cost calculation distributed setup
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What do you expect from a
Cellular service Provider
- LOW SUBSCRIPTION FEE
- HIGH QUALITY CONNECTION
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Outline
Review of the wireless network operation
Limitations of the current network architecture
Description of the new architecture and benefits Backhaul cost reduction: Analysis and results
Increased availability: Analysis and results
Conclusions
Further research topics
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A Simple Wireless NetworkMobile Data Set
PSTN
Packet
Network
MobileVoice Unit
Base TransceiverSystem (BTS)
Base StationController
(BSC)
MobileSwitching
Center (MSC)
Packet Inter-Working Function
Challenge is to keep connection and not loose any data during handoff operation
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The Components
BTS
BTS consists of one or more transceivers placed at a single location.The BTS terminates the radio path on the network side.
BSC
Provides allocation and management of radio resources.
SDU: Selection and distribution unit. Also responsible for handoffcoordination
MSC
Provides and controls mobile access to the PSTN. Interprets the
dialed number, routes and switches call to destination number. Alsomanages mobiles supplementary services. Maintains a register ofvisitors operating within the coverage area of the MSCs connectedBTSs.
PDSN: Packet data service node is basically a packet router.
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MSC PDSN
BSC(SDU)
BSC(SDU)
BSC(SDU)
BTS BTS BTS BTS BTS
- Backhaul cost is by $$$/mile
- 10-100 miles between BTS and BSC
- Voice or data use one DS0 channel at a time
- BTSs are located in the tower
- BSC and MSCs are located
in the central office
Current Wireless Network Architecture
BSC
BTS
24xDs0
in T1
PacketsTDM
channels
TDM
channels
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Soft Handoff between two BTS
Handoffs == ( Hard || Soft )
Handoff: A handoffmechanism is needed to maintain connectivity as devices
move, while minimizing disruptions to ongoing calls. This mechanismshould exhibit low latency, incur little or no data loss, and scale to a large
network.
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SDU and soft handoff
SDU -1
WR-A
SDU-1 -SDU -2
WR-B
-
- 3 to 6 BTSs involved in soft handoff- SDU changeover due to weak signal
from primary BTS
- BTS forwards even corrupted
radio frames to the SDU for selectionSDU -2-
BTS-1
BTS-2
BTS-3
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Problems with the current
architecture Duplicate traffic on the links: Frame selection is done at the BSC (One frame
is generated for each soft handoff leg.) This results in duplicate traffic flow at thebackhaul
No traffic aggregation: Each call is allocated DS0 capacity. Even when there isno activity on the call, the DS0 is reserved. At this rate, currently each BTS cansupport only around 20 calls per sector (normally 3 sectors per BTS). So, no trafficaggregation does not utilize statistical multiplexing (results in inefficient backhaullink provisioning)
If six BTS, then more overhead: Seventy percent (70%) of wirelessoperators expenditure is on RAN. Around 30% expenses are backhaul cost. Only15% of the BTS-BSC traffic is payload and rest is overhead. If six BTS are involved in
the soft handoff then the overhead will be lot higher. Carries dead payload: BTS forwards even error frames to BSC. Because the
selection is done at the BSC. This means we are carrying dead payload to BSC.
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Problems with the current
architecture (cont..) Uneven utilization of links:For data services as well as voice, IP
networks overlay on top of current wireless networks. This is very
inefficient, not cost effective, and very difficult to deploy the new services.
Performance:Less propagation delay. Currently, for some ofthe BTS-BSC configurations, the links run 100 miles, it means
several milliseconds of delay. This creates problem during soft
handoff.
Availability:Less availability due to single point of failure (interms of base stations, base station controllers and links
connecting between them)
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Review
Simple wireless network operation
Different components in the network
Wireless network topology
Mobility and soft handoff
Problems with the existing architecture
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33.1
33.2
33.3
33.4
33.5
33.6
33.7
33.8
33.9
-85.2 -85 -84.8 -84.6 -84.4 -84.2 -84
Typ
USBT
30x
mil
Urban
Rural highway
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2G/3G RAN Network (Traditional)
CO
BTS BTS BTS BTS BTS BTS
CO CO CO
BSC
Interoffice distance (costs per mile) cost + Fixed Cost
Channel
Termination
Cost
ChannelTermination
Cost
MSC
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What configuration is best in
terms of cost and availability Cost Reduction: How and where to place wireless router in the
RAN network with respect to network-level backhaul cost and
availability. For example, existing WR can be part of GSR (high endrouter) ? How close it to BTS
Higher Availability: Distributed IP-RAN for backhaul cost
savings and higher availability
Variables in analysis Different kinds of transport cost structures
Different types of links (T1/T3/Microwave etc.)
Different types of connectivity between BTS and wireless router
Number of carriers supported supported by BTS
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Cost Model Commercial BTS network topology. BTS are connected to BSC using the
chain of Central Offices. Real ILEC cost structure is assumed for the T1 leased lines from urban and
rural areas to the BSC.
