Supporting Adaptive Flows in a
Quality of Service Architecture
Andrew Campbell, Geoff Coulson and David Hutchison
Department of Computing,
Lancaster University,
Lancaster LA1 4YR, U.K.
{campbell, geoff, dh}@https://www.doczj.com/doc/984372608.html,
Abstract
Distributed audio and video applications need to adapt to fluctuations in delivered quality of service (QoS). By trading off temporal and spatial quality to available bandwidth, or manipulating the playout time of continuous media in response to variation in delay, audio and video flows can be made to adapt to fluctuating QoS with minimal perceptual distortion. In this paper we extend our previous work on a Quality of Service Architecture (QoS-A) by populating the QoS management planes of our architecture with a framework for the control and management of multi-layer coded flows operating in heterogeneous multimedia networking environments. Two key techniques are proposed: i) an end-to-end rate shaping scheme which adapts the rate of MPEG-coded flows to the available network resources while minimising the distortion observed at the receiver; and ii) an Adaptive Network Service, which offers “hard”
guarantees to the base layer of multi-layer coded flows, and “fairness” guarantees to the enhancement layers based on a bandwidth allocation technique called Weighted Fair Sharing. Keywords
Scalable flows, multimedia transport, dynamic QoS management, end-to-end QoS architecture 1. Introduction
The interplay between user-oriented quality of service (QoS) requirements [Zhang,95] multi-layer coded flows [Shacham,92], and end-to-end communication support [Campbell,95] is an interesting and active area of research [Pasquale,93], [Delgrossi,93], [Tokuda,92] [Hoffman,93]. The hierarchical coding techniques used by coders such as MPEG-1, MPEG-2 and H261 make possible a range of creative adaptation strategies whereby fluctuating bandwidth availability can be accommodated by selectively adding/ removing coding layers.
In this paper we introduce the concept of dynamic QoS management (DQM) which, by exploiting and extending the above principles, controls and manages multi-layer coded flows operating in heterogeneous, multicast, multimedia networking environments. Under the DQM heading, two main techniques are proposed to support scalable1 video over multimedia networks. These are i) end-to-end rate shaping which adapts the rate of multi-layer flows to the available network resources while minimising the distortion observed at the receiver, and ii) an adaptive network service which offers a combination of “hard” guarantees to the base layer of multi-layer coded flows, and “fairness” guarantees to the enhancement layers based on a new bandwidth allocation technique called weighted fair sharing. We also discuss a number of types of scaling object which are used to manage and control QoS. These include QoS filters which manipulate
1Media scaling is a general term, first proposed by [Delgrossi,93], we use to refer to the dynamic manipulation of media flows as they pass through a communications channel.
hierarchically coded flows as they progress through the communications system, QoS adaptors which scale flows at end-systems based on the flow's measured performance and user supplied QoS scaling policy, and QoS groups which provide baseline QoS for multicast flows.
All these components are inter-related in a Quality of Service Architecture (QoS-A) [Campbell,94] which has been developed over the last three years at Lancaster [Campbell,93]. This research has been conducted in co-operation with ATM switch manufacturer GDC (formally Netcomm Ltd) in the UK. The QoS-A is a layered architecture of services and mechanisms for quality of service (QoS) management and control of continuous media flows in multiservice networks. The architecture incorporates the following key notions: flows characterise the production, transmission and eventual consumption of single media streams (both unicast and multicast) with associated QoS; service contracts are binding agreements of QoS levels between users and providers; and flow management provides for the monitoring and maintenance of the contracted QoS levels. The realisation of the flow concept demands active QoS management and tight integration between device management, thread scheduling, communications protocols and networks.
The structure of the paper is as follows. We first present, in section 2, background on the QoS-A. Following this, we describe the salient features of scalable video flows in section 3 before describing, in section 4, the set of scaling objects used in our architecture together with the application programming interface (API) to DQM. Section 5 then presents our scheme for end-to-end DQM. In this section the detailed operation of a number of specific types of scaling object is described. Following this, section 6 introduces our adaptive network service, defines the notion of weighted fair share resource allocation, explains the rate control scheme used in the network, and describes the use of some network oriented QoS filters. Finally in section 7 we present the status of our work and offer some concluding remarks.
2. The Lancaster Quality of Service Architecture
The QoS-A is based on a set of principles that govern the realisation of end-to-end QoS in a distributed systems environment:
i) the integration principle states that QoS must be configurable, predicable and maintainable
over all architectural layers to meet end-to-end QoS [Campbell,93];
ii)the separation principle states that information transfer, control and management are functionally distinct activities in the architecture and operate on different time scales [Lazar,90];
iii)the transparency principle states that applications should be shielded from the complexity of handling QoS management [Campbell,92];
iv)the performance principle guides the division of functionality between architectural modules (viz. end-to-end argument [Saltzer,84], application layer framing and integrated layer processing [Clark,90], and the reduction of layered multiplexing [Tennenhouse,90]).
In functional terms, the QoS-A (see Figure 1) is composed of a number of layers and planes. The upper layer consists of a distributed applications platform augmented with services to provide multimedia communications and QoS specification in an object-based environment [Coulson,93]. Below the platform level is an orchestration layer which provides jitter correction and multimedia synchronisation services across multiple related application flows [Campbell,92]. Supporting this is a transport layer which contains a range of QoS configurable services and mechanisms. Below this, an internetworking layer and lower layers form the basis for end-to-end QoS support. See [Campbell,94] for full details on the QoS-A.
QoS management is realised in three vertical planes in the QoS-A. The protocol plane, which consists of distinct user and control sub-planes,is motivated by the principle of separation. We use
separate protocol profiles for the control and data components of flows because of the essentially different QoS requirements of control and data: control generally requires a low latency full duplex assured service whereas media flows generally require a range of non-assured, high throughput and low latency simplex services. The QoS maintenance plane contains a number of layer specific QoS managers. These are each responsible for the fine grained monitoring and maintenance of their associated protocol entities. For example at the orchestration layer the QoS manager is interested in the tightness of synchronisation between multiple related flows. In contrast, the transport QoS manager is concerned with intra-flow QoS such as bandwidth, loss, jitter and delay. Based on flow monitoring information and a user supplied service contract, QoS managers maintain the level of QoS in the managed flow by means of fine grained resource tuning strategies. The final QoS-A plane pertains to flow management, which is responsible for flow establishment (including end-to-end admission control, QoS based routing and resource reservation), QoS mapping (which translates QoS representations between layers) and QoS Scaling (which constitutes QoS filtering and adaptation for coarse grained QoS maintenance control).
Figure 1: QoS-A
Recent work on the QoS-A has concentrated on realising the architecture in an environment comprising an enhanced Chorus micro-kernel [Coulson,95] and an enhanced multimedia transport service and protocol [Campbell,94] in the local ATM environment.
3. Scalable Video Flows
The fundamental design goal of digital audio-visual information representation schemes in the past several decades has been that of compactness: describe the signal's content with as few bits as possible. The algorithmic foundation of this work has been based on the assumption that information transport occurs over constant bandwidth and constant delay channels: an assumption that does not necessarily hold valid in an environment of packet switched networks working on the premise of multiplexing gain.
Our primary focus in this paper is MPEG-2 coded video. Within this framework, there are two alternative techniques which underpin QoS adaptation: intrinsic and extrinsic techniques. The former are provided by the encoder, and are embedded in the coded bitstream. The latter are provided by QoS filters that operate directly on the compressed bitstream, performing the desired manipulations. Their difference lies in their complexity and performance. Intrinsic techniques can have a very simple implementation, but as we will see offer only a discrete range of possibilities.
Extrinsic techniques are computationally more complex but can operate on a continuum of possibilities. In the following we briefly describe the architecture of MPEG-2, with particular emphasis on the intrinsic adaptation capabilities it provides in the form of scalability profiles. Extrinsic adaptation can be provided through the use of dynamic rate shaping QoS filters [Eleftheriadis,95], which are discussed in section 5.2.1.
3.1 MPEG-2
The algorithmic foundation of MPEG is motion-compensated, block-based transform coding MPEG-2 [H.262,94]. Each block is transformed using the Discrete Cosine Transform (DCT), and is subsequently quantised. Quantisation is the sole source of quality loss in MPEG-2 and, of course, a major source of compression efficiency. The quantised coefficients are converted to a one-dimensional string using a zig-zag pattern and then run-length encoded. There are three types of pictures in a sequence: I, P, and B. I or intra pictures are individually coded, and are fully self-contained. P pictures are predicted from the previous I or P picture, while B (or bi-directional) pictures are interpolated from the closest past and future I or P pictures. Prediction is motion-compensated: the encoder finds the best match of each macroblock in the past or future picture, within a prespecified range. The displacement(s), or motion vector(s), is sent as side information to the decoder.
In order to increase the coding efficiency, MPEG-2 relies heavily on entropy coding. Huffman codes (variable length codewords) are used to represent the various bitstream quantities (run-length codes, motion vectors, etc.). As a result, the output of an MPEG-2 encoder is inherently a variable rate bitstream: the ratio of bits per pixel varies from one block to the next. In order to construct a constant rate bitstream, rate control is used. This is achieved by connecting a buffer to the output of the encoder. The buffer is emptied at a constant rate, and its occupancy is fed back to the encoder. This information is used to control the selection of the quantiser for the current macroblock. High buffer occupancy leads to more coarsely quantised coefficients, and hence less bits per block, and vice versa. Through this self-regulation technique one can achieve a constant output rate.
For transport purposes, video and audio are multiplexed according to the system layer of MPEG-2, which defines the packetisation structure and synchronisation algorithms between the audio and video signals. Two different packetisation structures are defined, namely program streams and transport streams. Both are logically constructed from “packetised elementary stream”(PES) packets; these are the basic units in which individual audio, video, and control information is carried. Program streams are designed for use in relatively error-free environments, use variable length packets, and combine PES packets that have a common time base. Transport streams are designed for noisy channels, utilise fixed-length packets (188 bytes), and can carry programs with independent time bases. The system layer's timing model is based on the assumption that a constant delay transport mechanism is used. Although deviations from this are allowed, the way to address them is not specified. All timing information is based on a common system clock, and timestamps (i.e. an absolute timing method) ensure proper inter-media synchronisation between the audio and video signals upon presentation.
