The outstanding Internet Protocol Layers and its hidden way

Which protocols are used in internet? In order to make computers to communicate, we can not just plug some network cables between them and expect them to be recognized and work right away. Just as humans, computers need a group to rules and procedures on how to communicate, called “Protocols”. This post talks about the Internet Protocol layers explanation, or or TCP/IP, and what it is all about. This is not a in-depth anaylisis, just informative. Do you want to know what is the internet protocol and how does it work? Continue reading and learn a few of the steps that your computer and cellphone requires to do to reach the world.

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What are Internet Protocol Layers?

It's a group of communitation rules and protocols used to communicate between computer, servers and many other devices. It's widely used in Internet (as the name suggests). It's role it to provide end-to-end communucation between devices. It specifies how data should be distributed, addressed, transmitted packetized, routed, sended and received.

Network Parts of TCP/IP

Network consists in many pieces. Some of them are:

• Protocols
• Routers
• Hosts
• Links
• Applications
• Hardware
• Algoritms

But not all of them work the same way, are in the same hierarchy or perform the same tasks. Let's see how it is organized.

Communication of Internet Protocol Layers

Internet Protocol is classified in abstract layers that are in charged to orgnanize, verify and route the traffic, both incoming and outgoing. From the bottom (physical) to the top (application), TCP/IP is organized in this order:

1. Application. It supports network applications.
2. Transport. It processes and manages all related to the transfer of information.
3. Network. It manages datagrams that crosses the network, from source to destination.
4. Link. It serves as passage to connect the neighboring elements in the network.
5. Physical. All related to the analogic phenomenon that actually carries the information from one place to another.

Airplane Analogy

Is it complicated to see it clearly? With an airplane analogy, it should be more understandable.

It is organized the same way as the illustration. The two stack on the left and right symbolizes two computers than want to exchange information. How would you proceed to travel by airplane? In this simplified graph, you get the ticket, check your bag, load it into the gate for your flight, use the ramp to take off and jump into the flight. When you land, you have to go backwards the same process. To sum up, here is organized by the internet protocol layers.

• Application: ticket.
• Transport: baggage.
• Network: gate.
• Link: takeoff or landing.
• Physical: airplane routing.

Each layer perform a specific service (as explained later) and each layer attaches its header or ‘indications' to the message sent by the application layer. Simply put, each layer is a program inside the device that is charge to serve other layers with valuable information.

Now, let's see some of the layers that composes this protocol.

Internet Protocol layers explained

Physical

Usually deployed in coaxial, twisted pair, fiber optics or wireless radio waves. It refers the physical media where the signals are going to be carried. The other layers of TCP/IP protocol work exactly despite being carried by a different physical nature.

Link

After the physical layer, a computer network has to realize the ‘existence' of nodes that internet many other computers, servers and, of course, the switches that interconnect them. This layer is all about linking the communication path. The Link Layer encapsulates a datagram (from Layer 3, the Transport Layer) by adding a ‘frame' header to it. Afterwards, it has the responsability to transfer it from one node to the next node.

Some of the services to the communication is flow control and determining if the connection is suitable for half-duplex or full-duplex. It also checks if there is parity in the last bit (the parity bit), to check if there was any mistakes or errors in the communication (in that specific packet).

Switches and access points are used to communicate between devices in this layer.

MAC Address

It is used in Link Layer to locate the nodes for comunication. It has a 48 bit address in hexadecimal numbers, such as 58-23-D7-FA-20-B3. The allocation of the addresses are managed by IEEE and it is assigned to every manufacturer. It is portable, since the network adapter can move from network to network. Do not confuse it with IP address.

Ethernet and Wi-Fi are different network adapters with different MAC addresses. Both can be connected to the same computer, yet connected to different networks. Here is an example, that compares Ethernet with Wi-Fi in practical situations. Click here to read about it.

Ethernet vs Wi-Fi

Network

Beyond recognizing nodes in the network, the Network Layer organizes the devices with a logic assignation (IP addresses). The device that communicates different networks is called router. Routing determines the path or route that packets should take from source to destination (in that networks in the reach of the routing device).

When a device receives a datagram, it uploads to the Transport Layer (if no error was detected). If it sends to the network, the segment get encapsulated into a datagram.

IP (IPv4 and IPv6)

It manages the addressing conventions, the format that the header of the datagram should have, how packets are handled and much more. The header include information, such as IP address from source and destination, checksum, time to live, IP version, length, etc.

IPv4 is a 32 bit address, usually presented in 4 pieces with numerical characters and it looks like this: 192.168.100.60. Commonly found in local are networks and many internet providers. Eventually it will be replaced with IPv6 which has more addressing capability with its 128 bit address. Typically, a IPv6 address would look like 2001:0db8:0000:0000:0000:4b2e:0444:7334 and it is composed by hexadecimal characters.

IP Protocol	Example
IPv4	192.168.100.60
IPv6	2001:0db8:0000:0000:0000:4b2e:0444:7334

RIP

It stands as Routing Information Protocol. It measures the number of hops from router to router in order to get the destination. Devices exchange routing information every 30 seconds.

