Study on the computer network knowledge point of "Garry the School Recruit"--android Foundation Series (II.)

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Well, there is nothing to complain about, continue to cheer up yourself ~, not learn not, can understand, but let blind spots! Absolutely cannot tolerate, is oneself gas to (cheers too much), hahaha, oneself gas oneself, I am really lovely ~ ~, do not say nonsense. (Recommended search problem Direct CTRL +f)

The following content for each road Daniel provide, I just a Daniel's Porter ~ ~, do a summary, convenient for everyone to find. (Of course, Garry I also need to read books, recommended books: Computer network (Shehiren)), the process of acquisition is not complete at once, Garry also did not fully thoroughly understand these knowledge, just as a share, and their own turn to see the use, must read more AH ~!

1. What is the difference between circuit switching and packet switching? Comparison of pros and cons.

A: The difference: circuit switching means that a dedicated physical connection is established between two sites (end devices), and the network must retain the Exchange capacity and channel capacity for the connected circuit. Therefore, the channel is exclusive and cannot be used for other connections even if it is not used before disconnecting. The packet interchange divides the data into variable-length groupings and sends groupings of the same or different paths to the destination station. The links between the nodes in the network can be shared between different virtual circuits or packets destined for different destination addresses.

Comparison: Here we expand into: a number of aspects compared circuit switching, message exchange and packet switching the main advantages and disadvantages

Answer: (1) Advantages of circuit switching: Two users always occupy end-to-end communication resources during a call. Cons: Very low line transfer efficiency user-occupied communication lines most of the time is idle, resources are not used and consumption (2) packet switching advantages: High exchange rate data transmission efficiency is very efficient, flexible and fast. Cons: cause delay, overhead

(3) Message Exchange advantages: Users can send messages at any time, reliability, easy to find code conversion and rate matching, while sending multiple destination address, priority message priority conversion, high communication line utilization. Cons: Longer latency.2. OSI layer Seven protocol, to be able to draw out, to understand the role of each layer

This is a very common test, to understand the OSI seven layer model, the basic knowledge of linking the OSI seven layer model and the common application of each layer, we need to take time to study through rather than just know. (Garry: Oh! ）

In summary, it is:

1th -transmission of raw bitstream (bit: bit)
2nd layer Data link Layer -This layer frames the data and handles flow control. This layer specifies the topology and provides hardware addressing        (frame: frame)
Layer 3rd Network layer -This layer establishes a connection between two nodes through addressing, which includes routing and relaying data through an interconnected network          (Packet: Package)
4th -general data Delivery-connection-oriented or no connection. Includes full-or half-duplex, flow control, and error recovery services          (data segment: Segment)
5th level Span style= "Color:rgb (255,0,0)" > Session layer -establishes an end connection between two nodes. This service includes establishing whether the connection is set in full or half-duplex, although you can handle duplex mode in Layer 4
6th -formatted data, To provide a common interface for your application. This can include cryptographic service  
7th Application layer -services directly to the application, which can vary, but include electronic message transmission

Common applications across layers (from high to low):

The application layer ....... ...... Computers: Applications, such as Ftp,smtp,http
The presentation layer ....... ...... Computer: Encoding method, image codec, URL field transfer code
The session layer ....... ...... Computer: Set up sessions, session authentication, breakpoint continuation
The transport layer ........ ..... Computers: Processes and ports
The network layer ..... ........ Network: Routers, firewalls, multilayer switches
Data link layer .... ..... Networking: network cards, bridges, switches
The physical layer ..... ........ Networks: Repeaters, hubs, network cables, hubs

Application summary of each layer: the first layer to the third layer, belonging to the lower level, and mobile data related, are in the network ; IV to seventh, high level, including application data ;

3.TCP/IPwhich layers, can draw a graph, know all the role of the number of layers, will enumerate the main protocol name.

