Exercises

1. Translate the text.

2. Match each routing scheme with its name

1. geocast b) unicast c) broadcast d) multicast  e) anycast

3. Name the grammar form of the underlined sentences, ask questions to these sentences.

Lesson 13

Network service

1. Read words with their translations.

network service – сервіси мереж

implement ['ɪmplɪmənt] – виконувати, постачати

throughput ['θruːput] – пропускна здатність

circuit switching network - мере́жа з комута́цією кана́лів

packet switched network - мережі пакетної комутації

jitter ['ʤɪtə] - вібрація

bit error rate – частота виникнення помилкових бітів

latency ['leɪt(ə)n(t)sɪ] - затримка

viz. - а саме

echo ['ekəu] – ехо-сигнал

enhancements [ɪn'hɑːn(t)smənt] -покращення, модернізація

queue [kjuː] - черга

network congestion - перевантаження мережі

deteriorate [dɪ'tɪərɪəreɪt] – погіршення, руйнування

exponential backoff  - експонентна відстрочки

reduction [rɪ'dʌkʃ(ə)n] – попередня обробка

implementing priority schemes - реалізація пріоритетних схем

alleviate [ə'liːvɪeɪt] - пом’якшувати

explicit allocation [ik'splisit] [ælə'keɪʃ(ə)n] - явне розміщення

network resilience [ri'ziliəns] - надійність мережі

acceptable [ək'septəb(ə)l] - підходящий

fault [fɔ:lt] – дефект, недолік

3. Read the text

In computer networking, a network service is an application running at the network application layer and above, that provides data storage, manipulation, presentation, communication or other capability which is often implemented using a client-server or peer-to-peer architecture based on application layer network protocols.

Each service is usually provided by a server component running on one or more computers (often a dedicated server computer offering multiple services) and accessed via a network by client components running on other devices. However, the client and server components can both be run on the same machine.

Clients and servers will often have a user interface, and sometimes other hardware associated with them.

Quality of service

Depending on the installation requirements, network performance is usually measured by the quality of service of a telecommunications product. The parameters that affect this typically can include throughput, jitter, bit error rate and latency.

The following list gives examples of network performance measures for a circuit-switched network and one type of packet-switched network, viz. ATM:

Circuit-switched networks: In circuit switched networks, network performance is synonymous with the grade of service. The number of rejected calls is a measure of how well the network is performing under heavy traffic loads. Other types of performance measures can include the level of noise and echo.

ATM: In an Asynchronous Transfer Mode (ATM) network, performance can be measured by line rate, quality of service (QoS), data throughput, connect time, stability, technology, modulation technique and modem enhancements.

There are many ways to measure the performance of a network, as each network is different in nature and design. Performance can also be modelled instead of measured. For example, state transition diagrams are often used to model queuing performance in a circuit-switched network. These diagrams allow the network planner to analyze how the network will perform in each state, ensuring that the network will be optimally designed.

Network congestion

Network congestion occurs when a link or node is carrying so much data that its quality of service deteriorates. Typical effects include queueing delay, packet loss or the blocking of new connections. A consequence of these latter two is that incremental increases in offered load lead either only to small increase in network throughput, or to an actual reduction in network throughput.

Network protocols which use aggressive retransmissions to compensate for packet loss tend to keep systems in a state of network congestion even after the initial load has been reduced to a level which would not normally have induced network congestion. Thus, networks using these protocols can exhibit two stable states under the same level of load. The stable state with low throughput is known as congestive collapse.

Modern networks use congestion control and congestion avoidance techniques to try to avoid congestion collapse. These include: exponential backoff in protocols such as 802.11's CSMA/CA and the original Ethernet, window reduction in TCP, and fair queueing in devices such as routers. Another method to avoid the negative effects of network congestion is implementing priority schemes, so that some packets are transmitted with higher priority than others. Priority schemes do not solve network congestion by themselves, but they help to alleviate the effects of congestion for some services. An example of this is 802.1p. A third method to avoid network congestion is the explicit allocation of network resources to specific flows.

Network resilience

Network resilience is "the ability to provide and maintain an acceptable level of service in the face of faults and challenges to normal operation.”