IPX/SPX Configuration and Management Manual

Protocol Interfaces and Services for NonStop™
IPX/SPX
IPX/SPX Configuration and Management Manual—425731-001
A-8
SPX Packet Header Format
IPX uses the MAC protocol to transmit packets from one node to another. A MAC
header consists of a source node address and a destination node address. The node
address is a 6-byte number that is usually assigned by the network interface card (NIC)
vendor.
SPX Packet Header Format
An SPX packet header is 12 bytes. Figure A-5 shows the format of an SPX packet
header.
Connection Control
specifies whether the packet is a system packet, is used to acknowledge data
packets, or is a data packet.
Data Stream Type
is either 0xFE for an End-of-Connection packet or 0xFF for an End-of-Connection-
Acknowledgment.
Source Connection ID
contains the connection-identification number assigned to the packet originator by
SPX.
Destination Connection ID
contains the connection-identification number assigned to the packet receiver by
SPX.
Sequence Number
is the counter that tracks the number of data packets that are sent by the connection
and acknowledged by the receiver.
Acknowledge Number
is the Sequence Number of the next data packet expected by SPX. Received packets
with a Sequence Number lower than their Acknowledge Number are assumed to be
duplicates and are dropped.
Figure A-5. SPX Packet Header Format
021CDT .CDD
Conn.
Control
Data
Strm
Type
Source
Connection
ID
1
Byte
1
Byte
2
Bytes
Destination
Connection
ID
Sequence
Number
Acknowledge
Number
Allocation
Number
2
Bytes
2
Bytes
2
Bytes
2
Bytes