Ana səhifə

Übersicht Ethernet Typen Seite 2 faq ethernet Seite 4


Yüklə 329.35 Kb.
səhifə1/4
tarix10.06.2016
ölçüsü329.35 Kb.
  1   2   3   4

Ethernet



Übersicht Ethernet Typen Seite 2


FAQ Ethernet Seite 4
Multicast und Broadcast Adressen Seite 20
Herstellerkennungen Seite 23

Übersicht Ethernettypen:





  • 10base5
    Standard Ethernet Koaxialkabel, „Thick Cable“, Bus-Topologie
    Ein Segment darf maximal 500m lang sein. Pro Segment können über MAU‘s (Medium Access Unit) 100 Stationen angeschlossen werden, deren Abstand am Kabel mindestens 2,5m betragen muß. Es sind zusätzlich maximal vier Repeater möglich, womit die Gesamtlänge eines 10base5-Netzes höchstens 2500m beträgt.

  • 10base2
    Flexibles Ethernet Koaxialkabel, „Thin Cable“, Bus-Topologie
    Auch als Cheapernet bezeichnetes Ethernet mit dünnem Koaxialkabel. Ein Segment darf maximal 185m lang sein. Pro Segment dürfen 30 Stationen angeschlossen werden. Die MAU’s befinden sich normalerweise auf der Netzwerkkarte, so daß diese dann über T-Stücke angeschlossen werden. Die Leitungsenden müssen mit einem 50 Widerstand abgeschlossen werden, um Reflexionen zu verhindern. Es sind wiederum vier Repeater zulässig, somit ist eine maximale Länge von 925m möglich.

  • 10baseT – UTP
    Paarweise verdrillte 4-Draht-Leitung, nicht geschirmt ,UTP (unshilded twisted pair), Stern-Topologie
    Hier ist der Einsatz eines Hub (Sternverteiler) notwendig. Jede Station wird über ein eigenes Kabel, welches max. 100m lang sein darf, an den Hub angeschlossen.

  • 10baseT – STP
    Paarweise verdrillte 4-Draht-Leitung, abgeschirmt, STP (shilded twisted pair), Stern-Topologie
    Wie 10baseT – UTP, aber das Kabel ist abgeschirmt.

  • 10baseF
    Lichtwellenleiter (LWL), Stern-Topologie
    Die maximale Länge eines Segments beträgt ca. 2000m . Es können sowohl die Multimode- oder die Monomode Faser verwendet werden. Beim Einsatz von Monomode Faser kann die Segmentlänge bis zu 25km betragen.

  • 10broad36
    modulierte Breitbandübertragung, Koaxialkabel, Bus-Topologie
    Der Abstand zwischen zwei Stationen darf max. 3600m betragen.

  • 1base5
    „StarLan“ 1MByte Punkt-zu-Punkt-Verbindung, Stern-Topologie
    Die Kabellänge zwischen zwei Stationen darf 250m nicht überschreiten.

  • 100baseT4
    100MBit/s Ethernet über vier verdrillte Paare (UTP), Stern-Topologie
    Die Kabellänge zwischen Hub und Station beträgt maximal 100m. Die Datenübertragung erfolgt auf vier Leitungspaaren mind. der Kabelkategorie 3 (d.h. für Datenübertragungen bis 10MBit/s). Diese Kabel sind günstiger als die für 100baseTX notwendigen, dafür sind aber Hubs und Adapter schwerer zu bekommen.

  • 100baseTX – UTP
    100MBit/s Ethernet über zwei verdrillte Paare, UTP, Stern-Topologie
    Die Kabellänge zwischen Hub und Station beträgt maximal 100m. Die Datenübertragung erfolgt auf zwei Leitungspaaren der Kabelkategorie 5 (d.h. Übertragungsraten bis 100MBit/s). 100baseTX ist der weitverbreitetste Fast-Ethernet-Typ.

  • 100baseTX – STP
    100MBit/s Ethernet über zwei verdrillte Paare, abgeschirmt (STP), Stern-Topologie
    Wie 100baseTX – UTP, nur abgeschirmt.

  • 100baseFX
    100MBit/s über Glasfaserverkabelung, Stern-Topologie
    Die maximale Länge zwischen Hub und Station beträgt 400m. Beim Einsatz von Monomode Faser kann die Segmentlänge bis zu 25km betragen.

