1.1. Details:
Measuring arrangements for the testing of call pathes:
The following table summarizes ports and their identifiers which take part in the interconnection:
Room | B.211 | B.211 | B.211 | B.212 | B.212 | B.212 | B.213 |
---|---|---|---|---|---|---|---|
Node | D1 | D1 MSS-2 | MSS-2 | MSS-1 | MSS-1 D2 | D2 | H3 |
Port type | 2wire VF | E1 | GBE/IP | GBE/IP | E1 | 2wire VF | E1 |
G.712 Port id. | A | D | --- | --- | D | A | |
Definity Port id. | 1a0203 | 1a10 1a11 | --- | --- | 1a11 1a10 | 1a0203 | |
AXD Port id. | --- | 1/3/1 | 1/5/2 | 1/4/2 | 1/6/1 1/6/2 | --- | 1/6/1 |
Cross connect | XC212/1a | XC211/1 | --- | --- | XC212/1e,2e XC212/1d,2d | XC212/1b |
The tested call path (switched voice frequency channel, B channel) terminates in the voice frequency ports (A ports) of the D1 and D2 exchanges.
These ports will used alternately by analogue telephones and PCM channel analyzer for
setting up connection between ports (call control and connection control) and doing tests (transmission performance analysis), respectively.
The receiver of the PCM channel analyzer can be connected to the D port of the call path, too. This feature allows the separate examination of the individual segments of the call path.
The signal converters of the tested call pathes have been summarized in the following table:
Room | Call Path | B.211 | B.211 | B.211 | B.212 | B.212 | B.212 | B.213 | |
---|---|---|---|---|---|---|---|---|---|
Node | D1 | D1 | MSS-2 | MSS-1 | D2 | D2 | H3 | ||
conversions (D1->D2 direction) | Main | 2/4 wire | A/D | TDM/IP/RTP | --- | IP/RTP/TDM | D/A | 4/2 wire | |
--- | Hybrid | Media Gateway | optical line (GBE) | Media Gateway | Hybrid | ||||
conversions (D2->D1 direction) | Main | 4/2 wire | D/A | IP/RTP/TDM | --- | TDM/RTP/IP | A/D | 2/4 wire | |
conversions (D2->H3 direction) | Auxiliary | -- | -- | -- | --- | --- | A/D | 2/4 wire | TDM/RTP/IP |
conversions (H3->D1 direction) | Auxiliary | 4/2 wire | D/A | -- | --- | --- | --- | IP/RTP/TDM |
This call will be an interurban one, because both Definity exchanges (D1, D2) and the VoIP trunk interconnecting the exchanges (MSS-1, GBE, MSS-2) take part in it.
1.2. Parameters of the call path under test (A port):
1.3. Parameters of the call path under test (D port): (Source: the configuration database of the Definity exchanges.)
1.4. Parameters of the routing:
Exchange | Dial plan | First digit | E1 port | Timeslot selection | Available timeslots |
---|---|---|---|---|---|
D1 | coordinated | 4xxx | 1a10 | ascend | 2,3,4 or 5 |
D2 | coordinated | 3xxx | 1a11 | ascend | 2,3,4 or 5 |
H3 | coordinated | 2xxx | Cisco 2600gw1 | ascend | 1 to 24 |
1.5. Parameters of the call path under test (GBE/IP port):
Actually, to find these parameters is a part of Task 2.4.
1.6. Call control:
Basically there is no connection between the A ports of the D1-D2 exchanges. Before starting the measuring - because it is a switched network - we have to set up the call path (the voice frequency channel) under test. While EP2 cannot dial, we will set up connection with telephones binded to the terminal of the channel. The dialing number of the A ports are: 3007 (D1), 4007 (D2).
Sending one of the two dialing numbers (towards of which we want to set up the call) to the caller exchange it will carry on the call setup with the sending of a DSS1 SETUP message in the 16th time slot of its E1 port. This message will be transparently forwarded through MSSs to the called exchange. After alerting and callee's hang up the call path will be established in a time slot according to the above routing table. The signal transmission on these call pathes (B channels) is not necessary transparent in MSSs, it is quasi transparent in good case depending on the configuration.
