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Making Cellular Networks
Scalable and Flexible
Li Erran Li
Bell Labs, Alcatel-Lucent
Joint work with collaborators at university of Michigan,
Princeton, and Stanford
LTE Cellular Network Architecture
Base Station (BS)
Serving Gateway
Packet Data
Network Gateway
Serving Gateway
Internet
User Equipment (UE)
access
core
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PART I: Radio Access
Networks
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Dense and Chaotic
Deployments
• Dense: high SNR per user leads to higher
capacity
o
Small cells, femto cells, repeaters, etc
4
Problems
•
Current LTE distributed control plane is ill-suited
o Hard to manage inter-cell interference
•
o Hard to optimize for variable load of cells
Dense deployment is costly
o Need to share cost among operators
o Maintain direct control of radio resources
o Lacking in current 3gpp RAN sharing standards
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SoftRAN: Big Base Station
Abstraction
Big Base Station
Radio Element 1
time
controller
frequency
Radio Element 2
time
time
Radio Element 3
frequency
time
frequency
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Radio Resource Allocation
3D Resource Grid
time
Flows
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7
SoftRAN: SDN Approach to RAN
Coordination :
X2 Interface
Control Algo
Control Algo
PHY & MAC
PHY & MAC
Control Algo
PHY & MAC
BS1
BS3
Control Algo
PHY & MAC
BS2
Control Algo
BS5
PHY & MAC
BS4
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SoftRAN: SDN Approach to RAN
Control Algo
Operator Inputs
Network OS
RadioVisor
PHY & MAC
PHY & MAC
PHY & MAC
RE3
RE1
RE5
PHY & MAC
Radio Element
(RE)
RE2
PHY & MAC
RE4
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SoftRAN Architecture Summary
CONTROLLER
RAN Information Base
Periodic Updates
Controller
API
•
•
•
RADIO ELEMENTS
Interference
Map
Bytes
Rate
Queue
Size
Flow
Records
Network
Operator
Inputs
QoS
Constraints
Radio
Element
API
Radio Element
3D Resource Grid
POWER
FLOW
Radio Resource
Management
Algorithm
Frequency
10
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RadioVisor Design
•
Slice manager
o
Traffic to
Slice
Mapping
3D Resource
Grid
Allocation &
Isolation
RadioVisor
Slice
Manager
•
•
Slice configuration, creation,
modification, deletion and multislice operations
Traffic to slice mapping at
RadioVisor and radio
elements
3D resource grid allocation
and isolation
o
Considers traffic demand,
interference graph and policy
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Summary
•
•
•
Dense deployment calls for central control of
radio resources
Deployment costs motivate RAN Sharing
We present the design of RadioVisor
o Enables direct control of per slice radio
resources
o Configures per slice PHY and MAC, and
interference management algorithm
o Supports flexible slice definitions and
operations
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PART II: Cellular Core
Networks
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LTE Cellular Network Architecture
Base Station (BS)
Serving Gateway
Packet Data
Network Gateway
Serving Gateway
Internet
User Equipment (UE)
access
core
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Cellular core networks are not flexible
• Most functionalities are implemented at
Packet Data Network Gateway
Packet Data
Network Gateway
– Content filtering, application identification,
stateful firewall, lawful intercept, …
• This is not flexible
Combine functionality from different vendors
Easy to add new functionality
Only expand capacity for bottlenecked functionality
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SoftCell Overview
Simple hardware
+ SoftCell software
Controller
Interne
t
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SoftCell Design Goal
Fine-grained service policy for diverse app needs
»
»
Video transcoder, content filtering, firewall
M2M services: fleet tracking, low latency medical
device updates
with diverse needs!
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SoftCell Design
Controller
1. Scalable system design
»
»
Classifying flows at access
edge
Offloading controller tasks
to switch local agent
2. Intelligent algorithms
»
»
LA
LA
Gateway Edge
LA
Enforcing policy
LA
consistency under mobility
Multi-dimension
Access
Edge
aggregation to reduce
~1K Users
~10K flows
switch rule entries
~1 million
Users
~10 million
flows
~up to 2 Tbps
~1 – 10 Gbps
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Summary
• SoftCell uses commodity switches and middelboxes to
build flexible and cost-effective cellular core networks
• SoftCell achieves scalability with
Data Plane
Control Plane
Asymmetric Edge Design
Multi-dimensional Aggregation
Hierarchical Controller Design
• Exploit multi-stage tables in modern switches
– Reduce m×n rules to m+n rules
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PART III: Cellular WAN
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LTE Cellular Network Architecture
Base Station (BS)
Serving Gateway
Packet Data
Network Gateway
Serving Gateway
Internet
User Equipment (UE)
access
core
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Current Mobile WANs
• Organized into rigid and very large regions
• Minimal interactions among regions
• Leads to poor user experience and poor
resource utilization
Two Regions
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SoftMoW Solution
• Hierarchically builds up a network-wide control plane
– Lies in the family of recursive SDN designs (e.g. XBAR,
ONS’13)
• In each level, abstracts both control and data planes
and exposes a set of “dynamically-defined” logical
components to the control plane of the level above.
– Virtual Base stations (VBS), Gigantic Switches (GS),
and Virtual Middleboxes (VMB)
Latency
Matrix
Union of
Coverage
Sum of
capacities
VBS
GS
VMB
Core Net
RadioAccess
Network
Policy
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Conclusion and Future Work
• CellSDN seeks to address fundamental
limitations of current cellular architecture
– Control plane abstractions: 3D resource grid,
big base station, virtual data plane
– Intelligent algorithms in the control plane to
achieve global objects: interference
management, routing
• Future work on CellSDN
– Security
– Scalable real-time monitoring and analytics
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Questions?
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