What is the minimum Ethernet frame size?

I read one article long time back. I liked the explanation.

Ethernet minimum packet size is 64 bytes for 10/100M but 512 bytes for 1000M. Minimum packet size is chosen on the basis that in case of half duplex, the sender should be able to detect collision before it finishes sending the frame.

At best the signals propagate (radiate) through free space at the speed of light (3*10^8 m/s). In contrast, the speed of propagation through twisted pair wire or coax is 2/3 of this value(2*10^8 m/s).

2*Maximum Distance between two hosts= speed of light in twisted pair * time

time=packet size/Bandwidth

For 10M, Bandwdith =10^7bps

time=8*64bits/10^7bps=51.2us

So Maximum Distance between two hosts=(2*10^8)*(51.2*10^-6)/2=5.12km

For 10Mbps, this LAN length was more than sufficient.

For 100Mbps, LAN length comes out to be 512m which is also good enough.

But for 1Gbps, LAN length comes out to be only 51.2m. So the solution proposed was to increase the minimum ethernet packet size to 4096bits, i.e., 512bytes.

So max LAN length becomes 409.6m.

I don't know why they chose only this length.

Unit of data on an Ethernet network

In computer networking, an Ethernet frame is a data link layer protocol data unit and uses the underlying Ethernet physical layer transport mechanisms. In other words, a data unit on an Ethernet link transports an Ethernet frame as its payload.[1]

An Ethernet frame is preceded by a preamble and start frame delimiter (SFD), which are both part of the Ethernet packet at the physical layer. Each Ethernet frame starts with an Ethernet header, which contains destination and source MAC addresses as its first two fields. The middle section of the frame is payload data including any headers for other protocols (for example, Internet Protocol) carried in the frame. The frame ends with a frame check sequence (FCS), which is a 32-bit cyclic redundancy check used to detect any in-transit corruption of data.

Structure

See also: Physical Coding Sublayer

A data packet on the wire and the frame as its payload consist of binary data. Ethernet transmits data with the most-significant octet (byte) first; within each octet, however, the least-significant bit is transmitted first.[a]

The internal structure of an Ethernet frame is specified in IEEE 802.3.[1] The table below shows the complete Ethernet packet and the frame inside, as transmitted, for the payload size up to the MTU of 1500 octets.[b] Some implementations of Gigabit Ethernet and other higher-speed variants of Ethernet support larger frames, known as jumbo frames.

The optional 802.1Q tag consumes additional space in the frame. Field sizes for this option are shown in brackets in the table above. IEEE 802.1ad (Q-in-Q) allows for multiple tags in each frame. This option is not illustrated here.

Ethernet packet – physical layer

Preamble and start frame delimiter

See also: Syncword

An Ethernet packet starts with a seven-octet preamble and one-octet start frame delimiter (SFD).[c]

The preamble consists of a 56-bit (seven-byte) pattern of alternating 1 and 0 bits, allowing devices on the network to easily synchronize their receiver clocks, providing bit-level synchronization. It is followed by the SFD to provide byte-level synchronization and to mark a new incoming frame. For Ethernet variants transmitting serial bits instead of larger symbols, the (uncoded) on-the-wire bit pattern for the preamble together with the SFD portion of the frame is 10101010 10101010 10101010 10101010 10101010 10101010 10101010 10101011;[3]: sections 4.2.5 and 3.2.2  The bits are transmitted in order, from left to right.[3]: sections 4.2.5 

The SFD is the eight-bit (one-byte) value that marks the end of the preamble, which is the first field of an Ethernet packet, and indicates the beginning of the Ethernet frame. The SFD is designed to break the bit pattern of the preamble and signal the start of the actual frame.[3]: section 4.2.5  The SFD is immediately followed by the destination MAC address, which is the first field in an Ethernet frame. SFD is the binary sequence 10101011 (0xD5, decimal 213 in the Ethernet LSB first bit ordering).[3]: sections 3.2.2, 3.3 and 4.2.6 

Physical layer transceiver circuitry (PHY for short) is required to connect the Ethernet MAC to the physical medium. The connection between a PHY and MAC is independent of the physical medium and uses a bus from the media independent interface family (MII, GMII, RGMII, SGMII, XGMII). Fast Ethernet transceiver chips utilize the MII bus, which is a four-bit (one nibble) wide bus, therefore the preamble is represented as 14 instances of 0x5, and the SFD is 0x5 0xD (as nibbles). Gigabit Ethernet transceiver chips use the GMII bus, which is an eight-bit wide interface, so the preamble sequence followed by the SFD would be 0x55 0x55 0x55 0x55 0x55 0x55 0x55 0xD5 (as bytes).

Frame – data link layer

Header

The header features destination and source MAC addresses (each six octets in length), the EtherType field and, optionally, an IEEE 802.1Q tag or IEEE 802.1ad tag.

The EtherType field is two octets long and it can be used for two different purposes. Values of 1500 and below mean that it is used to indicate the size of the payload in octets, while values of 1536 and above indicate that it is used as an EtherType, to indicate which protocol is encapsulated in the payload of the frame. When used as EtherType, the length of the frame is determined by the location of the interpacket gap and valid frame check sequence (FCS).

The IEEE 802.1Q tag or IEEE 802.1ad tag, if present, is a four-octet field that indicates virtual LAN (VLAN) membership and IEEE 802.1p priority. The first two octets of the tag are called the Tag Protocol IDentifier (TPID) and double as the EtherType field indicating that the frame is either 802.1Q or 802.1ad tagged. 802.1Q uses a TPID of 0x8100. 802.1ad uses a TPID of 0x88a8.

Payload

Payload is a variable-length field. Its minimum size is governed by a requirement for a minimum frame transmission of 64 octets (bytes).[d] With header and FCS taken into account, the minimum payload is 42 octets when an 802.1Q tag is present[e] and 46 octets when absent. When the actual payload is less than the minimum, padding octets are added accordingly. IEEE standards specify a maximum payload of 1500 octets. Non-standard jumbo frames allow for larger payloads on networks built to support them.

