Types of Access

• Direct ("on the net")
• Dial-up
  • MX records (directs mail to a "holding" host)
  • SL/IP (Serial line Internet Protocol)
  • PPP (Point-to-Point Protocol)
• Commercial providers for both types; varying usage policies on each net

Communications Issues

• Packet switching (TCP/IP) vs. circuit switching (telephones)
• Point-to-Point networks (cable, telephone)
• Local Area Networks (Ethernet, token bus or ring, IR, radio)
• Wide Area Networks (Telephone, satellite, radio, land lines)
• ATM (Asynchronous Transfer Mode): Open direct virtual circuits (compatible with TCP/IP)
• Store-and-forward: Current routing scheme, "dynamic" (15 hops not uncommon)

Telephone Service Grades

• Standard line: 0-19.2 KB, possibly higher with compression technology, ~50 KB
• Leased line: 56-64 KB
• T1 line: 1.544 MB
• T2 line: 6 MB (rare)
• T3 line: 45 MB

Other Means of Communications

• Packet radio -- portable networking
• Satellite

Coming Technologies

• Integrated Services Digital Network (ISDN; DOA?)
  • All-digital telephony
  • 1 16 KB "control" (A) channel
  • 2 64 KB "data" (B) channels
  • With multiplexing technology, \(~=300 KB today
  • Sun already ships ISDN port on all workstations
  • Baby Bells slow in deployment
• Asymmetric (mixed) technologies (example: cable in, telephone out)