Brief introduction
Network architecture
basic component
basic structure
A terminal communication device is a network entity to become a host system or the terminal , the main role is to collect end system, creating or processing data, so the end of the system can be divided into a client (client) and the server (Server), from one end to reach the other system a need to end system path, the path of the end system are connected together via a communication link (cable or radio) or a packet switch (packet switch with a common router (core network) and a link layer switch (access network)). Various small end systems are connected together by paths ISP (Internet Services Provider) maintenance.
A plurality of distributed applications within the end system to process-specific information, Application Programming Interface application rules specified application to the other end of the data exchange system. End system connected to the edge router through the access network, the edge router is an end system in a first router on the path. Common access network link with a telephone line, cable, fiber, radio.
Access Network
DSL access: transmitting terminal via a DSL modem and an analog signal through the frequency divider family, an analog signal of various frequencies transmitted by the telephone company DSLAM multiplexer into a digital signal, a digital signal via a communication network router outsiders . Upon receiving the signal router forwards the digital signals to the multiplexer, the multiplexer to a digital signal into an analog signal, an analog signal by the frequency divider and to the DSL transmission destination terminal. Network signaling and telephone signals at different frequencies transmitted through the frequency divider and a multiplexer for integration or separation.
Cable access: terminal via a cable modem digital signal to be transmitted into an analog signal, an analog signal transmitted through the coaxial cable to the fiber node the hub area, and then through a cable modem termination system to the optical transmission area (CMTS, Cable Modem Termination System, CMTS and cable headend routers), CMTS analog signals into digital signals and extraneous network traffic through a router. Hybrid fiber optic cable called hybrid fiber-coax (HFC, Hybrid Fiber Coax), the cable modem termination at the upstream and downstream HFC network into two channels, the downlink channels are typically higher than the rate of the upstream channel, the cable access characterized by a shared broadcast media, that is, people who came from a decline in long rates higher rate.
Optical Access: Active Optical Network (AON, Active Optical Network, an optical fiber from the local central office to single-family) and passive optical network (PON, Passive Optical Network, the central office by optical fiber dispenser to households). End systems through the router and the digital signals into analog optical signals through an optical network termination (ONT, Optical Network Termination), an optical fiber dispenser analog signal to the central office optical line terminator (OLT, Optical Line Termination) , OLT then the analog signals into digital signals.
Ethernet access: terminal directly connected by twisted-pair copper wire and an Ethernet switch
LAN access: via the LAN router connecting the user with the edge
WIFI Wireless Access: WLAN
Wide area radio access: a base station based on radio technology
Physical Media
Navigation data is divided into physical media flow guiding-type media and non-media type diffusion propagation guide.
Twisted-pair copper wire. Coaxial cable. optical fiber. Terrestrial radio channel. Satellite radio channel.
ISP
One Global bearer ISP ISP access all areas. A plurality of global areas bearing the respective ISP access ISP. ISP-layer access to the respective regions divided region. Regional or interregional rely on a point, multi-host, peer, the IXP composition of a more complex structure.
POP point of presence is a group of multiple vendor network routers at the same level position composed of high-speed links can be rented by POP. Multihoming is a plurality of access regions ISP supplier, or to enhance the disaster recovery capability. On the other is at the same hierarchical level ISP can be directly transmitted to each other without the need for traffic flow superior ISP, the ISP does not peer top billing each other. IXP can access multiple regions ISP and have them co-equal. Content provider network is a large local area network structure, through a global distribution and direct access to the underlying server and ISP to access multiple network IXP may reduce the fees paid to the top-level suppliers.
Data Exchange
Packet switching
Source end system packet and the packet will be assigned for each segment plus the header byte of the data blocks to form smaller, called packet Packet . End of the incoming packet from the router, and then forwarded by the router to another communication link, forwarding paths differ between different networks. Usually, the router will automatically configure a forwarding based on routing protocol, save the available neighboring routers. Packet switching provides better broadband sharing simple, effective and low cost, but is not suitable for real-time services.
