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4 ../../protocols/ipv6.rst:57

	English There are three main types of datalink layers. The simplest datalink layer is when there are only two communicating systems that are directly connected through the physical layer. Such a datalink layer is used when there is a point-to-point link between the two communicating systems. The two systems can be hosts or routers. :abbr:`PPP (Point-to-Point Protocol)`, defined in :rfc:`1661`, is an example of such a point-to-point datalink layer. Datalink layers exchange `frames` and a datalink :term:`frame` sent by a datalink layer entity on the left is transmitted through the physical layer, so that it can reach the datalink layer entity on the right. Point-to-point datalink layers can either provide an unreliable service (frames can be corrupted or lost) or a reliable service (in this case, the datalink layer includes retransmission mechanisms similar to the ones used in the transport layer). The unreliable service is frequently used above physical layers (e.g. optical fiber, twisted pairs) having a low bit error ratio while reliability mechanisms are often used in wireless networks to recover locally from transmission errors. 1140/10000 · 1140
4 ../../protocols/ppp.rst:9

	English Many point-to-point datalink layers [#flapb]_ have been developed, starting in the 1960s. In this section, we focus on the protocols that are often used to transport IP packets between hosts or routers that are directly connected by a point-to-point link. This link can be a dedicated physical cable, a leased line through the telephone network or a dial-up connection with modems on the two communicating hosts. 412/10000 · 412
4 ../../protocols/ppp.rst:15

	English While SLIP was implemented and used in some environments, it had several limitations discussed in :rfc:`1055`. The `Point-to-Point Protocol` (PPP) was designed shortly after and is specified in :rfc:`1548`. PPP aims to support IP and other network layer protocols over various types of serial lines. PPP is in fact a family of three protocols that are used together : 367/10000 · 367
4 ../../protocols/routing.rst:17

	English The first class of routing protocols are the `intradomain routing protocols` (sometimes also called the interior gateway protocols or :term:`IGP`). An intradomain routing protocol is used by all routers inside a domain to exchange routing information about the destinations that are reachable inside the domain. There are several intradomain routing protocols. Some domains use :term:`RIP`, which is a distance vector protocol. Other domains use link-state routing protocols such as :term:`OSPF` or :term:`IS-IS`. Finally, some domains use static routing or proprietary protocols such as :term:`IGRP` or :term:`EIGRP`. 618/10000 · 618
4 ../../protocols/rpc.rst:12

	English The caller places the values of the parameters at a location (register, stack, ...) where the callee can access them 116/10000 · 116
4 ../../protocols/ssh.rst:40

	English The secure shell (ssh) 22/10000 · 22
4 ../../protocols/tcp.rst:16

	English Email (:term:`SMTP`, :term:`POP`, :term:`IMAP`) 47/10000 · 47
4 ../../protocols/tls.rst:23

	English A TLS session operates over a TCP connection. TLS is responsible for the encryption and the authentication of the SDUs exchanged by the application layer protocol while TCP provides the reliable delivery of this encrypted and authenticated bytestream. TLS is used by many different application layer protocols. The most frequent ones are HTTP (HTTP over TLS is called HTTPS), SMTP :rfc:`3207` or POP and IMAP :rfc:`2595`, but proprietary application-layer protocols also use TLS [AM2019]_. 489/10000 · 489
4 ../../protocols/transport-service.rst:11

	English the `connection-oriented` or `byte-stream` service 50/10000 · 50
4 ../../protocols/transport.rst:13

	English The Real Time Transport Protocol (RTP), defined in :rfc:`3550` is another important protocol that is used by many multimedia applications. It includes functions that belong to the transport layer, but also functions that are related to the encoding of the information. Due to space limitations, we do not discuss it in this section. 332/10000 · 332
4 ../../protocols/udp.rst:14

	English the UDP service does not guarantee the delivery of SDUs (losses can occur and SDUs can arrive out-of-sequence) 110/10000 · 110
4 ../../protocols/wifi.rst:13

