Analyzing Daily Traffic Data

Everyday QoS team will prepare a KPI report which includes data of the current performance of the network.  Total network is divided cluster wise and those clusters were monitored by Engineers assigned to that section. So every cluster is monitored daily and necessary  actions will be taken immediately. Some of the important KPI values  in the form of an equation  are listed below.

• Accessibility to SDCCH without Location Update (LU) = (SDCCH assign success rate) / (SDCCH Assign Request Rate) 

• SDCCH Drop Rate = (SDCCH Assign Success Rate) / (SDCCH Drop Rate)

• Accessibility to TCH = (RTCH Assign Success Rate) / ( RTCH Assign Success Rate * unsuccessful RTCH Assign Rate)

• TCH drop rate = (TCH Assign Success Rate) / (TCH Drop Rate)

• Accessibility to TCH without congestion = TCH (Traffic channel)accessibility,without considering the assignment failure due to congestion of traffic on the cell

• Call success rate = (SDCCH Access Rate)  X (1-SDCCH Drop Rate) X (TCH Access Rate) X (TCH Drop Rate)

In addition to above QoS team will also prepare reports on following,

•  Total Carried Traffic = Average holding time × Busy hour call attempts

 [Average Holding Time = (Total usage time) / (Total successful call attempts)]

•  Offered Traffic = Carried Traffic + Blocked Traffic + guard time × call attempts(guard time = 3 s)
• Congestion (%) = [(period of all channels busy (s))/3600] X 100

To  calculate  above  indicators  we  need  to  collect  data  from  the  network  and  those  data  is analyzed  using predefined macro programs  to make those data much more human readable. I got a  chance to analyze daily reports and then check their issues using NPO (Network Performance Optimizer) and MapInfo Tools. If we identified any issue in a particular site due to poor performance indicated in the daily report, we can generate reports using NPO.  NPO receives  data  through  OMC-R  and  OMC-R  collects  those  data  from  BSCs.  Those  reports come with graphical aid, so it is a very easy and convenient way of troubleshooting.

Network Statistics/ Quality of Service (QoS)

Categories  of  QoS  are  shown  in  the  following  Figure:  QoS  Categories.  All  the  services provided to the subscribers through network are associated with the quality of service of  the network.

There are expected values, designed values of QoS and we need to measure QoS parameters. Those QoS statistics are connected in a chain as shown in the Figure: QoS Cycle.

Network Efficiency is also a measure of QoS. And it is measured as follows.

•   Network Efficiency = (Carried Traffic at Busy Hour) / (Capacity at 2% GOS)

 Definition  for  Grade  of  Service  (GOS):   Percentage  of  attempts  which  are  allowed  to  be blocked in the network when considering the availability of circuits  (CICs)  when calls are to be  made.  The  capacity  for  a  particular  GOS,  with  the  presence  of  particu lar  number  of circuits can be found from the Erlang B table.  Considering the Key Performance Indicators (KPIs),  it  can  be  defined  as  KPIs  related  to  successful  initiation  of  a  call  and  successful termination of a call. Here are some KPIs;

• SDCCH (Standard Dedicated Control Channel) Accessibility:  successful capture of a SDCCH time slot by the subscriber.

• SDCCH Drop Rate :  successful completion of the SDCCH phase and  then  releasing (loosing) the SDCCH channel.

• TCH  (Traffic  Channel)  Accessibility :  successful  capture  of  a  TCH  time  slot  by  the subscriber in a call attempt.

• TCH drop rate :  successful completion of the TCH phase and  then  releasing  (loosing) the TCH.

To keep the performance of the network at a higher level it is required to maintain QoS of the network. It is the responsibility of RAN team. They have defined some threshold values for KPIs.  Using  them  they  continuously  monitor  the  whole  network  every  day.  There  are  few

• methods where they can measure QoS of the network mentioned below.Analyzing Daily Traffic Data

• Analyze Drive Test Results

• Observing  the  daily  quality  of  service   parameters  using  Network  Performance Optimizer (NPO) tool

• Monitoring network using OMC-R

Site Survey

Roof Top Site Survey

Few steps involved in this process and they are listed below.

• Visibility/Availability

Due to nearby buildings some areas may not get covered. When signals gone through a wall 10 dB loss will be there. And we also note down possible locations to put our site and cabin of the site.

