86 Chapter 3: OSI Reference Model & Layered Communication
Figure 3-5
Frames, Packets, and Segments
The TCP/IP and NetWare Protocols
Two of the most pervasively deployed protocols are TCP/IP and Novell NetWare; these also are
the two key protocol architectures covered on the CCNA exam. TCP/IP and NetWare are
covered in much more detail in the upcoming chapters.
This short section compares TCP/IP, Novell, and OSI. The goal is to provide some insight into
what some popularly used terminology really means. In particular, routing is defined as a Layer
3 process; this section reviews how that term relates to TCP/IP and NetWare.
For perspective, Figure 3-6 shows the layers of these two protocols as compared with OSI.
Figure 3-6
OSI, TCP/IP, and NetWare Protocols
As Figure 3-6 illustrates, the IP and IPX protocols most closely match the OSI network layer--
Layer 3. Many times, even on the CCNA exam, IP and IPX will be called Layer 3 protocols.
Clearly, IP is in TCP/IP's Layer 2, but for consistent use of terminology, it is commonly called
a Layer 3 protocol because its functions most closely match OSI's Layer 3. Both IP and IPX
define logical addressing, routing, the learning of routing information, and end-to-end delivery
rules.
TCP
Data
IP
Data
LH
Data
LT
Frame
(L2 PDU)
Packet
(L3 PDU)
Segment
(L4 PDU)
Application
OSI
Presentation
Session
Transport
Network
Data Link
Physical
TCP/IP
Application
TCP
UDP
IP, ARP, ICMP
Network
Interface
NetWare
SAP, NCP
SPX
IPX
MAC
Protocols
ch03.fm Page 86 Monday, March 20, 2000 4:58 PM