PDP Context Activation - 2 Finding the GGSN

Transcription

1 Section 7 Dimensioning PDP Context Activation - 2 Finding the GGSN (1) SGSN gets the GGSN IP address from DNS BTS BSC SGSN 1. DNS APN maps to the GGSN IP address (2) SGSN sends "Create PDP Context Request" to GGSN PDP Type (IP) PDP Address (if empty=> dynamic address) Access Point Name QoS 2. GPRS Backbone IP Network Access Point Intranet GGSN DNS = Domain Name System = mechanism to map logical names to IP addresses

2 Section 7 Dimensioning PDP Context Activation - 3 Access Point Selection BTS BSC SGSN GPRS Backbone IP Network DNS GGSN Access Point Name refers to the external network the subscriber wants to use APN="Intranet.Ltd.com" Intranet Physical/logical interface in GGSN Access Point configuration in GGSN defines where to connect the user If dynamic address, allocated by GGSN Internet

3 PDP Context Activation - 4 Context Activated Section 7 Dimensioning BTS BSC (1) GGSN sends "Create PDP Context Response" back to SGSN (2) SGSN sends "Activate PDP Context Accept" to the MS SGSN now ready to route user traffic between MS and GGSN 2. SGSN GPRS Backbone IP Network 1. GGSN Intranet Internet

4 Section 7 Dimensioning Exercise Q1. How many PCMs are required for one BTS with 2,1,2 and other with 3,2,1 configuration? Q2. Calculate the free space loss for 20Km distance at 15GHz frequency? Q3. Calculate the 2 nd Fresnel Zone for total distance of 20Km at a distance of 10Km from one end. Frequency used is 15GHz. Q4. What precaution has to be taken to avoid the over reach problem in the microwave links?

5 Optimisation Section 8 Optimisation

6 Objective The Trainee will be able to understand: signaling delay in the network Effect on the network while introducing the new releases Impacts of subscriber behavior TCP/IP concepts

7 Introduction The goal of optimization is to ensure the network is operating at optimum efficiency and within the defined quality of service constraints. This is achieved by implementing corrective action and procedures to rectify network problems identified though analysis of performance management monitoring parameters. Vendors are continually seeking ways of maximizing revenue generation with minimum additional investment. One way of achieving this is to identify areas where the network is not operating at peek efficiency and making adjustments for improvement.

8 Optimization is a Cyclic Process Section 8 Optimisation

9 Signaling Delay The signaling network delay depends on a variety of parameters, among others: bit error rate, signaling link propagation and processing time, average link load, mean MSU length on link, mean MSU length of transmitted signal, number of signaling links in signaling path, number of STPs in signaling link path, buffering and queuing times in STP etc. Key parameters that are varied are mean MSU-length, mean signaling link load, and number of STPs and signaling links in path.

10 Typical values used for calculating the delay: Bit Error Rate on link Mean MSU lengths STP delay 8.3x10-4 a) 23 oct b) 74 oct 20ms Signaling link propagation and processing 10ms

11 For a constant bit error rate of 8.3x10-4 and basic error correction, the waiting times (Tw) on the outgoing side are shown in table below for mean MSU length 23 octets and for mean MSU lengths of 74 octets. Section 8 Optimisation

12 STP Delay (TSTP): In CCITT Blue Book, a cross STP delay of 20ms is estimated for 0.2 link load. Propagation and Processing Time (TL): This includes transmission time on link and processing time of message. The overall main part of TL is the transmission time. For ground-installed links for which basic error correction is used, TL should be less than 15ms.

13 Signaling Network Delay Example: Consider two cases 1. the signal passes one intermediate STP before reaching its destination 2. the signal passes two intermediate STPs before reaching its destination

14 Signaling Network Delay with one intermediate STP. The signaling link delay, SLD is derived from: SLD = 2x(TW + TL) + TSTP Signaling Network Delay with two intermediate STPs. The signaling link delay, SLD is derived from: SLD = 3x(TW + TL) + 2xTSTP

15 It is to be mentioned that dependence between the MSU lengths and the delay times is not necessarily linear.

16 Impacts On Capacity When introducing a new release New releases typically mean a drop of 10-15% of system capacity. The BSC decrease is often less than for MSC. The reason is that new BSC releases often contain more O&M improvements than traffical ones. Subscriber Behavior The call type affects the capacity required per call, e.g., the load per call is different depending on type of call. Load per call is defined as the execution time of a call. This is the time necessary to execute the program code for a call in the CP (Central Processor). By a call is meant a call setup, call release and information sent in connection with the call.

17 Call attempts have the highest impact on capacity. One call setup plus clear consumes about 25 ms execution time. SMS point-topoint takes about 2/3 of call execution in the BSC (2/3 of 25 ms). Most SMS/ptp are mobile terminated, and need paging as well. Registrations take roughly 1/3 of call execution in the BSC. Due to the big number of them, the total CP load from registrations is often higher than for calls.

18 Network Configuration The number of BSCs per MSC can have a major impact on the system capacity due to the shift of intra-bsc handovers to the inter-bsc handovers, which will increase in case of a higher number of BSCs. An increase of the number of inter-bsc handovers with a factor of 10 will take 7% more of the capacity. A MSC configuration with stand alone HLR will increase the capacity of the MSC with 15% compared to a MSC with integrated HLR (worth mention that this 15% figure has been derived from comparing the total MSC/HLR capacity with the maximum capacity of a MSC without HLR).

19 The BSC covering areas should generally be chosen so that the boundaries as far as possible are located in areas with low handover intensity. The reason is that high handover frequency decreases MSC and BSC capacity. Consequently, boundaries through city kernels and areas close to highways should, if possible, be avoided. The value that the periodic location update is set to affects the capacity. The period can be set between 6 and 1530 minutes in steps of 6 minutes. The minimum period sustainable by the system depends on the number of subscribers and their traffic behavior.

20 The number of periodic location updates has a significant impact on the MSC capacity, therefore it is advisable to set the periodic location update timer very carefully. Most operators choose a short period for the forced registration, caused by the fear of loosing track of the subscribers. In case of system recovery after a large restart the periodic location update rate will impact the recovery time severely. Therefore the recommendation is to use 120 minutes for the timer value. It is worth mention that the positive effect on the MSC may impact the BSC performance negatively due to a higher number of pagings.