Frame check sequence

The frame check sequence (FCS) is a four-octet cyclic redundancy check (CRC) that allows detection of corrupted data within the entire frame as received on the receiver side. According to the standard, the FCS value is computed as a function of the protected MAC frame fields: source and destination address, length/type field, MAC client data and padding (that is, all fields except the FCS).

Per the standard, this computation is done using the left shifting CRC32 BZIP2 (poly = 0x4C11DB7, initial CRC = 0xFFFFFFFF, CRC is post complemented, verify value = 0x38FB2284) algorithm. The standard states that data is transmitted least significant bit (bit 0) first, while the FCS is transmitted most significant bit (bit 31) first.[3]: section 3.2.9  An alternative is to calculate a CRC using the right shifting CRC32 (poly = 0xEDB88320, initial CRC = 0xFFFFFFFF, CRC is post complemented, verify value = 0x2144DF1C), which will result in a CRC that is a bit reversal of the FCS, and transmit both data and the CRC least significant bit first, resulting in identical transmissions.

The standard states that the receiver should calculate a new FCS as data is received and then compare the received FCS with the FCS the receiver has calculated. An alternative is to calculate a CRC on both the received data and the FCS, which will result in a fixed non-zero "verify" value. (The result is non-zero because the CRC is post complemented during CRC generation). Since the data is received least significant bit first, and to avoid having to buffer octets of data, the receiver typically uses the right shifting CRC32. This makes the "verify" value (sometimes called "magic check") 0x2144DF1C.[5]

However, hardware implementation of a logically right shifting CRC may use a left shifting Linear Feedback Shift Register as the basis for calculating the CRC, reversing the bits and resulting in a verify value of 0x38FB2284. Since the complementing of the CRC may be performed post calculation and during transmission, what remains in the hardware register is a non-complemented result, so the residue for a right shifting implementation would be the complement of 0x2144DF1C = 0xDEBB20E3, and for a left shifting implementation, the complement of 0x38FB2284 = 0xC704DD7B.

End of frame – physical layer

The end of a frame is usually indicated by the end-of-data-stream symbol at the physical layer or by loss of the carrier signal; an example is 10BASE-T, where the receiving station detects the end of a transmitted frame by loss of the carrier. Later physical layers use an explicit end of data or end of stream symbol or sequence to avoid ambiguity, especially where the carrier is continually sent between frames; an example is Gigabit Ethernet with its 8b/10b encoding scheme that uses special symbols which are transmitted before and after a frame is transmitted.[6][7]

Interpacket gap – physical layer

Interpacket gap (IPG) is idle time between packets. After a packet has been sent, transmitters are required to transmit a minimum of 96 bits (12 octets) of idle line state before transmitting the next packet.

Types

There are several types of Ethernet frames:

• Ethernet II frame, or Ethernet Version 2,[f] or DIX frame is the most common type in use today, as it is often used directly by the Internet Protocol.
• Novell raw IEEE 802.3 non-standard variation frame
• IEEE 802.2 Logical Link Control (LLC) frame
• IEEE 802.2 Subnetwork Access Protocol (SNAP) frame

The different frame types have different formats and MTU values, but can coexist on the same physical medium. Differentiation between frame types is possible based on the table on the right.

In addition, all four Ethernet frame types may optionally contain an IEEE 802.1Q tag to identify what VLAN it belongs to and its priority (quality of service). This encapsulation is defined in the IEEE 802.3ac specification and increases the maximum frame by 4 octets.

The IEEE 802.1Q tag, if present, is placed between the Source Address and the EtherType or Length fields. The first two octets of the tag are the Tag Protocol Identifier (TPID) value of 0x8100. This is located in the same place as the EtherType/Length field in untagged frames, so an EtherType value of 0x8100 means the frame is tagged, and the true EtherType/Length is located after the Q-tag. The TPID is followed by two octets containing the Tag Control Information (TCI) (the IEEE 802.1p priority (quality of service) and VLAN id). The Q-tag is followed by the rest of the frame, using one of the types described above.

Ethernet II

Ethernet II framing (also known as DIX Ethernet, named after DEC, Intel and Xerox, the major participants in its design[8]), defines the two-octet EtherType field in an Ethernet frame, preceded by destination and source MAC addresses, that identifies an upper layer protocol encapsulated by the frame data. Most notably, an EtherType value of 0x0800 indicates that the frame contains an IPv4 datagram, 0x0806 indicates an ARP datagram, and 0x86DD indicates an IPv6 datagram. See EtherType § Values for more.

As this industry-developed standard went through a formal IEEE standardization process, the EtherType field was changed to a (data) length field in the new 802.3 standard.[g] Since the recipient still needs to know how to interpret the frame, the standard required an IEEE 802.2 header to follow the length and specify the type. Many years later, the 802.3x-1997 standard, and later versions of the 802.3 standard, formally approved of both types of framing. Ethernet II framing is the most common in Ethernet local area networks, due to its simplicity and lower overhead.

In order to allow some frames using Ethernet II framing and some using the original version of 802.3 framing to be used on the same Ethernet segment, EtherType values must be greater than or equal to 1536 (0x0600). That value was chosen because the maximum length of the payload field of an Ethernet 802.3 frame is 1500 octets (0x05DC). Thus if the field's value is greater than or equal to 1536, the frame must be an Ethernet II frame, with that field being a type field.[9] If it's less than or equal to 1500, it must be an IEEE 802.3 frame, with that field being a length field. Values between 1500 and 1536, exclusive, are undefined.[10] This convention allows software to determine whether a frame is an Ethernet II frame or an IEEE 802.3 frame, allowing the coexistence of both standards on the same physical medium.

