Ethernet Switch Management Features, Modbus TCP

RuggedServer™ RS401

4-Port Serial Device Server with Integrated 4-Port Managed Ethernet Switch

Ethernet Switch Management Features

Serial IP Encapsulation

Many 'legacy' devices (RTU, PLC, IED, etc.) only support serial communications via RS232 or RS485. ROS encapsulates the serial data within a TCP connection allowing these devices to be reached via an IP network. A wide range of baud rates, frame packetization options, and diagnostics allows any serial protocol to function. The RS401 has specific support for the following serial protocols:

. Raw Socket serial encapsulation . Modbus TCP (client and server) . DNP 3

. WIN and TIN . Microlok

MODBUS TCP

The Modbus protocol is ubiquitous in the industrial control and automation world. ROS converts Modbus RTU master/slave serial data packets to Modbus TCP client/server packets for transmission over an IP network. This allows communications to Modbus RTU slaves via Ethernet and allows multiple masters to poll the same slave device.

Remote Dial-Up Access

A v.90 modem coupled with the PPP (Point to Point Protocol) allows ROS to provide dial-up access via POTS (plain old telephone system) providing connectivity to serial devices and Ethernet LAN. PAP/CHAP authentication provide security against

unauthorized access.

Rapid Spanning Tree Protocol (IEEE 802.1w)

RSTP allows the creation of fault-tolerant ring and mesh Ethernet networks that incorporate redundant links that are 'pruned' to prevent loops. The ROS optimized version of RSTP yields worst-case failovers of 5ms times the 'bridge diameter' and allows rings of up to 80 switches. For example, a ring of ten switches will have failover times under 50ms. ROS implements both STP and RSTP to ensure interoperability with commercial switches unlike other proprietary 'ring' based solutions.

Quality of Service (IEEE 802.1p)

Some networking applications such as real-time control or VoIP (voice over IP) require predictable arrival times for Ethernet frames. Switches can introduce latency in times of heavy network traffic due to the internal queues that buffer frames and than transmit on a first come first serve basis. ROS supports 'Class of Service' in accordance

with IEEE 802.1p that allows time critical traffic to jump ahead to the front of the queue thus minimizing latency and reducing jitter to allow such demanding applications to operate correctly. ROS allows priority classification by port, tags, MAC address, and IP type of service (TOS). A configurable "weighted fair queuing" algorithm controls how frames are emptied from the queues.

VLAN (IEEE 802.1q)

Virtual local area networks (VLAN) allow the segregation of a physical network into separate logical networks with independent broadcast domains. A measure of security is provided since hosts can only access other hosts on the same VLAN and traffic storms are isolated. ROS supports 802.1q tagged Ethernet frames and VLAN trunks. Port based classification allows legacy devices to be assigned to the correct VLAN.

IGMP Snooping

ROS uses IGMP snooping (Internet Group Management Protocol v1&v2) to intelligently forward or filter multicast traffic streams (e.g. MPEG video) to or from hosts on the network. This reduces the load on network trunks and prevents packets from being received on hosts that are not involved. ROS has a very powerful implementation of IGMP snooping that:

.Can be enabled on a per VLAN basis

.Detects and filters all multicast streams regardless of whether subscribers exist

.Supports "router-less" operation by supporting an "active" mode

.Restores traffic streams immediately after an RSTP topology change

Ethernet Port Mirroring

ROS can be configured to duplicate all traffic on one port to a designated mirror port. When combined with a network analyzer, this can be a powerful troubleshooting tool.

Ethernet Port Configuration and Status

ROS allows individual ports to be 'hard' configured for speed, duplex, auto-negotiation, flow control and more. This allows proper connection with devices that do not negotiate or have unusual settings. Detailed status of ports with alarm and SNMP trap on link problems aid greatly in system troubleshooting.

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