CAP for Mobility Support Yuanjie Li 1 , Zengwen Yuan 1 , Chunyi Peng - - PowerPoint PPT Presentation

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CAP for Mobility Support Yuanjie Li 1 , Zengwen Yuan 1 , Chunyi Peng - - PowerPoint PPT Presentation

Jan 07, 2024 343 likes •672 views

CAP for Mobility Support Yuanjie Li 1 , Zengwen Yuan 1 , Chunyi Peng 2 , Songwu Lu 1 1 University of California, Los Angeles 2 The Ohio State University New Mobile Services in Future 5G Real-time virtual reality Remote mobile

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SLIDE 1

CAP for Mobility Support

Yuanjie Li1, Zengwen Yuan1, Chunyi Peng2, Songwu Lu1

1University of California, Los Angeles 2The Ohio State University

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SLIDE 2

New Mobile Services in Future 5G

ed r y er ,

  • Real-time virtual reality

Mission-critical communication Remote mobile healthcare Emergency communication Safe autonomous driving High-speed mobility

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SLIDE 3

Key Enablers for 5G Mobile Services

Advanced wireless technologies Advanced mobility support

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SLIDE 4

Wide-Area Mobility via Cellular Networks

Cellular Networks (e.g., 3G/4G) ...

ed r y er ,

  • 4
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SLIDE 5

Tracking Area 2 Tracking Area 1

How does Mobility Support Work in 4G LTE?

  • Span on multiple network nodes
  • Involve multiple control procedures

Base station (eNB) Gateway (SGW/PGW) Mobility controller (MME) User profile database (HSS)

Radio conn. setup Session state transfer Routing update User profile update Location update accept Internet Location update request

Data-plane Control-plane

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SLIDE 6

Three Expectations for Mobility Support

Immediate data service Correct data service Continuous data service

Once route is connected Forward packets under right policies Even in presence

  • f failures

Can we always achieve all of them?

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SLIDE 7

This talk

  • A formal analysis of fundamental limits in mobility support
  • From the distributed system perspective
  • Fundamental limits: CAP theorem on generic mobility support
  • Rethink the tradeoff between different properties
  • Argument: 5G needs a paradigm shift in its mobility support

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SLIDE 8

Outline

  • Q1: What properties do we want?
  • Q2: Can we achieve all properties simultaneously?
  • Q3: How to balance different properties?

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SLIDE 9

What properties do we want?

From mobile user demands to formalization

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SLIDE 10

Tracking Area 2 Tracking Area 1

What Properties do We Want?

Base station (eNB) Gateway (SGW/PGW) Mobility controller (MME) User profile database (HSS)

Internet

Data-plane Control-plane

  • Correctness: Forward every packet under correct policies

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SLIDE 11

Tracking Area 2 Tracking Area 1

What Properties do We Want?

Base station (eNB) Gateway (SGW/PGW) Mobility controller (MME) User profile database (HSS)

Radio conn. setup Session state transfer Routing update User profile update Location update accept Internet Location update request

Data-plane Control-plane

  • Correctness: Forward every packet under correct policies
  • 4G LTE: correctness via sequential consistency
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SLIDE 12

What Properties do We Want?

Base station (eNB) Gateway (SGW/PGW) Mobility controller (MME) User profile database (HSS)

Radio conn. setup Location update request Session state transfer Routing update User profile update Location update accept

  • Correctness: Forward every packet under correct policies
  • 4G LTE: correctness via sequential consistency
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SLIDE 13

Tracking Area 2 Tracking Area 1

What Properties do We Want?

Base station (eNB) Gateway (SGW/PGW) Mobility controller (MME) User profile database (HSS)

Internet

Data-plane Control-plane

  • Correctness: Forward every packet under correct policies
  • Availability: start data service once route is connected

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SLIDE 14

Tracking Area 2 Tracking Area 1

What Properties do We Want?

Base station (eNB) Gateway (SGW/PGW) Mobility controller (MME) User profile database (HSS)

Internet

Data-plane Control-plane

Session state transfer

  • Correctness: Forward every packet under correct policies
  • Availability: start data service once route is connected
  • Partition tolerance: continuous operation once route is connected

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SLIDE 15

Can we achieve all properties?

CAP theorem on mobility support

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For any mobility support, it is impossible to always guarantee sequential consistency, availability, and control-plane partition tolerance simultaneously. CAP Theorem for Mobility

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Tracking Area 2 Tracking Area 1

Example: Control-Plane Partition Between 4G Tracking Areas

Base station (eNB) Gateway (SGW/PGW) Mobility controller (MME) User profile database (HSS)

Session state transfer Internet

Data-plane Control-plane

How should I operate now?

