ISWN (Integrated Services Wireless Network)

Richard Akester

UCL

Introduction

• Test network– Software

• DVB-T– Stream Types – Multiplexes

• 802.11– Infrastructure/Ad-hoc– Unicast/Multicast

• Network Support• Future Work

Test network

DVB-T

ADSL

802.11b

Software

tzap

ts2ps

tuner

kernel App space

demux

TV SERVER CLIENT

App space kernel

udprecv

mplayerALSA

X11

MulticastOver 802.11

Elementary Stream (ES)

Video (MPEG2): I B B P B B P B B P B B P I

I: Intra frames, P: Predictive frames, B: Bi-directional framesGOP: 12, (~2 GOPs/sec@25fps [PAL]), 4-6Mbps

Audio (MP2): A A A A A A A A

A: Audio frames (1152 audio samples [24ms@48kHz, ~42fps])128-256kbps

Packetized Elementary Stream (PES)

00Header: 00 01 PT

PT (Payload Type): 0xE0=1st video stream, 0xC0=1st audio streamLength: usually 2048 (2K) bytes (but can be less)

Length Flag1 Flag2 hlength pts

Transport Stream (TS)

Header: 0x47 Flags PID Flags Adaptation Field

Header+Body = 188 bytes

PID (Program ID): allows programs to be multiplexed, but alsodistinguishes between substreams [eg BBC1 PIDs: 600 (video),601 (audio), 603 (subtitles), 4167 (teletext)]

Special PIDs: NIT (Network Information Table), SDT (ServiceDescription Table), PMT (Program Map Tables), PAT (ProgramAssociation Table).

DVB-T Multiplexes

• 1 (18Mbps): BBC 1, BBC 2, BBC 3, BBC News 24, CBBC

• 2 (24Mbps): ITV 1, ITV 2, Channel 4, Teletext, ITV News, FourText, Ch 14

• A (24Mbps): five, TV Travel Shop, QVC, bid-up.tv, ntl, Ch 15, BBC Radio 1, 2, 3, 4

• B (18Mbps): BBC 4, CBeebies, BBC Parliament, 1Xtra, BBC R5 Live, BBC 5L SportsX, BBC 6 Music, BBC 7, BBC Asian Net, Community, 701, 702, 703

• C (18Mbps): UK History, Sky News, Sky Travel, Sky Sports News, Magic, Hits Radio

• D (18Mbps): The HITS, TMF, f tn, UKBrightIdeas, CBM, Free2Play, Q, Magic, Hits Radio, BBC World Sv, oneword, jazz fm, Kerrang!, Smash Hits!, Kiss

802.11 ad-hoc network

• Consumer electronic devices may use this mode (no access point)

• No option to use PCF (have to use DCF)– Although IEEE802.11e…

• Distributed beaconing

Unicastsender receiver

RTS (Request To Send)

CTS (Clear To Send)

DATA

ACK

Multicastsender receiver

DATA

RTP (Realtime Transport Protocol)

• RFC2250 (how to carry MPEG2 video and audio in RTP)– A) encapsulate PS/TS in RTP headers

• Often done (eg dvbstream)

– B) encapsulate ES in RTP headers with extra header info added

• Not so common…

Streaming software

• Dvbstream– Designed for dvb-s (satellite) but could be rewritten for

dvb-t

– Sends TS/PS encapsulated in RTP

• ffmpeg/ffserver– ffmpeg can transcode MPEG2->MPEG4

– ffserver can serve resulting “file” over HTTP

• VideoLAN– Vlc: client/player that can also transcode/act as a server

Future Work

• Partial transcoding (http://www.ecse.rpi.edu/CNGV/publications/1998_PR/iab_talk_jw.pdf)

• Subtitles/EPG incorporating into OSD• Channel zapper: web interface?• PVR

– Programmable by web interface

– Time/Date/Channel OR just click on program name!