IPX / SPX
Novell NetWare Network
In order to adapt to the network development, Novell has converted the host network to a PC network and developed a Novell NetWare network system. This system is based on client / server mode. As a client as a client with a general PC, serve the server as a server, providing document services, database services, and other services to clients.
Like the previous SNA model, Novell NetWare is also earlier than the OSI model, so it cannot be strictly corresponding to the OSI model, but there is also a significant correspondence. At the main level, it is closer to the TCP / IP model.
The following figure is a diagram of the Novell NetWare system corresponding to the OSI model:
As can be seen from the figure, IPX / SPX is an important part of the NetWare structure. IPX / SPX provides transport services on NetWare's LAN, and also provides information on network control information (such as routing information) and information available on the network. IPX / SPX has a complete route capability that can realize communication between multiple network segments, which can be used in large enterprise networks.
NetWare does not have the session layer and representation in the OSI model, all application protocols correspond to OSI's application layer, such as SAP, file service, etc.
NetWare implements the management of services through the Service Advertising Protocol, SAP. The server broadcasts SAP packets every 60 seconds [1], gives its address and service, and the gateway server collects the SAP packet and established network routing database.
Due to the restrictions on the high-rise broadcast communication mechanism by the SAP protocol, NetWare routing the number of hosts in the network should not exceed thousands. Although the limitations of SAP have been overcome by intelligent routers and server configurations, the management of large-scale IPX / SPX networks is still very difficult.
IPX protocol
InternetWork Packet Exchange, IPX) protocol corresponds to the network layer of OSI, is an unreliable connection protocol. IPX is mainly used to control the addressing, route and transfer of packets between local area or local area networks, not guaranteeing the integrity of messages, and does not provide error correction services.
In the connection transmission, each time the packet is transmitted, the session does not need to be configured, and the load is lighter than the orientation connection. Unconnected processing intermittent data transmission efficiency is higher than the connection-oriented transmission.
The IPX protocol is a peer-to-peer network protocol that provides no connection packet transfer, control address, and data routing service inside or online.
When transmitting a packet in a local area network, if the receiving node is within the same network segment, the IPX protocol passes the data directly to it; if the receiving node is not in the same network segment, then the IPX protocol will pay the packet to the NetWare gateway server, the gateway Network route is processed by the database.
The above figure is the packet format of IPX, where
Packet length: Points the length of the entire packet, including header and data.
Transmission control: Every time you experience a network, record how many networks that have undergone this packet. This packet is abandoned when the record number reaches the maximum.
Group Type: Used to mark different control packets.
Destination address, source address: contains a 32-bit network number and a 48-bit machine number (socket).
Data field: It is full of remaining packet space, which is determined by the lower network.
NCP and SPX protocol
The IPX protocol is a connection-oriented Transfer Protocol, NCP or sequenced packet exchange (SPX) protocol. These two protocols correspond to the transport layer of the OSI model.
NCP is the heart of NetWare, in addition to user transmission, providing a variety of other services, such as file services. SPX only provides transport services, Lotus Notes uses SPX. (Because this transmission service is mainly discussed here, the following uses SPX, refers to NCP and SPX.) In the LAN, the SPX protocol is primarily responsible for the integrity of packet transmission. There is no error handling for the data of the entire transmission, that is, error correction.
Connecting the connection service needs to be configured. Once the connection is established, it is no longer necessary to spend energy on the data transfer. For continuous data transmission, the connection-oriented transmission is high than the transmission efficiency of the connection. SPX provides a reliable data transfer service that tracks the transmission of data including many dispersed packets.
SPX monitors the process of packet transfer by confirming and confirming the package delivery, which also provides error control capabilities, if the package content is not available, can be responsible for resending the package.
Restriction and enhancement of the SPX protocol
SPX has two limitations:
1. The packets output at all times cannot exceed one; 2, the maximum value of each packet is 576 byte.
These two restrictions have restricted the performance of the SPX protocol on large broadband online, in order to break through these two restrictions, enhance the performance of large networks, and SPXII has the following characteristics:
1.SPX II allows multiple packets to be output.
2.SPX II allows for larger packets. The maximum value of the packet is as large as the bandwidth of the LAN. For example, in Ethernet, SPX II can use 1518 Byte.
[1] See Andrew S.Tanenbaum, translation of Xiong Gui, Wang Xiaohu. Computer NetWorks (3). Tsinghua University Press, 1998.7 33-34