Novell raw IEEE 802.3

Novell's "raw" 802.3 frame format was based on early IEEE 802.3 work. Novell used this as a starting point to create the first implementation of its own IPX Network Protocol over Ethernet. They did not use any LLC header but started the IPX packet directly after the length field. This does not conform to the IEEE 802.3 standard, but since IPX always has FF as the first two octets (while in IEEE 802.2 LLC that pattern is theoretically possible but extremely unlikely), in practice this usually coexists on the wire with other Ethernet implementations, with the notable exception of some early forms of DECnet which got confused by this.

Novell NetWare used this frame type by default until the mid-nineties, and since NetWare was then very widespread, while IP was not, at some point in time most of the world's Ethernet traffic ran over "raw" 802.3 carrying IPX. Since NetWare 4.10, NetWare defaults to IEEE 802.2 with LLC (NetWare Frame Type Ethernet_802.2) when using IPX.[11]

IEEE 802.2 LLC

Main article: IEEE 802.2

Some protocols, such as those designed for the OSI stack, operate directly on top of IEEE 802.2 LLC encapsulation, which provides both connection-oriented and connectionless network services.

IEEE 802.2 LLC encapsulation is not in widespread use on common networks currently, with the exception of large corporate NetWare installations that have not yet migrated to NetWare over IP. In the past, many corporate networks used IEEE 802.2 to support transparent translating bridges between Ethernet and Token Ring or FDDI networks.

There exists an Internet standard for encapsulating IPv4 traffic in IEEE 802.2 LLC SAP/SNAP frames.[12] It is almost never implemented on Ethernet, although it is used on FDDI, Token Ring, IEEE 802.11 (with the exception of the 5.9 GHz band, where it uses EtherType)[13] and other IEEE 802 LANs. IPv6 can also be transmitted over Ethernet using IEEE 802.2 LLC SAP/SNAP, but, again, that's almost never used.

IEEE 802.2 SNAP

Main article: Subnetwork Access Protocol

By examining the 802.2 LLC header, it is possible to determine whether it is followed by a SNAP header. The LLC header includes two eight-bit address fields, called service access points (SAPs) in OSI terminology; when both source and destination SAP are set to the value 0xAA, the LLC header is followed by a SNAP header. The SNAP header allows EtherType values to be used with all IEEE 802 protocols, as well as supporting private protocol ID spaces.

In IEEE 802.3x-1997, the IEEE Ethernet standard was changed to explicitly allow the use of the 16-bit field after the MAC addresses to be used as a length field or a type field.

The AppleTalk v2 protocol suite on Ethernet ("EtherTalk") uses IEEE 802.2 LLC + SNAP encapsulation.

Maximum throughput

We may calculate the protocol overhead for Ethernet as a percentage (packet size including IPG)

Protocol overhead = Packet size − Payload size Packet size {\displaystyle {\text{Protocol overhead}}={\frac {{\text{Packet size}}-{\text{Payload size}}}{\text{Packet size}}}}

We may calculate the protocol efficiency for Ethernet

Protocol efficiency = Payload size Packet size {\displaystyle {\text{Protocol efficiency}}={\frac {\text{Payload size}}{\text{Packet size}}}}

Maximum efficiency is achieved with largest allowed payload size and is:

1500 1538 = 97.53 % {\displaystyle {\frac {1500}{1538}}=97.53\%}

for untagged frames, since the packet size is maximum 1500 octet payload + 8 octet preamble + 14 octet header + 4 octet trailer + minimum interpacket gap corresponding to 12 octets = 1538 octets. The maximum efficiency is:

1500 1542 = 97.28 % {\displaystyle {\frac {1500}{1542}}=97.28\%}

when 802.1Q VLAN tagging is used.

The throughput may be calculated from the efficiency

Throughput = Efficiency × Net bit rate {\displaystyle {\text{Throughput}}={\text{Efficiency}}\times {\text{Net bit rate}}\,\!}

where the physical layer net bit rate (the wire bit rate) depends on the Ethernet physical layer standard, and may be 10 Mbit/s, 100 Mbit/s, 1 Gbit/s or 10 Gbit/s. Maximum throughput for 100BASE-TX Ethernet is consequently 97.53 Mbit/s without 802.1Q, and 97.28 Mbit/s with 802.1Q.

Channel utilization is a concept often confused with protocol efficiency. It considers only the use of the channel disregarding the nature of the data transmitted – either payload or overhead. At the physical layer, the link channel and equipment do not know the difference between data and control frames. We may calculate the channel utilization:

Channel utilization = Time spent transmitting data Total time {\displaystyle {\text{Channel utilization}}={\frac {\text{Time spent transmitting data}}{\text{Total time}}}}

The total time considers the round trip time along the channel, the processing time in the hosts and the time transmitting data and acknowledgements. The time spent transmitting data includes data and acknowledgements.

Runt frames

A runt frame is an Ethernet frame that is less than the IEEE 802.3's minimum length of 64 octets. Runt frames are most commonly caused by collisions; other possible causes are a malfunctioning network card, buffer underrun, duplex mismatch or software issues.[14]

Notes

1. ^ The frame check sequence (FCS) uses a different bit ordering.[2]
2. ^ The bit patterns in the preamble and start of frame delimiter are written as bit strings, with the first bit transmitted on the left (not as octet values, which in Ethernet are transmitted least significant bit(s) first). This notation matches the one used in the IEEE 802.3 standard.
3. ^ Preamble and start frame delimiter are not displayed by packet sniffing software because these bits are stripped away at OSI layer 1 by the network interface controller (NIC) before being passed on to the OSI layer 2, which is where packet sniffers collect their data. There are layer-2 sniffers that can capture and display the preamble and start frame delimiter, but they are expensive and mainly used to detect problems related to physical connectivity.
4. ^ Minimum payload size is dictated by the 512-bit slot time used for collision detection in the Ethernet LAN architecture.
5. ^ Both 42 and 46 octet minimums are valid when 802.1Q is present.[4]
6. ^ A version 1 Ethernet frame was used for early Ethernet prototypes and featured 8-bit MAC addresses and was never commercially deployed.
7. ^ Original Ethernet frames define their length with the framing that surrounds it, rather than with an explicit length count.

