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Link technologies Reaching the Network of networks Alberto Escudero-Pascual Royal Institute of Technology.

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Presentation on theme: "Link technologies Reaching the Network of networks Alberto Escudero-Pascual Royal Institute of Technology."— Presentation transcript:


2 Link technologies Reaching the Network of networks Alberto Escudero-Pascual Royal Institute of Technology Sweden 1st International Workshop on Open Access 4-7 June 2003, Stockholm, Sweden

3 Link level technologies… or how to get connected to the Internet Goal: Brief technical overview of some of the most common technologies to connect to Internet in developing countries… How: What is the Internet? What is to be connected? Review five (radio) link level technologies.

4 What is the Internet? Federal Networking Council (DoD, NASA et al), Internet Monthly Reports, October 1995 agrees that the following language reflects our definition of the term "Internet". "Internet" refers to the global information system that: is logically linked together by a globally unique address space based on the Internet Protocol (IP) or its subsequent extensions/follow-ons; is able to support communications using the Transmission Control Protocol/Internet Protocol (TCP/IP) suite or its subsequent extensions/follow-ons, and/or other IP-compatible protocols; and provides, uses or makes accessible, either publicly or privately, high level services layered on the communications and related infrastructure described herein.

5 What is the Internet? The Internet is a group of interconnected networks which has evolved more-or-less independently of any social, political, or governmental control. The Internet is a network of networks - billions of computers, all connected together. The Internet is the internet of networks

6 What is the Internet? Humanities and Arts: Sharing Center Stage on the Internet, IETF RFC2150, 1997 People, computers and information electronically linked around the world by a common Protocol for communicating with each other.

7 We, the linked…

8 Connected to the Internet? Reach a computer that can exchange IP packets with other computers around the world at anytime. Reach the linked, reach those connected. or reach a concrete service gateway. Connect to the Internet is to make sure that the information that we send (receive) can reach a place where can be routed (forwarded) inside of IP packet to others. Connect to the Internet is being able to reach a IP-based Post office

9 Reaching the linked world… VSAT DVB (MPE) Wi-Fi (IEEE ) Packet Radio (AX.25) HF-Mail


11 VSAT, very small aperture terminal





16 The frequency bands can be any of C band 4/6 GHz, Ku band 10-12/14 GHz Bi-directional Central Hub is connected 270 ms delay 1 Mbps 500–700 USD


18 DVB (Digital Video Broadcast) Users access Web sites through their low-speed Internet connection Receive multimegabit data streams back through a TV dish antenna on the roof. The DVB cards convert incoming RF satellite signals and place them back in the TCP/IP stack. DVB uses IP encapsulation technology to make Internet traffic look like MPEG-2 data. Cheap receivers (200 USD)

19 DVB (Digital Video Broadcast) Sending Wi-Fi (LaoTel) Receiving (DVB-IP) Sending VSAT (SCPC) Receiving (DVB-IP)

20 Wi-Fi (IEEE )

21 IEEE (Wi-Fi) Used for terrestrial outdoor link Connecting to the connected (range of 1-30 Kms) Low power (100 mW – 1W) Requires line-of-sight Mass-produced equipment, open standard

22 Wi-Fi: The radio technology 2.4 Ghz radio band Following the ETSI regulations Unlicenced spectrum Running IEEE b (WiFi). Using Open Source code (GNU/Linux) PtP links ~ 2000 USD

23 Wi-Fi: PtP Radio link with repeater

24 Wi-Fi: Hardware Antennas Low loss cable Connectors Radio transcivers Radio Bridges (Linux) Routers

25 Wi-Fi: Radio Equipment

26 Wi-Fi: Radio Kits

27 Wi-Fi: Radio Kits (Supermarket technology)

28 Wi-Fi : Nora-Digerberget-Ås Ås Nora 4.5 Km 5.3 Km

29 Wi-Fi: Ås - Digerberget

30 Wi-Fi: Ås school

31 Wi-Fi: Line-of-sight

32 Packet Radio (AX.25)

33 AX.25 is considered the defacto standard protocol for amateur radio since early 70s 3-30 Mhz (HF), 140 Mhz (VHF) and 435 Mhz (UHF) Connected & connectionless modes of operation, and is used either by itself for point-point links, or to carry other protocols such as TCP/IP and NetRom. For HF packet, 300 BPS data is used over single side band (SSB) modulation. For 1200/2400 bps UHF/VHF packet, commonly available narrow band FM voice radios are used. For high speed packet (starting at 9600 bps), special radios or modified FM radios must be used.

34 Packet Radio (AX.25)

35 More info

36 HF mail gateway

37 HF-mail gateway Connect to a connected service as a mail server via a HF (100 – > 1000 Kms) Using two HF radio modems talking: Codan 9002 SCS PTC-II Clover-2000 Clover-500 Pactor-1 Pactor-2 SITOR

38 HF-mail gateway HF radio modes SITOR ARQ 100 bits/second Open standard upper case only, no error correction CCIR-476 Same as SITOR AMTOR Same as SITOR PACTOR bits/sec G-TOR 300 bits/sec PACTOR bits/sec Clover bits/sec Clover bits/sec Clover bits/sec (minus overhead: 1936 bits/second uncompressed) Codan bits/sec + built-in compression = 6000 bits/sec or 1475 bits/sec uncompressed

39 How is the Internet World?



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