应用层 ITELNET FTPH SMTP, RPC TFTP 传输层 TCP UDP 网络层 ICMP IP IGMP ARP RARP Ethernet. Token Ring. FDDLPPP/SLIP.X 25RPC SNMP DNS TFTP NFS TELNET FTP HTTP SMTP Telnet 应用层 传输层 TCP UDP 网络层 ICMP IP IGMP ARP RARP Ethernet,Token Ring,FDDI,PPP/SLIP,X.25