Service Access Point Research Articles

Adaptive rate allocation and resource planning for service level agreement maintenance in satellite communications

The paper deals with protocol architectures to support mapping of Quality of Service (QoS) between protocol layers of telecommunications networks. The Satellite Independent – Service Access Point, currently under study within the European Telecommunications Standardization Institute (ETSI), is taken as technological reference. The key elements of the ETSI solution are outlined in detail. A novel control algorithm is also proposed to tune bandwidth dimensioning within the envisaged architecture. The joint optimization of loss and delay performance metrics, together with the presence of mapping operations, introduce the generalization of the regular concept of “equivalent bandwidth”. The generalization leads to the study of a proper measurement-based tool, able to capture the most stringent QoS requirement over time (between loss and delay) and the related instantaneous bandwidth need at the lower layer of the protocol stack. The control methodology is tested through real fading and traffic traces to highlight its effectiveness to support bandwidth dimensioning during mapping operations.

Ethernet aggregation and core network models for effcient and reliable IPTV services

With the growing interest on wireline network architectures for residential triple-play and business Ethernet services there is a renewed demand for efficient and reliable packet-based transport capabilities between the content providers and the end users. Voice and data traffic carried over a variety of access technologies is collected via technology-specific access networks (e.g., digital subscriber line [xDSL], passive optical network [xPON], and wireless fidelity [WiFi]). Metro and core networks need to aggregate the various user flows from different access network nodes and provide scalable and cost-effective distribution of various flow types (e.g., Internet access, voice, video on demand, and broadcast TV services) to the relevant service access points. Varying quality of service and resiliency requirements for these services are being reflected in a new breed of converged Ethernet and optical network elements with capabilities to interwork the bearer-planes of these two networking technologies seamlessly. Network elements based on Ethernet/Optical converged technology are able to select the most fitting mechanisms from each networking technology to meet the transport requirements for each individual service demand better while providing significantly enhanced implementation and operational efficiencies. This paper discusses network architecture models and network elements addressing these goals. © 2007 Alcatel-Lucent.

E-coupons: An Efficient, Secure and Delegable Micro-Payment System

In this paper, we propose a new efficient and secure micro-payment scheme, named e-coupons, which can provide the users the facility of delegating their spending capability to other users or their own devices like Laptop, PDA, Mobile Phone, and such service access points. The scheme has the promise of becoming an enabler for various Internet-based services involving unit-wise payment. It gives flexibility to the users to manage their spending capability across various access points for a particular service without obtaining an authorization for each and every access point from a facilitating bank. This flexibility which is not present in the existing micro-payment schemes is essential for accessing ubiquitous e-services and other Internet-based applications. The facility of delegation introduces a slight overhead in respect of the proof or verification of the delegated authorization and security provided to the payments. The payoff from the facility of delegation takes away the burden of the overhead. The paper discusses the design of the protocol and provides a basic analysis of the performance of the system. e-coupons is based on PayWord, a single-seed one-way hash chain for unit-wise payment, TESLA for payment security and SPKI/SDSI as underlying PKI framework for its unique delegation feature. The results obtained from the implementation of e-coupons are quite acceptable and show near real-time response. Our scheme uses multi-seed one-way hash chains for unit-wise payment. Furthermore, it allows an ordered transfer of the portions of payment chains to others. Because of this user's spending capability can be used from different service access points to access the subscribed service, concurrently.

On-line bandwidth control for quality of service mapping over satellite independent service access points

The Quality of Service (QoS) provision requires the cooperation of all network layers from bottom to top. More specifically, for Broadband Satellite Multimedia (BSM) communications, the physical layers (strictly satellite dependent) are isolated from the rest by a Satellite Independent Service Access Point (SI-SAP), which should offer specific QoS to IP and the upper layers. The structure of SI-SAP and the BSM protocol model “opens the door” to the problem of mapping the performance requests of Satellite Independent layers over Satellite Dependent technology. In such a context, a QoS mapping problem arises when different encapsulation formats are employed along the protocol stack of the SI-SAP interface, for instance, when IP packets are transferred over an ATM, DVB or MPLS core network. In this perspective, we investigate here a novel control algorithm to estimate the bandwidth shift required to keep the same performance guarantees, independent of the technology change. By exploiting Infinitesimal Perturbation Analysis to capture the network performance sensitivity, we obtain an adaptive control law suitable for on-line control on the basis of traffic samples acquired during the network evolution. Owing to the generality of the mathematical framework under investigation, our control mechanism can be generalized for other network scenarios and functional costs.

