CS434/534: Topics in Networked (Networking) Systems

Transcription

1 CS434/534: Topics in Networked (Networking) Systems Mobile Networking System: Making Connections: Cloud; NFC Yang (Richard) Yang Computer Science Department Yale University 208A Watson

2 Admin. Project planning Checkpoint II: Apr. 20 Initial design; feedback from instructor/tf Checkpoint III: Apr. 27 Design refined; key components details Final due: May 4 No more than 6 page write up 2

3 Recap: Making Bluetooth Conn. Underlying technology Nodes form piconet: one master and upto 7 slaves A node makes itself discoverable The slaves discover the master and follow the pseudorandom jumping sequence of the master Higher-layer introduces profiles to provide specific functions Android Bluetooth software API Configuration: Announce Bluetooth permission Intent to request systems service: turn on BT, become discoverable Obtaining bonded devices: query, register broadcast receiver Connection: A piconet Server: mbluetoothadapter.listenusingrfcommwithservicerecord(sname, MY_UUID); 3

4 Recap: Making WiFi Direct Conn. 4

5 WiFi Direct Software Framework (Android) Setup permission in Manifest Create IntentFilter and Broadcast Receiver to obtain related updates intentfilter.addaction WIFI_P2P_STATE_CHANGED_ACTION WIFI_P2P_PEERS_CHANGED_ACTION WIFI_P2P_CONNECTION_CHANGED_ACTION WIFI_P2P_THIS_DEVICE_CHANGED_ACTION /** register the BroadcastReceiver with the intent values to be matched public void onresume() { super.onresume(); receiver = new WiFiDirectBroadcastReceiver(mManager, mchannel, this); registerreceiver(receiver, intentfilter); public void onpause() { super.onpause(); unregisterreceiver(receiver); } Initiate action Call discoverpeers mmanager.discoverpeers(mchannel, new WifiP2pManager.ActionListener() { Call connect Create group 5

6 Recap: Making Cellular Conn. Issue: Given the large overhead to set up radio resources, UMTS implements radio resource control (RRC) state machine on mobile devices IDLE CELL_FACH CELL_DCH Channel Not allocated Shared, Low Speed Dedicated, High Speed Radio Power Almost zero Low High How to best design this framework (or more generally power management framework for wireless) is not fully solved. 6

7 Outline Admin Android Platform overview Basic concepts Inter-thread: execution model with multiple threads Inter-process: component composition Inter-machine: network-wise composition Service discovery Make connections Bluetooth WiFi Direct Cellular Mobile cloud 7

8 Discussion: Mobile Cloud Connections What are some reasons (services) you can think of involving mobile-cloud connections? 8

9 Example Mobile Cloud Services Push notification service Storage and sync, e.g., Syncing and storage service (icloud) Compute and split architecture, e.g., Siri, Amazon silk ( uide/introduction.html) 9

10 Outline Admin Android Platform overview Basic concepts Inter-thread: execution model with multiple threads Inter-process: component composition Inter-machine: network-wise composition Service discovery Make connections Bluetooth WiFi Direct Cellular Mobile cloud» Cloud push notification 10

11 Setting: Data Refresh A typical design pattern is that a device updates/receives data (e.g., news) from publisher A first solution is mobile pull, but this can create large overhead 11

12 Shared Push Service A single persistent connection from device to a cloud push service provider Multiple application providers push to the service provider Service provider pushes to a device using the persistent connection Two examples Apple Push Notification Service (APNS) Firebase (Google) Cloud Messaging (FCM/GCM) 12

13 Design Requirements of a Shared Push Service Security/Authorization Do not allow arbitrary app to push to a device Scalability A large scale system may have millions of clients Fault tolerance Client/device, push servers all can fail Generality Can be used by diverse applications 13

14 Design Point: Authorization /Sub-Pub Management Many options, e.g., Open group, e.g., publishers push topics and devices subscribe to topics Closed group Registration(DEV_ID, App_ID) App Device Device notifies registration ID to its server; 14

