10 Gbps for the Network

Who would ever need 10 Gbps bandwidth on the network? The similar question was probably raised when 100 Mbps Ethernet was announced, and then when 1 Gigabit Ethernet came into being. So it's likely that even 10 Gbps will be superceded. But for now, the 10 Gigabit Ethernet technology (10G) has a limited application, though important. This is the ability to offer ten times the speed of Gigabit Ethernet up to a distance of 40 Kms. It will deployed in building MANs (Metropolitan Area Networks). 

Though the communication medium for 10G is fiber, it has also been tested over copper cable, which is cost effective. However, long distance data transfers can't be done with copper. 

The basic technical differences between 10G and 1 Gigabit Ethernet are the addition of a layer in the PHY (physical) layer of the OSI model, and use of a different encoding scheme, (64/66b), for better error rate detection during data transfer. Plus, 10G supports full duplex transmission only. 

So to achieve 10 Gbps, most of the changes are made in the PHY layer. 

Changes in the PHY layer 



The Ethernet standard defines two PHY types, LAN PHY and WAN PHY. 10G allows LANs in different cities to be connected over existing SONET/ SDH/TDM network using WAN PHY. Gigabit Ethernet didn't support SONET. 

PHY layer is further divided into two sub layers, PMD (Physical Media Dependant) and PCS (Physical Coding

Sublayer). PCS is responsible for coding and

encoding data streams to and from the MAC layer, while PMD layer has been added to enable data transmission over single or multi-mode fiber.

To achieve 10 Gbps speed, XGMII interface is added between the MAC and PHY layers. The interface provides full duplex transmission between MAC and

PHY. XGMII has limitation of transferring data to larger distances. To overcome this, 10 Gigabit Attachment Unit Interface

(XAUI) is added. XAUI is a full duplex interface that uses four serial links. Each serial link gives speed of 3.125

Gbps. 

XGXS (XAUI Extended Sublayer) does the conversion between XGMII and XAUI. XGMII interface is composed of four lanes of eight bits. Data flows at a speed of 3.125 Gbps in each lane. When data flows from XGMII to XAUI with clock signal, data is converted inside XGXS and encoded into data stream. The total speed achieved is 10

Gbps. The exact happens when data flows from XAUI to XGMII. 

The physical layer can be implemented either in serial or parallel configuration. Serial configuration uses one

PCS/PMA/PMD circuit, while parallel configuration has multiple PCS/PMA/PMD circuit to achieve 10 Gbps speed. 

Applications and benefits



As 10G becomes more popular, several applications could use the extra bandwidth. These include high bandwidth-intensive applications such as video on demand, distributed computing, medical imaging and scientific simulation. Universities, Research centers, enterprises having campus spread over long distance and offices spread across cities will find the technology useful. Enterprise can set up buildings at larger distances within campus and link them. This will enable extensive-bandwidth applications such as

VOIP, digital video conferencing easily accessible. Enterprise can locate their data centers, disaster recovery centers in a different city and yet get faster access.

10G will enable Network Managers to scale from 10,100, 1000 Mbps to 10 Gigabit. The cost of moving from Gigabit to 10 Gigabit will be two to three times

more, but the performance gain might be worth it. It is expected that the cost of 10G products will decrease gradually. 

Gigabit Ethernet storage servers and tape libraries are there in market. 10G will offer superior data carrying capacity compared to other storage interface technologies such as fiber channel, Ultra160 or 320 SCSI, and ATM OC-3.

Availability



A wide range of 10G fiber products is already available from vendors such as Cisco, 3Com, D-Link, Force 10 and Foundry Networks. Intel is the first company to have introduced 10G network interface cards (Intel PRO/10GbE) for servers. These, however, are mostly for communication over fiber. As for the copper, several vendors such as SYSTIMAX and Krone have introduced structured cabling solutions for 10G.

Sushil Oswal