•   Near Field and Far Field obstruction

In order to connect the site to the transmission network, there should be Line of Sight (LOS) between the existing sites and the proposed new site location. During the site survey we should check for the obstructions in both near field and far field.

•   Access path

This is important in future maintenance. If there is a proper access path, it will make maintenance Engineers job easier.

•   Power

Whether commercial power is available or not.

•   150-200 m clearance from high tension line

•   Obstruction from the same building

If this equation H > D/2 satisfied it is acceptable. Otherwise main lobe will be obstructed
from the same building.

•   Then reference photographs of the site location are taken, these photographs will include:

*Visibility of the area from the site location (including panoramic photographs)
*Measured land area for the proposed site location
*Accessibility/Access path to the site location
*Availability of the Commercial power
*Terrain conditions of the land
*Neighboring buildings

• Detailed sketch of the location is drawn

This sketch should include: Geo-graphical north referring to the drawing,  Access to the site location,  proposed  sit  location  of  the  selected  land,  landmarks  (nearby  buildings,  houses, power lines, trees).

 Deviations in a sharing site

In addition to the normal site survey process, in this process the BTS cabins are planned to install in other operator‟s site location premises. Therefore a suitable location with required dimensions (i.e. 16 ft X 12 ft) is measured. In selecting a cabin location we have to consider the distance from the existing site, cable ladder of the existing site etc.

 Green Field Site Survey

Majority  of  Green  field  sites  are  set  up  in  rural  areas.  There  are  few  deviations  from  the above mentioned Site  Survey process exists when we consider a GF site. And they are: need to conduct a soil test, and availability of commercial power. Also we have to consider the terrain condition. Other things are same as the roof top site survey.

 Technical Site Survey (TSS) Form

After completing the surveying process, TSS form was prepared for each new site.  And this form is then handed over to the PROJECTS section to proceed with the project.  TSS  form should include the following details.

•  General Data of the site (Site name, Site Identification Code (SIC), etc.)

•  Geo-coordinates of the site location

•  For Roof Top sites : 

 *Height of the building
 *Microwave planning data: Azimuths and distance to three nearest microwave points. 

• For Green Field site :

*Tower type : self-support / COW
*Tower height : 60 m/ 45 m/ 30 m

• Location planning data : coverage objective, coverage area and distances  to  adjacent sites

• BTS antenna related data;

*Antenna model e.g. 90 Dual Band
*Installation height of the antenna
*Antenna azimuths
*Mechanical and electrical tilt

• Clearance to the nearest high tension line

• Terrain condition (for Green Field sites)

• Power availability

• Column/beam under pole location (for Roof Top sites)

• Site location marked on a map

Planning New Sites

Before  setting  up  a  new  site  RAN  Engineers  examine  the  area  using  Planning  Tools  and Maps (Google Map and Google Earth). They will obtain coverage predictions with the aid of AIRCOM‟s ASSET tool and ALCATEL‟s Radio Network Planning Tool. Why we need new sites?

•   Coverage for roads
•   Coverage for populated areas
•   To overcome Capacity issues (Reduce congestion of nearby sites)

As a company we wanted to generate revenue. Therefore to get an approval for a new site Engineer needs to prove the revenue that can be generated by setting up that new site. We will get a feedback from Regional Business Managers and Marketing section about current status  and  future  growth  of  that  area.  Drive  test  results  and  customer  complaints  are  also taken into consideration.  Then a suitable location is chosen.  Contractor will try to acquire a land as closer as possible  to the given coordinates.  Based on the location and requirement we decide which type of Site is to set up.

How we do Site Survey will be explained in the next post!!!!

Mobile Call Flow (Timing) Diagram

A timing diagram of a Call Flow is shown below. And a small description is also included after the image. Consider a situation where in a mobile telecommunication network Mobile Subscriber 1 (MS1) is originating a call for Mobile Subscriber 2 (MS2). (Call from MS1 to MS2)

1.  CM Service Request

Sent to MSC as request to access the network. MSC may ask MS to authenticate itself or MSC may allow the MS to access and use the resources of the network. Temporary Mobile Subscriber Identity (TMSI) is also attached to this message.

2.  Ciphering

The process which creates a logical tunnel between the MSC and MS.

3.  Set up message

Contains the number of called party and calling party.

