Chapter One
1. What is a computer network?
The computer network is a collection of interconnected computers, autonomy
Autonomous: a computer system independently of one another, or master-slave relationship with the control of the control does not exist
Interconnection: link using a communication line, connected to each other independent computer system
2. What are the three elements of the network protocol that? What is the meaning of each element?
Syntax: configuration information exchange format between the entities defined
Semantics: time information exchange definition entities that specific meaning information transmission control information, information, control information for a different meaning, how the information receiving terminal in response to
Sequence: sequence for exchanging information between the entities defined, and how to match the speed or adapted to one another, also referred to as synchronization.
3. What is the function of the computer network?
Rapid exchange of information between different hosts.
Software and hardware resource sharing, sharing of information resources
4. Press coverage of the network division, mainly to the types of computer networks? What are the characteristics?
Personal Area Network: network type proposed by the rapid development of portable mobile
LAN: deploy in the office, office buildings, campus area
MAN: covering a city network
WAN: across a larger geographical space, but to achieve remote interconnection
5. Press the topology of the network division, mainly to the types of computer networks? What are the characteristics?
1. Star: used for local area networks, personal area network.
Pros: has monitoring and management, fault diagnosis and isolation is easy
Disadvantages: the central node is the network bottleneck in case of failure paralyzed the whole network, limited to the size of the central node port number
2. Tree: bus or star-shaped expansion
Advantages: easy to extend, easy fault isolation
Disadvantages: root demanding
3. bus: using the broadcast channel as a common transmission medium, all nodes are connected to the bus Korea, via the communication bus.
Advantages: simple structure, a small number of cables required, easy to expand
Disadvantage: the limited range of communication, fault diagnosis and isolation is difficult, prone to conflict
4. Mesh: a node with a plurality of nodes are connected to a link, called full mesh topology, mesh topology or a non-fully
Advantages: reliable, one or more link fails, the network can still Unicom.
Disadvantages: complex structure, high cost costs
The annular: using a communication link to all nodes connected into a closed loop, and a common local area network MAN.
Advantages: the desired cable length is short, the optical fiber may be used, easy to avoid conflict
Disadvantages: easily lead to a node failure the entire network paralysis, a new node is added and the withdrawal of trouble, there is a latency problem.
6. Mixed: a simple mixing together of two or more topologies
Advantages: easy to expand, can build networks of different sizes
Disadvantages: complex structure, management and maintenance of complex
6. Computer network architecture which includes several parts? What are the main functions of each part?
1. Network edge: to provide network application services for network users
2. Access Network: network-centric and implement computer links
3. Core network: the network data between the relay and the forward edge of the host (using data exchange)
7. Briefly describe your understanding of access networks, which are what are the characteristics? Often used is the kind of network?
1. Access telephone number: using the telephone network;
A digital signal modulated by the modem to an analog telephone line, as a carrier by an analog voice signal transmitted to the distal end of the telephone network, using a modem and then demodulate the digital signal from the analog signal.
2.ADSL Asymmetric Digital Subscriber Line: based on frequency division multiplexing to achieve telephone voice communication with the digital communication;
Share a subscriber line, a communication network can be telephone voice communications at the same time.
Asymmetric: upstream bandwidth is achieved because the subscriber line smaller than offline
3.HFC Hybrid Fiber Coax: CATV networks network access
Based on the frequency division multiplexing technique
Asymmetric: less upstream bandwidth than downstream bandwidth
4. LAN: Hey all hosts connected to external networks needs to access, via the core network connected to the enterprise edge router.
The mobile access network: using a mobile communication network
Commonly used are:
ADSL, HFC access networks, and mobile
8. DESCRIPTION circuit switched and circuit switched during operation characteristics
Process: establishing circuit - data transmission - removal circuit
Advantages: high embodiment, a small delay and jitter
Disadvantages: the burst data transmission, a channel utilization is low, a transmission rate of a single
9. What is packet switching? What is packet switching? Excellent comparison between the two slightly
1. The packet switching: the address information of the sender and receiving host sending additional transmission and other control information, then the unit of packet switched network between the nodes stored - transmitted forward manner until the service object host.
2. The packet switching: the data to be transmitted into smaller data blocks, each data block an additional address, serial number and other control information, and data packets, each independent transmission destination, receiving the packets arriving reassembled packets reduction .
3. packets advantages:
Switching equipment require low storage capacity
Switching speed
Reliable transmission of high efficiency
More equitable
10.OSI reference model that includes several layers? What each main function is?
Layer 7
Are: physical, link, network, transport, session, presentation, application
11.TCP / IP reference model consists of several layers? Each layer includes those agreements?
