Toward Next-Gen Low Latency Mobile Networks Zengwen Yuan - PowerPoint PPT Presentation

Toward Next-Gen Low Latency Mobile Networks Zengwen Yuan University of California, Los Angeles 2018-05-06 WiNG Wireless Networking Group

More time spent on mobile Internet than ever �2

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!

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?

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]

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 LTE control-plane operations precede data forwarding Base (a) User profile stations (f) server mobile OS Mobility Web Application (c) controller server (HTTP/DNS) ? TCP/IP stack (c) Internet (d) (d) modem (b) (e) (c) chipset Gateway LTE interface (d) Gateway

A Close Look on Latency BoIleneck

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? HTTP HTTP Page OS DNS TCP connection overhead query request transmission rendering Latency model for Web using HTML APIs

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 breakdown, LTE control-plane procedures take 172 ms (40% of LTE control-plane operations incur sizable latency for total latency), during TCP connection setup mobile Web and other apps HTTP HTTP Page OS DNS TCP connection overhead query request transmission rendering TCP SYN TCP data SYN ACK TCP layer LTE control plane Data access request LTE data plane LTE data

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 http://mobileinsight.net

LTE data access latency: how long? �11 77 — 2956 msec in 500K samples Average Latency by LTE Data Access Setup (no mobility) • Varies among different mobile carriers 200 196 • Insensitive to varying radio link quality 165 162 150 153 147 100 50 0 AT&T T-mobile Sprint Verizon Project Fi

LTE data access latency: how long? �12 77 — 2956 msec in 500K samples 3,000 • Varies among different mobile carriers • Total Latency (ms) Insensitive to varying radio link quality 1,000 500 200 100 50 -130-120-110-100 -90 -80 -70 -60 -50 -40 Signal Strength (dBm)

LTE data access latency: how frequent? �13 Frequent data access setup operations • every 58.8 sec (median); 133.6 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)

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 800 domainLookupStart requestStart unloadEventStart domInteractive domainLookupEnd responseStart Total latency fetchStart connectStart responseEnd loadEventEnd Latency (ms) connectEnd LTE latency 600 HTTP HTTP Page OS DNS TCP connection 400 overhead query request transmission rendering TCP SYN TCP data SYN ACK TCP layer 200 LTE control plane Data access request 0 LTE data plane LTE data 0 25 50 75 100 Normalized sorted sample (%)

� � 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 800 App init App connect Next New message Server ACK w/ server idle message Total latency Latency Latency (ms) LTE latency 600 TCP SSL TCP OS DNS TCP connection SSL Data overhead query ACK Data ACK 400 SYN SYN ACK TCP data TCP layer 200 LTE control plane Data access request 0 LTE data plane LTE data 0 25 50 75 100 Normalized sorted sample (%)

DPCM: A New Design for Low Latency Mobile Network* *ACM MobiCom 2017, Joint work with Yuanjie Li and Chunyi Peng http://metro.cs.ucla.edu/dpcm.html

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

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

From a distributed state-mgmt point of view �19 Location Location Location Location Location ACL ACL ACL ACL ACL Billing Billing Billing Billing Billing Billing Billing Device-side state replica: Almost “always-on” IP IP IP IP IP Security Security Security Security Security Security QoS QoS QoS QoS QoS QoS QoS Network-side state replica: On multiple nodes

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

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

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

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

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