  • 1000baseT
    1000MBit/s Ethernet über UTP, Stern-Topologie
    Die Kabellänge zwischen Hub und Station beträgt maximal 100m. Es müssen Kabel der Kategorie 5 eingesetzt werden.

  • 1000baseCX
    1000MBit/s Ethernet über STP, Stern-Topologie
    Die Kabellänge zwischen Hub und Station beträgt maximal 25m.

  • 1000baseSX
    1000MBit/s Ethernet über Multimode Glasfaser, Sterntopologie
    Die Kabellänge zwischen Hub und Station beträgt maximal 550m.

  • 1000baseLX
    1000MBit/s Ethernet über Monomode Glasfaser, Sterntopologie
    Die Kabellänge zwischen Hub und Station beträgt maximal 5km.



FAQ’s


Sections:

02: General information about Ethernet and standards.

03: Ethernet Cabling Information.

04: Ethernet Devices and Components.

05: Errors and Related Terms.

06: Testing and Troubleshooting.

07: Additional Information.

02.07Q: What is the difference between an Ethernet frame and a IEEE802.3

frame? Why are there two types? Why is there a difference?

A: Ethernet was invented at Xerox Palo Alto Research Center and later

became an international standard. IEEE handled making it a

standard; and their specifications are slightly different from the

original Xerox ones. Hence, two different types. 802.3 uses the

802.2 LLC to distinguish among multiple clients, and has a "LENGTH"

field where Ethernet has a 2-byte "TYPE" field to distinguish among

multiple client protocols.

TCP/IP and DECnet (and others) use Ethernet_II framing, which is

that which Xerox/PARC originated.

02.08Q: What is SNAP

A: Sub-Network Access Protocol, an extention to the original 802.2

data link level format. (SNAP is described in IEEE 802-1990) The

802.2 data link format replaced the Ethernet Protocol Type concept

with two 8 bit fields; Source SAP, and Destination SAP.

Unfortunately that causes problems with migration of protocols, and

the lack of SAP space that is available. So one SAP as allocated

for this scheme which greatly expands the available protocol space.

When using the SNAP SAP the first 5 bytes of data are used as a

protocol ID. The first 3 bytes should be a value allocated to you

as a vendor id, the same as you get for Source address values. The

is called the OUI (Organizationally Unique ID) The second 2 bytes

is a protocol type.

Note that this is 802.2 and applies across all 802 LAN media types.

For translation bridging, there is a convention, if you set the OUI

to zero, you are representing a mapped Ethernet frame. So that a

bridge will translate such a frame back into Ethernet format, and

not into an 802.3 frame format.

802.2 SNAP frame:

+-------+------+------+------+-------+------+------+

| MAC | DSAP | SSAP | UI | OUI | Type | data |

| Header| 0xAA | 0xAA | 0x03 | 3bytes|2bytes| |

+-------+------+------+------+-------+------+------+

This will appear the same on all 802 compliant LAN media. On

802.3, there will be a Length field between the SA and the DSAP but

not on 802.5 or FDDI.

02.09Q: Where can I find out which Protocols use which Ethernet type

numbers?


A: Look at IETF RFC-1700 - Assigned Numbers RFC.

02.10Q: What is a MAC address?

A: It is the unique hexadecimal serial number assigned to each Ether-

net network device to identify it on the network. With Ethernet

devices (as with most other network types), this address is

permanently set at the time of manufacturer, though it can usually

be changed through software (though this is generally a Very Bad

Thing to do).

02.11Q: Why must the MAC address to be unique?

A: Each card has a unique MAC address, so that it will be able to

exclusively grab packets off the wire meant for it. If MAC

addresses are not unique, there is no way to distinguish between

two stations. Devices on the network watch network traffic and

look for their own MAC address in each packet to determine whether

they should decode it or not. Special circumstances exist for

broadcasting to every device.

02.12Q: Is there a special numbering scheme for MAC addresses?

A: The MAC addresses are exactly 6 bytes in length, and are usually

written in hexadecimal as 12:34:56:78:90:AB (the colons may be

omitted, but generally make the address more readable). Each

manufacturer of Ethernet devices applies for a certain range of MAC

addresses they can use. The first three bytes of the address

determine the manufacturer. RFC-1700 (available via FTP) lists

some of the manufacturer-assigned MAC addresses. A more up-to-date

listing of vendor MAC address assignments is available on

ftp.lcs.mit.edu in pub/map/Ethernet-codes.