4th floor
Network Interface Layer:
Network interconnection layer: BGP / OSPF / RIP / IGMP
Transport Layer: TCP / UDP
Application Layer: HTTP, FTP, SMTP, POP3
12.
dc、dq、dt=L/R、dp=D/V
Skip time: dh = dc + dq + dt + dp
Delay bandwidth product: G = dp * R (bandwidth)
First, to distinguish between propagation delay and transmission
Transmission delay: transmitting data to the conveyor belt
Propagation delay: the time to send data to each other
13. Throughput -Thr: unit time from the source host to the destination host data amount reaches
Measure the actual transmission capacity
Chapter two
1. Application of computer network applications can be divided into several types of what architecture? What type is characterized by a variety of applications?
C / S structure: intended to be a communication between the client and server, the client does not communicate directly with the customer
Pure P2P structure: not always online server, between any end systems / nodes may communicate directly, highly scalable, difficult to manage
Mixed structure: the presence of both the central server, but also direct communication between the end peers
2. Why is client-server communication is the fundamental way applications communicate with the network?
Clients are active party initiating communication, passive receiving communications server, communications server must be able to run up and ready to communicate.
3. The application communication network, you need that information to identify an application process?
IP address, socket bound to port
4. Description of the hierarchy is the Domain Name System
Top-level domain nTLD
Generic top-level domain name to the gTLD
Infrastructure domain: arpa
5. Give an example of what is a recursive DNS resolution process? What is DNS iterative resolution process?
Recursive: the domain name resolution tasks to the contacted server
Iteration: DNS server name is returned query server
Popular talk is I do not know this person, but you can ask other people
6. What is the local domain name server? How to determine the host is the local name server?
7. HTTP1.0 get a brief reference to the communication process 10 small JPEG images of webpages
HTTP client process to the server port (such as 80) to establish a TCP connection request
HTTP client process sends a TCP connection is established to the server a HTTP request packet, the packet contains the path name / cs / .html
8. What is non-persistent HTTP? What is non-persistent HTTP pipelining is? What are persistent HTTP pipelining is? Brief interaction.
Non-persistent divided into: series, parallel
Connected in series: the request object, every time a new TCP connection is established, there are several established several pictures
Parallel connection: request to establish a TCP connection, there are a few pictures while establishing several connections, one-time to complete
Persistent connection is divided into: non-water way, water way
1) The minimum time: when a local DNS server contains the URL you want to access the corresponding IP address, the time required to a minimum, as RTTd.
The maximum time: When the local domain name resolver does not contain the required time and the longest time required parsing the root name server, resolve the path as follows: client - the local domain name server, the local domain name server - root name server, the local domain name server -com .cn, cn-com, the local domain name server - authoritative name server, so the time is 5RTTd.
2) the need html file itself plus the eight small picture connection. Time includes initiating a TCP connection is established RTTh, HTTP request transmission process of a Web object round trip time RTTh. A total of 2 * (8 + 1) = 18 RTTh
3) the beginning of a TCP connection to obtain index.html file 2 RTTh. Then the image information of the address, to complete the work loading eight images in the two parallel processing. 2 * 2 RTTh. 2 + 4 = 6 RTTh
4) the absence of water, the client just before a response is received after sending a new request, each of the referenced objects takes a RTTh.
There are circumstances under running water, as long as the client encounters a reference on the request as soon as possible.
No water: 2 + 8 = 10 RTTh. Flowing water: 2 + 1 = 3 RTTh
10. e-mail that is mainly composed of several parts?
Mail servers, Simple Mail Transfer Protocol SMTP, user agent Foxmail, Mail Access Protocol, pop, imap, http
11. Description of the SMTP mail process
The core application layer protocol, short message transfer protocol
Process: the handshake, the message transfer phase, the closing phase
12.FTP of "out of band control" feature What is the meaning? Control and data connections What are the characteristics? What use are they?
14. Description of TCP client and TCP server program SockertAPI basic functions of the calling process
Server:
Bind a port number
Server starts listening, waiting for the client sends a request.
Receiving a request sent by the client to establish the connection.
Then wait for the client to send data over.
After doing the appropriate treatment, sent to the client.
If at this time the two sides have been completed, it closes the TCP connection;
The end of the program, quit
Client:
No fixed port assignment, but get a temporary port by calling the socket interface;
Use the temporary port and server to establish a TCP connection;
After the other party to accept the connection, the client begins requesting data;
Waiting for the server response data sent back, if necessary, send a request to call again;
After sending all the data, the interface may close the TCP connection;
The end of the program, quit
15. Description of the basic functions SockertAPI UDP client and UDP server program calls the process
Obtaining a fixed port number;
Port number, and server bind; wait for the client to send data
Receiving a data request sent by the client;
After receiving treatment, transmits response data to the client;
Receiving again if necessary, treatment response;
After completion, close the connection.
