HP Hewlett Packard Network Card 180 Degree Turn User Manual

The Ethernet Evolution  
The 180 Degree Turn  
(C) Herbert Haas 2005/03/11  
1
 
History: Initial Idea  
Shared media CSMA/CD as access algorithm  
COAX Cables  
Half duplex communication  
Low latency No networking nodes  
(except repeaters)  
One collision domain and also one broadcast domain  
10 Mbit/s shared  
by 5 hosts 2  
Mbit/s each !!!  
3
(C) Herbert Haas 2005/03/11  
The initial idea of Ethernet was completely different than what is used today  
under the term "Ethernet". The original new concept of Ethernet was the use of  
a shared media and an Aloha based access algorithm, called Carrier Sense  
Multiple Access with Collision Detection (CSMA/CD). Coaxial cables were  
used as shared medium, allowing a simple coupling of station to bus-like  
topology.  
Coax-cables were used in baseband mode, thus allowing only unicast  
transmissions. Therefore, CSMA/CD was used to let Ethernet operate under the  
events of frequent collisions.  
Another important point: No intermediate network devices should be used in  
order to keep latency as small as possible. Soon repeaters were invented to be the  
only exception for a while.  
An Ethernet segment is a coax cable, probably extended by repeaters. The  
segment constitutes one collision domain (only one station may send at the same  
time) and one broadcast domain (any station receives the current frame sent).  
Therefore, the total bandwidth is shared by the number of devices attached to the  
segment. For example 10 devices attached means that each device can send 1  
Mbit/s of data on average.  
Ethernet technologies at that time (1975-80s): 10Base2 and 10Base5  
3
 
History: Multiport Repeaters  
Demand for structured cabling (voice-grade  
twisted-pair)  
10BaseT (Cat3, Cat4, ...)  
Multiport repeater ("Hub") created  
Still one collision domain  
("CSMA/CD in a box")  
4
(C) Herbert Haas 2005/03/11  
Later, Ethernet devices supporting structured cabling were created in order to  
reuse the voice-grade twisted-pair cables already installed in buildings. 10BaseT  
had been specified to support Cat3 cables (voice grade) or better, for example  
Cat4 (and today Cat5, Cat6, and Cat7).  
Hub devices were necessary to interconnect several stations. These hub devices  
were basically multi-port repeaters, simulating the half-duplex coax-cable, which  
is known as "CSMA/CD in a box". Logically, nothing has changed, we have still  
one single collision and broadcast domain.  
Note that the Ethernet topology became star-shaped.  
4
 
History: Bridges  
Store and forwarding according destination MAC  
address  
Separated collision domains  
Improved network performance  
Still one broadcast domain  
Three collision  
domains in this  
example !  
5
(C) Herbert Haas 2005/03/11  
Bridges were invented for performance reasons. It seemed to be impractical that  
each additional station reduces the average per-station bandwidth by 1/n. On the  
other hand the benefit of sharing a medium for communication should be still  
maintained (which was expressed by Metcalfe's law).  
Bridges are store and forwarding devices (introducing significant delay) that can  
filter traffic based on the destination MAC addresses to avoid unnecessary  
flooding of frames to certain segments. Thus, bridges segment the LAN into  
several collision domains. Broadcasts are still forwarded to allow layer 3  
connectivity (ARP etc), so the bridged network is still a single broadcast domain.  
5
 
History: Switches  
Switch = Multiport Bridges with HW acceleration  
Full duplex Collision-free Ethernet No CSMA/CD  
necessary anymore  
Different data rates at the same time supported  
Autonegotiation  
VLAN splits LAN into several broadcast domains  
Collision-free  
plug & play  
1000 Mbit/s  
scalable Ethernet !  
100 Mbit/s  
100 Mbit/s  
10 Mbit/s  
6
(C) Herbert Haas 2005/03/11  
Several vendors built advanced bridges, which are partly or fully implemented in  
hardware. The introduced latency could be dramatically lowered and  
furthermore other features were introduced, for example full duplex  
communication on twisted pair cables, different frame rates on different ports,  
special forwarding techniques (e,g, cut through or fragment free), Content  
Addressable Memory (CAM) tables, and much more. Of course marketing rules  
demand for another designation for this machine: the switch was born.  
Suddenly, a collision free plug and play Ethernet was available. Simply use  
twisted pair cabling only and enable autonegotiation to automatically determine  
the line speed on each port (of course manual configurations would also do). This  
way, switched Ethernet become very scalable.  
Furthermore, Virtual LANs (VLANs) were invented to split the LAN into several  
broadcast domains. VLANs improve security, utilization, and allows for logical  
borders between workgroups.  
6
 
