174实体、协议、服务和服务访问点

1.7.4„„„„LEC.4„„„„„nn+1SAPSAP„„„„„((100%)100%)““””“”………………„„„„100%100%„„„„„OSITCP/IPOSIIP(TELNET,FTP,SMTP)(TCPUDP)TCP/IP()TCP/IPTCP/IPAB4321TCP/IPEverythingoverIPIPIPoverEverythingIPHTTPHTTPSMTPSMTPDNSDNSRTPRTPTCPTCPUDPUDPIPIP………1231.8-„„„„„„„„„„„„„„„TCP/IP(TCPIP311221122*2.1*2.22.32.4*2.5*2.6SONETSDH2.72.1„¾¾¾„„„„2.2„——„12„„„„„„„„„——„———“”„„——„——“”——„¾¾¾™¾¾¾¾¾¾¾¾„„„PCPCPCM„——„——„——()„——(baseband)(broadband)„10„„„——„———„¾12„„——„„„——„——„——„„••(broadband)„=+