	English While most of the frequency ranges of the radio spectrum are reserved for specific applications and require a special license, there are a few exceptions. These exceptions are known as the `Industrial, Scientific and Medical <http://en.wikipedia.org/wiki/ISM_band>`_ (ISM) radio bands. These bands can be used for industrial, scientific and medical applications without requiring a license from the regulator. For example, some radio-controlled models use the 27 MHz ISM band and some cordless telephones operate in the 915 MHz ISM. In 1985, the 2.400-2.500 GHz band was added to the list of ISM bands. This frequency range corresponds to the frequencies that are emitted by microwave ovens. Sharing this band with licensed applications would have likely caused interference, given the large number of microwave ovens that are used. Despite the risk of interference with microwave ovens, the opening of the 2.400-2.500 GHz allowed the networking industry to develop several wireless network techniques to allow computers to exchange data without using cables. In this section, we discuss in more detail the most popular one, i.e. the WiFi [IEEE802.11]_ family of wireless networks. Other wireless networking techniques such as `BlueTooth <http://en.wikipedia.org/wiki/BlueTooth>`_ or `HiperLAN <http://en.wikipedia.org/wiki/HiperLAN>`_ use the same frequency range. 1365/10000 · 1365
4 ../../index.rst:21

	English The source code of the entire textbook is written in `reStructuredText <http://docutils.sourceforge.net/rst.html>`_ and uses several `sphinx <https://www.sphinx-doc.org>`_ features. You can browse these sources from `github <https://github.com/CNP3/ebook/tree/master>`_ You can download a pdf version from :download:`tmp/latex/CNP3.pdf` 336/10000 · 336
4 ../../exercises/network.rst:21

	English Open questions 14/10000 · 14
4 ../../principles/naming.rst:15

	English In the early days of the Internet, only a few hosts (mainly minicomputers) were connected to the network. The most popular applications were :term:`remote login` and file transfer. By 1983, there were already five hundred hosts attached to the Internet [Zakon]_. Each of these hosts were identified by a unique address. Forcing human users to remember the addresses of the hosts that they wanted to use was not user-friendly. Humans prefer to remember names, and use them when needed. Using names as aliases for addresses is a common technique in Computer Science. It simplifies the development of applications and allows the developer to ignore the low level details. For example, by using a programming language instead of writing machine code, a developer can write software without knowing whether the variables that it uses are stored in memory or inside registers. 870/10000 · 870
4 ../../protocols/dns.rst:16

	English DNS messages are composed of five parts that are named sections in :rfc:`1035`. The first three sections are mandatory and the last two sections are optional. The first section of a DNS message is its `Header`. It contains information about the message type and the content of the other sections. The second section contains the `Question` sent to the nameserver or resolver. The third section contains the `Answer` to the `Question`. When a client sends a DNS query, the `Answer` section is empty. The fourth section, named `Authority`, contains information about the servers that can provide an authoritative answer if required. The last section contains additional information that is supplied by the resolver or nameserver but was not requested in the question. 765/10000 · 765
4 ../../bibliography.rst:10

	English LAN/MAN Standards Committee of the IEEE Computer Society, `IEEE Standard for Local and metropolitan area networks Media Access Control (MAC) Bridges <http://standards.ieee.org/getieee802/download/802.1D-2004.pdf>`_ , IEEE Std 802.1DTM-2004, 2004, 246/10000 · 246
4 ../../principles/sharing.rst:18

	English The first and more important resource inside a network is the link bandwidth. There are two situations where link bandwidth needs to be shared between different users. The first situation is when several hosts are attached to the same physical link. This situation mainly occurs in Local Area Networks (LAN). A LAN is a network that efficiently interconnects several hosts (usually a few dozens to a few hundreds) in the same room, building or campus. Consider for example a network with five hosts. Any of these hosts needs to be able to exchange information with any of the other hosts. A first organization for this LAN is the full-mesh. 640/10000 · 640
4 ../../principles/transport.rst:36

	English The client-server model was the first model to be used to develop networked applications. This model comes naturally from the mainframes and minicomputers that were the only networked computers used until the 1980s. A minicomputer_ is a multi-user system that is used by tens or more users at the same time. Each user interacts with the minicomputer by using a terminal. Such a terminal was mainly a screen, a keyboard and a cable directly connected to the minicomputer. 470/10000 · 470
5 ../../exercises/sockets.rst:98

	English The socket API is quite low-level and should be used only when you need a complete control of the network access. If your application simply needs, for instance, to retrieve data from a web server, there are much simpler and higher-level APIs. 243/10000 · 243

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