References

1. ^ a b "3.1.1 Packet format". 802.3-2018 - IEEE Standard for Ethernet. IEEE. 14 June 2018. doi:10.1109/IEEESTD.2018.8457469. ISBN 978-1-5044-5090-4.
2. ^ 802.3-2018 – IEEE Standard for Ethernet. IEEE. 14 June 2018. Section 3.3 and annex 31A. doi:10.1109/IEEESTD.2018.8457469. ISBN 978-1-5044-5090-4. Opcodes are transmitted high-order octet first. Within each octet, bits are transmitted least-significant bit first. [...] Each octet of the MAC frame, with the exception of the FCS, is transmitted least significant bit first.
3. ^ a b c d e f 802.3-2018 – IEEE Standard for Ethernet. IEEE. 14 June 2018. doi:10.1109/IEEESTD.2018.8457469. ISBN 978-1-5044-5090-4.
4. ^ "Annex G". IEEE Standard for Local and metropolitan area networks--Media Access Control (MAC) Bridges and Virtual Bridged Local Area Networks. doi:10.1109/IEEESTD.2011.6009146. ISBN 978-0-7381-6708-4.
5. ^ "Specification of CRC Routines V4.5.0 R4.1 Rev 3" (PDF). AUTOSAR. p. 24.
6. ^ Charles E. Spurgeon (February 2000). Ethernet: The Definitive Guide. O'Reilly. pp. 41, 47. ISBN 9780596552824. Retrieved 30 June 2014.
7. ^ "40.1.3.1 Physical Coding Sublayer (PCS)". 802.3-2018 - IEEE Standard for Ethernet. IEEE. 14 June 2018. doi:10.1109/IEEESTD.2018.8457469. ISBN 978-1-5044-5090-4.
8. ^ Drew Heywood; Zubair Ahmad (2001). Drew Heywood's Windows 2000 Network Services. Sams. p. 53. ISBN 978-0-672-31741-5.
9. ^ LAN MAN Standards Committee of the IEEE Computer Society (20 March 1997). IEEE Std 802.3x-1997 and IEEE Std 802.3y-1997. The Institute of Electrical and Electronics Engineers, Inc. pp. 28–31.
10. ^ "3.2.6 Length/Type field". 802.3-2018 - IEEE Standard for Ethernet. 14 June 2018. doi:10.1109/IEEESTD.2018.8457469. ISBN 978-1-5044-5090-4.
11. ^ Don Provan (17 September 1993). "Ethernet Framing". Newsgroup: comp.sys.novell. Usenet: . (HTML-formatted version Archived 18 April 2015 at the Wayback Machine)  — a classic series of Usenet postings by Novell's Don Provan that have found their way into numerous FAQs and are widely considered the definitive answer to the Novell Frame Type usage.
12. ^ A Standard for the Transmission of IP Datagrams over IEEE 802 Networks. Network Working Group of the IETF. February 1988. doi:10.17487/RFC1042. RFC 1042.
13. ^ Computer Society, IEEE (2016). IEEE Std 802.11-2016: Part 11: Wireless LAN Medium Access Control IEEE (MAC) and Physical Layer (PHY) Specifications. New York, NY: IEEE. p. 249.
14. ^ "Troubleshooting Ethernet". Cisco Systems. Retrieved 13 August 2016.

Further reading

Wikiversity has learning resources about Topic:Web Science/Part1: Foundations of the web/Internet Architecture/Ethernet

• Video which explains how to build an Ethernet Frame

• Minimum Frame Length in Ethernet explained

Retrieved from "https://en.wikipedia.org/w/index.php?title=Ethernet_frame&oldid=1124373916"

Page 2

Standards for Ethernet at ten times the speed of Gigabit Ethernet

10 Gigabit Ethernet (10GE, 10GbE, or 10 GigE) is a group of computer networking technologies for transmitting Ethernet frames at a rate of 10 gigabits per second. It was first defined by the IEEE 802.3ae-2002 standard. Unlike previous Ethernet standards, 10 Gigabit Ethernet defines only full-duplex point-to-point links which are generally connected by network switches; shared-medium CSMA/CD operation has not been carried over from the previous generations Ethernet standards[1] so half-duplex operation and repeater hubs do not exist in 10GbE.[2]

The 10 Gigabit Ethernet standard encompasses a number of different physical layer (PHY) standards. A networking device, such as a switch or a network interface controller may have different PHY types through pluggable PHY modules, such as those based on SFP+.[3] Like previous versions of Ethernet, 10GbE can use either copper or fiber cabling. Maximum distance over copper cable is 100 meters but because of its bandwidth requirements, higher-grade cables are required.[a]

The adoption of 10 Gigabit Ethernet has been more gradual than previous revisions of Ethernet: in 2007, one million 10GbE ports were shipped, in 2009 two million ports were shipped, and in 2010 over three million ports were shipped,[4][5] with an estimated nine million ports in 2011.[6] As of 2012[update], although the price per gigabit of bandwidth for 10 Gigabit Ethernet was about one-third compared to Gigabit Ethernet, the price per port of 10 Gigabit Ethernet still hindered more widespread adoption.[7][8]

Standards

Over the years the Institute of Electrical and Electronics Engineers (IEEE) 802.3 working group has published several standards relating to 10GbE.

Physical layer modules

To implement different 10GbE physical layer standards, many interfaces consist of a standard socket into which different physical (PHY) layer modules may be plugged. PHY modules are not specified in an official standards body but by multi-source agreements (MSAs) that can be negotiated more quickly. Relevant MSAs for 10GbE include XENPAK[10][11][12] (and related X2 and XPAK), XFP and SFP+.[13][14] When choosing a PHY module, a designer considers cost, reach, media type, power consumption, and size (form factor). A single point-to-point link can have different MSA pluggable formats on either end (e.g. XPAK and SFP+) as long as the 10GbE optical or copper port type (e.g. 10GBASE-SR) supported by the pluggable is identical.