Packet switch at the input end of a link using store and forward transmission mechanism, i.e. the switch must receive a complete packet before the first bits of a packet to the output link transmissions. After the completion of receiving packets, the packet switch examines the packet header first need to determine which output port from forwarding, this is called the delay processing delay Processing Delay Nodal . After the incoming packet switch the packet, if the output link is a transmission of other packets, the arrival of the switch need to be queued, this delay is called queuing delay Delay Queue . The packet switch of each link connected to provide an output buffer Buffer Output , if the output buffer filled packets or packets arriving in the queue is discarded, this phenomenon is referred to as a packet loss pocket lost or packet loss . Packet incoming link to the first bit of the last bit time of the incoming link needs referred propagation delay Delay Transmission . The first bit of the packet from the incoming link to a next packet arrival time called switch requires propagation delay Delay propagation .
High-speed router processing delay is typically of magnitude of microseconds or less, depending on the degree of congestion queuing delay in practice is usually on the order of milliseconds or subtle, depending on the output of the delay link transmission rate and the packet length is usually micro ms Pulp link delay for the order of seconds greater propagation delay depending on the length of the link and physical medium is typically a few milliseconds to hundreds of milliseconds subtle. Transmission delay is the source starts sending data to the transmission medium, transmission medium reception completion time required, the time packet switch is typically required to launch the packet, which is a function of the packet length and the link transmission rate. Propagation delay spread is a packet switch to another packet switch time required, which is a function of the distance between two routers. Delay is the sum of the above four nodes Nodal overall delay Delay Total . Certain other service agreements also set the delay.
Assume that the packet length L, the incoming packet switch average rate of a, packet switch link transmission rate is R, the ratio La / R is called traffic intensity , the queuing delay will be infinite if the traffic intensity is greater than 1, so the flow engineering need to control the traffic intensity. For the traffic intensity is less than 1, if the (L / R) n n packets arrive simultaneously at the second, the n-th packet queuing delay (n-1) L / R in.
For a number of packets for the packet P is, if the packet size is L bit transfer rate of the link number R N, the total of the total transmission delay including other packet before the last time a packet transmission delay and packet end of the last the total transmission delay (ignoring propagation delay) side, i.e., transmission delay as: (P-1 + N) (L / R)
Circuit Switched
And during the call ends before the system will remain connected to establish and maintain a connection status and cache set aside for that connection or constant transmission rate, such stable connection is called a circuit . Circuit switched real time and rate stability but have a silent period occupying idle network.
A communication link may have a plurality of circuit, dividing circuit embodiment is referred multiplexing, there are frequency division multiplexed (FDM, Frequency Division Multiplexing) and time division multiplexing (TDM, Time Division Multiplexing). Band telephone networks typically 4kHz, this band is called bandwidth. Time division multiplexing, the link is first segmented into a different frame, the frame is subdivided into different time slots in each frame of a circuit composed of a particular time slot, the transmission rate of the circuit is equal to the frame rate multiplied by the number of bits within the slot .
For circuit-switched, first need to create a time circuit, followed by the transmission time required, final consideration propagation time, generally, the transmission rate is equal to the file size divided by the transmission rate of the circuit.
Throughput
Certain bit size transmission-end document spent some time, the average transfer rate of the average throughput throughput Average , the instantaneous rate is the instantaneous throughput. Throughput depends on the path bottleneck link, for connecting a plurality of links having a shared throughput averaging a single connection, therefore, shares the flow link interference can affect throughput.
Hierarchical model
Since packets can not be transmitted directly to the physical medium, the transmission medium is required division multiple functions, and then to divide the entire network hierarchy may, in accordance with the data transmission unit may choose to use different types at different levels in accordance with the same functionality as network transmission. For layered structure, each layer having a different task or function, the upper layer used as a lower layer service, changing the implementation of the rules will not affect the levels of other components within the system without affecting the case where a predetermined input and output rules. However, the actual implementation of the hierarchical level may be the underlying functional redundancy, wherein a layer function relies on data of other layers to achieve.
protocol
It is a standard protocol, the network protocol rules data exchange network, standard or convention, to define and control the message syntax, semantics, and the sequence of events for exchanging data between two or more communication entities.
