Ethernet Structured Wiring ITL. ITL: ©2000-2005 Hans Kruse, Shawn Ostermann, Carl Bruggeman2...

EthernetStructured Wiring

ITL

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


Transmission Systems

• Basic multiplexing– DS-n (T1, DS3)– SONET (OC-3, OC-12, etc)– WDM

• Multiplexing and Other Functions– Ethernet– Frame Relay– ATM


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


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)


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)


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


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


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)


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


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


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


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


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)


Structured Wiring

• Main Cross-Connect (Main Distribution Frame)– Riser Cable(“Backbone”)

• Intermediate Cross-Connect (Int. Dist. Frame)– Horizontal Wiring

• Jack Field– Drop Cable

• Workstation


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


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)


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


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


ApplicationsSource: Lucent Technologies


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


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

Ethernet Structured Wiring ITL. ITL: ©2000-2005 Hans Kruse, Shawn Ostermann, Carl Bruggeman2...

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