for healthy network the drop call rate should be less than 1

For healthy network the drop call rate should be less than 1%. There are again number of reasons, which could contribute towards higher dropped call rate is :

1. Drop on Handover

2. Low signal Level

3. Adjacent channel Interference

4. Co-channel Interference

5. Extraneous Interference

6. Link Imbalance

Optimization for Tips :

1. Drop on Handover

The call may drop on handover. It’s mostly high neighbor interference on the target cell, which causes the main problem. Sometime the mobile is on the wrong source cell (not planed for that area but serves due to the antenna overshoot) which may the result in the drop call.

TIPS :

Within optima, monitor the following statistic. Theses statistics are defined under the category of BSC level statistics.

a. total and successful handover on UL/DL quality

b. total and successful handover on UL/DL signal strength.

c. total and successful power budget handovers.

From the above statistics, quality or level must be estimated.

2. Low signal Level

Signal level below -95 dBm is considered to be poor. If the mobile is unable to handoff to a better cell on level basis, the call will possibly be dropped. Topology or Morpology issues may also be there like if Mobile enters into a tunnel or a building , higher RF losses will be develoved.

TIPS:

First of all path balances should be checked. If path balances are deviating fro the standard value then check the BTS transmited power with the help of wattmeter. BTS may transmit low power because of the malfunctioning of radio or higher combiner losses. Also check the feeder losses, antenna connectors. Enable Downlink power control. Power control is be directional. The lower and Upper recieve level downlink power control values should be properly defined.

a. I_Rx Lev_DL_p

Defined the lower value for receive level for the power control to be triggered.

Range 0 to 63

Where 0 = -110 dBm

1 = -109 dBm

63 = -47 dBm

Example : If the value of 20 is set it means that the BTS will start transmitting more if it senses that downlink receive level is below -90 dBm.

b. U_RxLev_DL_p

Defines the upper threshold value for receive level for the power control to be triggered (Range is same as described above).

Example : On setting the value of 50 (equivalent to -60 dBm) BTS will lower down the power.

3. Adjacent and Co-channel Interference

Frequency planning plays a major role to combat adjecent channel and Co-channel Interference. Co channel is observed mostly when mobile is elevated and receives signals from cell far away but using the same frequencies.

TIPS :

An Optimization tools like Neptune could be helpful in identifying the interference on the particular area. Such frequencies can be cleaned from existing frequency plan. The following statistic can also be monitored to confirm that there interferences issues in the cell. These stats are defined in optima under the category of BSC stats.

a. TCH Interference level 1

b TCH Interference level 2

c. TCH Interference level 3

d. TCH Interference level 4

When a TCH timeslot is idle it is constantly monitored for an uplink ambient noise. During a SACCH Multiframe an idle timeslot is monitered 104 times. These samples are the processed to procedure a noise level average per 480 ms. An interference band is allocated to an idle slot depending upon the interference level. The threshold for these levels can be set in the system parameters. Interference level 1 being the least ambient and interference level 4 being the most ambient. While planning the Network care should be taken that the cell do have the proper frequency spacing.

4. Extraneous Interference

Extraneous Interference might be from :

a. Others mobile network

b. Military communication

c. Cordless Telephones

d. Illegal radio communition equipment.

TIPS :

External interference is always measured through spectrum analyser which can scan the whole band. Some spectrum analyser can even decode voice from AMPS circuits or Cordless Phones.

5. Link Imbalance

Sometime the multifunctionality of vendor hardware becomes responsible for high Call Drop Rate. One of the possible scanarios could be :

a. Transmited and receiving antenna facing different direction

b. Transmited and receiving antennas with different tilts.

c. Antenna feeder demage, crossion or water ingress.

d. Physical obstruction.

Traffic Statistics Index AnalysisAt the network optimization stage, the traffic statistics indexes are the basis for network performance optimization. For network optimization, the KPIs, such as congestion rate, call drop rate, and handover success rate, are in common use. These indexes are the external representation of network quality. The radio coverage quality, channel capacity, and cell parameters are the internal factor to affect the network quality. The traffic statistics analysis

aims to look into these internal factors through external factors. Since the mobile network is a complex system, you should consider related DT information, signaling messages, and alarm information for the overall analysis.

1 General Analysis Method

Traffic statistics analysis is performed from BSC overall performance to cell performance, from primary indexes to secondary indexes.

First you should have a rough understanding of the network performance through BSC performance analysis. Here the indexes such as THC traffic intensity, TCH call drop rate, TCH congestion rate, and inter-cell handover success rate should be considered. Attention that in addition to check the percentages of the indexes, you should also check the absolute numbers of the indexes, because the percentages may sometimes hide some cell problems.

After having understood the indexes about the overall network performance, you should analyze the indexes for each cell if finding abnormal indexes. First you should judge if the abnormal index is a common phenomenon or it is really an abnormal one. If it is a common phenomenon, you should begin the analysis from the perspective of coverage, capacity, frequency planning, and cell parameters. If it is really an abnormal case, you should register the corresponding traffic sub-items and analyze them in detail. In addition, you should also make an overall judgment through collecting the information about alarm, engineers' operation, and other external causes. If the traffic statistics analysis cannot contribute a correct judgment, you should employ DT equipment and signaling analyzer for help.