The end of the program, quit
Client:
Interface to obtain a temporary port by calling the socket;
With this port transmits data to the server;
After data transmission, the receiving server waits for a response;
And closing the corresponding port is connected;
The end of the program, quit.
third chapter
The main measures 1. To achieve reliable transmission of those? These measures are mainly used to solve those problems?
2.UDP and TCP multiplexing, respectively, how to break down?
UDP by <destination IP address, destination port number>
Destination IP address of the data to determine the host
Destination port number, the destination host is determined by the transport layer to the application that port
TCP <source IP address, source port number, destination IP address, destination port number> These four configuration TCP socket
Source IP address:
Source port number:
Destination IP Address:
Destination port number:
3. Draw a TCP segment structure, and a brief description of the main fields of action
P113
4.TCP why the three-way handshake to establish a connection, the use of secondary handshake can do? why?
p115
Three times to ensure that the connection is duplex, reliable, more retransmission mechanism is guaranteed by
Can not
The first two to ensure the server to the client is able to receive and make the right response and into
After two to ensure that the client can receive information on the server and can make the right response
5. Description TCP connection establishment and disconnection, and to give the main state transition
p116
How 6.TCP ensure reliable data transmission?
Stop use and other agreements, after stopping on behalf of the packets sent to stop waiting to receive confirmation put
Other is the receiver sends an ACK or NCK, NCK occurs retransmits
7. Description of the working process GBN protocol and protocol are SR
Step rollback N: 1 is only receiving window, only receive a packet arrive out of order, the packet will not arrive in order to be dropped, lost is necessary to send the notification sent all subsequent elimination.
Disadvantages: a waste of communication resources
ARQ: receiving window> 1, but out of sequence packets to the correct cache, but the sender is required to put the retransmission packet acknowledgment is not received
8. Description Protocol TCP sliding mechanism, the sliding similarities and differences TCP protocol and protocol comparison GBN
P106
What is the main difference 9.TCP and UDP is?
UDP: connectionless unreliable datagram transmission service every effort to complete the task
10.TCP how to implement congestion control?
Slow Start
Congestion Avoidance
Fast retransmit
Fast Recovery
11. Suppose both parties using GBN protocol to send packets segment A has been sent numbered 0 to 7 segment. When the timer expires, if A only received confirmation segment No. 0 and No. 3, the armor needs to be retransmitted segment is what?
4 5 6 7
12. A and B by the host 128 kbit / s satellite channel interconnection, sliding window protocol data transmission, the link is one-way propagation delay of 250 ms, packet length of 1000 bytes. Acknowledgment packets without regard to cost, as the channel utilization is not less than 80%, the median number of packets to reach at least how many?
P108-p109
13. If the established TCP connection between A and B, congestion control in the congestion avoidance phase, the threshold value is 8 MSS, when the congestion window size A timeout occurs when the 24 MSS, the A and the congestion window is adjusted to the threshold number ? (125 last paragraph)
Congestion window: 1,
Threshold 24/2 = 12
A TCP connection has been established, the host B sends A two consecutive TCP segments to the host, each comprising 300 bytes and 500 bytes of the payload between the host A and the host B 14, a serial number for the first segment after 200, the host b correctly receives two segments, acknowledgment is sent to the host a sequence number is the number?
1000
official:
16. established between the host A and the host B a TCP connection, the two sides have continued data transmission, and data loss and error-free. If A receives a packet from B TCP segment, the segment number is 1913, the acknowledgment number 2046, a payload of 100 bytes, the A number and the acknowledgment number transmitted immediately to the TCP segment B, respectively, how many?
A TCP connection is established between the host A and the host B 17, A always transmits MSS = 1 KB data segment size, and the data has been transmitted; B each receive a segment will be sent to a receiving window confirm segment of 10KB. A case if congestion occurs at the time t timeout window is 8KB, starting from the time t, timeout does not happen, after 10 RTT, A's send window is how much?
10KB
18 has been established between the host A and the host B a TCP connection, TCP maximum segment length is 1000 bytes. If the host A current congestion window is 4000 bytes, when the host A after two consecutively transmitted maximum segment B to the host, confirmation of successful receipt of the first segment of the host B sent in acknowledgment segment received window size advertised is 2000 bytes, then the maximum number of bytes a host can continue to send to the host B is the number? (2010, 39 questions)
1000
