
202763c38f1ea71202d235442469c75a.ppt
- Количество слайдов: 54
Layer One and Two LAN Networking Wires and connections Station to station packet transmission
OSI: Open Systems Interconnection Reference Model LAN
OSI Reference Model Application Presentation Session Transport Network Data Link Physical ©”A Guide to Networking Essentials”, 1998, Course Technology.
Open Systems Interconnection (OSI) z. International Standard z. Written to be a manufacturing standard, but never built z. Used as a vocabulary short hand z. Applies to all extensions of networks
OSI Reference Model
OSI Layer 1 Local Area Network protocols Physical layer: standards for physical connections (e. g. plugs and connectors) Responsible for getting bits from one location to another. z Medium z Connectors z Representation of signals
Media z. Twisted Pair Copper Wire shielded vs unshielded plenum vs PVC z. Coaxial Copper Cable thinnet and thicknet z. Fiber single mode and multi-mode z. Microwave z. Infrared, Radio
Unshielded Twisted Pairs z. Cheapest alternative for LAN cabling z. Already exists in most offices z. Adapts to star wiring and hub systems z. Trend in modern LAN installations z. New technologies adapt to it z. Shielded cable used where electronic interference a problem
Cat 5 Twisted Pair Wiring
Twisted Pair Signals Reverse phases to cancel noise LINE 1 + LINE 2 -
Cable categories
Twisted Pair Connectors z. Wiring Pairs yblue, white-blue yorange, white-orange ygreen, white-green ybrown, white-brown z. RJ-11 and RJ-45 z. D connectors
RJ-45 (Registered Jack 45): 8 wires for Ethernet
RJ-11 (4 or 6 wire versions) for telephones
Unshielded Twisted Pairs z. Phones use 1 pair z 10 Base. T uses 2 pairs of Category 5 copper z 100 Base. FX uses multimode fiber
10 Base. T Ethernet Wiring
Fiber Optic Cables z. Longer distances z. High data rate requirements z. High interference situations z. High security situations z. Connections more difficult than with UTP
Fiber Optic Single Mode Laser 8/125 micron Up to 50 miles LED Multimode 62. 5/125 micron Up to 2000 meters
Fiber-optic Connectors
Wireless z. Infrared z. Radio y. Microwave y. Radio Frequency x. Spread Spectrum & Wi-Fi (IEEE 802. 11) z. Wireless security
Wireless LAN Access
Local Area Networks Layer 2
"Gentlemen! Start — your — laptops!" Copyright 1998 Doug Adams
Local Area Networks that move data from station to station using a common set of layer 1 and layer 2 protocols. y. Common broadcast domain y. Local ownership y. Common operating system y. Machine ID addressing
OSI Reference Model Application Presentation Session Transport Network Data Link Physical ©”A Guide to Networking Essentials”, 1998, Course Technology.
Data Link - Layer 2 2. Data link layer: protocols for error free transmission from station to station The data link is responsible for node to node validity and integrity of the transmission. The transmitted bits are divided into frames; for example, an Ethernet, Token Ring or FDDI frame in local area networks. Layers 1 and 2 are required for every type of communications.
Data Link - Layer 2 functions
Data Link Sub-layers z. Media Access Control (MAC) y. Standards for addressing and locating nodes z. Logical Link Control (LLC) y. Standards for communication with higher layers
LAN Operating Protocols z. Ethernet open standard, cheap, most common z. Token Ring IBM proprietary, high quality, expensive z. Others
Network Interface Cards z. Build, send out and accept frames z. Usually a daughter board on PC z. Must match LAN and CPU z. Require drivers to operate
Network Interface Cards (NIC)
Ethernet Carrier Sense Multiple Access/Collision Detection Trailer Body Listen before transmit Contention access Retransmit on collision Header
Ethernet: CSMA/CD (IEEE 802. 3) Carrier Sense Multiple Access with Collision Detection y. Compare channel voltage to reference level y. Any node can transmit if channel free y. Collision detection during transmission x. Jamming x. Random back off y. Slot time and minimum packet size
Manchester Encoding (self-clocking bit stream) 0 1 0 High-to-Low = 0 Low-to-High = 1 Switch voltage at each time point
Ethernet Packets z. Synchronization z. Data transparency z. MAC addresses z. Minimum length z. Error check z. Alternate Ethernet packet formats
Ethernet Packet Structure
Administration z. Acknowledgements z. Address announcements (identification) z. Slot time z. Card streaming z. Hub access z 10 Base. T, 100 Base. T, Gigabit Ethernet
10 Base. T Specifications (Twisted Pair Ethernet) z 100 m to hub z 1024 stations per network z 10 mbps z. UTP z. Star/bus
LAN Logical/Physical Topologies Bus Ring Star
Network Logical Topologies are determined by the technologies that run the network z Bus: Ethernet z Ring: Token ring SONET, FDDI z Star: Mainframe Switched Ethernet
Ethernet: Physical Star, Logical Bus
LAN with hubs
Hubs or Switches
Switches (Layer 2) z. Route packets to destination nodes based on MAC addresses y. Limit traffic on unused branches y. Provide additional security y. Connect 10 Mb and 100 Mb branches z. Operate in firmware
Switch (CISCO Catalyst 1928)
Ethernet Switching
Token Ring (IEEE 802. 5) z. Allocated access via electronic token z. Priority access reservation z. Confirmed packet delivery z. Multiple monitor functions
Token Ring
Token Ring Message Token access Equal access Collision avoidance CRC Body Header
Empty Token Structure
Dataframe Token Structure
Topology: Logical or Physical? Bus Ring Star
Network Topologies are determined by the technologies that run the network z Bus: Ethernet z Ring: Token ring SONET, FDDI z Star: Mainframe Switched Ethernet