An E-1 digital trunk operates at 2.048 Mbps divided into 32 time slots with each time slot operating at 64 kbps. These 32 time slots include:
With this method of signaling, each traffic channel has a dedicated signaling channel, that is, channel associated signaling (CAS). The signaling for a particular traffic circuit is permanently associated with that circuit. For E-1 CAS, the signaling channel for each traffic channel is located in time slot 16, which is multiplexed between all 30 traffic channels.
E-1 CAS service is available in Europe, Africa, Australia, and in parts of Asia and South America. The Conference des Administrations Europeenes des Postes et Telecommunications (CEPT) defines how a PCM carrier system in E-1 areas will be used. In addition, the E-1 CAS service may carry national and international signaling bits set in time slot 0:
For each E-1 CAS call, signaling information is sent to the local CO and then to each successive CO until the destination CO is reached. The destination CO attempts to connect to the called party. Concurrently, the destination CO sends back signaling information representing the condition or status of the called party's line. This signaling information passes through the network as audio tones. R2 MF signaling is the international standard for conveying call status using these audio tones. However, the number of tones used, the frequency combinations used, and the adherence to the R2 standard can vary from country to country.
Also, whenever a call is switched via networks or protocols that do not support full R2 MF signaling, call information may be lost. Although many protocols do not require call analysis because the called party condition is received via R2 tones, when operating in environments where call information may be lost, call progress tones (busy, ringback, SIT tones, etc.) may be useful in determining the condition of a call.
The following paragraphs describe R2 MF signaling as it is used in a full R2 network, global tone detection considerations, and Global Call call analysis capability. The protocols do not require call analysis because the called party condition is received via R2 tones; but you can modify the country dependent parameters (.cdp) file so that the protocol can use either call progress tones or call analysis.
Click here to contact Telecom Support Resources
Copyright 2002, Intel Corporation