Data Link Layer: some question.

[tsunamoro]

Hi all.

I have some doubt about how the DLL handles network topology, flow control and ordered delivery of frames (pag. 24-25 sixth edition).

My understanging is:

network topology - thinking of a switch, the port where a particular host (physical address) is connected, then the tool is filter table. This is also related to logical topology (for example, ports of various switches/routers "used" by the frames to go from a point to another one in the network).

flow control - CSMA/CD in Ethernet.

ordered delivery of frames - no idea (!). I mean, I know what means ordered delivery, but I can't imagine how it is obtained in the DLL, specifically in the Ethernet environment.


Another question. Written Lab 1.2 3rd description. What does it mean service access points? I wasn't able to answer the question...

Would you help me?

Thank you.

[tsunamoro]

Serching for more info, I found out (I hope so) the answer to the second question (and possibly to the third). The answer is LLC sublayer in Ethernet.
Another protocol that works in the DLL is PPP, and it can accomplish to both flow control and ordered delivery.

Could somebody (Todd ?) confirm what I'm saying?

Thank you.

[dbeare]

The main things to remember about layer 2, the Data Link Layer, is that its main concern is with frames, and we need to remember that frames contain hardware (MAC) addresses. At layer 2, there are no IP addresses, so as far as the network topology is concerned, we are looking at switches at layer 2, since they forward frames based on MAC addresses. You will learn more about this in later chapters. Other protocols that work at layer 2 are PPP, Frame Relay and HDLC. These you will look at much more in depth in chapter 14, so for now, just remember that they operate at this layer, and layer 1. For now, just remember what sort of traffic is handled at which layers of the model, and you will be fine. The specifics will be handled in later chapters. This chapter is mainly for the basics from what I can tell.

[sukarabi]

I had the same prob with Service Access Point (SAP) but because I read first 5th edition of Mr Lammle's book I was able to answer. But something I don't understand is why Mr Lammle gave a lot of explanations in his previous book about SAP and nothing in the last one. I'm wondering if we can have this style of question at exam.
If yes, it would be interesting to know what's missing in the book.

[lammle]

I took out unnecessary information, like detailed information about the LLC sublayer of the Data Link layer.

You have enough to learn already, you do need to study old information.
When we use Ethernet, you'd be hard pressed to find any frame type of Ethernet_II in use. Wireless may use SNAP and others, but again, frame types are not an objective in the CCNA exam.

Cheers!
Todd Lammle

[kesnet]

I took out unnecessary information, like detailed information about the LLC sublayer of the Data Link layer.

You have enough to learn already, you do need to study old information.
When we use Ethernet, you'd be hard pressed to find any frame type of Ethernet_II in use. Wireless may use SNAP and others, but again, frame types are not an objective in the CCNA exam.

Cheers!
Todd Lammle

I see ,too.
I come from china,but my En is very pool,so I read the ch of your CCNA's book(604-802),now.:D