XENPAK was the first MSA for 10GE and had the largest form factor. X2 and XPAK were later competing standards with smaller form factors. X2 and XPAK have not been as successful in the market as XENPAK. XFP came after X2 and XPAK and it is also smaller.

The newest module standard is the enhanced small form-factor pluggable transceiver, generally called SFP+. Based on the small form-factor pluggable transceiver (SFP) and developed by the ANSI T11 fibre channel group, it is smaller still and lower power than XFP. SFP+ has become the most popular socket on 10GE systems.[15][13] SFP+ modules do only optical to electrical conversion, no clock and data recovery, putting a higher burden on the host's channel equalization. SFP+ modules share a common physical form factor with legacy SFP modules, allowing higher port density than XFP and the re-use of existing designs for 24 or 48 ports in a 19-inch rack width blade.

Optical modules are connected to a host by either a XAUI, XFI or SerDes Framer Interface (SFI) interface. XENPAK, X2, and XPAK modules use XAUI to connect to their hosts. XAUI (XGXS) uses a four-lane data channel and is specified in IEEE 802.3 Clause 47. XFP modules use a XFI interface and SFP+ modules use an SFI interface. XFI and SFI use a single lane data channel and the 64b/66b encoding specified in IEEE 802.3 Clause 49.

SFP+ modules can further be grouped into two types of host interfaces: linear or limiting. Limiting modules are preferred except when for long-reach applications using 10GBASE-LRM modules.[14]

Optical fiber

There are two basic types of optical fiber used for 10 Gigabit Ethernet: single-mode (SMF) and multi-mode (MMF).[20] In SMF light follows a single path through the fiber while in MMF it takes multiple paths resulting in differential mode delay (DMD). SMF is used for long-distance communication and MMF is used for distances of less than 300 m. SMF has a narrower core (8.3 μm) which requires a more precise termination and connection method. MMF has a wider core (50 or 62.5 μm). The advantage of MMF is that it can be driven by a low cost Vertical-cavity surface-emitting laser (VCSEL) for short distances, and multi-mode connectors are cheaper and easier to terminate reliably in the field. The advantage of SMF is that it can work over longer distances.[21]

In the 802.3 standard, reference is made to FDDI-grade MMF fiber. This has a 62.5 μm core and a minimum modal bandwidth of 160 MHz·km at 850 nm. It was originally installed in the early 1990s for FDDI and 100BASE-FX networks. The 802.3 standard also references ISO/IEC 11801 which specifies optical MMF fiber types OM1, OM2, OM3 and OM4. OM1 has a 62.5 μm core while the others have a 50 μm core. At 850 nm the minimum modal bandwidth of OM1 is 200 MHz·km, of OM2 500 MHz·km, of OM3 2000 MHz·km and of OM4 4700 MHz·km. FDDI-grade cable is now obsolete and new structured cabling installations use either OM3 or OM4 cabling. OM3 cable can carry 10 Gigabit Ethernet 300 meters using low cost 10GBASE-SR optics.[22][23] OM4 can manage 400 meters.[24]

To distinguish SMF from MMF cables, SMF cables are usually yellow, while MMF cables are orange (OM1 & OM2) or aqua (OM3 & OM4). However, in fiber optics there is no uniform color for any specific optical speed or technology with the exception being angular physical connector (APC), it being an agreed color of green.[25]

There are also active optical cables (AOC). These have the optical electronics already connected eliminating the connectors between the cable and the optical module. They plug into standard SFP+ sockets. They are lower cost than other optical solutions because the manufacturer can match the electronics to the required length and type of cable.[citation needed]

10GBASE-SR

10GBASE-SR ("short range") is a port type for multi-mode fiber and uses 850 nm lasers.[26] Its Physical Coding Sublayer (PCS) is 64b/66b and is defined in IEEE 802.3 Clause 49 and its Physical Medium Dependent (PMD) sublayer in Clause 52. It delivers serialized data at a line rate of 10.3125 Gbd.[27]

The range depends on the type of multi-mode fiber used.[22][28]

MMF has the advantage over SMF of having lower cost connectors; its wider core requires less mechanical precision.

The 10GBASE-SR transmitter is implemented with a VCSEL which is low cost and low power. OM3 and OM4 optical cabling is sometimes described as laser optimized because they have been designed to work with VCSELs. 10GBASE-SR delivers the lowest cost, lowest power and smallest form factor optical modules.

There is a lower cost, lower power variant sometimes referred to as 10GBASE-SRL (10GBASE-SR lite). This is inter-operable with 10GBASE-SR but only has a reach of 100 meters.[29]

10GBASE-LR

10GBASE-LR (long reach) is a port type for single-mode fiber and uses 1310 nm lasers. Its 64b/66b PCS is defined in IEEE 802.3 Clause 49 and its PMD sublayer in Clause 52. It delivers serialized data at a line rate of 10.3125 GBd.[27]

The 10GBASE-LR transmitter is implemented with a Fabry–Pérot or Distributed feedback laser (DFB). DFB lasers are more expensive than VCSELs but their high power and longer wavelength allow efficient coupling into the small core of single-mode fiber over greater distances.[citation needed]

10GBASE-LR maximum fiber length is 10 kilometers, although this will vary depending on the type of single-mode fiber used.

