2014 soft test programmer-frequent test knowledge point review notes [Chapter 6]

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What is the layer-7 structure of the OSI model, and the TCP/IP model structure?

OSI reference model

Data encapsulation process in OSI reference model

The following chart tries to display the positions of different TCP/IP and other protocols in the original OSI model:

7 Application layer such as HTTP, SMTP, SNMP, FTP, telnet, sip, ssh, NFS, RTSP, XMPP, Whois, ENRP

6 presentation layer such as XDR, ASN.1, SMB, AFP, and NCP

5 session layers such as ASAP, TLS, ssh, ISO 8327/CCITT x.225, RPC, NETBIOS, ASP, WinSock, BSD sockets

4. Transport Layer, such as TCP, UDP, RTP, sctp, SPX, ATP, and IL

3 network layers such as IP, ICMP, IGMP, IPX, BGP, OSPF, Rip, IGRP, VPN, ARP, RARP, and X.25

2. data link layer, such as Ethernet, Token Ring, HDLc, frame relay, ISDN, ATM, 802.11 WiFi, FDDI, and PPP

1 physical layer such as wire, radio, fiber optic, and carrier pigeon

TCP/IP Reference Model

The TCP/IP Reference Model consists of four layers: application layer, transmission layer, Network Interconnection layer, and host-to-network layer:

Layer Structure of TCP/IP Reference Model

Generally, the top layer (application layer, presentation layer, and Session Layer) of the OSI model is an application layer in a TCP/IP group. Because TCP/IP has a relatively weak Session Layer, it consists of opening and closing connections under TCP and RTP, and different applications under TCP and UDP provide different port numbers, these features can be added to a single application (or databases used by those applications. Similarly, the IP address is designed based on the idea of treating the network below it as a black box, so that it can be considered as an independent layer when discussing TCP/IP.

4 Application Layer

(Osi5 to Layer 7) such as HTTP, FTP, DNS

(For routing protocols such as BGP and rip, although they run on TCP and UDP respectively for various reasons, they can still be seen as part of the network layer)

3 Transport Layer

(Osi4 and layer 5) such as TCP, UDP, RTP, sctp

(A routing protocol such as OSPF can be considered as part of the network layer even if it runs on an IP address)

2 Network Interconnection layer

(Osi3 layer) for TCP/IP, this is an Internet Protocol (IP)

(A required protocol such as ICMP and IGMP can be considered as part of the Network Interconnection layer even though it runs on an IP address; ARP does not run on an IP address)

1 Network Interface Layer

(Osi1 and Layer 2) such as Ethernet, Wi-Fi, MPLS, etc.

Application Layer

This layer includes all protocols for working with applications to exchange application-specific data using the basic network. The application layer is the layer used by most common network-related programs to communicate with other programs through the network. The processing process at this layer is unique to the application. Data is transmitted from Network-related programs in the internal format used by the application and then encoded into the standard protocol format.

Some specific programs are considered to run on this layer. They provide services to directly support user applications. These programs and their corresponding protocols include HTTP (the Worldwide Web), FTP (file transfer), SMTP (email), SSH (secure remote login), DNS (name <-> ip address search), and many other protocols.

Once the data from the application is encoded into a standard application layer protocol, it will be transferred to the next layer of the IP stack.

At the transport layer, TCP or UDP is the most common application, and the server application is often associated with a public port number. The ports of the server application are officially allocated by internetassigned Numbers Authority (IANA). However, developers of some new protocols often choose their own port numbers. Because there are few or more server applications on the same system, there are few problems caused by port conflicts. Application Software usually allows users to forcibly specify the port number as a running parameter.

Client programs that connect to the outside usually use a random port number allocated by the system. Applications that listen to a port and then send that port to another copy of the application through the server to establish a peering connection (such as DCC File Transfer on IRC) can also use a random port, however, applications generally allow defining a specification for a specific port range to allow a port to be mapped to an internal vro that implements network address translation (NAT.

Each application layer (the top layer of the TCP/IP Reference Model) Protocol generally uses one of the two transport layer protocols: connection-oriented TCP transmission control protocol and connectionless packet transmission UDP user data packet protocol.

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