Today  
No collisions no distance limitations !  
Gigabit Ethernet becomes WAN  
technology !  
Over 100 km link span already  
Combine several links to "Etherchannels"  
Acts as single link from the spanning-tree view  
Cisco: Port Aggregation Protocol (PAgP)  
IEEE 802.1ad: Link Aggregation Control Protocol  
(LACP)  
1 Gbit/s or even 10 Gbit/s long reach connection !!!  
7
(C) Herbert Haas 2005/03/11  
Today, Gigabit and even 10 Gigabit Ethernet is available. Only twisted pair and  
more and more fiber cables are used between switches, allowing full duplex  
collision-free connections. Since collisions cannot occur anymore, there is no  
need for a collision window anymore! From this it follows, that there is virtually  
no distance limit between each two Ethernet devices.  
Recent experiments demonstrated the interconnection of two Ethernet Switches  
over a span of more than 100 km! Thus Ethernet became a WAN technology!  
Today, many carriers use Ethernet instead of ATM/SONET/SDH or other rather  
expensive technologies. GE and 10GE is relatively cheap and much simpler to  
deploy. Furthermore it easily integrates into existing low-rate Ethernet  
environments, allowing a homogeneous interconnection between multiple  
Ethernet LAN sites. Basically, the deployment is plug and play.  
If the link speed is still too slow, so-called "Etherchannels" can be configured  
between each two switches by combining several ports to one logical connection.  
Note that it is not possible to deploy parallel connections between two switches  
without an Etherchannel configuration because the Spanning Tree Protocol (STP)  
would cut off all redundant links.  
Depending on the vendor, up to eight ports can be combined to constitute one  
"Etherchannel".  
7
 
What About Gigabit Hubs?  
Would limit network diameter to 20-  
25 meters (Gigabit Ethernet)  
Solutions  
Frame Bursting  
Carrier Extension  
No GE-Hubs available on the market  
today forget it!  
No CSMA/CD defined for 10GE (!)  
8
(C) Herbert Haas 2005/03/11  
Remember: Hubs simulate a half-duplex coaxial cable inside, hence limiting the  
total network diameter. For Gigabit Ethernet this limitation would be about 25  
meters, which is rather impracticable for professional usage. Although some  
countermeasures had been specified in the standard, such as frame bursting and  
carrier extension, no vendor developed an GE hub as for today. Thus: Forget GE  
Hubs!  
The 10 GE specification does neither consider copper connections nor hubs. 10  
GE can only run over fiber.  
At this point please remember the initial idea in the mid 1970s: Bus, CSMA/CD,  
short distances, no network nodes.  
Today: Structured cabling (point-to-point or star), never CSMA/CD, WAN  
capabilities, sophisticated switching devices in between.  
8
 
MAC Control Frames  
Additional functionality easily integrated  
Currently only Pause-Frame supported  
Always 64 bytes  
8 bytes  
6
6
2
2
44  
4
preamble DA  
SA  
8808h  
MAC-ctrl opcode  
MAC-ctrl parameters FCS  
MAC-ctrl opcode ........... Defines function of control frame  
MAC-ctrl parameters .... control parameter data (always filled up to 44 bytes)  
9
(C) Herbert Haas 2005/03/11  
Different data rates between switches (and different performance levels) often  
lead to congestion conditions, full buffers, and frame drops. Traditional Ethernet  
flow control was only supported on half-duplex links by enforcing collisions to  
occur and hereby triggering the truncated exponential backoff algorithm. Just let  
a collision occur and the aggressive sender will be silent for a while.  
A much finer method is to send some dummy frames just before the backoff  
timer allows sending. This way the other station never comes to send again.  
Both methods are considered as ugly and only work on half duplex lines.  
Therefore the MAC Control frames were specified, allowing for active flow  
control. Now the receiver sends this special frame, notifying the sender to be  
silent for N slot times.  
The MAC Control frame originates in a new Ethernet layer—the MAC Control  
Layer—and will support also other functionalities, but currently only the "Pause"  
frame has been specified.  
9
 
