ethernet structured wiring itl. itl: ©2000-2005 hans kruse, shawn ostermann, carl bruggeman2...
TRANSCRIPT
ITL: ©2000-2005 Hans Kruse, Shawn Ostermann, Carl Bruggeman 2
Transmission Media
• Guided Media– Twisted Pair
– Coaxial Cable
– Optical Fiber
• Unguided Media– “Broadcast”-type radio transmission
• Wireless LANs, Cell Phones, PCS
– Satellite
– Point-to-Point Microwave
ITL: ©2000-2005 Hans Kruse, Shawn Ostermann, Carl Bruggeman 3
Transmission Systems
• Basic multiplexing– DS-n (T1, DS3)– SONET (OC-3, OC-12, etc)– WDM
• Multiplexing and Other Functions– Ethernet– Frame Relay– ATM
ITL: ©2000-2005 Hans Kruse, Shawn Ostermann, Carl Bruggeman 4
Ethernet
• Designed as a broadcast medium; each transmission is received by every station
• Based on a bus architecture• Manchester Encoding• Several Media Types
– 10Base5– 10Base2– 10Base-T– 10Base-F
ITL: ©2000-2005 Hans Kruse, Shawn Ostermann, Carl Bruggeman 5
10Base-T
• Simulates the Ethernet bus using an active star topology.
• Uses unshielded twisted pair wiring.• “4-pair” (8 conductor) wiring is normally used,
but only 2 pairs are used – 1 transmit pair one receive pair
• Each station connects to a central hub.– Cables are wired “straight through”– Hub ports are “crossed” (transmit/receive are reversed)
ITL: ©2000-2005 Hans Kruse, Shawn Ostermann, Carl Bruggeman 6
Fast Ethernet
• All use a star topology• 100Base-TX
– Two pair copper wire (Cat 5)– Same pin-out at 10Base-T, better wire
• 100Base-FX– Two fibers
• 100Base-T4– Rarely used; 4 pair lower quality (cat 3) wires
• 1000Base-X (4 pair Cat 5 or 5E)
ITL: ©2000-2005 Hans Kruse, Shawn Ostermann, Carl Bruggeman 7
Ethernet Logic
• Ethernet is a CSMA/CD network– Carrier Sense
• Before sending a signal, listen to see if anyone else is transmitting
– Multiple Access • ... because there can be many devices on the same wire trying
to send
– Collision Detection• If, while transmitting a signal, you detect another signal• Yours was “probably” lost• You should “wait a while” and then send it again
ITL: ©2000-2005 Hans Kruse, Shawn Ostermann, Carl Bruggeman 8
Ethernet Frames
• To facilitate sharing, we bound the length of a message– Upper bound ensures that a single device can’t use the
channel for too long• 1514-1520 bytes maximum
– Lower bound helps make guarantees about collision detection
• 54 bytes minimum
– These individual messages traveling on physical hardware are called “Frames”
– Same term used for most network technologies
ITL: ©2000-2005 Hans Kruse, Shawn Ostermann, Carl Bruggeman 9
Frame Format
• Ethernet uses a fairly simple framing format– Initial pattern of bits referred to as a preamble
• 64 bits (10101010...101011)
– Addressing information– The data we’re trying to send– Error detection data
• 32-byte “Cyclic Redundancy Check” (CRC)
• Also called FCS (Frame Check Sequence)
ITL: ©2000-2005 Hans Kruse, Shawn Ostermann, Carl Bruggeman 10
Ethernet Frame Types
802.3
Type II
802.3 SNAP
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.“802.3 raw”
from http://www.wildpackets.com/compendium/EN/L1-Enet.html
ITL: ©2000-2005 Hans Kruse, Shawn Ostermann, Carl Bruggeman 11
Physical Address• Each machine attached to a packet switch network is
assigned a unique physical address– Sender must supply destination address when transmitting a
packet– In most technologies, sender supplies source address as
well
• Each technology defines its own address scheme– Ethernet in particular
• 48-bit address obtained when device is manufactured• All 1s address reserved for broadcast• One-half of the addresses reserved for multicast (a restricted form of
broadcast); assigned by customer
