System Network Architecture

System Network Architecture (SNA) by IBM is a suite of protocols mainly used with IBM mainframe and AS/400 computers. Two SNA protocols are:

●     APPC - Advanced Peer-to-Peer Communications provides peer to peer services at the transport and session layer.

●     APPN - Advanced Peer-to-Peer Networking supports the computer connections at the network and transport layers.

Microsoft produced the SNA Server so PC networks could connect with SNA networks.

SNA Layers

SNA has its own network model which is:

●     Physical

●     Data link - Uses protocols such as token-ring or Synchronous Data Link Control (SDLC).

●     Path Control - Performs routing, division, and re-assembly of data packets.

●     Transmission - Connection software

●     Data flow - Prevents data overflows by monitoring and handling traffic

●     Presentation - Handles interfaces to applications

●     Transaction - Provides an interface for applications to use network services

SNA Network Devices

●     host systems

●     terminals

●     Output devices

●     Communications controllers

●     Cluster controllers - Allow many devices to connect through them. They connect ot a host or communications controller.

SNA Network Categories

●     Nodes

❍     Type 2 - PCs, terminals and printers

❍     Type 4 - Communications controllers

❍     type 5 - Host computers used to manage the network

• Data links - Connection between combinations of hosts, cluster controllers, or nodes. 

Possible SNA communications architectures

●     SDLS - Synchronous Data Link Control

●     BSC - Binary Synchronous Communication sends bits in frames which are timed sequences of data.

●     Token-ring

●     X.25

●     Ethernet

●     FDDI

SNA units

NAU - Network Addressable Units

●     LU - Logical Units are ports that users use to access network resources

❍     Type 1 - An interactive batch session

❍     Type 2 - An IBM 3270 terminal

❍     Type 3 - An IBM 3270 printer

❍     Type 6.2 - A program to program session

❍     Type 7 - An IBM 5250 family session

●     PU - Physical Units are a network device used to communicate with hosts.

❍     Type 2 - Cluster controllers

❍     Type 3 - Front end process

❍     Type 5 - Host communications software

SNA software components

●     SSCP - Systems Services Control Point manages all resources in the host's domain.

●     NCP - Network Control Program performs routing, session management tasks. It runs in the communications controller. 

IPX/SPX

IPX/SPX is a routable protocol and can be used for small and large networks. The following protocols are part of the IPX/SPX suite:

●     SAP - Service Advertising Protocol packets are used by file and print servers to periodically advertise the address of the server and the services available. It works at the application, presentation, and session levels.

●     NCP - NetWare Core Protocol provides for client/server interactions such as file and print sharing. It works at the application, presentation, and session levels.

●     SPX - Sequenced Packet Exchange operates at the transport layer providing connection oriented communication on top of IPX.

●     IPX - Internetwork Packet Exchange supports the transport and network layers of the OSI network model. Provides for network addressing and routing. It provides fast, unreliable, communication with network nodes using a connection less datagram service.

●     RIP - Routing Information Protocol is the default routing protocol for IPX/SPX networks which operates at the network layer. A distance-vector algorithm is used to calculate the best route for a packet.

ODI - Open Data-link Interface operates at the data link layer allowing IPX to work with any network interface card. 

NetWare frame types

Novell NetWare 2.x and 3.x use Ethernet 802.3 as their default frame type. Novell NetWare 4.x networks use Ethernet 802.2 as their default frame type. If communication does not occur between two NetWare computers it is a good idea to check the netware versions of the two computers to be sure their frame types match. If the frame types do not match on an ethernet network, the computers cannot communicate.