Auto Negotiation  
Enables each two Ethernet devices to  
exchange information about their  
capabilities  
Signal rate, CSMA/CD, half- or full-duplex  
Using Link-Integrity-Test-Pulse-Sequence  
Normal-Link-Pulse (NLP) technique is used  
in 10BaseT to check the link state (green LED)  
10 Mbit/s LAN devices send every 16.8 ms a  
100ns lasting NLP, no signal on the wire  
means disconnected  
10  
(C) Herbert Haas 2005/03/11  
Several Ethernet operating modes had been defined, which are incompatible to  
each other, including different data rates (10, 100, 1000 Mbit/s), half or full  
duplex operation, MAC control frames capabilities, etc.  
Original Ethernet utilized so-called Normal Link Pulses (NLPs) to verify layer 2  
connectivity. NLPs are single pulses which must be received periodically  
between regular frames. If NLPs are received, the green LED on the NIC is  
turned on.  
Newer Ethernet cards realize auto negotiation by sending a sequence of NLPs,  
which is called a Fast Link Pulse (FLP) sequence.  
10  
 
Fast Link Pulses  
Modern Ethernet NICs send bursts of  
Fast-Link-Pulses (FLP) consisting of  
17-33 NLPs for Autonegotiation  
signalling  
Each representing a 16 bit word  
GE sends several "pages"  
11  
(C) Herbert Haas 2005/03/11  
A series of FLPs constitute an autonegotiation frame. The whole frame consists  
of 33 timeslots, where each odd numbered timeslot consists of a real NLP and  
each even timeslot is either a NLP or empty, representing 1 or 0. Thus, each FLP  
sequence consists of a 16 bit word.  
Note that GE Ethernet sends several such "pages".  
11  
 
100 Mbit Ethernet Overview  
IEEE 802.3u  
IEEE 802.12  
Signaling Schemes  
Demand Priority  
Fast Ethernet  
100BaseX  
Signaling  
Fast Ethernet  
100Base4T+  
Signaling  
100VG-AnyLAN  
100BaseT4  
(half duplex)  
100BaseFX  
100BaseTX  
HP and AT&T  
invention for real time  
applications  
"100BaseT"  
12  
(C) Herbert Haas 2005/03/11  
The diagram above gives an overview of 100 Mbit/s Ethernet technologies,  
which are differentiated into IEEE 802.3u and IEEE 802.12 standards. The IEEE  
802.3u defines the widely used Fast Ethernet variants, most importantly those  
utilizing the 100BaseX signaling scheme. The 100BaseX signaling consists of  
several details, but basically it utilizes 4B5B block coding over only two pairs of  
regular Cat 5 twisted pair cables or two strand 50/125 or 62.5/125-µm multimode  
fiber-optic cables.  
100Base4T+ signaling has been specified to support 100 Mbit/s over Cat3 cables.  
This mode allows half duplex operation only and uses a 8B6T code over 4 pairs  
of wires; one pair for collision detection, three pairs for data transmission. One  
unidirectional pair is used for sending only and two bi-directional pairs for both  
sending and receiving.  
The 100VG-AnyLAN technology had been created by HP and AT&T in 1992 to  
support deterministic medium access for realtime applications. This technology  
was standardized by the IEEE 802.12 working group. The access method is  
called "demand priority". 100VG-AnyLAN supports voice grade cables (VG) but  
requires special hub hardware. The 802.12 working group is no longer active.  
12  
 
4B/5B Coding  
MII  
16 code  
groups  
0
0
0
1
4 x 25  
Mbit/s  
PCS  
32 code  
groups  
4B/5B Encoder/Decoder  
0
1
0
0
1
PMA  
125 MBaud  
13  
(C) Herbert Haas 2005/03/11  
The diagram above shows the basic principle of the 4B5B block coding principle,  
which is used by 802.3u and also by FDDI. The basic idea is to transform any  
arbitrary 4 bit word into a (relatively) balanced 5 bit word. This is done by a fast  
table lookup.  
Balancing the code has many advantages: better bandwidth utilization, better  
laser efficiency (constant temperature), better bit-synchronization (PLL), etc.  
Note that the signaling overhead is 5/4 12.5 %.  
13  
 
Gigabit Ethernet  
Media Access Control (MAC)  
Gigabit Media Independent Interface (GMII)  
1000Base-X  
1000Base-T  
8B/10B encoder/decoder  
encoder/decoder  
1000Base-CX  
Shielded  
1000Base-LX  
LWL  
Fiber Optic  
1000Base-SX  
SWL  
Fiber Optic  
1000Base-T  
UTP  
Balanced  
Copper  
Cat 5e  
IEEE 802.3ab  
physical layer  
IEEE 802.3z physical layer  
14  
(C) Herbert Haas 2005/03/11  
Gigabit Ethernet has been defined in March 1996 by the working group IEEE  
802.3z. The GMII represents a abstract interface between the common Ethernet  
layer 2 and different signaling layers below. Two important signaling techniques  
had been defines: The standard 802.3z defines 1000Base-X signaling which uses  
8B10B block coding and the 802.3ab standard uses 1000Base-T signaling. The  
latter is only used over twisted pair cables (UTP Cat 5 or better), while  
1000BaseX is only used over fiber, with one exception, the twinax cable  
(1000BaseCX), which is basically a shielded twisted pair cable.  
BTW: The "X" stands for block coding.  
14  
 
