The components of a network

Building a simple network involves the following network devices:

  • Network card (computer networking equipment)
  • Repeater (physical layer extended network equipment)
  • Bridge (Data Link Layer extension network device)
  • Router (network layer data forwarding device)
  • Layer 4 to 7 switches (dealing with network transmission devices above the transport layer)
  • Gateway (Conversion protocol device)

Each network device is connected to each other by cables, and cables can be divided into several types. I won’t go into details here, but there are two terms that must be explained

bandwidth

Bandwidth is also called transmission rate (BPS). The transmission rate refers to the capacity of transmitting data in a transmission pipeline, that is, the amount of data transmitted per unit of time. First of all, it must be known that the flow speed of the signal in the transmission medium is constant. Even if the transmission rate of the data link is not the same, the transmission speed will not be fast or slow. A low-speed data link is like a road with fewer lanes and cannot transmit large amounts of data simultaneously, while a high-speed data link is like a road with multiple lanes and can transmit large amounts of data simultaneously.

throughput

The actual transmission rate between hosts is also called throughput, also in unit of Bit per second (BPS). Throughput not only measures the bandwidth, but also includes the processing capacity of the host CPU and the degree of network congestion.

Equipment details

The details of each device are described below

The network card

Each nic has a unique MAC address (48-bit serial number) and therefore belongs to the first layer of OSI, the physical layer. When any computer is connected to a network, it must use a network card, which allows users to connect to each other by cable or wirelessly.

repeater

A repeater is also an extended network device at the physical layer, layer 1 of the OSI model. It is suitable for extending network distance under a local area network, but it is not a network interconnection device. The repeater will pass into light signals or electrical signals to adjust or enlarge to transfer to another cable, it can be applied to two of the same communication media conversion work, also can apply to two completely different communication media, such as optical signal turn electrical signals, it is responsible for the pure signal conversion between 0 and 1 bit stream, don’t care about the correctness of the data.

Multiple port Repeaters can also be hubs.

The bridge

A bridge is a device that connects two networks at the data link layer, layer 2 of the OSI model. It can identify the data frame in the data link layer, and then regenerate the signal as a new frame and forward to another connected network segment.

The bridge can identify the FCS in the data link to determine whether the data is correctly delivered to the destination. The bridge can avoid sending corrupt data by checking this value.

Because these functions are at Layer 2 (data link layer) of the OSI reference model, Bridges are also known as Layer 2 switches (L2 switches)

Bridges have generally been replaced by switches with more ports that also isolate conflicting domains.

The router

A router is a device that connects two networks at the third layer of the OSI model, the network layer, and forwards packets.

Both routers and switches can connect to multiple devices at the same time, so here are the differences:

  • Routers can automatically assign IP and virtual dialing to lans, whereas switches are only used to distribute network data.
  • Routers, at the network layer, address by IP address, while switches, at the relay layer, address by “MAC” address.
  • A router can assign one IP address to multiple hosts with the same external IP address, while a switch can connect multiple hosts with different external IP addresses.
  • Routers are used to make internetwork connections, that is, to connect different networks, and switches are used to expand LAN access points, to connect more computers to the LAN.

The short answer is that routers also function as switches.

Layer 4 to 7 switches

Layer 4 to 7 switches are primarily responsible for processing data from the transport layer to the application layer on the OSI model. In fact, it is based on the transmission layer of TCP and other protocols and the application layer above it, analyzing and transmitting data, and carrying on special processing to it, such as: load balancer, wan accelerator and firewall and so on.

The gateway

A gateway is a device in the OSI reference model responsible for transforming and forwarding data from the transport layer to the application layer. In short, everyone knows that it is necessary to go from one room to another through a door. Similarly, messages sent from one network to another must pass through a “gateway”, called a gateway.

The Gateway, also known as the internetwork connector or protocol converter, processes data from the transport layer to the application layer just like switches at layer 4 to 7. It does not only forward data, but also converts data, translates it between two protocols that cannot communicate directly, and finally realizes the communication between them.

Here’s a vivid example from the Internet:

Let’s say your name is Little Spot, you live in a big yard, your neighbors have a lot of small friends, and your parents are your gateways. When you want to play with someone in the yard, just shout his name in the yard and he will hear you and run out to play with you.

But your parents do not allow you to go out of the door, you want to communicate with the outside world, all must be by the parents (gateway) to help you contact by phone. If you want to talk to your classmate Xiao Ming, Xiao Ming lives in another yard far away. He also has his parents at home (Xiao Ming’s gateway). But you don’t know xiao Ming’s phone number, but your homeroom teacher has a list of all the students in your class and a comparison table of phone numbers, your teacher is your DNS server. So you have the following conversation with your parents at home:

Little Spot: Mom (or Dad), may I ask the head teacher for Xiaoming’s phone number? Parent: Ok, you wait. (Then your parents give your head teacher a call to find out Xiao Ming’s number.) Yes, his home number is 211.99.99.99

Tiny Spot: That’s great! Mom (or dad), I want to find Xiaoming, please help me to contact Xiaoming.

Parent: No problem. (Then the parents sent a request to the telephone office to connect xiaoming’s phone number, the last pass of course is transferred to Xiaoming’s parents, and then his parents transferred the phone to Xiaoming).

So you got in touch with Xiao Ming.

Write in the last

Refer to the article

Diagram to TCP/IP

This will be updated irregularly as a recent long-term goal.