Network World

research center:

Search / DocFinder:
Advanced search
Research Centers
Vendor Solutions
Site Resources
Special Issues

Signature SeriesEnterprise All-Stars
Enterprise All-Stars NEW

You in action
You in action

New Data Center The New Data Center: Wireless & Mobility
Wireless & Mobility NEW

The New Data Center: Server Virtualization
Server Virtualization

10 Gigabit Ethernet

From its inception, 10G Ethernet was intended to retain backward compatibility and full interoperability with 10/100/1000M bit/sec Ethernet while adding a tenfold increase in performance.

In 10/100 and Gigabit Ethernet, the MAC layer works in a linear manner - data moves serially in and out of the MAC layer with all the starting and ending control messages (including clocking and synchronization) embedded inside the datastream. With 10G Ethernet, it is much more complex.

To attain a 10G bit/sec bandwidth rate, the IEEE altered the way that MAC layer interprets signaling. Rather than producing a serial stream, the 10G Ethernet layer operates in parallel to interpret data. The transmit and receive paths each comprise four data lanes, and the datastream broken down into bytes is handled in round-robin fashion across the four lanes, numbered 0 to 3. On the transmit path, for example, the first byte aligns to Lane 0, the second byte to Lane 1, the third byte to Lane 2, the fourth byte to Lane 3, the fifth byte back to Lane 0, and so on.

Ethernet frames have clearly defined beginning and ending boundaries, or delimiters. These are marked by special characters and a 12-byte interpacket gap (IPG) that dictates the minimum amount of space or idle time between packets.

Because of the parallel nature of the 10G Ethernet MAC layer, it is impossible to predict the lane in which the ending byte of the previous datastream will fall. This makes finding the starting bit - a requirement for maintaining timing and synchronization - more difficult. The 802.3ae standard mandated an elegant solution: the "start control character," or very first byte of a new data frame, must always align on Lane 0. However, this solution complicates the way the MAC handles the IPG, directly affecting performance. Nevertheless, the IEEE provided three options for the vendors to address this issue: 1) pad (increase), 2) shrink, or 3) average the "minimum" IPG.

Padding increases the IPG

If the ending character of the previous packet falls into 12th slot in the 12-byte IPG, the MAC layer does nothing and maintains the 12-byte minimum IPG, and the starting character of the next packet automatically aligns in Position A of Lane 0. If, however, the ending character of the previous packet falls into other positions, the MAC layer must add bytes respectively into the IPG to ensure that the starting character of the next packet aligns properly in Position A of Lane 0. This results in a minimum IPG that ranges from 12 to 15 bytes (12-byte minimum plus additional pad).

Increasing the size of the IPG beyond the 12-byte minimum decreases the available bandwidth on the 10G Ethernet link by as much as 10%, depending on packet size.

Shrinking the IPG

After padding bytes to the IPG to ensure the starting character aligns to Position A, the MAC eliminates the middle column of idle characters. This results in an IPG that ranges from eight to 11 bytes (12-byte minimum plus padding minus the four idle bytes).

Decreasing the 10G Ethernet IPG by eliminating the middle column of idle bytes provides an additional 5% available bandwidth on the 10G Ethernet link, depending on packet size.

Averaging the IPG

This option uses a combination of options 1 and 3 with the addition of a deficit idle counter, which keeps track of the number of added or deleted idle bytes (ranging from 0 to 3). In some cases, the MAC layer will add and, in others, eliminate bytes. Over the long run, the net result will be an average 12-byte minimum 10G Ethernet IPG.

Averaging the 10G Ethernet IPG ensures that the port delivers 100% of the available bandwidth and lets the connection maintain zero-loss line-rate performance.

From Achieving true 10 Gig performance
Network World Tech Update, 01/06/03.


Additional resources

Breaking 10G newsLatest news from Network World.

10 Gigabit Ethernet News
More breaking news.

Topic: Metropolitan NetworksLatest news, analysis and opinion from Network World Fusion.

Topic: Routers/Switches
Breaking news and analysis from Network World Fusion.


10G On Copper
by Amul

Good I have learn today that the 10G can also run on copper cabling.

We are planning to shift our Campus network from ATM to 10G Network.

I will like to know the cisco switch which can be used on distribution layer to connect internal floor using copper cabling.

Add a comment

NOTE: Comments are reviewed by an editor before being posted.

Your rating of this resource (with 5 the best)
1 2 3 4 5


Your user name (what other users will see on the review):

Your real name (for our records only):

Your e-mail (ditto):

Your comments (Use a blank line to separate paragraphs):

Vendor Solutions

White Papers


Research Centers: Applications | Application Development | Applications-Standards | Applications Vendor Solutions | Collaboration | CRM / ERP | Databases | Directories | Grid Computing | Java | Messaging | .Net | RFID | SOAP | Web Services | XML | Convergence & VoIP | Convergence Regulatory | Convergence Services | Convergence Standards | Convergence VoIP Vendor Solutions | Video | IP PBX | SIP | VoIP | VoIP Services | E-Business | DNS | RFID | Supply Chain | Web security LANs & Routers | Acceleration | Gigabit Ethernet | Lans-Standards | Routers | Wireless LANs | Network Management | Application Management | Desktop Management | Management Test Patch Management | Operating Systems | Linux | NetWare | Unix | Windows Outsourcing | Managed Services | Offshoring Security | Firewalls - VPN - Intrusion | Identity management | Patch Management | Microsoft Security | Privacy | Security Standards | Spam & Phishing | Viruses & worms | Web Security | Wireless Security | Servers & Desktop | Backup-Recovery | DataCenter | Desktops | Desktop Management | Grid | Servers | Server Blades | Servers Desktops | Utility Computing | Small & Medium Business | Broadband | Telework | Handhelds & PDAs | Home Networking | Security | Storage | Compliance | Infiniband | Network-Attached Storage | SANs | Storage Management | Storage Virtualization | Virtualization | Vendor News | Bankruptcy | Earnings | Lawsuits | Layoffs | Standards | Start Ups | Vendor Markets | Education | Financial | Healthcare | HIPAA | Manufacturing | Retail | Wide Area Network | Broadband | Carriers | Frame Relay | Metro Ethernet | MPLS | Service providers | Wireless services | Wireless & Mobile | Wireless LANs | PDAs & handhelds | Wireless Security | Wireless Services | Wireless Standards | Wireless Switches | All Company Profiles