홈페이지를 통한 대학도서관 서비스 접근성 평가 분석

본 연구는 국내 대학도서관 홈페이지상의 도서관서비스 항목의 접근성을 평가 분석해 봄으로써 이용자에게 어떻게 하면 효율적인 서비스를 할 수 있을 것인가에 대한 방향을 제시하는데 목적을 두었다. 조사대상은 전국적으로 4년제 국<TEX>$\cdot$</TEX>공립 및 사립대학교도서관 가운데 69개관을 계층적 표집방법에 의해 선정하여 홈페이지의 접근성을 평가하였으며, 평가항목은 네 개의 평가영역과 23개의 평가질문으로 구성하였고 이의 분석은 SPSS 12.0을 통하여 통계처리하였다. 평가영역에 대한 가설검증을 통해 결론을 도출하였고 이를 바탕으로 대학도서관에서의 홈페이지를 통한 보다 효율적인 도서관서비스를 위한 제안을 하였다. The purpose of this study is to provide directions for more effective and efficient service for library user by evaluating and analyzing library service access points on university library homepages. 69 national/public and private university libraries throughout the country are selected by stratified sampling method. The items used for evaluation are composed of 4 areas and 23 questions, and SPSS 12.0 is used for statistical analysis. The results are elicited through the hypothesis testing, and some suggestions are made for the effective university library homepage service.

H [formula omitted] N [formula omitted]: Network support for scaling of large-scale services

With the explosive growth of demand for services on the Internet, the networking infrastructure (routers, protocols, servers) is under considerable stress. Mechanisms are needed for current and future IP services to scale in a client-transparent way. We present H YDRA N ET, an infrastructure that allows to dynamically distribute IP services by placing service agents (caching agents, mirrors, replicas) that are under the server's control at strategic points in the internetwork. H YDRA N ET is based on replicating transport-level service access points (TCP or UDP ports in the case of IP) for transparent distribution or replication of IP services. Measurements on a local testbed show that the overhead of our scheme is small. This form of service access point replication is widely applicable. We use H YDRA NET to implement H YDRA W EB, a system for Web server replication to realize intelligent, client-transparent, Web caching. Similarly, H YDRA N ET can be used to implement highly fault-tolerant servers or application-level gateways.

Design and implementation of a Network Service Access Point (NSAP) for OSI-compatibility

We describe the design and implementation of a network layer interfacing scheme, which permits an OSI-8072 transport layer process to operate on a variety of network layer implementations. We describe a mapping function that would create a correspondence between the network services required by the correspondent transport process and the set of network services available. Further, we describe the design and implementation of an OSI-8072 Class-4 transport layer protocol. This transport layer service is implemented as a set of C library routines. The services are based on the networking interface scheme mentioned above. Using these services, users may design their own OSI compatible networking applications from the session layer upwards and run them on all network layer implementations supported by the UNIX networking environment.

Utilizing the Technical Services Staff on a Public Service Desk

The Governors State University Library in Illinois has a strong commitment to providing service to students, faculty and community. In an effort to provide additional public service access points, the technical services staff is being utilized at a public service desk. This article presents the results of a survey concerning the technical services employees staffing a public services desk. The practice of utilizing technical services staff to serve at a public desk (in this case, a Serials/Documents Information Desk) may become more prevalent as other university libraries contend with increasing student enrollments and stagnant, or decreasing, library staff size. The participants in this survey also provide information about the negative and positive impact this is having on job performance and morale.

A collision problem in OSI standard formal specifications

Abstract A collision problem is presented which can occur between two adjacent protocol entities, a user and its local provider. We consider synchronous and asynchronous communication mechanisms at the Service Access Point between the entities; this is normally an implementation choice. It is shown that even if the problem is limited by using a synchronous communication mechanism, instead of an asynchronous one, it still occurs. We suggest that whenever this case is found, the service provided by the protocol entity must be interpreted differently by its user, ignoring some primitives. When an asynchronous communication mechanism is used, care must be taken to verify that those primitives to be ignored cannot be misinterpreted as new primitives; finally, we point out that the protocol specification could be redesigned to handle these collision cases properly.

Standardization of network addressing in picture archiving and communications systems utilizing the ISO OSI protocols

The establishment of a communications network requires the definition of addressing schemes to identify systems attached to the network. When it is anticipated that such a network will interconnect to, or communicate with, other similar networks it is beneficial to define standardized addressing schemes. This paper discusses the need for the standardization of network service access point (NSAP) addresses in picture archiving and communications systems (PACS) which use the open systems interconnect (OSI) communications protocols. Possible methods for establishing the necessary hierarchy of address registration authorities are discussed, along with the corresponding address formats.

Connection management for the transport layer: service specification and protocol verification

A symmetric connection management service between two service access points is specified, using a state transition system and safety and progress requirements. At each access point. the user can request connection establishment, request connection termination, and signal whether or not they are willing to accept connection requests from the remote user. The protocol can indicate connection establishment, connection termination, and rejection of a connection establishment request. The authors then specify a protocol and verify that it offers the service, given communication channels between the access points that can lose, reorder, and duplicate messages, but which guarantee delivery of a message that is repeatedly sent. The protocol achieves the service using 2-way and 3-way handshakes, and can be directly combined with any existing single-connection data transfer protocols to provide a transport layer protocol that offers both connection management and data transfer services. The protocol and service are compared to TCP and its intended service, and to ISO TP Class 4 and its intended service.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Fiber-to-the-curb systems: Architectural alternatives

Abstract Several fiber-to-the-curb (FTTC) systems have been proposed in response to the present high cost of fiber-to-the-home (FTTH) systems for plain old telephone service (POTS). With FTTC systems, fiber is brought only as far as the service access point (SAP). From there, copper drops carry POTS signals from the SAP to several residences. Due to the extensive sharing of optical sources and the fibers running to the SAP, the per-subscriber system cost is reduced to levels comparable to that of a copper-bused digital loop currier distribution system. This paper presents an analysis of three different fiber-to-the-curb distribution networks that serve up to 96 customers, initially providing two POTS channels to each customer. These systems serve four customers per SAP through star, distributed star, or bus topologies that offer differing levels of sharing of fiber and optoelectronic components. We estimate the installed first costs (IFC) of the distribution link (remote node to customer) for the three FT...

A star‐configured fiber‐to‐the‐curb system

AbstractFiber‐to‐the‐curb (FTTC) system proposals have arisen because of the present high cost of fiber‐to‐the‐home (FTTH) systems. With FTTC systems, fiber is brought only as far as the service access point (SAP). From there, copper drops carry signals from the SAP to several residences. Owing to the extensive sharing of optical sources and the fibers running to the SAP, the per‐subscriber system cost is greatly reduced relative to the per‐subscriber cost of a FTTH system. In addition, elimination of the optical network unit (ONU) at the home may offer new options for powering and battery back‐up.This paper presents an analysis of a star‐configured, fiber‐to‐the‐curb distribution network that serves up to ninety‐six customers, initially providing two plain old telephone service (POTS) channels to each customer. Three system variations, serving either four, six, or eight customers per SAP, are examined. We also estimate the installed first costs (IFC) of the distribution link (remote node to customer) for the three FTTC scenarios and compare them to the IFC of a FTTH system with similar capabilities. Star‐configured FTTC architectures can be installed for substantially less ($1180‐$825/customer for four to eight customers per SAP) than the estimated $2920 per subscriber cost associated with FTTH systems. Finally, we propose an upgrade strategy, consistent with the passive photonic loop (PPL) network, to support future high bandwidth services.

New results on deriving protocol specifications from service specifications

Previous papers describe an algorithm for deriving a specification of protocol entities from a given service specification. A service specification defines a particular ordering for the execution of service primitives at the different service access points using operators for sequential, parallel and alternative executions. The derived protocol entities ensure the correct ordering by exchanging appropriate synchronization messages, between one another through the underlying communication medium. This paper presents several new results which represent important improvements to the above protocol derivation approach. First the language restriction to finite behaviors is removed by allowing for the definition of procedures which can be called recursively. Secondly, a new derivation algorithm has been developed which is much simpler than the previous one. Third, the resulting protocol specifications are much more optimized than those obtained previously.

Performance Evaluation of Multireject, Selective Reject, and Other Protocol Enhancements

This study compared the effects on performance of four features of the LAPB and LAPD protocols. LAPB is the link level for the X.25 protocol, and LAPD is the link level for the ISDN "D" signaling channel. The features were: multireject in which additional reject or selective reject frames can be retransmitted under certain conditions, selective reject in which an entity can request selected frames to be retransmitted, the null information frame (NIF) with which additional control frames are sent to help detect missing frames, and multiple service access points (SAP's) in which several link-level protocol handlers are multiplexed on the same physical link (a feature unique to LAPD). Results indicate that the current standard LAPB/D protocol with multireject is the preferred protocol. Selective reject generally performed worse than the standard protocol, and offered improvement only with complex and expensive enhancements. The NIF feature yielded a virtually unnoticeable performance improvement. Multi-SAP introduced a virtually unnoticeable impairment when it was used to carry the same traffic load as a single SAP.

OSI service specification: SAP and CEP modelling

Within the effort of ISO standarization, service specifications have been thought to be an important tool for formal verification of protocols. The paper discusses the modelling of some concepts quite related with the service: service access points and abstract service primitives. Firstly, ISO concepts are explained. Then, a service architectural model is developed as a refinament of the service access point idea using the connection end point concept. A finite state machine approach is shown to specify the behavior of the modules of such architecture. This lead us to consider the service access point represented as a single state automaton that consists of several connection end point automata. Thus, service access points allow the specification of services, and provide an abstraction of interfaces between adjacent layers of the Open System Interconnection model of ISO.