3.2 MPEG-2 Scalability Modes
From the above discussion it is clear that MPEG-2 is especially tuned for transmission over traditional constant bandwidth and delay channels. Some support for flexible and/or robust transmission is provided through the use of scalability modes for channels exhibiting dynamic behaviour. The situation is even more challenging for scalable flows, i.e. in cases where the available bandwidth may vary over time. However, here benefits of multiplexing gain are possible.
MPEG-2 provides for the simultaneous representation of a video signal at various different levels of quality, through the use of multiple independent bitstreams or sub-signals. This is achieved through the use of pyramidal, or hierarchical coding: one first constructs a coarse or base representation of the signal, and then produces successive enhancements. The latter assume that the
base representation is available, and only encode the incremental changes that have to be performed to improve the quality. There are four different scalability modes: spatial, SNR, temporal, and data partitioning. MPEG-2 allows the simultaneous use of up to two different scalability modes (except from data partitioning) in any combination, hence resulting in a 3-level representation of the signal. In spatial scalability, the base and enhancement layers operate at different spatial resolutions (e.g. standard TV and HDTV). In SNR scalability, both layers have the same resolution and the enhancement refines the quantisation process performed in the base layer. In temporal scalability the enhancement layer increases the number of frames per second of the base layer (e.g., from 30 frames per second to 60 fps). Data partitioning is slightly different from the other three scalability modes in the sense that the encoder does not maintain two different prediction loops and hence the base layer is not entirely self-contained. Its benefit is that it can be applied even in single-layer encoders.
As an example, the spatial scalability mode can be used to transmit digital TV in both standard and HDTV formats. Although two sub-signals are actually generated, this is not identical to simulcast: the total bandwidth required is much smaller, since the HDTV layer uses the base, standard TV layer as a reference point. Scalability can be very useful in transmission of video over adaptive channels.
3.3 Discrete and Continuous QoS Adaptation
Although MPEG-2's scalability features are useful in resolving heterogeneity problems described above [Delgrossi,93], and are useful in numerous applications, their use in continually QoS-varying channels is problematic. This is because they only allow the representation of the signal at a fixed number of discrete quality points (temporal or spatial resolution, or spatial quality). These points are typically significantly apart, and transitions between the two are perceptually significant. Table 1 [Paek,95] shows an example of hybrid scalability with spatial (E1) and SNR (E2) enhancement layers.
layer name profile symbol frame size bit rate subjective QoS
base layer main BL 304x112 0.32 Mbps VHS
enhancement 1 layer spatial E1 608x224 0.83 Mbps super VHS
enhancement 2 layer SNR E2 608x224 1.85 Mbps laser disc Table 1: MPEG-2 hybrid scalable bitstream using spatial and SNR scalability (24 fps)
Consider, for example, a channel that temporarily undergoes rate variability for a period of a few seconds. Switching to a lower quality point (by discarding the enhancement layer(s)) for such a brief interval will create a perceptual “flash” that is very annoying to users. An additional issue is that, as soon as compression parameters are established, it is impossible to modify them later on (after compression is completed). Hence scalability modes can only really be used for well-defined, simple channels that vary slowly. Since the wide range of different access mechanisms to multimedia information makes it very difficult to select a priori a set of universally interoperable coding parameters, it is necessary to provide extrinsic mechanisms that allow the representation of the “signal at a continuum of qualities and rates” [Delgrossi,93], so that scalable flows can be accommodated.
This is possible through the use of a class of dynamic rate shaping QoS filters [Eleftheriadis,95b] and the provision of adaptive network services - providing a QoS continuum for fully scalable flows. The adaptive service introduced in this paper uses explicit feedback from network resource management to dynamically shape the video source based on available network resources. Some benefits of an adaptive scheme are non-reliance on video modelling techniques and statistical QoS specification and specific support for the semantics of scalable video flows e.g.
MPEG-2 scalable profiles. Dynamic rate shaping filters manipulate the rate of MPEG-coded video, matching it to the available bandwidth (indicated by the adaptive service) while minimising the distortion observed by the receiver.
4. Scaling Objects and API Extensions
In this section, we introduce a set of scaling objects used to manipulate hierarchically coded flows as they progress through the communications system. These comprise QoS adaptors, QoS filters and QoS groups as defined in section 1. We also introduce an extension to the QoS-A application programmer’s interface which gives access to the scaling object types.
4.1 Scaling Objects
4.1.1 QoS Adaptors
QoS adaptors are used in conjunction with the QoS-A flow monitoring function to ensure that the user and provider QoS specified in the service contract are actually maintained. In this role QoS adaptors are seen as quality of service arbiters between the user and network. QoS adaptors scale flows at the end-systems based on a user supplied QoS scaling policy (see section 4.2) and the measured performance of on-going flows. QoS adaptation is discussed in detail in section 5.
4.1.2 QoS Filters
QoS filters manipulate multi-layer coded flows [Shacham,92], [Hoffman,93] [Zhang,95] at the end-systems and as they progress through the network. We describe three distinct styles of QoS filters:
i) shaping filters, which manipulate coded video and audio by exploiting the structural
composition of flows to match network, end-system or application QoS capability; shaping filters are generally situated at the edge of the network at the source; they require non-trivial computational power; examples are the dynamic rate shaping (DRS) filter and the source bit rate (SBR) filter - see section 5.2;
ii) selection filters, which are used for sub-signal selection and media dropping (e.g. video frame dropping) are of low complexity and low computational intensity - selection filters are designed to operate in the network and are located at switches; they require only minimal computational power; examples are sub-signal filter, hierarch filter, hybrid filter -see section 6.3;
iii)temporal filters, which manipulate the timing characteristics of media to meet delay bound QoS are also low in complexity and trivial computationally - temporal filters are generally placed at receivers or sinks of continuous media where jitter compensation or orchestration of multiple related media is required; examples are sync filter, orch filter - see section 5.3).
4.1.3 QoS Groups
Before potential senders and receivers can communicate they must first join a QoS group [Aurrecoechea,95]. The concept of a QoS group is used to associate a baseline QoS capability to a particular flow. All sub-signals of a multi-layer stream can be mapped into a single flow and multicast to multiple receivers [Shacham,92]. Then, each receiver can select to take either the complete signal advertised by the QoS group or a partial signal based on resource availability. Alternatively each sub-signal can be associated with a distinct QoS group. In this case, receivers “tune” into different QoS groups (using signal selection) to build up the overall signal. Both methods are supported in DQM. Receivers and senders interact with QoS groups to determine what the baseline service is, and tailor their capability to consume the signal by selecting filter styles and specifying the degree of adaptability sustainable (viz. discrete, continuous; see section 4.2).
4.2 QoS Specification API
In the original QoS-A we designed a service contract based API which formalised the end-to-end QoS requirements of the user and the potential degree of service commitment of the provider. In this section, we detail extensions to the flow specification, QoS commitment and QoS scaling clauses of the service contract required to accommodate adaptive multi-layer flows. The API presented here is not complete in that there are no primitives given for establishing and renegotiating connections or for manipulating QoS groups. Full details of these aspects are given in [Campbell,94].
typedef enum {MPEG1, MPEG2, H261, JPEG} mediaType;
typedef enum {besteffort, adaptive, deterministic} commit;
typedef enum {continuous, discrete} adaptMode;
typedef enum {
DRS, SBR, sub_signal, hierarch, hybrid, sync, orch
} filterStyle;
typedef struct {
adaptMode adaptation;
filterStyle filtering;
events adaptEvents;
actions newQoS;
signal bandwidth;
signal loss;
signal delay;
signal jitter
} QoSscalingPolicy;
typedef struct {
gid flow_id;
mediaType media;
commit commitment;
subFlow BL;
subFlow E1;
subFlow E2;
int delay;
int loss;
int jitter;
QoSscalingPolicy qospolicy
} flowSpec;
Multi-layered flows are characterised by three sub-signals in the flowSpec flow specification: a base layer (BL) and up to two enhancement layers (E1 and E2). Each layer is represented by a frame size and subjective or perceptive QoS as illustrated in Table 1. Based on these characteristics, the MPEG-2 coder [Paek,95], [Eleftheriadis,95] determines approximate bit rate for each sub-layer. In the case of MPEG-2's hybrid scalability, BL would represent the main profile bit rate requirement (e.g. 0.32 Mbps) for basic quality, E1 would represent the spatial scalability mode bit rate requirement (e.g. 0.83 Mbps) for enhancement, and E2 would represent the SNR scalability mode bit rate requirement (e.g. 1.85 Mbps) for further enhancement. The remaining flow specification performance parameters for jitter, delay and loss are assumed to be common across the all sub-signals (i.e. a single layer of a multi-layer video flow). The QoS commitment field has been extended to offer an adaptive network service that specifically caters for the needs of scalable audio and video flows in heterogeneous networking environments (see section 6).
The QoSscalingPolicy field of the flowSpec characterises the degree of adaptation that a flow can tolerate and still achieve meaningful QoS. The scaling policy consists of clauses that cover adaptation modes, QoS filter styles, and event/ action pairings for QoS management purposes. Two types of adaptation mode are supported: continuous mode, for applications that can exploit any availability of bandwidth above the base layer; and discrete mode for applications which can only accept discrete improvement in bandwidth based on a full enhancement (viz. E1, E2).
The QoS scaling policy provides user-selectable QoS adaptation and QoS filtering. While receivers select filter styles to match their capability to consume media at the receiver (from the set of temporal filters), senders select filter styles to shape flows in response to the availability of network resources such as bandwidth and delay (from the set of shaping filters). Network oriented filters (i.e. selection filters) can be chosen by either senders or receivers.
In addition, senders and receivers can both select periodic performance notifications including available bandwidth, measured delay, jitter and losses for on-going flows. The signal fields in the scaling policy allow the user to specify the interval over which a QoS parameter is to be monitored and the user informed. Multiple signals can be selected depending on application needs.
