Newsletter: GL Announces Support for DS3 Subrate and Scrambling

Welcome to another January 2013 issue of GL Communications' Newsletter providing information on DS3 Subrate and Scrambling feature recently introduced into our T3 (DS3) E3 Analyzer software.

Overview

GL's T3 (DS3) E3 Analyzer Pod is one of the smallest and lightest (weighing only 1.75 lbs) analyzer units on the market. The pod when connected to Notebook PC is capable of capturing two full T3 (DS3) / E3 data streams, dropping and inserting T1 or E1, and Analysis of HDLC, ATM, Frame Relay, and PPP Protocols. 

T3 (DS3) or E3 can be channelized (structured) or unchannelized (unstructured).

• In Channelized (Structured), a T3 (DS3) consists of 7 T2s (DS2) and each T2 consists of 4 T1s (DS1), thus a total of 28 T1s, or 672 full duplex voice channels are provided. Similarly, an E3 consists of 4 E2s and each E2 consists of 4 E1s, thus a total of 16 E1s, or 480 full duplex voice channels are provided
• In Unchannelized (Unstructured), T2s or T1s or E2s or E1s DO NOT exist within T3 or E3. Instead, most of the capacity within 44.736 Mbps for T3 and 34.368 Mbps for E3 is used for data, with a small amount for overhead. With the advent of the internet, T3 (DS3) and E3 can be used to transport not only data, but also packetized voice, and packetized video. Example protocols include Asynchronous Transfer Mode (ATM), PPP, HDLC, and Frame Relay. This is shown in the diagram below.

In the typical unchannelized circuit below, both ends will be set for scrambling, which can be vendor specific. If the scrambling is implemented in the router, then all vendor settings may be available. Subrate allows fractional bandwidth, i.e. less than the full 44.736 Mbps. Scrambling improves synchronization performance by randomizing repetitive patterns and long strings of zeros.

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Enhancement – T3 (DS3) Scrambling and Subrate Support

GL's T3 (DS3) E3 Analyzer is now enhanced with scrambling and subrate features. Sub rate allows DSU manufacturers to control bandwidth from the service provider end and sell user specific bandwidth. Data Service Unit (DSU) Subrate feature in T3 (DS3) E3 Analyzer allows to configure the DS3 network for the following DSU vendors' algorithms for T3 interface: Digital Link, Larscom, Verilink, and Adtran.

A typical DS3 framing format (known as standard C-bit Parity) is as shown below. Except for the overhead bits (in white), all other bits are available for payload data (shaded). The frame size is 4760 bits and repeats at a rate of 9398.3 Hz = 44.736 Mbps, but 56 bits are overhead and cant be used for data. Therefore 4704 bits x 9398.3 Hz is available for payload data, or 44.21 Mbps. Usually vendors and carriers make available different increments up to 44.21 Mbps. It is vitally important that both sides be configured for the precisely the same settings.

C-Bit Parity DS3 Format

The analyzer allows to choose scrambling in each DSU mode. Scrambling was implemented to address various 0s-density when used in WAN interface. User can monitor such communications using GL's USB T3 E3 Analyzer.

The below block diagram illustrates subrate implementation in the analyzer

Data Descrambler

• After the data is descrambled, the data descrambler block is used to descramble incoming data using a configured polynomial.
• The scrambler can be turned off for data not using descrambling.
• This block uses a normal descrambling serial polynomial which can be configured for multiple polynomials

Data Filter

• The Data filter uses a multi-framed aligned block RAM which is used to enable or disable the incoming data.
• By enabling or disabling the incoming data, software can configure the incoming data to support the different DS3 DSU vendor subrates

Filter Descrambler

• Some Vendors only support scrambled data of the subrate. The unused payload is left unscrambled.
• This block descrambles the data using a similar polynomial descrambler as the first descrambler block but only on the incoming filtered bandwidth data.

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Screenshots

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Other features and benefits

• One of the smallest and lightest T3 (DS3) E3 analysis platforms with dual data stream capture capability
• Multiple interfaces for analysis (T3 (DS3) E3, T1 E1 and Ethernet) and control (USB and Ethernet) to support a wide array of testing scenarios
• Plug and play through USB 2.0 control interface
• Software selectable T3 (DS3) E3 interface along with T1 (DS1) and E1 Drop and Insert.
• Dual T3 E3 Receivers and Transmitters for non-intrusive and intrusive testing of both eastbound and westbound signals at the same time
• General T3 (DS3) E3 signal testing capabilities
• Channelized (Structured) Testing
• Unchannelized (Unstructured) Testing
• Simultaneously record / playback the entire T3 (DS3) E3 in framed or unframed modes up to hard disk capacity
• Flexible clocking - internal, recovered (from T3 (DS3) E3, T1 (DS1) or E1) and external
• Scripting and Automation through GL's well-known Windows Client Server (WCS) approach
• Monitor / Manage the Analyzer remotely via Ethernet port (future enhancement)

For comprehensive information on the application, please visit T3 (DS3) E3 Analyzer web page.

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