2 High Call Drop Rate Analysis

If the uplink and downlink quality deteriorates to a level that cannot hold normal conversation, the conversation will be disconnected. This is defined as call drop. Since the user mobility and radio propagation is uncertain, call drop always exists in a mobile network. However, optimization measures can be adopted to reduce the call drop rate.

When the call drop rate of the BSC overall performance is found abnormal, you can check TCH performance to judge whether the call drop is just a common phenomenon or it is an individual phenomenon. After that, you can judge whether the high call drop rate occurs in several cells or in all the BTSs. If the call drop is a common phenomenon, you should make an overall check towards the coverage planning, cell parameter planning, and frequency planning to analyze whether the link budget meet the requirements, whether the configuration of the path failure counter is rational, and whether the network interference is too great. In addition, you should also check the BSC hardware, and then perform drive test to check the network coverage.

If it the abnormality is caused by the severe call drop in individual cells, you should confirm whether it is equipment failure that caused the call drop. Generally, alarm messages are always come together with equipment failure, so you can take equipment failure as a reference.

After the equipment failure is excluded, you can analyze the call drop rate from the perspective of interference, coverage, and handover.

1) Interference is divided into uplink interference and downlink interference. You can analyze the uplink interference according to the number of interference bands into which the idle TCHs drop. It is normal that the idle TCHs drop into interference band 1 and interference band 2. For the network with aggressive frequency reuse, it is acceptable that the idle TCHs drop into interference band 3. Here the frequency hopping, PBGT handover and coverage control must be considered. If the idle TCHs drop into interference band 4 or above, you should carefully check the interference. Generally, the interference within the network increases with the traffic volume. The increase of the Rxqual class can be seen through the Rxqual measurement task and Rxlev measurement task. The poor handover

ratio can be seen arising through inter-cell handover performance measurement. In addition, the handover re-establishment failures will result in more handover failures.2) If the coverage is inadequate or it is unbalance on the uplink and downlink, the call drop will also be resulted. You can judge if the Rxlev is adequate through the mean Rxlev of the power control measurement task and the power class. If the Rxlev is still low when the transmitter power reaches the maximum, there are areas with poor coverage. Meanwhile, you can take the mean Rxqual and Rxlev during call drop as a reference. The distribution of TA (timing advance) values can help you estimate the radius of subscriber distribution. Through checking the received channel strength of the neighbor cells, you can analyze the cell coverage. Generally, drive test is needed for a detailed analysis.If the uplink coverage and downlink coverage are unbalance, RF component failure or cable connection problem will occur. The path unbalance can be seen from the path balance measurement task, power measurement task, and call drop measurement task. At this time, the alarm information and user complaint also deserve your attention.

3) Handover failure will prevent the MS from moving to the best cell. In this case, call drop may be resulted. In addition, cross-cell handover and target cell congestion may cause call drop. To solve this problem, you can add neighbor cell relationship and balance the traffic within the cells.The high SDCCH call drop rate analysis is similar to high TCH call drop rate analysis. Acting as the point-to-point signaling channel, the SDCCH is more sensitive to the interference than TCH. In this case, the common method to reduce the call drop rate is to adjust the access threshold and reduce interference.

3 High TCH Congestion Rate Analysis

This section discusses TCH congestion, including the congestion caused by TCH seizure all busy and the congestion caused by TCH seizure failure.

When the congestion rate of the BSC overall performance is found abnormal, you can find out the cells with high congestion rate through checking the TCH performance statistics. In this case, you can discover the problems through analyzing each functional sub-item of the TCH performance statistics of this cell. In addition, you should check whether there is transmission problem, clock problem, or hardware problem through considering the alarm information.

It is a must to analyze the load according to the TCH traffic intensity and the configured TCH capacity.

1) Check if the THC congestion rate is caused by TCH seizure all busy through analyzing the TCH performance measurement of the cell. If the congestion is caused by heavy traffic, you should predict the real traffic of the cell and check if other cells can share the traffic. If it is beyond the optimization capability to enable other cells to share the traffic, you should consider expanding the capacity of the network. The adjustment measures for traffic balance may not be consistent with the principle of minimum radio path loss, so they are applied to emergent causes only. In most cases, you can balance the traffic through adjusting coverage scope, adjusting access threshold, adjusting CRO and handover threshold, or enabling load handover. If the congestion is not caused by TCH seizure all busy, go on with the check.2) Check if the TRXs of the congestion cell work normally. The damage or performance decline of the uplink channels may prevent the MS from accessing other cells. In this case, many cells will be seized, which will cause congestion. The incoming cell handover performance measurement will show that many handovers towards this cell are failures. In this case, you should query the statue of each TRX within each cell through querying the Rxlev performance measurement task or Rxqual performance measurement task. In addition, you should find out which TRX is related to the abnormality through querying the uplink and downlink measurement reports of the same TRX.

