《计算机网络和 与因特网》课件第十三章硬件编址和 与帧类型标识.ppt

works and s
《计算机网络与因特网》课件
林坤辉
PART II Packet Transmission
Chapter 13 Hardware Addressing
and Frame Type Identification
硬件编址与帧类型标识
Introduction
Physically,any signal sent across a work reaches all attached stations.
At a given station,work interface hardware detects the electrical signal and extracts a copy of the frame.
Communication does not usually involve all stations. Instead,munication occurs because an application program on puter sends data directly to an application program on another.
Specifying A Recipient指定接收方
Most LAN technologies use an addressing scheme to provide munication.
Each station on the LAN is assigned a unique numeric value called a physical address(物理地址),hardware address(硬件地址),or media access address(MAC).
A frame sent across a LAN contains the address of the puter,called a source address,and the address of the intended recipient,called the destination address.
How LAN Hardware Uses Addresses To Filter Packets局域网硬件如何使用地址过滤包
The LAN hardware in puter pletely separate from puter’s CPU and memory.
The LAN interface hardware handles all the details of sending and receiving frame on the shared medium without using puter’s CPU.
网卡的任务:
检测帧是否存在
有效性检验
判断是否接收
CPU的任务
判断是否传给上层处理
分层处理的目的:减少CPU的负荷
数据包过滤是通信接收方的动作
通过检测数据的标识,对符合接收条件的:
复制帧
中断CPU,将复制后的帧交给CPU
继续等待下一个帧
对不符合接收条件的:放弃接收,继续等待下一个帧
Format of A Physical Address
Physical Address
必须是所在局域网内的唯一标识
局域网内要对物理地址提供检索的功能
Three broad categories:
Static address(静态地址)
出厂前由生产厂家一次性配置完成
全球唯一硬件标识,不会出现地址冲突
一次生成,永久使用
地址较长,查询慢
Configurable address (可配置地址)
系统出厂后,用户动态分配,保持局域网内唯一
地址短,查询快
地址可以永久有效,也可以随需求改变
Dynamic address (动态地址)
每当系统启动的时候动态分配,局域网内唯一
地址短,查询快
有可能出现地址冲突
地址动态改变,不利于地址映射表的维护