collection of communicating finite state machines (FSMs) with two parts, pruning and a guided random walk procedure, is presented. First the protocol is pruned to various sets of machines; each set provides only one service. This significantly reduces the test sequence length. Then a g...

The design, analysis, and implementation of an end-to-end transport protocol that is capable of high throughput consistent with the evolving high-speed physical networks based on fiber-optic transmission lines and high-capacity switches are presented. Unlike current transport protocols in which changes in control/state information are exchanged bet...

The wide range and high complexity of services expected from a communication protocol have made the process of protocol conformance testing a challenging task. Formal methods are required to thoroughly test these complex protocols. This paper reviews the four major methods of conformance test generation reported in the literature: transition tours,...

This paper presents an algorithmic procedure for checking logical correctness of communication protocols and discusses its application to the Q.931 Integrated Services Digital Network (ISDN) network layer protocol. A protocol is specified as a collection of communicating finite-state machines (FSMs). The procedure described here consists of two ste...

With the recent expansion of data communications networks, computers and terminals from different manufacturers must be interconnected. Before being connected to the network, these interacting elements should be tested to ensure that they conform to the network's protocol specifications. We describe an algorithmic method (which is based on unique i...

A procedure for checking safety properties of communication protocols is presented. A protocol is specified as a collection of communicating finite-state machines (FSMs). Two novel algorithms used in this procedure are described. The first algorithm does incremental composition and reduction of FSMs. It uses three heuristic rules which reduce the n...

Several protocol controllers for the IEEE 802 local area networks are surveyed and some characteristics for classifying them are given. Some case studies from these controllers are given as illustrations. Two new developments-the protocol engine and the programmable protocol engine-are also described. The protocol engine, currently under developmen...

We present a design and preliminary analysis of an end-to-end transport protocol that is capable of high throughput consistent with the evolving wideband physical networks based on fiber optic transmission lines and high capacity switches. Unlike the current transport protocols in which changes in control state information are exchanged between the...

A technique for detecting and diagnosing faults at the processor level in a multiprocessor system is described. A process is assigned whenever possible to two processors: the processor to which it would normally be assigned (primarily) and an additional processor that would otherwise be idle (secondary). Two strategies are described and analyzed: o...

Complete behavior of a communication protocol can be very large. It is worth investigating whether partial exploration of the behavior generates reasonable results. We present such a procedure which performs partial exploration using most-probable-first search. Some of the ideas used in this procedure are based on a convolutional decoding procedure...

A procedure presented here generates test sequences for checking the conformity of an implementation to the control portion of a protocol specification, which is modeled as a deterministic finite-state machine (FSM). A test sequence generated by the procedure given here tours all state transitions and uses a unique signature for each state, called...

An algorithmic procedure for protocol verification is presented. A protocol is described as a collection of processes interacting with one another using CSP-type input/output operations. The safety properties of each process are described by a finite-state machine and the liveliness properties of each process by a collection of temporal logic formu...

A procedure presented here generates test sequences for checking the conformity of an implementation to the control portion of a protocol specification, which is modeled as a deterministic finite-state machine (FSM). A test sequence generated by the procedure given here tours all state transitions and uses a unique signature for each state, called...

We present two protocols for information exchange between multiple identical senders and a single receiver. At each instant, every sender sends one bit, and the bits from all of senders are or-ed together into one bit before being received by the receiver. If a sender has a data message to send, it sends the message bits one by one; otherwise it se...

A description is given of an experience in estimating fault coverage of a test sequence designed to test the control portion of a protocol. The control portion of this protocol is modeled as a finite-state machine. This study uses Monte Carlo simulation and introduces a novel notion of machine equivalence. An algorithm given checks for this notion...

A technique is described for detecting and diagnosing faults at the processor level in a multiprocessor system. In this method, a process is assigned whenever possible to two processors: the processor that it would normally be assigned to (primary) and an additional processor which would otherwise be idle (secondary). Two strategies will be describ...

A technique is described for detecting and diagnosing faults at the processor level in a multiprocessor system. In this method, a process is assigned whenever possible to two processors: the processor that it would normally be assigned to (primary) and an additional processor which would otherwise be idle (secondary). Two strategies will be describ...

In this correspondence a system-level, comparison-based strategy for identifying faulty processors in a multiprocessor system is described. Unlike other strategies which have been proposed in the literature, the comparison approach is more efficient and relies on more realistic assumptions about the system under consideration. The new strategy is s...

Verifying a communication protocol means ensuring that it is free of logical errors prior to implementing it. That is, the goal of verification is to guarantee that the protocol does exactly what the designer intended. Techniques for verifying protocols differ depending on the protocol modeling techniques used. All techniques begin by modeling the...

A new connection establishment procedure for point-to-multipoint data transfer, the multiple attempts in one shot (MAOS) procedure, is proposed. The MAOS procedure is shown to have substantially lower connection establishment time compared to the conventional procedure used in protocols such as HDLC.

A novel procedure presented here generates test sequences for checking the conformity of protocol implementations to their specifications. The test sequences generated by this procedure only detect the presence of many faults, but they do not locate the faults. It can always detect the problem in an implementation with a single fault. A protocol en...

Two retransmission procedures, the go-back- N (GBN) scheme and the selective repeat (SR) scheme, have been analyzed for data transfer from one transmitter to many receivers. We consider transfer of error-controlled bulk data over a satellite broadcast channel. Two retransmission strategies, the dynamic retransmission group reduction (DRGR) techniqu...

A multidestination protocol is a data transfer procedure from one transmitter to many rceivers. We specify and verify such a protocol, the Selective Repeat procedure. The communication medium assumed is a satellite broadcast channel shared by using a time division multiplexed technique.The Selective Repeat procedure is modeled as a parallel program...