TDC 461 Basic Communications Systems Local Area Networks 29 May, 2001.
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TDC 461 Basic Communications Systems Local Area Networks 29 May, 2001
Agenda Local Area Networks –Components –Topologies –Transmission Media –Network Interface Cards (NICs) –Network Operating System software Client vs Server functions Peer-to-Peer vs. Server- based Local Area Network Technologies –Ethernet –Token Ring LAN Interconnection –LAN Switches –Routers
Twisted Pair Unshielded Twisted Pair (UTP) –Similar to telephone cable, but Usually 4-pair cable is used UTP Category ratings –Category 3 - 10 Mbps up to 100 meters –Category 4 - 16 Mbps up to 100 meters –Category 5 - 100 Mbps up to 100 meters Shielded Twisted Pair (STP) –
Coaxial Cable LAN coaxial cable is similar to Cable TV cable (and can be identical) –Construction –Advantages –Disadvantages
LAN Standards IEEE 802 Committee Standards –802.3 - Ethernet –802.5 - Token Ring
LAN Standards IEEE 802 Standards include –Physical (Layer 1) Cable Types Maximum length restrictions Data rate and bit encodings –Medium Access Control (Layer 2) Access control protocol (determines which device can transmit when Frame header/trailer format
Ethernet MAC Protocol Medium Access Control (MAC) layer protocol is identical for all Ethernets: –Ethernet Frame format –Carrier Sense Multiple Access with Collision Detection (CSMA/CD) used to determine which workstation can send at any given time.
Carrier Sense Multiple Access with Collision Detection To transmit data packet: –First, listen to see if any other station is transmitting (Carrier Sense) –When network is quiet, start transmitting
Carrier Sense Multiple Access with Collision Detection Station Backoff –Each station involved in collision: –As number of collisions grows, range of random values (N) increases (“exponential backoff”)
Switches vs. Routers How is Switch different than a Router? –Addressing Switch uses layer 2 MAC addresses Router uses layer 3 IP address –Speed & security Switch forwards packets fast (~50-100 nsec). Router takes more time (~1-50 msec) and provides other security features
Switches vs. Hubs How is Switch different than a Hub? –Broadcasting (and Security) Hub broadcasts every packet to every device Switch forwards packet out single port –Matching Data Rates All ports on hub must run at same data rate Switch ports can run at different rates (can buffer incoming packet at one data rate and re-transmit at another data rate).
Full-Duplex Ethernet Full-Duplex Ethernet allows a workstation to send and receive data simultaneously. Requirements –Must have a full-duplex NIC card –Must be connected to Ethernet switch
Switched Hierarchy Switches allow network manager to put bandwidth where it is needed. –Some users get 10 Mbps shared (hub) –Some users get 10 Mbps dedicated (switch) –Some users get 100 Mbps shared (hub) –Some users get 100 Mbps dedicated (switch)