Technology Overview

A DS3 has a bandwidth of 44.736 Mbps, which is the capacity of 28 T1 spans (28 times the DS1 rate of 1.544 Mbps) with approximately 1.5 Mbps left over. With this leftover bandwidth, every 85th bit in a DS3 bit sequence is used for overhead functions such as frame alignment, error detection, and terminal-to-terminal data communication. All other bits are payload bits.

The CSP software supports the DS3 card on the CSP 2090 chassis, with common DS3 L3 configuration, T1 Robbed Bit Signaling, Cross Connections, and other functionality. A full switching matrix resides on the DS3 card.

The DS3 card resides in a line card slot and routes data on the midplane buses (HDLC and PCM). The diagram below shows how the DS3 card integrates into the CSP architecture.

The DS3 framer is automatically brought into service when the DS3 card is brought into service. Once in service, DS3 status changes are reported to the host in the Alarm messages (0x00B9). If the DS3 circuit is not ready for operation, DS3 alarms may be disabled by placing the DS3 framer out of service. To do this, send a Service State Configure message (0x000A) with the DS3 Offset AIB (0x32) and an action of 0x0F (Take Out of Service). Refer to the API Reference for the format of the message.

If the host does take the DS3 Framer Out of Service, it is the host’s responsibility to bring it back in service. If the host does not bring the DS3 Framer back in service, the CSP will send a NACK 0x005A (DS3 Out of Service) when it receives the Service State Configure message to Bring Span In Service.

The DS3 signal format typically transports 672 channels at 64 Kbps per channel. The DS3 signaling interface is bipolar with Bit 3 Zero Substitution (B3ZS).

Digital communications link - voice, data, and video at a 1.544 Mbps rate (24 64 Kbps channels)

Signaling method used with T1 connections where bits are “robbed” from voice data. Increases possibility of transmission and detection errors, and reduces voice quality.

See Pulse Code Modulation.

A group of data bits in a specific format, with a flag at each end to indicate the beginning and the end of the frame.

The condition of a component at a given instant. The current "context" of a PPL object, such as Idle, Seizing, Answered. In PPL files, a State is represented by a circle.

See Address Information Block.

Negative acknowledgement to a message.

Range of channels provided by T1 or E1 transmission service. A physical span is a group of channels taking up a single physical wire. A logical span is a group of channels taking up less than a single logical wire, or carried over more than one physical wire.