### Technical Briefing

Issue TB96/01
April, 1996

# Dedicated Token Ring

Dedicated Token Ring (DTR) is a new standard for high-speed data transfer, based on existing 802.5 Token Ring specifications. DTR provides a dedicated bandwidth of 16 Mbps, which can be further increased to 32 Mbps when operating in full duplex mode.

- Classic Token Ring
- DTR Adapters
- DTR Cabling
- DTR Concentrators
- Standard Updates
- How DTR works
- Coexistance of CTR with DTR
- Madge Position

## Overview

To obtain the benefits of DTR, a DTR concentrator device is needed. This will typically be a Token Ring switch which is used with installed adapters to establish a dedicated connection to the desktop. When an adapter is connected to a DTR concentrator port, the station has a full 16 Mbps bandwidth available, which can be increased to 32 Mbps if both station and port operate in Full Duplex mode.

### Customer Benefits

- Investment protection of existing Token Ring installed base.
- Easy upgrade path to increase bandwidth to the desktop and for high speed inter-switch links
- Proven multi-vendor interoperability.

## Classic Token Ring

With the advent of DTR, the new term 'Classic Token Ring' (CTR) has been born to describe the standard implementation that has been used for many years, where multiple stations are connected via a logical ring topology and share the available bandwidth.

## DTR Adapters

Most current shipping adapters from leading vendors can support DTR through a simple driver upgrade, but old adapters from some vendors cannot be upgraded. Optimum investment protection accrues from adapters that conform fully to the DTR standard and support connections to both CTR and DTR concentrators. These adapters will auto-configure to the highest bandwidth option offered by the concentrator port.

## DTR Cabling

DTR operates over both UTP/STP copper and fiber Token Ring cabling. It uses standard cable pin-outs and works over existing transmit and receive pairs.

## DTR Concentrators

A typical DTR concentrator is a switch acting as a fast multi-port bridge, supporting source routing and/or transparent bridging methods. A DTR concentrator differs from a CTR concentrator in that each port, known as a 'C-port', contains a Media Access Control (MAC) function to receive and transmit frames. A CTR concentrator port does not contain a MAC and merely consists of relays which can be open or closed to provide insertion to the ring. C-ports can be connected to CTR adapters, DTR adapters, CTR concentrator ports or DTR concentrator ports.

## Standards Update

DTR has been incorporated into a draft international standard that is expected to be ratified during 4Q96 by the IEEE as 802.5r. As members of the IEEE committee, Madge and IBM have been primary architects of the DTR technical specification. It is important to acknowledge that DTR is the result of unprecedented pre-standard multi-vendor co-operation and advanced interoperability testing which ensures that customers have real choice and flexibility when they implement DTR solutions that conform to this open standard. Some vendors are making early 'final draft' DTR upgrades available to their customers from 2Q96, to enable them to gauge the impact of this new technology on their networks ahead of time.

## How DTR Works

A DTR connection uses a standard Token Ring cable containing two twisted wire pairs. In CTR, the pairs are 'chained' to form a single data path providing a shared bandwidth of 16 Mbps. In DTR, the pairs are dedicated to a single connection that uses the full 16 Mbps bandwidth (CTR mode), or 32 Mbps when both pairs operate simultaneously (Full Duplex mode).

In CTR, nodes connect to a hub and the twisted pairs form a ring. Each node's MAC uses the standard Token Passing (TKP) protocol to transmit data, and each node shares access to the 16 Mbps bandwidth. In DTR (above right), the full 16 Mbps is dedicated to a single node (an adapter or a port) when operating in Classic mode using TKP.

As DTR is a point-to-point connection between two stations with dedicated transmit and receive paths, there is no need for the token-based contention mechanism used by CTR. The proposed DTR standard defines a new token-less mode of operation that employs a streamlined access protocol, known as Transmit Immediate (TXI). It is this protocol that allows a node to transmit and receive in 'Full Duplex' mode, achieving 32 Mbps bandwidth.

## Coexistence of CTR with DTR

DTR is designed to be backwards compatible with existing CTR installations: CTR adapters can connect to DTR concentrator C-Ports, and DTR adapters to Classic concentrator ports, and function fully. A DTR-capable adapter determines the capabilities of the port to which it is connected before any transmissions start, and the benefits of DTR are only obtained when both adapter and port are DTR-capable. DTR concentrator C-ports can also connect to other DTR C-ports or to CTR concentrator ports.

### Application 1: Server Access

DTR allows enterprise servers to connect directly to a Token Ring backbone using classic or full duplex modes. Users can then implement data centre-based server farms to optimize client-server response times, and to increase security and manageability. Heavily loaded servers with high levels of read and write transactions will benefit most from the simultaneous transmission capability of full duplex mode.

### Application 2: Backbone Switching

DTR is an ideal method for connecting concentrators over high speed 32 Mbps links, and is most useful for Token Ring switch applications (where end-to-end latency is critical) as frames can traverse the backbone via multiple switches without the overhead and inefficiency of layer 3 translation. Employing DTR with 'cut-through' switching concentrators enables the benefits of streaming data transfers to be retained across multiple network hops.

## Madge Position

Madge has a realistic and clear strategy for customers wishing to use DTR in their networks. Madge has worked closely with other vendors at interoperability forums (e.g. the University of New Hampshire) to ensure that the emerging DTR standard will be widely supported as a common specification by the time that it is ratified. Until then, Madge will work closely with customers to trial 'final draft standard' DTR for backbone and server interconnect applications.

The following Madge products will support DTR via a software-only upgrade:

- Smart Ringswitch (all versions 1995+)
- Smart 16/4 Ringnodes*
- Blue+ 16/4 ISA Adapters (all versions: 1995+)

The Smart Ringswitch now supports 32 Mbps Full Duplex inter-switch links (based on the 'final draft standard') as a standard product feature, which is also available as a software upgrade for older installations via the Madge BBS or WWW.

* All shipping Madge adapters are 'DTR-ready', with DTR network drivers to be included in the next major release of Madge adapter software. In the interests of providing a robust and timely DTR solution for key environments, Madge has concentrated upon validating its DTR solution with the most popular network operating systems(i.e. NetWare, NT, OS/2) in EISA and PCI-based server platforms only.

Included on the CD-ROM in the \LSS.500\DTR directory are pre-release versions of the Netware, NT and OS/2 server drivers. These have not been tested to the same standards as the main drivers. You may use these drivers if you wish to evaluate DTR, but be aware of the limitations.

Customers requiring further information should contact their local Madge sales representative.