Файл: Учебнометодическое пособие по английскому языку для специалистов и бакалавров 2 курса института ртс. Москва 2019.docx

3. Davies is credited with coining the modern term______.

4. Packets are received, buffered, queued and ______.

5. Circuit switching is characterized by a fee per unit of_____.

Task 5. Scan the text to mark the statements below true or false.

1. In the early 1970s, American computer scientist Paul Baran developed the concept Distributed Adaptive Message Block Switching.

2. Packet switching allows delivery of variable bit rate data streams, realized as sequences of packets.

3. Packets are normally forwarded by intermediate network nodes asynchronously using first-in, first-out buffering.

4. Packets can not be forwarded according to some scheduling discipline for fair queuing, traffic shaping, or for differentiated or guaranteed quality of service.

5. Packet-based communication may be implemented with or without intermediate forwarding nodes (switches and routers).

---

Text B

Connectionless and connection-oriented packet switching
Packet switching may be classified into connectionless packet switching, also known as datagram switching, and connection-oriented packet switching, also known as virtual circuit switching. Examples of connectionless systems are Ethernet, Internet Protocol (IP), and the User Datagram Protocol (UDP). Connection-oriented systems include X.25, Frame Relay, Multiprotocol Label Switching (MPLS), and the Transmission Control Protocol (TCP).

In connectionless mode each packet is labeled with a destination address, source address, and port numbers. It may also be labeled with the sequence number of the packet. This information eliminates the need for a pre-established path to help the packet find its way to its destination, but means that more information is needed in the packet header, which is therefore larger. The packets are routed individually, sometimes taking different paths resulting in out-of-order delivery. At the destination, the original message may be reassembled in the correct order, based on the packet sequence numbers. Thus a virtual circuit carrying a byte stream is provided to the application by a transport layer protocol, although the network only provides a connectionless network layer service.

Connection-oriented transmission requires a setup phase in each involved node before any packet is transferred to establish the parameters of communication. The packets include a connection identifier rather than address information and are negotiated between endpoints so that they are delivered in order and with error checking. Address information is only transferred to each node during the connection set-up phase, when the route to the destination is discovered and an entry is added to the switching table in each network node through which the connection passes. The signaling protocols allow the application to specify its requirements and discover link parameters. Acceptable values for service parameters may be negotiated. Routing a packet requires the node to look up the connection ID in a table. The packet header can be small, as it only needs to contain this code and any information, such as length, timestamp, or sequence number, which is different for different packets.

Packet switching in networks

Packet switching is used to optimize the use of the channel capacity available in digital telecommunication networks, such as computer networks, and minimize the transmission latency (the time it takes for data to pass across the network), and to increase robustness of communication.

The best-known use of packet switching is the Internet and most local area networks. The Internet is implemented by the Internet Protocol Suite using a variety of Link Layer technologies. For example, Ethernet and Frame Relay are common. Newer mobile phone technologies (e.g., GPRS) also use packet switching.

Task 1. Read and translate text B.

Task 2. Discuss the meaning of the words and phrases. Give definitions to these words.

Connectionless packet switching, datagram switching, connection-oriented packet switching, virtual circuit switching, Ethernet, Internet Protocol, User Datagram Protocol, Transmission Control Protocol, out-of-order delivery, virtual circuit, byte stream, transport layer protocol, connectionless network layer service, to increase robustness, channel capacity.

Task 3. Scan the text to mark the statements below true or false.

1. Packet switching may be classified into connectionless packet switching, also known as datagram switching.

2. Connection-oriented packet switching is known as datagram switching.

3. Examples of connectionless systems are Ethernet, Internet Protocol (IP), and the User Datagram Protocol (UDP).

4. Connection-oriented systems include only Ethernet and Internet Protocol.

5. In connectionless mode each packet is labeled with a destination address, source address, and port numbers.

Task 4. Complete the sentences according to the text.

1. 
   A destination address, source address and port numbers eliminate the need for a pre-established path to help the packet…
   
2. 
   In connectionless mode each packet is labeled with….
   
3. 
   The packets are routed individually, sometimes taking different paths…
   
4. 
   Thus a virtual circuit carrying a byte stream is provided to the application by…
   
5. 
   Packet switching is used to increase robustness of ….
   

---

Task 5. Choose the correct word from the text to complete the sentences.

1. The packets are routed individually, sometimes taking different paths_____ in out-of-order delivery.

2. In connectionless mode each packet is labeled with a _____ ______, source address, and port numbers.

3. At the destination, the original message may be reassembled in the ____order, based on the _____ sequence numbers.

4. Connection-oriented transmission requires a setup phase in each involved node before any packet is _____to establish the parameters of communication.

5. The signaling protocols _____the application to specify its requirements and discover link parameters.

6. Packet switching is used to optimize the use of the _____capacity available in digital telecommunication networks.

---

Text C

Circuit switching
Circuit switching is a method of implementing a telecommunications network in which two network nodes establish a dedicated communications channel (circuit) through the network before the nodes may communicate. The circuit guarantees the full bandwidth of the channel and remains connected for the duration of the communication session. The circuit functions as if the nodes were physically connected as with an electrical circuit.

The defining example of a circuit-switched network is the early analog telephone network. When a call is made from one telephone to another, switches within the telephone exchanges create a continuous wire circuit between the two telephones, for as long as the call lasts.