4.  MSC checking VLR profile

To identify allowed services for MS1. If outgoing calls are allowed MSC will send an
assignment request to the corresponding BSC to allocate a TCH for the call (CIC- Circuit
Identification Code).

5.  Send Routing Information (SRI)

SRI message consists of IMSI of MS1 and MSISDN of MS2. HLR will look up for MS2 s
profile and extracts current VLR/MSC.

6.  Provide Roaming Number (PRN)

PRN consists MS2 s IMSI and then it will be forwarded to the MS2 s serving MSC (MSC2).

7.  MSC2 will allocate an MSRN number from its MSRN pool to the IMSI of MS2.

8.  PRN response

Contains the MSRN of MS2 allocated by MSC2.

9.  SRI response

Contains the MSRN number.

10. Initial Address Message

After MSC1 receives the MSRN it will check the routing table to resolve the routing path for
that number. After resolving the routing path MSC1 will be instructed to communicate with
MSC2. IAM contains MSRN, Called party number, CIC.

11.  After receiving the IAM message MSC2 will execute following,

•   Check the MSRN table and resolve IMSI for MS2
•   Check MS2 VLR profile
•   Resolve MS2 s LAC and check the LAC table
•   Resolve the BSCs inside that LAC

12.  As requested from MSC2, paging is done in all the BSCs inside that LAC using the
TMSI of MS2

13. Paging response

When MS2 receives paging request it will send a paging response to the MSC2.

14. Setup

MSC will identify the response and then it will originate setup message to MS2.

15. Alert setup

This message is sent to the MSC2 and MS2 will start ringing.

16.  MSC2 will send an assignment request to the BSC of MS2. Therefore a CIC is

allocated to proceed with the call.

17. Address Complete Message

This is sent to MSC1 to notify that the voice path is established.

18. Alerting

MS1 starts hearing ringing tone of MS2.

19.  Connect

When MS2 answers the call, connect message will be sent.

20. Answer Message

MSC2 will connect the call to MS2 and at the same time it will send the answer message to
MSC1.

21.  Disconnect

MS1 is disconnecting the call (MS2 may also disconnect before MS1).

22. Release

With the disconnect a release message will be sent to MSC2. Allocated CIC will be released.

23. Release complete

An acknowledgement for the release message.

Software Defined Networking (SDN)

Moving the control function out of data plane elements is the main concept behind Software Defined Networking (SDN). 

Features

• ·         Decoupled Data and Control plane                                            
•        Can Evolve Independently
• ·         Can have different Network Topologies
• ·         Can use Different Technologies

     Why SDN ?

One Possible SDN Design: Push all the control functionality to a Centralized Controller

But Controller may become the Bottleneck in this kind of a setup. As the network grows there will be more events and requests sent to the controller. At some stage controller unable to handle all those requests. In a typical design we may go up to about 30k requests per second which will be sufficient for a sizable enterprise. But we can’t go for Data-centre like environment with this setup. 

How we can overcome?

• Level Parallelism in multicore systems
• Improve I/O performance
• Reduce the number of requests forwarded to controller: Short lived packets will be handled in the data path. Only larger flows are forwarded to the controller.

Another possible SDN Design: Distribute state and/or Computation of the Control Functionality over Multiple Controllers

Having a centralized view is by no means an intrinsic characteristic of SDN. All we need is a unified network wide view to get benefits of SDN. Following are few examples of such implementations.

 

Onix

NIB (Network Information Base): Holds a collection of Network Entities, each of which holds a set of key-value pairs. If a state changes such as adding new switches and ports will be registered in the NIB.

Some more examples will be Hyper Flow and Kandoo.

Steps of Flow setup process

 

Steps involved in Converging on a link Failure

 

 

Resiliency to failures and convergence time are key concerns in Network Performance. If we use a single controller, resiliency to failures will be a major issue. We can use multi-controller networks with appropriate controller discovery mechanisms.

SDN @ Different Network settings

·         Data Centres

o   Thousands of Switching Elements

o   Grow at a fast rate

o   Large number of requests for controller

o   Use Kandoo, Onix or Hyper Flow

·         Service Provider Networks

o   Don’t have as many switches as in Data centres

o   Partition into separate groups

Reference: On Scalability of Software-Defined Networking Paper published by Soheil Hassas, Yeganeh, Amin Tootoonchian and Yashar Ganjali University of Toronto.