Exit Zen
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../../principles/transport.rst:219
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Transport layer services
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../../glossary.rst:243
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The Internet Corporation for Assigned Names and Numbers (ICANN) coordinates the allocation of domain names, IP addresses and AS numbers as well protocol parameters. It also coordinates the operation and the evolution of the DNS root name servers.
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../../exercises/network.rst:374
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Consider the same distance vector protocol, but now with `triggered updates`. When link `B-C` fails, assume that `B` updates its routing table immediately and sends its distance vector to `A` and `D`. Assume that both `A` and `D` process the received distance vector and that `A` sends its own distance vector, ... Indicate all the distance vectors that are exchanged and update the table above each time a distance vector is sent by a router (and received by other routers) until all routers have learned a new route to each destination. How many distance vector messages must be exchanged until the network converges to a stable state ?
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../../principles/reliability.rst:239
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`0` : `0110000` b
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../../principles/sharing.rst:269
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`Deterministic` or `pessimistic` MAC algorithms. These algorithms assume that collisions are a very severe problem and that they must be completely avoided. These algorithms ensure that at any time, at most one device is allowed to send a frame on the LAN. This is usually achieved by using a distributed protocol which elects one device that is allowed to transmit at each time. A deterministic MAC algorithm ensures that no collision will happen, but there is some overhead in regulating the transmission of all the devices attached to the LAN.
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../../principles/transport.rst:222
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When two applications need to communicate, they need to structure their exchange of information. Structuring this exchange of information requires solving two different problems. The first problem is how to represent the information being exchanged knowing that the two applications may be running on hosts that use different operating systems, different processors and have different conventions to store information. This requires a common syntax to transfer the information between the two applications. For this chapter, let us assume that this syntax exists and that the two applications simply need to exchange bytes. We will discuss later how more complex data can be encoded as sequences of bytes to be exchanged. The second problem is how to organize the interactions between the application and the underlying network. From the application's viewpoint, the `network` will appear as the `transport layer` service. This `transport layer` can provide three types of services to the applications :
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../../glossary.rst:42
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IETF
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../../exercises/network.rst:376
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Consider again the network shown above. After some time, link state routing converges and all routers compute the same routing tables as above.
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../../principles/reliability.rst:240
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`z` : `1111010` b
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../../principles/sharing.rst:270
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`Stochastic` or `optimistic` MAC algorithms. These algorithms assume that collisions are part of the normal operation of a Local Area Network. They aim to minimize the number of collisions, but they do not try to avoid all collisions. Stochastic algorithms are usually easier to implement than deterministic ones.
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../../principles/transport.rst:224
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the `connectionless service`
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../../glossary.rst:44
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The Internet Engineering Task Force is a non-profit organization that develops the standards for the protocols used in the Internet. The IETF mainly covers the transport and network layers. Several application layer protocols are also standardized within the IETF. The work in the IETF is organized in working groups. Most of the work is performed by exchanging emails and there are three IETF meetings every year. Participation is open to anyone. See https://www.ietf.org
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../../exercises/network.rst:378
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An important difference between OSPF and RIP is that OSPF routers flood link state packets that allow the other routers to recompute their own routing tables while RIP routers exchange distance vectors. Consider that link `B-C` fails and that router `B` is the first to detect the failure. At this point, `B` cannot reach anymore `C`, `D` and `E`. `C` cannot reach `B` and `A` anymore.
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../../principles/network.rst:302
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Dealing with heterogeneous datalink layers
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../../principles/reliability.rst:241
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`@` : `1000000` b
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../../principles/sharing.rst:273
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We first discuss a simple deterministic MAC algorithm and then we describe several important optimistic algorithms, before coming back to a distributed and deterministic MAC algorithm.
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../../principles/transport.rst:225
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the `connection oriented service`
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../../glossary.rst:147
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IGP
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../../exercises/network.rst:380
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Router `B` will flood its updated link state packet through the entire network and all routers will recompute their forwarding table. Upon reception of a link state packet, routers usually first flood the received link-state packet and then recompute their forwarding table. Assume that `B` is the first to recompute its forwarding table, followed by `D`, `A`, `C` and finally `E`.
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../../principles/network.rst:304
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Sometimes, the network layer needs to deal with heterogeneous datalink layers. For example, two hosts connected to different datalink layers exchange packets via routers that are using other types of datalink layers. Thanks to the network layer, this exchange of packets is possible provided that each packet can be placed inside a datalink layer frame before being transmitted. If all datalink layers support the same frame size, this is simple. When a node receives a frame, it decapsulates the packet that it contains, checks the header and forwards it, encapsulated inside another frame, to the outgoing interface. Unfortunately, the encapsulation operation is not always possible. Each datalink layer is characterized by the maximum frame size that it supports. Datalink layers typically support frames containing up to a few hundreds or a few thousands of bytes. The maximum frame size that a given datalink layer supports depends on its underlying technology. Unfortunately, most datalink layers support a different maximum frame size. This implies that when a host sends a large packet inside a frame to its nexthop router, there is a risk that this packet will have to traverse a link that is not capable of forwarding the packet inside a single frame. In principle, there are three possibilities to solve this problem. To discuss them, we consider a simple scenario with two hosts connected to a router as shown in the figure below.
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