3) Check if the congestion rate is related to interference, namely, check if any abnormality is present from the interference band 1 to interference band 5 in the traffic statistics. If the interference is present in a cell, the call drop rate of the cell will be high, and the SDCCH congestion rate will increase accordingly. Moreover, the RACH in the random access performance measurement may be congested, and the immediate assignment success rate will decrease.4) Under some conditions, the congestion of some cells is a result of large coverage. In this case, you should analyze the relationship between TA value and Rxlev through querying the power control mean level, the mean level during call drop, and TA. In addition, you should also use drive test to define the coverage area of the cell. Through querying the TCH availability of the neighbor cell, you can confirm if the congestion is caused by neighbor cell failures. Through querying path balance performance measurement, you can judge if the reason for the TCH seizure failure is that the downlink power is greater than the uplink power.5) Frequent handovers can also cause TCH congestion. Through querying the ratio of the handovers to the call seizure successes, you can check if the ratio is rational. Through querying the incoming and outgoing ratio, you can check if the congestion is caused by irrational handover.

4 High SDCCH Congestion Rate Analysis

The SDCCH congestion rate is mainly caused by heavy traffic. First you should define if the congestion is a common phenomenon or if it is just an individual phenomenon. If it is a common phenomenon, you should analyze if the location update timer is irrationally set, and then calculate the SDCCH capacity to see if it meets system requirement. If it is just an individual phenomenon, you should analyze it from the perspective of equipment, location area, and interference.

1) From the perspective of equipment, you should first check the TRX sound ratio in the BSC overall performance measurement and the SDCCH availability in the SDCCH performance measurement, and then check the TCH activation NACK/TIMEOUT in the TCH performance measurement. After that, you can define if the congestion is caused by board problem.2) Check the messages for SDCCH bearer location update. Irrational location area planning will cause frequent location update, which will result in SDCCH congestion. You are required to analyze of the edge of the location is set at the areas with a great number of subscribers by checking the location area planning and actual drive test. In addition, you are also required to check if the location update messages accounts a too larger percentage of the SDCCH seizure requests at the edge. The method is to query the ratio of the successful SDCCH seizures (location update) to the total SDCCH seizure successes in the SDCCH performance measurement.3) Interference also causes SDCCH congestion. Especially for the networks in which the distance between BTSs is small and the BCCH frequency is aggressive, the system may receive more interference random access signals. The network will allocate a SDCCH for each random access, which causes SDCCH congestion. In this case, the immediate assignment success rate will decrease, the paging success rate will decrease, and the RACH in the random access performance measurement may be overloaded.

5.4.5 Low Handover Success Rate Analysis

The analysis for handover success rate is quite complicated, because it involves capacity, coverage, clock, signaling, equipment, and even MS.

1) If the handover success rate of all cells is low, you should check the problem from the perspective of handover parameters, A-interface circuit, and BSC clock.

2) Filter the cells with poor handover. If a network is run by the equipments of different carriers, you should check if it interoperability problem by comparing the inter-BSC handover success rata with the intra-BSC handover success rate in the handover performance measurement. Generally, the inter-BSC handover success rate is a little lower than the intra-BSC handover success rate. In addition, you need to monitor the signaling messages and data configuration between BSCs and analyze the radio link budget and clock of each carrier.3) Check if any problem is present at the Um interface through comparing the handover success rate and radio handover success rate. The radio handover success rate is equal to or greater than the handover success rate. If the handover success rate is far smaller than the radio handover success rate, you should analyze the ground link and capacity. If the difference between the radio handover success rate and the handover success rate, you need to consider the interference.4) Analyze if it is incoming handover failure or it is outgoing handover failure through querying the incoming cell handover success rate and outgoing handover success rate in the handover performance measurement. After that, analyze the outgoing cell handover performance measurement and incoming cell handover performance measurement of the problem cell so as to find out the incoming handover failure cells from the outgoing cell performance measurement. Confirm if the poor handover is caused by target cell congestion through analyzing the "incoming cell handover failures", "TCH traffic intensity", and "TCH congestion rate (all busy)" of all the incoming handover failure cells.5) Check if any equipment fails through querying the TRX sound ratio, TCH availability, and TCH activation NACK/TIMEOUT of the target cell. Analyze if the TRX performance decreases through querying the Rxlev performance measurement of the target cell.6) Check if any ground link equipment fails through querying the A-interface failures and the ground link breaks during TCH seizure.When the microwave is used for the transmission or during inter-BSC handover, the clock deviation is another cause for poor handover. And this can be proved by the intra-BSC handover failures. For the cells where the clock synchronization is unavailable, the BSIC cannot be decoded, so the handover can never occur. In this case, you need to check if the clock is normal and analyze the call drop rate.

If these two causes are excluded, you need to make adjustment from the perspective of coverage and interference.

