T3/DS3
T3 Network Elements
Many types of network elements have DS3 interfaces. An M13 MUX multiplexes 28 DS1′s into a single DS3. A DS3 NIU may be installed by the phone company at the customer prem to isolate the customers circuit from the network. A fiber MUX may have one or more DS3 low speed tributaries and has a high speed (OC-3, OC-12, OC-48,etc.)output.
DS3 Signal
A DS3 signal consists of digital data transmitted at 44.736 Mbps. Coaxial cables carry the DS3 signal, with the actual signal found on the center conductor. The outer conductor is grounded. The electrical signal uses a bipolar format with B3ZS. This B3ZS code prevents the DS3 receiver from losing syncronization with the signal when no 1′s are present. The cicuit has a characteristic impedance of 75 ohms and can be transmitted up to 450 feet over coaxial cable .
M23 And C-Bit Parity Framing
Framing is provided on a DS3 signal for a number of reasons. It allows the two terminals of a DS3 line to synchronize on the signal and demultiplex subchannels in a pre determined order. It also allows a variety of maintenance and operational benefits.
There are two common types of DS3 framing, M23 and C-Bit. In the M23 MUX framing application, 7 DS2′s are multiplexed into a single DS3. Each DS2 is itself created from four multiplexed DS1′s. The DS2 framing is called M12 framing. The DS2′s are allowed to exist as independent signals which can be plugged into other equipment. The 28 DS1′s, 7 Ds2′s and 1 DS3 are not frequency-locked with respect to each other. As a result, a bit-stuffing algorithm is provided within the M12 and M23 frame formats to allow the minor frequency variations to occur without causing any bit errors in the transmitted data.
C-Bit parity framing was created because DS2′s typically do not need to exist independently with varying frequencies. Instead, most commercial multiplex equipment operates in an M13 mode, multiplexing 28 DS1′s directly into a DS3. DS2 signals are still multiplexed within the DS3, but the DS2′s timing is frequency-locked to the DS3 which frees up the M23 stuff bits to be used for other purposes. C-Bit parity framing enables end-to-end performance monitoring of DS3 circuits. In this way, a telephone company or end user can verify the end-to-end performance of a circuit while it is in service.
The best meter we have found for test and troubleshooting DS3/T3 problems is the T-Berd 2310.
2 Responses
VOIP is very good specially if you have lots of voice and data traffic that are to be sent simultaneously”;;
When I originally commented I clicked the -Notify me when new comments are added- checkbox and now every time a comment is added I get 4 emails with the same comment. Is there any means you’ll be able to remove me from that service? Thanks!
Leave a Reply