I thought I had a fairly good grasp on TCP/IP and OSI concepts but taking the practice test I got the following question wrong and am rather confused and I definitely dont want to make a similar (and costly) mistake in the exam so I'm hoping someone can straighten me out.
29. Which three statements about TCP are accurate? (Choose three.)
TCP operates at Layer 3 of the TCP/IP stack.
TCP is a connection-oriented protocol.
TCP provides no error checking.
TCP packets are numbered and sequenced so that the destination can reorder packets and determine if a packet is missing.
TCP provides no recovery service.
Upon receipt of one or more TCP packets, the receiver returns an acknowledgement to the sender indicating that it received the packets.
The correct answers are in bold. Now perhaps they felt the other answers may be simply "better" but that seems very relative to me and my answer was very Black and White. "TCP and UDP operate at L3 of the TCP model."
have I been staring at my computer screen too long (13+ hours) and I am overlooking something obvious? i expected the exam to be tricky but not semantic chicanery. im taking the test this week and my confidence has been somewhat shaken.
thanks for any help!
in the OSI model TCP and UDP are both Transport layer protocols i.e. Layer 4
Layer 3 is the network layer where IP operates.
TCP and UDP both operate at Transport (L-4) of OSI.
and they operate at L-3 of Tcp/IP Stack.
TCP/IP Layers are
Application, Transport, Internetwork And Network Interface Layer
But I have also encountered some literature that states that TCP/IP has 5 layers:
Application, Transport, Internet , Data Link and Physical
So some combine Data Link and Physical into single layer Network Interface Layer..
I think you also faced the same issue..
I think we should trust the following link by Cisco (4 LAYERS of TCP/IP):
Here is what microsoft thinks (Five Layers of TCP/IP):
Look at the following links:
Microsoft says in this link that TCP/IP has Five Layers:
Cisco says in this link that TCP/IP has Four Layers:
So according to cisco, TCP,UDP operate at L-3 of TCP/IP Stack
But according to microsoft, TCP,UDP opearte at L-4 of TCP/IP Stack
Perhaps this question contains an error... I don't think Cisco deliberately tries to trick you in this way. I think the first statement in the choices is not meant to say TCP/IP stack and should say OSI model.
If ambiguity like this did happen in the actual exam you'd certainly want to make a note and then comment on it at the opportunity you're given at the end of the test.
thanks all.. you reiterated what i believed i knew... just wanted to make sure im not losing it in the 11th hour.. oh.. by the way what is this "microsoft" you speak of and why would they consider themselves justified of contradicting Cisco re: TCP/IP and OSI models... ?
any one else (cough moderators? cough) possibly have any feedback on whether this type of thing is to be expected or might merit revising module 1 of the practice exam available on this very website?
In case you have not heard this before.. remember..
All People Seem To Need Data Processing
Now.. Here is a good question! At what layer of the OSI model do collisions occur?
Since actual data ( in the form of electrical, optical or radio wave signals) is traversed only on the PHYSICAL Layer. so I guess collisions occur only at Physical Layer of OSI.
However it is the function of upper layers to detect the occurence of collisions and take appropriate measure by using methods like CSMA/CD, CSMA/CA or RTS/CTS or TCP ACKnowledgement system etc..
But look at the very next question
Q: Which characteristic is similar between TCP and UDP?
A: Operates at Layer 4 (transport layer) of the OSI model and the TCP/IP stack.
So Cisco is definitely saying TCP and UPD are Layer 4 no matter what. Which makes no sense to me.
TCP and UDP are both a Layer 4 protocol, IP is Layer 3.
UDP basically unreliable transport and less overhead. TCP has reliable transport and more overhead UDP is choosen when transport doesn not need Error Control like with Voice and Streaming Video.
So Layer 3 IP is using TCP/UDP to get data to the correct application by the means of port numbers.
Ok. That makes sense in the OSI model, but does not in the TCP/IP Stack. If you count up 3 layers, you have 1. Network Interface, 2. Internet, 3. Transport, and Transport = TCP. Yet this statement is not accurate? "TCP operates at Layer 3 of the TCP/IP stack". It is unnecessarily contradictory.
Yes, that is quite confusing, but looking at the TCP/IP a.k.a DOD model, IP is not at layer 3 but in Layer 2. So eventually IP (Internet) needs to go up 1 layer to ask TCP for transportation.