Called layered protocol stack, according to an Internet application layer, transport layer, network layer, data link layer, the physical layer is divided, OSI seven layer reference model is also divided into an application layer the application layer, presentation layer, session layer.
OSI Reference Model
Application Layer Application exchanged between the application responsible for the form of data, application software and provides an interface provided to set the communication between the other software applications. Data type (group) is referred to as the application layer packets Message .
DHCP DNS FTP Gopher HTTP HTTPS IMAP4 IRC NNTP XMPP POP3 SIP SMTP SNMP · SSH · TELNET · RPC · RTCP · RTP ·RTSP · SDP · SOAP · GTP · STUN · NTP · SSDP
Presentation The presentation layer converts the data format compatible with the recipient's system and a format suitable for transmission, even if the application can interpret the meaning of exchanging data, including data compression, data encryption, data description.
Session session layer is responsible for setting up and maintaining a communication connection between two computers in the computer network data transmission, a synchronous data exchange and delimitation functions, including checkpoint and recovery programs.
Transport the transport layer to provide data exchange between the application endpoints, embodied as the transmission header (TH) is added to the data to form a packet, the header contains the transmission protocol used for transmitting information. It referred to the transport layer packet segment segment .
TCP · UDP · TLS · DCCP · SCTP RSVP · PPTP
Network layer network provides data exchange between the host determines the routing and forwarding of data, which the network header (NH) was added to a packet, to form a packet, the network header includes a data network. It referred to as a data packet network layer datagrams datagram or packet Packet
IP (IPv4 · IPv6) · ICMP · ICMPv6 · IGMP · IS-IS · IPsec · BGP · RIP · OSPF
Data Link Layer Data link between the network layer is responsible for routing data switching node for network addressing, error detection and error correction. When the header and tail to be added to the data packet, it forms a frame. Data list head (DLH) a method comprising physical address and the error detection and error correction. Data end of the list (the DLT) is a string of data indicating the end of a string of packets. There may be a plurality of links of different physical media path, i.e., a packet may pass through different data link layer protocols of different services. Link layer packet called a frame Frame .
Wi-Fi (IEEE 802.11) · WiMAX (IEEE 802.16) · ARP · RARP · ATM · DTM · · the FDDI token ring Ethernet · · FR · GPRS · EVDO · HSPA · HDLC · PPP · L2TP · ISDN · STP
Physical physical layer data exchange between the nodes responsible for the frame bit to a next node, which is responsible for managing the intercommunication between the computer and the communication network media device. It includes pins, voltages, cable specifications, hubs, repeaters, network card, the host adapter. Data Unit Bit of
· · Ethernet modem line communication (PLC) · SONET / SDH · G.709 · · twisted fiber-coax
Package
After the outgoing message, the additional layer is converted and feature information (header field) when the transfer layer by layer, since the application layer is attached on top of the header field, the physical layer is the basic unit for processing a data transmission at the bottom there is no extra information. Remaining data header field is removed is called a payload field for storing the packet layer. The transport layer header field contains specific information allows a receiver to transmit transport layer of a particular application. The network layer header information field contains the address of the source end system, and the like. In addition to the link layer header field as well as a tail field, see the data link layer.
Other models
TCP / IP four-layer model application layer, presentation layer, session layer to a uniform application layer, data link layer and the physical layer network interface layer is a uniform, but actually defines the protocol of the network interface layer, the whole mainstream the network is divided into five layers.
Application layer
Principle agreement
Brief introduction
Service target application is an application layer, application of rules for exchanging data between defined, without the need to achieve further additional communication lines between the end system concerned. For multiple end systems to exchange data, there are currently two main interactive data structure, CS architecture in the form of one to many, not direct communication between the client, in order to enhance service capacity CS architecture will build a large number of host configuration the data center. P2P architecture in the form of many to many, or the server does not rely on small, the client is also a server, referred to as a peer, data is transferred directly between the host user, does not require such a large structure is not only the server device and the bandwidth, but also through data distribution services to enhance the capacity of the entire system.
