Скачать презентацию More on LANs Module C Copyright 2001 Prentice Скачать презентацию More on LANs Module C Copyright 2001 Prentice

f26640d85abb5b513cea4465a0cfbc6e.ppt

  • Количество слайдов: 22

More on LANs Module C Copyright 2001 Prentice Hall More on LANs Module C Copyright 2001 Prentice Hall

More on LANs • More on Ethernet – 802. 3 10 Base 5 and More on LANs • More on Ethernet – 802. 3 10 Base 5 and 10 Base 2 – 100 Base-TX signaling – Ethernet II versus 802. 3 – 802. 2 Logical Link Control Layer Frame • More on 802. 5 Token-Ring Networks • 802. 11 Wireless LANs • Bridges versus Switches

Ethernet Recap • Created by Digital Equipment Corporation, Intel, and Xerox • Taken over Ethernet Recap • Created by Digital Equipment Corporation, Intel, and Xerox • Taken over by the 802. 3 Working Group of the IEEE 802 LAN MAN Standards Committee • 802. 3 has since produced many standards – Especially at the physical layer: 10 Base 5, 10 Base 2, 10 Base-T, 100 Base-TX, 1000 Base-X – Only one MAC layer standard--the 802. 3 MAC layer standard for framing and CSMA/CD

Original Ethernet Versus 802. 3 10 Base 5 • Created by Digital, Intel, and Original Ethernet Versus 802. 3 10 Base 5 • Created by Digital, Intel, and Xerox – Popular version was Ethernet II • 802. 3 Working Group took over – Created the first Ethernet standard, 802. 3 – Slightly changed the physical layer; became 10 Base-5 – Changed the data link layer (later) • 10 Base 5 – 10 Mbps, baseband, 500 meters/segment

Ethernet 10 Base 5 • Multidrop Layout – Main trunk cable: thick coaxial cable Ethernet 10 Base 5 • Multidrop Layout – Main trunk cable: thick coaxial cable • Up to 500 meters long – Drop cable: 15 -wire cable • Up to 50 meters • Also called the attachment unit interface (AUI) Drop Trunk Cable (AUI) Up to 500 meters

Ethernet 10 Base 5 NIC 15 -pin AUI Connector Trunk Cable Coaxial Cable 500 Ethernet 10 Base 5 NIC 15 -pin AUI Connector Trunk Cable Coaxial Cable 500 m maximum Drop Cable (Attachment Unit Interface or AUI) 15 wires 50 m maximum N-Connector Transceiver (Medium Attachment Unit)

Ethernet 10 Base 5 1. Sending NIC Transmits a bit 2. Transceiver Broadcasts the Ethernet 10 Base 5 1. Sending NIC Transmits a bit 2. Transceiver Broadcasts the bit 3. Each Transceiver Sends the bit to Its NIC

Ethernet 10 Base 5 • Broadcast (Bus) Topology – Station B transmits – Signal Ethernet 10 Base 5 • Broadcast (Bus) Topology – Station B transmits – Signal travels down trunk to all other stations A B C

Ethernet 10 Base-5 • Up to 5 segments connected by repeaters – 2, 500 Ethernet 10 Base-5 • Up to 5 segments connected by repeaters – 2, 500 meters maximum distance between farthest stations – Four repeaters maximum – No loops Drop cable Repeater Segment of Trunk Cable Repeater AUI Port

Ethernet 10 Base 2 (802. 3 a) • Cheaper Physical Layer Standard – NICs Ethernet 10 Base 2 (802. 3 a) • Cheaper Physical Layer Standard – NICs have BNC connector – T-connector attaches to it – T-connector has BNC connectors for cable runs attaching it to adjacent stations To next NIC To next T-connector NIC BNC NIC

Ethernet 10 Base 2 (802. 3 a) • Segments are thin coaxial cable – Ethernet 10 Base 2 (802. 3 a) • Segments are thin coaxial cable – Run only between NICs – Daisy chain of NICs is a segment – Terminator at end of each segment – Up to 30 stations per segment – 5 segments (4 repeaters) maximum – 10 Base 2: 185 meters/segment Terminator NIC NIC

