Salman A. Baset

An Analysis of the Skype Peer-to-Peer Internet Telephony Protocol

Skype is a peer-to-peer VoIP client developed in 2003 by the organization that created Kazaa. Skype claims that it can work almost seamlessly across NATs and firewalls and has better voice quality than other VoIP clients. It encrypts calls end-to-end, and stores user information in a decentralized fashion. Skype also supports instant messaging and conferencing. This paper analyzes key Skype functions such as login, NAT and firewall traversal, call establishment, media transfer, codecs, and conferencing under three different network setups. Analysis is performed by careful study of the Skype network traffic and by intercepting the shared library and system calls of Skype. We draw a map of super nodes to which Skype establishes a TCP connection at login.

Cloud SLAs: present and future

The variability in the service level agreements (SLAs) of cloud providers prompted us to ask the question how do the SLAs compare and how should the SLAs be defined for future cloud services. We break down a cloud SLA into easy to understand components and use it to compare SLAs of public cloud providers. Our study indicates that none of the surveyed cloud providers offer any performance guarantees for compute services and leave SLA violation detection to the customer. We then provide guidance on how SLAs should be defined for future cloud services.

Can software routers scale

Software routers can lead us from a network of special-purpose hardware routers to one of general-purpose extensible infrastructure - if, that is, they can scale to high speeds. We identify the challenges in achieving this scalability and propose a solution: a cluster-based router architecture that uses an interconnect of commodity server platforms to build software routers that are both incrementally scalable and fully programmable.

The delay-friendliness of TCP for real-time traffic

TCP has traditionally been considered inappropriate for real-time applications. Nonetheless, popular applications such as Skype use TCP since UDP packets cannot pass through restrictive network address translators (NATs) and firewalls. Motivated by this observation, we study the delay performance of TCP for real-time media flows. We develop an analytical performance model for the delay of TCP. We use extensive experiments to validate the model and to evaluate the impact of various TCP mechanisms on its delay performance. Based on our results, we derive the working region for VoIP and live video streaming applications and provide guidelines for delay-friendly TCP settings. Our research indicates that simple application-level schemes, such as packet splitting and parallel connections, can reduce the delay of real-time TCP flows by as much as 30% and 90%, respectively.

NetServ Framework Design and Implementation 1.0

Eyeball ISPs today are under-utilizing an important asset: edge routers. We present NetServ, a programmable node architecture aimed at turning edge routers into distributed service hosting platforms. This allows ISPs to allocate router resources to content publishers and application service providers motivated to deploy content and services at the network edge. This model provides important benefits over currently available solutions like CDN. Content and services can be brought closer to end users by dynamically installing and removing custom modules as needed throughout the network. Unlike previous programmable router proposals which focused on customizing features of a router, NetServ focuses on deploying content and services. All our design decisions reflect this change in focus. We set three main design goals: a wide-area deployment, a multi-user execution environment, and a clear economic benefit. We built a prototype using Linux, NSIS signaling, and the Java OSGi framework. We also implemented four prototype applications: ActiveCDN provides publisher-specific content distribution and processing; KeepAlive Responder and Media Relay reduce the infrastructure needs of telephony providers; and Overload Control makes it possible to deploy more flexible algorithms to handle excessive traffic.

Skype relay calls: Measurements and experiments

Skype, a popular peer-to-peer VoIP application, works around NAT and firewall issues by routing calls through the machine of another Skype user with unrestricted connectivity to the Internet. We describe an experimental study of Skype video and voice relay calls conducted over a three-month period, where approximately 18 thousand successful calls were made and over nine thousand Skype relay nodes were found. We have determined that the relay call success rate depends on the network conditions, the presence of a host cache, and caching of the callees reachable address. From our experiments, we have found that Skype relay selection mechanism can be further improved, especially when both caller and callee are behind a NAT.

The delay-friendliness of TCP

TCP has traditionally been considered unfriendly for real-time applications. Nonetheless, popular applications such as Skype use TCP since UDP packets cannot pass through many NATs and firewalls. Motivated by this observation, we study the delay performance of TCP for real-time media flows. We develop an analytical performance model for the delay of TCP. We use extensive experiments to validate the model and to evaluate the impact of various TCP mechanisms on its delay performance. Based on our results, we derive the working region for VoIP and live video streaming applications and provide guidelines for delay-friendly TCP settings. Our research indicates that simple application-level schemes, such as packet splitting and parallel connections, can reduce the delay of real-time TCP flows by as much as 30% and 90%, respectively.

vDelay: A Tool to Measure Capture-to-Display Latency and Frame Rate

We present vDelay, a tool for measuring the capture-to-display latency (CDL) and frame-rate of real-time video applications such as video chat and conferencing. vDelay allows measuring CDL and frame-rate without modifying the source code of these applications. Further, it does not require any specialized hardware. We have used vDelay to measure the CDL and frame-rate of popular video chat applications such as Skype, Windows Live Messenger, and GMail video chat. vDelay can also be used to measure the CDL and frame-rate of these applications in the presence of bandwidth variations.

Open source cloud technologies

Open source cloud technologies such as OpenStack, CloudStack, OpenNebula, Eucalyptus, OpenShift, and Cloud Foundry have gained significant momentum in the last few years. For a researcher and practitioner, they present a unique opportunity to analyze, contribute, and innovate new services using these technologies. The first part of the tutorial will provide an overview of OpenStack and CloudStack, two open source infrastructure as a service (IaaS) cloud platforms. The second part of the tutorial will present a detailed analysis of different OpenStack components, namely, glance (image service), nova (compute service), keystone (security service), quantum (network service), and swift (object storage service). In particular, the tutorial will describe the scheduling and provisioning process in OpenStack, and how different configuration options lead to myriad provisioning performance. Further, the tutorial will describe how OpenStack has evolved over releases. Finally, the tutorial will describe weaknesses of OpenStack and highlight important areas where researchers can contribute.

How green is IP-telephony?

With constantly increasing costs of energy, we ask ourselves what we can say about the energy efficiency of existing VoIP systems. To answer that question, we gather information about the existing client-server and peer-to-peer VoIP systems, build energy models for these systems, and evaluate their power consumption and relative energy efficiency through analysis and a series of experiments. Contrary to the recent work on energy efficiency of peer-to-peer systems, we find that even with efficient peers a peer-to-peer architecture can be less energy efficient than a client-server architecture. We also find that the presence of NATs in the network is a major obstacle in building energy efficient VoIP systems. We then provide a number of recommendations for making VoIP systems more energy efficient.