Network Hardware Lecture 5

Fundamental Terminology (continued)

• Another categorization of packet switched networks is
• virtual circuit
• packets all take same route, set up in advance
• datagram
• each packet routed independently, no connection established
• typically more robust

Fundamental Terminology (continued)

• Packets typically consist of
• header
• source and destination addresses
• sequence number
• data portion
• trailer
• error detecting and correcting information
• Packets may be fixed or variable length

• head

• data

• tail

Network Standards Organizations

• International Standards Organization (ISO)
• makes standards for many different activities
• American National Standards Institute (ANSI)
• US representative to ISO
• CCITT
• one part of the UN agency International Telecommunications Union
• concerned with telephone and data communication services
• US representative is the State Department

Network Standards Organizations (cont.)

• National Instituted of Standards and Technology (NIST)
• standards body for US government purchases
• Institute of Electrical and Electronics Engineers (IEEE)
• key standards for LANs
• Internet Engineering Task Force (IETF)

Local Area Network Standards

• Ethernet (IEEE 802.3)
• Carrier Sense Multiple Access / Collision Detect (CSMA/CD)
• listen to cable, no one transmitting go ahead
• if collide, delay random time and retransmit
• multiple topologies
• multiple media
• coaxial cable (thick or thin)
• twisted pair wire (10BaseT)
• minimum packet size 64 bytes
• heavy overhead for one byte of data
• fast ethernet technologies allow 100 Mbps on twisted pair
• 1000 Mbps now available on optical fiber