To reduce call drop rate and enhance handover success rate, you can leave a margin for the Rxlev and Rxqual during handover. If the Rxlev of a cell is lower than -90dBm during handover, you should check the mean Rxlev and TA value of TCH call drop in the call drop performance measurement and analyze drive test to see if the coverage distance of the cell is too long and if the signal is not strong enough.

For the networks in which better cell algorithms are enabled, you should check the "attempted handovers (better cell)". It is better that the percentage it accounts 60% of the handover causes.

The interference will also affect the handover success rate. When the interference is present, the voice quality will decrease and the call drop rate will increase.

Handover problems are rather complicated. To solve the problems arising in actual work, you are supposed to integrate the methods introduce above, the signaling analyzer, equipment condition, and drive test into consideration

Signalling protocols are decomposed into layers, each layer having a specific function.

Example :

The protocols used in BSS are :

On Layer 1 :

G.703. This protocol is used in the Transmission Network ( A, A-bis) Signalling processing and Radio. This used in the Radio Network ( Um)

On Layer 2 :

LAPD (Link Access Procedure on D-Channel). This protocol is used on A-bis, for safe transport of BTS O&M and Traffic Management messages. BTS O&M use the OML Link, Traffic Management use the RSL Link.

LAPDm. This protocol is use on Um, for safe transport of Traffic management messages between Mobile and BTS.

On layer 3 :

BTS O&M. This protocol is only used on A-bis (between BTS and BSC), for operation and maintenance of the BTS’s.

Traffic Management. This protocol is used on all interfaces ( between Mobile, BTS, BSC and MSC) to handle the phone calls.

Signalling used layer 1, 2 and 3 while speech and data only layer 1.

Golden Rules for collecting Data during drive test:

1- Choose the site under surveying to be above the clutter and repeat types of the clutter you would be looking at.

2- Any thing with clutter less than 100 is not enough.3- Make sure that the GPS surveying option is the same as the one used

where the drive test is being performed.4- Make sure that the Dautch value of the GPS is the same as the one set for

the country where the drive test is being made.5- Better collect data in the format of, Degrees: Decimal Points Degrees.6- Every 6 degrees you move result is one point change in the whole picture

the UK being the reference point at 30, To the left it increases and to the right it decreases.

7- Sampling rate, 40 Samples per 40 wavelengths. To reduce the effect of Radio fading.

8- Sampling can be in Distance and Time. Better do it in Distance especially if you are driving in traffic jams.

9- Do not drive away too much from the site.10- Drive in to the Site passing through the clutter as well as crossing the

clutter11- Try and drive many roads close to the site unless the clutter is so

important.12- Try to avoid driving the same road twice.

13- Do not drive over a bridge or in to a tunnel inside a clutter area, otherwise take that parts of data a out of the data file collected for this clutter.

14- Make short calls and Long calls, Short calls is the average duration by customers, short calls are to know whether calls will survive the setup and the termination successfully, it also determines the setup time…

15- Long calls are to test the hand over capabilities.16- Adjacent channels are channels with coverage of 9db more than the serving

cell.17- The co-channel interference is interference from channels have frequency

lower the serving channel.18- For the adjacent channel you could be served from this adjacent channel

but the system can not read it and it gives the name of another channel19- The 6 neighboring cells are those who are listed in the scan list these do

not mean that these are the only channels that the phone can see.20- You have to make sure of the values you are getting out of the surveying

equipment do actually make sense.21- Know the exact power out of the antenna, ERP level, (Effective Radiation

Power).22- Everything about the antenna conditions, during the test time should be

reported in the final report.23- Weather conditions should be reported as well.24- Know the distance and direction of any buildings blocking your way.25- Finally, report all sorts of problems.

Systematic Important Timers

1 T3101

I. Definition

T3101 is the BSC timer controlling time of immediate assignment process.

II. Format

T3101 ranges from 0 to 255s. The recommended value is 3s.

III. Configuration and Influence

In an immediate assignment process, the BSC requires BTS to provide SDCCH to set up signaling channel. When the BSC sends a channel activation message, T3101 starts timing. When the BSC receives the setup instruction sent by BTS, T3101 stops timing. When T3101 expires, the system releases corresponding SDCCH resources. Proper configuration of T3101 reduces congestion due to dual assignment SDCCH effectively.

The greater the T3101 is, the longer the inefficient time for using signaling resources is. For example, if the extended transmission delay is improperly configured (usually the sum of T and S is over small), the MS fails in responding to the network side, so the MS resends the random access request message.

Therefore, the network side will assign SDCCH (the network cannot distinguish the repeated sending access request from the first send). For better use of signaling resources, especially in activating queue function, you must configure T3101 to a smaller value. The minimum interval for sending channel activation message and receiving setup indicator is 600ms. For non-overload BSS, the maximum interval is 1.8s.

2 T3103

I. Definition

In inter- and intra-BSS handover, the BSC determines the time for keeping TCH both in handover-originated cell and target cell. When the time receives handover completion (intra-BSC) or clearing (inter-BSC) message, T3103 stops.

