Toward Next-Gen Low Latency Mobile Networks

Transcription

1 Toward Next-Gen Low Latency Mobile Networks Zengwen Yuan University of California, Los Angeles WiNG Wireless Networking Group

2 More time spent on mobile Internet than ever 2

3 Every millisecond counts in delivering mobile data 3 Users want fast mobile network experience 1 second latency in page response 7% reduction in PV [KissMetrics 2011] Websites lose revenue due to long latency Every 100 ms costs Amazon 1% ($1.6 bn) in sales An extra 400 ms latency drops daily Google searches per user by 0.6% Latency ma:ers!

4 Latency peaormance: are we there? 4 If you ever encountered slow loading webpage Common sense: radio quality/data bandwidth dominates latency Not aways true! Why perceivable latency still observed when radio quality/bandwidth is good in 4G LTE networks? What is the contributing latency bottleneck? How to reduce latency with new design?

5 Outline 5 What is the contributing latency bo:leneck? LTE control-plane latency: An often overlooked bottleneck How to reduce latency with new design? DPCM: A control-plane perspective in latency reduction [ACM MobiCom 17]

6 Background: how do mobile apps work over LTE? 6 What happens under the hood? How LTE impacts perceived latency on mobile app? Cellular network (4G LTE) Safari WhatsApp (a) LTE control-plane operations precede data forwarding (b) (f) mobile OS Application (HTTP/DNS) TCP/IP stack (e) modem chipset LTE interface (c) (d) Base stations (c) Mobility controller (c) Internet Gateway? User profile server Gateway (d) (d) Web server

7 A Close Look on Latency BoIleneck

8 Pinpoint latency boileneck in LTE: An example 8 Run a small webpage (4 KB) in Chrome on Android User is static, under good 4G LTE signal (-95 dbm), T-Mobile Total Latency: 420 msec Clicking URL page loading complete, Steps (a) (f) Pinpointing the latency bo:leneck How to breakdown? OS overhead DNS query TCP connection HTTP request HTTP transmission Page rendering Latency model for Web using HTML APIs

9 Latency component breakdown 9 Major component: TCP connection setup, 283 ms out of 420 ms (67 %) Is the server slow to handle connection? No. It is 3x longer than average phone-server roundtrips (HTTP RTT, 71ms) Through fu\her LTE control-plane breakdown, LTE operations control-plane incur procedures sizable latency take 172 for ms (40% of total latency), during TCP connection mobile Web setup and other apps OS overhead DNS query TCP connection HTTP request HTTP transmission Page rendering TCP layer TCP SYN SYN ACK TCP data LTE control plane Data access request LTE data plane LTE data

10 An olen overlooked latency source: LTE C-plane 10 A new source of latency LTE control plane operations Our 20-month user study [1] unveils: 148 ms to 196 ms average data access setup latency among five US carriers It may go up to 2.96 seconds in rare cases Visible impact on apps: 40.4% of overall web latency on average 51.4% of overall instant-messaging app latency on average [1] 5M 4G signaling messages collected by MobileInsight dataset at

11 LTE data access latency: how long? msec in 500K samples Varies among different mobile carriers Insensitive to varying radio link quality Average Latency by LTE Data Access Setup (no mobility) AT&T T-mobile Sprint Verizon Project Fi

12 LTE data access latency: how long? msec in 500K samples 3,000 Varies among different mobile carriers Insensitive to varying radio link quality Total Latency (ms) 1, Signal Strength (dbm)

13 LTE data access latency: how frequent? 13 Frequent data access setup operations every 58.8 sec (median); sec (average) cause: frequently entering power-saving mode Sho4-lived Radio connectivity lifetime every 10.8 sec (median); 17.3 sec (average) cause: inactivity timer (regulated by standards)

14 Impact on mobile Web app: Chrome 14 Average page loading time for tested webpage: 319 ms LTE data access setup: 129 ms 40.4% total latency perceived Similar results for Safari latency on ios unloadeventstart fetchstart OS overhead TCP layer DNS query LTE control plane LTE data plane domainlookupstart domainlookupend connectstart connectend TCP connection TCP SYN Data access request SYN ACK requeststart dominteractive responsestart responseend loadeventend HTTP request LTE data HTTP transmission TCP data Page rendering Latency (ms) Total latency LTE latency Normalized sorted sample (%)

15 Impact on instant-messaging: WhatsApp 15 Average time grst data packet being ACKed: 341 ms LTE data access setup: 175 ms 51.4% total latency perceived App init OS overhead TCP layer DNS query LTE control plane LTE data plane App connect w/ server TCP connection SYN idle SYN ACK New message Latency SSL Data Data access request Server ACK TCP ACK SSL Data TCP data LTE data Next message TCP ACK Latency (ms) Total latency LTE latency Normalized sorted sample (%)

16 DPCM: A New Design for Low Latency Mobile Network* *ACM MobiCom 2017, Joint work with Yuanjie Li and Chunyi Peng

17 Sequential LTE control-plane is slow 17 Example: LTE data access setup as the device moves Non-mandatory procedures block data Mobile Network (4G LTE) Parallelizable procedures are forced to run sequentially New Failures block the entire operations Old P1. Radio connection setup Sequential, slow! Data Access Setup Latency P2. Session state migration (, billing, security, ) P3. Authentication & security P4. Routing path update P5. User profile location update UL/DL data service available Control-plane Data-plane

18 Accelerating LTE control-plane 18 Challenges 1. How to retain the control/data-plane correctness? 2. How to efficiently perform acceleration?

