Cisco Support Community
cancel
Showing results for 
Search instead for 
Did you mean: 
cancel
Community Member

Packet explanation

Hi there,

ICND1 defined a packet is

A logical grouping of bytes that includes the network layer header and encapsulated data, but

specifically does not include any headers and trailers below the network layer.

I understand the 1th line, but the 2th line needs to be corrected ? doesn't it ?

becasue below the network layer the packet has to be fame after the data link header and the trailer are added.

Another Q

clocking

The process of supplying a signal over a cable, either on a separate pin on a serial cable or as

part of the signal transitions in the transmitted signal, so that the receiving device can keep

synchronization with the sending device

What does separate oin on a serial mean ?

thanks

1 ACCEPTED SOLUTION

Accepted Solutions
Hall of Fame Super Blue

Re: Packet explanation

Martin

A logical grouping of bytes that includes the network layer header and encapsulated data, but

specifically does not include any headers and trailers below the network layer.

I understand the 1th line, but the 2th line needs to be corrected ? doesn't it ?

It's basically a terminology issue. At the network layer you have packets and these would only have a L3 network layer header added to the actual data. However at the data link layer a further L2 header is added, whether it be ethernet, frame relay, ATM etc. When that further header has been added it is then called a frame and not a packet.

So you are right in that for the data to be actually transmitted a network layer header is not enough.

I guess you are studying the OSI model and they have strict definitions depending which layer you are at. That said a lot of people, me included, are not always so precise in their terminology and most people would understand whichever you used.

What does separate oin on a serial mean ?

In serial and ethernet cables there are a physical number of separate wires. These separate wires can be used for different things eg. transmitting and receiving data, flow control etc. The separate wires are referred to as pins and you often see pinout diagrams/descriptions which simply state which wires are used for which function.

Jon

9 REPLIES
Hall of Fame Super Blue

Re: Packet explanation

Martin

A logical grouping of bytes that includes the network layer header and encapsulated data, but

specifically does not include any headers and trailers below the network layer.

I understand the 1th line, but the 2th line needs to be corrected ? doesn't it ?

It's basically a terminology issue. At the network layer you have packets and these would only have a L3 network layer header added to the actual data. However at the data link layer a further L2 header is added, whether it be ethernet, frame relay, ATM etc. When that further header has been added it is then called a frame and not a packet.

So you are right in that for the data to be actually transmitted a network layer header is not enough.

I guess you are studying the OSI model and they have strict definitions depending which layer you are at. That said a lot of people, me included, are not always so precise in their terminology and most people would understand whichever you used.

What does separate oin on a serial mean ?

In serial and ethernet cables there are a physical number of separate wires. These separate wires can be used for different things eg. transmitting and receiving data, flow control etc. The separate wires are referred to as pins and you often see pinout diagrams/descriptions which simply state which wires are used for which function.

Jon

Community Member

Packet explanation

I think clocking is defined generally, It's not clear enough

As you said before, thay are not always so precise in their terminology

so what is your preferable reference for networking terms rather than Cisco glossary ?

Thanks jon

Hall of Fame Super Blue

Re: Packet explanation

Martin

I don't really have a reference guide for networking terms,, you just pick them up as you learn and from experience. Most terminology used by Cisco is used by other vendors as well so you won't go far wrong either way.

What you may find with any glossary is that it does not go into enough details, but then you just have to use the web or places like these forums if you want a more detailed explanation.

Jon

Community Member

Re: Packet explanation

Thanks Jon

Super Bronze

Re: Packet explanation

Disclaimer

The  Author of this posting offers the information contained within this  posting without consideration and with the reader's understanding that  there's no implied or expressed suitability or fitness for any purpose.  Information provided is for informational purposes only and should not  be construed as rendering professional advice of any kind. Usage of this  posting's information is solely at reader's own risk.

Liability Disclaimer

In  no event shall Author be liable for any damages whatsoever (including,  without limitation, damages for loss of use, data or profit) arising out  of the use or inability to use the posting's information even if Author  has been advised of the possibility of such damage.

Posting

Different parts of computer systems, including communications, to work optimally, often need to coordinate their time, or work using coordinated time and so "clocking" is the process of keeping those different parts' times coordinated.

In our world, if you wanted to take multiple buses/trains/flights to get from one place to another, you'll probably want to know their scheduled departure and arrival times.  Knowing that, you can plan your trip using the least amount of time.  For this to work well, though, you and all the buses/trains/flights need to agree to use same time from the same "clock" (in our world, it's based on UCT).  However, beyond agreeing to use the same "clock" time there's the issue of keeping everyone synchronized to it.

In the computer world, communications senders and receivers also need to coordinate using the same "clock" time.  Keeping synchronized to the same "clock" is "clocking".

As your OP noted "clocking" might be embedded in the data signal or it might be a separate signal.  If a separate signal, it's often on its own wire, and as wires often terminate in plugs, and those plugs have pins (or sockets), particular pins (and sockets) are dedicated to specific wires.  So, a certain plug's pin (and socket) might be assigned to a separate clock signal.

Community Member

Re: Packet explanation

Hi Jose,

Could you tell me what are the serial link plug's pin that assigned ta a separete clock signal ?

Thanks in advanced

Super Bronze

Re: Packet explanation

For what kind of plug?

Community Member

Re: Packet explanation

Serial cable

Super Bronze

Re: Packet explanation

Disclaimer

The  Author of this posting offers the information contained within this  posting without consideration and with the reader's understanding that  there's no implied or expressed suitability or fitness for any purpose.  Information provided is for informational purposes only and should not  be construed as rendering professional advice of any kind. Usage of this  posting's information is solely at reader's own risk.

Liability Disclaimer

In  no event shall Author be liable for any damages whatsoever (including,  without limitation, damages for loss of use, data or profit) arising out  of the use or inability to use the posting's information even if Author  has been advised of the possibility of such damage.

Posting

There are many kinds of serial cables, many different serial plugs.

Whatever you'll looking for, you should be able to search the Internet for pin outs.

633
Views
0
Helpful
9
Replies
CreatePlease to create content