II. Format

T3103 ranges from 0 to 255s. The recommended value is 5s.


The following paragraph is an example of inter-BSS handover.

When T3103 receives the handover command, it is reset and starts timing. When it receives clearing command, it is reset. This means that T3103 reserves two channels when it is timing, one channel for source BSC, and one channel for target BSC. If it is over long, two channels are occupied for a long time and resources might be wasted.

According to the tests, if the NSS timer is properly configured, the handover process occurs within 5s. Therefore, the recommended value is 5s.

3 T3105

I. Definition

See the protocol 0408 and 0858. When sending physical information, the network starts T3105. If the timer expires before receiving any correct frames from MS, the network resends physical information and restarts the T3105. The maximum repeated times is Ny1.

II. Format

T3105 ranges from 0 to 255, with unit of 10ms.


The physical information is sent on FACCH. The time for sending four TDMA in a time on FACCH is about 18ms. If the next physical information is just sent 18ms after the first one, probably the first physical information is still being sent. The minimum time for sending physical information continuously and most quickly is 20ms.

IV. Precautions

T3105 is related to the timer NY1. If T3105 is small, configure NY1 to a greater value. If a handover trial fails and the T3105 of the target cell expires for Ny times before the original

cell receives the HANDOVER FAILURE message, the target BTS sends the CONNECTION FAILURE INDICATION message to the target BSC.

The counter of target BSC is renewed though MS might return to the original channel. To avoid this, the T3105 must meet the following foulard:

Ny * T3105 > T3124 + delta

Wherein, delta is the time between expiration of T3124 and receiving HANDOVER FAILURE message by original BSC.

4 T3107

I. Definition

T3107 is a BSC timer, restricting the time for executing TCH assignment instruction. It caters for TCH assignment of intracell handover and channel assignment of calling.

II. Format

T3107 ranges form 0s to 255s. The recommended values are as follows:

10s when channel resources are enough.

5s when channel resources are limited.


T3107 starts after the BSC sends the ASS_CMD message to BTS. It stops after the BSC receives the ASS_CMP or ASS_FAIL message sent by BTS. If T3107 expires, the system judges that the MS disconnects to the network, so the occupied resource is released to other MSs. According to the measured statistics result of network, the channel assignment is complete within 2s. If the BSC does not receive ASS_CMP message after 2s, the assignment command fails.

If the radio link is bad and some information must be resent, the process might be prolonged to 5s. To avoid premature disconnection, configure T3107 to 10s. In this way, the MS can reuse the original channel when handover or assignment fails. Therefore the call drop due to intracell handover decreases or the system service quality of re-assignment is improved (if the system supports re-assignment function). However, the channel resource might be wasted for several seconds. When the network capacity is limited, you must save the resource as possible.

5 T3109

I. Definition

The BSC restricts the releasing resource of SACCH by T3109.

II. Format

T3109 ranges from 3s to 34s. The recommended T3109 is as follows:

T3109 = a + RdioLinktimeOut x 0.480s, a = 1s or 2s.


T3109 measures the time for channel releasing indicator after sending MS clearing instructions. It starts after the BSC sends DEACT_SACCH message to BTS. It stops after the BSC receives the REL_INC message sent by BTS. When T3109 expires, the BSC sends the CLEAR REQUEST message to MSC.

IV. Precautions

The sum of T3111 and T3109 must be greater than RadioLinkTimeOut. If T3109 is over small, the corresponding radio resources are re-allocated before RadioLinkTimeOut is due (radio link is not released).

6 T3111

I. Definition

T3111 is a connection release delay timer, used in deactivation of delayed channel after disconnection of major signaling link. T3111 aims to spare some time for repeated disconnections. When BSC receives the REL_IND message sent by BTS, T3111 starts. For time protection, T3111 stops until expiration and the BSC sends the RF_CHAN_REL message to BTS.

II. Format

T3111 ranges from 0s to 5s.

The recommended value is 2s.


After the disconnection of major signaling link, T3111 delays the release of channels. It allows the base station to retransmit the instruction for releasing radio channels to MS within delayed time. After the base station sends a release request massage, the radio resources remain for T3111 time.

If the system capacity is small, configure T3111 as short as possible. The minimum value of T3111 is 2s, over five multiples of the time for resending MS the instruction for releasing radio channel resources. A greater T3111 might be of no help, but affects congestion of SDCCH and TCH easily.

7 Parameter T3212

I. Definition

In a GSM network, the causes to location updating are as follows:

The MS attach.

The MS detects that its location area changes.

The network forces MS to update location periodically.The network controls how frequent the MS updates location, and the period for location updating is determined by the parameter T3212.

II. Format

T3212 ranges from 0 to 255, with unit of 6 minutes (1/10 hour). If T3212 = 1, it means that T3212 is 6 minutes. If T3212 = 255, it means that T3212 is 25 hours and 30 minutes. If T3212 = 0, it means that MS is not required for periodical location updating in the cell. The recommended T3212 is 240.