19 From a distributed state-mgmt point of view 19 ACL ACL ACL ACL ACL Device-side state replica: IP Almost always-on IP IP IP IP Network-side state replica: On multiple nodes

20 Accelerating LTE control-plane (cont d) 20 Challenges 1. How to retain the control/data-plane correctness? 2. How to efficiently perform acceleration? Insights 1. Accelerate via distributed state management Correctness achieved via equivalent but faster state operations 2. Use state replicas that readily exist on device and in network Device and network nodes have up-to-date state replicas in many cases Without waiting for a single node (mobility controller) to become bottleneck

21 DPCM: a new perspective on data latency in LTE 21 We revisit LTE control-plane functions from distributed state mgmt perspective Non-mandatory procedures block data Pipeline control procedures w/ data forwarding Parallelizable procedures are forced to run sequentially Parallelize multiple control procedures Failures block the entire operations Bypass slow bottleneck control procedures

22 Acceleration with State Replicas: Bypass the Slow Control Procedures Bypass Pipeline Control-plane Data-plane Parallelize ACL ACL ACL ACL IP IP IP IP Shorter side-path with device-side state replica

23 Acceleration with State Replicas: Pipeline the Data and Control Control-plane Data-plane Bypass Pipeline Parallelize ACL ACL ACL ACL IP IP IP IP UL/DL data ACL services IP available IP Data In-band signaling installs states earlier on the data path

24 Acceleration with State Replicas: Parallelize the Control Procedures Control-plane Data-plane Bypass Pipeline Parallelize Locatio n ACL ACL ACL ACL IP IP IP IP Concurrent operations via replicas Mobility Controller has the final say

25 DPCM: a new perspective on data latency in LTE 25 We revisit control-plane functions in LTE from distributed state mgmt perspective Oh wait Non-mandatory procedures block data Pipeline control procedures w/ data forwarding Parallelizable procedures are forced to run sequentially Parallelize multiple control procedures Failures block the entire operations Bypass slow bottleneck control procedures How are transient failures handled? Replicas tolerates failures and prevents control-plane blocking What if concurrent state conflicts arise? Infrequent: 1.3% possible RW conflicts from operational LTE traces Fingerprint check + mobility controller final say -> no worse than LTE

26 Implementation 26 A sohware extension of OpenAirInteiace (OAI) Incremental deployability and backward compatibility Network-side vi\ualization + device-side daemon Supported device Extension daemon 4G-LTE stack Legacy 4G device 4G-LTE stack Base Station 4G-LTE stack shim layer Mobility Controller 4G-LTE stack shim layer Data plane Control plane Gateway 4G-LTE stack shim layer

27 Evaluation 27 Testbed conggured to approximate real networks Network: 7 VMs running OAI+DPCM Device: OAI s built-in emulator Parameters/latencies/failures from user study logs Compare with 4G LTE in three dimensions Control-plane latency reduction Benefits for mobile applications System overhead

28 Control-plane latency reduction 28 DPCM 4G LTE DPCM 5G (projection) x x Latency (ms) x Latency (ms) x 0 Static Mobility 4G LTE Greater latency reduction in mobility scenario 0 Static Mobility 5G New Radio Projection Control (Assuming plane latency 1ms radio dominates latency) if radio latency greatly reduces More reductions in failure handling: up to 11s (11.5x in 4G, 317.8x in 5G)

29 BeneUt on mobile apps 29 DPCM 4G LTE DPCM 4G LTE x x Latency (s) x Latency (s) x 0 Web loading YouTube buffering 0 Web loading YouTube buffering w/o failure w/ failure Apps experience longer delay than data access latency due to imperfect adaptations

30 Acceptable system overhead 30 Overhead Network Node Mobile Device Signaling 56 bytes/msg 312 bytes/msg CPU 1.3% 0.1% Memory 53.9 MB 3.5 MB

31 Insights 31 Current LTE control plane operations are network-centric and sequential Sequentiality + network-centric is simply and natural engineering solution Correctness is probably a very important consideration DPCM: a device-centric initiative benefits from distributed state management Break the traditional smart-core, dumb-end constraint in telecom Accelerate using parallelization, with good understanding of domain knowledge Corner cases are non-negligible! Need new/creative solution (Fast Paxos ) and engineering tradeoff (how frequent?)

32 Towards next-gen low-latency mobile networks 32 Low-latency mobile networks are critical for future-proof designs (5G, self driving, ) Explore the paradigm shih to device-centric, veri3able mobile networking Device-centric: correctness guarantee, verifiable U.S. Cellular Verifiable: designer for networks, not plumber Example: multi-carrier access design in Google Project Fi T-Mobile Sprint (b) (d) Project Fi (c) User Space Hardware Fi SIM card (a) Google Server Device-side solution providing better network access w/o infrastructure upgrade Apply new verifiable design to take full advantage of device-centric approach

33 Conclusion 33 New source of latency for mobile apps LTE control plane operations Our breakdown analysis fu\her deciphers the components and root causes We take a device-centric approach to speed up current LTE control-plane operation with new design [DPCM, MobiCom 2017] Preliminary release on GitHub Full possibilities for future low-latency network design!

34 Q & A