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Looking at the OSI 7 Layer Reference Model

The "Open Systems Interconnection" reference model is the only internationally accepted hierarchy of standards for communicating between different systems, made by different vendors. It's goal was to create an open systems networking environment where any vendor's computer system, connected to any network, can easily share data with any other computer system on that network. It is important to note that OSI is just a model and not an actively used protocol.

The seven layers consist of:

1. Physical - connects electrical/optical signals, wires/wireless. For example it defines signals like POTS, T1, xDSL, SONET, satellite, wireless, microwave. And defines physical shapes such as jacks and connectors (RJ11, RJ45, RJ48, DSX, CSU-DSU, X.21, RS-232, etc.).

We need standard physical protocols so we can easily connect different devices together.

Using a railroad as a metaphor, layer 1 puts the packages into the trucks.

2. Data Link - makes the connections and provides synchronization/signaling. Where bits are organized, signaled to one another and where software is used to manage the process. For example it defines the WAN: point-to-point/private line, asynchronous transfer mode, frame relay, multi-protocol label switching, etc.. And also defines the LAN: local area network protocols like Ethernet, Token Ring, Appletalk (+ links and switches).

At the data link layer 2, information is packaged or encapsulated (capsule) into packets, frames, cells, datagrams. You have probably encountered "gelcaps" which put a shell of "gel" around your aspirin or othe pill. Encapsulation is like the color around this which contains the information.

Using a railroad as a metaphor, layer 2 creates the "boxcars" - packets creates the packages.

3. Network - routes the information by providing destination and direction of data. Stamps an address on data, and everything which involves routing is based on addressing. An example of an IPv4 data address would be, which is 32 address bits (IPv6 is 128 address bits).

The network layer is responsible for forwarding, i.e. if it's not for this location (router), let's forward that packet to the next router (hop), it might go there.

Routers (aka hops) of data pathways. Supports multiple bandwidth speeds, routes, protocols (IP, frame, ATM, token ring, Ethernet). Aides in scheduling, buffering, queuing, and manages overflow- i.e. hey email packet, you have to wait because i have a priority video packet ahead of you.

Layer 3 - protocol puts or encapsulates into datagrams (capsules) with source and destination address (IPv4 address used currently), IPv6 like zipcode plus is now available with 128 bit addresses, which are compatible with IPv4 by pre-pending (adding 96 zeros in front of the IPv4 address). Layer 3 fragments the data which allows data to be sent in pieces (packets) like moving your stuff- may be placed in more than one moving van and they may go over different routes to the destination and then reassembled- from IP to LAN (local area network) Ethernet address (MAC - media access control) - to frame relay, PTP, MPLS, or other layer 2 protocol.

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