In telephony, Common Channel Signaling (CCS), in the US also Common Channel Interoffice Signaling (CCIS), is the transmission

Transmission (telecommunications)

Transmission, in telecommunications, is the process of sending, propagating and receiving an analogue or digital information signal over a physical point-to-point or point-to-multipoint transmission medium, either wired, optical fiber or wireless...

 of signaling information

Information

Information in its most restricted technical sense is a message or collection of messages that consists of an ordered sequence of symbols, or it is the meaning that can be interpreted from such a message or collection of messages. Information can be recorded or transmitted. It can be recorded as...

 (control information) on a separate channel from the data, and, more specifically, where that signaling channel controls multiple data channels.

For example, in the public switched telephone network

Public switched telephone network

The public switched telephone network is the network of the world's public circuit-switched telephone networks. It consists of telephone lines, fiber optic cables, microwave transmission links, cellular networks, communications satellites, and undersea telephone cables, all inter-connected by...

 (PSTN) one channel of a communications link is typically used for the sole purpose of carrying signaling for establishment and tear down

Clearing (telecommunications)

Clearing, in telecommunications means:* A sequence of events used to disconnect a call and return to the ready state. It is sometimes, particularly in the context of common channel signaling, called teardown....

 of telephone call

Telephone call

A telephone call is a connection over a telephone network between the calling party and the called party.-Information transmission:A telephone call may carry ordinary voice transmission using a telephone, data transmission when the calling party and called party are using modems, or facsimile...

s. The remaining channels are used entirely for the transmission of voice data. In most cases, a single 64kbit/s channel

Data link

In telecommunication a data link is the means of connecting one location to another for the purpose of transmitting and receiving information. It can also refer to a set of electronics assemblies, consisting of a transmitter and a receiver and the interconnecting data telecommunication circuit...

 is sufficient to handle the call setup and call clear-down traffic for numerous voice and data channels.

The logical alternative to CCS is Channel Associated Signaling

Channel Associated Signaling

Channel Associated Signaling , also known as per-trunk signaling , is a form of digital communication signaling. As with most telecommunication signaling methods, it uses routing information to direct the payload of voice or data to its destination. With CAS signaling, this routing information is...

 (CAS), in which each bearer channel has a signaling channel dedicated to it.

CCS offers the following advantages over CAS, in the context of the PSTN:

• Faster call set-up time
  Call set-up time
  In telecommunication, the term call set-up time has the following meanings:#The overall length of time required to establish a circuit-switched call between users....
  
  
• No falsing
  Falsing
  In telecommunications, falsing describes a decoder assuming that it is detecting a valid input when one is not present. This is also known as a false decode...
  
   interference between signaling tones by network and speech frequencies
• Greater trunking efficiency due to the quicker set up and clear down, thereby reducing traffic on the network
• No security issues related to the use of in-band signaling
  In-band signaling
  In telecommunications, in-band signaling is the sending of metadata and control information in the same band or channel used for data.-Telephone:...
  
   with CAS
• Can transfer additional information along with the signaling traffic, providing features such as caller ID
  Caller ID
  Caller ID , also called calling line identification or calling number identification or Calling Line Identification Presentation , is a telephone service, available in analog and digital phone systems and most Voice over Internet Protocol applications, that transmits a caller's number to...
  
  

The most common CCS signaling methods in use today are Integrated Services Digital Network

Integrated Services Digital Network

Integrated Services Digital Network is a set of communications standards for simultaneous digital transmission of voice, video, data, and other network services over the traditional circuits of the public switched telephone network...

 (ISDN) and Signaling System 7 (SS7).

ISDN signaling is used primarily on trunks connecting end-user private branch exchange (PBX) systems to a central office. SS7 is primarily used within the PSTN. The two signaling methods are very similar since they share a common heritage and in some cases, the same signaling messages are transmitted in both ISDN and SS7.

CCS is distinct from in-band

In-band signaling

In telecommunications, in-band signaling is the sending of metadata and control information in the same band or channel used for data.-Telephone:...

 or out-of-band signaling, which are to the data band what CCS and CAS are to the channel.