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../../exercises/tls.rst:8
English
One of the first motivations for the deployment of wide area networks such as the Internet was to enable researchers to connect to distant servers. For many years, these connections were carried out by using a simple application layer protocol such as telnet over a TCP connection. With telnet, all the characters typed by the user are sent in cleartext over the TCP connection. This implies that if someone is able to capture the packets transmitted over the network, he/she can collect sensitive information such as user names or passwords.
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../../exercises/trace.rst:8
English
When debugging networking problems or to figure out performance problems, it is sometimes useful to capture the segments that are exchanged between two hosts and to analyze them.
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../../protocols/bgp.rst:7
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As explained earlier, the Internet is composed of more than 45,000 different networks [#fasnum]_ called `domains`. Each domain is composed of a group of routers and hosts that are managed by the same organization. Example domains include belnet_, sprint_, level3_, geant_, abilene_, cisco_ or google_ ...
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../../protocols/congestion.rst:11
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In an internetwork, i.e. a networking composed of different types of networks (such as the Internet), congestion control could be implemented either in the network layer or the transport layer. The congestion problem was clearly identified in the later 1980s and the researchers who developed techniques to solve the problem opted for a solution in the transport layer. Adding congestion control to the transport layer makes sense since this layer provides a reliable data transfer and avoiding congestion is a factor in this reliable delivery. The transport layer already deals with heterogeneous networks thanks to its `self-clocking` property that we have already described. In this section, we explain how congestion control has been added to TCP and how this mechanism could be improved in the future.
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../../protocols/dnssec.rst:9
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The Domain Name System provides a critical service in the Internet infrastructure since it maps the domain names that are used by end users onto IP addresses. Since end users rely on names to identify the servers that they connect to, any incorrect information distributed by the DNS would direct end users' connections to invalid destinations. Unfortunately, several attacks of this kind occurred in the past. A detailed analysis of the security threats against the DNS appeared in :rfc:`3833`. We consider three of these threats in this section and leave the others to :rfc:`3833`.
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../../protocols/ethernet.rst:12
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Ethernet was designed in the 1970s at the Palo Alto Research Center [Metcalfe1976]_. The first prototype [#fethernethistory]_ used a coaxial cable as the shared medium and 3 Mbps of bandwidth. Ethernet was improved during the late 1970s and in the 1980s, Digital Equipment, Intel and Xerox published the first official Ethernet specification [DIX]_. This specification defines several important parameters for Ethernet networks. The first decision was to standardize the commercial Ethernet at 10 Mbps. The second decision was the duration of the `slot time`. In Ethernet, a long `slot time` enables networks to span a long distance but forces the host to use a larger minimum frame size. The compromise was a `slot time` of 51.2 microseconds, which corresponds to a minimum frame size of 64 bytes.
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../../protocols/http2.rst:10
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During the last decade, a growing number of services have been supported by world wide web servers. The web protocols are not only used to deliver static documents, they are also used to deliver streaming music or video. They also enable clients to use interactive applications including games or productivity applications. These services and applications have more stringent performance requirements than the delivery of static documents. Many researchers and companies have proposed solutions to improve the performance of web services and protocols during the last decade [KR2001]_ [WBK2014]_. We discuss a subset of them in this section.
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../../protocols/lan.rst:8
English
In this section, we review the key characteristics of several datalink layer technologies. We discuss in more detail the technologies that are widely used today. A detailed survey of all datalink layer technologies would be outside the scope of this book.
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../../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.
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../../protocols/rpc.rst:8
English
In the previous sections, we have described several protocols that enable humans to exchange messages and access to remote documents. This is not the only usage of computer networks and in many situations applications use the network to exchange information with other applications. When an application needs to perform a large computation on a host, it can sometimes be useful to request computations from other hosts. Many distributed systems have been built by distributing applications on different hosts and using `Remote Procedure Calls` as a basic building block.
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../../protocols/ssh.rst:11
English
One of the initial motivations for building computer networks was to allow users to access remote computers over the networks. In the 1960s and 1970s, the mainframes and the emerging minicomputers were composed of a central unit and a set of terminals connected through serial lines or modems. The simplest protocol that was designed to access remote computers over a network is probably :term:`telnet` :rfc:`854`. :term:`telnet` runs over TCP and a telnet server listens on port `23` by default. The TCP connection used by telnet is bidirectional, both the client and the server can send data over it. The data exchanged over such a connection is essentially the characters that are typed by the user on the client machine and the text output of the processes running on the server machine with a few exceptions (e.g. control characters, characters to control the terminal like VT-100, ...) . The default character set for telnet is the ASCII character set, but the extensions specified in :rfc:`5198` support the utilization of Unicode characters.
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../../protocols/tcp.rst:12
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The Transmission Control Protocol (TCP) was initially defined in :rfc:`793`. Several parts of the protocol have been improved since the publication of the original protocol specification [#ftcpspecs]_. However, the basics of the protocol remain and an implementation that only supports :rfc:`793` should inter-operate with today's implementation.
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../../protocols/tls.rst:11
English
The Transport Layer Security family of protocols were initially proposed under the name Secure Socket Layer (SSL). The first deployments used this name and many researchers still refer to this security protocol as SSL [FKC1996]_. In this chapter, we use the official name that was standardized by the IETF: TLS for `Transport Layer Security`.
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../../protocols/transport-service.rst:8
English
Networked applications rely on the transport service. As explained earlier, there are two main types of transport services :
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../../protocols/transport.rst:9
English
Transport protocols rely on the service provided by the network layer. On the Internet, the network layer provides a connectionless service. The network layer identifies each (interface of a) host by using an IP address. It enables hosts to transmit packets that contain up to 64 KBytes of payload to any destination reachable through the network. The network layer does not guarantee the delivery of information, cannot detect transmission errors and does not preserve sequence integrity.
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../../protocols/udp.rst:11
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The User Datagram Protocol (UDP) is defined in :rfc:`768`. It provides an unreliable connectionless transport service on top of the unreliable network layer connectionless service. The main characteristics of the UDP service are :
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../../protocols/wifi.rst:7
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The radio spectrum is a limited resource that must be shared by everyone. During most of the twentieth century, governments and international organizations have regulated most of the radio spectrum. This regulation controls the utilization of the radio spectrum, in order to prevent interference among different users. A company that wants to use a frequency range in a given region must apply for a license from the regulator. Most regulators charge a fee for the utilization of the radio spectrum and some governments have encouraged competition among companies bidding for the same frequency to increase the license fees.
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../../bibliography.rst:9
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LAN/MAN Standards Committee of the IEEE Computer Society. `IEEE Standard for Information Technology - Telecommunications and information exchange between systems - local and metropolitan area networks - specific requirements - Part 11 : Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications <http://standards.ieee.org/getieee802/802.11.html>`_. IEEE, 1999.
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../../exercises/ex-sharing.rst:15
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Medium Access Control
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../../principles/sharing.rst:16
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A network is designed to support a potentially large number of users that exchange information with each other. These users produce and consume information which is exchanged through the network. To support its users, a network uses several types of resources. It is important to keep in mind the different resources that are shared inside the network.
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