20-30 Node network in urban area and 10 BTS in rural areas.
Soft hand factor of 2.0: How many BTS are in soft handoff
1.5 T1 per BTS per carrier BTS Network Regions: I) Dense Urban, ii) Urban iii) Suburban iv) Rural
Cost models
Channel termination costs
Interoffice fixed costs
Per mile costs: Transport cost changes according to distance and the type of
transport (T1/T3/OC3)
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Configurations
Four BTS network configuration are considered:1. Traditional BTS-BSC network (Config-1, fully star, call it
Traditional)
2. One Wireless Router supporting multiple BTSs (10-30). Forexample, existing WR can be part of GSR (high end router) ? How
close it to BTS (Config-2, call it star)
3. Meshed Wireless Routers (Config-3, one wireless router per BTS,
full mesh within the central office region. Call this WR)
4. Meshed Wireless Routers (WR) and each WR connected tomultiple Gateway Routers for higher availability (Config-4, with
connection to all the nearby high end routers. Call this WR-HA)
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2G/3G RAN Network (Traditional)
CO
BTS BTS BTS BTS BTS BTS
CO CO CO
BSC
Interoffice distance (costs per mile) cost + Fixed Cost
ChannelTermination
Cost
ChannelTermination
Cost
MSC
- Around 150 BTS per BSC
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WR supports multiple BTS (10-20). Selection and distribution is done in the WR. WR collocated with CO
WR supporting multiple BTSs (Star Topology)
WR
WR-BTS
links
BTS BTS BTS BTS BTS BTS
WR
WR-BTS
links
BTS BTS BTS BTS BTS BTS
CO CO
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Solution: Distributed Control
GRGateway Router
WR
WR
WR
WR
WR
WR
WR
WR
WR
WR
WR
WR
WR
WR
WR
WR
WR
WR
GRGateway Router
Radio frames
Embedded in
IP packets
Each packet
Contains several
radio frames.
Wireless Router is an IP router
with RF termination. Functions
include BTS, SDU, power
control, and handoff control
Gateway Router is a IP routerconnected to the internet core
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WR-WR
Links
WR-WR
Links
WR
WR/BTSWR/BTS
WR/BTSWR/BTS
GRGateway Router
WR
WR/BTSWR/BTS
WR/BTSWR/BTS
GRGateway Router
GR-GR links
WR-GR links
Solution (cont.)
- Radio frame routing
using IP routing
- Radio neighbors exchange
resource info. using IP
routing protocols
- Mobility is handled through
IP signaling protocols
- Radio resource management
is handled by IP traffic
management
- WR assumes SDU function
Transit traffic management is
handled by IP routing, QoS
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Solution (cont.)
Distributed SDU. Distributed bearer and control Radio Routing Protocol: IP routing merged with Radio frame
routing for soft handoff and mobility. Wireless extensions of OSPFwith radio neighbors.
Radio Discovery Protocol: Discovering Radio Neighbors Radio Resource Management: IP traffic management
merged/enhanced with Radio Traffic Management. Radio PowerControl integrated and aligned with IP QoS
RSVP extensions for Radio: IP resource managementmerged/enhanced with Radio Resource Management. For example,
Radio Resource Management and soft hand off signaled withRSVP.
IP transport in Radio Access Network
Disruptive Technology
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Benefits
Cost Reduction: Efficient use of backhaul links and
aggregation. Only 15% of the BTS-BSC traffic is payload
and rest is overhead. Around 30% expenses are backhaul
cost.Objective is to reduce the backhaul traffic and smallnumber of high speed backhaul links.
Scalability: Separation of call processing and bearer paths
Distributed SDU and Distributed Control
Ability to provide coverage and capacity during peak hours
Redundancy and Availability: Due to meshed architecture,
network is robust and works around the failures.
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Benefits (continued)
Marriage of IP and wireless protocols: Seamless operation of
IP-Network-Layer with Radio Control.
Reuse already deployed routers in the Central Offices.
New wireless services:Automatic Reconfiguration of Radio AccessNetwork. Expand cell attributes to provide more capacity
Performance:Less propagation delay. Currently, for some of theBTS-BSC configurations, the links run 100 miles, it means several
milliseconds of delay. This creates problem during soft handoff. Due to
short lengths between base stations, the delay will be negligible.
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WR collocated with BTS (WR)
WR-GRlinks
WR
WR/BTSWR/BTS
WR/BTSWR/BTS
Central Office
WR-WR
Links
GR
Gateway Router
WR-GRlinks
WR
WR/BTSWR/BTS
WR/BTSWR/BTS
Central Office
WR-WR
Links
GR
Gateway Router
* WR-GR link (primarily) used for backhauling selected traffic to the destination
* WR-WR link (primarily) is used for selection and distribution traffic between
two wireless routers.
