computer network
Chapter 1 Overview
1.1 computer networks have a role in the information age
1.2 Overview of the Internet
1.2.1 Network Network
Computer network link by a number of these nodes is composed of nodes and links.
Network connecting many computers together, and put a lot of Internet network connected through a router. A computer connected to the network is often referred to as the host.
Three stages of development of the Internet infrastructure 1.2.2
The first stage is the process of development of the Internet from a single network ARPANET.
It Features The second stage is to build Internet tertiary structure.
The characteristics of the third phase of the Internet is gradually formed a multi-level structure of the ISP.
1.2.3 Internet standardization
1.3 Composition of the Internet
- Edge portions
- core part
1.3.1 edge portion of the Internet
At an edge portion of the Internet is connected to all hosts on the Internet, also known as the host system side.
Communication between end-system can be divided into two categories: client - server mode (C / S mode) and peer to peer mode (P2P mode).
1. The client - server mode
2. Peer connection
1.3.2 The core part of the Internet
Play a special role in the network core part of the router. He is a dedicated computer (but not called the host). Router is the key to the realization of building a packet-switched, packet forwarding its role is to receive, which is the core part of the network's most important functions.
1. The main characteristics of the circuit-switched
2. The main features of packet switching
Packet switching is used store and forward technology. We usually single piece of data to be transmitted is called a packet. Before sending the message, the first long message is divided into a number of smaller data segments of equal length, e.g., each data segment is 1024bit. In front of each data segment, plus some control information composed of the necessary after the first part, they constitute a group. Packet also known as a "package", a packet header may also be referred to as a "header." Packet data units are transmitted in the Internet. Packet header is very important. The packet header contains important control information such as destination and source addresses, each independently selected packet in the Internet to transfer data, and is delivered to the correct end packet transmission.
1.4 Computer Development in China
1.5 computer networks category
1.5.1 the definition of computer network
1.5.2 Several different types of computer networks
1. scope classified according to the network
- WAN WAN
- MAN MAN
- LAN Local Area Network
- PAN Personal Area Network
2. classified according to the user's network
- Public network
- Private Network
3. it is used to access the Internet network users
1.6 Computer Network Performance
Performance indicators 1.6.1 computer network
1. rate
2. Bandwidth
3. Throughput
Throughput in unit time represents the actual amount of data in a network.
4. Delay
- Send delay
- Propagation delay
- Processing delay
- Queuing delay
- Delay-bandwidth product
- The RTT
- Utilization
1.6.2 Non-performance characteristics of the computer network
1.7 Computer Network Architecture
Forming a computer network architecture 1.7.1
1.7.2 agreement with the division level
1.7.3 has a five-layer protocol architecture
OSI seven-layer protocol architecture.
TCP / IP protocol is a four-layer architecture.
1. The application layer
Task application layer is accomplished by interaction between application processes specific network applications.
For example DNS, HTTP protocol, SMTP protocol, the application layer data unit is called interactive message
2. Transport Layer
Task transport layer is responsible for providing universal data transmission services in the process of communication between two hosts.
Transport layer is mainly using the following two protocols:
- --- the TCP transmission control protocol provides reliable data transmission services, connection-oriented data transfer unit is a segment
- User Datagram Protocol UDP --- provides connectionless, best effort to make data transmission services, the unit of data transmission is user datagram
3. Network Layer
The network layer is responsible for providing communications services to different hosts packet switched network. When transmitting data, segment the transport layer, network layer or user-generated data packets encapsulated into packets or a packet is transmitted. In the TCP / IP system, since the network layer using the IP protocol, and therefore also known as an IP datagram packet, or simply packet data.
4. Data Link Layer
The data link layer is often referred to as the link layer. The data link layer network layer down cross-assembled IP datagram framing, frame transmitted on the link between two adjacent nodes. Each frame comprising data and control information necessary (e.g., synchronization information, address information, error control, etc.)