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SLIDE 18

Tracking Area 2 Tracking Area 1

Option 1 (4G LTE): Consistency Over Availability

  • Suspend data service until the partition is recovered
  • Guaranteed correctness

Base station (eNB) Gateway (SGW/PGW) Mobility controller (MME) User profile database (HSS)

Session state transfer Internet

Data-plane Control-plane

✓ ✓ ✓ ✓

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Option 1 (4G LTE): How Much Delay in Reality?

  • Comparable to radio latency L: 193.8ms-6.4s (29.8-69.6%)

25 50 75 100 500 1,000 1,500 2,000

Normalized sorted sample (%) Suspension (ms)

25 50 75 100 500 1,000 1,500 2,000

Normalized sorted sample (%) Suspension (ms)

Total suspension

25 50 75 100 500 1,000 1,500 2,000

Normalized sorted sample (%) Suspension (ms)

Total suspension Routing update State transfer (ctrl→ctrl)

25 50 75 100 500 1,000 1,500 2,000

Normalized sorted sample (%) Suspension (ms)

Total suspension Routing update State transfer (ctrl→ctrl) Radio conn. setup

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Option 1 (4G LTE): How Much Delay in Reality?

  • Comparable to radio latency L: 193.8ms-6.4s (29.8-69.6%)
  • Failure recovery incurs extra delay L: 500ms-30s

25 50 75 100 500 1,000 1,500 2,000

Normalized sorted sample (%) Suspension (ms)

25 50 75 100 500 1,000 1,500 2,000

Normalized sorted sample (%) Suspension (ms)

Total suspension

25 50 75 100 500 1,000 1,500 2,000

Normalized sorted sample (%) Suspension (ms)

Total suspension Routing update State transfer (ctrl→ctrl)

0.5 1 1.5 2 0.5 1 1.5 2 Extra suspension for failure recovery (s) Normal data suspension (s) 0.5 1 1.5 2 0.5 1 1.5 2 w

  • r

s e Extra suspension for failure recovery (s) Normal data suspension (s) 0.5 1 1.5 2 0.5 1 1.5 2 w

  • r

s e Extra suspension for failure recovery (s) Normal data suspension (s)

T-Mobile AT&T Sprint Project-Fi

25 50 75 100 500 1,000 1,500 2,000

Normalized sorted sample (%) Suspension (ms)

Total suspension Routing update State transfer (ctrl→ctrl) Radio conn. setup

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Tracking Area 2 Tracking Area 1

Option 2: Availability Over Consistency

  • Delivery user data without latest data session states
  • No guaranteed correctness: sequential consistency violated

Base station (eNB) Gateway (SGW/PGW) Mobility controller (MME) User profile database (HSS)

Session state transfer Internet

Data-plane Control-plane

? ? ? ?

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Summary: Impact of CAP Theorem

Consistency over Availability

  • Guaranteed correctness J
  • Long data service delay L

Availability over Consistency

  • Correctness unguaranteed
  • Immediate data service J

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How to Balance Properties?

Between availability, consistency and fault tolerance

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Correctness, Not Sequential Consistency!

Availability Correctness Partition Tolerance Sequential Consistency

≠

  • Sequential consistency is more than necessary for correctness

More flexible consistency model to achieve all!

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Tracking Area 2 Tracking Area 1

What Consistency is Required for Correctness?

  • Function 1: Data forwarding to correct location
  • Only a subset of network nodes need latest user location

Base station (eNB) Gateway (SGW/PGW) Mobility controller (MME) User profile database (HSS)

Internet

Data-plane Control-plane

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Tracking Area 2 Tracking Area 1

What Consistency is Required for Correctness?

  • Function 2: Volume-based data billing
  • Decouple packet counting and billing policy
  • Packet counting can be performed together with data forwarding

Base station (eNB) Gateway (SGW/PGW) Mobility controller (MME) User profile database (HSS)

Internet

Data-plane Control-plane

1 1 + ?

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Other Cellular Functions in Paper

  • Radio access control
  • Cryptography over the air
  • QoS policy

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Future Directions

  • What is the minimal consistency model for mobility support?
  • Can we have a continuous (thus tunable) balancing mechanism?
  • Will unreliable wireless connectivity affect the tradeoffs?

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Conclusion

  • No free lunch for perfect mobility support
  • Sequential consistency is more than necessary for correctness
  • More flexible balance between C, A and P can benefits 5G

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Backup

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What Consistency is Required for Correctness?

  • Function 3: Radio access control
  • Observation: per-group access control in 4G LTE
  • No need to wait for per-device radio access control list

4G Radio Access Control List Granularity Forbidden Tracking Area List (TS24.301) Per tracking area Forbidden PLMN list (TS24.301) Per roaming network Closed subscriber group (TS29.281) Per cell (private Femtocell)

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