Uh, pack 13, watch the spray on me, below (feel dead.) ）

The TCP/IP protocol is organized into four conceptual layers, with three layers corresponding to the corresponding layers in the ISO reference model. The ICP/IP protocol family does not contain the physical layer and the data link layer, so it cannot complete the function of the whole computer network system independently, and must work in conjunction with many other protocols.

Table 1-1 is the TCP/IP four-tier model and the OSI seven-tier model counterpart table. We mapped the OSI layer Seven Network model to the Linux TCP/IP four layer conceptual model, and then categorized the various network protocols.

Table 1-1 TCP/IP four-tier model and OSI seven-tier model correspondence table

OSI Layer Seven Network model	Linux TCP/IP four-layer conceptual model	Corresponding network protocol
Application Layer (application)	Application Layer	TFTP, FTP, NFS, WAIS
Presentation Layer (Presentation)		Telnet, Rlogin, SNMP, Gopher
Conversation Layer (session)		SMTP, DNS
Transport Layer (Transport)	Transport Layer	TCP, UDP
Networking Layer (Network)	Internet Layer	IP, ICMP, ARP, RARP, AKP, UUCP
Data Link Layer	Network interface	FDDI, Ethernet, Arpanet, PDN, SLIP, PPP
Physical Layer (physical)		IEEE 802.1A, IEEE 802.2 to IEEE 802.11

Summary: TCP/IP Total four: 1. Network interface 2. Internetwork Layer 3. Transport Layer 4. Application Layer

The role of each layer, too many words attached link: I am the Portal ~

4.Computer network architecture? A: A word-----The computer network is a collection of hierarchical structures and protocols. 5. The concept and function of the hardware (MAC) address. concept: The MAC address is the address used on the media access layer, also called the physical address, hardware address, or link address, which is cured in the adapter ROM. The visible MAC address is actually the adapter address or adapter identifier. When a computer uses an adapter, the identifier on the adapter becomes the MAC address of the computer. The MAC address length is 6 bytes (48 bits) and is managed by the IEEE Registration management structure RA.

Function: The MAC address is a unique identifier of the computer, and in the data link layer, the switch transmits the packet by identifying the MAC address.

6.Data Link Layer Interconnect device

A: (1) Bridge: Interconnect two with different Data Link layer protocol, different transmission media and different transmission rate of the network, the Network Bridge interconnection in the data link layer above the same protocol.

(2) The switch implements the interconnection storage and forwarding device on the data link layer. The switch corresponds to the MAC address of each package in relatively simple decision information forwarding, the switch corresponding to the hardware device, the bridge corresponding software.

7.EthernetMACframe format?

For:

Destination Address (6 bytes)

Source Address (6 bytes)

Type (2 bytes)

Data (+-- -bytes)

FCS(4 bytes)

8. Virtual LANVLAN？

A: (1)VLAN is only a kind of service provided by LAN to users, not a new local area network. VLANs Limit the number of workstations that receive broadcast messages, so that the network does not cause performance degradation due to the propagation of too much broadcast information (that is, broadcast storms).

(2) method of dividing VLAN : Port based, MAC address based, IP address.

    (3 ) vlan frame format

Destination Address (6 bytes)

Source Address (6 bytes)

VLAN tag (indicates which VLAN the station belongs to)

Type (2 bytes)

Data (+-- -bytes)

FCS(4 bytes)

9. What is the difference between switching and routing?VLANWhat are the characteristics?

A: Switching refers to the forwarding and filtering of frames, which is the work of the switch, which is in the second layer of the OSI Reference Model, and routing refers to the non-direct link in the network line, which is the work of the router in the third layer of the OSI Reference Model. Switching and routing are many differences, first of all, the exchange is not required IP address, and routing needs, because the IP is the third layer of protocol, the second layer needs the MAC address, and then, the second layer of technology and the third layer of the different, the second layer can do VLAN, port bundle, and the third layer can do nat,acl, QoS, and so on.
VLAN is the abbreviation of virtual LAN, it is a pure two-layer technology, it has three characteristics: control broadcasting, security, flexibility and extensibility.

.What is Rarp??