As an important means, the periodical location updating enables network to connect to MSs closely. Therefore, the short the period is, the overall service performance of the network is. Anyhow frequent periodical location updating brings two negative aspects:

The signaling flow of the network increases sharply and the utilization of radio resource declines. When the period is over long, the processing capability of network elements (NE, including MSC, BSC, and BTS) is directly affected.

The MS must transmit signals with greater power, so the average standby time is shortened sharply.

Therefore, configure T3212 according to resource utilization in various aspects of network.

T3212 is configured by equipment room operators. Its value depends on the flow and processing capability of each NE. Configure T3212 as follows:

Configure T3212 to a greater value (such as 16 hours, 20 hours, or even 25 hours) in areas with heavy traffic and signaling flow.

Configure T3212 to a smaller value (such as 3 hours or 6 hours) in areas with low traffic and signaling flow.

Configure T3212 to 0 in areas with traffic overrunning the system capacity.

To configure T3212 properly, you must permanently measure the processing capability and flow of each UE in the running network, such as:

The processing capability of MSC and BSC

A interface, Abis interface, and Um interface

The capability of HLR and VLR

If any of the previously listed NEs is overloaded, you can consider increasing T3212.

IV. Precautions

T3212 cannot be over small. Otherwise, the signaling flow at each interface increases sharply and the MS (especially handset) consumes increasing power. If the T3212 is smaller than 30 minutes (excluding 0), the network will be fiercely impacted.

Configuring T3212 of different cells in the same location area to the same value is recommended. In addition, the T3212 must be consistent with related parameters of switching side (smaller than the implicit detach timer at switching side).

If the T3212 of different cells in the same location area is the same, in the cell reselection, the MS continues to time according the T3212 of the original cell. If the T3212 of the original and target cell in the same location area is different, the MS uses the T3212 of the original cell modulo that of the serving cell.

According to the actual tests of MS in the network, if the T3212 in the same location area is different, after the MS performs modulo algorithm based on behaviors of some users, the MS might power on normally. However, the MS fails in originating location updating, so the network identifies it as implicit detach. Now the MS powers on normally, but a user has powered off prompt appears when it is called.

8 T3122

I. Definition

T3122 defines the period that the MS must wait for before the second trial calling if the first trial calling fails. It aims to avoid congestion of SDCCH due to repeated trial calling by MS and to relieve system load.

II. Format

T3122 ranges from 0s to 255s. The recommended value is 10s.


The value of T3122 is included in the immediate assignment reject message. After the MS receives the immediate assignment reject message (no channels for signaling, A interface failure, overload of central processing unit, namely, CPU), it can send new trial calling request after T3122. T3122 aims to relieve radio signaling and voice channel resources.

T3122 also help avoid systematic overload. When the CPU is overloaded, the system multiplies T3122 by a factor (determined by processorLoadSupconf) to increase T3122 through overload control. In peak load time, you can manage network access by increasing T3122. Namely, you can increase the interval between two continuous trial callings to relieve network load.

9 T3124

I. Definition

T3124 is used in occupation process in asynchronous handover. It is the time for MS to receive the physical information send by network side.

II. Format

Configure it to 675ms when the channel type of assigned channel for HANDOVER COMMAND message is SDCCH (+ SACCH). Configure it to 320ms in other situations.


When the MS sends the HANDOVER ACCESS message on the primary DCCH, T3124 starts. When the MS receives a PHYSICAL INFORMATION message, the MS stops T3124, stops sending access burst, activates the PCH in sending and receiving mode, and connects to the channel if necessary.

If the assigned channel is a SDCCH (+ SACCH), you must enable MS to receive a correct PHYSICAL INFORMATION message sent by network side in any block. If T3124 expires (only in asynchronization) or the low layer link fails in the new channel before sending the HANDOVER COMPLETE message, the MS proceeds as follows:

1) Deactivate the new channel

2) Restart the original channel

3) Reconnect to TCH

4) Trigger to setup primary signaling link

Then the MS sends the HANDOVER FAILURE message on the primary signaling link and return normal operation before trial handover. The parameters for returning the original channel are those before response to the HANDOVER COMMAND message (such as in encryption mode).

10 T11

I. Definition

T11 is an assignment request queue timer.

II. Format

T11 is determined by equipment room operators. It indicates the maximum queuing delay for assignment request.


When the BSC is sending the ASSIGNMENT REQUEST message, no TCHs are available. The ASSIGNMENT REQUEST message must be put to a queue and the BSC sends the QUEUING INDICATION message to MSC. Meanwhile, T11 starts timing.

When the BSC sends the ASSIGNMENT COMPLETE message (TCH is successfully assigned) or the ASSIGNMENT FAILURE message (TCH is not assigned) to MSC, T11 stops timing.