10GBASE-LRM

10GBASE-LRM, (long reach multi-mode) originally specified in IEEE 802.3aq is a port type for multi-mode fiber and uses 1310 nm lasers. Its 64b/66b PCS is defined in IEEE 802.3 Clause 49 and its PMD sublayer in Clause 68. It delivers serialized data at a line rate of 10.3125 GBd.[30] 10GBASE-LRM uses electronic dispersion compensation (EDC) for receive equalization.[31]

10GBASE-LRM allows distances up to 220 metres (720 ft) on FDDI-grade multi-mode fiber and the same 220m maximum reach on OM1, OM2 and OM3 fiber types.[22] 10GBASE-LRM reach is not quite as far as the older 10GBASE-LX4 standard. Some 10GBASE-LRM transceivers also allow distances up to 300 metres (980 ft) on standard single-mode fiber (SMF, G.652), however this is not part of the IEEE or MSA specification.[32] To ensure that specifications are met over FDDI-grade, OM1 and OM2 fibers, the transmitter should be coupled through a mode conditioning patch cord. No mode conditioning patch cord is required for applications over OM3 or OM4.[33]

10GBASE-ER

10GBASE-ER (extended reach) is a port type for single-mode fiber and uses 1550 nm lasers. Its 64b/66b PCS is defined in IEEE 802.3 Clause 49 and its PMD sublayer in Clause 52. It delivers serialized data at a line rate of 10.3125 GBd.[27]

The 10GBASE-ER transmitter is implemented with an externally modulated laser (EML).

10GBASE-ER has a reach of 40 kilometres (25 mi) over engineered links and 30 km over standard links.[22][12]

10GBASE-ZR

Several manufacturers have introduced 80 km (50 mi) range under the name 10GBASE-ZR. This 80 km PHY is not specified within the IEEE 802.3ae standard and manufacturers have created their own specifications based upon the 80 km PHY described in the OC-192/STM-64 SDH/SONET specifications.[34]

10GBASE-LX4

10GBASE-LX4 is a port type for multi-mode fiber and single-mode fiber. It uses four separate laser sources operating at 3.125 Gbit/s and Coarse wavelength-division multiplexing with four unique wavelengths around 1310 nm. Its 8b/10b PCS is defined in IEEE 802.3 Clause 48 and its Physical Medium Dependent (PMD) sublayer in Clause 53.[22]

10GBASE-LX4 has a range of 10 kilometres (6.2 mi) over SMF. It can reach 300 metres (980 ft) over FDDI-grade, OM1, OM2 and OM3 multi-mode cabling.[b] In this case, it needs to be coupled through a SMF offset-launch mode-conditioning patch cord.[22]: subclauses 53.6 and 38.11.4 

10GBASE-PR

Main articles: 10G-EPON and Ethernet in the first mile

10GBASE-PR originally specified in IEEE 802.3av is a 10 Gigabit Ethernet PHY for passive optical networks and uses 1577 nm lasers in the downstream direction and 1270 nm lasers in the upstream direction. Its PMD sublayer is specified in Clause 75. Downstream delivers serialized data at a line rate of 10.3125 Gbit/s in a point to multi-point configuration.[22]

10GBASE-PR has three power budgets specified as 10GBASE-PR10, 10GBASE-PR20 and 10GBASE-PR30.[22]: 75.1.4 

10GBASE-BR

Multiple vendors introduced single strand, bi-directional 10 Gbit/s optics capable of a single-mode fiber connection functionally equivalent to 10GBASE-LR or -ER, but using a single strand of fiber optic cable. Analogous to 1000BASE-BX10, this is accomplished using a passive prism inside each optical transceiver and a matched pair of transceivers using two different wavelengths such as 1270 and 1330 nm. Modules are available in varying transmit powers and reach distances ranging from 10 to 80 km.[35][36]

These advances were subsequently standardized in IEEE 802.3cp-2021 with reaches of 10, 20, or 40 km.

Copper

10 Gigabit Ethernet can also run over twin-axial cabling, twisted pair cabling, and backplanes.

10GBASE-CX4

10GBASE-CX4 was the first 10 Gigabit copper standard published by 802.3 (as 802.3ak-2004). It uses the XAUI 4-lane PCS (Clause 48) and copper cabling similar to that used by InfiniBand technology with the same SFF-8470 connectors. It is specified to work up to a distance of 15 m (49 ft). Each lane carries 3.125 GBd of signaling bandwidth.

10GBASE-CX4 has been used for stacking switches.[37] It offers the advantages of low power, low cost and low latency, but has a bigger form factor and more bulky cables than the newer single-lane SFP+ standard, and a much shorter reach than fiber or 10GBASE-T. This cable is fairly rigid and considerably more costly than Category 5/6 UTP or fiber.

10GBASE-CX4 applications are now commonly achieved using SFP+ Direct Attach and as of 2011[update], shipments of 10GBASE-CX4 have been very low.[38]

SFP+ direct attach

Also known as direct attach (DA), direct attach copper (DAC), 10GSFP+Cu, 10GBASE-CR [39] or 10GBASE-CX1. Short direct attach cables use a passive twinaxial cabling assembly while longer ones, sometimes called active optical cable (AOC) use short wavelength optics.[40] Both types connect directly into an SFP+ housing. SFP+ direct attach has a fixed-length cable, up to 15 m for copper cables,[41] or up to 100 m in for AOC.[40] Like 10GBASE-CX4, DA is low-power, low-cost and low-latency with the added advantages of using less bulky cables and of having the small SFP+ form factor. SFP+ direct attach today is tremendously popular, with more ports installed than 10GBASE-SR.[38]

Backplane

Backplane Ethernet, also known by the name of the task force that developed it, 802.3ap, is used in backplane applications such as blade servers and modular network equipment with upgradable line cards. 802.3ap implementations are required to operate over up to 1 metre (39 in) of copper printed circuit board with two connectors. The standard defines two port types for 10 Gbit/s (10GBASE-KX4 and 10GBASE-KR) and a single 1 Gbit/s port type (1000BASE-KX). It also defines an optional layer for forward error correction, a backplane autonegotiation protocol and link training for 10GBASE-KR where the receiver tunes a three-tap transmit equalizer. The autonegotiation protocol selects between 1000BASE-KX, 10GBASE-KX4, 10GBASE-KR or 40GBASE-KR4 operation.[c]

10GBASE-KX4

This operates over four backplane lanes and uses the same physical layer coding (defined in IEEE 802.3 Clause 48) as 10GBASE-CX4.