5. Dynamic QoS Management
5.1 Architectural Components
Dynamic QoS management spans the QoS-A QoS maintenance and flow management planes. In the QoS maintenance plane, the most important aspect of DQM is QoS adaptation in the end-systems. Based on the receiver supplied QoS scaling policy, QoS adaptors take remedial action to scale flows, inform the user of a QoS indication and degradation, fine tune resources and initiate complete end-to-end QoS renegotiation based on a new flowSpec [Campbell,94]. In the flow management plane, DQM consists of two sub-components: QoS group management maintains and advertises QoS groups created by senders for the benefit of potential receivers; filter management [Yeadon,94] instantiates and reconfigures filters in a flow at optimal points in the media path at flow establishment time, when new receivers join QoS groups or when a new flowSpec is given on a QoS renegotiation.
In implementation, each of these architectural modules has well defined interfaces and methods defined in CORBA IDL. CORBA [OMG,93] runs on the end-systems and in the ATM switches, providing a seamless object oriented environment throughout the communication system base (see [Aurrecoechea,94] for full details).
5.1.1 Illustrative Scenario
DQM can be viewed as operating in three distinct domains:
i) sender-oriented DQM, where senders select source filters and adaptation modes, and
establish flow specifications. The sender-side transport protocol provides periodic bandwidth and delay assessments to the source filters (i.e. DRS or SBR filters) which regulate the source flow. Senders create QoS groups which announce the QoS of the flow to receivers via QoS group management;
ii) receiver-oriented DQM, where receivers join QoS groups and select the portion of the signal which matches their QoS capability. Receiver selected network based filters propagate through the network and perform source and signal selection. In addition, receiver-based QoS filters (i.e. sync-filter and orch-filter) are instantiated by default unless otherwise directed. These filters are used to smooth and synchronise multiple media. The receiver-side transport protocol provides bandwidth management and produces adaptation signals according to the QoS scaling policy;
iii) network-oriented DQM, which provides an adaptive network service (see section 6) to
receivers and senders. Network level QoS filters (i.e. sub-signal, hierarch and hybrid-filters) are instantiated based on user selection, and propagated in the network under the control of filter management.
In Figure 1 a sender at end-system A creates a flow by instantiating a QoS group which announces the characteristics of the flow (viz. layer, frame size, subjective quality) and its adaptation mode. Receivers at end-systems B, C and D join the QoS group. In the example scenario shown the receivers each “tune” into different parts of the multi-layer signal: C takes BL, the main profile (which constitutes a bandwidth of 0.32 Mbps for VHS perceptual QoS), B takes BL and E1 (which constitutes an aggregate bandwidth of 1.15 Mbps for super VHS perceptual QoS), and D takes the complete signal BL+E1+E2 (which constitutes an aggregate bandwidth of 3 Mbps for laser disc perceptual QoS). In this example the complete signal is multiplexed onto a single flow, therefore, sub-signal selection filters are propagated by filter management. Receivers, senders, or any third party or filter management can select, instantiate and modify source, network and receiver-based QoS filters.
Figure 1: Dynamic QoS management of scalable flows
5.2 Sender-Oriented DQM
Figure 2 shows the functions of the sender-side transport protocol supporting dynamic QoS management, and the interface to a dynamic rate shaping filter. Currently, senders can select from two types of shaping filter at the source: dynamic rate shaping (DRS) and source bite rate (SBR) QoS filters. Both of these QoS filters manipulate the signal to meet the available bandwidth by keeping the signal meaningful at the receiver. The sender-side transport mechanisms includes a QoS adaptor, flow monitor and media scheduler. Bandwidth updates are synchronously received by the flow monitor mechanism from the network as part of the adaptive service (described in section 6). The QoS adaptor is responsible for synchronously informing the source filter of the current bandwidth availability (B flow) and measured delay (D flow), and calculating new schedules and deadlines for transport service data units [Coulson,95]. Media progresses from the source filter to the TSAP, and is scheduled by the media scheduler to the network at the NSAP based on the calculated deadlines.
The QoS adaptor is also responsible for informing the sending application of the on-going QoS based on options selected in the QoS scaling policy. Informing the application of the current state of the resources associated with a specific flow is key in implementing adaptive applications in end-systems. In this case the application manages the flow by receiving updates and interacting with the QoS adaptor to adjust the flow, e.g. change adaptation mode from continuous to discrete,
request more bandwidth for BL, E1 and E2, or change the characteristics of the source filter, etc.
5.2.1 The DRS Filter
We define rate shaping as an operation which, given an input video bitstream and a set of rate constraints, produces a video bitstream that complies with these constraints. For our purposes, both bitstreams are assumed to meet the same syntax specification, and we also assume that a motion compensated block-based transform coding scheme is used. This includes both MPEG-1 and MPEG-2, as well as H.261 and so-called “motion” JPEG.
Although a number of techniques have been developed for the rate shaping of live sources [Kanakia,93] these cannot be used for the transmission of pre-compressed material (e.g. in VoD systems). The dynamic rate shaping filter is interposed between the encoder and the network and ensures that the encoder's output can be perfectly matched to the network's quality of service characteristics. The filter does not require interaction with the encoder and hence is fully applicable to both live and stored video applications.
Figure 2: Sender-side transport QoS mechanisms
Because the encoder and the network are decoupled, universal interoperability can be achieved both between codecs and networks, and also among codecs with different specifications. An attractive aspect is the existence of low-complexity algorithms which allow software-based implementation in high-end computers. In order for rate shaping to be viable it has to be implementable with reasonable ease while yielding acceptable visual quality. With respect to complexity, the straightforward approach of decoding the video bitstream and recoding it at the target rate would be obviously unacceptable; the delay incurred would also be an important deterrent. Hence only algorithms of complexity less than that of a cascaded decoder and encoder are of practical interest. These algorithms operate directly in the compressed domain of the video signal, manipulating the bitstream so that rate reduction can be effected. In terms of quality, it should be noted that recoding does not necessarily yield optimal conversion; in fact, since an optimal encoder (in an operational rate-distortion sense) is impractical due to its complexity, recoding can only serve as an indicator of an acceptable quality range. In fact, regular recoding can be quite lacking in terms of quality, with dynamic rate shaping providing significantly superior results.
The rate shaping operation is depicted in Figure 3. Of particular interest is the source of the rate constraints B flow(t). In the simplest of cases, B flow(t) may be just a constant and known a priori (e.g. the bandwidth of a circuit-switched connection). It is also possible that B flow(t) has a well known statistical characterisation (e.g. a policing function). In our approach B flow(t) is generated by the adaptive network service.
Figure 3: Dynamic rate shaping scheme
The objective of a rate shaping algorithm is to minimise the conversion distortion, i.e.: min
()()
()()
B t B T t y t y t
The attainable rate variation (B ^B) is in practice limited, and depends primarily on the number
of B pictures of the bitstream; no assumption is made on the rate properties of the input bitstream,which can indeed be arbitrary. There are two fundamental ways to reduce the rate:
i) by modifying the quantised transform coefficients by employing coarser quantisation, and ii) by eliminating transform coefficients.
In general, both schemes could be used to perform rate shaping; requantisation, however, leads to recoding-like algorithms which are not amenable to fast implementation and do not perform as well as selective-transmission ones. A selective transmission approach gives rise to a family of different algorithms, that perform optimally under different constraints; for full details see [Eleftheriadis,95b].
5.3 Receiver-Oriented DQM
QoS adaptors, which are resident in the transport protocol at both senders and receivers,arbitrate between the receiver specified QoS and the monitored QoS of the on-going flow. In essence the transport protocol “controls” the progress of the media while the receiver “monitors and adapts” to the flow based on the flow specification and the scaling policy. When the transport protocol is in monitoring mode [Campbell,94] the flow monitor uses an absolute timing method to determine frame receptions times based on timestamps/sample-stamps [Jeffay,92], [Jacobson,93],[Shenker,93]. The flow monitor, as shown in Figure 4, updates the flow state to include these measured reception times statistics. Based on these flow statistics, the sync-filter (see section 5.3.3) derives new playout times used by the media scheduler to adjust the playout point of the flows to the decoding delivery device.
QoS mechanisms that intrinsically support such adaptive approaches were first recognised in the late 70's by Cohen [Cohen,77] as part of research in carrying voice over packet-switched networks. More recently, adaptive QoS mechanisms have been introduced at part of the Internet suite of application-level multimedia tools (e.g., vat [Jacobson,93], ivs [Turletti,93], and vic [McCanne,94]). Vat which is used for voice conferencing, recreates the timing characteristics of voice flows by having the sender timestamp on-going voice samples. The receiver then uses these timestamps as a basis to reconstruct initial flow, removing any network induced jitter prior to playout. These multimedia tools are widely used in the Internet today and have proved moderately successful - given the nature of best effort delivery systems, i.e., no resource reservation is made. In the near future, however, an integrated services Internet [Braden,94] will offer support for flow reservation (e.g., RSVP [Zhang,95]) and new QoS commitments (e.g., predictive QoS [Shenker,95]) which are more suitable for continuous media delivery.
Receiver-oriented adaptation can be broken down into a number of receiver-side transport functions, i.e. bandwidth management, late frame management and delay jitter management, which are described in the following sub-sections (please refer to figure 4). We argue in this paper that these adaptive QoS mechanisms are inherently part of the transport potocol and not, as in the case of vat, ivs and vic, part of the application domain itself.
Figure 4: Receiver-side transport QoS mechanisms
5.3.1 Bandwidth Management
Bandwidth management receives bandwidth indications in the control message portion of the TSDU (or in separate control messages) and adapts the receiver appropriately. The adaptive service, built on the notion of weighted fair share resource allocation, (see section 6.1) periodically informs the receiver that more bandwidth is available or announces that the flow is being throttled back. Bandwidth management only covers the enhancement signals of multi-resolution flows. The base layer is not included since resources are guaranteed to the base layer. The announcement of available bandwidth on a flow allows the receiver to take either a full or partial enhancement layer. The choice depends on whether the flow is in continuous or discrete adaptation mode.
