Study Notes: Chapter 1-Overview of computer networks

Study Notes: Chapter 1-Overview of computer networks

1.0Definition of Computer Network:A set of self-governing computers is called computer networks.

1.1The role of computer networks in the Information Age:Connectivity and sharing.

1.2Internet Overview:

Concept of Network: A network is composed of several nodes and links connecting these nodes.

Nodes in the network can be computers, hubs, switches, and routers;

The network and network are connected through vrouters;

The Internet is the largest network in the world.

1.3Composition of the Internet:

The Internet is divided into the following two fast ways:

(1)Edge: It is composed of all hosts connected to the Internet;

Purpose: users directly use it for Communication (data transmission, audio, video) and resource sharing.

The communication between the end system and the running program of the edge part can be divided into two categories:

C/S (Client/Server):

This method is the most common and traditional method. The customer is the service requestor, and the server is the service provider. Both parties must use the services provided by the core part of the network. Service programs and customer programs have their own characteristics and functions.

Peer connection (P to P or P2P): The two hosts do not distinguish the server requester or service provider during communication. As long as they have installed P2P software, they can perform peer-to-peer communication.

(2)Core: Consists of a large number of networks and routers that understand these networks;

Purpose: This part provides services for the edge part.

The core part of the network is the most complex part of the Internet, because the core part of the network must provide connection communication to a large number of hosts on the edge of the network, enable any host in the edge part to communicate with other hosts.

The core part of the network is some vrouters that play a special role;

A vro is a dedicated computer (but not a host );

A vro is a key component for Packet Exchange. Its task is to forward received groups, which is the most important function of the core part of the network;

The switch mode of the core part routing:

1)Circuit Switching: The bit stream of the entire packet continues from the source point to the end point, as if to be transmitted in a pipeline; has the actual line (such as a fixed phone number), has the characteristics of exclusive line.

2)Packet Exchange: The entire packet line is transmitted to adjacent nodes. After all the packets are stored, the forwarding table is searched and forwarded to the next node.

3)Group exchange: A single group (a part of the entire packet) is transmitted to adjacent nodes. After the group is stored, it finds the specific table and forwards it to the next node. Split and send data into data blocks.

We mainly use the group exchange method, which has the following advantages:

Efficient: dynamically allocates transmission bandwidth to improve bandwidth utilization;

Flexible: The group transmission unit and query, with low latency and high flexibility;

Fast: No connection required

Reliable: guaranteed by many network protocols

Of course, the disadvantages are not none:

First, there will be a certain latency when queuing; second, the information of each header will cause a certain amount of overhead.

1.4Connection Type of the Computer Network:

(1) Star (most common );

(2) bus type;

(3) ring type (common in core devices );

(4) There are also compound types. Which of the above types is integrated.

1.5Several different types of networks:

Wan (Wide Area Network), such as multinational networks;

MAN (Metropolitan Area Network) is 5 ~ 10 km;

Local Area Network (LAN), such as campus network and Enterprise Network;

Personal Area Network (PAN), for example, a wireless personal area network.

1.6Computer network performance indicators:

(1) speed;

(2) bandwidth;

(3) throughput. (the first three statements are the same, but the unit names are different)
(4) latency: it includes the transmission, transmission, processing, and queuing latency. We generally say that increasing the data transmission rate only reduces the data transmission latency;

(5) latency bandwidth product: = propagation latency * bandwidth;

(6) round-trip time RTT;

(7) utilization rate: When the utilization rate reaches a certain level, the latency will increase dramatically. Therefore, when the channel utilization rate reaches % 50 or more, you should consider resizing to increase the line bandwidth.

1.7Five-layer protocol architecture:

(1) Application Layer: the highest level of the entire system. The Application Layer directly provides services for your processes; DNS, RTP, SMTP, and HTTP

(2) Transport Layer: provides services for communication between processes in two hosts; TCP, UDP, and sctp

(3) network layer: the network layer is responsible for grouping and exchanging different hosts on the network to provide communication services;

(4) data link layer: Link Layer for short. The link layer assembles the IP data handed over by the network layer into frames and transmits the data in transparent frames on the link between two adjacent nodes;

(5) Physical Layer: Unit (BIT ). The physical layer task is transparent transmission of bit streams.

1.8Entity/protocol/service and service access point:

When studying information exchange in an open system, the entity is often used as an abstract term to represent any hardware or software process that sends or accepts information;

A protocol is a set of rules that control communication between two peer entities (or multiple entities;

Under the control of the protocol, communication between two peer entities enables the current layer to provide services at the upper layer. To implement this layer protocol, the services provided at the following layer must also be used;

A service access point is a place where two adjacent entities in the same system interact (that is, information exchange.

Study Notes: Chapter 1-Overview of computer networks