One of the most frustrating yet relatable experiences shared by almost everyone in this
day and age is suddenly finding your internet connection is down for no apparent
reason. A network failure that takes your business offline? That’s a huge headache with
major consequences to your bottom line.
Sometimes the reason for network failure is apparent, like power failure, but other times
it takes an IT expert to make a proper diagnosis and get it back up and running again.
For businesses that don’t have the budget for a full-time IT staff, it may be in your best
interest to become familiar with OSI layers and how they can be used to treat several
IT-related business problems, including troubleshooting your network issues. When you
can successfully troubleshoot these kinds of issues independently, you may no longer
have to tolerate any significant amount of network (and thus business) downtime.


Understanding The Seven OSI Layers
The OSI model is made up of two major parts:

1. The reference model

2. The protocols
The reference model is simply another way to characterize the 7 OSI layers. In this
model, each layer within your network is compatible with the layers immediately below
and above it, so software and tools in layer 3 can work directly with tools and software
in layers 2 and 4.
The protocols enable the OSI layers on a host to properly communicate with the same
layer on a different host, i.e., you can use Gmail (a Layer 7 application) to email
someone, hundreds of miles away from you who uses Microsoft Outlook’s email service
(another Layer 7 application).


Layer 1: Physical
When troubleshooting any issue related to electronic devices, Layer 1 is where you ask
and answer the question of whether or not the device is plugged in.
This is the lowest layer of the OSI model and deals primarily with the physical
transmission of data between network devices and infrastructure. This is accomplished
through electrically (or optically) transmitting raw unstructured data bits over the
network.
Important specifications to consider at the physical layer include:
● Voltages
● Pin layout
● Cable size
● Signal frequencies


Layer 2: Data Link
This layer focuses on media and is where you’d be dealing with the switches used to
start up or turn off communication between connected devices. It’s made up of two
sublayers: Media Access Control (MAC) and Logical Link Control (LLC).
Getting more technical, the layer specifically acts as a medium for node-to-node
transfers of data between frames, which are simple containers used for a single network
packet, between two devices that are physically connected.
MAC is what determines how the devices in a given network attain access to a medium
and get permission to transmit data. LLC deals with the identification and encapsulation
of network layer protocols, checks and corrects for errors made at the physical layer,
and handles frame synchronization.
Important specifications at the data link layer include:
● Network topology
● Flow control
● Physical address
● Error notification
● Frame sequence


Layer 3: Network
Layer 3 is another media layer and is home to routers and IP addresses in search of the
most efficient comms pathways, specifically for packets that contain control information
and or user data (AKA, a payload).
If the packet layer is too big for transmission, it can be split apart into smaller fragments
which are shipped out before being reassembled upon arrival. This layer is also home to
firewalls and 3-layer switches.
The frames received at the Network Layer come from the Data Link Layer below it. It
identifies the destination of the data it receives through the use of logical addresses
such as Internet Protocol (IP).
However, for the Network Layer to do its job, it needs to route information to its proper
destinations.
Important specifications at the Network Layer include:
● Best available path
● Traffic controls
● Priority of Service
● Network characteristics


Layer 4: Transport
Think of the Transport Layer as a kind of digital post office that coordinates data
transfers between different systems and hosts. That’s its function in a nutshell.
This layer acts as a host that figures out how much data to send, at what rate to
transmit the data, the data’s destinations, and more. Appropriately, additional firewalls
live in this layer and so do gateways.
Additional functions of this layer include checking for errors, identifying duplication of
data, handling failed deliveries that need to be resent, and keeping track of all the data
packets.


Layer 5: Session
The Session Layer of the OSI model functions like a moderator that controls the
communication between devices and or servers—think of it as a meeting host or
mediator between different computers (though it’s not limited to just computers).
It establishes pathways, creates limits for response wait time, authenticates
sessions—a session is an interactive exchange of data between two entities in a given
network—and terminates them.
A common example of this layer in action includes HTTPS and sessions, which enable
users to visit and browse sites on the internet.


Layer 6: Presentation
Here is where data is translated and formatted so that networks, devices, and
applications can actually understand and work with the data they’re receiving. This layer
relates to data compression, conversion, code translation, encryption, and decryption.
This layer is also known as the syntax later because it maps the semantics and syntax
of data so that any received information is able to be understood by any distinct network
entity.
When you’re using an encryption-based communication app and transfer data, that data
is formatted and encrypted at this layer before being launched across the network.
Once the data arrives where it’s supposed to it’s decrypted and formatted into plain text
or media information, this layer is also responsible for the serialization of complex data
into transportable formats—and then deserializes and reassembles it into its original
format destination.


Layer 7: Application
The Application layer is likely what most end-users are familiar with as it is where
Application Programming Interfaces (API) lives, which allow remote file access,
resource sharing, and other things. When you think of this layer, think of web browsers
and apps like Gmail and Slack.
If your business creates applications like that, then this is the layer where your
customers will likely be engaging with your products. The layer determines resource
availability, ensures the quality of communication, and identifies communication
components.
It also allows for network resources and uses common protocols like Telnet, Hypertext
Transfer Protocol (HTTP), Simple Mail Transfer Protocol 9SMTP), and File Transfer
Protocol (FTP). However, it should be noted that most traffic monitoring solutions don’t
operate in Layer 7.
It would actually benefit your business to use traffic monitoring solutions that utilize
Layer 7 because you’d be able to gain visibility into a significant amount of end-user
behavior that can help mitigate risks of cyberattacks and even help with load balancing,
among other things.
For instance, where you or an IT professional analyze Application Layer analytics, you
may be able to detect suspicious behavior (like DDoS traffic) and deal with the threat
without hurting the experience of legitimate users.


Managing Your Business’s Network Service
Understanding the OSI model can certainly help with DIY network troubleshooting, but
that’s probably not a responsibility you want to deal with on top of managing the
day-to-day of your business.
While it’s great to be able to handle your own network troubles, why not off-load that
task to us with our Network & Wireless Connections service?
After all, a functioning network is a crucial component of your business’s IT security.
Your network is the primary piece of infrastructure that facilitates access and delivers
connectivity to all your servers, files, devices, and more.
We’ll take a close look at your unique situation to come up with a working solution that
fits the way you do business. Click here for a free consultation: www.commprise.com

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