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../../protocols/ipv6.rst:59
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The second type of datalink layer is the one used in Local Area Networks (LAN). Conceptually, a LAN is a set of communicating devices such that any two devices can directly exchange frames through the datalink layer. Both hosts and routers can be connected to a LAN. Some LANs only connect a few devices, but there are LANs that can connect hundreds or even thousands of devices.
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../../protocols/ppp.rst:13
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The first solution to transport IP packets over a serial line was proposed in :rfc:`1055` and is known as `Serial Line IP` (SLIP). SLIP is a simple character stuffing technique applied to IP packets. SLIP defines two special characters : `END` (decimal 192) and `ESC` (decimal 219). `END` appears at the beginning and at the end of each transmitted IP packet and the sender adds `ESC` before each `END` character inside each transmitted IP packet. SLIP only supports the transmission of IP packets and it assumes that the two communicating hosts/routers have been manually configured with each other's IP address. SLIP was mainly used over links offering bandwidth of often less than 20 Kbps. On such a low bandwidth link, sending 20 bytes of IP header followed by 20 bytes of TCP header for each TCP segment takes a lot of time. This initiated the development of a family of compression techniques to efficiently compress the TCP/IP headers. The first header compression technique proposed in :rfc:`1144` was designed to exploit the redundancy between several consecutive segments that belong to the same TCP connection. In all these segments, the IP addresses and port numbers are always the same. Furthermore, fields such as the sequence and acknowledgment numbers do not change in a random way. :rfc:`1144` defined simple techniques to reduce the redundancy found in successive segments. The development of header compression techniques continued and there are still improvements being developed now :rfc:`5795`.
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../../protocols/ppp.rst:17
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The `Point-to-Point Protocol` defines the framing technique to transport network layer packets.
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../../protocols/routing.rst:19
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These intradomain routing protocols usually have two objectives. First, they distribute routing information that corresponds to the shortest path between two routers in the domain. Second, they should allow the routers to quickly recover from link and router failures.
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../../protocols/rpc.rst:13
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The caller transfers the control of execution to the callee's procedure
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../../protocols/ssh.rst:46
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The secure shell protocol was designed in the mid 1990s by T. Ylonen to counter the eavesdropping attacks against :term:`telnet` and similar protocols [Ylonen1996]_. :term:`ssh` became quickly popular and system administrators encouraged its usage. The original version of :term:`ssh` was freely available. After a few years, his author created a company to distribute it commercially, but other programmers continued to develop an open-source version of :term:`ssh` called `OpenSSH <http://www.openssh.com>`_. Over the years, :term:`ssh` evolved and became a flexible applicable whose usage extends beyond remote login to support features such as file transfers, protocol tunneling, ... In this section, we only discuss the basic features of :term:`ssh` and explain how it differs from :term:`telnet`. Entire books have been written to describe :term:`ssh` in details [BS2005]_. An overview of the protocol appeared in [Stallings2009]_.
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../../protocols/tcp.rst:17
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World wide web ( :term:`HTTP`, ...)
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../../protocols/tls.rst:30
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A TLS session can be initiated in two different ways. First, the application can use a dedicated TCP port number for application layer protocol x-over-TLS. This is the solution used by many HTTP servers that reserve port :math:`443` for HTTP over TLS. This solution works, but it requires to reserve two ports for each application : one where the application-layer protocol is used directly over TCP and another one where the application-layer protocol is used over TLS. Given the limited number of TCP ports that are available, this is not a scalable solution. The table below provides some of the reserved port numbers for application layer protocols on top of TLS.
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../../protocols/transport-service.rst:13
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The connectionless service allows applications to easily exchange messages or Service Data Units. On the Internet, this service is provided by the UDP protocol that will be explained in the next chapter. The connectionless transport service on the Internet is unreliable, but is able to detect transmission errors. This implies that an application will not receive data that has been corrupted due to transmission errors.
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../../protocols/udp.rst:15
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the UDP service will not deliver a corrupted SDU to the destination
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../../protocols/wifi.rst:15
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Today, WiFi is a very popular wireless networking technology. There are more than several hundreds of millions of WiFi devices. The development of this technology started in the late 1980s with the `WaveLAN <http://en.wikipedia.org/wiki/WaveLAN>`_ proprietary wireless network. WaveLAN operated at 2 Mbps and used different frequency bands in different regions of the world. In the early 1990s, the IEEE_ created the `802.11 working group <http://www.ieee802.org/11/>`_ to standardize a family of wireless network technologies. This working group was very prolific and produced several wireless networking standards that use different frequency ranges and different physical layers. The table below provides a summary of the main 802.11 standards.
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../../bibliography.rst:17
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Androutsellis-Theotokis, S. and Spinellis, D.. .. 2004. `A survey of peer-to-peer content distribution technologies <http://doi.acm.org/10.1145/1041680.1041681>`_. ACM Computing Surveys 36, 4 (December 2004), 335-371.
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../../index.rst:37
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Part 1: Principles
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../../glossary.rst:15
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anycast
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../../exercises/ex-sharing.rst:66
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In a shared medium, a collision may happen if two hosts transmit at almost the same time as shown in the example below.
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../../exercises/reliability.rst:22
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A version of the Alternating Bit Protocol supporting variable length frames uses a header that contains the following fields :
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../../exercises/network.rst:67
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Routing protocols used in data networks only use positive link weights. What would happen with a distance vector routing protocol in the network below that contains a negative link weight ?
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../../exercises/sockets.rst:102
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A detailed discussion of the socket API is outside the scope of this section and the references cited above provide a detailed discussion of all the details of the socket API. As a starting point, it is interesting to compare the socket API with the service primitives that we have discussed in the previous chapter. Let us first consider the connectionless service that consists of the following two primitives :
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../../exercises/transport.rst:38
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Continue the connection so that `Host B` sends `Hello` as data and `Host A` replies by sending `Pleased to meet you`. After having received the response, `Host B` closes the connection gracefully and `Host A` does the same. Discuss on the state that needs to be maintained inside each host.
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../../principles/naming.rst:19
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The first solution that allowed applications to use names was the :term:`hosts.txt` file. This file is similar to the symbol table found in compiled code. It contains the mapping between the name of each Internet host and its associated address [#fhosts]_. It was maintained by SRI International that coordinated the Network Information Center (NIC). When a new host was connected to the network, the system administrator had to register its name and address at the NIC. The NIC updated the :term:`hosts.txt` file on its server. All Internet hosts regularly retrieved the updated :term:`hosts.txt` file from the SRI_ server. This file was stored at a well-known location on each Internet host (see :rfc:`952`) and networked applications could use it to find the address corresponding to a name.
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