Network Hardware Lecture 5

Local Area Network Standards (continued)

• Token ring (IEEE 802.5)
• token determines which host gets to transmit
• special bit pattern used for token
• when station wants to transmit
• watch network for token
• take token off ring and transmit packet
• drain packet as it comes around again
• put token back on ring when done
• single topology
• one node monitors ring to regenerate token if necessary

Local Area Network Standards (continued)

• Ethernet
• faster access if light load
• degrades rapidly as load increases
• > 60% utilization is a problem
• no guaranteed access
• host can “starve”
• most popular LAN technology

Local Area Network Standards (continued)

• Token ring
• minimum delay to transmit, since have to wait for token
• delivers much better performance under heavy load
• can reach close to 100% utilization
• fair
• host can hold token for 10 msec, then must put back on network
• each host gets token at least every 10 * number of hosts msec
• “sick” monitor station can cause problems

Frame Relay and ATM

• Frame Relay
• virtual circuit organization
• uses leased or private lines
• vc set up at time subscribers are connected to the network
• “light” protocol
• no error checking by network, just delivery mechanism
• 64 Kbps to 45 Mbps

ATM

• Asynchronous Transfer Mode (ATM)
• being standardized by CCITT
• switched, virtual circuit approach
• allows reserving network capacity
• uses fixed size packets
• easier for hardware to handle
• twisted pair or fiber medium
• 100 m to few km
• 155 Mbps to 2400 Mbps
• also used for LAN interconnect as backbone