Inter- Exchange Signaling

We have separated to 2 types.
CAS: Channel Association Signaling
It is signaling that relates to speech channel, such as MFC CCITT R2. For this signaling is included with On-speech Path signaling and Channel Association.
On-Speech Path is signaling that is included in Speech Channel. The register signaling (Pulse) is one type of this signaling.
Channel Association is the signaling that is separated from Speech Channel. Line signaling is the one type of this signaling.
CAS is the transmission of signaling information within the information band, or in-band signaling. This means that voice signals travel on the same circuits as line status, address, and alerting signals.

CCS: Common Channel Signaling
It is like data packets. It is separated from speech channel. CCS is the transmission of signaling information out of the information band. The important and widely used form of this signaling type ISDN and SS7.
CCS offers the following advantages over CAS:
- Faster call setup.
- No interference between signaling tones by network and frequency of human speech pattern.
- Greater trunking efficiency due to the quicker set up and tear down, thereby reducing traffic on the network.
- No security issues related to the use of in-band signaling with CAS.
The most common inter exchange signaling methods in use today are SS7 and R2. (Use for interconnection between PSTN to PSTN, PSTN to PLMN and PLMN to PLMN)
MFC-R2 signaling
R2 signaling is a channel associated signaling (CAS) system developed in the 1960s that is still in use today in Europe, Latin America, Australia, and Asia. R2 signaling exists in several country versions or variants in an international version called Consultative Committee for International Telegraph and Telephone (CCITT-R2). The R2 signaling specifications are contained in International Telecommunication Union Telecommunication Standardization Sector (ITU-T) Recommendations Q.400 through Q.490. E1 R2 signaling is an international signaling standard that is common to channelized. E1 networks. E1 R2 signaling operates across E1 digital facilities. The E1 digital facilities carrier runs at 2.048 Mbps and has 32 time-slots. E1 time-slots are numbered TS0 to TS31, where TS1 through TS15 and TS17 through TS31 are used to carry voice, which is encoded with pulse code modulation (PCM), or to carry 64 kbps data. This image shows the 32 time-slots of an E1 frame:

The two elements to R2 signaling are line signaling (supervisory signals) and register signaling (call setup control signals). Most country variations in R2 signaling are with the register signaling configuration.
Register Signaling (Call Setup Control Signals)
The concept of address signaling in R2 is slightly different than that used in other CAS systems. In R2 signaling, the exchanges are considered registers and the signaling between these exchanges is called Register signaling. Register signaling uses forward and backward in-band Multi-frequency signals in each time slot to transfer called and calling party numbers, as well as the calling party category.
Note: Some countries use two-out-of-six in-band dual tone Multi-frequency (DTMF) instead of forward and backward in-band Multi-frequency signals. Multi-frequency signals used in Register signaling are divided in forward signal groups (I and II), and backward signal groups (A and B). Register signaling starts after the "Seize-ACK" of the line signaling. This diagram and table illustrate forward and backward signal information:

These Register group sequence rules are used to identify the group to which the signal belongs:
·The initial signal received by the incoming exchange is a Group I signal.
·Outgoing exchanges consider backward signals as Group A signals.
·Group A signals received by outgoing exchanges are used to identify whether the next signal is a Group B signal.
·Group B signals always indicate an end-of-signaling sequence.
There are three types of Register signaling:
·R2-Compelled—When a tone-pair is sent from the switch (forward signal), the tones stay on until the remote end responds (sends an ACK) with a pair of tones that signals the switch to turn off the tones. The tones are compelled to stay on until they are turned off.
·R2-Non-Compelled —The tone-pairs are sent (forward signal) as pulses so they stay on for a short duration. Responses (backward signals) to the switch (Group B) are sent as pulses. There are no Group A signals in non-compelled Register signaling.
Note: Most installations use the non-compelled type of Register signaling.
·R2-Semi-Compelled—Forward tone-pairs are sent as compelled. Responses (backward signals) to the switch are sent as pulses. It is the same as compelled, except that the backward signals are pulsed instead of continuous.

Line Signaling
You can use line signaling, which uses TS16 (bits A, B, C, and D), for supervisory purposes such as handshaking between two offices for call setup and termination. In the case of CCITT-R2 signaling, only bits A and B are used (bit C is set to 0 and bit D is set to 1). For two-way trunks, the supervision roles for forward and backward signaling vary on a call-by-call basis. This table illustrates the R2 supervision signal, transition, and direction used on digital trunks:
Line signaling is defined with these types:
·R2-Digital—R2 line signaling type ITU-U Q.421, typically used for PCM systems (where A and B bits are used).
·R2-Analog—R2 line signaling type ITU-U Q.411, typically used for carrier systems (where a Tone/A bit is used).
·R2-Pulse—R2 line signaling type ITU-U Supplement 7, typically used for systems that employ satellite links (where a Tone/A bit is pulsed).
Note: R2-Pulse reflects the same states as the analog signaling. But the analog signal is a steady state (continuous signal), while the pulsed signal stays on for only a short duration. Pulsed is just a single pulse to reflect the state change.

Important Parameter for configured E1 R2
Cyclic Redundancy Check (CRC)
CRC or "cyclic redundancy code" A number derived from, and stored or transmitted with, a block of data in order to detect corruption. By recalculating the CRC and comparing it to the value originally transmitted, the receiver can detect some types of transmission errors. A CRC is more complicated than a checksum. It is calculated using division either using shifts and exclusive ORs or table lookup (modulo 256 or 65536). The CRC is "redundant" in that it adds no information. A single corrupted bit in the data will result in a one bit change in the calculated CRC but multiple corrupted bits may cancel each other out.
Almost use CRC-4 for E1 R2 signaling.

Line Codes
We shall select Line Codes to map with Transmission type.
NRZ for Optic, RZ, AMI, HDB3 use for cable line 2,8,32 Mbit/s via Coaxial Cable, CMI