15 Design Point: What to Push? Option 1: Just push signal (data available) to devices and then devices fetch from app servers Option 2: push app data App Device 15

16 Apple Push Notification Service ios device maintains a persistent TCP connection to an Apple Push Notification Server (APNS) A push notification from a provider to a client application Multi-providers to multiple devices 16

17 APNS Authorization: Device Token Device token Contains information that enables APNS to locate the device Client app needs to provide the token to its app provider Device token should be requested and passed to providers every time the application launches 17

18 Apple Push Notification Data Each push notification carries a payload 256 bytes maximum Best effort delivery App provider provides a JSON dictionary object, which contains another dictionary identified by the key aps App specifies the following actions An alert message to display to the user A number to badge the application icon with A sound to play 18

19 APNS Example: Client 1. - (BOOL)application:(UIApplication *)application didfinishlaunchingwithoptions:(nsdictionary *)launchoptions 2. { 3. // Let the device know we want to receive push notifications 4. [[UIApplication sharedapplication] registerforremotenotificationtypes: 5. (UIRemoteNotificationTypeBadge UIRemoteNotificationTypeAlert)]; UIRemoteNotificationTypeSound return YES; 8. } 9. - (void)application:(uiapplication*)application didreceiveremotenotification:(nsdictionary*)userinfo 10. {//userinfo contains the notification 11. NSLog(@"Received notification: %@", userinfo); 12. } (void)application:(uiapplication*)application didregisterforremotenotificationswithdevicetoken:(nsdata*)devicetoken 14. { 15. NSLog(@"My token is: %@", devicetoken); 16. } 19

20 APNS Example: Server 1. $devicetoken ='f05571e4be60a4e11524d76e f430522fb470c46fc6810fffb07af7 ; 2. // Put your private key's passphrase here: 3. $passphrase = 'PushChat'; 4. // Put your alert message here: 5. $message = CS434: my first push notification!'; 1. $ctx = stream_context_create(); 2. Stream_context_set_option($ctx, 'ssl', 'local_cert', 'ck.pem'); 3. stream_context_set_option($ctx, 'ssl', 'passphrase', $passphrase); 4. // Open a connection to the APNS server 5. $fp = stream_socket_client( 6. 'ssl://gateway.sandbox.push.apple.com:2195', $err, 7. $errstr, 60, STREAM_CLIENT_CONNECT STREAM_CLIENT_PERSISTENT, $ctx); 8. if (!$fp) 9. exit("failed to connect: $err $errstr". PHP_EOL); 10. echo 'Connected to APNS'. PHP_EOL; 20

21 APNS Example: Server (cont ) 16. // Create the payload body 17. $body['aps'] = array( 18. 'alert' => $message, 19. 'sound' => 'default' 20. ); 21. // Encode the payload as JSON 22. $payload = json_encode($body); 23. // Build the binary notification 24. $msg = chr(0). pack('n', 32). pack('h*', $devicetoken). pack('n', strlen($payload)). $payload; 25. // Send it to the server 26. $result = fwrite($fp, $msg, strlen($msg)); 27. if (!$result) 28. echo 'Message not delivered'. PHP_EOL; 29. else 30. echo 'Message successfully delivered'. PHP_EOL; 31. // Close the connection to the server 32. fclose($fp); 21

22 Firebase Cloud Messaging Very similar to APNS FCM Servers FCM is a newer version of GCM 22

23 Outline Admin Android Platform overview Basic concepts Inter-thread: execution model with multiple threads Inter-process: component composition Inter-machine: network-wise composition Service discovery Make connections Bluetooth WiFi Direct Cellular Mobile cloud» Basic use» Thialfi as an implementation example 23

24 Example Implementation: Thialfi Deployed in Chrome Sync, Contacts, Google Plus Goals Scalable: tracks millions of clients and objects Fast: notifies clients in less than a second Reliable: even when entire data centers fail 24

25 Thialfi Overview Register X Notify X Thialfi client library Register Client Data center Client C1 Register Client C2 Update X Thialfi Service Notify X X: C1, C2 Notify X Application Update X backend 25

