 to repeat himself or herself when there is a problem with the delivery of the voice packets. TCP/IP Layer 4 is the realm of applications protocols and relates to OSI Layers 5, 6, and 7. These are utilities that allow applications to access particular network services: Telnet for remote terminal access File Transfer Protocol (FTP) for batch transmission Simple Mail Transfer Protocol (SMTP) for sending e-mail Post Office Protocol (POP) for receiving e-mail Hypertext Transfer Protocol (HTTP) for accessing and downloading Web- based (HTML-formatted) information Simple Network Management Protocol (SNMP) for network management Real-Time Transport Protocol (RTP) for transport of real-time audio and video The TCP Stack Versus the OSI Model Figure 5.10 shows the TCP stack and how it relates to the OSI model. The OSI Reference Model and the TCP/IP Reference Model OSI Model TCP Stack Application 2nd Generation: Archie, Gopher, HTTP, Time/NTP/SNTP 1st Generation: Telnet, FTP, SMTP/POP, NNTP, SNMP, X Window, DNS, traceroute Presentation Session Transport TCP, UDP Network IP, ICMP, IGMP, ARP/RARP Gateway Protocols: RIP, OSPF, EGP, BGP Data Link Network Access Protocols: HDLC, SLIP, CSLIP, PPP Physical 10BASE2/5/T, RS-232, V.35, MMF/SMF Figure 5.10 The TCP/IP-OSI hybrid model (five layers) This page intentionally left blank Chapter Local Area Networking This book uses terminology that comes from the domain of local area networking, and in this chapter, you'll become familiar with the basics of local area network (LAN) components-the history of LANs, the key issues in the various architec- tures, and issues related to LAN interconnection and internetworking. LAN Basics In the early 1980s, when most businesses were still using networked mainframes, two changes took place in computing infrastructures. First, there was a general growth in the number of devices in organizations, which created traffic growth. Sec- ond, skilled, technically oriented users began sneaking their own workstations in to work, and they would ask the compan