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| IntServ | |
|---|---|
| Name | IntServ |
| Focus | Network quality of service |
| Introduced | Early 1990s |
| Standards | Integrated Services Architecture |
| Protocols | RSVP |
| Related | Differentiated Services, Multiprotocol Label Switching, Real-time Transport Protocol |
IntServ IntServ is an architectural framework for providing end-to-end quality of service (QoS) on packet-switched networks. Developed in the early 1990s alongside RSVP, IntServ defines per-flow resource reservation and admission control to guarantee bandwidth, latency, and jitter for applications such as voice, video, and real-time control. The model influenced standards bodies and protocols in the Internet Engineering Task Force and informed commercial offerings in service provider networks and academic testbeds.
IntServ originated from efforts at institutions such as University of Southern California and Carnegie Mellon University and was advanced through the work of the Internet Engineering Task Force and working groups including the Integrated Services WG. It contrasts with approaches championed by groups like the Differentiated Services proponents and with packet-labeling strategies such as Multiprotocol Label Switching. IntServ provides per-flow semantics similar to guaranteed service paradigms found in circuit-switched systems such as the Public Switched Telephone Network but operates over datagram networks like those used by ARPANET successors. The design goals were influenced by real-time multimedia research from projects at Bell Labs and multimedia testbeds funded by agencies including the National Science Foundation.
The IntServ architecture defines two principal service classes: Guaranteed Service and Controlled-Load Service, specified in standards produced by the Internet Engineering Task Force. Key components include end hosts, routers with per-flow state, and signaling entities implementing the Resource Reservation Protocol. Admission Control modules in routers consult classifiers and packet schedulers, including algorithms like token bucket shapers related to work from Van Jacobson and schedulers inspired by research at Stanford University and MIT. Packet classifiers identify flows using header fields standardized in protocols such as Transmission Control Protocol and User Datagram Protocol combined with Internet Protocol addresses and port numbers. Router queuing disciplines compatible with IntServ include priority queuing, weighted fair queuing (WFQ), and variants derived from research presented at conferences like SIGCOMM.
RSVP is the signaling protocol designed to carry reservation requests in IntServ deployments. RSVP messages traverse network elements registered in standards and were specified in RFCs produced by the Internet Engineering Task Force. The protocol operates with soft-state, requiring periodic refresh messages, a design choice influenced by scalability trade-offs discussed in publications from Bellcore and IBM Research. RSVP supports both unicast and multicast reservations and interacts with admission control and policy modules, which can be administered by entities such as network operators or institutions following frameworks like those from the Internet Architecture Board. RSVP’s design draws on prior signaling work from the Integrated Services Digital Network and concepts evaluated in projects like Mbone.
IntServ provides quantitative QoS by specifying parameters for each flow: bandwidth, maximum packet delay, and jitter bounds. Guaranteed Service offers hard bounds based on tight mathematical models developed in queuing theory literature from researchers at Princeton University and University of California, Berkeley. Controlled-Load Service approximates unloaded best-effort behavior and relies on stochastic models similar to research published at INFOCOM. Implementation requires packet schedulers supporting work-conserving and non-work-conserving modes and policing mechanisms that enforce token bucket parameters derived from admission decisions. Policy enforcement can integrate with directory services and authentication frameworks used by organizations such as IETF-affiliated projects and commercial systems from vendors like Cisco Systems and Juniper Networks.
A central criticism of IntServ is scalability: per-flow state and RSVP signaling burdens were shown in studies at Lucent Technologies and university testbeds to limit applicability in core network routers handling millions of flows. Soft-state refresh traffic and per-flow queuing increase memory and CPU demands, creating operational challenges for backbone operators such as AT&T and Verizon Communications. Solutions proposed include aggregation of reservations, hierarchical signaling inspired by telecommunication standards like those from the International Telecommunication Union, and hybrid models combining per-flow reservation at network edges with aggregate treatment in cores, an idea that influenced the development of Differentiated Services and Multi-Protocol Label Switching.
IntServ found niche deployment in campus networks, specialized research networks, and multimedia testbeds run by institutions such as University of Washington and California Institute of Technology. Use cases included real-time teleconferencing, distributed simulation, and remote instrumentation in scientific collaborations funded by agencies like the National Aeronautics and Space Administration and the Defense Advanced Research Projects Agency. Commercial deployments were limited; when adopted, IntServ features often appeared in access networks and edge devices provided by vendors such as Nortel Networks and Ericsson to support premium multimedia services.
IntServ differs fundamentally from Differentiated Services: IntServ enforces per-flow guarantees with explicit reservation signaling and per-flow state, whereas DiffServ uses coarse-grained per-class marking at network boundaries without per-flow state in core routers. The trade-offs reflect contrasting priorities evident in standards discussions at the Internet Engineering Task Force and operational choices by carriers like Sprint and Deutsche Telekom. DiffServ's scalability and simpler deployment model led many service providers to favor class-based QoS and to combine edge-based reservation or admission control with core DiffServ forwarding, a hybrid approach studied in trials involving vendors such as Cisco Systems and research labs at Bell Labs.
Category:Computer networking