TCP/IP Tutorial for Beginner

What is a protocol?

A protocol is a set of rules and procedures, such as what format to use, when should data be send, what are the numbers in the data mean, what commands to use, what error code are there and their meaning, etc.

When two computers exachange data, they can understand each other if both uses the same protocol.

Overview of How Internet Works

Suppose you are viewing a web page, or chat with a friend online, or downloading a file. What happens underneath?

The app (email, chat, etc) breaks the data into thousands of tiny independent pieces. Each piece is called a packet (or datagram). Each packet has embedded with it the destination IP address. Your computer send this packet to your router , and the router send it to another router that's closer to the destination.

This process continues until the designated machine with the IP address receives it. This is done for each and every packet.

On the receiving machine, it re-assembles all these packets into the original whole piece in the right order, and send it to the right application on that machine. (The app is often the email server, or web server, or chat server. these servers in turn, repeat the same thing to send it to your friend's machine.)

Computer software follow a set of standardized rules of procedure when talking to each other. This standardized rules of procedure used for internet is called the Internet Protocol Suite (aka TCP/IP).

Networking Hardware

Before we talk about internet protocol, lets take a look at hardware needed, because hardware gives us a good overview of how things are connected.

The essential hardware for internet to work, for our purposes, are:

• Network Adapter (aka Network Interface Controller, NIC)
• Router

Network Interface Controller

Network Interface Controller (NIC) (aka network adapter, network card network interface card, LAN adapter ) is a hardware that lets your computer talk to the internet. All internet-capable device has at least one. Today's computer usually has two, one for Ethernet (wired) and one for wireless.

Network Interface Controller provides one of:

• wired ethernet port
• wireless internet transceiver

As of year 2020, every phone, laptop, desktop computer has wireless network adapter builtin. And every phone has wireless network adapter builtin.

How to list all Network Interface?

• Linux: Type ip link or ifconfig -a
• Windows: Type ipconfig /all

• Linux: Networking Commands Tutorial
• Windows: Networking Commands Tutorial

Router

Then, the second most important hardware is Router . Router transfer packets between internet devices.

The Network Adapter (wired or wireless) in your computer send signals to the router, then the router either send it to other computer in your home, or send it to the internet via physical cable or phone line connected to it (typically a device called Cable Modem) .

Typically, each internet device start with its software sending info to the Network Adapter, then the Network Adapter send it to a router, then router send it to another router, and so on, until a router send it to a destination computer's Network Adapter. (the destination is usually a corporation's machine, we call it “server”. (e.g. when you goto google.com or any or any website.) The server, either stores your info (e.g. photos), or send it to another user's machine (e.g. online chat messages).)

Internet Addresses

In order to send info, devices must have addresses for destination. Two of them are most important:

• MAC Adddress
• IP Address

MAC Address (aka Hardware Address, Physical Address)

• Network: MAC Address

Binary Number, Hexadecimal Number

When working with networking protocols, you need to understand Binary Number and Hexadecimal Number in detail, and you need to be able to convert them.

bit means binary digit. A binary digit is either 1 or 0. e.g. 4 bits looks like this: 1001, or 0011, or 1100, etc.

octet means 8 bits.

byte means 8 bits. (wasn't so before 1990s)

1 hexadecimal digit is equivalent to 4 bits.

• Binary/Hexadecimal Converter
• What is Binary Number
• What is Byte
• What is Hexadecimal Number

IP Address

• Network IP Address

Host, Hostname

• Network: Host, Hostname

TCP/IP Protocol Layers

• “Host” means a computer.
• The “process” means a running software program, such as web browser.
• The “link” means “router”.
• {Ethernet, fiber, satellite} are physical links (e.g. cable or radio wave transmissions.)

TCP/IP is a set of protocols that are logically separated into 4 layers. They are:

• Application layer
• Transport layer
• Internet layer
• Link layer

Each layer down covers more detail about how to send a datagram.

Here's a human example. If i send you a letter, i'm not concerned about how it gets there, by car, by plane, boat, or who delivers the letter, or what happens if its raining. All I care, is the mail content and address, and whether you got the letter (and how soon you can get it). This is the highest level. But beneath it, there must be a system, such as address system, transportation system, government law or structure for delivering mail, etc.

In TCP/IP, the highest layer, the Application Layer, is concerned only about software sending some content (a sequence of bytes) to another address such as email address or URL or IP address. The lowest layer, the link layer, is concerned about how to actually connect hardware things physically, over cable/wire or radio waves. Such as the design of the cable, the electric signals.

Here's more detail about each layer.

Application layer (process-to-process): This is the high level layer. Application layer are protocols that focus communication from the application's perspective. Such as, send or receive the data, or the format of the data. For example, {HTTP (web), SMTP (email), DHCP (automatic host config)} are protocols at this level.

Transport layer (host-to-host): provides end-to-end communication services for applications. The transport layer provides convenient services such as connection-oriented data stream support, reliability, flow control, and multiplexing. Two most used protocols in this layer are TCP and UDP.

Internet layer (internetworking): The internet layer is about exchanging datagrams across machines. This layer defines the addressing and routing structures used in TCP/IP. The primary example is the IP (Internet Protocol), which defines IP addresses. Its function in routing is to send datagrams to the next router that is closer to the destination IP address.

Link layer: This layer is pretty much about physical connection technology. That is, translating packets to various electric or optical wire signals, or wireless by radio waves or satellite transmission. The Ethernet cable is considered a standard of the link layer.

• Sample encapsulation of data in TCP/IP.
• At top, the highests abstraction layer, the data is simply what we want to send, such as chat text. Then, the data is broken into many small packets.
• Below it, the Transport layer, it shows a datagram. It adds a “header” to the datagram. This header contain info such as how exactly we send it, should be connection oriented or not, etc.
• Below it,
• the IP header, contains even more lower level info. And so on.

Network Port Number

• Network Port Number

Network Socket

• Network Socket

Connection Oriented vs Connectionless

There are 2 types of connection in TCP/IP:

• Connection Oriented.
• Connectionless.

TCP/IP by nature is a connectionless network, because each packet is independent. This is called Packet switching networking technology. (meaning, lots of small data “packets” are sent. Each one independent of another. They swarm towards destination, via routing (the “switch” part))

Packet Switching is in contrast to circuit switching tech.

Circuit Switching network is a connection-oriented networking approach. when a caller calls another, a electric circuit is established between the callers. It is used by early analog telephone networks. Circuit switching network in a sense dedicates the cable (or channel, medium) per active call/connection. Circuit switching

However, a packet switching network (tcp/ip) can emulate the effects of physical connection by using protocols that acknowledge transmission, then establishing a virtual connection. TCP does this.

Here's how connection-oriented networking works. When a packet is sent, the receiver sends back acknowledgement. If the sender don't receive this, it re-sends. When a session of communication is over, the sender and receiver say goodbye to each other, therefore “closes” the connection. In this way, communication is established as if thru physical connection, even though the data units transmitted is actually discrete and goes thru many routers that doesn't have any notion about who is connected to whom.

• TCP is a connection oriented protocol.
• UDP is a connectionless protocol.

IP Datagram

An IP packet consists of a header section and a data section.

An IP packet has no data checksum or any other footer after the data section. Typically the link layer encapsulates IP packets in frames with a CRC footer that detects most errors, and typically the end-to-end TCP layer checksum detects most other errors.

• IPv4#Header
• List of IP protocol numbers

• ICMP = 1
• TCP = 6
• UDP = 17

Routing schemes: unicast, anycast, multicast, broadcast

Routing

The Internet Protocol addressing system recognize 3 main types of addressing.

• Unicast addressing uses a one-to-one association between destination address and network endpoint: each destination address uniquely identifies a single receiver endpoint.
• Broadcast or multicast addressing uses a one-to-many association, datagrams are routed from a single sender to multiple endpoints simultaneously in a single transmission. The network automatically replicates datagrams as needed for all network segments (links) that contain an eligible receiver.
• Anycast addressing routes datagrams to a single member of a group of potential receivers that are all identified by the same destination address. This is a one-to-one-of-many association.

Transmission Control Protocol (TCP)

• Transmission Control Protocol (TCP)

UDP (User Datagram Protocol)

• UDP (User Datagram Protocol)

Address Resolution Protocol (ARP)

Address Resolution Protocol = a protocol that creates a look-up table for mapping IP address to MAC address.

• Each host has a ARP cache.
• If a host want to send data to another host in the same segment, it checks if the MAC address is in the ARP cache, if not, the host sends a broadcast called ARP request frame.
• The receiver with the IP address will respond and give it's MAC address.

Reverse Address Resolution Protocol (RARP) is obsolete, replaced by Bootstrap Protocol (BOOTP) then by Dynamic Host Configuration Protocol (DHCP).

Internet Control Message Protocol (ICMP)

• Internet Control Message Protocol (ICMP)

How to see the routing table of my computer?

• Linux: Type ip route or route
• Windows: