Computer network Overview

Internet
Computer network performance indicators
Network Communication
Three exchange methods
Network layered protocol model

Internet

Composition:

• Edge
  • Composed of all hosts connected to the Internet
  • It is directly used by users for data exchange (Transfer Data, audio or video) and resource sharing.
• Core
  • Function:
    • Provides connectivity to a large number of hosts at the edge of the network so that any host in the edge part can communicate with other hosts (that is, transmitting or receiving various forms of data ).
  • Key components:
    • A router is a key component of packet switching. A task is a group that receives packets. This is the most important function in the core part of the network.
  • Provided by the Internet service provider (ISP)

Level 3 computer network:

• Backbone Network
• Regional Network
• Campus Network/Enterprise Network

The most important functions that computer networks provide to users:

• Connectivity: allows Internet users to exchange information.
• Sharing: Resource Sharing (information sharing software sharing hardware sharing)

Network Architecture:

Structure:

Features:

• • Fault Tolerance
  • Scalability
  • Security
    • Network security measures include:
      • Prevent unauthorized disclosure or theft of information
      • Prevent unauthorized modification of information
      • Methods To prevent Denial of Service from achieving these goals include
    • Ensure confidentiality:
      • User Authentication
      • Data Encryption
    • Maintain communication integrity:
      • Digital Signature
    • Ensure availability:
      • Firewall
      • Redundant Network Infrastructure
      • Hardware that prevents spof

Network Division:

• By scope:
  • Wan (Wide Area Network)
  • LAN (local area network)
  • MAN (Metropolitan Area Network)
  • Personal Area Network (PAN)
• Divided by users:
  • Public Network)
  • Private Network)

Computer network performance indicators

Rate)

Defines the rate at which a host connected to a computer network transmits data over a digital channel. The unit is bit)

Bandwidth)

The ability of the network's student lines to transmit data
The definition originally refers to the frequency band width of a signal, in the unit of HEH (or qihe,, gihe, etc.). Now it refers to the "highest data rate" that a digital channel can transmit ", the Unit is "bit per second" or B/S (bit/s)

 

Throughput (throughput)

Defines the data volume of a network (or channel, interface) per unit time
Note that the throughput is limited by the bandwidth of the network or the rated rate of the network.

 

Latency (Delay)

Category:

• • Transmission latency (transmission latency)
    • When data is sent, the time required for the data block to enter the transmission media from the node, that is, the time required to send the first bit of the data frame to the last bit of the frame.
  • Propagation latency
    • The time it takes for an electromagnetic wave to spread in a channel.
  • Processing latency
    • The time it takes for the exchange node to perform some necessary processing for storage and forwarding.
  • Queue latency
    • Definition:
    • Latency experienced by group queuing in node cache queues
    • Deciding factors:
    • The length of the queue latency usually depends on the current traffic in the network.
    • Category:
    • Queue waiting for processing in the input queue
    • Waiting for processing in the output queue

Total latency:

Total latency = Sending latency + propagation latency + Processing latency

Note:

For high-speed network links, we only increase the data transmission rate rather than the bit transmission rate on the link. This increases the link bandwidth and reduces the data transmission latency.

Illustration:

 

Latency bandwidth product

Latency bandwidth product = bandwidth × propagation latency

 

Round-trip time RTT (round-trip time)

Time Value from sending data to receiving confirmation from the recipient

 

Utilization

• Channel utilization the percentage of time a channel has been used (when data passes through, the utilization rate of completely idle channels is zero, and the channel utilization rate is not higher, the better)
• The network utilization rate is the weighted average value of the channel utilization rate of the entire network.

Network Communication

Two communication methods in the network:

Client/Server mode _ C/S (Client/Server mode)

• • Definition:
    • Describes the relationship between services and services between processes.
  • Client:
    • Actively initiate communication (active) to the remote server during communication)
    • No special hardware or complicated operating systems (simple)
    • The client program address is variable (the IP address is not fixed)
  • Server:
    • Passively waiting for communication requests can simultaneously process requests from multiple remote or local customers (passively)
    • Requires strong hardware and advanced operating system support. (complex)
    • The IP address of the server program is fixed)

Peer-to-peer (P2P)

• • Connection method:
    • Both hosts run peer-to-peer connection software (P2P software), which enables equal and peer-to-peer connection communication.
  • Features:
    • The communication process does not distinguish between a service requester and a service provider. Both parties can download shared documents that the other party has stored on the hard disk.

Browser/Server _ B/S (Browser/Server mode)

• • Note:
    • With the rise of internet technology, it expands the C/S model application. In this structure, the user's work interface is implemented through the IE browser.
  • Client (also has three features of the C/S client): browser (generally no user program is required)
  • Server (also has three features of the C/S client): Web Server
  • Advantages:
    • It is distributed and can be used for query, browsing, and other business processing anytime and anywhere.
    • Business expansion is simple and convenient. You can add server functions by adding web pages.
    • The maintenance is simple and convenient. You only need to change the webpage to synchronize updates for all users.
    • Simple development and high sharing
  • Disadvantages:
    • Personalized features are significantly reduced, and personalized functional requirements cannot be achieved.
    • The operation is the most basic operation method, and cannot meet the requirements of quick operation.
    • The page is refreshed dynamically, and the response speed is significantly reduced.
    • Paging display is not possible, which puts a lot of pressure on database access.
    • It is difficult to meet special functional requirements in the traditional mode.

