DECnet Routing and DECnet Router

DECnet Routing

During the development of the DECnet phases, DEC defined different levels of routing:

• Phase II: Point-to-point routing, allowing a node to send packets to physically adjacent nodes only. Adjacent nodes are linked directly by a physical line. (This would not be called "routing" nowadays at all.)
• Phase III: full routing, allowing one node to send packets to any other node in the same network. The source and destination nodes do not need to be adjacent because each packet is routed through any nodes that fall in between them.
• Phase IV:
  • Level 1 Routing, performing intra-area routing within a single area of the network.
  • Level 2 Routing, performing intra-area routing within its own area and interarea routing between its area and one or more other areas of the network.

Phase III Routing

A Phase III network can include three types of nodes, which support different degrees of routing function. A node's type determines its position within a Phase III configuration.

• Routing nodes. A routing node can forward packets to other nodes in the network and can be adjacent to all other types of nodes.
• Nonrouting nodes. A nonrouting node can send packets to other nodes in the network but packets cannot be forwarded or routed through it. It can be adjacent to one other node only; therefore it is always an end node in a Phase III configuration.
• Phase II nodes. A Phase II node is a node that runs a Phase II implementation of DECnet and therefore does not support full routing. It can send packets to adjacent nodes only and it cannot forward packets it receives onto other nodes in the network. It can be adjacent to one or more full routing nodes and/or to other Phase II nodes. Logically, it is an end node within a Phase III configuration.

Phase IV Routing

In Phase IV of DECnet, the following terms were generally introduced:

• End Node (was "nonrouting node" before)
• Full Function Node (was "routing node" before)

Phase IV added routing between different Typess of data links, e.g.:

• DDCMP
• X.25
• CI
• Ethernet

Area Routing

(to be added)

DECnet Router

With the introduction of DECnet Phase III, the need arose to provide devices that handle routing.

DECnet Router Types

While any general-purpose computer with sufficient resources, network interfaces and an operating system with routing capabilities can provide routing functions, there are also dedicated routing devices using special software optimized for routing.

There are two kinds of DECnet routers:

• General purpose computer routers
• Dedicated routers

How to choose the optimal DECnet Router Type

The selection of the optimal DECnet router type depends on several factors.

Arguments for a general purpose computer router:

• Flexibility
• Expandability
• Free resources on a computer scheduled for routing
• Usage of existing hardware and software

Arguments for a dedicated router:

• Price for new purchase
• Limited resources on a computer scheduled for routing
• Low space requirements and low energy consumption
• Operation independent of other applications

General Purpose Computer Routers

The following DEC computers, operating systems and network software products are known to have routing capabilities (assuming appropriate software versions):

• PDP-11 computers running:
  • RSX-11M & DECnet-11M
  • RSX-11M-PLUS & DECnet-11M-PLUS
  • RSTS/E & DECnet/E
• VAX computers running:
  • VMS & DECnet-VAX
  • VAX RSX & DECnet-11M-PLUS

Dedicated Routers

Dedicated DECnet Routers

Order Name	Sales Name	Serial Lines	Ethernet
DECSA	DECnet Router	8 sync/16 async	1
DEMSA	DECrouter 2000	4 synchronous	1
DSRVC	DECrouter 200	8 asynchronous	1
DSRVR	DECrouter 250	8 sync/async	1
DSRVJ	DECrouter 150	2 sync/async	1
DEWAR	DECwanrouter 90	1 sync/async	1

Some of the DECnet dedicated routers had special variants or software to enable routing of TCP/IP and/or over X.25 lines.