Computer networks--specific protocols for each layer

• TCP/IP (transmission Control protocol/internet Protocol) has become a de facto industrial
  Standard.
  TCP/IP is synonymous with a set of protocols, and it also includes many protocols that make up the TCP/IP protocol cluster.
  TCP/IP protocol cluster is divided into four layers, IP is located in the second layer of the Protocol cluster (corresponding to the third layer of the OSI), TCP is located in the Protocol cluster
  Layer three (corresponding to the fourth layer of the OSI).
  TCP and IP are the middle two layers of TCP-IP protocol cluster, which is the core of the whole protocol cluster, which plays a connecting role.
  1. Interface Layer
  The lowest layer of TCP/IP is the interface layer, and the common interface layer protocols are:
  Ethernet 802.3, Token Ring 802.5, x., Frame Reley, HDLC, PPP and so on.
  2. Network layer
  Network layer includes: IP (Internet Protocol) protocol, ICMP (Internet Control Message Protocol)
  Control Message Protocol, ARP (address Resolution Protocol) addresses translation protocol, RARP (Reverse ARP) reverse
  Address Translation protocol.
  IP is the core of the network layer, and the next hop IP is encapsulated by routing to the interface layer. IP datagram is a no-connect service
  。
  ICMP is a supplement to the network layer and can be returned to the delivery paper. Used to detect whether the network is unobstructed.
  The ping command sends an ICMP echo packet, which is tested via echo relay.
  ARP is a forward address Resolution protocol that finds the MAC address of the corresponding host through a known IP.
  Rarp is a reverse address Resolution protocol that determines the IP address by MAC address. such as diskless workstations and DHCP services.
  3. Transport Layer
  The Transport layer protocol is mainly: TCP (transmission Control Protocol) and User Datagram Association
  UDP (User Datagram rotocol).
  TCP is a connection-oriented communication protocol that establishes a connection through a three-time handshake, which is to be removed when the communication is complete, due to TCP

• Is connection-oriented, so it can only be used for point-to-point traffic.
  TCP provides a reliable data flow service that uses the "positive acknowledgement of retransmission" technology to achieve reliable transmission
  . TCP also uses a method called "sliding window" for traffic control, so-called window actually represents the ability to receive, with
  to limit the sending speed.
  UDP is for a non-connected communication protocol, the UDP data includes the destination port number and the source port number information, because the communication does not need to
  the connection, therefore can implement the broadcast sends. The
  UDP communication does not require the receiver to confirm, is not reliable transmission, may drop packet phenomenon, actual application requirements
  in programmer programming verification. The
  4, Application layer
  Application tier is typically user-oriented. such as FTP, TELNET, DNS, SMTP, POP3. The
  FTP (file transmision Protocol) is the files Transfer protocol, generally uploads the download with the FTP service, the data port
  is 20H, the control port is 21H. The
  Telnet Service is a user remote login service, using 23H port, using the plaintext transmission, the confidentiality is poor, simple and convenient. The
  DNS (domain Name Service) is the domain name resolution service that provides conversions between domain names to IP addresses. The
  SMTP (Simple Mail Transfer Protocol) is an easy mail Transfer protocol that controls the sending of letters, medium
  .
  POP3 (Post Office Protocol 3) is the 3rd version of the Post Office protocol that is used to receive messages.
  Data format:
  Data frame: Frame header +ip packet + frame tail (frame header includes source and destination host MAC address and type, end of frame is check word)
  IP packet: IP header +tcp Data information (IP headers include source and destination host IP address, type, lifetime, etc.)
  TCP Data information: TCP headers + actual data (TCP header includes source and destination host port number, shun sequence number, confirmation number, school
  Check word, etc.)

• When it comes to networking, the OSI Reference Model, the full name of the OSI Reference Model (OSI/RM), is the Open Systems Interconnect Reference Model (open System Interconnection Reference model,osi/rm), It is a network system interconnection model proposed by ISO. Although the practical application of the OSI Reference model is not very significant, it really helps to understand the operation of the network protocol, and provides a good reference for us to learn the network protocol ...

• The physical layer specifies the mechanical, electrical, functional, and process characteristics that activate, maintain, and close communication endpoints. This layer provides a physical medium for the upper level protocol to transmit data.
  In this layer, the unit of data is called the bit (bit).
  Typical canonical representatives belonging to the physical layer definition include: Eia/tia RS-232, Eia/tia RS-449, v.35, RJ-45, etc.

  The data link layer provides reliable transmission on unreliable physical media. The functions of this layer include: Physical address addressing, data framing, flow control, data error checking, re-sending, etc.
  In this layer, the units of the data are called frames.
  The Data Link layer protocol includes: SDLC, HDLC, PPP, STP, Frame Relay, and so on.

  The network layer is responsible for routing data packets between subnets. Network layer can also realize congestion control, Internet interconnection and other functions.
  At this level, the unit of data is called a packet (packet).
  Network layer protocol representatives include: IP, IPX, RIP, OSPF, and so on.

  The transport layer is the first end-to-end, that is, the host-to-host hierarchy. The transport layer is responsible for segmenting the upper data and providing an end-to-end, reliable, or unreliable transmission. In addition, the transport layer also handles end-to-end error control and flow control issues.
  In this layer, the unit of data is called the Data segment (segment).
  The Transport Layer protocol includes: TCP, UDP, SPX, and so on.

  The session layer manages the session process between hosts, which is responsible for establishing, managing, and terminating sessions between processes. The session layer also uses the insertion of checkpoints in the data to synchronize data.
  The presentation layer transforms the upper data or information to ensure that one host application layer information can be understood by another host's application. The data transformation of the presentation layer includes data encryption, compression, format conversion, and so on.
  The application layer provides an interface for operating system or network applications to access network services.
  Application-layer protocols include: Telnet, FTP, HTTP, SNMP, etc.

Computer networks-specific protocols for each layer