Question about gig fiber

borumas

I had a practice question ask what type of collision avoidance is used on a gigabit fiber link and the choices where:
CSMA/CA
CSMA/CD
Logic Link Control

there was one more choice but I can't remember what it was.

Now CSMA/CA is used in 802.11 wireless LANs from what I've read
CSMA/CD is used in ethernet and after more research I found that ethernet covers 10mb-1000fiber so that should be the answer right?
Logic Link Control is a sublayer of the Data link layer so that should not be the answer.

Just wanted to get this clear, I'm taking the ICND again soon.

dtlokee

Somthing to think about, if gig fiber is always full duplex, does it need a collision avoidance method? When an interface is in full duplex mode, the collison detection circuits are disabled.

borumas

dtlokee wrote:

Somthing to think about, if gig fiber is always full duplex, does it need a collision avoidance method? When an interface is in full duplex mode, the collison detection circuits are disabled.

I wondered about that, that in full duplex mode no collisions should occur and only in half duplex they are possible.

Netstudent

With high bit rates like that, I believe you would worry not about collisions, but rather worry about flow control.

rjbarlow

I think the right answer is not between You posted, the collision avoidance method used by fiber should have to be token passing, however never I read this on the manuals I purchased in order to preparate the ccna, i just remember this from a question I don't remember where, this is the type of question I fear much to find in the exam, like details of cabling standards etc...

borumas

rjbarlow wrote:

I think the right answer is not between You posted, the collision avoidance method used by fiber should have to be token passing, however never I read this on the manuals I purchased in order to preparate the ccna, i just remember this from a question I don't remember where, this is the type of question I fear much to find in the exam, like details of cabling standards etc...

Token passing is used in Token ring networks, not in an ethernet network so that should not be a correct answer.

rjbarlow

borumas wrote:

rjbarlow wrote:

I think the right answer is not between You posted, the collision avoidance method used by fiber should have to be token passing, however never I read this on the manuals I purchased in order to preparate the ccna, i just remember this from a question I don't remember where, this is the type of question I fear much to find in the exam, like details of cabling standards etc...

Token passing is used in Token ring networks, not in an ethernet network so that should not be a correct answer.

Fiber networks are not Ethernet...

borumas

rjbarlow wrote:

borumas wrote:

rjbarlow wrote:

I think the right answer is not between You posted, the collision avoidance method used by fiber should have to be token passing, however never I read this on the manuals I purchased in order to preparate the ccna, i just remember this from a question I don't remember where, this is the type of question I fear much to find in the exam, like details of cabling standards etc...

Token passing is used in Token ring networks, not in an ethernet network so that should not be a correct answer.

Fiber networks are not Ethernet...

802.3 commonly referred to as "ethernet" consists of 10MB copper to 1000MB copper and fiber http://en.wikipedia.org/wiki/IEEE_802.3

The original Ethernet is called "Experimental Ethernet" today. It was developed by Robert Metcalfe in 1972 (patented in 197 and was based in part on the wireless ALOHAnet protocol. It is not in use anywhere, but is thought to be the only Ethernet by some purists. The first "Ethernet" that was generally used outside Xerox was the DIX Ethernet. However, as DIX Ethernet was derived from Experimental Ethernet, and as many standards have been developed that are based on DIX Ethernet, the technical community has accepted the term Ethernet for all of them. Therefore, the term "Ethernet" can be used to name networks using any of the following standardized media and functions:
Ethernet Standard Date Description
Experimental
Ethernet 1972 2.94 Mbit/s (367 kB/s) over coaxial cable (coax) cable bus
Ethernet II
(DIX v2.0) 1982 10 Mbit/s (1.25 MB/s) over thin coax (thinnet) - Frames have a Type field. This frame format is used on all forms of Ethernet by protocols in the Internet protocol suite.
IEEE 802.3 1983 10BASE5 10 Mbit/s (1.25MB/s) over thick coax - same as DIX except Type field is replaced by Length, and an 802.2 LLC header follows the 802.3 header
802.3a 1985 10BASE2 10 Mbit/s (1.25 MB/s) over thin Coax (thinnet or cheapernet)
802.3b 1985 10BROAD36
802.3c 1985 10 Mbit/s (1.25 MB/s) repeater specs
802.3d 1987 FOIRL (Fiber-Optic Inter-Repeater Link)
802.3e 1987 1BASE5 or StarLAN
802.3i 1990 10BASE-T 10 Mbit/s (1.25 MB/s) over twisted pair
802.3j 1993 10BASE-F 10 Mbit/s (1.25 MB/s) over Fiber-Optic
802.3u 1995 100BASE-TX, 100BASE-T4, 100BASE-FX Fast Ethernet at 100 Mbit/s (12.5 MB/s) w/autonegotiation
802.3x 1997 Full Duplex and flow control; also incorporates DIX framing, so there's no longer a DIX/802.3 split
802.3y 1998 100BASE-T2 100 Mbit/s (12.5 MB/s) over low quality twisted pair
802.3z 1998 1000BASE-X Gbit/s Ethernet over Fiber-Optic at 1 Gbit/s (125 MB/s)
802.3-1998 1998 A revision of base standard incorporating the above amendments and errata
802.3ab 1999 1000BASE-T Gbit/s Ethernet over twisted pair at 1 Gbit/s (125 MB/s)
802.3ac 1998 Max frame size extended to 1522 bytes (to allow "Q-tag") The Q-tag includes 802.1Q VLAN information and 802.1p priority information.
802.3ad 2000 Link aggregation for parallel links
802.3-2002 2002 A revision of base standard incorporating the three prior amendments and errata
802.3ae 2003 10 Gbit/s (1,250 MB/s) Ethernet over fiber; 10GBASE-SR, 10GBASE-LR, 10GBASE-ER, 10GBASE-SW, 10GBASE-LW, 10GBASE-EW
802.3af 2003 Power over Ethernet
802.3ah 2004 Ethernet in the First Mile
802.3ak 2004 10GBASE-CX4 10 Gbit/s (1,250 MB/s) Ethernet over twin-axial cable
802.3-2005 2005 A revision of base standard incorporating the four prior amendments and errata.
802.3an 2006 10GBASE-T 10 Gbit/s (1,250 MB/s) Ethernet over unshielded twisted pair(UTP)
802.3ap exp. 2007 Backplane Ethernet (1 and 10 Gbit/s (125 and 1,250 MB/s) over printed circuit boards)
802.3aq 2006 10GBASE-LRM 10 Gbit/s (1,250 MB/s) Ethernet over multimode fiber
802.3ar exp. 2007 Congestion management
802.3as 2006 Frame expansion
802.3at exp. 2008 Power over Ethernet enhancements
802.3au 2006 Isolation requirements for Power Over Ethernet (802.3-2005/Cor 1)
802.3av exp. 2009 10 Gbit/s EPON
802.3 HSSG exp. 2009 Higher Speed Study Group. 100 Gb/s up to 100 m or 10 km using MMF or SMF optical fiber respectively