Repeaters can Mix 802. 3 PHY Standards Repeaters must have the correct ports Repeater Repeaters can Mix 802. 3 PHY Standards Repeaters must have the correct ports Repeater RJ-45 10 Base-T UTP Repeater AUI Connectors BNC 10 Base 2 NIC Drop Cables 10 Base 5 Trunk Cable

Ethernet II vs 802. 3 Frames • Ethernet II Frame – Ethertype field (2 Ethernet II vs 802. 3 Frames • Ethernet II Frame – Ethertype field (2 bytes) – Tells protocol of message in data field (e. g. , IP) – No length field – No 802. 2 LLC layer; Full data link layer protocol Ethernet II Frame Preamble SFD DA SA Ethertype Data FCS 802. 3 Frame Preamble SFD DA SA Length LLC frame FCS

Ethernet II vs 802. 3 Frames • Why the Differences – Lack of a Ethernet II vs 802. 3 Frames • Why the Differences – Lack of a length field could cause problems – 802 would create multiple standards; Giving them all the same connection to the next higher layer (802. 2 seemed wise) Ethernet II Frame Preamble SFD DA SA Ethertype Data FCS 802. 3 Frame Preamble SFD DA SA Length LLC Frame FCS

Ethernet II vs 802. 3 Frames • Telling them Apart – NIC must recognize Ethernet II vs 802. 3 Frames • Telling them Apart – NIC must recognize incoming frame’s type – If 2 bytes after SA <= 1500, must be 802. 3 because of maximum length limitation in 802. 3 – If 2 bytes after SA >1500, it’s an Ethertype Ethernet II Frame Preamble SFD DA SA Ethertype Data FCS 802. 3 Frame Preamble SFD DA SA Length LLC Frame FCS

802. 2 LLC Layer Functions • Logical Link Control Layer (LLC) – Links subnet 802. 2 LLC Layer Functions • Logical Link Control Layer (LLC) – Links subnet to next-higher-layer (internet) – One LLC standard (802. 2) for all 802 LANs – Makes interface to internet layer simple Internet Layer 802. 2 LLC 802. 3 MAC 802. 5 MAC 802. 3 10 Base-T 802. 3 100 Base-T 802. 5 16 Mbps

802. 2 LLC Layer Functions • Logical Link Control – At the MAC layer, 802. 2 LLC Layer Functions • Logical Link Control – At the MAC layer, the destination NIC discards incorrect MAC layer frames – 802. 2 standard provides optional error correction to retransmit lost or discarded LLC frames

802. 2 LLC Frame • Fields – Destination Service Access Point (DSAP) designates the 802. 2 LLC Frame • Fields – Destination Service Access Point (DSAP) designates the next-higher layer protocol on the receiving device (IP, IPX, etc. ) – There can be multiple internet layer programs on the destination machine; DSAP designates the specific one to get the frame’s data field – SSAP: Source Service Access Point Data Field Control SSAP DSAP

802. 2 LLC Frame • Fields – Control field contains instructions to the receiver’s 802. 2 LLC Frame • Fields – Control field contains instructions to the receiver’s LLC process on the NIC – Data field contains message of the next higher layer (usually internet) Data Field Control SSAP DSAP

802. 2 LLC Frame • Subnet Access Protocol (SNAP) Alternative for IP and other 802. 2 LLC Frame • Subnet Access Protocol (SNAP) Alternative for IP and other TCP/IP internet layer standards – DSAP = AA hex – SSAP = AA hex – Control = 03 hex Data Field Ethertype SNAP message Org Code Control SSAP DSAP =03 =AA

802. 2 LLC Frame • Subnet Access Protocol (SNAP) Alternative for IP and other 802. 2 LLC Frame • Subnet Access Protocol (SNAP) Alternative for IP and other TCP/IP internet layer standards – Org code lists the organization maintaining a list of protocol codes for next higher layer – Ethertype (Ethernet type) code names a specific protocol for the data field Data Field Ethertype SNAP message Org Code Control SSAP DSAP =03 =AA

802. 2 LLC Frame • Subnet Access Protocol (SNAP) Alternative for IP and other 802. 2 LLC Frame • Subnet Access Protocol (SNAP) Alternative for IP and other TCP/IP internet layer standards – Data field has message of that protocol Data Field Ethertype SNAP message Org Code Control SSAP DSAP =03 =AA