System information

The Transport Layer
Book Title
8-140
Figure 8-3 Ethernet, IEEE 802.3, and IPX Encapsulation Formats
To route packets in an internetwork, IPX uses a dynamic routing protocol called the Routing
Information Protocol (RIP). Like XNS, RIP derived from work done at Xerox for the XNS protocol
family.
In addition to the difference in encapsulation mechanisms, Novell also added a protocol called the
Service Advertising Protocol (SAP) to its IPX protocol family. SAP allows nodes that provide
services (such as file servers and print servers) to advertise their addresses and the services they
provide.
Novell also supports IBM logical unit (LU) 6.2 network addressable units (NAUs). LU 6.2 allows
peer-to-peer connectivity across IBM communication environments. Using NetWare’s LU 6.2
capability, NetWare nodes can exchange information across an IBM network. NetWare packets are
encapsulated within LU 6.2 packets for transit across the IBM network.
The Transport Layer
Sequenced Packet Exchange (SPX) is the most commonly used NetWare transport protocol. Novell
derived this protocol from the XNS Sequenced Packet Protocol (SPP). As with the Transmission
Control Protocol (TCP) and many other transport protocols, SPX is a reliable, connection-oriented
protocol that supplements the datagram service provided by Layer 3 protocols.
Novell also offers Internet Protocol (IP) support in the form of User Datagram Protocol (UDP)/IP
encapsulation of other Novell packets, such as SPX/IPX packets. IPX datagrams are encapsulated
inside UDP/IP headers for transport across an IP-based internetwork.
Upper-Layer Protocols
NetWare supports a wide variety of upper-layer protocols, but several are somewhat more popular
than others. The NetWare shell runs in clients (often called workstations in the NetWare community)
and intercepts application I/O calls to determine whether they require network access for
satisfaction. If they do, the NetWare shell packages the requests and sends them to lower-layer
software for processing and network transmission. If they do not, they are simply passed to local I/O
resources. Client applications are unaware of any network access required for completion of
application calls. NetWare remote-procedure call (NetWare RPC) is another more general
redirection mechanism supported by Novell.
NCP is a series of server routines designed to satisfy application requests coming from, for example,
the NetWare shell. Services provided by NCP include file access, printer access, name management,
accounting, security, and file synchronization.
Ethernet
Destination address
Source address
Type
Upper-layer
data
CRC
Standard IEEE 802.3
Destination address
Source address
Length
802.2 header
802.2 data
CRC
IPX
Destination address
Source address
Length
IPX data
CRC