5.3.2 Late Frame Management
Late frame management monitors late arrivals in relation to the loss metric and the current playout times and takes appropriate action to trade off timeliness and loss. Packets that arrive after their expected playout points are discarded by the media scheduler and the late-packet metrics in the playout statistics are updated. The media scheduler is based on a split-level scheduler architecture [Coulson,95] which provides hard deadline guarantees to base layer flows via admission control, and best effort deadlines to enhancements layers. Some remedial action may be taken by the QoS adaptor should the loss metric exceed the loss parameter in the flow specification. If the QoS adaptor determines that too many packet losses have occurred over an era, it pushes out the playout time to counteract the late state of packets from the network. Similarly, if loss remains well within the prescribed ranges then the QoS adaptor will automatically and incrementally “pull in” the playout time until loss is detected.
5.3.3 Delay Jitter Management
Our transport protocol utilises sync-filters for delay-jitter management by calculating the playout times of flows based on the user supplied jitter parameter in the flow specification1. Sync filters calculate the mean and variation in the end-to-end delay based on reception times measured
1Temporal filters can also operate on multiple related audio and video flows to provide low-level orchestration management (in conjunction with the orch-filter). These filter types, however, are not discussed further in this paper.
by the flow monitor. Sync filters take the absolute, mean and variation in delay into account when calculating the playout estimate. A smoothing factor based on a linear recursive filtering mechanism characterised by a smoothing constant is used to dampen the movement of the playout adjustment. Intuitively, the playout time needs to be set “far enough” beyond the delay estimate so that only a small fraction of the arriving packets are lost due to late packets. The QoS adaptor trades off late packets versus timeliness based on the delay and loss parameters in the flow specification. The objective of delay jitter management is to pull in the playout offset, while the objective of late-packet management is not to exceed the loss characterised in the service contract. The QoS adaptation manager moderates between timeliness and loss. Based on these metrics the adaptation policy can adjust the damping factor, and acceptable ranges over which the playout point can operate.
time
Figure 5: Sync-filter: timeliness and packet loss regulation Figure 5 [Zhang,94] shows packets arriving at the receiving end-system. Each packet includes a timestamp used in calculating the flow statistics for delay-jitter management. Selection of the playout point is important: an aggressive playout time which favours timeliness (such as t1) will results in a large number of late-packets. In contrast, a conservative playout point (such as t3) will be less responsive and timely but will result in no identifiable packet loss. In the DQM scheme late packets are the same as lost packets, and therefore the loss parameter in the flow specification moderates. An optimum playout schedule is represented by t2 in the diagram; here, continuous media delivery benefits from timely delivery with the exception of some packet loss - which may be deemed acceptable to the receiver in media perception terms.
6. Adaptive Network Service
The adaptive network service provides “hard” guarantees to the base layer (BL) of a multi-layer flow and “weighted fair share” (WFS) guarantees to each of the enhancement layers (E1 and E2). To achieve this, the base layer undergoes a full end-to-end admission control test [Coulson,95]. On the other hand, enhancement layers are admitted without any such test but must compete for residual bandwidth among all other adaptive flows. Enhancement layers are rate controlled based on explicit feed back about the current state of the on-going flow and the availability of residual bandwidth.
6.1 Weighted Fair Share Resource Partitioning
Both end-system and network communication resources are partitioned between the deterministic and adaptive service commitment classes. This is achieved by creating and maintaining “firewall” capacity regions for each class. Resources reserved for each class, but not currently in use can be “borrowed” by the best effort service class on condition of pre-emption [Coulson,95]. The adaptive service capacity region (called the available capacity region and denoted by B avail) is further sub-divided into two regions: i) guaranteed capacity region (B guar),
which is used to guarantee all base rate layer flow requirements; and ii) residual capacity region (B resid ), which is used to accommodate all enhancement rates where competing flows share the residual bandwidth.
Three goals motivate our adaptive service design. The first goal is to admit as many base layer (BL) sub-signals as possible. As more base layers are admitted the guaranteed capacity region B guar grows to meet the hard guarantees for all base signals. In contrast, the residual capacity region B resid shrinks as enhancement layers compete for diminishing residual bandwidth resources.The following invariants must be maintained at each end system and switch:
B avail = B guar +B resid , and
BL (i )i =1
N
∑≤B avail
Our second goal is to share [Steenstrup,94], [Tokuda,92] the residual capacity B resid among
competing enhancement sub-signals based on a flow specific weighting factor, W , which allocates residual bandwidth in proportion to the range of bandwidth requested that in turn is related to the range of perceptual QoS acceptable to the user. In DQM, residual resources are allocated based on the range of bandwidth requirements specified by the users (i.e. BL.. BL+E1+E2 is the range of bandwidth required, e.g. from 0.32 Mbps to 3 Mbps for the hybrid scalable MPEG-2 flow in Table 1). As a result, as resources become available each flow experiences the same “percentage increase” in the perceptible QoS, we call this weighted fair share (WFS). W is calculated for each flow as the ratio of a flow's perceptual QoS range to the sum of all perceptual QoS ranges.
W (i )=(BL i
+E 1i +E 2i )
/
(BL j +E 1j j =1
N
∑+E 2j )
All residual resources B resid are allocated in proportion to the W metric. Using this factor we
calculate the proportion of residual bandwidth allocated to a flow to be B wfs (i)=W (i).B resid and the proportion of the available bandwidth allocated to be B flow (i)= B wfs (i)+ BL(i).
Our third and final goal is to adapt flows both discretely and continuously, based on the adaptation mode. In the discrete mode no residual bandwidth is allocated by the WFS mechanism unless a complete enhancement can be accommodated (i.e., B wfs (i) = E1(i) | E1(i)+E2(i), e.g. 0.83Mbps or 2.68 Mbps from Table 1). In continuous mode any increment of residual bandwidth B wfs (i) can be utilised (i.e. 0 < B wfs (i) ≤ E1(i) + E2(i), e.g. from 0 to 2.68 Mbps from Table 1).6.2 Rate Control Scheme
We build on the rate-based scheme described in [Campbell,94] where the QoS-A transport protocol at the receiver measures the bandwidth, delay, jitter and loss over an interval which we call an “era”. An era is simply defined as the reciprocal of the frame rate in the flow specification (e.g. for a frame rate of 24 frames per second as shown in Table 1 the interval era is approximately 42 ms). The receiver-side transport protocol periodically informs the sender-side about the currently available bandwidth, and the measured delay, loss and jitter. This information is used by the source or virtual source 1 to calculate the rate to use over the next interval. The reported rate is temporally correlated with the on-going flow. An important result in [Kanakia,93] shows that variable rate encoders can track QoS variations as long as feedback is available within four frame times or less. This feedback is used by the dynamic rate shaping filter and network based filters to control the data generation rate of the video or the selection of the signal respectively. In the case of dynamic rate shaping, the rate is adjusted while keeping the perceptual quality of the video flow meaningful to the user.
Based on the concept of eras, control messages are forwarded from the receiver-side transport protocol to either virtual source or the source-side transport protocol using reverse path
1
We use the term virtual source to represent a network switch that modifies the source flow via filtering.
forwarding. A core-switch [Ballardie,93] where flows are filtered is always considered to be a virtual source for one or more receivers; for full details see [Aurrecoechea,94]. The WFS mechanism updates the advertised rate as the control messages traverse the switches on the reserve path to the source or virtual source. Therefore any switch can adjust the flow's advertised rate before the source or virtual source receives the rate based control message. The source-side transport protocol hands the measured delay and aggregate bandwidth off (B flow ) to the dynamic rate shaping filter.
DQM maintains flow state at each end-system and switch that a flow traverses. Flow state is updated by the WFS algorithm and the rate-based flow control mechanism and comprises:
i) capacity (viz. B avail , B guar , B resid );ii) policy (viz. filterStyle, adaptMode);iii)flowSpec (viz. BL, E1, E2) ;iv)WFS share (viz., B flow , B wfs , W ).
The end-systems hold an expanded share tuple for measured delay, loss and jitter metrics. An admission control test is conducted at each end-system and switch on route to the core for the base layer signal. This test simply determines whether there is sufficient bandwidth available to guarantee the base layer BL given the current network load:
BL (j )j =1
N
∑≤B avail
If the admission control test is successful, WFS determines the additional percentage of the
residual bandwidth made available (B wfs ) to meet any enhancement requirements in the flowSpec:
B wfs (i )=W fact (i ).(B avail ?
BL (j )j =1
N
∑)The WFS rate computation mechanism causes new B wfs rates to be computed for all adaptive
enhancement signals that traverse the output link of a switch; switches are typically non-blocking which means the critical resources are the output links, however, our scheme can be generalised to other switch architectures [Coulson,95].6.3 Network Filtering
Currently our scheme supports two types of selection filters in the network. These are low complexity and computationally simple filters for selecting sub-signals. Selection filters do not transform the structure of the internal stream, i.e. they have no knowledge of the format of the encoded flow above differentiating between BL, E1 and E2 sub-signals. The two basic types of section filter used are:
i) sub-signal filters : these manipulate base and enhancement layers of multi-layer video multiplexed on a single flow. The definition of sub-signals is kept general here; a flow may be comprised of an anchor and scalable extensions or the I and P pictures of MPEG-2's simple profile, or the individual hybrid scalable profile. Sub-signal filters are installed in switches when a receiver joins an on-going flow;ii) hierarchical filters : these manipulate base and enhancement layers which are transmitted and received on independent flows in a non multiplexed fashion. In functional terms sub-signal and hierarchical filters can be considered to be equivalent in some cases. In sub-signal filtering one flow characterises the complete signal and in hierarchical-filtering a set of flows characterise the complete signal.