02.13Q: What is a preamble ?

A: A seven octet field of alternating one and zero binary bits sent

prior to each frame to allow the PLS circuitry to reach its steady

state synchronization with received frame timing. (802.3 standard,

page 24,42).

02.14Q: What is a Start Frame Delimiter (SFD)?

A: A binary sequence of '10101011' immediately following the preamble

and indicating the beginning of a frame. (802.3 standard, page

24).

02.15Q: What does CRC mean?



A: Cyclical Redundancy Check - A method of detecting errors in a

message by performing a mathematical calculation on the bits in the

message and then sending the results of the calculation along with

the message. The receiving work-station performs the same

calculation on the message data as it receives it and then checks

the results against those transmitted at the end of the message.

If the results don't match, the receiving end asks the sending end

to send again.

02.13Q: What is a broadcast address?

A: The unique address that identifies a packet as appropriate to all

receiveing stations. In 802.3 any address in which the second byte

is an odd number. (1,3,...F).

02.14Q: What exactly do 10Base5, 10BaseT, 10Base2, 10Broad36, etc mean?

A: These are the IEEE names for the different physical types of

Ethernet. The "10" stands for signalling speed: 10MHz. "Base"

means Baseband, "broad" means broadband. Initially, the last

section as intended to indicate the maximum length of an unrepeated

cable segment in hundreds of meters. This convention was modified

with the introduction of 10BaseT, where the T means twisted pair,

and 10BaseF where the F means fiber (see the following Q&A for

specifics). This actually comes from the IEEE committee number for

that media.

In actual practice:

10Base2 Is 10MHz Ethernet running over thin, 50 Ohm baseband

coaxial cable. 10Base2 is also commonly referred to

as thin-Ethernet or Cheapernet.

10Base5 Is 10MHz Ethernet running over standard (thick) 50

Ohm baseband coaxial cabling.

10BaseF Is 10MHz Ethernet running over fiber-optic cabling.

10BaseT Is 10MHz Ethernet running over unshielded, twisted-

pair cabling.

10Broad36 Is 10MHz Ethernet running through a broadband cable.

02.15Q: What does FOIRL mean?

A: Fiber Optic Inter Repeater Link. A "IEEE 802 standard" worked out

between many vendors some time ago for carrying Ethernet signals

across long distances via fiber optic cable. It has since been

adapted to other applications besides connecting segments via

repeaters (you can get FOIRL cards for PCs). It has been

superseded by the larger 10BaseF standard.

02.16Q: What is LattisNet?

A: LattisNet is a pre-10BaseT quasi-standard for running Ethernet over

twisted-pair cabling. It was developed by Synoptics, and several

other vendors made compatible equipment for a while. LattisNet is

not compatible with 10BaseT, but you can have LattisNet hubs and

10BaseT hubs in the same hub chassis or connected to the same

network backbone. The primary difference is that 10BaseT synchron-

izes the signals at the sending end, while LattisNet syncrhonizes

at the receiving end.

02.17Q: What is StarLAN-10?

A: StarLAN-10 is AT&T's variety of Ethernet over twisted-pair cabling.

Older StarLAN-10 is not 100% 10BaseT compliant, as it does not

provide link integrity to the AUI. However, many 10BaseT

interfaces can be configured to work with StarLAN-10 hubs,

alongside StarLAN-10 NICs. Beware, though, that the original

StarLAN-10 is NOT in any way compatible with 10BaseT, and worse,

there seems to be no way to tell other than trying it to see what

happens.

The current StarLAN products supported by AT&T/NCR are fully 802.3

compliant. This includes the SmartHUB model E, SmartHUB model B,

SmartHUB XE, and the other fiber and wire SmartHUB models.

03.01Q: What is coax?

A: Coaxial cable (coax) is a metallic electrical cable used for RF

(radio frequency) and certain data communications transmission.

The cable is constructed with a single solid or stranded center

conductor that is surrounded by the dielectric layer, an insulating

material of constant thickness and high resistance. A conducting

layer of aluminum foil, metallic braid or a combination of the two

encompass the dielectric and act as both a shield against

interference (to or from the center conductor) and as the return

ground for the cable. Finally, an overall insulating layer forms

the outer jacket of the cable. Coaxial cable is generally

superior in high-frequency applications such as networking.