In the actual measuring arrangement the call control messages of the D1-D2 exchanges do not influence the operation of switches, signal converters (Media Gateways) of MSSs. In this case MSSs will be configured (regarding connection control) through the control interface of MSSN (MGC).
1.7. Connecting the EP2 after the setup of the call path:
After setting up the connection we should detach the telephones from the line and attach EP2 to line so that the DC loop may not be cut off. In this will help us current loops which are two-poles with low impedance on DC, but high impedance in sound frequencies. Connecting a current loop to the line in parallel it closes the line at DC, but not in sound frequencies, so the signals of the EP2 connected to the line will get into the channel. On receiver side current loop can be substituted with a 600 ohm resistor, however, in this case the receiver of the measuring equipment should be set to "high impedance input" mode.
Exercise the usage of EP2 with the help of the following task:
Switch the EP2 on, connect the output of the voice frequency measuring interface
with the input of the interface, and measure the "transmission characteristic" of
the measuring cord. Display the results graphically, and with numeric characters.
Report is not necessary.
Settings of the EP2 are the following:
MEAS_ITEM | CONFIG | VARIABLE_PARAM | RELATIVE LEVELS |
---|---|---|---|
GAIN | A-A | FREQUENCY | 0 dBr |
First of all we examine the transmission performance characteristics of a classical digital voice path exempt from VoIP conversion. We connect EP2 to the "A" ports and "D" ports of "D2" exchange and carry out the measurements mentioned in the following table using the setting described in the table:
Measured parameter | MEAS_ITEM | CONFIG | VARIABLE_PARAM |
---|---|---|---|
Gain | GAIN | A-D (CH 2..5) | NONE (TONE 1020 Hz, -10dBm0) |
Frequency characteristics (gain versus frequency) | GAIN | A-D (CH 2..5) | FREQUENCY (200..3600 Hz) |
Group delay | GROUP_DELAY | A-D (CH 2..5) | FREQUENCY (200..3600 Hz) |
linearity (gain vs. signal level) | GAIN | A-D (CH 2..5) | TX_LEVEL (-60 .. +5 dBm0) |
Quantization distortion | TOTAL_DIST | A-D (CH 2..5) | TX_LEVEL (-60 .. +5 dBm0) |
Noise | WEIGHTED_NOISE | A-D (CH 2..5) | TIME (60 sec) |
Notes:
Menu | Item | Next Menu | Data |
---|---|---|---|
Voice/Media Gateway | Open Devices | Media Gateway/Devices (list) | |
Media Gateway/Devices | Select b211/1/3/1 or b212/1/6/1 | Media Gateway/Device | |
Media Gateway/Device | Click Physical Location 1-3-1 or 1-6-1 | Media Gateway/Call Path Tracing (list) | Connection list in a Media Gateway |
Media Gateway/Call Path Tracing | Click a Termination Id. | Media Gateway/Call Path Trace Details | administrative, IP and VoIP attributes of a Connection |
- | |||
Voice/Mediation Logic | Open Devices | Mediation Logic/Devices | |
Mediation Logic/Devices | Filter MG name b212, Device type any | Mediation Logic/Devices (list) | |
Mediation Logic/Devices | Select b212/1/6/1 | Mediation Logic/Device | |
Mediation Logic/Device | Click Switch Device Id. | Mediation Logic/Call Path Tracing (list) | Connection list in a Mediation Logic (Call Server) |
Mediation Logic/Call Path Tracing | Select a Switch Device | Mediation Logic/Call Path Trace Details | administrative, IP and VoIP attributes of a Connection in the Mediation Logic |
- | |||
Voice/Media Gateway | Open Media Gateways | Media Gateway/Media Gateways (list) | |
Media Gateway/Media Gateways | Select b211 | Media Gateway/Media Gateway | |
Media Gateway/Media Gateway | Modify IP Parameters | Media Gateway/IP parameters | Diffserv, Jitter buffer |
Media Gateway/Media Gateway | Interface related IP addresses | Media Gateway/Interface related IP addresses | Routing control parameters |
- | |||
IP Services/Address Administration | Open IP addresses | Address Administration/Open IP addresses | List of used IP addresses |
For the explanation of unknown attributes use the index!
