BTS Internet Integration

1
BTS - Internet Integration

• Sreedhar Mukkamalla
• Bhaskaran Raman
• Jimmy Shih

2
Big Picture Our Goals

• Integrate BTS with the internet and incorporate
  it into our testbed infrastructure
• Demonstrate advantages of a flexible service
  architecture built on a packet-switched IP core
  network by implementing cool new services
• Study and analyze scalability issues and
  bottlenecks in performance

3
Big Picture Our Goals

• Understand the issues involved in Voice over IP
• Naming
• QoS
• Security
• Mobility

4
Summary of Work Done

• Implemented functionality to place call between
  VAT and cell phone (DEMO)
• Integration with IVR room control application
• i.e. use cell phone to do room control (DEMO)
• Integration with information dissemination
  application
• i.e. receive news briefs and stock quotes over
  cell phone (DEMO)

5
System Architecture
Original Plan
Control Signaling
Internet
IP-PAD
GSM Signaling
UPSim
E1
BTS
Ethernet
Traffic
E1
Traffic
Voice_at_13kb/s
Data_at_12kb/s
E1
in 16kb/s
Voice_at_64kb/s
ZAK/TRAU
Data_at_12kb/s in 64kb/s
GSM Phone
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System Architecture
Actual approach
Control Signaling
Internet
IP-PAD
GSM Signaling
UPSim
E1
BTS
Ethernet
Traffic
E1
Voice_at_13kb/s
Data_at_12kb/s
in 16kb/s
ZAK/TRAU functionality implemented in IP-PAD
software
GSM Phone
7
Components of the Integration Architecture

• BTS
• handles radio transmission (air interface) and
  has little other functionality
• RBS 2202, indoor version
• 2 TRXs (max6) supports upto 14 simultaneous
  phone calls
• currently operating with dummy loads at lowest
  power setting (coverage area is east half of 4th
  floor of Soda Hall)

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Components of the Integration Architecture

• UPSim
• Used to control BTS for setting up phone calls
• UPSim software running on SCO UNIX PC
• GPC board talks to BTS over an E1 line (on-board
  processors speak LAPD)
• TRAFFIC program running on UPSim
• (written in PLUS language) running on UPSim
• simulates BSC, MSC etc. and is used to set up
  phone calls

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Components of the Integration Architecture

• IP-PAD (IP Packet Assembler/Disassembler)
• Serves as gateway for data between BTS and
  Internet GSM frames ltgt RTP audio packets
• Performs rate adaptation function of ZAK/TRAU in
  software
• PC running Windows NT 4.0
• Has Thor-2 E1 interface board

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Voice call - PC to GSM phone
Internet
Internet
IP-PAD
UPSim
BTS
PC running VAT
GSM Phone
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Voice call - PC to GSM phone

• Internet host running VAT
• VAT is an Internet audio tool intended mainly for
  multiparty Mbone conferences
• VAT has no signaling
• Uses RTP format for transport of audio data
• Supports GSM audio format

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Data PathGSM frames ltgt RTP packets
0
2 bits from an E1 time slot one 16kbps stream
1
2
32 E1 time slots per E1 frame
8 bits per E1 time slot
31
13
Data PathGSM frames ltgt RTP packets
flag
flag
320 bits (40 bytes) from a 16kbps stream
260 bit (32.5 byte) GSM audio frame
IP packet
RTP payload 33 byte GSM frame
RTP header
IP header
UDP header
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Control Path SIP and H.323

• Internet signaling protocols
• SIP (Session Initiation Protocol)
• simple signaling protocol for Internet
  conferencing (unicast and multicast sessions)
• H.323
• An umbrella of ITU standards for multimedia
  communication over LANs.
• Places the telephone network functionality onto
  the Internet

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SIP vs H.323

• Which one do we want to use ?
• Advantages of SIP
• Extensibility scalability
• Modularity
• Advantages of H.323
• Industry support (Microsoft)
• We can leverage of existing products

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Next six months...

• Implement control path and signaling, DTMF tones
• Data path for data calls/RLP
• Study performance (latency) and scalability
  issues at IP-PAD
• Integrate with H.323 gateway

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Future Work

• Further issues (setting up testbed)
• Naming of different entities
• VAT
• phones
• services/proxies
• RSVP
• Security and billing
• Mobility management, handoffs