I had an interesting twenty-four hours at work trying to figure out how best I tin hand notice setup a service for a customer who is sending UDP licensing traffic through around high-end networking devices over VPN. UDP past times pattern is unreliable. This was causing issues equally the UDP packet size was over the recommended size. The champaign size sets a theoretical restrain of 65,535 bytes (8 byte header + 65,527 bytes of data) for a UDP data-gram. The practical restrain for the information length which is imposed past times the underlying IPv4 protocol is 65,507 bytes (65,535 − 8 byte UDP header − 20 byte IP header. Their packet was fragmenting in addition to I had to become dorsum to networking basics in addition to kickoff from Layer 2. Found the work inwards Layer 4 (yes, it’s UDP fragmentation issue). I found the next OSI model explanation useful.
The OSI model breaks the network communications procedure into vii split layers. I found few articles interesting in addition to decided to splice them to exercise a post.
Layers v through 7 are to a greater extent than oft than non referred to equally the upper layers. Conversely, Layers 1 through 4 are collectively called the lower layers. Here are around mnemonic phrases to help you lot yell back the layers of the OSI model:
- “Please Do Not Throw Salami Pizza Away”
- “All People Seem To Need Data Processing”
- “Please Do Not Tell Secret Passwords Anytime”
From the top, or the layer closest to the user, down, these layers are:
- Layer 1 – Physical: The Physical layer’s yell says it all. This layer defines the electrical in addition to physical specifications for the networking media that acquit the information bits across a network.
- Layer 2 – Data Link: As its yell suggests, this layer is concerned amongst the linkages in addition to mechanisms used to movement information nigh the network, including the topology, such equally Ethernet or Token Ring, in addition to deals amongst the ways inwards which information is reliably transmitted.
- Layer three – Network: This is the layer on which routing takes place, and, equally a result, is peradventure the most of import OSI layer. The Network layer defines the processes used to road information across the network in addition to the construction in addition to utilisation of logical addressing.
- Layer 4 – Transport: The functions defined inwards this layer supply for the reliable transmission of information segments, likewise equally the dis-assembly in addition to assembly of the information earlier in addition to later on transmission.
- Layer v – Session: The Session layer establishes, maintains, in addition to manages the communication session betwixt computers.
- Layer half dozen – Presentation: This layer is concerned amongst information representation in addition to code formatting.
- Layer 7 – Application: The Application layer provides services to the software through which the user requests network services. Your reckoner application software is non on the Application layer. This layer isn’t nigh applications in addition to doesn’t comprise whatever applications. In other words, programs such equally Microsoft Word or Corel are non at this layer, simply browsers, FTP clients, in addition to post service clients are.
PDU Names on the Layers of the OSI Model
Each layer of the OSI model formats the information it receives to arrange the functions to survive performed on that layer. In general, the packet of information that moves through the layers is called a Protocol Data Unit (PDU). However, equally the information is reformatted in addition to repackaged, it takes on unique names on for certain layers. Table 1 lists the yell each layer uses to refer to a message.
Absolutely memorize the information inwards Table 1 to the indicate that you lot tin hand notice recite the information unit of measurement yell associated amongst each of the OSI model’s layers.
| OSI Layer | PDU Name |
| Application | Data |
| Presentation | Data |
| Session | Data |
| Transport | Segment |
| Network | Packet |
| Data Link | Frame |
| Physical | Bits |