In addition, hybrid filters combine the characteristics of sub-signal and hierarchical filtering techniques to meet the needs of complex sub-signal selection. For example hierarchical filters allow the BL, E1 and E2 to be carried over distinct flows, and the user can accordingly tune into each sub-signal as required. As an example, the base and enhancement layers of the hybrid scalable MPEG-2 flow are each in turn made up of I, P and B pictures at each layer i.e. BL (I,P,B), E1 (I,P,B) and E2 (I,P,B). Using hybrid filters, the receiver can join the BL QoS group for the main profile and the E1 QoS group for the spatial enhancement and then select sub-signals within each profile as required (e.g. the I and P pictures of the BL).
7. Conclusion
At Lancaster University we are investigating heterogeneity issues present in applications, communications systems and networks. Resolving heterogeneous QoS demands in networked multimedia systems is a particularly acute problem that we are addressing within the framework of our QoS-A. As part of that work we have described a scheme for the dynamic management of multi-layer flows in heterogeneous multimedia and multicast networking environments. Dynamic QoS management manipulates and adapts hierarchically coded flows at the end-systems and in the network using a set of scaling objects. The approach is based on three basic concepts: the scalable profiles of the MPEG-2 standard that can provide discrete adaptation, dynamic rate shaping algorithms for compressed digital video that provide continuous adaptation, and the weighted fair share service for adaptive flows. At the present time DQM is being implemented at Lancaster University. The experimental infrastructure at Lancaster is based on 80486 machines running a multimedia enhanced Chorus micro-kernel [Coulson,95] and connected by programmable Olivetti Research Limited 4x4 ATM switches. This work is being carried out collaboratively with Columbia University in the US. At Columbia we are currently using CORBA [Lazar,94] to propagate selection filters in the network using ASX200 switches. In addition to the implementation we are conducting an extensive simulation study into the feasibility of the adaptive network service for large scale use, and investigating the feasibility of extending the adaptive service concept into our enhance Chorus micro-kernel itself [Coulson,95]. In other QoS related research at Lancaster we are developing a networked scalable multimedia storage system [Pegler,95] based on the dynamic allocation of compressed file components within a hierarchy of heterogeneous servers, and specialised filter servers [Yeadon,94] which implement transcoder QoS filters.
8. Acknowledgement
The authors would like to thank members of the Multimedia Projects Group at Lancaster and the ISO QoS Working Group for the many enlightening discussions on end-to-end QoS. In particular. The authors are very grateful to the Alexandros Eleftheriadis and Cristina Aurrecoechea for their thoughtful comments and suggestions on this work. The research on Dynamic Rate Shaping was the subject of Alexandros Eleftheriadis' Thesis at Columbia University.
The QoS-A project is funded as part of the UK SERC Specially Promoted Programme in Integrated Multiservice Communication Networks (GR/H77194) in co-operation with GDC (formally Netcomm Ltd). Andrew Campbell wishes to thank the EPSRC for their kind support while he was visiting the Center for Telecommunications Research, Columbia University.
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地理位置 位于墨西哥大学城以南的库库尔坎（Kukulcan），是玛雅文化前古典期晚期（公元前800年——公元前200年）中部高原文化的重要文化遗址之一，“库库尔坎”的原意是“舞蹈唱歌的地方”，或表示“带有羽毛的蛇神”。 建筑结构 “库库尔坎”金字塔是我们现在看到的早期墨西哥金字塔是一座用土筑成的 九层圆形祭坛，高29米 ，周边各宽55米多，周长250米左右，最高一层建有一座6米高的方形坛庙，库库尔坎金字塔高约30 米，四周环绕91 级台阶，加起来一共364级台阶，再加上塔顶的羽蛇神庙，共有365阶，象征了一年中的365 天。台阶的两侧宽达1米的边墙，北边墙下端，有一个带羽行的大蛇头石刻，蛇头高1.43米，长达1.80米，宽1.07米，蛇嘴里吐出一条大舌头，颇为独特。 这座古老的建筑，在建造之前，经过了精心的几何设计，它所表达出的精确度和玄妙而充满戏剧性的效果，令后人叹为观止：每年春分和秋分两天的日落时分，北面一组台阶的边墙会在阳光照射下形成弯弯曲曲的七段等腰三角形，连同底部雕刻的蛇头，宛若一条巨蛇从塔顶向大地游动，象征着羽蛇神在春分时苏醒，爬出庙宇。每一次，这个幻像持续整整3 小时22 分，分秒不差。这个神秘景观被称为“光影蛇形”。 每当“库库尔坎”金字塔出同蛇影奇观的时候，古代玛雅人就欢聚在一起，高歌起舞，庆祝这位羽毛蛇神的降临。 库库尔坎金字塔，是玛雅人对其掌握的建筑几何知识的绝妙展示，而金字塔旁边的天文台，更是把这种高超的几何和天文知识表现得淋漓尽致。 建造工艺 在没有金属工具、没有大牲畜和轮车的情况下，古代玛雅人却能够开采大量重达数十吨的石头，跋山涉水、一路艰辛地运到目的地，建成一个个雄伟的金字塔。金字塔最高的可达70米，其规模之巨大、施工难度之高，令人吃惊。 古代玛雅的金字塔和古埃及的金字塔在建筑形式上有着明显的不同。埃及的金字塔的塔顶是尖的，而玛雅金字塔却是平顶，塔体呈方形，底大顶小，层层叠叠，塔顶的台上还建有庙宇；在用途上也不一样：埃及金字塔是法老的陵墓，而玛雅的金字塔除个别外，一般是用来祭祀或观察天象的。除金字塔外，玛雅人还兴建了不少功能性强，技艺高的民用建筑，主要有：房屋（包括庙宇、府邸、民居等）、公共设施（球场、广场、集市等）、基础设施（桥梁、大道、码头、堤坝、护墙等）和水利工程（水渠、水库、水井、梯田）等。