ITL: ©2000-2005 Hans Kruse, Shawn Ostermann, Carl Bruggeman 12
Ethernet Hub aka Repeater
• Hardware device that connects two Ethernet cable segments and makes them appear to be a single cable– Repeats all packets from one cable to the other and vice
versa– Performs the service one bit at a time– Introduces delay of 1 bit-time– Called “level 1” interconnect– Generalized to form a star rather than a bus – Can be very inexpensive, ≈ $20
ITL: ©2000-2005 Hans Kruse, Shawn Ostermann, Carl Bruggeman 13
Ethernet Bridge aka Switch
• Similar purpose as a repeater, but generally much smarter– Repeats at the packet level
• Introduces delay of 1 packet-time• Does not forward collisions or noise
– Does forward all broadcast packets– Adaptively “learns” source addresses and forwards
only as needed– Called “level 2” interconnect– Can be very inexpensive, ≈ $40
ITL: ©2000-2005 Hans Kruse, Shawn Ostermann, Carl Bruggeman 14
Network Interface Cards• Sends frames
– Adds the preamble and CRC– Performs all of the collision detection and backoff
• Receives frames– Sees all frames on the wire
• Knows its address (often on ROM on the card• May also answer to other addresses (multicast• Only interrupts the CPU when a packet for the local computer
arrive
– Can generally be put in promiscuous mode• Forwards all frames to the CPU
– Useful for debugging/monitoring(/stealing)
ITL: ©2000-2005 Hans Kruse, Shawn Ostermann, Carl Bruggeman 15
Structured Wiring
• Main Cross-Connect (Main Distribution Frame)– Riser Cable(“Backbone”)
• Intermediate Cross-Connect (Int. Dist. Frame)– Horizontal Wiring
• Jack Field– Drop Cable
• Workstation
ITL: ©2000-2005 Hans Kruse, Shawn Ostermann, Carl Bruggeman 16
Why use Hierarchical Wiring?• Flexibility = Lower Cost
From Bates, Voice and Data Communications Handbook:– Estimated Cost for 50 single wire pulls:
$15,568– Estimated Cost for 50 dual wire pulls:
$16,935
ITL: ©2000-2005 Hans Kruse, Shawn Ostermann, Carl Bruggeman 17
Wiring Standards
• Building Wiring Standards– Electronic Industries Association
– Telecommunications Industry Association
– EIA/TIA 568 Commercial Building Wiring Standard
• “Outside Plant”– Bell Labs technical publications
– Now maintained by Telcordia (formerly Bellcore)
ITL: ©2000-2005 Hans Kruse, Shawn Ostermann, Carl Bruggeman 18
RJ-What?
• As an aside for the eternally curious:
The RJxx nomenclature appears in the legal documents used by the FCC to identify permitted methods to connect telecom equipment to the network
• For the really, really curious:
Title 47 CFR, Part 68, Subpart F, Section 502
ITL: ©2000-2005 Hans Kruse, Shawn Ostermann, Carl Bruggeman 19
Wiring StandardsLevel/CAT 1 1Mbps
Level/ CAT 2 4Mbps
Level/ CAT 3 16Mbps
Level/ CAT 4 20Mbps
Level/ CAT 5 100Mbps1000 Mbps (4 pair)
100m max distance
Level/ CAT 5E 100Mbps1000 Mbps (4 pair)
Level/ CAT 6 200-250MHz Not yet a standard
ITL: ©2000-2005 Hans Kruse, Shawn Ostermann, Carl Bruggeman 20
ApplicationsSource: Lucent Technologies
ITL: ©2000-2005 Hans Kruse, Shawn Ostermann, Carl Bruggeman 21
FDDI
• 100 Mbps Ring• Usually based on optical fiber• Based on the Token Ring Standard• Provides capacity pre-allocation• Economics:
– Ethernet is cheaper than token ring and does almost as good a job – so it wins
– Fast Ethernet is cheaper than FDDI and does almost as good a job – so it wins
ITL: ©2000-2005 Hans Kruse, Shawn Ostermann, Carl Bruggeman 22
FDDI Details
• Ring:– Everything you send eventually comes back to you
– A sender looks at the data coming back to ensure that it wasn’t “garbled”
– Contention for the wire is handled by a circulating “token”
– To send, a station waits for the token• Grab the token
• Send your data
• Re-insert the token