Introduction to Novell IPX
411
Novell IPX Protocol Stack
IPX doesn't map directly to the OSI model, but its protocols do function in
layers. Back when they designed IPX, engineers were more concerned with
performance than they were with strict compliance to existing standards or
models. Even so, comparisons can be made.
Figure 8.1 illustrates the IPX protocols, layers, and functions relative to
those of the OSI model.
F I G U R E 8 . 1
IPX protocol stack and the OSI model
IPX
Internetwork Packet Exchange performs functions at layers 3 and 4
of the OSI model. It controls the assignment of IPX addresses (software
addressing) on individual nodes, governs packet delivery across internet-
works, and makes routing decisions based on information provided by
the routing protocols, RIP, Cisco EIGRP, or Novell NLSP. IPX is a con-
nectionless protocol (similar to TCP/IP's IP), so it doesn't require any
acknowledgment that packets were received from the destination node.
To communicate with the upper-layer protocols, IPX uses sockets. A
socket
is similar to TCP/IP ports in that it's used to address multiple, inde-
pendent applications running on the same machine.
SPX
Sequenced Packet Exchange adds connection-oriented communica-
tions to the otherwise connectionless IPX. Through it, upper-layer protocols
can ensure data delivery between source and destination nodes. SPX works
Application
OSI Reference Model
Presentation
Session
Transport
Network
Data Link
Physical
7
6
5
4
3
2
1
Applications
NETBIOS
NCP
SAP
RIP
NLSP
SPX
IPX
(Internetwork Packet Exchange)
Media Access Protocols
(Ethernet, Token Ring, WAN, others)
Novell NetWare Protocols
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