库库尔坎金字塔位于墨西哥尤卡坦半岛北部，是曾经古玛雅人留下的文明遗址。 库库尔坎在玛雅文化中是带羽蛇神的意思，被誉为是太阳的化身，即太阳神。羽蛇神主宰着晨星、发明了书籍、立法，而且给人类带来了玉米，还代表着死亡和重生，也是祭司们的保护神。古典时期，玛雅“真人”手持权杖，权杖一端为精致小形、中间为小人的一条腿化作蛇身、另一端为一蛇头。到了后古典时期，出现了多种变形，但基本形态完全变了，成为上部羽扇形、中间蛇身下部蛇头的羽蛇神形象。 羽蛇神与雨季同来，而雨季又与玛雅人种玉米的时间相重合，因而羽蛇神又成为玛雅农人最为崇敬的神明。在玛雅人眼中羽蛇神与犬神有同样高的地位 在现今留存的最大的玛雅古城奇岑－伊扎，库库尔坎金字塔屹立其中。它的每个面有91级台阶，4个面象征一年四季，共364级台阶，加上塔顶的神殿共365级，象征一年365天。4个边缘分别代表春分、秋分、夏至和冬至。在金字 塔的北面两底角雕有两个蛇头。每年春分、秋分两天，太阳落山时，可以看到蛇头投射在地上的影子与许多个三角形连套在一起，成为一条动感很强的飞蛇。好像从天空中游向大地，栩栩如生。春分蛇由上至下出现，仿佛从神庙中爬出来一样，秋分则由下至上出现，像是爬进去一样。只有每年的这两天里才能看到这一奇景。所以，现在它已经成为墨西哥的一个著名旅游景点。而在当年，玛雅人可以借助这种将天文学与建筑工艺精湛地融合在一起的直观景致，准确把握农时。与此同时，也准确把握崇拜羽蛇神的时机。考古学家在玛雅神庙下方发现神秘的坑洞，进一步的考察发现，坑洞是自然形成的，延伸大约34米，深度为20米 左右。最新的消息指出，神秘下方的洞穴可连接到其他洞穴或者地下湖泊，同时具有深层次的宗教意义，在玛雅文化中处于非常重要的地位。这座寺庙名称为Kukuerkan，即库库尔坎金字塔，这是中美洲最著名的古文明遗址之一，是玛雅文明的巅峰之作。那么金字塔下方的洞穴为何会存在呢，具有何种宗教意义？ 考古学家发现玛雅人在1000年前建造了金字塔，位于一个巨大的天然深坑 上，他们相信建立在深坑顶部的建筑是宗教信仰的一部分，因为库库尔坎金字塔内有一尊玛雅蛇神，或者认为是有羽毛的蛇，它是玛雅人非常崇拜的蛇神。由于蛇神需要水，因此神殿下方是一个被填满水的深坑，水流的运行由北向南。考古学家通过一种新的探测技术对神殿下方的结构进行研究，发现了深坑的存在，探测器能够探测到岩石结构走向，分辨出水流和岩石的相对位置。
2019年(春)六年级美术下册第1课《追寻文明的足 迹》说课教案人美版 教材分析： 本课是“欣赏`评诉”领域的内容。世界文化遗产是人类进步的闪光足迹，是全世界共同的财富。通过本课的欣赏活动，让学生了解人类的智慧和壮举，了解不同历史时期的文化现象，从而引发学生对人类文化遗产的关注，激发学生的求知欲。 教学内容与目标： 认知： 1、知道什么叫文化遗产，能说出7处-10处世界文化遗产。 2、能够对世界文化遗产的保护有正确的认识。 情意： 1、让学生认识到文化遗产是人类共同的财富，增强保护文化遗产的意识和方法。 2、学习了解各个国家不同时期的文明足迹，尊重不同文化背景下的文化现象，接纳多元文 化，拓展国际视野。 能力： 1、能够运用美术知识制作宣传栏，传播世界文化遗产知识。 2、能够收集世界文化遗产的相关资料，初步认识、了解自己感兴趣的文化遗产。 教学重点与难点： 重点： 1、通过资料阅读、课上交流等途径，认识7处—10处世界文化遗产，较细致的了解2处— 3处世界文化遗产。 2、能够从文化遗产的历史背景、审美价值、社会影响、经典特征等方面，介绍2处—3处 世界文化遗产。 难点：有步骤、有层次的介绍2处—3处世界文化遗产。 学习材料： 资料、剪刀、彩纸等 教学过程： 一、了解不同背景的世界文明遗迹 1、课前将学生分成四个组：阿布辛拜勒神庙（非洲）、库库尔坎金字塔（美洲）、法隆寺 （亚洲）、奥林匹亚遗址（欧洲） 每个学生根据书中的问题，查找最下边的 一行图片资料。 （1）《掷铁饼者》、《竞技表演》是哪方面的内容？用的是什么手法？ （2）阿布辛拜勒神庙建造于什么地方、什么时代、有什么特点？ （3）库库尔坎金字塔的所在地、建造时间、艺术特色。说一说它和埃及金字塔有什么相同与不同之处？ （4）法隆寺的建筑特点，它和中国的塔有什么相同与不同之处？ 教学意图：培养学生收集信息、整理信息的能力，以及小组合作、探究的意识。 二、欣赏分析多元的世界文化遗产
(完整word版)人美版六年级美术试题 亲爱的读者： 本文内容由我和我的同事精心收集整理后编辑发布到文库，发布之前我们对文中内容进行详细的校对，但难免会有错误的地方，如果有错误的地方请您评论区留言，我们予以纠正，如果本文档对您有帮助，请您下载收藏以便随时调用。下面是本文详细内容。 最后最您生活愉快 ~O(∩_∩)O ~
六年级美术试 一、填空。. 1、《哪吒闹海》是一幅__壁_画，作者张仃在这幅画中运用了中国传统壁画表现手法，又借鉴了构图的理念，在色彩、造型等方面都进行了成功的探索。 2、拉斯科洞窟的岩画是人类最早的绘画。 3、法隆寺是世界上最古老的木建筑之一。 4、装饰画偏重表现形式的装饰画偏重表现形式的装饰性，不强调真实光影和透视关系，注重色彩的象征性及整体的和谐，多以夸张、变形、简洁的手法，给人以明快、强烈的艺术美感。 5、农民画家敢于把牛画的艳丽，显示了他们对色彩生活丰富的想象力和对的无限热爱。 6、雕版印刷三大特点:主板线稿多块色板鬃毛刷。 7、我们曾学过纸版画对印版画粉印版画拓印版画等许多版画制作方法。 8、肌理是指由于材料的不同配列、组成和构造而使人得到的触觉质感和质地。手感触感织法性质纹理等说法都可包含在肌理之中。 9、第一部动画片是《一张滑稽面孔的幽默姿态》，第一部有声动画片是《威利号汽船》，第一部彩色动画片《白雪公主，第一部三维动画片是《玩具总动员》。 10、传统民间门神形象中取自《封神演义》的是赵公明和燃灯道人。 11、许多文化遗产是、文字、绘画、建筑、遗址、口传方式记录下来的，非物质文化遗产是不用文字以民间戏曲为主的活态文化，如各民族的文字绘画建筑遗址口传方式民间戏曲舞蹈神话传说节日礼仪刺绣玩具剪纸面花皮影等。 12、抓髻娃娃是我国北方民间剪纸中一个典型的形象，它既象征着性生命
六年级 美术(电子备课) 于颖 目录: 六年级下册: 第1课追寻文明的足迹 第2课探访自然的器官 第3课装饰色彩 第4课装饰画 第5课彩球的设计 第6课城市雕塑 第7课各种材料来制版 第8课装饰柱 第9课精彩的戏曲 第10课戏曲人物 第11课画故事 第12课动画片的今夕 第13课拟人化的动漫形象 第14课留给母校的纪念 第15课我的成长记录 第16课剪纸中的古老记忆 第17课绣在服装上的故事
第18课复制与传播 学情分析: 本学期我教的就是六年级三个班的美术课,随着学生年龄的增长、生理、身心健康的不断发展,学生们对美术的要求有所不同,对美术知识、技能的掌握程度也不同。她们更多地追求现实的、真实的东西或喜欢目前流行的“动漫”,对此进行大量的临摹在绘画技巧上显得成熟,线条也十分流畅,但画风呆板,表现欲下降,缺少童趣。但她们对色彩有辨别能力,把握物体形状的能力很强,乐于动手,对手工制作课充满了极高的热情。对美具有了较高的欣赏能力。 这学期就是她们迈入初中的过渡时期,既要努力响应学生目前的兴趣爱好,又要深入浅出地灌输客观的美术学科理论知识,与初中知识进一步接轨,将平时教给学生的初中知识更加明朗化介绍给学生,使她们从儿童绘画到少年绘画的转型,更重视有欣赏内容与工艺设计教学,即学生的创造能力上的培养,其实就就是对儿童想象力的深化,转变为更理论性含量的创造能力。 知识要点: 该教材贴近学生的心理,符合学生的年龄特点,每课的主题都有美术带来的有趣的惊喜。六年级美术教材一共分为19课。每一课都侧重于“造型·表现”、“设计·应用”、“欣赏·评述”、“综合·探索”四个学习领域中的一个方面,同时也有不少系列的课,教学内容前后联系比较紧密,非常适合学生较深入地做一个专题。并且有些教学内容还设计成了案例学习、问题学习与项目学习,这就要求我们老师应多引导学生进行主动的探究学习,增加学生集体合作的机会。其次本册教材继续体现了人美版教材的可操作性强、贴近生活、关注美术文化的渗透与注重学生学习兴趣的培养等特点。 “造型·表现”:在教学中,让学生运用形、色与肌理等美术语言,选择合适自己的各种工具、材料,记录与表现所见所闻、所感所想的事物,发展美术创作能力,传递自己的思想与情感。 “设计·应用”:运用对比与与谐、对称与均衡、节奏与韵律等组合原理,了解一些简单的创意、设计方法与媒材的加工方法,进行设计与装饰,美化身边的环境。“欣赏·评述”:欣赏认识自然美与美术作品的材料、形式与内容等特征,通过描述、分析与讨论等方式,了解美术表现的多样性,能用一些简单的美术术语,表达自己对美术作品的感受与理解。 “综合·探索”:结合学校与社区的活动,以美术与科学课程与其她课程的知识、技能相结合的方式,进行策划、制作、表演与展示,体会美术与环境及传统文化的关系。 【授课内容】1、追寻文明的足迹 【课时建议】1课时 【教程目标】 知识与技能:知道什么叫文化遗产,能说出7-10处世界文化遗产。能够对世界文化遗产的保护有正确的认识。 过程与方法:通过资料阅读、课上交流等途径,认识了解2处-3处世界文化遗产;能够从文化遗产的历史背景、审美价值、社会影响、经典特征等方面,介绍2-3处世界文化遗产。 情感、态度与价值观:通过本课学习,认识到文化遗产就是人类共同的财富,增强保护文化遗产