Answer: The Reverse Address Resolution Protocol, the role is to complete the hardware address to the IP address mapping, mainly used for diskless workstations, because the diskless workstation configured IP address can not be saved. Workflow: Configure a RARP server in the network, which holds the mapping relationship between the IP address and the MAC address, when the diskless workstation starts, encapsulates a RARP packet, has its MAC address, and then broadcasts to the network, when the server receives the request packet, The IP address of the corresponding MAC address is loaded into the response message and sent back to the requestor. Because a broadcast request message is required, the RARP can only be used for networks with broadcast capability.

What is the purpose and algorithm of the ARP protocol, and at which level is ARP used?

The purpose of the ARP protocol: To solve the problem of mapping the IP address and MAC address of the host or router in the same LAN.

Algorithm: In the host's ARP cache should hold a map from the IP address to the MAC address, and this mapping table is also frequently updated dynamically (new or time-out delete).

ARP is used at the network layer.

CRC redundancy Check algorithm, anti-code and test algorithm. Basic principle:

A data block is known to contain K bits of data block, the transmitter produces a sequence containing n bits, this sequence is called the frame Test sequence (FCS), the FCS is added to the data block after the formation of a k+n-containing transmission frame t, so that T can be divisible by a known quantity p, the receiver to divide the received frame by P, no remainder, It is considered that there is no error.

Basic algorithm: Modulo 2 algorithm, polynomial.

Paste in more detail Daniel Blog: I am a cow 1 I am a cow 2

13. How to achieve transparent transmission. Basic concepts of transparent transmission:
① data transparent transmission is the user is not subject to any restrictions in the protocol, can randomly transmit arbitrary bits of encoded information
② users can completely avoid having to know the bit encoding or other control characters of the end segment specified in the protocol, thus unrestricted transmission.
Data Transparent transmission technology:
① Escape Character Fill method
② 0-bit filling method
③ uses a special signal and coding method: IEEE802.3 (due to the use of CSMA/CD protocol, there is no end word string; IEEE802.4 (token bus, end delimiter sd/in start delimiter ed these two fields are used for analog encoding instead of 0 and 1) ; IEEE802.5 (token Ring, illegal Manchester code)
④ determination length method, fixed data segment length method: The length of each control field is fixed, the data section length is also fixed, so there is no need to set the terminator in the frame format, and do not have to set the data length field.14. What the routing table does. A: Destination address (Destination): Used to identify the IP packet destination address or destination network. The netmask, the output interface (Interface, some routes have multiple interfaces), and the next-hop IP address (nexthop).15. Packet forwarding algorithm.

(1) First extract the IP address D of the destination host from the IP datagram header, and obtain the network n where it resides.
(2) If n is a network directly connected to this router, it will be delivered directly without having to go through another router
Forward and deliver the datagram directly to the destination host. Otherwise it will be executed (3)
(3) If the routing table has a specific host route with Destination D, the datagram is passed to the next hop router indicated in the routing table. otherwise execution (4)
(4) If the routing table has a route to reach network N, the datagram is passed to the next hop router indicated in the routing table. otherwise execution (5)
(5) If there is a default route in the routing table, the datagram is passed to the default router as indicated by the default route. otherwise execution (6)
(6) Error reporting forwarding packet.

The above reference from: "Computer network fifth edition" Shehiren p128

.IPThe format of the message, the meaning of each field of the format to be understood.

http://blog.csdn.net/xieyutian1990/article/details/24179181

(The blogger will help you here, other self-care ~)

The concept of TCP and UDP, the difference between the pros and cons. The format of the TCP message, the meaning of the field. 19.TCP What measures are adopted to ensure reliable transmission? 20. Three-time handshake, four-time disconnection process. 21. Blocking mode and non-blocking mode, blocking connect and non-blocking connect. (more difficult, interested to understand) 22. HTTP basic format. (Java programmer must master)

Study on the computer network knowledge point of "Garry the School Recruit"--android Foundation Series (II.)