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Bit Inspection Technical Standard. Aluminum Drill Pipe Inspection. Browse Publishers. Top Sellers. New Releases. My Account. Corporate Sustainability. Investor Relations. All Rights Reserved. Frame synchronization is necessary to identify the timeslots within each channel frame. Synchronization takes place by allocating a framing, or rd, bit. A superframe consists of twelve consecutive bit frames, whereas an extended superframe consists of twenty-four consecutive bit frames of data.
Due to the unique bit sequences exchanged, the framing schemes are not compatible with each other. Connectivity refers to the ability of the digital carrier to carry customer data from either end to the other. In some cases, the connectivity may be lost in one direction and maintained in the other. In all cases, the terminal equipment, i. Alarms are normally produced by the receiving terminal equipment when the framing is compromised.
There are three defined alarm indication signal states, identified by a legacy color scheme: red, yellow and blue. Red alarm indicates the alarming equipment is unable to recover the framing reliably. Corruption or loss of the signal will produce "red alarm". Connectivity has been lost toward the alarming equipment. There is no knowledge of connectivity toward the far end. Yellow alarm , also known as remote alarm indication RAI , indicates reception of a data or framing pattern that reports the far end is in "red alarm".
For SF framed signals, the user bandwidth is manipulated and "bit two in every DS0 channel shall be a zero. Blue alarm , also known as alarm indication signal AIS indicates a disruption in the communication path between the terminal equipment and line repeaters or DCS. If no signal is received by the intermediary equipment, it produces an unframed, all-ones signal. The receiving equipment displays a "red alarm" and sends the signal for "yellow alarm" to the far end because it has no framing, but at intermediary interfaces the equipment will report "AIS" or Alarm Indication Signal.
AIS is also called "all ones" because of the data and framing pattern. The meaning of CGA is that connectivity on the digital carrier has failed. The result of the CGA condition varies depending on the equipment function. Voice equipment typically coerces the robbed bits for signaling to a state that will result in the far end properly handling the condition, while applying an often different state to the customer equipment connected to the alarmed equipment.
Simultaneously, the customer data is often coerced to a 0x7F pattern, signifying a zero-voltage condition on voice equipment. Data equipment usually passes whatever data may be present, if any, leaving it to the customer equipment to deal with the condition. While both carry voice telephone calls in similar fashion, PRIs are commonly used in call centers and provide not only the 23 actual usable telephone lines Known as "B" channels for bearer but also a 24th line Known as the "D" channel for data  that carries line signaling information.
However, PRIs handle this more efficiently. While an inband T1 seemingly has a slight advantage due to 24 lines being available to make calls as opposed to a PRI that has 23 , each channel in an inband T1 must perform its own setup and tear-down of each call. Although an inband T1 has 24 channels, the 23 channel PRI can set up more calls faster due to the dedicated 24th signalling channel D Channel. T1 CAS is not common today but it still exists.
It is also referred to as Robbed Bit Signaling. CAS is a technology with roots in the 60's and before. The naming system ended with the letter T, which designated fiber networks. DS-1 means "Digital Service — Level 1," and had to do with the signal to be sent—as opposed to the network that delivers it originally 24 digitized voice channels over the T1. Since the practice of naming networks ended with the letter "T,"  the terms T1 and DS1 have become synonymous and encompass a plethora of different services from voice to data to clear-channel pipes.
The line speed is always consistent at 1. Dark fiber : Dark fiber refers to unused fibers , available for use. Dark fiber has been, and still is, available for sale on the wholesale market for both metro and wide area links, but it may not be available in all markets or city pairs. Dark fiber capacity is typically used by network operators to build SONET and dense wavelength division multiplexing DWDM networks, usually involving meshes of self-healing rings.
Now, it is also used by end-user enterprises to expand Ethernet local area networks, especially since the adoption of IEEE standards for gigabit Ethernet and 10 Gigabit Ethernet over single-mode fiber. Running Ethernet networks between geographically separated buildings is a practice known as " WAN elimination".