科潘玛雅古迹遗址 科潘玛雅古迹遗址位于洪都拉斯西部边境，遗址面积数十平方公里，1980年入选《世界遗产名录》。科潘属于玛雅文明古典期（公元250—900年），为玛雅文明最盛时期。金字塔式寺庙较为精美，台顶神殿有大量浮雕。科潘是玛雅文化的学术中心，不少建筑遗址与天文、历法等学术活动有关。这里保存了玛雅文化中最长的铭刻，多达2500字，号称“象形文字的梯道”。科潘玛雅遗址是玛雅文明最重要的地区之一，有着宏大的建筑，还有丰富的象形文字，是极少数起源于热带丛林的文明的例证。这些建筑表明科潘的玛雅人有高度发展的经济和文化。 公元1839年，美国探险学家史蒂芬斯(JohnlioydStephens)和卡瑟伍德(FrederikCatherWood)受到一个古老传说的暗示，披荆斩棘，深入浓荫蔽日的雨林之中，然而，他们没有找到被巫师催眠的美丽公主，却发现了一座已荒废千年的古代城市遗址。在这座叫作科潘的旧城废墟上，高大的纪念碑被藤条缠绕，湮没在荆棘之中；雄伟的金字塔上长满了粗壮的树木，变成一座座荒丘。史蒂芬斯他们被眼前的这一切惊呆了，这些遗迹所代表的就是辉煌灿烂的玛雅文明。 玛雅文明是世界著名的古代文明之一，也是唯一诞生在热带丛林而非大河流域的文明。玛雅人具有的抽象思维能力让同时代的旧大陆文明相形见绌。他们创造了精确的数学体系和天文历法系统，以及至今仍有待我们去破译的象形文字系统。玛雅人最重视对太阳和月亮的观测，他们能算出日蚀和月蚀出现的时间，并已将七大行星都列入了研究范围。他们对金星运行周期的计算和现代科学实测结果完全一致。玛雅历法体系由"神历"、"太阳历"和"长纪年历"组成。玛雅人有一个独特的数学体系，在这个体系中，最先进的部分便是"0"这个符号的使用，它的发明和使用比欧洲大约早了800年。玛雅的数学体系的适用性和科学性，使他们能在许多科学和技术活动中解决各种难题。在世界各古代文明中，除了起源于印度的阿拉伯数字之外，玛雅数字要算是最先进的了。但非常可惜，有关玛雅数学的图书或文献一本也没有流传下来。玛雅的象形文字对现代人来说真是一部天书，它的谜底直到今天仍未解开。玛雅象形文字以近似圆形或椭圆为主，字符的线条更多地依随图形起伏变化、圆通流畅。 科潘是玛雅象形文字研究最发达的地区，它的纪念碑和建筑物上的象形文字符号书写最美、刻制最精、字数最多，例如，在科潘遗址中，有一条六七十级的梯道，用2500多块加工过的方石砌成，这是一座纪念性的建筑物，梯道建在山坡上，直通山顶的祭坛。宽10米，两侧各刻着一条花斑巨蟒，蟒尾在山丘顶部：梯道的每块方砖上都刻着象形文字，每个形文字的四周均雕有花纹，梯道共刻了2000多个象形文字符号，它是玛雅象形文字最长的铭刻，也是世界题铭学上少见的珍贵文物，由此被称为"象形文字梯道。" 不仅如此，科潘的经济与政治实力仅次于蒂卡尔而远远超过其他城邦，在文化上则完全可以和蒂卡尔并肩而立，甚至还略有超越，有学者认为科潘的重要意义决不在蒂卡尔之下，它们如双峰并立，是玛雅文明两座最伟大的灯塔。确实，从考古发掘的城市遗址看，科潘在规模上可能略逊于蒂卡尔，但美丽却有过之而无不及。据记载公元805年以后，玛雅人突然弃科潘城北迁，科潘城随之变成一片废墟。 奇琴伊察玛雅城邦遗址曾是古玛雅帝国最大最繁华的城邦。遗址拉于尤卡坦半岛中部。始建于公元514年。城邦的主要古迹有：千柱广场、武士庙及庙前的斜倚的两神石像。9层，高30米的呈阶梯形的库库尔坎金字塔以及圣井(石灰岩竖洞)和筑在高台上呈蜗形的玛雅人古
六年级美术下册--《追寻文明的足迹》说课教案（人美版） 教材分析： 本课是“欣赏`评诉”领域的内容.世界文化遗产是人类进步的闪光足迹，是全世界共同的财富.通过本课的欣赏活动，让学生了解人类的智慧和壮举，了解不同历史时期的文化现象，从而引发学生对人类文化遗产的关注，激发学生的求知欲. 教学内容与目标： 认知： 1、知道什么叫文化遗产，能说出7处-10处世界文化遗产. 2、能够对世界文化遗产的保护有正确的认识. 情意： 1、让学生认识到文化遗产是人类共同的财富，增强保护文化遗产的意识和方法. 2、学习了解各个国家不同时期的文明足迹，尊重不同文化背景下的文化现象，接纳多元文化， 拓展国际视野. 能力： 1、能够运用美术知识制作宣传栏，传播世界文化遗产知识. 2、能够收集世界文化遗产的相关资料，初步认识、了解自己感兴趣的文化遗产. 教学重点与难点： 重点： 1、通过资料阅读、课上交流等途径，认识7处—10处世界文化遗产，较细致的了解2处—3 处世界文化遗产. 2、能够从文化遗产的历史背景、审美价值、社会影响、经典特征等方面，介绍2处—3处世 界文化遗产. 难点：有步骤、有层次的介绍2处—3处世界文化遗产. 学习材料： 资料、剪刀、彩纸等 教学过程： 一、了解不同背景的世界文明遗迹 1、课前将学生分成四个组：阿布辛拜勒神庙（非洲）、库库尔坎金字塔（美洲）、法隆寺（亚 洲）、奥林匹亚遗址（欧洲）
每个学生根据书中的问题，查找最下边的 一行图片资料. （1）《掷铁饼者》、《竞技表演》是哪方面的内容？用的是什么手法？ （2）阿布辛拜勒神庙建造于什么地方、什么时代、有什么特点？ （3）库库尔坎金字塔的所在地、建造时间、艺术特色.说一说它和埃及金字塔有什么相同与不同之处？ （4）法隆寺的建筑特点，它和中国的塔有什么相同与不同之处？ 教学意图：培养学生收集信息、整理信息的能力，以及小组合作、探究的意识. 二、欣赏分析多元的世界文化遗产 1、教师讲述关于拉斯科岩画的故事. （1）这幅画表现的什么？让你联想到什么？ （2）猜猜当时的人用什么工具创作的？ （3）他们为什么要画这些壁画？ 2、2008年8月8日在北京将要发生一件非常重要的事情，是什么？有谁知道这界奥运会是 第几届？第一届奥运会在哪里召开的？这个国家在哪个洲？ （1）教师介绍希腊奥运之城. （2）请学生代表介绍查找到的关于《竞技表演》、《掷铁饼者》的资料 小结：古代的建筑、雕塑和体育已经完美的结合了，说说你还知道奥运会的那些项目？书中还有哪些建筑在欧洲？ 3、学生介绍有关阿布辛拜勒神庙资料. 小结：由此我们知道建筑、雕塑和宗教也有着亲切的联系，你还知道埃及有什么建筑？他们是哪个洲的文明遗迹？说说埃及金字塔和库库尔坎金字塔有什么不同？在美洲还有什么文明遗迹，请你说说. 4、对于美洲古代文明遗迹你有什么感想？ 5、法隆寺的建筑特点，它和中国的塔有什么相同与 不同之处？书中还有哪个是亚洲的建筑？ 6、亚洲还有什么文明遗迹？ 教学意图：
The stepped pyramids, temples, columned arcades, and other stone structures of ChichénItzá were sacred to the Maya and a sophisticated urban center of their empire from A.D. 750 to 1200. Viewed as a whole, the incredible complex reveals much about the Maya and Toltec vision of the universe—which was intimately tied to what was visible in the dark night skies of the Yucatán Peninsula. The most recognizable structure here is the Temple of Kukulkan, also known as El Castillo. This glorious step pyramid demonstrates the accuracy and importance of Maya astronomy—and the heavy influence of the Toltecs, who invaded around 1000 and precipitated a merger of the two cultural traditions. The temple has 365 steps—one for each day of the year. Each of the temple’s four sides has 91 steps, and the top platform makes the 365th. Devising a 365-day calendar was just one feat of Maya science. Incredibly, twice a year on the spring and autumn equinoxes, a shadow falls on the pyramid in the shape of a serpent. As the sun sets, this shadowy snake descends the steps to eventually join a
库库尔坎金字塔 库库尔坎金字塔 库库尔坎金字塔在墨西哥尤卡坦半岛北部，有座著名的古建筑称为库库尔坎金字塔，是曾经的古代玛雅人留下的文明遗址。库库尔坎在玛雅文中是带羽毛之神蛇的意思，被誉为是太阳的化身。 基本认识 地理位置 位于墨西哥大学城以南的库库尔坎（Kukulcan），是玛雅文化前古典期晚期（公元前800年——公元前200年）中部高原文化的重要文化遗址之一，“库库尔坎”的原意是“舞蹈唱歌的地方”，或表示“带有羽毛的蛇神”。 建筑结构 “库库尔坎”金字塔是我们现在看到的早期墨西哥金字塔是一座用土筑成的九层圆形祭坛，高29米 库库尔坎金字塔 ，周边各宽55米多，周长250米左右，最高一层建有一座6米高的方形坛庙，库库尔坎金字塔高约30 米，四周环绕91 级台阶，加起来一共364级台阶，再加上塔顶的羽蛇神庙，共有365阶，象征了一年中的365 天。台阶的两侧宽达1米的边墙，北边墙
下端，有一个带羽行的大蛇头石刻，蛇头高1.43米，长达1.80米，宽1.07米，蛇嘴里吐出一条大舌头，颇为独特。这座古老的建筑，在建造之前，经过了精心的几何设计，它所表达出的精确度和玄妙而充满戏剧性的效果，令后人叹为观止：每年春分和秋分两天的日落时分，北面一组台阶的边墙会在阳光照射下形成弯弯曲曲的七段等腰三角形，连同底部雕刻的蛇头，宛若一条巨蛇从塔顶向大地游动，象征着羽蛇神在春分时苏醒，爬出庙宇。每一次，这个幻像持续整整3 小时22 分，分秒不差。这个神秘景观被称为“光影蛇形”。每当“库库尔坎”金字塔出同蛇影奇观的时候，古代玛雅人就欢聚在一起，高歌起舞，庆祝这位羽毛蛇神的降临。库库尔坎金字塔，是玛雅人对其掌握的建筑几何知识的绝妙展示，而金字塔旁边的天文台，更是把这种高超的几何和天文知识表现得淋漓尽致。[1] 建造工艺 库库尔坎金字塔资料图(5张) 在没有金属工具、没有大牲畜和轮车的情况下，古代玛雅人却能够开采大量重达数十吨的石头，跋山涉水、一路艰辛地运到目的地，建成一个个雄伟的金字塔。金字塔最高的可达70米，其规模之巨大、施工难度之高，令人吃惊。古代玛雅的金字塔和古埃及的金字塔在建筑形式上有着明显的不同。埃及的金字塔的塔顶是尖的，而玛雅金字塔却是平顶，塔体呈方形，底大顶小，层层叠叠，塔顶的台上还建有庙宇；在用途上也不一样：埃及金字塔是法老的陵墓，而玛雅的金字塔除个别外，一般是用来祭祀或观察天象的。除金字塔外，玛雅人还兴建了不少功能性强，技艺高的民用建筑，主要有：房屋（包括庙宇、府邸、民居等）、公共设施（球场、广场、集市等）、基础设施（桥梁、大道、码头、堤坝、护墙等）和水利工程（水渠、水库、水井、梯田）等。 历史溯源 玛雅文化的历史
