NSN RU10 Interface Dimensioning (IP Part)

Slide 1Wroclaw, 27-29.02.2008
* © Nokia Siemens Networks Interface Dimensioning (IP Part) / COO RA MRD SA NE / Wojciech Bigos
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Content
The following session covers dimensioning and configuration aspects of the RNC related interfaces:
IP Iub
IP Iu-CS
IP Iu-PS
IP Iur
NNI stands for Network-Network-Interface, like Iu-CS, Iu-PS and Iur
MSS/MSC
RNC
BTS
BTS
BTS
BTS
BTS
BTS
BTS
BTS
RNC
MGW
SGSN
3G-SGSN
Iu-CS
Iu-PS
Iur
Iub
Iub
UNI
UNI
UNI
NNI
NNI
NNI
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Session Outline
Functional Overview
Iub Dimensioning
Capacity-related parameters
Dimensioning steps
Iub Configuration
IP Addressing
VLAN Assignment
2. Dimensioning Iur, Iu-CS and Iu-PS
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IP-based Iub
Functional Description (1)
IP Based Iub allows usage of 3GPP Rel-5 compliant IP transport between the RNC and the WCDMA BTS.
Opex and capex savings for the operator due to the lower cost of the UTRAN Access IP / Ethernet transport.
E1
BTS
E1
BTS
Eth
BTS
Eth
BTS
STM1
Eth
ATM
PDH
IP
RNC
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3GPP Rel-5 / Rel-6 compliant protocol stack
IP Diff Serv for QoS support
IPv4 support
IP fragmentation/reassembly
VLANs
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IP CAC: Functional Description (1)
IP Connection Admission Control (CAC) allocates the guaranteed bit rate on Iub for each RAB connection subject to CAC -> CAC_Guaranteed_Bitrate RAB.
The CAC is performed against the specified guaranteed capacity (IPRoute_Commited_BW, usually the Iub bottleneck)
An incoming RAB connection on Iub is admitted by IP CAC provided that the residual Iub bandwidth is more than or equal to CAC_Guaranteed_Bitrate RAB.
It is performed by the RNC in DL and by the BTS in UL.
CAC applies to:
HSPA interactive (with RAN1004)
HSPA background (with RAN1004)
IP CAC
First functional component of the IP-based Iub is CAC. CAC decides whether an incoming connection can be admitted depending on the currently available resources on Iub.
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IP CAC: Functional Description (2)
Set of 4 traffic descriptors for each bearer, one for UL and one for DL:
Maximum bit rate in IP layer
Average bit rate in IP layer
Maximum size of one IP packet
Average size of one IP packet.
Parameters include IP overhead, but do not include Ethernet overhead.
Traffic descriptors are defined in the RNC, and forwarded to the BTS by using a private NBAP message.
CAC-guaranteed BW per RAB connection:
CAC_Guaranteed_Bitrate RAB =
IP CAC
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QoS support with IP DiffServ
With DiffServ packets are classified into PHBs according to DiffServ Code Point (DSCP) field in the IP header and based on this information the RNC and the routers will handle the packets.
Up to 6 PHBs are supported (Expedited Forwarding, Assured Forwarding 1-4, Best Effort),
To get the full functionality (6 PHBs) RAN1253 ‘IP Transport QoS’ must be activated. Without RAN 1253 only 3 PHBs are supported, for RT DCHs, nRT DCHs and HSPA.
DSCPs are operator configurable. UMTS traffic classes can be mapped to one of these DSCPs as appropriate.
If VLANs are enabled, a PHB to VLAN priority bits mapping is defined
Not required in RU10
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Transport QoS mapping schemes on IP-based Iub
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EF is served as Strict Priority
Other PHBs are served as Weighted Fair Queue (WFQ)
Highest priority queue is rate limited
Lowest priority queues are controlled by a WFQ scheduler (weights: w1-w5)
Aggregate (interface) traffic is shaped to the specified transport service capacity.
Note: Having a separate queue per PHB implies that traffic should be dimensioned separately per PHB class and then summed up.
