Networking protocol stacks
Computers on a network communicate in agreed ways called
protocols. Protocols dictate which signals computers use across
cables, how they tell one another that they have received
information, and how they exchange information.
Protocols are more accurately termed protocol
``stacks'' or protocol ``suites'' because
the communications functions are complex and are usually
divided into independent layers or levels.
A stack is a collection of protocol layers that implement
network communication.
The protocol associated with each layer communicates only with the
layers immediately above and below it, and assumes the support of
underlying layers.
Lower layers are closer to the hardware and
higher layers are closer to the user. The number of layers and
tasks that each layer performs depends on which stack you
are using.
Table 1-2 Supported protocol stacks
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Provided by Provided by other Supported by SCO
Protocol stack SCO System SCO products network drivers
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TCP/IP yes - yes
IPX/SPX yes - yes
NetBEUI - yes yes
SCO OpenServer also provides two operating system packages
that permit UNIX and XENIX® systems
to communicate as part of a remote network:
Although these packages are not protocol stacks, they are discussed here because they provide low-cost alternatives to LANs based on specialized hardware and software.
The relative advantages of the SCO connectivity packages are: