SoftMoW: A Dynamic and Scalable Software Defined Architecture for Cellular WANs

SoftMoW: A Dynamic and Scalable

Software Defined Architecture for Cellular

WANs Mehrdad Moradi† Li Erran Li⋆ Z. Morley Mao†

Bell Labs, Alcatel-Lucent⋆ University of

Michigan†

Current Mobile WANs • Organized into rigid and very large regions

• Minimal interactions among regions

• Centralized policy enforcement at PGWs

Two Regions 2

What about device-to-device?

Mobile WANs Problems • Suboptimal routing in large carriers

o Lack of sufficiently close PGW is a major cause of path inflation (Path Inflation,

[PAM’14])

• Lack of support for seamless inter-region mobility o Users crossing regions experience service interruption (DMM, Zuniga et.al., 2013)

• Scalability and reliability o The sheer amount of traffic and centralized policy enforcement

• Ill-suited to adapt to the rise of new applications o E.g., machine-to-machine (telehealth )

o All users’ outgoing traffic traverses a PGW to the Internet, even for reaching a user served by a close base station in a neighbor region

3

SoftMoW Motivation Question: How to make the packet core scalable, simple, and

flexible for tens of thousands of base stations and millions of

mobile users?

• Mobile networks should have fully connected core topology,

small logical regions, and more egress points

• Operators should leverage SDN to manage the whole network

with a logically-centralized controller: o Directs traffic through efficient network paths that might cross region boundaries

o Handles high amount of intra-region signaling load from mobile users

o Supports seamless inter-region mobility and optimizes its performance

o Performs network-wide application-based such as region optimization

4

SoftMoW Solution • Hierarchically builds up a network-wide control plane

o 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. o Virtual Base stations (VBS), Gigantic Switches (GS), and Virtual Middleboxes (VMB)

5 Core Net

GS

Latency Matrix

Radio Net

VBS

Union of Coverage

Policy

VMB

Sum of capacitie

s

• New Dynamic Feature: In each level, the control logic

can modify its logical components for optimization

purposes o E.g., merge/spilt and move operations

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SoftMoW Solution

GSW1

GSW2

GSW1

GSW2

VBS2

VBS3

VBS1

VBS1

VBS2

VBS3Move and Split

GSW1

GSW2

GSW3

Merge/Split

First Level-SoftMoW Architecture • Replace inflexible and expensive hardware devices (i.e., PGW, SGW) with

SDN switches

• Perform distributed policy enforcement using middle-box instances

• Partition the network into independent and dynamic logical regions

• A child controller manages the data plane of each regions

BS1BS2 BS3

BS5BS4 BS6

E1

E2 E3

E4

I1 MM

M M

M

MM

M

MM

Boundary

Child A

Agent ALocal Apps

Region A Region B

NIB

GS Rules &

ActionsEvents

1

2 3

54

6

7 8

9 10

Bootstrapping phase:

based on location and processing capabilities of

child controllers

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Second Level-SoftMoW Architecture • A parent runs a global link discovery protocol

o Inter-region links are not detected by BDDP and LLDP

• A parent participates in the inter-domain routing protocol

• A parent builds virtual middlebox chains and egress-point policies, and dictates to GSs

M

2M

M

M

E4E3E2E1

Parent

I-Mobility Manager

Middlebox

Optimizer

Egress

SelectionRegion

Optimizer

I1

Internal

VBS1

Border

VBS1

Border

VBS2

Internal

VBS2

GS Protocol

-----

BGP

sessions

GSA GSBM

2M

M

M

NIB

BS1BS2 BS3

BS5BS4 BS6

E1

E2 E3

E4

I1 MM

M M

M

MM

M

MM

Boundary

Child A

Agent ALocal Apps

Region A Region B

NIB

GS Rules &

ActionsEvents

1

2 3

54

6

7 8

9 10

8

Hierarchical Traffic Engineering

BS1BS2 BS3

BS5BS4 BS6

E1

E2 E3

E4

I1 MM

M M

M

MM

M

MM

Boundary

Child A

Agent ALocal Apps

Region A Region B

NIB

GS Rules &

ActionsEvents

1

2 3

54

6

7 8

9 10

M

2M

M

M

E4E3E2E1

Parent

I-Mobility Manager

Middlebox

Optimizer

Egress

SelectionRegion

Optimizer

I1

Internal

VBS1

Border

VBS1

Border

VBS2

Internal

VBS2

GS Protocol

-----

BGP

sessions

GSA GSBM

2M

M

M

NIB

Latency (P1,E2)=300 Latency (P1,E4)=100

Web Voice GS Rules

9

• A parent pushes a global label into each traffic group

• Child controllers perform label swapping o Ingress point: pop the global label and push some local labels for intra-region paths

o Egress point: pop the local labels and push back the global label

Push W Pop W

Push W

Push W

Push W2 Push W1

Pop W2

Pop W

Pop W1

Time-of-day Handover Optimization E2

E1

Border

VBS1

GSA

M

3M

2M

M

E4E3

Border

VBS2

Internal

VBS2

GSBM

M M

GSA

Internal

VBS2

Border

VBS2

Internal

VBS1

Border

VBS1

1000300 2000Min Cut

Handover graph

10

BS1BS2 BS3

BS5BS4 BS6

E1

E2 E3

I1 MM

M M

M

MM

M

MM

Boundary

Region A Region B

Child B

1

2 3

54

6

7 8

9 10

Child A

New

Border

Old

Border

M

2M

M

M

E4E3E2E1

Parent

I1

Internal

VBS1

Border

VBS1

Border

VBS2

Internal

VBS2

GSA GSBM

2M

M

M

Q: How can an operator reduce inter-region handovers in peak hours?

Abstraction update

GS Rule: Move Border VBS1

coordination

Conclusion

SoftMoW:

• Brings both simplicity and scalability to the control

plane of very large cellular networks o decouples control and data planes at multiple levels ( focused only on

two levels here)

• Makes the deployment and design of network-wide

applications feasible o E.g., seamless inter-region mobility, time-of-day handover optimization,

region optimization, and traffic engineering

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Questions!

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