GE Signaling  
IEEE 802.3  
Ethernet  
IEEE 802.3z  
Gigabit Ethernet  
ANSI X3T11  
Fibre Channel  
FC-4  
802.2 LLC  
IEEE 802.2 LLC  
upper layer mapping  
CSMA/CD  
or full duplex MAC  
FC-3  
common services  
802.3 CSMA/CD  
Reconciliation Sublayer  
FC-2  
signalling  
802.3 PHY  
PCS  
FC-1  
encoder/decoder  
PHY  
PMA  
PMD  
FC-0  
interface and media  
15  
(C) Herbert Haas 2005/03/11  
Gigabit Ethernet layers have been defined by adaptation of the LLC and MAC  
layers of classical Ethernet and the physical layers of the ANSI Fiber Channel  
technology. A so-called reconciliation layer is used in between for seamless  
interoperation. The physical layer of the Fiber Channel technology uses 8B10B  
block coding.  
15  
 
GE 8B/10B Coding  
GMII  
Only used  
by  
1
1
1
1
1
1
1
1
256 code groups  
8 x 125 Mbit/s  
1000BaseX  
PCS  
1024 code groups  
8B/10B Encoder/Decoder  
125 million code  
groups per  
second  
1
1
1
1
1
1
1
1
1
1
PMA  
1250 Mbaud  
16  
(C) Herbert Haas 2005/03/11  
8B10B block coding is very similar to 4B5B block coding but allows fully  
balanced 10-bit codewords. Actually, there are not enough balanced 10-bit  
codewords available. Note that there are 256 8-bit codewords which need to be  
mapped on 1024 10-bit codewords. But instead of using a fully balanced 10-bit  
codeword for each 8-bit codeword, some 8-bit codewords are represented by two  
10-bit codewords, which are sent in an alternating manner. That is, both  
associated 10-bit words are bit-complementary.  
Again, the signaling overhead is 12.5%, that is 1250 Mbaud is necessary to  
transmit a bit stream of 1000 Mbit/s.  
16  
 
1000BaseX  
Two different wavelengths supported  
Full duplex only  
1000Base-SX: short wave, 850 nm MMF  
1000Base-LX: long wave, 1300 nm MMF or SMF  
1000Base-CX:  
Twinax Cable (high quality 150 Ohm balanced  
shielded copper cable)  
About 25 m distance limit, DB-9 or the newer  
HSSDC connector  
17  
(C) Herbert Haas 2005/03/11  
Gigabit Ethernet can be transmitted over various types of fiber. Currently (at  
least) two types are specified, short and long wave transmissions, using 850 nm  
and 1300 nm respectively. The long wave can be used with both single mode  
(SMF) and multimode fibers (MMF). Only SMF can be used for WAN  
transmissions because of the much lower dispersion effects.  
Note that there are several other implementations offered by different vendors,  
such as using very long wavelengths at 1550 nm together with DWDM  
configurations.  
The twinax cable is basically a shielded twisted pair cable.  
17  
 
1000BaseT  
Defined by 802.3ab task force  
UTP  
Uses all 4 line pairs simultaneously for duplex  
transmission! (echo cancellation)  
5 level PAM coding  
4 levels encode 2 bits + extra level used for Forward  
Error Correction (FEC)  
Signal rate: 4 x 125 Mbaud = 4 x 250Mbit/s data  
rate  
Cat. 5 links, max 100 m; all 4pairs, cable must  
conform to the requirements of ANSI/TIA/EIA-568-A  
Only 1 CSMA/CD repeater allowed in a  
collision domain  
18  
(C) Herbert Haas 2005/03/11  
It is very difficult to transmit Gigabit speeds over unshielded twisted pair cables.  
Only a mix of multiple transmission techniques ensure that this high data rate can  
be transmitted over a UTP Cat5 cable. For example all 4 pairs are used together  
for both directions. Echo cancellation ensures that the sending signal does not  
confuse the received signal. 5 level PAM is used for encoding instead of 8B10B  
because of its much lower symbol rate. Now we have only 125 Mbaud x 4  
instead of 1250 Mbaud.  
The interface design is very complicated and therefore relatively expensive.  
Using Cat 6 or Cat 7 cables allow 500 Mbaud x 2 pairs, that is 2 pairs are  
designated for TX and the other 2 pairs are used for RX. This dramatically  
reduces the price but requires better cables, which are not really expensive but  
slightly thicker. Legacy cable ducts might be too small in diameter.  
18  
 