Per IP Based Route
Q5
Q6
W4
AF1
BE
W5
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RNC DiffServ Scheduler (2)
There is a logical SP+WFQ scheduler per IP Based route (BTS)
The interface scheduler is also SP+WFQ, which aggregates traffic from each traffic class in each IP Based Route
Aggregate (interface) traffic is shaped to the specified transport service capacity.
Q1
Q2
Q3
Q4
SP+WFQ
SP+WFQ
SP+WFQ
Rate limiting
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IPRoute_BW: Total IP bandwidth per Iub
Iub_Ethernet_Cap: Total bandwidth per Iub on Transport level (incl. Ethernet OH)
RNC_Ethernet_Cap: Total bandwidth per RNC Ethernet port grouping multiple logical Iubs
RNC
IP_Route
Commited_BW
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Calculating CAC-guaranteed BW
Calculating Effective Transport Capacity
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Conversational/Streaming Applications
Video calls Release 99 CS S UDI 64
Audio Streaming Rel’99 PS S RAB or Rel. 5, 6 Streaming HSPA
Video Streaming Rel. 5,6 Streaming HSPA
PS Interactive/Background Applications
PS Interactive/Background Release 5 HSDPA DCH/HS-DSCH or
PS Interactive/Background Release 6 HSPA E-DCH/HS-DSCH
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How the user traffic is represented:
Mean traffic in Busy Hour per subscriber +service mix (e.g. 40% C/S services, 60% I/B services)
Mean traffic in BH per subscriber per service
Offered traffic Service = # Subscr Service × Mean traffic per subscriber Service
The value of Mean_traffic RAB is defined by the operator. Alternatively it can be taken from the Reference Traffic Model:
User Application
Media Streaming
=>
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UMTS transport bearer
UMTS Service class
DSCP Value (default)
Conversational
Streaming
Yes
Yes
Yes
Yes
Yes
Yes
Yes
No
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IP_Route_Comm_BW is shared by:
U-Plane traffic: R’99 DTCHs (C/S/I/B CS and PS RABs), DCCHs, CCHs and HSPA (if subject to CAC)
C-Plane traffic: C-NBAP, D-NBAP
RNC
IP_Route
Commited_BW
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For calculating C-Plane traffic (IP_Route_C-Plane_comm_BW ) refer to [RU10 Signaling Dimensioning Guide]
For the O&M traffic (IP_Route_O&M_comm_BW ) a 64 kbps IP transport channel is assumed.
Calculation of the U-plane traffic (IP_Route_U-plane_comm_BW ):
will be explained next.
Open issues to be clarified and confirmed
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Real Time U-Plane traffic (RT_U-Plane_comm_BW)
It is recommended to dimension the RT traffic (i.e. Conversational and Streaming Rel’99 DCHs and Streaming HSPA) with MD-Erlang formula, separately for each PHB class:
RT_IP_Route_comm_BW PHB = MD-Erlang [Gross_peak_rate RAB 1, Off_traffic RAB 1, Bl_Pr RAB 1 ; … ; Gross_peak_rate RAB n, Off_traffic RAB n, Bl_Pr RAB n] (3)
Gross peak rate RAB = CAC_Guaranteed_BW RAB_DTCH + CAC_Guaranteed_BW RAB_DCCH (4)
where:
n is the number of RT services (RABs) within a given PHB class,
Gross peak rate RAB, is a sum of CAC-guaranteed bit rates for RT DTCH and DCCH RABs:
Offered_traffic RAB is the mean traffic per service (RAB) in [erlang] extended with SHO_factor:
Offered_traffic RAB = Mean_traffic RAB [erlang] × (1+ SHO_Factor) (5)
Bl_Pr RAB is the service blocking probability. Usually assumed values are 0.1% – 1%.
