software? Of course, that depends on what is inside the data field. If the data came from the
Novell server, then PC1 hands the data off to the NetWare client code. If the data comes from
the Sun FTP server, PC1 hands it off to the TCP/IP code.
the data field.
header has a field with a code that means IP, or IPX, or some other designation defining the type
of protocol header that follows. The first item to examine in the header is the 802.2 DSAP field.
In the first frame in Figure 3-14, the destination service access point (DSAP) field has a value
of E0, which means that the next header is a Novell IPX header. In the second frame, the DSAP
field is AA, which implies that a SNAP header follows. Next, the type field in the Subnetwork
Access Protocol (SNAP) header, which has a value of 0800, signifies that the next header is an
IP header. RFC 1700, the "Assigned Numbers" RFC (http://www.isi.edu/in-notes/rfc1700.txt),
lists the SAP and SNAP Type field values and the protocol types they imply.
is atypical to have end-user devices attached to either of these types of data links. In this case,
routers provide an example more typically found in most WAN environments, as shown in
Figure 3-15.