Computer network and Internet core network, computer network internet

Computer network and Internet core network, computer network internet

1. Mesh Router

Vro links constitute the core of the network.

Any vro or line is disconnected, but the network is still accessible. This is a feature of the internet.

How is data transmitted?

1) The circuit switching proprietary line, like a phone, each line has a line.

2) packet-switching packaging: data is divided into one package for data delivery.

1.1 circuit switching

First, we need to create an end to connect them through resource allocation.

This line must pass through the router, so the bandwidth of the router will affect the transmission speed.

On each link, the bandwidth is reserved, which means a dedicated bandwidth.

Exclusive resources cannot be shared. Even if this line is not used, other transmission requests cannot obtain this line.

However, it must have an action to create a connection.

Two methods to implement this mode:

1) Time Division

2) frequency Segmentation

It is actually the division of resources, space or time.

Before and when it happened, we talked about the occupation of bandwidth, which can be Baidu.

1.2 packet-switching

Split the data into packages one by one, and use all links on the network for full-speed transmission when using the data.

In this case, User A & User B is the share network resource. Therefore, he wants to compete for resources.

However, the bandwidth of the router is always limited, and there are usually congestion problems with a large number of network requests.

The packets are placed in the router queue.

The router is stored first and then transferred.

The forwarding process is disordered, that is, the packets of A and B are randomly arranged, and each packet needs to compete for resources.

In addition, the time for User A and User B to send data is uncertain, so the network bandwidth can be fully utilized.

The packet is collected first, and then you can see where to put it, and then put it in the Queue.

1.2.1 comparison of two modes

Assume that there is a link with a bandwidth of 1 M/s.

Assume that there are N users and the data to be sent is sent at 100 kb.

It is not alway on, and it only sends 10% of the time

Therefore, if it is circuit switching, you can only divide it into 10 users, but you only use 10% of the time, and the rest

Time is a waste.

For packet-switching and 35 users, the probability of more than 10 users at the same time is less than 0.004.

Therefore, it can be considered to support 35 users at the same time.

Applicable scenarios for packet-switching,

1) bursty data contains a large amount of data, but a short period of data. Since it is both bursty, You can stagger the sending time, so it is best. Suitable for sending packets.

If data bursts occur for multiple users at the same time, the router can Queue them up and send them when the network is idle.

Of course, there may also be too much data on the end. If the peak value is exceeded, the packet may be dropped. Therefore, it can create multiple connections to reduce this probability.

However, bursty data may cause the packet's delay & loss.

Therefore, a better protocol is needed to provide a reliable transmission mechanism.

2) how to provide functions similar to circuit?

We hope to apply audio/video. 5 MB of bandwidth is required, but the bandwidth may only be 5 kb. Therefore, the bandwidth is not guaranteed because the internet needs to compete.

This is very difficult only through the Protocol. The current location is still an open problem.

 

1.2.2 store & forward

Assume that there is data to be sent from one end and there are two routers.

The bandwidth of each segment is R.

The packet length is L.

Suppose L = 7.5 M

R = 1.5 M

Therefore, it takes five seconds for L/R to send a packet.

Each segment is sent for 5 seconds. It is sent for a segment, and then the store is on the vro and then on the store.

Delay = N * L/R

N is the number of lines.

If we cut 7.5 M into pice. For example, it is 5000 copies. Each Packet Only has 1.5 kb, so the time for sending a packet becomes 1 ms.

It can use the pipelining method,

I sent the first packet, 1 ms.

When sending the second packet, you can send the first packet in the next section.

Therefore, each network segment is sending data, rather than waiting.

So it takes 5002 ms for me to finish it.

Therefore, the package should not be too large, so that he can pipeling

However, each packet has a segment header, so the smaller the switch, the better.

1.2.3 select path

When data is transmitted, it must go through different routers and have many paths. How can this problem be solved?

Path Selection Algorithm. What should I do if the connection of a vro is constantly changing, for example, congested or disconnected?

You can select the path with the least number of routers, but it is not necessarily the fastest, such as the path with a wireless router.

1) Each packet needs to include the address of the other party. This is the IP address. Just like a letter, it must be the address of a recipient.

2) In the process of a connection, the path of packet transmission may change, just like driving a car, not recognizing the road. Therefore, you should ask every time you open a section.

3) virtual circuit network: Add a tag to each packet, and each router will know where to go when it sees the tag.

Because a fixed path is required, it takes some time to establish a connection. The router needs to control the status of each call. It's a blue tag.

A clear path.

Summary:

The entire communication network is divided into two parts,

VPC and Packaging Machine

VPC: OFDM & TDM

Packets: packets with IP addresses are sent by routers. Vrouters exchange their information.

When the package comes in, the router will create a table, and the router will communicate regularly and irregularly.

We hope to take a fixed route under the packet-switching mechanism, that is, VCs.