玛雅遗址的建筑历史详细介绍 蒂卡尔是玛雅文明的文化和人口中心之一。这里最早的纪念碑建造于公元前四世纪。城市在玛雅古典时期——大约公元200年到公元850年左右，达到顶峰。 蒂卡尔的历史可以追溯到公元前1世纪，起先她只是个二流城邦，奉北部城邦米拉多为盟主，蒂卡尔可能从公元二世纪开始奉行与中美洲当时的大国提奥提华坎友好的政策，并取得成功使自己国力大涨，从而成为玛雅世界最强大的城邦之一。 公元292年，Balam Ajaw(传统上译为“Decorated Jaguar”，被装饰过的美洲虎)继位为蒂卡尔国王，开始了强大的蒂卡尔王朝。在一块刻有他形象的石碑上记录有公元292年7月8日的日期。这个时间也通常被历史学家当作玛雅古典文明的开始之日。 公元360年，Chak Toh Ich’ak I 美洲虎之爪一世(Jaguar Paw I)为国王之时，蒂卡尔空前强大，“美洲虎之爪一世”的弟弟“吸烟的青蛙”于公元378年1月16日征服邻邦乌夏克吞(Uaxactun)，并成为乌夏克吞的君主。
美洲虎之爪一世以后的蒂卡尔国王叫做Nun Yax Ayin，(King Curl-Nose 蜷鼻王) 是一个来自提奥提华坎的贵族，于379年继位，蜷鼻王虽来自提奥提华坎，但却也是个地道的蒂卡尔国王，保持着蒂卡尔的强大与繁荣。 公元411年至公元456年，Siyah Chan K'awil II 暴风雨天空二世(Stormy Sky II) 为国王。从美洲虎之爪一世到暴风雨天空二世的一百年间是蒂卡尔历史上第一个强大的时期。 此后蒂卡尔以北的城邦卡拉克穆尔强大，蒂卡尔出现了一个衰落时期，直到公元7世纪，Hasaw Chan K’awil 阿赫卡王(双月，巧克力领主Double Moon or Lord Chocolate 682年-734年在位)，蒂卡尔重新强大，打败卡拉克穆尔，使得蒂卡尔重新成为玛雅中部地区的霸主。以后是Yik’in Chan Kawil 雅克金王(734年-766年在位)和Yax Nuun Ayiin II 奇坦王(Chitam 768年-790年在位)，在这一百年间是蒂卡尔第二次鼎盛时期。蒂卡尔壮丽的遗迹主要也是这三位国王在位期间筑成。 奇坦王之后，与同一时期其他玛雅城邦一样，蒂卡尔迅速衰落，已知可考的最后一位国王是Jasaw Chan K'awiil II (869年-889年在位) 在这之后，没有建造什么主要的纪念碑。一些宫
六年级美术练习题 一、填空1、《哪吒闹海》是一幅有民族气派的现代（壁画），画家（张仃）在画中运用了传统壁画的表现手法，又借鉴了现代装饰画的理念，在（构图）（色彩）（造型）等方面都进行了成功的探索，（构图）新颖、色彩绚丽，颇有（旋转感）和装饰意趣。 2、《拉斯科洞窟的岩画》被称为“史前的卢浮宫”，产生于1.5万年前的旧石器时代，这是人类最早的绘画。是用蕨草、羽毛等工具，木炭、矿砂等颜料画成的。书中画的是（马）。 3、墨西哥的《库库尔坎金字塔》与埃及金字塔不同，埃及金字塔外表的四个面是（平）的，顶端是（尖）的；《库库尔坎金字塔》外表呈（阶梯）形，塔顶是（平）的，是羽蛇神庙，它产生于2000多年前的玛雅文明，由9层晒台91级台阶组成。 阿布辛拜勒神庙前的拉美西斯二世雕塑始建于公元前1300年——公元前1233年。它是埃及最强大的国王拉美西斯二世时期建造的。 4、日本的《法隆寺》建于1400年前，是最古老的木建筑，它与中国传统的塔造型相近，但比中国的塔纤秀、飘逸一些，檐翼宽大，塔顶尖细。 5、奥林匹克运动会起源于公元前776年古希腊的运动竞赛，由古希腊的一个地名奥林匹亚而得名。古希腊雕塑是世界雕塑史上的一座丰碑，健美的运动员，造型高度写实，姿态优雅，容貌端正，反映古希腊人对美的追求。（掷铁饼者公元前450年、竞技表演公元前510年）哈夫拉金字塔埃及公元前2500年、巨石阵英国公元前3100-公元前1100年、毛阿伊石像智利公元700-800年、比萨斜塔意大利1173-1350年、圣瓦西里大教堂俄罗斯1561年。 6、世界第一峰是珠穆朗玛峰，海拔8844.43米，藏语中，其含义是（圣母）的意思。尼泊尔人称它是（“萨加玛塔峰”），意思是“摩天峰”。 7、《巨人之路》位于英国，它的四万根石柱，完全是（大自然）的杰作。 大堡礁位于澳大利亚东北部，由2900个珊瑚礁组成，是世界七大自然奇景之一。 自然美是一个整体，天空、大地、山峦、河流、树木……构成了和谐之美。自然美不是精致的，而是动态的，有四季、气候、生命的变化……我们可以亲身感受他们的芬芳、声音、冷暖……自然美的特征有a 自然本身的质地、材料、色彩、形状等。B 自然偏重于形式。C 自然具有联想性等。 维多利亚瀑布非洲津巴布韦，加兰巴国家公园非洲刚果民主共和国，科罗拉多大峡谷美洲美国，罗斯格拉西亚雷斯冰川国家公园莫雷罗冰川美洲阿根廷，马埃谷地自然保护区非洲塞舌尔，乌卢鲁国家公园的艾尔斯巨石大洋洲澳大利亚吴哥古迹柬埔寨亚洲、科罗拉多大峡谷美国美洲
世界著名旅游景点一览秘鲁印加遗址——Machu Picchu – Peru 20世纪初，人们传说在秘鲁安第斯山脉的崇山峻岭中有一座神秘的古城。西班牙人在长达300年的殖民统治期间对它一无所知，秘鲁独立后100年间也无人涉足。400多年的时光，只有翱翔的山鹰一睹古城的雄姿。它就是今天的马丘比丘印加遗址。
墨西哥玛雅古迹——Chichen Itza - Mexico 奇琴伊察玛雅城邦遗址曾是古玛雅帝国最大最繁华的城邦。遗址拉于尤卡坦半岛中部。始建于公元514年。城邦的主要古迹有：千柱广场，它曾支撑巨大的穹窿形房顶。可见此建筑物之大。武士庙及庙前的斜倚的两神石像。9层高30米的呈阶梯形的库库尔坎金字塔。以及圣井(石灰岩竖洞)和筑在高台上呈蜗形的玛雅人古天文观象台，称“蜗台”。
印度泰姬陵——Taj Mahal 泰姬陵是莫卧儿王朝第五代君主沙杰罕为宠姬泰吉·玛哈尔修筑的陵墓，整个建筑通体用白色大理石砌成，外形端庄华美，无懈可击，寝宫门窗及围屏都用白色大理石镂雕成菱形带花边的小格，墙上用翡翠、水晶、玛瑙、红绿宝石镶嵌着色彩艳丽的藤蔓花朵，光线所至，光华夺目，璀璨有如天上的星辉。几百年来，不知有多少文人墨客为泰姬陵折腰，写下无数
动人的诗篇。但是当你真正站在她面前时，才会深深体会到，泰姬陵之美，原来是任何文字都无法书写的。绝代有佳人，遗世而独立。俏立于亚穆纳河畔那个洁白晶莹、玲珑剔透的身 影，秀眉微蹙，若有所思。 好望角——Cape Town 非洲西南端的岬角。1488年葡萄牙航海家迪亚士在寻找欧洲通向印度的航路时到此，因多风暴，取名风暴角。但从此通往富庶的东方航道有望，故改称好望角。苏伊士运河通航前，来往于亚欧之间的船舶都经过好望角。现特大油轮无法进入苏伊士运河，仍需取此道航行。好望角多暴风雨，海浪汹涌，位于来自印度洋的温暖的莫桑比克厄加勒斯洋流和来自南极洲水域
《追寻文明的足迹》创新教案 学习目标： 1能够收集世界文化遗产的相关资料，初步认识、了解自己感兴趣的文化遗产。 2通过本课学习，认识到文化遗产是人类共同的财富，增强保护文化遗产的意识及方法。 3学习了解各个国家不同时期的文明足迹，尊重不同文化背景下的文化现象，接纳多元文化，拓展国际视野。 教学重、难点： 重点：1通过资料阅读、课上交流等途径，认识7处~10处世界文化遗产，较细致地了解2处~3处世界文化遗产；2能够从文化遗产的历史背景、审美价值、社会影响、经典特征等方面，介绍2处~3处世界文化遗产。 难点：有步骤、有层次地介绍2处~3处文化遗产。 课前准备： 教师：文化遗产高清组图，视频资料等； 学生：搜集感兴趣的文化遗产资料（格式不限）。 教学过程： 一、我们一起来了解一下奥运会的发祥地——希腊。 1、欣赏图片，了解奥林匹亚遗址及有关奥运会知识。 希腊属于欧洲，首都是雅典。奥林匹亚是奥林匹克运动的发祥地。这里气候宜人，景色优美，到处都是橄榄树、桂树和柏树。古奥运会起源于公元前776年，终止于公元394年，共举行293届，绵延1170年。1896年4月6日至15日，第一届现代奥运会终于在雅典隆重举行。奥林匹克运动从此开始了一个崭
新的纪元。现代奥林匹克运动会虽然改在各国轮流举行，但仍然沿用这一名称，并且在这里点燃各届奥运会的圣火。奥林匹亚有世界上最古老的运动场。 2、欣赏《掷铁饼者》，了解相关内容。 在古代奥运会上获一次冠军者，可以在运动场墙壁上镌刻自己的名字；三次夺冠，雕塑家就会找上门来，为你塑像。我们看到的《掷铁饼者》就是这样一尊雕塑，它属于圆雕作品。大家看到这尊雕塑有什么感受？ 刻画的是一名强健的男子掷铁饼的过程。在作品中创造了一个出色的健美而又富于力感的运动员形象。 雕塑选择的是将铁饼摆到最高点、即将抛出的一刹那，有着强烈的“引而不发”的吸引力。虽然是一件静止的雕塑，但艺术家把握住了从一种状态转换到另一种状态的关键环节，达到了使观众心理上获得“运动感”的效果，成为后世艺术创作的典范。这尊雕像被认为是“空间中凝固的永恒”，直到今天仍然是代表体育运动的最佳标志。 此雕塑由米隆创作于约公元前450年，被公认为体育运动和健美体魄的象征。这是雕刻家从实际生活中观察得来的真实形象。我们看到的大理石雕复制品，高约152厘米，罗马国立博物馆、梵蒂冈博物馆、特尔梅博物馆均有收藏，原作为青铜材质。 3、欣赏《竞技表演》。 《竞技表演》也是一座以表现奥林匹克运动为内容的雕塑作品，它属于浮雕。从图片上大家可以看出哪些内容？（一些运动员的动作，各种运动项目。）从这些人物的表现上你感觉这些运动员身体素质怎样？（非常健美，有力量的感觉。）这座浮雕通过表现竞技场上的运动员们在精神上与肉体上的坚强有力和美感，向我们传达出生命的健美、庄重与和谐，给我们带来美的享受。 二、了解其它世界文化遗产。