The total RT bandwidth is a sum of RT bandwidth portions in individual PHB classes
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Calculating Real Time U-Plane traffic with MD-Erlang
Blocking Pr = 0.1%, SHO_Factor = 30%; MBR: Max Bit rate, GBR: Guaranteed Bit Rate; DCCH 3.4 kbps
MD-Erlang
CAC-guaranteed BW [kbps]
EF: 288 kbps AF1: 390 kbps Total: 678 kbps (+30%)
Option 2
Total (EF): 510 kbps
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Non Real Time U-Plane traffic – Option 1
To dimension NRT traffic (i.e. Interactive/Background Rel’99 DCHs and I/B HSPA, if subject to CAC) two options are proposed:
Option 1: Estimate the number of parallel NRT connections in Busy Hour and apply to them the set of traffic descriptors. The number of parallel connections of a given NRT RAB type is calculated as:
Parallel connections RAB = round-up [Offered_traffic RAB / (Service_bitrate RAB × Activity_factor RAB)] (6)
where:
Offered_traffic RAB is the mean traffic per service (RAB) in [kbps] extended with SHO_factor
Service_bitrate RAB is the nominal RAB bit rate in [kbps] above the Frame Protocol level
NRT_U-Plane_comm_BW PHB = Parallel connections RAB, PHB × (CAC_Guar_BW RAB_DTCH + CAC_Guar_BW RAB_DCCH )
The total NRT bandwidth is a sum of NRT bandwidth portions in individual PHB classes
The CAC-guaranteed bandwidth for NRT traffic within a single PHB is calculated as:
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Non Real Time U-Plane traffic – Option 2
Option 1 does not explicitly take into account any QoS parameters e.g. in terms of blocking or transfer delay assurances in dimensioning of NRT traffic. Therefore, Option 2 is proposed:
Option 2: Calculate the NRT U-plane traffic with M/G/R-PS formula:
NRT_U-Plane_comm_BW PHB = M/G/R-PS [Total_off_traffic; Gross_peak_rate RAB 1, Transfer_delay RAB 1 ; … ; Gross_peak_rate RAB n, Delay_factor RAB n ] (8)
where:
Total_offered_traffic RAB is the total mean traffic summed over all services (RABs):
Total_offered_traffic = Mean_trafficRAB × (1+ SHO_Factor) (9)
With this set of inputs, M/G/R-PS is repeated n times, separately for each NRT RAB service, and the Max value over all calculations is picked-up.
Use of M/G/R-PS is recommended when the QoS measures in terms of transfer delay on Iub must be explicitly taken into account.
Delay_factor RAB reduces the effective bit rate perceived by the end-user of an NRT application as compared with the nominal CAC_Guar_Bitrate. Suggested values of Delay_factor RAB on Iub are 5-10%.
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Example:
Calculating Non Real Time U-Plane traffic (DL) with M/G/R-PS (Option 2)
Delay Factor = 10%, SHO_Factor = 30%; DCCH 3.4 kbps
Total off. traffic [kbps]
CAC-guaranteed BW [kbps]
AF1: 699 kbps AF2: 759 kbps Total: 1458 kbps (+ 6%)
Option 2
M/G/R-PS
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CCH U-Plane traffic
The CCH bandwidth is calculated out of the CCH traffic descriptors assuming the number of CCHs as resulting from the number of cells per BTS (with 4 CCHs per cell: FACH-C, FACH-U, RACH and PCH).
CCH
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Shared_BE_IP_Allocation: non-CAC guaranteed BW per logical Iub for low-priority BE traffic; provides an extra add-on on Iub to accommodate this type of traffic.
Currently only I/B HSPA can fall under the non CAC-guaranteed traffic.
RNC
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Calculating Non CAC-Guaranteed Traffic (2)
The Non CAC-guaranteed traffic can be calculated based on the mean traffic of I/B HSPA users :
Shared_BestEffort_IP_Allocation = #_of_Subs I/B HSPA × Mean_traffic_per_subs I/B HSPA (10)
where:
the value of mean I/B HSPA traffic per subscriber is defined by the operator. Alternatively it can be taken from the traffic model.
Typical QoS_Factor values are around 20%
Alternatively, this can be extended with an additional QoS overhead, to account for instantaneous I/B HSPA bursts above the average value:
Shared_BestEffort_IP_Allocation = #_of_Subs I/B HSPA × Mean_traffic_per_subs I/B HSPA × (1 + QoS_Factor) (11)
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Calculating Total IP Bandwidth (1)
IPRoute_BW determines the total bandwidth per logical Iub on IP level
With respect to this parameter a rate limiting is performed in RNC and BTS → the non-conforming traffic is dropped.
