与各种不同的通信协议和帧结构。L2数据网络

各种L2数据网具有不同的通信协议与帧结构，其网络节点设备可以是各种类型的数据交换机（X.25、FR、Ethernet和ATM等分组交换机）；而L3数据网（IP网或internet）具有统一的TCP/IP通信协议和分组结构，全网采用统一格式的IP地址， 节点设备统一采用面向无连接的路由器。为便于理解，我们可以将L3数据网简单地理解为构建在L2数据网平台上的一个路由器网。-L2 data network with a variety of different communication protocol and frame structure, the network node device can be of various types of data switches (X.25, FR, Ethernet and ATM packet switches, etc.) and L3 data network (IP network or internet) have a unified TCP/IP communication protocol and packet structure, the whole network using a unified format for the IP address, node equipment reunification-oriented connectionless router. In order to facilitate understanding, we can L3 data network simply interpreted as a data network built on the L2 platform for a network router.