Circuit switching contrasts with packet switching, which divides the data to be transmitted into packets transmitted through the network independently. In packet switching, instead of being dedicated to one communication session at a time, network links are shared by packets from multiple competing communication sessions, resulting in the loss of the quality of service guarantees that are provided by circuit switching.

In circuit switching, the bit delay is constant during a connection, as opposed to packet switching, where packet queues may cause varying and potentially indefinitely long packet transfer delays. No circuit can be degraded by competing users because it is protected from use by other callers until the circuit is released and a new connection is set up. Even if no actual communication is taking place, the channel remains reserved and protected from competing users.

Virtual circuit switching is a packet switching technology that emulates circuit switching, in the sense that the connection is established before any packets are transferred, and packets are delivered in order.

While circuit switching is commonly used for connecting voice circuits, the concept of a dedicated path persisting between two communicating parties or nodes can be extended to signal content other than voice. The advantage of using circuit switching is that it provides for continuous transfer without the overhead associated with packets, making maximal use of available bandwidth for that communication. One disadvantage is that it can be relatively inefficient, because unused capacity guaranteed to a connection cannot be used by other connections on the same network.

Task 1. Read and translate text C.

Task 2. Discuss the meaning of the words and phrases. Give definitions to these words.

Telecommunications network, network nodes, a dedicated communications channel, communication session, telephone network, packet transfer delays, virtual circuit switching.

Task 3. Complete the sentences according to the text.

1. Circuit switching is a method of…

2. The circuit guarantees the full bandwidth of the channel and remains connected for…

3. The circuit functions as if the nodes were physically connected…

4. The defining example of a circuit-switched network is the early analog…

5. In circuit switching, the bit delay is constant during…

Task 4. Choose the correct word from the text to complete the sentences.

1. In circuit switching, the channel remains reserved and protected from ______users.

2. The advantage of using circuit switching is that it provides for continuous transfer without the ______associated with packets.

3. Circuit switching is making maximal use of _______bandwidth for the communication.

4. Virtual circuit switching is a packet switching technology that _____circuit switching.

Text D

Bandwidth
Bandwidth is a term related to digital communications. It refers to the bit-rate of the available or exhausted information capacity in digital networking. In simpler words, bandwidth is synonymous to the exact rate of data transfer. It refers to the exact amount of data that can be carried between two data points at a specified time period. Generally, network bandwidth is expressed metrically in the form of bits per seconds (BPS). However, the modern networks now measure their speeds in millions of bits every second, which is also referred as megabits per second (MBPS). Similarly, billions of bits every second, referred as gigabits per second (Gbps) is also a part of digital networking.

---

While understanding bandwidth, we should note that it is not the only vital factor that affects the performance of a digital network. However, other relevant factors like data loss, latency issues, lags and speed breaks may also affect the network and make it seem like a low-bandwidth issue. The bandwidth required for all digital networks may not be the same. While an IM conversation may take less than 1000 bps, a VoIP conversation is likely to exhaust 56 kbps for coming up glitch free and ostensible sounds. Again, while a standard video will exhaust 1-2 Mbps, an HD video will exhaust around 4-5 Mbps.
What is an effective bandwidth?

The term ‘effective bandwidth’ refers to the maximum and best reliable transmission rate that a network path can come up with, which is measured by a bandwidth test. This rate can be authentically determined by constantly checking the time needed for a specific file/document to leave its source point and finally download the destination source. However, in some networking platforms like the home broadband, the effective bandwidth is limited to a certain extent.
Original meaning of bandwidth

While studying about bandwidth, we should note that it is also a range of several frequencies. More specifically, it can be termed as the differences between the highest and the lowest frequency of the signal component. Just like a conventional signal frequency, the unit for measuring bandwidth is also the hertz. This is the original and the most authentic meaning of bandwidth. However, in modern times, bandwidth is strongly associated with digital networking.
What is the importance of bandwidth?

Bandwidth is highly significant for determining how fast a web page loads on a browser. In fact, it is also one of the essential things to consider while you’re choosing a platform for web hosting. The bandwidth can be significantly affected by the website and the internet connection used for accessing it. Generally, a website loaded with heavy graphics will need higher bandwidth of 10 gigs or more. Similarly, a simple website will require comparatively smaller bandwidth. Just as fast internet connection allows you to download web pages and videos flawlessly, higher bandwidth will improve effectively the work of the user.

Task 1. Read and translate text D.

Task 2. Discuss the meaning of the words and phrases. Give definitions to these words

Bandwidth, digital communications, bit-rate¸ information capacity, digital networking, the exact rate of data transfer, to affect the network.

Task 3. Complete the sentences according to the text 1. What does metrology study?

1. Bandwidth is a term related to…

2. It refers to the bit-rate of the available or exhausted information capacity in…

3. While understanding bandwidth, we should note that it is not the only vital factor that…

4. Other relevant factors like data loss, latency issues, lags and speed breaks may also…

5. The term ‘effective bandwidth’ refers to the maximum and best reliable transmission rate that…

Task 4. Scan the text to mark the statements below true or false

1. In simpler words, bandwidth is synonymous to the exact rate of data transfer.

2. Bandwidth is the only vital factor that affects the performance of a digital network.

3. Data loss, latency issues, lags and speed breaks may also affect the network.

4. Transmission rate can be authentically determined by constantly checking the time needed for a specific file/document to leave its source point and finally download the destination source.

5. Bandwidth is strongly associated with digital networking.

---