Experimental Evaluation of Transport Services CoAP, HTTP and SPDY for Internet of Things

Transcription

1 Experimental Evaluation of Transport Services CoAP, HTTP and SPDY for Internet of Things Laila Daniel, Markku Kojo and Mikael Latvala Department of Computer Science University of Helsinki Mosa Consulting, Finland September 23, 2014

2 Overview of the presentation 1 Transport Services for IoT 2 Overview of the results 3 Experimental setup 4 Analysis of the results 5 Conclusions and future work September 23,

3 Transport Services for IoT To extend Internet services to the IoT devices a suitable transport service is needed The transport service should be Compatible with the TCP/IP suite Open standard and proven to be scalable Efficient in the resource constrained IoT environment In this study we consider three transport services HTTP (HyperText Transfer Protocol) SPDY (pronounced as Speedy) CoAP (Constrained Application Protocol) How close to CoAP can HTTP/SPDY be? Do IoT devices that are less constrained require very light-weight transport service like CoAP? September 23,

4 HTTP and SPDY HTTP SPDY De-facto standard of information transfer in the Internet TCP is the transport protocol for HTTP Problems of HTTP in IoT environment Lengthy HTTP headers, For smaller packets, the protocol header overhead is around 150 % The need to establish TCP sessions for each request-reply data transfer. For short data transfers, TCP connection establishment time will be up to 50% of the total transfer time Originally from Google to make HTTP faster, basis for HTTP/2 Allows many concurrent HTTP requests in a single SPDY session over a single TCP connection Similar problems as that of HTTP September 23,

5 HTTP: Downloading a 10-byte object - phases of data transfer Legacy browser is used TCP connection establishment GET request Get./10 HTTP/1.1 Details of the browser, OS Accepted data types, encoding and encryption schemes ACCEPT + Data HTTP 1.1/ 200 OK Date and time Server details, name, last updated Total bytes transferred 1546 bytes including TCP ACKs HTTP-Client Start 1 RTT SYN SYN-ACK GET ACCEPT+Data HTTP-Server 48 B 48 B 588 B 502 B September 23,

6 CoAP: Downloading a 10-byte object phases of data transfer Specifically designed for constrained devices and constrained networks HTTP-CoAP proxy to connect to the Internet, scalability issues Operates in request-response mode Short binary header of 4-bytes UDP is the transport protocol, so no connection establishment phase Supports optional reliability Problems in IoT environment Error-prone and/ or congested paths, slow recovery of packets CoAP-Client Start 1 RTT Request Reply CoAP-Server 39 B 47 B September 23,

7 How to make HTTP and SPDY better suited for IoT? Minimize the connection establishment time Reduce the size of the headers associated with HTTP and SPDY, many headers are not really needed We introduce IoT-HTTP and IoT-SPDY Adaptations of HTTP and SPDY for IoT environment Able to send request at the TCP connection establishment phase using TCP Fast Open (TFO) Reduced headers September 23,

8 Object Download time Object download time (seconds) HTTP SPDY IoT-SPDY IoT-HTTP CoAP Object size (bytes) Object download time : time duration between the client request and the arrival of the final byte of the object data September 23,

9 Total bytes transferred to fetch an object Total Bytes Transferred HTTP SPDY IoT-SPDY IoT-HTTP CoAP Object size (bytes) Total bytes transferred includes all headers September 23,

10 Experimental Setup Linux Netem emulates IoT link of data rate 20 Kbps and link delay of 20 ms. Link MTU 128 bytes. The link characteristics roughly corresponds to Zigbee Error-free links September 23,

11 Transport Services used in the experiments CoAP - libcoap client and server (libcoap) HTTP - Google Chrome client and Apache server SPDY - Google Chrome client and Apache server with mod-spdy enabled IoT-HTTP - A simple Web server and client + TFO IoT-SPDY - spdyd server and spdy-python client+tfo Object sizes - 10B, 50B, 100B, 200B, 500B and 1000B September 23,

