u_course

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8.A participant may require an independent metadata repository.

9.A DSSP offers several interrelated services on the dataspace, some of which are generalizations of components provided by a traditional DBMS.

10.A DSSP does not assume complete control over the data in the dataspace.

5. SPEAKING

Work in two groups, A and B. Think of advantages and possible disadvantages of dataspaces in information management field. Then together consider how the disadvantages can be minimized. Use the Notes below.

Group A. Advantages of dataspaces	Group B. Disadvantages of dataspaces

Notes:

CLARIFICATION

-I'm afraid it's not quite clear what you mean by...

-I'm sorry I didn't quite follow what you said about...

-I'm afraid I don't understand what... mean(s).

-When you say..., do you mean that...?

ASKING QUESTIONS

-I'd like to know what/when/why/how/who/if...

-Could you tell me what/when/why/how/who/if...?

-I wonder what/when/why/how/who/if...

-Would you tell me what/when/why/how/who/if...?

-It's interesting to know (to find out) what/when/why/how/who/if...

6.WRITING

Write an annotation to the text “From Databases to Dataspaces: A New Abstraction for Information Management”. (See Supplement 3)

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Unit 3

Is Real-Time Operating System worth it?

1. PRE-READING ASSIGNMENT

1.1. Translate the vocabulary used in the text below:

real-time OS	corrupted
an embedded system	stringent
a constraint	temporary
a chunk	an add-on component
to launch	to implement
to assign	consumption
priority	airborne computer
scheduling	to impose
2. READING

2.1.Read the text and choose a suitable title.

v Embedded systems as one kind of operating systems v Basic concepts of real-time operating systems

v Development of real-time operating systems

v Real-time and embedded systems in comparison

Real-time and embedded systems operate in constrained environments in which computer memory and processing power are limited. They often need to provide their services within strict time deadlines to their users and to the surrounding world. It is these memory, speed and timing constraints that dictate the use of real-time operating systems in embedded software.

Basic kernel services

The kernel is the part of an operating system that provides the most basic services to application software running on a processor.

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The kernel of a real-time operating system (RTOS) provides an “abstraction layer” that hides from application software the hardware details of the processor (or set of processors) upon which the application software will run. This is shown in Figure 6.

Fig. 6. An RTOS Kernel provides an Abstraction Layer between Application Software and Embedded Hardware

In providing this “abstraction layer” the RTOS kernel supplies five main categories of basic services to application software, as seen in Figure 7.

Fig. 7. Basic Services Provided by a Real-Time Operating System Kernel

The most basic category of kernel services, at the very center of Figure 7, is Task Management. This set of services allows application software developers to design their software as a number of separate “chunks” of software – each handling a distinct topic, a distinct goal, and perhaps its own real-time deadline. Each separate “chunk” of software is called a “task”. Services in this category include the ability to launch tasks and assign priorities to them. The main RTOS service in this category is the scheduling of tasks as the embedded system is in operation.

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The Task Scheduler controls the execution of application software tasks, and can make them run in a very timely and responsive fashion.

The second category of kernel services, shown at the top of Figure 7, is Intertask Communication and Synchronization. These services make it possible for tasks to pass information from one to another, without danger of that information ever being damaged. They also make it possible for tasks to coordinate, so that they can productively cooperate with one another. Without the help of these RTOS services, tasks might well communicate corrupted information or otherwise interfere with each other.

Since many embedded systems have stringent timing requirements, most RTOS kernels also provide some basic Timer services, such as task delays and time-outs. These are shown on the right side of Figure 7.

Many (but not all) RTOS kernels provide Dynamic Memory Allocation services. This category of services allows tasks to “borrow” chunks of RAM memory for temporary use in application software. Often these chunks of memory are then passed from task to task, as a means of quickly communicating large amounts of data between tasks.

Many (but not all) RTOS kernels also provide a “Device I/O Supervisor” category of services. These services, if available, provide a uniform framework for organizing and accessing the many hardware device drivers that are typical of an embedded system.

