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2 ../../protocols/ssh.rst:11
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — 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. 1049/10000 · 1049
4 ../../protocols/rpc.rst:12
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — The caller places the values of the parameters at a location (register, stack, ...) where the callee can access them 116/10000 · 116
5 ../../protocols/ssh.rst:46
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — 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]_. 937/10000 · 937
5 ../../protocols/tcp.rst:17
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — World wide web ( :term:`HTTP`, ...) 35/10000 · 35
6 ../../protocols/tcp.rst:18
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — Most file transfer protocols ( :term:`ftp`, peer-to-peer file sharing applications , ...) 89/10000 · 89
7 ../../protocols/rpc.rst:15
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — The callee places the return value(s) at a location (register, stack, ...) where the caller can access them 107/10000 · 107
7 ../../protocols/tcp.rst:19
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — remote computer access : :term:`telnet`, :term:`ssh`, :term:`X11`, :term:`VNC`, ... 83/10000 · 83
8 ../../exercises/routing-policies.rst:63 • ../../exercises/routing-policies.rst:96
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — Consider the interdomain topology shown in the figure below. Assuming, that `AS1` advertises prefix ``2001:db8:1::/48``, `AS2` prefix ``2001:db8:2::/48``, ... compute the routing tables of the different ASes. 209/10000 · 209
8 ../../protocols/tcp.rst:20
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — non-interactive multimedia applications (flash, ...) 52/10000 · 52
9 ../../exercises/dns.rst:36
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — `type` is the type of DNS record that is requested by the query such as `NS` for a nameserver, `A` for an IPv4 address, `AAAA` for an IPv6 address, `MX` for a mail relay, ... 174/10000 · 174
9 ../../protocols/rpc.rst:18
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — This model was developed with a single host in mind. How should it be modified if the caller and the callee are different hosts connected through a network ? Since the two hosts can be different, the two main problems are the fact they do not share the same memory and that they do not necessarily use the same representation for numbers, characters, ... Let us examine how the five steps identified above can be supported through a network. 441/10000 · 441
11 ../../index.rst:176
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — :ref:`genindex` 15/10000 · 15
11 ../../protocols/http2.rst:62
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — A second way to improve the web performance is to reduce the time required to retrieve web objects. While the first web servers returned an HTML documents with possibly a few images, today's rich web servers return one HTML document with associated style sheets, javascript code, images, fonts, ... Some of these web objects come from the original server while others are hosted on different servers. Today, a typical web page contains almost 2 MBytes of data on average. The size of the web pages continues to grow according to statistics collected by `httparchive.org`. Web pages targeted to mobile devices are slightly smaller. 630/10000 · 630
12 ../../index.rst:177
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — :ref:`search` 13/10000 · 13
12 ../../protocols/ethernet.rst:81
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — The Ethernet frame format shown above is specified in [DIX]_. This is the format used to send both IPv4 :rfc:`894` and IPv6 packets :rfc:`2464`. After the publication of [DIX]_, the Institute of Electrical and Electronic Engineers (IEEE) began to standardize several Local Area Network technologies. IEEE worked on several LAN technologies, starting with Ethernet, Token Ring and Token Bus. These three technologies were completely different, but they all agreed to use the 48 bits MAC addresses specified initially for Ethernet [IEEE802]_ . While developing its Ethernet standard [IEEE802.3]_, the IEEE 802.3 working group was confronted with a problem. Ethernet mandated a minimum payload size of 46 bytes, while some companies were looking for a LAN technology that could transparently transport short frames containing only a few bytes of payload. Such a frame can be sent by an Ethernet host by padding it to ensure that the payload is at least 46 bytes long. However since the Ethernet header [DIX]_ does not contain a length field, it is impossible for the receiver to determine how many useful bytes were placed inside the payload field. To solve this problem, the IEEE decided to replace the `Type` field of the Ethernet [DIX]_ header with a length field [#ftypelen]_. This `Length` field contains the number of useful bytes in the frame payload. The payload must still contain at least 46 bytes, but padding bytes are added by the sender and removed by the receiver. In order to add the `Length` field without significantly changing the frame format, IEEE had to remove the `Type` field. Without this field, it is impossible for a receiving host to identify the type of network layer packet inside a received frame. To solve this new problem, IEEE developed a completely new sublayer called the Logical Link Control [IEEE802.2]_. Several protocols were defined in this sublayer. One of them provided a slightly different version of the `Type` field of the original Ethernet frame format. Another contained acknowledgments and retransmissions to provide a reliable service... In practice, [IEEE802.2]_ is never used to support IP in Ethernet networks. The figure below shows the official [IEEE802.3]_ frame format. 2223/10000 · 2223
13 ../../principles/sharing.rst:117
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — Sharing resources is important to ensure that the network efficiently serves its user. In practice, there are many ways to share resources. Some resource sharing schemes consider that some users are more important than others and should obtain more resources. For example, on the roads, police cars and ambulances have priority. In some cities, traffic lanes are reserved for buses to promote public services, ... In computer networks, the same problem arise. Given that resources are limited, the network needs to enable users to efficiently share them. Before designing an efficient resource sharing scheme, one needs to first formalize its objectives. In computer networks, the most popular objective for resource sharing schemes is that they must be `fair`. In a simple situation, for example two hosts using a shared 2 Mbps link, the sharing scheme should allocate the same bandwidth to each user, in this case 1 Mbps. However, in a large networks, simply dividing the available resources by the number of users is not sufficient. Consider the network shown in the figure below where `A1` sends data to `A2`, `B1` to `B2`, ... In this network, how should we divide the bandwidth among the different flows ? A first approach would be to allocate the same bandwidth to each flow. In this case, each flow would obtain 5 Mbps and the link between `R2` and `R3` would not be fully loaded. Another approach would be to allocate 10 Mbps to `A1-A2`, 20 Mbps to `C1-C2` and nothing to `B1-B2`. This is clearly unfair. 1513/10000 · 1513
16 ../../protocols/http2.rst:79
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — To understand the benefits of pipelining, let us consider a simple but illustrative example. A client needs to retrieve 5 web objects that are each 100 bytes. The underlying transport connection has a 1 Gbps bandwidth but a one-way delay of 100 msec. A normal HTTP/1.x client would send the first request, wait 200 msec to receive the answer, then send another request... It would need one entire second to retrieve the five web objects. This is illustrated in the figure below. 478/10000 · 478
17 ../../principles/reliability.rst:53
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — 1 Gbps 6/10000 · 6
17 ../../exercises/dns.rst:52
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — Use `dig` to send a query to one of these root servers to find the IPv6 address of the DNS server(s) (NS record) responsible for the `org` top-level domain 155/10000 · 155
17 ../../exercises/tcp-2.rst:95
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — This TCP segment is sent immediately by the stack. The ``SYN`` flag is set and the dot next to the ``S`` character indicates that the ACK flag is also set. The SYN+ACK segment does not contain any data but its acknowledgment number is set to 1 (relative to the initial sequence number). For outgoing packets, packetdrill_ does not verify the value of the advertised window. In this line, it also accepts any TCP options (``<...>``). 432/10000 · 432