Internal factors that affect the success of network communication include:

• Message Size
• Message complexity
• Message importance

Communication elements:

• Three common elements:
  • Message Source
  • Channel
  • Destination Address of the message
• Message transmission method:
  • Segment-divide communication into multiple segments.
  • Multiplexing-Alternate transmission of media fragments

Network composition and connection:

Three exchange methods Circuit Switching

Features:

• • Connection-oriented
  • Low data transmission efficiency (due to the bursty nature of computer data, which leads to low utilization of communication lines)

Three phases of circuit switching:

• • Establish a connection
  • Communication
  • Release connection

Meaning of "switching" for circuit switching:

Transfer (transfer one telephone line to another to connect them)

Packet Exchange

Packet features:

• • The sender adds the first part of the data segment to form a message.
  • After receiving the packet, the receiver removes the first packet to obtain the packet.

Packet header:

• • The header of the message contains address and other control information.
  • The Node switch in the packet forwarding network forwards the packet to the next Node switch based on the address information in the received packet header.

The router processes packets:

• • Put received packets into cache (temporarily stored)
  • Find the forwarding table and find the port from which the destination address should be forwarded.
  • Forward packets to appropriate ports

Group exchange

Grouping features:

• • SenderDivides long packets into short, fixed-length data segments. Each data segment is first added to form a group. "group" is used as the data transmission unit, and each group is sent to the receiving end in turn.
  • AcceptorAfter receiving the packet, remove the first packet and restore it to the original packet.

Group header:

• • Each group header contains address and other control information.
  • The Node switch in the group exchange network forwards the group to the next Node switch based on the address information in the first part of the received group.

Vro grouping process:

• • Put the received group into cache (temporarily stored)
  • Find the forwarding table and find the port from which the destination address should be forwarded.
  • Send the group to the appropriate port for forwarding

The core part of the Internet adopts the advantages of group exchange:

• • EfficientDynamically allocates transmission bandwidth, which occupies segments for communication links
  • FlexibleGroup-based transmission unit and query route
  • FastNo need to establish a connection to send groups to other hosts
  • ReliableNetwork Protocol to ensure reliability

Problems caused by group exchange:

• • Groups need to be queued when storing and forwarding data at each node, which causes a certain latency.
  • The header that a group must carry (containing necessary control information) also causes certain overhead.

Comparison of Three Types of forwarding

 

Network layered protocol model

Name the PDU based on the protocol of the TCP/IP protocol cluster:

• Application Layer data generally refers to the PDU used by the application layer.
• Transport Layer Data Segment transport layer PDU
• Network layer packet network layer PDU
• Link layer frame network access layer PDU
• The PDU used when the physical layer bit (BIT) actually transmits data through the media

 

OSI 7-component protocol model

• Application LayerSuch as HTTP, SMTP, SNMP, FTP, telnet, sip, ssh, NFS, RTSP, XMPP, Whois, ENRP
• Presentation LayerFor example, XDR, ASN.1, SMB, AFP, and NCP
• Session LayerSuch as ASAP, TLS, ssh, ISO 8327/CCITT x.225, RPC, NETBIOS, ASP, WinSock, BSD sockets
• Transport LayerFor example, TCP, UDP, RTP, sctp, SPX, ATP, and IL
• Network LayerFor example, IP, ICMP, IGMP, IPX, BGP, OSPF, Rip, IGRP, VPN, ARP, RARP, and X.25
• Data Link LayerSuch as Ethernet, licensing ring, HDLc, frame relay, ISDN, ATM, IEEE 802.11, FDDI, PPP
• Physical LayerFor example, line, radio, and optical fiber

 

Advantages of layering:

• Each layer is independent.
• Good Flexibility
• Structure can be split
• Easy to implement and maintain
• Promote standardization

Related Concepts:

• Entity)Any hardware or software process that can send or receive information
• ProtocolA set of rules that control the communication between two peer entities (The Protocol is "horizontal" and the rule for controlling communication between peer entities. The following protocols are transparent to the service users.)
• ServiceThe service is "vertical" and is provided by the lower layer up or the upper layer to the lower layer through the interface between layers.

Protocol Model:

Packet Packaging Process

The data unit sent from TCP to IP is called TCP segment or TCP segment, and the data unit sent to the network interface layer is called IP datagram ). A bit stream transmitted over Ethernet is called a frame)

Package Splitting Process

Direct protocol relationships between different layers

Different BSD versions and their important TCP-IP Characteristics

Computer network Overview