WAN Services

Question 1

ISDN - Integrated Services Digital Network

Answer 1

• BRI – Basic Rate Interface (2B+D)
  
  • Two 64 kbit/s bearer (B) channels
  • One 16 kbit/s signaling (D) channel

• PRI – Primary Rate Interface
  • Delivered over a T1 or E1
  • T1 – 23B + D
  • E1 – 30B + D + alarm channel
  • Commonly used as connectivity from the PSTN to 
     large phone systems (PBX)

Question 2

T1 / E1

Answer 2

• T-Carrier Level 1
  
  • Time-division multiplexing
  • North America, Japan, South Korea
  • 24 channels - 64 kbit/s per channel
  • 1.544 Mbit/s line rate
• E-Carrier Level 1
  
  • E is for Europe
  • 32 channels - 64 kbit/s per channel
  • 2.048 Mbit/s line rate

Question 3

T3 / DS3 / E3

Answer 3

• T-Carrier Level 3
  
  • Delivered on coax (BNC connectors)
  • DS3 is the data carried on a T3
• T3
  
  • Twenty-eight T1 circuits - 44.736 Mbit/s
• E3
  
  • Sixteen E1 circuits - 34.368 Mbit/s

Question 4

DSL

Answer 4

• ADSL (Asymmetric Digital Subscriber Line)
• Uses telephone lines

• Download speed is faster than the upload speed
(asymmetric)
• ~10,000 foot limitation from the central office (CO)
• 52 Mbit/s downstream / 16 Mbit/s upstream are
common
• Faster speeds may be possible if closer to the CO

Question 5

Metro Ethernet

Answer 5

• Metropolitan-area network
  
  • A contained regional area
• Connect your sites with Ethernet
  
  • A common standard
  • Not your typical WAN connection

• The Ethernet is usually running over a different
topology
• Pure Ethernet
• Ethernet over SDH, MPLS, or DWDM

Question 6

Cable broadband

Answer 6

• Broadband
  
  • Transmission across multiple frequencies
  • Different traffic types

• Data on the “cable” network
• DOCSIS (Data Over Cable Service Interface
Specification)

• High-speed networking
  
  • 4 Mbits/s through 250 Mbits/s are common
  • Gigabit speeds are possible
  • Multiple services - Data, voice

Question 7

Dialup

Answer 7

• Network with voice telephone lines
  
  • Analog lines with limited frequency response
• 56 kbit/s modems - Compression up to 320 kbit/s
• Relatively slow throughput - Difficult to scale
• Legacy systems, network utility
  
  • May be difficult to find a modem