If T11 expires, the corresponding ASSIGNMENT REQUEST message is removed from queue and the BSC sends a CLEAR REQUEST message with the cause of no radio resource available to MSC to clear calling. Assignment queuing helps reduce service rejection times due to congestion, so enabling it is recommended in a network. Anyhow, T11 cannot be over great and it must be configured according to customer habits.

11 T200

I. Definition

T200 is important (both the MS and base station have T200) at Um interface in data link layer LAPDm. LAPDm has different channels, such as SDCCH, FACCH, and SACCH, and the transmission rate of different channel is different, so T 200 must be configured with different values. The type of the channels corresponding to T200 is the value of the T200.

II. Format

Different channels corresponds different values of T200. According to the protocol, when SAPI = 0 and SAPI = 3, the T200 of corresponding data link is dependently implemented, depending on delay of synchronous processing mechanism and process in layer 1 and layer 2.

Table 7-1 Value range and default of each type of T200

T200Minimu

mMaximu

mDefault

T200_SDCCH_SAPI0 50 100 60; /* = 60 * 5 ms */

T200_FACCH_Full_Rate 40 100 50; /* = 50 * 5 ms */

T200_FACCH_Half_Rate 40 100 50; /* = 50 * 5 ms */

T200_SACCH_TCH SAPI0 120 200150; /* = 150 * 10 ms */

T200_SACCH_TCH SAPI3 120 200150; /* = 150 * 10 ms */

T200_SACCH_SDCCH 50 100 60; /* = 60 * 10 ms */

T200_SDCCH_SAPI3 50 100 60; /* = 60 * 5 ms */


T200 avoids deadlock in sending data in data link layer. The data link layer changes the physical link in which error occurs easily to data link with no errors. At the two ends of the data link communication system, a confirm-to-resend mechanism is used. Namely, receiving a message by the receiver must be confirmed by the sender.

If it is unknown that the message is lost, both two ends wait for messages, so the system confronts a deadlock. Therefore, T200 is used by the sender. When T200 expires, the sender judges that the receiver fails in receiving the message, so it resends the message.

When the sender needs to confirm whether the receiver has received the message, T200 starts. When the sender receives the response from the receiver, T200 stops. When T200 expires, the resending mechanism starts. If the sender receives no response from the receiver after multiple resendings, it sends ERROR INDICATION (T200 expiration) to layer 3.

IV. Precautions

T200 must be properly configured to ensure a predictable behavior at Um interface. The rules for configuring T200 include:

The potentially-existing lost frames in radio link must be detected as possible.

Necessary retransmission of frames must start at the earliest possible moment.

If the response is delayed due to UE failure, the T200 cannot expire before receiving and processing the next frame from the opposite end.

If T200 expires and no other frames are sent by preference, the related frames must be resent in the message block.

T 200 starts immediately after next PH-READY-TO-SEND.

12 N200

I. Definition

N200 is the resending times after expiration of T200.

II. Format

To configure N200, follow rules below:

1) When SAPI = 0 or 3, N200 depends on the state and the channel used.When multiframe operation is set up, it ensures a common time value for layer 2 link failure in all channels. For layer 2 link establishment and release, configure N200 to 5.

2) In timer recovery state, configure N200 as below:

5 (SACCH)

23 (SDCCH)

34 (FACCH of full rate)

29 (FACCH of half rate)

3) When SAPI is unequal to 0 or 3, configure N200 to 5, as shown in Table 1-6.

Table 7-2 Situations of SAPI unequal to 0 or 3

SAPI ChannelValid

response delay

Minimum

resending delay

Maximum resending delay

Tresp Trmin Trmax Note 3

0 SDCCH MS: 11 51 51

BSS: 32

0FACCH/Full rate

9 26 39

0FACCH/Half rate

10 34 44

3 SDCCH MS: 11 51 51 Note 1

BSS: 32

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3SACCH(with TCH)

25/129 Note 2

312 416 Note 2

The TDMA frame is the measurement unit of values in this table, equal to 120/26ms (approximately 4.615ms)

Note 1: It caters for the process without SAPI 0 transmission. Otherwise, it does not have a upper limit due to the priority of SAPI 0 transmission.

Note 2: You can configure it to a greater value only when PCH is unavailable due to SAPI frame transmission if SAPI = 3.

Note 3: It caters only for sending monitoring frames that are available and without F equal to 1.


If the BSC fails in receiving lay 2 response message after multiple resending, it sends the ERROR INDICATION message (T200 expires) to layer 3. The BSC takes statistics of ERROR INDICATION message by corresponding traffic measurement counter. When T200 or N200 is configured to an over small value, call drop occurs probably due to ERROR INDICATION.

Much has recently been made of my ethnic identity although this is a matter of no relevance whatsoever to a reasoned discourse on the existence of the Ethiopia Commodity Exchange. However, when the unnecessary gets in the way of the important, however unpleasant it may be, it must be faced. I am Ethiopian, as truly and wonderfully as that is, and no one has the right to define, reduce, or otherwise dismiss my identity. I do not apologize for or defend who I am, as each one of us, whoever we are, has a God-given set of circumstances that uniquely defines us.