10GBASE-KR

This operates over a single backplane lane and uses the same physical layer coding (defined in IEEE 802.3 Clause 49) as 10GBASE-LR/ER/SR. New backplane designs use 10GBASE-KR rather than 10GBASE-KX4.[38]

10GBASE-T

10GBASE-T, or IEEE 802.3an-2006, is a standard released in 2006 to provide 10 Gbit/s connections over unshielded or shielded twisted pair cables, over distances up to 100 metres (330 ft).[43] Category 6A is required to reach the full distance and category 5e or 6 may reach up to 55 metres (180 ft) depending on the quality of installation.[44] 10GBASE-T cable infrastructure can also be used for 1000BASE-T allowing a gradual upgrade from 1000BASE-T using autonegotiation to select which speed is used. Due to additional line coding overhead, 10GBASE-T has a slightly higher latency (2 to 4 microseconds) in comparison to most other 10GBASE variants (1 microsecond or less). In comparison, 1000BASE-T latency is 1 to 12 microseconds (depending on packet size[d]).[45][46]

10GBASE-T uses the IEC 60603-7 8P8C modular connectors already widely used with Ethernet. Transmission characteristics are now specified to 500 MHz. To reach this frequency Category 6A or better balanced twisted pair cables specified in ISO/IEC 11801 amendment 2 or ANSI/TIA-568-C.2 are needed to carry 10GBASE-T up to distances of 100 m. Category 6 cables can carry 10GBASE-T for shorter distances when qualified according to the guidelines in ISO TR 24750 or TIA-155-A.

The 802.3an standard specifies the wire-level modulation for 10GBASE-T to use Tomlinson-Harashima precoding (THP) and pulse-amplitude modulation with 16 discrete levels (PAM-16), encoded in a two-dimensional checkerboard pattern known as DSQ128 sent on the line at 800 Msymbols/sec.[47][48] Prior to precoding, forward error correction (FEC) coding is performed using a [2048,1723]2 low-density parity-check code on 1723 bits, with the parity check matrix construction based on a generalized Reed–Solomon [32,2,31] code over GF(26).[48] Another 1536 bits are uncoded. Within each 1723+1536 block, there are 1+50+8+1 signaling and error detection bits and 3200 data bits (and occupy 320 ns on the line). In contrast, PAM-5 is the modulation technique used in 1000BASE-T Gigabit Ethernet.

The line encoding used by 10GBASE-T is the basis for the newer and slower 2.5GBASE-T and 5GBASE-T standard, implementing a 2.5 or 5.0 Gbit/s connection over existing category 5e or 6 cabling.[49] Cables that will not function reliably with 10GBASE-T may successfully operate with 2.5GBASE-T or 5GBASE-T if supported by both ends.[50]

10GBASE-T1

10GBASE-T1 is for automotive applications and operates over a single balanced pair of conductors up to 15 m long, and is standardized in 802.3ch-2020.[51]

WAN PHY (10GBASE-W)

At the time that the 10 Gigabit Ethernet standard was developed, interest in 10GbE as a wide area network (WAN) transport led to the introduction of a WAN PHY for 10GbE. The WAN PHY was designed to interoperate with OC-192/STM-64 SDH/SONET equipment using a light-weight SDH/SONET frame running at 9.953 Gbit/s. The WAN PHY operates at a slightly slower data-rate than the local area network (LAN) PHY. The WAN PHY can drive maximum link distances up to 80 km depending on the fiber standard employed.

The WAN PHY uses the same 10GBASE-S, 10GBASE-L and 10GBASE-E optical PMDs as the LAN PHYs and is designated as 10GBASE-SW, 10GBASE-LW or 10GBASE-EW. Its 64b/66b PCS is defined in IEEE 802.3 clause 49 and its PMD sublayers in clause 52. It also uses a WAN interface sublayer (WIS) defined in clause 50 which adds extra encapsulation to format the frame data to be compatible with SONET STS-192c.[22]

Notes

1. ^ Category 6 cable supports runs up to 55 meters. Category 6A or higher is good for lengths up to 100 meters.
2. ^ All these fiber types are specified to have a minimum modal bandwidth of 500 MHz × km at 1300 nm.
3. ^ 40GBASE-KR4 is defined in 802.3ba.[42]
4. ^ A maximum Gigabit Ethernet packet requires 12.2 μs for transfer (1526 × 8 ÷ 109) for store-and-forward, this adds to hardware latency.

See also

• GG45
• List of interface bit rates
• Optical communication
• Optical fiber cable
• Parallel optical interface
• TERA
• XAUI

