ethernet, line coding, csmd

[sarahr202]

Hi everybody.

Let say we have  hosts h1 and h2 connected via ethernet.

hi-----ethernet---h2.

H1 wants to send some data to H2,

Ethernet uses line coding referred as 8/10B where 8 bits of data are represented using 10 bits.

My question after we have line coding in 10 bits representing some data at h1, will these bits are directly put onto the wire or do we use some carrier to encode these bits and then carrier is put on the wire?

Thanks and have a great weekend.

[Peter Paluch · Accepted solution]

Hello Sarah,

You've got a great question here.

Technically, none of the 'Base' Ethernets uses a carrier, meaning 10Base5, 10Base2, 10BaseT, 100BaseTX, 1000BaseT - they all use baseband signalling, i.e. using a signal with discrete values to encode the individual bits or groups of bits. No harmonic carrier is used, as opposed to, say, DSL or WiFi. To my best knowledge, only the 10Base36 Ethernet used a broadband signalling and used a modulated carrier wave to carry data.

The 8B/10B code is used for 1Gbps Ethernet. 10Mbps version does not use any similar coding step and 100Mbps is using 4B/5B code. So in 1Gbps Ethernet, after the 8B/10B coding and scrambling, the resulting code groups are mapped to voltage levels and put onto wire.

The gory details about 1Gbps Ethernet can be found here:

https://www.iol.unh.edu/services/testing/ge/knowledgebase/pcs.pdf

Best regards,

Peter

[sarahr202]

thanks Peter.

[Alexander Maroukian]

Hello Sarah,

Just want to add to what Peter said and to provide one more link which could be of interest:

http://www.cisco.com/web/about/ac123/ac147/ac174/ac199/about_cisco_ipj_archive_article09186a00800c85a6.html

Two signal encoding schemes are defined at the physical layer. The 8B/  10B scheme is used for optical fiber and shielded copper media, and the  pulse amplitude modulation (PAM) 5 is used for UTP.

Best regards,

Alex

[Peter Paluch]

Hi Alex,

Good link!

Best regards,

Peter