12 TCP Fast Open (TFO) TFO enables safe data exchange during TCPs initial handshake Decreases application network latency by full RTT, decreasing the delay experienced by short TCP transfers Server uses a security cookie to authenticate a client initiating a TFO connection, so no need of 3-way handshake for additional TCP connections between the same hosts Internet Draft - draft-cheng-tcpm-fastopen-09.txt. Y. Cheng, J. Chu, S. Radhakrishnan and A. Jain. A paper from the authors in ACM CoNEXT 2011 September 23,

13 TCP Fast Open (TFO) TCP Client A Closed TCP Server B Listen First TCP Connection SYN-SENT ESTABLISHED Caches Cookie Requesting Fast open cookie in connection 1 SYN+TFO-cookie request SYN-ACK+TFO-Cookie C Conitues as regular TCP connection SYN-RCVD Generating cookie by encrypting client IP TCP Client A Closed Later TCP Connections ESTABLISHED Performing TCP Fast open in connection 2 SYN =x, Cookie C+ Data SYN =y, ACK=x+len(Data A)+1 TCP Server B Listen Server validates the Cookie C Sends the DATA A to application and acknowledges the data More data packets send to client while handshake is in progress ESTABLISHED Conitues as regular TCP connection September 23,

14 Message Sequence Chart for 10-bytes object download CoAP-Client CoAP-Server HTTP-Client HTTP-Server SPDY-Client SPDY-Server Start 0.08 s Request Reply 39 B 47 B Start 0.099s 0.16s SYN+GET (1) 98 B SYN-ACK 48 B ACK 40 B ACCEPT (1) 57 B ACCEPT (2)+Data 101 B ACK 40 B Start 0.10s SYN+GET (1) SYN-ACK SETTINGS ACK GET (2) ACK 108 B 48 B 60 B 40 B 87 B 40 B ACCEPT (1) 78 B 0.25s ACCEPT (2)+Data 66 B ACK 40 B CoAP IoT-HTTP IoT-SPDY September 23,

15 Summary of analysis of downloading a 10-byte object Network environment Zigbee-like environment Link data rate 20 Kbps, link MTU 128 bytes Error-free links Metrics CoAP IoT-HTTP IoT-SPDY SPDY HTTP Object download time 0.08s 0.16s 0.25s 0.68s 0.79s #Packets TotalBytes September 23,

16 Protocol Overhead: CoAP, IoT-HTTP and IoT-SPDY Protocol overhead (bytes) SPDY HTTP TCP CoAP UDP IP 0 SPDY1000 SPDY10 HTTP1000 HTTP10 CoAP1000 CoAP10 September 23,

17 Protocol Overhead: CoAP, IoT-HTTP and IoT-SPDY Transport Protocol overhead Services IP UDP TCP CoAP HTTP SPDY 10-byte CoAP object HTTP SPDY byte CoAP object HTTP SPDY September 23,

18 Object Download time Object download time (seconds) IoT-SPDY IoT-HTTP CoAP Object download time (seconds) IoT-SPDY IoT-HTTP CoAP Object size (bytes) Object size (bytes) Data rate 250 Kbps, MTU 128 B Data rate 250 Kbps, MTU 1280 B September 23,

19 Total bytes transferred to fetch an object Total Bytes Transferred IoT-SPDY IoT-HTTP CoAP Total Bytes Transferred IoT-SPDY IoT-HTTP CoAP Object size (bytes) Data rate 20 Kbps, MTU 128 B Object size (bytes) Data rate 250 Kbps, MTU 1280 B September 23,

20 Conclusions CoAP is the best in constrained environments with no link errors IoT-HTTP and IoT-SPDY reduce the object download time by 50 % to 75 % compared to HTTP and SPDY When data rate increases, object download times for CoAP and IoT-HTTP are comparable When MTU size increases, total bytes transferred by HTTP and SPDY decrease In not so constrained environments, IoT-HTTP and IoT-SPDY can be used September 23,

21 Plans for future experiments Study the behaviour of CoAP, IoT-HTTP and IoT-SPDY in error-prone/congested IoT environments Improve SPDYs compression techniques Incorporate RObust Header Compression (ROHC) with TCP Further TCP enhancements September 23,

22 Thank You for your attention! Any questions, comments? September 23,