
VINES Overview
117372-A Rev. A 1-7
VINES Data Link Protocols
The VINES data link protocols support the exchange and broadcast of data frames
between neighboring server and client nodes on the network. The maximum frame
size is 1500 bytes.
In addition to supporting most of the IEEE standards, the VINES Fragmentation
Protocol breaks up packets that are too large to travel over certain media into
smaller-sized frames and reassembles them. However, the Fragmentation Protocol
supports routers configured over synchronous lines only. For example, if a node
on an IBM PC LAN attempts to send a packet to a node on an Ethernet LAN over
a synchronous network, the Fragmentation Protocol fragments the packet into
smaller-sized frames. This enables the router to transport the packets over an
Ethernet LAN.
The Fragmentation Protocol has a 2-byte header that stores information and
follows the data link header in a VINES frame (F
igure 1-4).
Figure 1-4. VINES Fragmentation Protocol Header
The first byte of the header contains a control field and the second byte contains a
sequence number. The value of the control field indicates whether the frame
begins or ends in a VINES IP packet. Only the first fragment includes the VINES
IP header.
The value of the sequence number field is modulo 256. The node that originated
the frame determines this value. The receiving node uses this value to determine
the correct order in which to reassemble the data packet as it receives fragments. If
the receiving node receives the fragments out of order, the intermediate node
discards all fragments and the partially reassembled packet.
Bits 0 to 5 Not Used
Bit 6 - If set to 1, frame ends a VINES IP packet
Control Field Sequence Number
Bit 7 - If set to 1, frame begins a VINES IP packet
1 byte 1 byte
VN0004A
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