In addition to kernel services, many RTOSs offer a number of optional addon operating system components for such high-level services as file system organization, network communication, network management, database management, user-interface graphics, etc. Although many of these add-on components are much larger and much more complex than the RTOS kernel, they rely on the presence of the RTOS kernel and take advantage of its basic services. Each of these add-on components is included in an embedded system only if its services are needed for implementing the embedded application, in order to keep program memory consumption to a minimum.

Many non-real-time operating systems also provide similar kernel services. The key difference between general-computing operating systems and real-time operating systems is the need for “deterministic” timing behavior in the real-time operating systems. Formally, “deterministic” timing means that operating system services consume only known and expected amounts of time.

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Real-time and embedded systems are used in many applications such as airborne computers, medical instruments and communication systems. Embedded systems are characterized by limited processor memory, limited processing power, and unusual interfaces to the outside world. Real-time requirements impose stringent time deadlines for delivering the results of embedded processing.

3. POST-READING

3.1.Answer the questions to the text:

1.What are the constraints that dictate the use of real-time operating systems?

2.What is an “abstraction layer” in RTOS?

3.What are main categories of basic services in RTOS?

4.Intertask Communication and Synchronization controls the execution of application software tasks, does it?

5.Does Device I/O Supervisor or Dynamic Memory Allocation service tasks to “borrow” chunks of RAM memory?

6.Are add-on components always included in an embedded system?

7.What does “deterministic” timing mean?

3.2.Look through the text again and copy out the main terms. Find their definition in the Glossary.

3.3.Using the following terms fill in the gaps in the text.

a)kernel

b)deterministic timing behavior

c)real-time requirements

c)Intertask Communication and Synchronization

d)Time Management

e)real-time system

f)Dynamic Memory Allocation

g)Timer

h)Device I/O Supervisor

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___________ operates in constrained environment in which computer memory and processing power are limited. ____________ impose stringent time deadlines for delivering the results of embedded processing. The RTOS ________

supplies five main categories of basic services to application software. Services in

_________ include the ability to launch tasks and assign priorities to them. Without the help of __________ service, tasks might communicate corrupted information or otherwise interfere with each other. Some basic _____ services provided by RTOS kernels are delays and time-outs. __________ allows tasks to borrow chunks of RAM memory for temporary use in application software. A uniform framework for organizing and accessing hardware device drivers are provided by _____________. In the real-time operating systems there is a need for

___________ that means that operating system services consume only known and expected amounts of time.

4. WRITING

Find additional information about real-time operating systems and extend the content of the text.

5. SPEAKING

Round-table discussion.

Prepare for discussion on the topic “General-Computing Operating System or Real-Time Operating Systems. Pros and cons”. Use Table 2.

Table 2

Expressions for discussions

Discussion.	Agreeing. Disagreeing.
I would like to begin the discussion on	I agree
the subject by saying that…	I generally agree
First of all I must say…	I quite agree here.
I’d just like to say…	I strongly agree.
I think (suppose, guess, believe, dare	I fully agree.
say)…	I’m of the same opinion.
In my opinion…	It goes without saying that…

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Well, my opinion is… If you ask me…

As I see it… The point is…

My point of view is… Besides…

There is one more thing to be noted. Moreover…

In addition…

You may be right, but… I wouldn’t say that… On the one hand…

On the other hand… Generally speaking… It depends.

I’m not sure. I doubt it.

I’m afraid I don’t agree. I object to it.

I disagree

I generally disagree I strongly disagree

I can’t agree with you. Don’t you agree that…? I think you’re mistaken.

I don’t think you are right. I shouldn’t say so. Nothing of the kind.

On the contrary! Certainly not. Quite so! Certainly. Exactly. Definitely. Absolutely. Beyond all doubt. Looks like that. Just a minute…

Someone has told me …

I’m afraid I don’t know much about… Well I don’t think…

I don’t quite see what you mean, I’m afraid.