By application process communication process through the socket (Socket) interface to a network software to send and receive packets, the socket is an interface between the application layer and the transport layer, also referred to as API. Between the host addressed via IP implementation, addressing inter-process implemented by the port number. The application must specify a particular transport protocol to exchange data in the form of a carrier and certain service match the application requirements, the reliability of the data service used, throughput requirements, transmission timing, security.
service
TCP is a reliable connection-oriented data transmission services, generally used for e-mail, file transfer, remote host access, Web and file transfer and other financial services deliver data-intensive applications. UDP is not connection-oriented and unreliable, and the like commonly used in multimedia applications tolerate data loss.
For certain bandwidth-sensitive applications, it is necessary to ensure that the transport layer can be specified transmission throughput, typically bandwidth-intensive multimedia applications, and e-mail, file transfer, the Web application may be adaptively transmitting elastic current throughput.
For interactive real-time applications such as VoIP, virtual environment, multi-games, need to ensure that the source side injection applied socket end bit reaches the receiving socket of the bit time is not less than a certain value in order to ensure the validity of the data transmission.
For some confidentiality services, all data transport layer encryption sending process and delivered to the receiving process to decrypt the data before the data. In addition, data integrity, and port identification also belong to the security services. Whether TCP or UDP, both before and after the transmission is not encrypted, implements the Secure Sockets SSL at the application layer, it can strengthen the TCP, provide encryption, data integrity, authentication port services.
TCP provides reliable and secure data transmission, but the TCP or UDP are currently no service designed to provide bandwidth or timing.
definition
We need to implement an application layer protocol defines the following rules: the packet switching type, semantics, and transmits the response message packet types of syntax rules, field.
The most common network application services are HTTP-based Web services, FTP-based file transfer services, SMTP-based e-mail service, DNS-based directory service, P2P sharing services.
HTTP protocol
World Wide Web is the most widely used Web, Web feature is the flexibility to transfer all types of files. Web application layer protocol is HTTP Hypertext Transfer Protocol, HTTP defines message structure client and server exchange messages and exchange ways, Web page file object through URL address, URL by two parts, the server the path name of the host name and an object. HTTP protocol uses TCP as the support, prior to the need to establish a connection request, the data transmission can be reliably transmitted to the terminal, the terminal does not save the status of the request information, the stateless protocol HTTP belongs.
For applications requiring multiple requests, each request if using different TCP connections called non-persistent connection, if the same TCP connection is called a persistent connection for connection provided by default, but can be configured using non-persistent connection. Non-persistent connection may be configured as a serial or parallel, using parallel can reduce the response time. HTTP request connection before the setup process for the host sends a small TCP segment to the server asks, and then a small server TCP segment response, the host server again officially HTTP request, the server is the official response. Define round trip time (RTT Round-Trip Time) comprises a processing delay, queuing delay, propagation delay, then a single HTTP request, and comprising two end RRT transmission time. Visible, non-persistent connections not only increased the burden on the server also increases the delivery delay. Typically, HTTP persistent connection and configuration using a timeout interval, if the access time is not disconnected.
Message format
The first action request message request line , the successor of the line is called the header row , the request line consists of three fields: the method field, URL field, HTTP protocol version field. Blank lines request line and the subsequent entity body (entity body) partition. Common header row has indicated host Host, Connection if the connection is closed after the required request, User-agent specified in the client browser type, Accept-language represents the response language version desired.