IPRoute_BW is a user-configurable parameter at RNC and BTS
RNC
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Calculating Total IP Bandwidth (2)
Total IP Bandwidth is a sum of the CAC-guaranteed and the non CAC-guaranteed traffic:
IP_based_Route_BW = IP_based_Route_commited_BW + Shared_BestEffort_IP_Allocation
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Iub_Ethernet_Capacity is the Iub bandwidth on Transport level (incl. Ethernet OH).
It determines the effective Iub capacity to be installed on Ethernet transport links at BTS side.
RNC_Ethernet_Cap is the bandwidth per single RNC Ethernet port grouping multiple logical Iubs.
It determines the effective Iub capacity to be installed on Ethernet transport links at RNC side.
With respect to this parameter a rate limiting is performed in RNC.
RNC_Ethernet_Cap is a user-configurable parameter at RNC.
RNC
IP_Route
Commited_BW
Rnc_Ethernet_Cap
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Calculating Effective Transport Capacity (2) Transport Capacity per Iub (Iub_Ethernet_Capacity)
The effective Iub capacity on the transport level should be increased by applying additional Ethernet overhead:
Iub_Ethernet_Capacity = IP_based_Route_BW × (1 + Weighted_Ethernet_OH) (13)
where:
Weighted_Ethernet_OH is the mean Ethernet transport overhead weighted over the services supported on Iub:
Length of Ethernet frame header is assumed 38 bytes w/o VLAN and 42 bytes with VLAN.
Ethernet overhead for single RAB is calculated out of the traffic descriptors:
Eth_OH RAB [%] = (15)
Weighted_Ethernet_OH = (14)
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Calculating Effective Transport Capacity (3) Transport Capacity per RNC port (RNC_Ethernet_Capacity)
In addition, the total capacity per physical RNC interface IP_Port is defined as a sum of the capacities of all Iubs terminated at this physical port:
RNC_Ethernet_Capacity (IP_Port) = (16)
where logical_Iub IP_Port denotes logical Iubs terminated at the physical interface IP_Port.
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Estimating Timing over Packet (ToP) Bandwidth
ToP solution comprises a timing master and timing slaves. The master sends synchronization messages to the slaves. By using a specific algorithm the slaves can recover the timing reference from the synchronization messages send by the master.
Sync messages are based on Precise Time Protocol (PTP) defined in IEEE 1588 v2 standard.
The bandwidth requirement of the ToP stream depends on the frequency of the Sync Msg exchange and the Sync Msg length:
ToP_BW [kbps] = (Eth/IP/UDP_Hdr_length + PTP_Sync_Msg_size [bits] / 1000) × PTP_Sync_Msg_rate [1/s] (17)
PTP_Sync_Msg_rate is configurable in range of 0.5/s to 128/s. Default value is 16/s.
The PTP_Sync_Msg_size is 44 bytes.
The ToP bandwith for the default value of the Sync Msg rate and assuming 42 byte Eth frame hdr (incl. VLAN Tag) is ~ 24 kbps.
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VLAN Assignment Options
A single VLAN can be allocated per logical Iub (i.e. ‘IP Route’), per single RNC port or per multiple RNC ports. No VLAN can also be used. VLAN assignment per traffic class is not required.
CIR Iub = IP_based_Route_commited_Bitrate × Weighted_Ethernet_OH (18)
Option 1: Single VLAN per logical Iub
Commited Information Rate (CIR) and Excessive Information Rate (EIR) setting:
Option 2: Single VLAN per RNC port
EIR Iub = Iub_Ethernet_Capacity (19)
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Setting WFQ Scheduler Weights
To assure a fair access to link recourses, WFQ Weights should be set proportional to the dimensioned IP bandwidth per PHB.
By replacing Average_Queue_RatePHB by IPRoute_BW PHB in (22) one gets:
WAF1 : WAF2 : WAF3 : WAF4 : WBE = IP_BWAF1 : IP_BWAF2 : IP_BWAF3 : IP_BWAF4 : IP_BWBE (23)
(22)
For WFQ, queues AF4 - BE shall be assigned a weight (W1 – W5) that determines the share of the available capacity that they will have, according to the following formula:
Q1
Q2
Q3
Q4
EF
AF4
AF3
AF2
W1
W2
W3
SP
WFQ
Q5
Q6
W4
AF1
BE
W5
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IP-based Iub Transport flow configuration in DL
At Layer 4 UMTS transport bearers are identified by UDP/SCTP ports
At Layer 3 transport flows are allocated IP addresses. In BTS one IP address is allocated commonly for the U-Plane and C-Plane traffic. In RNC there are two separate addresses for the U-Plane and C-Plane traffic.