* GR-GR links are links between two IP routers. These routers do not distinguish between wireless and wireline traffic
GR-GR links
WR ll t d ith BTS ith HA (WR HA)
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WR collocated with BTS with HA (WR-HA)
WR-GR
links
WR
WR/BTSWR/BTS
WR/BTSWR/BTS
Central Office
WR-WR
Links
GR
Gateway Router
WR
WR/BTSWR/BTS
WR/BTSWR/BTS
Central Office
WR-WR
Links
GR
Gateway Router
GR is collocated in the the closest CO
Connectivity to two (atleast) GRs is established for higher availability. The second GR is collocated in the
neighboring Central office.
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Traffic Models
scheduler
Overhead /container
Overhead/ stream
Overhead/ stream
voicestream
voicestream
multiplexer
packetizerDt
multiplexer
packetizerDt
Overhead/ stream
Overhead/ stream
datastream
datastream
Segment. Segment.
Traffic Mix
100% voice + 0% data
100% data, 14.4K, 64K and 144Kbps
80 % voice + 20% data, 14.4K, 64K and 144Kbps
20 % voice + 80% data, 14.4K, 64K and 144Kbps
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Cost ComparisonsUrban (30 node network)
0100000
200000
300000
400000500000
600000
700000
800000
WR(one per BTS)
WR with HATraditional
Star (10 BTS per WR)
No. of Carriers (increased bandwidth at BTS, 1carrier requires ~~2 Mpbs)
$$$$$
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Cost ComparisonRural (around 10 nodes)
0
100000
200000
300000
400000
500000
600000
1 2 3 4 5 6 7 8 9 10 11 12
WR
WRHA
Trad
Star
No. of Carriers (increased bandwidth at BTS, 1carrier requires ~~2 Mpbs)
$$$$
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Why less cost ??
Backhaul cost reduced with WR mesh architecture.Customer saves $$$$ (per mile backhaul cost)
Why is the backhaul much less with WR? What is
new with WR? Frame Selection is done at the WR. No duplicate traffic
after the selection is done
The aggregation of voice and data traffic from multiple
WRs enables better Statistical multiplexing and reduces thebackhaul requirement. This also enables customer to use lesscostly T3 and saves them more $$$$
Flexible and more reliable traffic routing.
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Review and Conclusions
Statistical multiplexing and compression techniques are not accounted
in the results described. If counted, more savings are realized
Cost savings for one carrier are not much but substantial for multiple
carriers. Star at the near-by-CO with a high speed (e.g., DS3/OC3) uplink is the
optimum but without higher availability.
Mesh is ideal for higher availability and cost savings
All the WR cases win over traditional deployment
Ongoing work: Different kinds of transport cost structures anddifferent types of links (T1/T3/Microwave etc.)
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Service Availability
CO CO CO CO
BSC
MSCBTS BTSBTS BTS BTS
BTSWR
WR
WR
WR
WR
WR
WR
WR
WR
- Rerouting around failed links/nodes
- Rerouting around congested links/nodes- Wireless router is also IP router hence no
need to deploy full mesh
- If BTS fails, neighboring resources can be
used to complete the calls.
-Single point of failure at BTS- Single point of failure at BSC
- No rerouting around congested nodes
possible.
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Availability Model (example)
Tower
WR
WR
WR
WR
WR
WR
WR
WR
GR
GR
Backplane
Line Card
Line card
Control
Processor
Control
Processor
SW
SW
Calculate MTBF and MTTR of all the components in each element
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Annual Down Time Comparison
Link Avail .99 .999 .9999 .99999
Traditional(Hours)
174 17.77 2.01 0.438
WR-HA
(Minutes)
5.25 5.25 5.25 5.25
BTS Availability: 0.99999
GR Availability: 0.99999
Link availability is varied from 0.99 to 0.99999 and downtime is computedFor traditional and WR-HA network topologies.
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Annual Down Time Comparison
Link Avail .99 .999 .9999 .99999
Traditional
(Hours)
174 17.77 2.01 0.438
WR-HA
(Minutes)
5.85 5.78 5.78 5.78
Assumptions:
BTS Availability: 0.99999
GR Availability: 0.99
Link availability is varied from 0.99 to 0.99999 and downtime is computed
For traditional (2G/3G) and WR-HA network topologies.
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RESULTS
In conventional case, when a link fails, the call level reliability is low
because the call is not redirected without dropping. However, in mesh
architecture, the call can still be maintained and the rerouting takes
place at the frame/packet level.
Though GRs availability is only 0.99, the overall service downtime is
not impacted due to the fact that there are multiple paths from BTS to
another GR.
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Review and Conclusions
Distributed RAN architecture saves backhaul cost (less than half of the
cost of existing architecture )
Distributed RAN architecture supports 99.999% service-level
availability compared to conventional network. In fact, full mesh is notrequired for realizing the 99.999% availability. Even partial mesh can
achieve this level of availability
Distributed architecture increases the complexity of control and
requires working prototype for understanding the new protocols.
Disruptive technology: Required new protocols design and approvalfrom vendor and hence may take long time to get to the field (this is
weakness in this architecture).
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