The last mile plus a history of the Internet

Derek Bridge

Department of Computer Science,
University College Cork

The last mile plus a history of the Internet

Aims:

• to appreciate the different technologies used for the last mile
• to know the main events in the history of the Internet

Connecting to the Internet

• Direct connections
  • A dedicated, permanent link to the Internet
  • Expensive to lease and to operate
  • Suited to large companies/universities
  • Employees/students connect to the company/university LAN
• Connecting from home to, e.g., an ISP: the last mile
  • Dial-up
  • DSL
  • Cable
  • Wireless & Mobile Wireless
  • http://www.mulley.net/2006/02/09/broadband-choices-in-ireland/

Bandwidth

• Bandwidth usually refers to the data-carrying capacity of a connection
  • the (theoretical) maximum amount of data that can pass from one point to another in a unit of time
  • measured in bits per second, e.g. 100 Mbps Ethernet
  • bps is bits per second and Bps is bytes per second (is it?) and M is...

    k (kilo)	103=1,000	210=1,024
    M (mega)	106=1,000,000	220=1,048,576
    G (giga)	109=1,000,000,000	230=1,073,741,824

• Warning! Many networking technologies are asymmetric
  • they offer higher bandwidth for download than for upload
  • marketing people only quote the download bandwidth

Latency

• Bandwidth on its own tells you very little
• Latency refers to how much time it takes for a packet of data to get from one point to another
  • often, the round-trip time
  • measured in milliseconds
• Latency depends on the following (and more):
  • transmission medium (copper wire, optical fibre,...)
  • number of hops
  • delays introduced by the devices encountered (modems, routers,...)
  • sending stuff that isn't raw data
  • poor configuration
  • contention

Throughput and speed

Throughput (actual thoughput, effective throughput)

A measure of how much actual data can be sent per unit of time across a connection

E.g. you are using 100 Mbps Ethernet but getting throughput of 71.9 Mbps

Speed

Sometimes informally used in place of bandwidth or latency or thoughput

Sometimes just used subjectively

http://www.speedtest.net/

Dial-up

• Exploits existing and near-universal infrastructure
• Cheap and easy to setup and use
• No contention until ISP
• Symmetric
• Low bandwidth: 56kbps
• Not 'always on'
• You can't phone while you surf

Digital Subscriber Line (DSL or xDSL)

• Exploits existing infrastructure but distance restrictions
• May be more expensive than dial-up
• No contention until ISP
• Typically asymmetric (ADSL)
• Download: 1.5Mbps-12Mbps; upload: 640kbps
• 'Always on'
• You can phone while you surf

Cable TV

Cable TV

• Exploits existing wiring but cable doesn't reach everyone
• May be more expensive than dial-up and may tie you in to a TV subscription
• Contention starts at the neighbourhood node
• Typically asymmetric
• Download: 1.5Mbps-6Mbps; upload: 300kbps
• 'Always on'
• You can watch TV while you surf

Fixed and Mobile Wireless

• No wiring; requires antenna (on roof, in home or plugged into computer) and transmitters; can reach the parts other providers cannot reach
• May be more expensive than dial-up
• No contention until ISP but possible interference
• Fixed
  • Asymmetric
  • Download: 1Mbs-8Mbs; upload: 256kbps-2Mpbs
  • Always on
• Mobile
  • Symmetric?
  • 1.4Mbps-3.6Mbps
  • Always on?