However, for shorter distances (up to 100 meters), UTP or STP cable

is generally just as reliable when using differential modulation

techniques (such as with 10BaseT).

There are three types of RG-58 cable, as far as I can tell. There

are probably other subtle differences, but for 10BASE2, impedance

and velocity of propagation are the important ones. The table

below summarizes:

Cable Impedance Velocity

---------- ---------- --------------

RG-58A/U 50 ohms .66 or .78

RG-58C/U 50 ohms .66

RG-58/U 53.5 ohms .66 or .695

03.02Q: What is UTP, STP?

A: Twisted pair cables. UTP is for UNshielded, twisted pair, while

STP is for SHIELDED, twisted pair. UTP is what's typically

installed by phone companies (though this is often not of high

enough quality for high- speed network use) and is what 10BaseT

Ethernet runs over. UTP is graded according to its data carrying

ability (e.g., Level 3, Level 4, Level 5). 10BaseT Ethernet

requires at least Level 3 cable. Many sites now install only

Level-5 UTP, even though level 4 is more than sufficient for

10BaseT, because of the greater likelihood that emerging high-speed

standards will require cable with better bandwidth capabilities.

STP is typically used for Token-Ring networks, where it is commonly

referred to IBM Type 1 (or 2, 3, 6, 8, etc); however there are

several manufacturers of Ethernet equipment and interfaces that

support Ethernet over STP. Nevertheless, Ethernet over STP is not

officially defined in any standards. While there is a good level

of interoperability with Ethernet over STP, (Lattisnet, developed

by Synoptics, is the recognized de facto standard in this area),

one should consider the long-term availability and cost of this

non-standard scheme before planning new networks around it.

03.03Q: Are there any restrictions on how Ethernet is cabled?

A: Yes, there are many, and they vary according to the media used.

First of all, there are distance limitations:

10Base2 limited to 185 meters (607 ft) per unrepeated cable

segment.

10Base5 limited to 500 meters (1,640 ft) per unrepeated cable

segment.

10BaseF depends on the signaling technology and medium used

but can go up to 2KM.

10BaseT generally accepted to have a maximum run of 100-150M,

but is really based on signal loss in Db's (11.5db

maximum loss source to destination).

10Broad36 limited to 3,600 meters (almost 2.25 miles).

Then there are limitations on the number of repeaters and cable

segments allowed between any two stations on the network. There

are two different ways of looking at the same rules:

1. The Ethernet way:

A remote repeater pair (with an intermediate point-to-point

link) is counted as a single repeater (IEEE calls it two

repeaters). You cannot put any stations on the point to point

link (by definition!), and there can be two repeaters in the

path between any pair of stations. This seems simpler to me

than the IEEE terminology, and is equivalent.

2. The IEEE way:

There may be no more than five (5) repeated segments, nor more

than four (4) repeaters between any two Ethernet stations; and

of the five cable segments, only three (3) may be populated.

This is referred to as the "5-4-3" rule (5 segments, 4

repeaters, 3 populated segments).

It can really get messy when you start cascading through 10BaseT

hubs, which are repeaters unto themselves. Just try to remember,

that any possible path between two network devices on an

unbridged/unrouted network cannot pass through more than 4

repeaters or hubs, nor more than 3 populated cable segments.

Finally, 10Base2 is limited to a maximum of 30 network devices per

unrepeated network segment with a minimum distance of 0.5m (1.5ft)

between T-connectors. 10Base5 is limited to a maximum of 100

network devices per unrepeated segment, with a minimum distance of

2.5m (8.2ft) between taps/T's (usually indicated by a marker

stamped on the cable itself every 2.5m). 10BaseT and 10BaseF are

star-wired, so there is no minimum distance requirement between

devices, since devices cannot be connected serially. You can

install up to the Ethernet maximum of 1024 stations per network

with both 10BaseT and 10BaseF.

0

03.04Q: Can I mix 10Base2 and 10Base5 cabling on a single segment?



A: It is not "legal", but the network police will not read you your

rights and drag you away. Ideally, you should use a repeater (or

bridge, router, etc...) between the different cabling types.