On DiffServ level traffic is classified as belonging to a number of different PHBs corresponding to different DSCP values.
PHBs are mapped to the Ethernet Class of Service (CoS) using Ethernet priority code point (PCP) corresponding to the IP DSCP value.
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Functional components incl. dimensioning and configuration approaches remain the same as for IP-based Iub
Material will be presented as a delta to the Iub dimensiong
MSS/MSC
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Dimensioning Iur Interface
Once having determined the Iur traffic, the same capacity components needs to be calculated as on Iub (RT, nRT CAC-guaranteed BW, non CAC-guaranteed BW, etc.)
CAC Traffic descriptors and Ethernet overheads are the same as on Iub.
MSS/MSC
Iur carries the traffic of the users being simultanously served by 2 RNCs
Iur is dimensioned based on the offered traffic of users in the inter-RNC handover state.
The inter-RNC handover traffic can be estimated using one of the 2 options:
ex-North :
Iur traffic is 4-9 % of the Iu traffic per RNC
ex-South:
Number of subscribers in the inter-RNC handover is determined with Drift_Handover_Factor (set to 10 %):
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Dimensioning Iu-CS Interface
Offered_traffic RAB is the mean traffic per RAB per RNC in [erlang] (w/o SHO_factor)
Bl_Pr RAB is the service blocking probability. Usually assumed values are 0.1% – 1%.
MSS/MSC
Iu-CS groups the CS traffic from RNC towards MGW.
The calculation method is the same as in Iub RT U-Plane traffic, which is MD-Erlang:
where:
Gross peak rate RAB, is a sum of CAC-guaranteed bit rates for RT RABs:
Iu-CS_BW PHB = MD-Erlang [Gross_peak_rate RAB 1, Off_traffic RAB 1, Bl_Pr RAB 1 ; … ; Gross_peak_rate RAB n, Off_traffic RAB n, Bl_Pr RAB n] (24)
Gross peak rate RAB = CAC_Guaranteed_BW RAB (25)
Note 1: Due to a different data structure on Iu-CS, CAC traffic descriptors and Ethernet OHs on Iu-CS are different that the ones on Iub.
Note 2: Dimensioning should be done separately per PHB class.
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MSS/MSC
Iu-PS groups Rel’99 PS and HSPA traffic from RNC towards 3G-SGSN.
The calculation method depends on the supported traffic types and mixes:
Streaming HSPA should be dimensioned as RT CS (i.e. with MD-Erlang),
Rel’99 PS + I/B HSPA should be dimensioned using one of the options for dimensioning nRT U-plane traffic on Iub:
via Parallel Connections with IP CAC traffic descriptors, or
with M/G/R-PS
If there is a large share of PS Streaming, it should be dimensioned as RT CS (i.e. with MD-Erlang).
Note: Dimensioning should be done per PHB class.
Iu-PS transmission overhead depends on the packet size that has to be transmitted from RNC to 3G-SGSN. Subscriber data packet can vary from 64 Bytes to 64K Bytes.
Therefore IP traffic descriptors and Eth overhead will vary depending on the data packet size.
It seems reasonable to assume an average packet size of 512 bytes.
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MSS/MSC
30%
IU-PS OH chart
Active
3.4
3.4
40
136
5
176
4.4
1
3
200
5.0
5.6
65.8235294118
12.00%
24.76%
TrCH_RT_Data
Activity
Active
3.4
3.4
40
136
5
176
1
3
200
5.0
5.6
4.4
12.00%
24.76%
Signaling channel is only active when there is messages to send
å
Î
å
RAB
å
RAB
å
å
O&M
PCH, FACH,
O&M
PCH, FACH,

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NSN RU10 Interface Dimensioning (IP Part)

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