Measured parameter | MEAS_ITEM | CONFIG | VARIABLE_PARAM |
---|---|---|---|
Gain | GAIN | A-A | NONE (TONE 1020 Hz, -10dBm0) |
Frequency characteristics (gain versus frequency) | GAIN | A-A | FREQUENCY (200..3600 Hz) |
Group delay | GROUP_DELAY | A-A | FREQUENCY (200..3600 Hz) |
linearity (gain vs. signal level) | GAIN | A-A | TX_LEVEL (-60 .. +5 dBm0) |
Quantization distortion | TOTAL_DIST | A-A | TX_LEVEL (-60 .. +5 dBm0) |
Noise | WEIGHTED_NOISE | A-A | TIME (60 sec) |
Note that the measurements carried out up to now was an in-circuit examination, because we examine channel filters with the measurement of the gain vs. frequency and A/D-D/A converters with the measurement of linearity and total distortion. In the following we examine further circuits of the voice frequency subscriber interface.
During measurement in can be occured that telephone equipments used to set up the connection suffered from (positive) feedback through the handset. This phenomenon is caused by the final closing attenuations of hybrids on the analogue interface cards of the exchange. How large is this attenuation, that shall we determine in this measuring task.
We can not measure the closing attenuation "af" of the hybrid directly, but we can calculate it from a measurement on the 2 wire interface between "A-D" points. The epitomized measuring arangement containing only signal converters can be seen on the following figure:
+--EP2--+ | PCMRX | +---+---+ | srx |----ab3-------------------| +-----+ +--+----+ | +-----+ +->----| A/D |--|EC|VoIP|--+--| D/A |->-+ | A +-----+ +--+----+ +-----+ | +-EP2--+ BN--X-| |af |-X-stx-| VFTX | | | +-----+ +----+--+ +-----+ | +------+ +-<----| D/A |--|VoIP|EC|-----| A/D |-<-+ +-----+ +----+--+ +-----+ |----ab2-----------|------ab1-------------| rr 0 tr where: BN - Balanced Network - in the measurement a telephone device or a resistor of 600 ohms. EC - Echo cancellation tr = relative level of transmitter side rr = relative level of receiver side ao = pass attenuation of the hybrid af = closing attenuation of the hybrid stx = level of transmitted measuring signal srx = level of received measuring signal Attenuation of the individual parts of the whole transmission path: ab1= ao + tr = 3 + 3.5 = 6.5 dB ab2= - tr = - -3.5 = 3.5 dB ab3= + td = + 3.5 = 3.5 dB Closing attenuation of the hybrid: af = stx - srx - (ab1+ab2+ab3) dB
The attenuation can be derived from the measured values of signal level using the above mentioned correction.
The measuring arangement (We do not made a large mistake during the measurement when we connect to point "D" with high impedance mode instead of drop-insert mode.): We have to measure signal level in MEAS_ITEM>LEVEL mode.
Task: Derive the value of the closing attenuation of hybrid in D1 exchange at 1020 Hz with termination of a telephone and a 600 ohm resistor and with and without echo cancellation!
Last questions at the end of the mandatory tasks:
Measure the attenuation of the out of band input signals in a PCM channel at 8.5 kHz and -25dBm0.
The measuring signal can be inserted from an EMS 10 equipment into the channel. The
received component of 500 Hz can be measured with EP2 selectively. During measurement we sould break the measuring signal for a while to check if we really receive the signal caused by the measuring signal or not.