The first line of the response packet is the initial state of the line, is the first portion of the subsequent row, then the entity body, the status line includes three fields: a protocol version field, a status code, state information.
| method | effect |
|---|---|
| GET | Request page information specified, and returns the entity body |
| HEAD | Get no response is similar to the specific content, for obtaining the header |
| POST | Submitting data to the processing request specified resource (e.g., file submission form or upload) the data contained in the request body, or to modify a resource may lead to the establishment |
| PUT | Replace specific content of the document data transmitted to the client from the server |
| DELETE | Requests the server to delete the specified page |
| CONNECT | Reserved for connecting the pipe to a proxy server |
| OPTIONS | It allows the client to view server performance |
| TRACE | Echo server receives a request for testing or diagnosis |
| PATCH | Applied to modify resources |
Uniform resource identifier (Uniform Resource Identifiers, URI) that identifies the resource, Uniform Resource Locator (Uniform Resource Locator, URL) is commonly used URI. URL syntax is protocol: Protocol : // Authority : Port path Query the fragment
Interaction Management
cookie to record the user's access status, cookie technology component: in response cookie header line of the body, cookie request header packets line, cookie management client, server database. For the first time in response to the request and returns the cookie stored in the database server, follow-up visits will carry cookie cookie to query the database and management response.
session mechanism used to hold the server-side solution. As a result of the server to maintain state program on the client also needs to save a logo, so session cookie mechanisms may need the help of mechanisms to achieve the purpose of preservation of identity. Sometimes Cookie was artificially prohibited, so there are other mechanisms in order to still be able to transfer back to the server when SessionID Cookie is disabled. This technique is called URL rewriting, the SessionID is directly appended to the URL path, there are two additional ways, one is the additional information as a URL path, the other is as a query string appended to the URL.
For the session, unless the program notifies the server to delete a session, otherwise the server will remain. Due to close your browser does not result in session is deleted, forcing the server to set up a time to failure seesion, when a session using the distance on the client expiration time longer than this, the server can assume that the client has ceased its activities, will the session deleted to save storage space.
Buffer
Represents the initial buffer is Web server to satisfy the request of the network entity located between the client and the origin server, the client's request will be cached in the cache, the subsequent direct access to return if the access request is not cached original server. Buffer may reduce the response time and reduce network traffic applications to enhance performance. CDN content distribution network CDN company formed to make a lot of traffic by installing a large number of localized buffer.
When a cache requests cached object to the initial server, the response information typically comprise Last-modify header row, when the subsequent user request, the buffer will be judged whether the cached object up to date requested object original server via If-modify-since header row If yes, the initial server returns to the buffer 304 Not Modified response to tell the cache buffer may be returned to the user objects.
FTP
FTP control using parallel transfer files and data connections, control connections for transmitting control information between the host, such as a user ID, password, directory file manipulation commands, data connections actually used for file transfer. FTP is stateful, the server needs to bind user accounts and control connections, need to track the user's current directory location.
Separate control information is called band transmission , such as FTP, file control information together with the information referred to in-band transmission , such as HTTP.
DNS
DNS (Domain Name System) domain names and IP addresses for conversion to assembly: DNS distributed database, query on the application layer protocol, a port number 53.
Transport Layer
The transport layer implemented in the end system is provided for a process on the source end system logical communication , transport application layer packets are partitioned into small pieces and add header to generate a transport storage segment transport layer segment. Transport layer is located above the network layer, the network layer provides logical communication service, the transport layer, network layer between the host by impact. Network layer protocol IP networking, IP service model is a best-effort delivery, does not guarantee the integrity of the service, that is not reliable services.
Basic duty transport layer is a multiplexing and demultiplexing, multiplexing refers to the source of data on different sockets encapsulation header information generation segment and passed to the network layer. Demultiplexing is to segment the package delivered to the correct socket.
When lightweight UDP transport protocol, connectionless no handshake procedure, does not guarantee data reliability, no congestion control. UDP packets carrying the destination IP tuple identifier and destination port number, destination port for orienting the destination host.
TCP connection-oriented, reliable data transmission service, for preparation before connection for transmission, reliable transmission is intended to ensure that the value is not lost bytes or redundancy. TCP congestion control can suppress the equality of sending process when the network is congested. Unlike UDP, TCP source through the IP, source port, the purpose of the IP, the destination port quad, not only the orientation of the destination port also identifies the source port.
Network layer
Core network layer routing and packet forwarding, to choose the best path routing in all routers, packet forwarding path for packet transmission.