However, in reality, it will work fine, as long as none of the

other network parameters (lengths, numbers of stations, repeaters,

etc) are near the limit of the specification.

03.05Q: What about wireless Ethernets? Are there any?

A: Yes, and no. Many vendors offer equipment for Ethernet across a

variety of unbounded, or wireless, connections using lasers,

microwaves, and spread-spectrum radio transmissions. However, none

of these methods are organized by any standards body, so it is

unlikely to find equipment from any two different manufacturers

that work together.

03.06Q: When should I choose 10BaseT, when 10Base2 (or others)?

A: The specific environment and application must be considered when

selecting your media type. However, there are some general

rules-of-thumb that you can consider:

Avoid using copper between buildings. The electrical disturbances

caused by lightning, as well as naturally occurring differences in

ground potential over distance, can very quickly and easily cause

considerable damage to equipment and people. The use of

fiber-optic cabling between buildings eliminates network cabling as

a safety risk. There are also various wireless media available for

inter-building links, such as laser, spread-spectrum RF and

microwave. However, wireless media is much more expensive and less

reliable than fiber-optic, and should only be considered when it is

impossible to get right-of-way for fiber-optic cable.

10Base2 (thin Ethernet or Cheapernet) is the least expensive way to

cable an Ethernet network. However, the price difference between

10Base2 and 10BaseT (Ethernet over UTP) is rapidly diminishing.

Still, for small, budget-conscious installations, 10Base2 is the

most economical topology. The disadvantages of 10Base2 is that any

break in the cable or poor connection will bring the entire network

down, and you need repeaters if you have more than 30 devices

connected to the network or the cable length exceeds 185 meters

(607 feet).

10Base5 is generally used as a low-cost alternative to fiber-optic

media for use as a backbone segment within a single building. It's

extended length (500m or 1640ft), higher attached device count

(100) and better noise resistance make 10Base5 well suited for use

as a network trunk for one or more floors in a building. However,

the high cost of connecting each device (in addition to the

interface, you also need an external transceiver, or MAU, and an

AUI cable) makes 10Base5 too expensive for most LAN installations,

and like 10Base2, a single break or bad connection in the cable can

bring the entire network down.

10BaseT is the most flexible topology for LANs, and is generally

the best choice for most network installations. 10BaseT hubs, or

multi-hub concentrators, are typically installed in a central

location to the user community, and inexpensive UTP cabling is run

to each network device (which may be 100m, or 330ft, from the hub).

The signalling technology is very reliable, even in somewhat noisy

environments, and 10BaseT hubs will usually detect many network

error conditions and automatically shut-down the offending port(s)

without affecting the rest of the network (unless, of course, the

offending port was your server, shared printer, or router to the

rest of the world). While the hardware is more expensive than

10Base2, the cabling is cheaper and requires less skill to install,

making 10BaseT installation costs only slightly higher than

10Base2. The flexibility and reliability more than offset the

marginally higher price.

10BaseF, and its predecessor, FOIRL, are the only recommended

topologies for inter-building links. However, they need not be

limited to this role. 10BaseF can also be run to the desktop,

though the cost is prohibitively high in all but the most

0 specialized environments (generally, extremely noisy manufacturing

facilities, or very security-conscious installations). More

commonly, FOIRL (and now, 10BaseF) is used inside buildings to form

backbone networks and to connect wiring closets together.

03.07Q: What are the advantages/disadvantages of a star like cabling?

A: Old style Ethernet bus wiring (ie, taking the cable from one

machine to the next, and then to the next, etc) is prone to cable

failure and quickly consumes allowed distances due to aesthetic

wiring needs. If the wiring connection is broken at any point, the

entire network (segment) fails - and the much greater number of

connections increases the probability of a failure or break. On the

other hand, it's pretty easy to do for a layman and may involve

less actual wiring for small segments.

Star wiring eliminates the single point of failure of a common

wire. A central hub has many connections that radiate out to

hosts, if one of these hosts connections fails it usually doesn't

affect the others. Obviously, however, the hub becomes a central

point of failure itself, but studies show a quality hub is less

likely to fail before a heavily used strand of coax.

There are a bunch of other reasons hubs are desirable, but this is

  1   2   3   4


Verilənlər bazası müəlliflik hüququ ilə müdafiə olunur ©kagiz.org 2016
rəhbərliyinə müraciət