I don’t quite follow what you mean, I’m afraid.

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Module 2.

NETWORKS AND TELECOMMUNICATIONS

How are networks changing our lives?

Unit 1

1. PRE-READING ASSIGNMENT

What networking hardware do you know?

2. READING

2.1. Translate the vocabulary used in the text below:

an enterprise	congestion
adjacent	incremental
to extend	to destine
Token Ring	simultaneously
to segment	dedicated LAN
response time	to diminish

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a culprit

uncontested

2.2.Read the text and answer the following questions:

∙What are the similarities and differences between a router and a bridge?

∙What are switches used for?

The Networking

The term internetworking refers to linking individual LANs together to form a single internetwork. This internetwork is sometimes called an enterprise network because it interconnects all of the computer networks throughout the entire enterprise.

There are three major types of devices used for internetworking: bridges, routers, and switches.

Bridges and routers are both special kinds of devices used for internetworking LANs that is, linking different LANs or LAN segments together. Many organizations have LANs located at sites that are geographically distant from each other. Routers were originally designed to allow users to connect these remote LANs across a wide area network, but bridges can also be used for this purpose. By placing routers or bridges on LANs at two distant sites and connecting them with a telecommunications link, a user on one of the LANs can access resources on the other LAN as if those resources were local.

Bridges and routers link adjacent LANs. Local bridges and routers were first used to extend the area a network could cover by allowing users to connect two adjacent LANs to maintain performance by reducing the number of users per segment. Both Ethernet and Token Ring specify limits on maximum distances between workstations and hubs, hubs and hubs, and a maximum number of stations that can be connected to a single LAN. To provide network connectivity for more people, or extend it to cover a larger area, it is sometimes necessary to link two different LANs or LAN segments. Bridges and routers can both provide this function.

Today, however, these internetworking devices are also increasingly used to segment LANs to maintain performance by reducing the number of users per segment. When users on a single LAN begin to experience slower response times, the culprit is often congestion: too much traffic on the LAN. One method users are

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employing to deal with this is to break large LANs with many users into smaller LANs, each with fewer users. Adding new network users may require the organization to create new LANs to accommodate them. Implementing new applications on an existing LAN can create so much incremental traffic that the organization may need to break the LAN into smaller LANs segments to maintain acceptable performance levels.

In all of these cases, it is still critical that users on one LAN be able to reach resources on other LANs within the organization. But the LANs must be connected in such a way that packets are filtered, so that only those packets that need to pass from one LAN to another are forwarded across the link. This keeps the packets sent between two stations on any one LAN from crossing over onto the other LANs and thereby congesting them. A general rule of thumb suggests that 80 percent of the packets transmitted on a typical workgroup or department LAN are destined for stations on that LAN. Both bridges and routers can be used to segment LANs.

Bridges are the simpler, and often less expensive, type of device. Bridges filter packets between LANs by making a simple forward/don't forward decision on each packet they receive from any of the networks they are connected to. Filtering is done based on the destination address of the packet. If a packet's destination is a station on the same segment where it originated, it is not forwarded. If it is destined for a station on another LAN, it is connected to a different bridge port and forwarded to that port. Many bridges today filter and forward packets with very little delay, making them good for large traffic volumes.

Routers are more complex internetworking devices and are also typically more expensive than bridges. They use Network Layer Protocol Information within each packet to route it from one LAN to another. This means that a router must be able to recognize all of the different Network Layer Protocols that may be used on the networks it is linking together. This is where the term multiprotocol router comes from a device that can route using many different protocols. Routers communicate with each other and share information that allows them to determine the best route through a complex internetwork that links many LANs.

Switches are another type of device used to link several separate LANs and provide packet filtering between them. A LAN switch is a device with multiple ports, each of which can support a single end station or an entire Ethernet or Token Ring LAN. With a different LAN connected to each of the switch's ports, it can