26 Outline Admin Android Platform overview Basic concepts Inter-thread: execution model with multiple threads Inter-process: component composition Inter-machine: network-wise composition Service discovery Make connections Bluetooth WiFi Direct Cellular Mobile cloud» Basic use» Thialfi as an implementation example» Overview, abstraction 26

27 Thialfi Abstraction Objects have unique IDs and version numbers, monotonically increasing on every update Delivery guarantee Registered clients learn latest version number Reliable signal only: cached object ID X at version Y Why signal only: For most applications, reliable signal is enough 27

28 Thialfi Client API 28

29 API Without Failure Recovery Register(objectId) Unregister(objectId) Notify(objectId, version) Client Library Thialfi Service Publish(objectId, version) 29

30 Architecture Registrations, notifications, acknowledgments Client library Client Data center Client Bigtable Registrar Each server handles a contiguous range of keys Each server maintains an in-memory version Bigtable: log structured, fast write Object Bigtable Matcher Notifications Application Backend Matcher: Object ID à registered clients, version Registrar: Client ID à registered objects, notifications 30

31 Life of a Notification Ack: x, xv7 Client C2 Client Bigtable C1: x, v5 v7 C2: x, v5 v7 C1: x, v7 Notify: x, v7 Registrar C2: x, v7 Data center Object Bigtable x: v5; v7; C1, C2 x, v7 Matcher Publish(x, v7) 31

32 Outline Admin Android Platform overview Basic concepts Inter-thread: execution model with multiple threads Inter-process: component composition Inter-machine: network-wise composition Service discovery Make connections Bluetooth WiFi Direct Cellular Mobile cloud» Basic use» Thialfi as an implementation example» Overview, abstraction» Failure recovery 32

33 Possible Failures Client Store Client Library Server state loss/ Network Partial Client Data center state restart storage failures loss unavailability schema migration Client Bigtable Registrar Client Bigtable Registrar Object Bigtable Matcher... Object Bigtable Matcher Data center 1 Thialfi Service Publish Feed Data center n 33 3/5

34 Failures Client restart Client state loss Network failures Partial storage unavailability Server state loss / schema migration Publish feed loss Data center outage 34

35 How to Handle Failures Principle: Soft state only, where a state at the third party is soft state if the the entity who sets up the state does not refresh it, the state will be pruned at the third party Thialfi has two types of states, and both are soft state registration state notification state State recovery Registration state registratinoreissueregistrations() at client Registration Sync Protocol to propagate to server Notification state recovery allow NotifyUnknown() 35

36 Recovering Client Registrations ReissueRegistrations() x x y Registrar y Register(x); Register(y) Object Bigtable Matcher 36

37 Syncing Client Registrations Register: x, y x Hash(x, y) Hash(x, Reg sync y) x y Registrar y Object Bigtable Matcher Merkle tree for syncing large number of objects Goal: Keep client-registrar registration state in sync Every message contains hash of registered objects Registrar initiates protocol when detects out-of-sync Allows simpler reasoning of registration state 37

38 Recovering From Lost Versions Versions may be lost, e.g. schema migration Inform client with NotifyUnknown(objectId) Client must refresh, regardless of its current state 38

39 Notification Latency Breakdown Notification latency (ms) Matcher to Registrar RPC (Batched) Matcher Bigtable Read Matcher Bigtable Write (Batched) Bridge to Matcher RPC (Batched) App Backend to Bridge Batching accounts for significant fraction of latency 39

40 Thialfi Usage by Applications Application Language Network Channel Chrome Sync C++ XMPP 535 Contacts JavaScript Hanging GET 40 Google+ JavaScript Hanging GET 80 Client Lines of Code (Semi-colons) Android Application Java C2DM + Standard GET 300 Google BlackBerry Java RPC