It is often referred to it as “routing by rumor” and it has flaws with the spread of information. RIP can be summed up as “good news travel fast, bad news travel slow”.

OSPF

It stands of Open Shortest Path First and it is based in the Dijkstra's algorithm. It uses the technique to flood (send discovery packets) all over the network and available nodes to draw a “topology” map. Contrary to RIP, it measures cost path instead of hops and OSPF messages are authenticated to leave intruders out.

DHCP

It stands for Dynamic Host Configuration Protocol and it provides an IP address to a device recently connected to the network. It is intended to work as a plug and play feature. If this feature would not exist, then a network manager should assign manually each IP address to each computer or device that connects to a network. Note that is may see as an tedious task but it can increase security in a network.

Transportation

Once networks have been established, how should packets arrive to the destination in a speedy, efficient and reliable way? Should we send them in order or as they become available?

The Transportation Layer is in charge to manage the packets sent and received from the other end of the communication. In the TCP/IP protocol, two protocols are commonly used to exchange information. It uses segments to carry information related to this process such as ports from the source and destination.

UDP

It stands for User Datagram Protocol. It does not establishes a connection between the host and cliente, or source and destination. When an application does not require a 100% reliable information communication, UDP may be a good option. Some packets may be lost or delivered out of order. Such applications could be a Zoom call, a movie streaming service, a GPS location service or an online videogame where 1 out of 20 or 2000 packets could be lost and the application could still work properly.

Some of its advantages are:

1. No connection (it starts right away).
2. Simpler.
3. Smaller header size.
4. No congestion control.

TCP

It stands for Transmission Control Protocol. TCP ensures that a file is delivered to and received by other device in a reliable way. It features:

1. Flow control. It doesn't send more information than it is received.
2. Segment structure. Timeout in delayed packets, acknowledgement, etc.
3. Congestion control: sender is throttled if its network is overloaded or unresponsive.
4. Reliability. Files and information are identical on both sides.
5. Connection management. Host and client have ‘handshaked' before.

There is a feature in this frame called the checksum, which function is to check if there is any errors in the received package. If there is a mistake, then this layer won't upload the information into the Application Layer.

Application

All related to the programs on the operating system or a device that require to communicate outside its device. The Application Layer, from the internet protocol layers, are ‘seeable' from the user or client screen. It is composed by programs such as:

• web browsing
• e-mail
• remote login
• P2P file sharing
• real time conferencing
• audiocalls

HTTP

It stands for Hypertext Transfer Protocol. It is the foundation on how websites works all around the world (including this one!). It consists in objects in which a client (like a user) interacts with the website, such as HTML code and files, audio and video files, etc. Every object has it addressable URL such as:

www.techzorro.com/content/picture.jpg

where “www.techzorro.com” is the name of the host and “/content/picture.jpg” is the name of the path. The default port for HTTP is 80.

FTP

It stands for File Transfer Protocol. It establishes a set of rules in order to pass a file (or several of them) from a computer host to a computer client. One important feature is its reliability; the file MUST NOT arrive to client with corrupted, incomplete and false data. Such files can be pictures, PDFs, binary or system files, etc.

The default port for FTP is 21 for control connection and 20 for data connection. Both of them uses TCP from the Transport Layer.

SMTP

It stands for Simple Mail Transfer Protocol. Electronic mail uses different protocols, such as SMTP which is in charge of the delivery and storage in the receiver's server. Other protocols involves the retrival from server, such as POP, IMAP and even HTTP.

SMTP involves user agents, mail servers and the protocol itself.

• User agent. It is the mail reader app, such as Thunderbird or Outlook.
• Mail servers. The mailbox with all the content in the server, ready to send to the user.
• SMTP. It transfers from receiving server to sending server.

Is uses TCP to transfer e-mails from client to server, using port 25.

DNS

It stands for Domain Name System. Like humans, computers uses name and identifiers. It is a giantic database of name servers with their corresponding addresses distribuited worldwide.

• Humans have ID cards and names.
• Servers and computers have IP addresses.

For example, when you typed www.techzorro.com in your web browser, it searched in the closest DNS server and it returned its corresponding IP address to reach it. Computers doesn't understand names of servers!

Some of the benefits of not centralizing DNS are:

• If one server shuts down or breaks down, other DNS servers are still operational.
• It handles traffic better. It scales better!
• Shorter distance to travel, quicker the response.
• It eases maintenance.

SSH

It stands for Secure Shell Protocol. It is a crypted protocol of communitation for services from a client to a host. Typically, it is used for remote login in a computer in the same local network (but often beyond it!) as well as command line execution.

First, IP address must be written down and then the user and password of the host computer or server. If the connection is established, then remote access to the command line or command prompt of the target computer is given.

Conclusion of the Internet Protocol Layers

In this post, a brief overview has been written about Internet Protocol Layers, also known as TCP/IP. A general description about each layer is given and the role it performs. Furthermore, some protocols from each layer are explaned in a few sentences to have an idea about the different services they provide.

Resources

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1. Internet protocol suite. Wikipedia. Link.
2. Computer Networking: A Top-Down Approach 6th Edition. Jim Kurose, Keith Ross.
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   2. Editor's Link.