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webtp - WebTP A Transport-Layer Dierentiated Services...

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WebTP - A Transport-Layer Differentiated Services Architecture Ye Xia * Hoi-Sheung Wilson So Jeng Lung Yogesh K. Bhumralkar Jean Walrand David Tse Department of Electrical Engineering and Computer Science University of California, Berkeley Abstract We introduce an experimental transport protocol, the WebTP, that can be used to provide differentiated quality-of-service (QOS) to flows in a “best effort” fashion on network segments. WebTP encapsulates TCP and UDP packets, aggregates many flows for integrated conges- tion control and schedules the transmission of their packets. Compared with layer-3 QOS- provisioning framework, WebTP can be deployed gradually with less overall planning, mainly due to its adaptive nature and its automatic gateway discovery mechanism. In this paper, we describe the WebTP protocol and its implementation on the Linux operating system. 1 Introduction In this paper, we report the design and implementation of the WebTP protocol. The WebTP protocol can be viewed as a layer-3/layer-4 hybrid under the OSI model, and can be understood in relation to two streams of active research during the past decade. It was first conceived as a new end-to-end transport protocol, which tries to integrate and implement various recommendations for protocol improvement based on extensive research on TCP. Second, it tries to provide quality of service (QOS) to connections, which is a goal shared by some IP-layer network control frameworks, most noticeably, DiffServ [8] and MPLS [16]. 1.1 Transport Functions: Application Support and Network Control The primary function of the transport layer is to establish a logical end-to-end communication path between the sending application and the receiving application, shielding the applications from the actual network that may consist of heterogeneous pieces with different technologies, topology, bandwidth, routing/forwarding behaviors and reliability levels. A transport packet typically has identifiers for the sending and receiving application, such as the port numbers in TCP and UDP. The network may corrupt data packets in a variety of ways. It may also delay or drop packets when congested. It may route packets through different network paths, causing them to arrive out-of-order at the receiver. If reliable communication is required, a reliable transport protocol * This project is funded by NSF Award #9872764. 1
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such as TCP is used to correct packet errors caused by imperfect networks. TCP can recover packet losses through retransmission of the lost packets, re-sequence packets that are misordered by the network, and detect duplicated or erroneous packets. In order to do so, the transport layers at the two hosts typically establish a reverse communication channel for passing feedback or acknowledgment information, notifying the sender the reception status of data packets. When the communication is not required to be reliable, an unreliable transport protocol such as UDP is used. UDP does not have a feedback path and cannot perform most of the error recovery functions.
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