Several Physical Media Supported  
Logical Link Control LLC  
MAC Control (optional)  
Data Link Layer  
Media Access Control MAC  
PLS  
AUI  
Reconciliation  
Reconciliation  
Reconciliation  
GMII  
MII  
PLS  
AUI  
MII  
PCS  
PMA  
PMD  
MDI  
PCS  
PHY  
PMA  
PMA (MAU)  
MDI  
PMA  
MDI  
PMD  
MDI  
Medium  
Medium  
Medium  
Medium  
1-10 Mbit/s  
10 Mbit/s  
100 Mbit/s  
1000 Mbit/s  
AUI Attachment Unit Interface, PLS  
PCS Physical Coding Sublayer, MII  
Physical Layer Signaling, MDI  
Medium Dependent Interface  
Gigabit Media Independent  
Media Independent Interface, GMII  
Interface, PMA Physical Medium Attachment, MAU Medium Attachment Unit, PMD Physical Medium  
Dependent  
19  
(C) Herbert Haas 2005/03/11  
The diagram above shows various physical media designs supported by the  
official GE standard. Each modern GE card could theoretically support the old  
10 Mbit/s standard as well. However many vendors create GE NICs that only  
support GE or GE and FE—who would connect a precious GE interface with  
another interface, which is 100 times slower?  
19  
 
10 Gigabit Ethernet / IEEE 802.3ae  
Only optical support  
850nm (MM) / 1310nm /1550 nm (SM only)  
No copper PHY anymore !  
Different implementations at the  
moment – standardization not finished!  
8B/10B (IBM), SONET/SDH support, …  
XAUI ("Zowie") instead of GMII  
20  
(C) Herbert Haas 2005/03/11  
10 GE only supports optical links. Note that GE is actually a synchronous  
protocol! There is no statistical multiplexing done at the physical layer anymore,  
because optical switching at that bit rate only allows synchronous transmissions.  
The GMII has been replaced (or enhanced) by the so-called XAUI, known as  
"Zowie".  
Note: At the time of writing this module, the 10 GE standard was not fully  
finished. Though, some vendors already offer 10 GE interface cards for their  
switches.  
These interfaces are very expensive but the investment ensures backward  
compatibility to lower Ethernet rates and at the same time provides a very high  
speed WAN interface.  
An alternative technology would be OC192, which requires a very expensive and  
complex SONET/SDH environment.  
20  
 
Note  
GE and 10GE use synchronous  
physical sublayer !!!  
Recommendation: Don't use GE over  
copper wires  
Radiation/EMI  
Grounding problems  
High BER  
Thick cable bundles (especially Cat-7)  
21  
(C) Herbert Haas 2005/03/11  
Both GE and 10GE are synchronous physical technologies on fiber. It not  
recommended to use GE over copper wires anymore although 802.3ab would  
specify it. This is because the whole electrical hardware (cables and connectors)  
are re-used from older Ethernet technologies and have not been designed to  
support such high frequencies.  
For example the RJ45 connector is not HF proof. Furthermore, shielded twisted  
pair cables require a very good grounding, seldom found in reality. The Bit Error  
Rate (BER) is typically so high that the effective data rate is much lower than  
GE, for example 30% only.  
21  
 
Summary  
Ethernet evolved in the opposite direction:  
Collision free  
WAN qualified  
Switched  
Several coding styles Complex PHY  
architecture  
Plug & play through autonegotiation  
Much simpler than ATM but no BISDN  
solution – might change!  
22  
(C) Herbert Haas 2005/03/11  
22  
 
Quizz  
Why tends high-speed Ethernet to  
synchronous PHY?  
Can I attach a 100 Mbit/s port to a  
1000 Mbit/s port via fiber?  
What is the idea of Etherchannels?  
(Maximum bit rate, difference to  
multiple parallel links)  
23  
(C) Herbert Haas 2005/03/11  
23  
 
Hints  
Q1: On fiber its difficult to deal with  
asynchronous transmission, photons  
cannot be buffered easily, store and  
forward problems  
Q2: No, autonegotiation on fiber  
does not care for data rates  
Q3: "normal" parallel links would be  
disabled by STP, Etherchannel  
supports up to 8 links  
24  
(C) Herbert Haas 2005/03/11  
24  
 

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