41 Pointers to Additional Work See Facebook Wormhole pub/sub design See Sapphire automatic mobile/cloud split design 41

42 Outline Admin Android Platform overview Basic concepts Inter-thread: execution model with multiple threads Inter-process: component composition Inter-machine: network-wise composition Service discovery Make connections Bluetooth WiFi Direct Cellular Mobile cloud Near Field Communication (NFC) 42

43 RFID (Radio Frequency Identification) The initial development of NFC is RFID, with many applications, e.g., Secure Entry cards Supply chain management 43

44 RFID Basic Architecture 44

45 RFID Tag Tag is a device used to transmit information such as a serial number to the reader in a contact less manner Classified as Passive energy from reader Active - battery battery Semi-passive battery and energy from battery and energy from reader 45

46 RFID Reader Also known an interrogator Reader powers passive tags with RF energy (for passive tags) Consists of: Transceiver Antenna Microprocessor Network interface 46

47 Nexus Hardware 1.Front-facing camera 2.Earpiece 3.Power button 4.Volume buttons 5.Headset jack 6.Speaker 7.USB Type-C port 8.Laser auto focus & dual- LED flash 9.Rear-facing camera 10.NFC 11.SIM card tray 12.Fingerprint sensor 47

48 RFID Passive Receiver: Foundation 48

49 Near Field RFID <= 100 Mhz 49

50 How far can a passive tag be read? Assume distance limited by power available to run the tag s circuits 50

51 Maximum Distances to Read UHF Passive Tag 51

52 Example NF Use: Contactless Smart Card Proximity Smart Cards (13.56 MHz) Range = 4 inches (10 centimeter) Baud rate = 106 kilobaud ISO/IEC Vicinity Smart Cards (13.56 MHz) Range = 3 feet (1 meter) Baud rate = kilobaud ISO/IEC Animal Identification (134 KHz, 125 KHz@US) ISO 11784/11785 VeriChip as human plantable RFID tag (134 KHz) 52

53 Far Field RFID 53

54 RFID MAC Protocol Select phase Single out particular tag population with one or more bits with query tree protocol protocol Inventory phase identify individual tag using Q protocol (slotted-aloha based) Reader sends Query with parameter Q and Session number (Q=4 is suggested default) Reader creates slotted time Tags pick random 16-bit number as handle Tags in requested session pick a random number in the range [0,2^Q-1] for slot_number If slot_number = 0, backscatter handle If slot_number!= 0, wait that number of slots to backscatter Reader ACKs individual tag with handle and goes to access phase. All other tags wait. If more that one tag answers, reader can send same Q again or send modified Q Access phase Reader interacts with tags requesting EPC number and any other information 54

55 Select Phase: Query Tree 55

56 Select Phase: Query Tree 56

57 Inventory Phase (Q Protocol; Slotted Aloha) 57

58 Android NFC User Programming API System discovers NFC tag Key issue: how to determine the application to be invoked Implication: need a tag dispatch system Android tag dispatch design Parsing the NFC tag and figuring out the MIME type or a URI that identifies the data payload in the tag. Encapsulating the MIME type or URI and the payload into an intent. Starts an activity based on the intent. 58

59 Tag to MIME/URI Requires tag uses NDEF (NFC Data Exchange Format), which consists of a sequence of NDEF records First record provides 3-bit TNF (type name format) 59

60 Intent Dispatch ACTION_NDEF_DISCOVERED: This intent is used to start an Activity when a tag that contains an NDEF payload is scanned and is of a recognized type. This is the highest priority intent, and the tag dispatch system tries to start an Activity with this intent before any other intent, whenever possible. ACTION_TECH_DISCOVERED: If no activities register to handle the ACTION_NDEF_DISCOVERED intent, the tag dispatch system tries to start an application with this intent. This intent is also directly started (without starting ACTION_NDEF_DISCOVERED first) if the tag that is scanned contains NDEF data that cannot be mapped to a MIME type or URI, or if the tag does not contain NDEF data but is of a known tag technology. ACTION_TAG_DISCOVERED: This intent is started if no activities handle the ACTION_NDEF_DISCOVERED or ACTION_TECH_DISCOVERED intents. 60

61 Backup Slides 61