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../../principles/transport.rst:664
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This `transport clock` can now be combined with an exchange of three segments, called the `three way handshake`, to detect duplicates. This `three way handshake` occurs as follows :
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../../glossary.rst:250
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nameserver
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../../principles/dv.rst:9
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Distance vector routing is a simple distributed routing protocol. Distance vector routing allows routers to automatically discover the destinations reachable inside the network as well as the shortest path to reach each of these destinations. The shortest path is computed based on `metrics` or `costs` that are associated to each link. We use `l.cost` to represent the metric that has been configured for link `l` on a router.
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../../principles/reliability.rst:416
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`1` is encoded as `111`
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../../principles/sharing.rst:562
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The pseudo-code below summarizes the operation of a CSMA/CA device. The values of the SIFS, DIFS, EIFS and :math:`slotTime` depend on the underlying physical layer technology [IEEE802.11]_
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../../principles/transport.rst:666
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The initiating transport entity sends a `CR` segment. This segment requests the establishment of a transport connection. It contains a port number (not shown in the figure) and a sequence number (`seq=x` in the figure below) whose value is extracted from the `transport clock`. The transmission of the `CR` segment is protected by a retransmission timer.
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../../glossary.rst:252
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A server that implements the DNS protocol and can answer queries for names inside its own domain.
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../../principles/dv.rst:11
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Each router maintains a routing table. The routing table `R` can be modeled as a data structure that stores, for each known destination address `d`, the following attributes :
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../../principles/reliability.rst:417
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`0` is encoded as `000`
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../../principles/sharing.rst:590
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Another problem faced by wireless networks is often called the `hidden station problem`. In a wireless network, radio signals are not always propagated same way in all directions. For example, two devices separated by a wall may not be able to receive each other's signal while they could both be receiving the signal produced by a third host. This is illustrated in the figure below, but it can happen in other environments. For example, two devices that are on different sides of a hill may not be able to receive each other's signal while they are both able to receive the signal sent by a station at the top of the hill. Furthermore, the radio propagation conditions may change with time. For example, a truck may temporarily block the communication between two nearby devices.
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../../principles/transport.rst:668
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The remote transport entity processes the `CR` segment and creates state for the connection attempt. At this stage, the remote entity does not yet know whether this is a new connection attempt or a duplicate segment. It returns a `CA` segment that contains an acknowledgment number to confirm the reception of the `CR` segment (`ack=x` in the figure below) and a sequence number (`seq=y` in the figure below) whose value is extracted from its transport clock. At this stage, the connection is not yet established.
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../../glossary.rst:165
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NAT
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../../principles/dv.rst:13
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`R[d].link` is the outgoing link that the router uses to forward packets towards destination `d`
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../../principles/reliability.rst:419
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For example, consider a sender that sends `111`. If there is one bit in error, the receiver could receive `011` or `101` or `110`. In these three cases, the receiver will decode the received bit pattern as a `1` since it contains a majority of bits set to `1`. If there are two bits in error, the receiver will not be able anymore to recover from the transmission error.
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../../principles/sharing.rst:597
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The hidden station problem
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../../principles/transport.rst:670
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The initiating entity receives the `CA` segment. The acknowledgment number of this segment confirms that the remote entity has correctly received the `CR` segment. The transport connection is considered to be established by the initiating entity and the numbering of the data segments starts at sequence number `x`. Before sending data segments, the initiating entity must acknowledge the received `CA` segments by sending another `CA` segment.
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../../glossary.rst:167
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A Network Address Translator is a middlebox that translates IP packets.
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../../principles/dv.rst:14
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`R[d].cost` is the sum of the metrics of the links that compose the shortest path to reach destination `d`
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../../principles/sharing.rst:603
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To avoid collisions in these situations, CSMA/CA allows devices to reserve the transmission channel for some time. This is done by using two control frames : `Request To Send` (RTS) and `Clear To Send` (CTS). Both are very short frames to minimize the risk of collisions. To reserve the transmission channel, a device sends a RTS frame to the intended recipient of the data frame. The RTS frame contains the duration of the requested reservation. The recipient replies, after a SIFS delay, with a CTS frame which also contains the duration of the reservation. As the duration of the reservation has been sent in both RTS and CTS, all hosts that could collide with either the sender or the reception of the data frame are informed of the reservation. They can compute the total duration of the transmission and defer their access to the transmission channel until then. This is illustrated in the figure below where host `A` reserves the transmission channel to send a data frame to host `B`. Host `C` notices the reservation and defers its transmission.
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../../principles/transport.rst:672
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The remote entity considers the transport connection to be established after having received the segment that acknowledges its `CA` segment. The numbering of the data segments sent by the remote entity starts at sequence number `y`.
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