My reality is that, born in Addis Ababa, I first left Ethiopia with my family at the age of four to live in New York city, accompanying my father, Zaude Gabre-Madhin, who was a senior United Nations official, prior to which he served in the Imperial government. Upon returning a few years later, my family then left Ethiopia again, escaping the chaos of the new Dergue regime, this time to Rwanda and later Togo, Malawi, and Kenya. I thus grew up in six different countries, going to school in French as well as English, and learning Swahili along the way. Throughout this time, my parents, to whom I owe everything, instilled in me and my sisters the deepest love and pride for our country Ethiopia. As I grew up in different cultures, grappling to understand my adolescent identity, I drew on the stories my parents told me of my heritage and of those who came before me. My mother, Bizuwork Bekele, who never missed a chance to boast about her beloved Harar, shared stories of my incredible great-grandmother, Imahoy Saba Yifat, from Menz and Gondar by origin, who lived in rural Hararghe as a widow after the Italian invasion and was one of the few women fighters of her time standing up to the invaders to defend the land and her six children. I heard about her son, my grandfather, Ato Bekele Haile, a respected magistrate serving as a judge in Harar town, himself of Gurage and Amhara ancestry, and of my mother’s birth in the historical site today known as the House of Rimbaud. As a young child, I loved to sit for hours with my maternal grandmother, Imahoy Beletshachew Habte-Giorgis, a witty, intelligent,and extremely strong-willed woman who would often exclaim in Afan Oromo which she and her children, including my mother, spoke fluently, as she laughed

recalling how she managed her coffee farms in the areas around Jijiga, Fedis, and Deder, where many of my relatives still live today.

My father, for his part, mostly to amuse his daughters, named the water tank in our UN provided house in Kigali, Rwanda, “Bulga Springs” to recall his father’s birthplace in northern Shewa. He would proudly speak of my grandfather, Fitawrari Gebremedhin, a noble and highly disciplined official in Emperor Menelik’s time, who later settled in Wolaita Soddo in the late nineteenth century, marrying my grandmother, Woizero Ayalech Alaye, niece of the great Wolaita King Tona. At the age of seven, I remember visiting Soddo where my father was born and where many of my relatives still live, to spend time in his last years with my grandfather who was then nearly a century old. A tall, dignified, and handsome man, deeply religious, my grandfather showed me and my sister his coffee farm and I remember him speaking of my much loved late grandmother, and of his childhood and the family still in Bulga, and his laughing politely, not understanding, as I chattered to him in English with children’s jokes I had learned in New York.

Thus I grew, within and outside Ethiopia, celebrating all the different identities and cultures that are woven beautifully into the tapestry of my identity as an Ethiopian. To my parents, always , we were Ethiopian and that was something to be deeply proud of, recognizing and cherishing all of our different ethnic strands. I never knew until much later, nor did it matter, which particular ethnic group I should claim. In my extended family, my aunt married a man from Wollega and my uncle married a woman from Asmara, my great aunt married into the Abba Jifar clan in Jimma, and the list goes on. So the Ethiopia I knew growing up with my cousins was a kaleidoscope of identities bound together in one Ethiopia.

This is my Ethiopian story, and it is unique to me, as each Ethiopian would similarly have. It is the story of my Ethiopia, the Ethiopia for which I have enduring love and to which I have returned after thirty years to contribute in the best way I know how. This is my Ethiopia to which I bring all the global experiences which have shaped me, as I have lived my adult years in Mali, Switzerland, and the United States, trained and worked in some of the best institutions, and traveled and explored dozens of countries around the world. This is my Ethiopia that represents all of my heritage, the strong and courageous women and men in my family through the ages whose blood flows in me. This is my Ethiopia for which I am willing to work, fight, and believe all things are possible. This is my Ethiopia to which I have brought my US-born sons, to instill in them the pride and love of all that we are as Ethiopians. I would like to teach them that in our increasingly inter-connected world, they are Ethiopians but also global citizens.

Ethiopia is ours, to claim, to build and to restore. Rather than engage in destructive ethnic bigotry, far better to embrace all of what we are and to build together a better future for our children. My personal identity is irrelevant to my choice or ability to lead an initiative to bring a better marketing system for all Ethiopians, regardless of their ethnic roots or which corner of the country they claim. A market is above all a connection between humans, an exchange of goods and money that links two sides. The market is neutral as to who is on either side, it is the connection that counts. I have always

found traders to be the most pragmatic people in the world. Let us too live by this market principle: we are far richer and far stronger if we build on our connectivity to each other in

meaningful ways, and that much weaker if we seek isolation and succumb to narrow divisiveness. Let us be like the market. I believe it is our only hope

By Eleni Zaude Gabre-Madhin, PhD

for healthy network the drop call rate should be less than 1

Documents

tch activation nack timeout

assignment success rate

handover success rate

error indication message

equipment room operators

clear request message

assignment reject message

assignment request message