计算机网络关键词复习 Computer Network Review

Definition

transport-layer multiplexing and demultiplexing

• The job of delivering the data in a transport-layer segment to the correct socket is called demultiplexing.
• The job of gathering date chunks at the source host from different sockets, encapsulating each data chunk with header information to create segments, and passing the segments to the network layer is called multiplexing.

Filtering

• Filtering is the switch function that determines whether a frame should be forwarded to some interface or should just be dropped.

Processing delay

• The time required to examine the packet’s header and determine where to direct the packet is part of the processing delay. The processing delay can also include other factors, such as the time needed to check for bit-level errors in the packet that occurred in transmitting the packet’s bits from the upstream node to router A.

round-trip time(RTT)

• The round-trip time (RTT), which is the time it takes for a small packet to travel from client to server and then back to the client.

Term Interpretation

IP

• The internet protocol.

CDMA

• Code division multiple access

HTTP

• Hyper Text Transfer protocol

POP

• Post Office Protocol

ARP

• Address Resolution Protocol

MAC

• Media access control

PPP

• The Point-to-Point Protocol

EDC

• Error Detection and Correction Techniques

VCs

• Virtual Circuits 虚拟电路

RFC

• Request for comment

UDP

• User Datagram Protocol

TCP

• Transmission Control Protocol

DNS

• Domain Name server

TDM

• Time Division Multiplexing

SNR

• Signal to Noise Rate 信噪比，信噪比是指信号与噪声的比值

NIC

• Network Interface Card

DIFS

• Distributed Inter-frame Space

Translation

Hosts associated with a base station are often referred to as operating in infrastructure mode, since all traditional network services (e.g., address assignment and routing) are provided by the network to which a host is connected via the base station. In ad hoc networks, wireless hosts have no such infrastructure with which to connect. In the absence of such infrastructure, the hosts themselves must provide for services such as routing, address assignment, DNS-like name translation, and more.

• 与基站相关联的主机通常被称为在基础设施模式下运行，因为所有传统的网络服务(例如，地址分配和路由)都是由主机通过基站连接到的网络提供的。在自组织网络中，无线主机没有这样的基础设施来连接。在没有这种基础设施的情况下，主机本身必须提供诸如路由、地址分配、类似dns的名称转换等服务。

Over the years, dozens of multiple access protocols have been implemented in avariety of link-layer technologies. Nevertheless, we can classify just about any multiple access protocol as belonging to one of three categories: channel partitioning protocols, random access protocols, and taking-turns protocols. The time-division multiplexing (TDM) and frequency-division multiplexing (FDM) are two techniques that can be used to partition a broadcast channel’s bandwidth among all nodes sharing that channel. A third channel partitioning protocol is code division multiple access (CDMA).

• 多年来，已经实现了几十种不同类型的多址访问协议链路层技术。然而，我们可以对任何多用户访问进行分类协议作为属于三大类之一:通道分区协议、随机协议接入协议和轮流协议。时分复用(TDM)和频分复用(FDM)是两种可用于分割a的技术共享该信道的所有节点之间的广播信道带宽。第三个通道分区协议是码分多址(CDMA)。

受到以太网及其随机接入协议巨大成功的启发，802.11 的设计者选择了一种用于802.11 无线局域网的随机接入协议。这种随机访问协议被称为避免冲突的 CSMA，或者更简洁地称为 CSMA/CA。与以太网的 CSMA/CD 一样，CSMA/CA 中的“CSMA”代表“载波检测多址接入”，意思是每个站点在发送之前检测信道，当信道被检测忙时不发送。

• Inspired by the great success of Ethernet and its random access protocol, the designers of 802.11 chose a random access protocol for 802.11 wireless Lans. This random access protocol is called conflict-avoidance CSMA, or more succinctly CSMA/CA. Like Ethernet's CSMA/CD, the "CSMA" in CSMA/CA stands for "carrier detection multiple access," meaning that each station detects the channel before sending it and does not send it when the channel is detected busy.

Short Answer Question

Why the IP datagram need be fragmented?

• Cause every different trans protocol has its own MTU, to satisfy different MTU it's needed to be segmented to small fragments.

What services can be offered by the Link Layer protocol?

• Ethernet, 802.11 WLAN, token ring, PPP.

Please describe the relationship of the BER, SNR and modulation technique

• 信噪比是信号与噪声的比值，误码率(Bit Error Rate BER) ，误码率是指信号中出现错误的概率，他们之间的关系是信噪比与误码率之间是反比关系，即信噪比越大，误码率越低，信噪比越低误码率越大。这是因为信噪比越大，传输所用的能量就越大，更容易分辨清楚信号和噪声，从而降低了错误概率。调制技术用于在理想无线信道上传输的编码信息。

Please describe the difference of the 802.11 frame and the Ethernet frame.

• 802.11和以太网帧的区别在于IEEE标准不同，802.11和以太网帧的结构、大小不同，错误监测方式不同，以太网使用CRC，802.11使用FCS，安全措施也不同。

The switching fabric is at the very heart of a router. Please describe the ways of the switching can be accomplished.

• 通过交换机内存交换，通过交换机单总线交换，通过互联的总线进行转发。

Please describe the major components of the TCP congestion-control algorithm.

• 拥塞避免，满开始，快速重传，拥塞窗口减半。