rjbarlow

No, if You take a branch of Ethernet clearly the method to avoid collisions is the same of the entire Ethernet LAN, nothing if You use switches. If You refer to a entire Fiber optic network like I think made the question, the right answer is token passing: look this very nice link for much arguments.

Netstudent

Well you could have fiber in Ethernet or Token ring networks. FDDI for one is a fiber network that uses token passing.

But the question asked about collision avoidance. Token passing isn't a collision avoidance technique but rather an Access method. A method of accessing the media. There are no collisions in tokenring so therefore there are no collision avoidance teqniques right?

I think this question is too vague and leaves the door open for too many options. If I had to guess I would say the answer is None of the above because giga fiber links are full duplex.

rjbarlow

Netstudent wrote:

Well you could have fiber in Ethernet or Token ring networks. FDDI for one is a fiber network that uses token passing.

But the question asked about collision avoidance. Token passing isn't a collision avoidance technique but rather an Access method. A method of accessing the media. There are no collisions in tokenring so therefore there are no collision avoidance teqniques right?

I think this question is too vague and leaves the door open for too many options. If I had to guess I would say the answer is None of the above because giga fiber links are full duplex.

Yes, effectively token passing is a method of Media Access Control who excludes radically possibility of collisions, like I told also me I read that question and as I told I hope much to not find a question like that on the exam...

dtlokee

Ok

1. Fiber GigabitEthernet (like 1000baseSX) is Ethernet, there is no token passing involved. The only topology I know of that used fiber and token passing was FDDI.

2. The correct answer was posted, by default ALL Gigabit Ethernet (operating as 1000Mb/s including fiber) are point to point full duplex. Therefore in full duplex there is no possibility of collisions, the collision detection circuits of the interface are turned off and CSMA/CD is NOT used.

3. CSMA/CA is not used for Ethernet of any kind

The correct answer is LLC, it only relies on interface queuing to send the packets, no collision detection required.

rjbarlow

Dtlokee, not for a moment I want discuss Your duct answer,.... But my impression is that the question involved fddi and not gigabit ethernet, then i answered so and I am sure also that the right answer was token passing, only i don't remember where I read it... Just i find i will post the exact text of the question.

borumas

Alright, thanks for the input guys, I think that is a problem with allot of this stuff is that it can be interpreted to ask different things.

dtlokee

rjbarlow wrote:

Dtlokee, not for a moment I want discuss Your duct answer,....

huh? What does duct have to do with this?

rjbarlow wrote:

But my impression is that the question involved fddi and not gigabit ethernet, then i answered so and I am sure also that the right answer was token passing, only i don't remember where I read it... Just i find i will post the exact text of the question.

FDDI = 100Mb/s always was, always will. The question asked about gig fiber.

rjbarlow

dtlokee wrote:

rjbarlow wrote:

But my impression is that the question involved fddi and not gigabit ethernet, then i answered so and I am sure also that the right answer was token passing, only i don't remember where I read it... Just i find i will post the exact text of the question.

FDDI = 100Mb/s always was, always will. The question asked about gig fiber.

Well, all Your answer was permeated of learning. I read that question and i'm sure it was about fddi and not fiber gigabit ethernet, then the question was reported wrong, however I did not remember that fddi is at 100-200Mbs and do not allow speeds over these. Cheers