MAR : A Commuter Router Infrastructure for the Mobile Internet Pablo Rodriguez, Rajiv Chakravorty, Julian Chesterfield, Ian Pratt, Suman Banerjee University of Cambridge computer Laboratory ACM MobiSYS '04

.Introduction.MAR System Architecture - adaptation layer - session protocol - proxy server.Exploiting Network Diversity.Experiment.Conclusions Outline

. Current communication systems are single input single output (SISO) systems - coverage is limited (eg. Hospital office ) - such systems cannot afford to exploit diversity. MAR is a wireless multi-homed device that can be placed in moving vehicles (e.g. car, bus, train) to enable high-speed data access. improve wireless system performance Introduction

MAR System Architecture l1 l2 l3 l4

.Provide a set of local interfaces.Provide a set of local interfaces 。.Local interfaces provide access to local mobile users 。.They include wireless technologies (eg. Ethernet bluetooth ) 。.Accommodate a variety of wide-area wireless technologies (eg. GRPS UMTS CDMA ) 。 MAR Adaptation Layer

.Provide a DHCP server 。.Mobile device are configured to use MAR as their default router and DNS server 。 MAR Adaptation Layer BACK

. Can aggregate the available bandwidth across all wireless interfaces 。. Offered a larger ， more stable pipe to end users 。. striping techniques 。 - different packets belonging to the same TCP connection can end up in different interfaces 。striping techniques MAR Session Protocol

.MAR session API that can also accommodate a wide-range of session scheduling policies to load balance packets / connection among different interfaces 。.Policies - round robin 。 - least loaded interface 。 - weighted 。 MAR Session Protocol

. MAR monitors the signal to noise ratio (SNR) and Bit Error Rate (BER) values and throughput of each interfaces 。 - standard Hayes AT commands - relies on past throughput information. Determine the weight of the load balance 。 - Interface busier, fewer TCP connection 。. Blackout / active interfaces 。. keeps monitoring 。standard Hayes AT commands MAR Session Protocol BACK

MAR Proxy Services. Option. Optimizations - striping protocol - application-level - compress data - proxy cache

. Technology diversity - two wireless devices that are operating using two different communication technologies 。 - CDMA. spread scheme - GPRS. time division multiple access scheme - data performance between the two interfaces in the MAR devices Exploiting network diversity

. Network diversity - different wireless devices ( mobile phone ) - using the same technology (GPRS) - connected to different operator ’ s network(opt1,opt2) Exploiting network diversity

. Channel diversity - A base station of a cellular network simultaneously assigns different channels to multiple devices - connected to the network of the same wireless cellular operator (opt1) Exploiting network diversity

Experimental Set-up. Three PCMCIA wireless cards with 4+1 slots (4 downlink GSM slot and 1 uplink). Two motorola phones. Average speed about 20 mph. Static and mobile Opt1: MHz Opt2: GHz Opt3: MHz Opt4:CDMA 1XRTT

Experimental Set-up

Experiment Result Interface 1

Experiment Result

Interface 1 Experiment Result Interface 1

Experiment Result

Pearson ’ s Correlation Coefficient X Y

Experiment Result

. a Mobile Access Router that multiple wireless access links to aggregate bandwidth and provide local users with a smoother, more reliable access network than can typically be provided by a single cellular link. Improvement performance Conclusion

Standard AT commands X1 Report basic call progress result codes and connections speeds (OK, CONNECT, RING, NO CARRIER (also, for busy, if enabled, and dial tone not detected), NO ANSWER, CONNECT XXXX, and ERROR. X2 Report basic call progress result codes and connections speeds, i.e., OK, CONNECT, RING, NO CARRIER (also, for busy, if enabled, and dial tone not detected), NO ANSWER, CONNECT XXXX, and ERROR. X3 Report basic call progress result codes and connection rate, i.e., OK, CONNECT, RING, NO CARRIER, NO ANSWER, CONNECT XXXX, BUSY, and ERROR. X4 Report all call progress result codes and connection rate, i.e., OK, CONNECT, RING, NO CARRIER, NO ANSWER, CONNECT XXXX, BUSY, NO DIAL TONE and ERROR. BACK

Form: A reliable and scalable striping protocol Striping Protocol

Form: A reliable and scalable striping protocol Striping Protocol BACK

GSM. Circuit-Switching.. 分頻 / 分時 (FDMA/TDMA) 的混合系統. 以 GSM900 系統為例，使用的頻率 Downlink890 ～ 915MHz ， Uplink935 ～ 960MHz 。. 每個頻段先利用分頻多工 (FDMA) 的方式，切割成許多的載波 (Carrier Frequency) ，相鄰的兩載波頻率之間的間隔為 200KHz 。對 於每個不同的載波頻率，又再透過分時多工 (TDMA) 的方式，將時 間切割成八個時槽 (Time Slot) ，每個時槽可以用來傳送一個用戶的 語音訊號. 最高只能以 9.6Kbps 的傳輸率來傳送資料，如果加上資料壓縮的功 能，最高也只能達到 14.4Kbps 。

GPRS (General packet radio service). Packet witch 技術. 四種編碼模式，提供不同的錯誤保護 (Error Protection) 能力. 每個時槽可提供的數據傳輸率 - CS-1(9.05Kbps) 。 - CS-2(13.4Kbps) 。 - CS-3(15.6Kbps) 。 - CS-4(21.4Kbps) 。 - 其中 CS-1 的保護最嚴密， CS-4 則完全未加任何保護。. 瞬間最大可使用八個時槽，所以 GPRS 的傳輸率號稱可高達 171.2Kbps(21.4Kbps x 8) 。

基地台 控制器

SGSN (Serving GPRS Support Node) 。 主要負責將手機所送出的數據資料正確地送到相對應之 Gateway GPRS Support Node ，以期正確地傳送到接收端終端機上. GGSN (Gateway GPRS Support Node) 負責將 GPRS SGSN 所送來的封包，正確無誤地送達其服務範圍內的 各個手機 HLR( 主位置暫存器 ) 存放的是用戶所有註冊相關資訊 VLR( 客位置暫存器 ) 存放足以讓客戶建立通訊連結的部分客戶資 訊 EIR( 設備識別碼暫存器 ) 是提供手機相關識別資訊 ( 如是否為合法的手機 ) 的資料庫。

UMTS (Universal Mobile Telecommunication System) 第三代行動通訊系統 - 提供較高的傳輸速率 (2 Mbps) - 核心網路 (Core Network, CN).Packet-Switching Ps.Circuit-Switching CS -UMTS 無線電存取網路 (UMTS Terrestrial Radio Access Network, UTRAN) -RNC Radio Network Controller

CDMA ( Code Division Multiple Access ) DSSS ( Direct Sequence Spread Spectrum ) Data rate of transmitting = bit stream * n (chip code) WCDMA 傳輸率每秒 384Kbps CDMA2000 1xEV-DO 可提供 400~600kbps 的平均傳輸速率，並可 達 2Mbps BACK