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../../protocols/dns.rst:52
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The `TTL` field indicates the lifetime of the `Resource Record` in seconds. This field is set by the server that returns an answer and indicates for how long a client or a resolver can store the `Resource Record` inside its cache. A long `TTL` indicates a stable `RR`. Some companies use short `TTL` values for mobile hosts and also for popular servers. For example, a web hosting company that wants to spread the load over a pool of hundred servers can configure its nameservers to return different answers to different clients. If each answer has a small `TTL`, the clients will be forced to send DNS queries regularly. The nameserver will reply to these queries by supplying the address of the less loaded server.
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../../protocols/routing.rst:46
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The RIP message format
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../../exercises/reliability.rst:35
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The delay between the two hosts is `s` seconds in both directions
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../../exercises/sockets.rst:135
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As the ``sendto`` function is generic, this function will work correctly independently from the fact that the peer's address is defined as a path on the computer filesystem or a network address.
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../../exercises/transport.rst:128
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Amazon provides the `S3 storage service <https://s3.amazonaws.com/>`_ where companies and researchers can store lots of information and perform computations on the stored information. Amazon allows users to send files through the Internet, but also by sending hard-disks. Assume that a 1 Terabyte hard-disk can be delivered within 24 hours to Amazon by courier service. What is the minimum bandwidth required to match the bandwidth of this courier service ?
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../../principles/referencemodels.rst:58
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An important point to note about the `Datalink layer` is that although the figure below indicates that two entities of the `Datalink layer` exchange frames directly, in reality this is slightly different. When the `Datalink layer` entity on the left needs to transmit a frame, it issues as many `Data.request` primitives to the underlying `physical layer` as there are bits in the frame. The physical layer will then convert the sequence of bits in an electromagnetic or optical signal that will be sent over the physical medium. The `physical layer` on the right hand side of the figure will decode the received signal, recover the bits and issue the corresponding `Data.indication` primitives to its `Datalink layer` entity. If there are no transmission errors, this entity will receive the frame sent earlier.
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../../principles/network.rst:76
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There are two possible organizations for the network layer :
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../../principles/reliability.rst:52
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1 Mbps
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../../protocols/dns.rst:54
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The `RDLength` field is the length of the `RData` field that contains the information of the type specified in the `Type` field.
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../../exercises/http.rst:50
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Footnotes
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../../exercises/reliability.rst:36
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there are no transmission errors
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../../exercises/sockets.rst:139
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Receiving data from a peer using a socket
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../../exercises/transport.rst:135
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Discussion questions
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../../principles/naming.rst:82
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This hierarchical naming scheme is a key component of the Domain Name System (DNS). The DNS is a distributed database that contains mappings between fully qualified domain names and addresses. The DNS uses the client-server model. The clients are hosts or applications that need to retrieve the mapping for a given name. Each :term:`nameserver` stores part of the distributed database and answers the queries sent by clients. There is at least one :term:`nameserver` that is responsible for each domain. In the figure below, domains are represented by circles and there are three hosts inside domain `dom` (`h1`, `h2` and `h3`) and three hosts inside domain `a.sdom1.dom`. As shown in the figure below, a sub-domain may contain both host names and sub-domains.
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../../principles/referencemodels.rst:69
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The Network layer
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../../principles/network.rst:78
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`datagram`
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../../principles/reliability.rst:52
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:math:`10^6`
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../../exercises/network.rst:132 • ../../exercises/network.rst:154 • ../../exercises/network.rst:184 • ../../exercises/network.rst:216
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Consider the network shown in the figure below.
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../../exercises/transport.rst:137
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In the transport layer, the receive window advertised by a receiver can vary during the lifetime of the connection. What are the causes for these variations ?
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../../principles/naming.rst:107
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A :term:`nameserver` that is responsible for domain `dom` can directly answer the following queries :
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