A Synchronous Optical Network (SONET) is designed to carry large amounts of traffic over fiber-optic cabling. Data transfer speeds are defined as Optical Carrier (OC) levels, ranging from 51.84 Mbps for the OC-1 base rate, to 40 Gbps for OC-768. OC networks break data into packets. These packets can include serial data, video data, IP data, or telephone data. As the speed of the SONET increases, direct low-speed serial data transfer becomes an increasingly inefficient use of the network resource. Encapsulating the serial data inside of IP preserves more of the network for high speed data delivery such as for video streaming.
A smart traffic center in the U.S. had been using an OC-1 SONET to send RS-232 serial data from dynamic messaging signs to four nodes, then RS-232 over Single Mode Fiber Optic (SMFO) backbone directly. OC-1 is sufficient for point-to-point video data, and more than sufficient for any serial data, but is not sufficient for multiple concurrent video feeds from cameras.
The traffic center wanted to implement new field network architecture and push all of the RS-232 data through Ethernet over a high-speed (2.488 Gbps) OC-48 SONET. The improved performance would allow them to send video data as well as more standard RS-232 types of data, including dynamic messaging signs and Pan Tilt Zoom (PTZ) controllers for cameras. To do this effectively, the OC-48 should be using IP based communications rather than just muxing serial channels.
Digi introduced the PortServer® TS 4 H MEI, a four-port serial-to-Ethernet device server designed with a hardened enclosure to withstand the extreme temperature ranges (-35° C to +70° C) common in traffic applications. The device server takes serial data and sends it over an IP-based WAN which has a high-speed SONET ring as its backbone. The result is serial tunneling over IP. The application speaks serial out of the central computer, and this serial data is sent over a fiber network to a remote device which speaks serially.
The PortServer TS 4 H MEI allowed the smart traffic center to:
- Maintain its current significant investment in RS-232 devices and equipment while migrating to a more flexible IP based infrastructure
- Complete a major bandwidth upgrade and move without the added cost of replacing all existing equipment
- Increase its deployment of video cameras and other monitoring equipment, without deploying additional fiber