References

1. ^ Michael Palmer (21 June 2012). Hands-On Networking Fundamentals, 2nd ed. Cengage Learning. p. 180. ISBN 978-1-285-40275-8.
2. ^ IEEE 802.3-2012 44.1.1 Scope
3. ^ Sharma, Anil (19 January 2011). "LightCounting forecasts CAGR of Over 300 Percent for 10GBASE-T Port Shipments Through 2014". TMCnet. Retrieved 7 May 2011.
4. ^ "Dell'Oro press release". Archived from the original on 19 July 2011. Retrieved 29 March 2011.
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6. ^ "Exclusive: Google, Amazon, and Microsoft Swarm China for Network Gear". Wired.
7. ^ 10 Gigabit Ethernet still too expensive on servers
8. ^ Soz, switch-fondlers: Doesn't look like 2013 is 10Gb Ethernet's year
9. ^ "IEEE P802.3ae 10Gb/s Ethernet Task Force". Retrieved 19 March 2013.
10. ^ a b "Common 10G Fiber Transceiver: 10G XENPAK, 10G X2, 10G XFP, 10G SFP+". Blog of Fiber Transceivers. 18 June 2013. Retrieved 26 August 2018.
11. ^ a b "End-of-Sale and End-of-Life Announcement for the Cisco 10GBASE XENPAK Modules". Cisco. 1 April 2015. Retrieved 26 August 2018.
12. ^ a b "Cisco 10GBASE XENPAK Modules". Cisco Systems. November 2011. Retrieved 12 May 2012.
13. ^ a b "10GbE Optical Component and SFP+ Modules: This Time It's Different by Andrew Schmitt". Retrieved 11 March 2008.
14. ^ a b Ryan Latchman; Bharat Tailor. "The road to SFP+: Examining module and system architectures". Archived from the original on 16 May 2008.
15. ^ "LightCounting's LightTrends April 2010". Retrieved 3 May 2010.[permanent dead link]
16. ^ a b Charles E. Spurgeon (2014). Ethernet: The Definitive Guide (2nd ed.). O'Reilly Media. ISBN 978-1-4493-6184-6.
17. ^ "Cisco 10-Gigabit Ethernet Transceiver Modules Compatibility Matrix". Cisco. 19 August 2018. Retrieved 26 August 2018.
18. ^ "Confused by 10GbE optics modules?". Network World. 12 June 2010. Retrieved 26 August 2018.
19. ^ a b "Network Topologies and Distances" (PDF). MC Communications. 14 November 2007. Retrieved 25 August 2018.
20. ^ "Optical Fiber and 10 gigabit Ethernet white paper by the 10GEA". Archived from the original on 14 June 2008.
21. ^ "Why choose Multimode fiber? by Corning" (PDF). Archived from the original (PDF) on 30 July 2014.
22. ^ a b c d e f g h i "IEEE 802.3 standard".
23. ^ "10 Gigabit Ethernet over Multimode Fiber by John George" (PDF). Archived from the original (PDF) on 10 September 2008. Retrieved 10 March 2008.
24. ^ IEEE 802.3 52.5 PMD to MDI optical specifications for 10GBASE-S
25. ^ "How to tell? MMF or SMF". Retrieved 6 September 2011.[unreliable source?]
26. ^ Held, Gilbert (19 April 2016). Windows Networking Tools: The Complete Guide to Management, Troubleshooting, and Security. CRC Press. ISBN 9781466511071.
27. ^ a b c IEEE 802.3 52.1.1.1.2 PMD_UNITDATA.request: When generated
28. ^ "Description of Cisco 10G optical modules". Retrieved 3 May 2010.
29. ^ Optics Modules and Cables (PDF), retrieved 28 June 2019
30. ^ IEEE 802.3 Table 68–3—10GBASE-LRM transmit characteristics
31. ^ "10GBase-LX4 vs 10GBase-LRM: A debate". Archived from the original on 21 July 2009. Retrieved 16 July 2009.
32. ^ IEEE 802.3 68.5 PMD to MDI optical specifications
33. ^ "Cisco 10GBASE SFP+ Modules Data Sheet". Cisco Systems. February 2012. Retrieved 12 May 2012.
34. ^ "Cisco 10GbE optics and 10GBase-ZR".
35. ^ "Cisco 10GBASE SFP+ Modules" (PDF). Cisco Systems. p. 6. Retrieved 28 September 2020.
36. ^ "10Gb/s Bidirectional 10km Gen2 SFP+ Optical Transceiver". Retrieved 28 September 2020.
37. ^ Dove, Dan (24 May 2004). "10GBase-CX4 lowers 10G Ethernet cost". Network World. Retrieved 19 December 2014.
38. ^ a b c "Another Serving of Alphabet Soup — by Intel". Archived from the original on 22 August 2011. Retrieved 4 September 2011.
39. ^ "Cables and Transceivers". Arista Networks. Retrieved 21 September 2012.
40. ^ a b "SFP+ AOC Cable active". fiber24.de. Retrieved 30 January 2017.
41. ^ "HP X242 SFP+ Direct Attach Copper Cable". Hewlett Packard. Archived from the original on 14 October 2012. Retrieved 27 March 2013.
42. ^ "IEEE P802.3ap Backplane Ethernet Task Force". Retrieved 30 January 2011.
43. ^ "IEEE Standards Status Report for 802.3an". Archived from the original on 5 September 2007. Retrieved 14 August 2007.
44. ^ "7100T Datasheet" (PDF). Arista Networks. The Arista 7100T switches support 10GBASE-T over Category 6a cabling up to 100m, but also support Category 5e (Performance of 10GBASE-T over Cat-5e cabling is not specified in the standard and thus cannot be guaranteed. Field testing is recommended before deployment to establish the feasibility of using existing Cat-5e cabling.) and Category 6 cabling with distances up to 55m.{{cite web}}: CS1 maint: url-status (link)
45. ^ 10GBASE-T for Broad 10 Gigabit Adoption in the Data Center (PDF), Intel, retrieved 21 December 2011
46. ^ SWITCHES SWITCH FROM 1000BASE-T TO 10GBASE-T NOW (PDF), Teranetics, October 2009, retrieved 21 December 2011
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48. ^ a b Ungerboeck, Gottfried (22 September 2006). "10GBASE-T: 10Gbit/s Ethernet over copper" (PDF). Vienna: Broadcom. Retrieved 7 August 2013.
49. ^ "IEEE 802.3 NGEABT Objectives approved by IEEE 802.3, March 12, 2015" (PDF).
50. ^ "NBaseT".
51. ^ Maguire, Valerie (4 June 2020). "IEEE Std 802.3ch-2020: Multi-Gig Automotive Ethernet PHY".

• IEEE 802.3-2018 - IEEE Standard for Ethernet

External links

• Ethernet Alliance website
• World's First Independent 10GBASE-T Comparative Test Study

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