Confused abt different WAN technologies..

Unanswered Question
Mar 1st, 2007

Hi everyone,

this is my first question on the forum.. so pls pardon me for asking silly stuff..

I am preparing for my CCNA and i am confused abt different WAN technologies.. if i'm not wrong then PPP, Frame Relay, ATM, ISDN etc are different WAN technologies.. right?? now while i was reading the chapter on PPP, it also talks abt HDLC encaptulation. then what is it? why it is used??

Is it an alternative to PPP (Point-to-Point) WAN connection?? some of you may already be laughing at my ignorance. but u see, i dont want to be laughed at all the time.

In an ideal scenario when will u be using PPP and when HDLC?? and for that matter other WAN technologies like Frame Relay, ISDN etc.. there is just so much to read and understand..

Also if anyone could pls suggest the best sources where i can practice the configuration of router and switches as i dont have any necessary equipments at home? any online simulation or something guys?? thanks a lot..

Sorry for the long question.. i hope i made myself understood there..

Thanks for the reply..

I have this problem too.
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scottmac Thu, 03/01/2007 - 19:40

To put things in context, there are many full, large books written about any one of the technologies you've listed.

In fairly basic, generic descriptions:

All of the technologies you've listed are considered WAN technologies.

HDLC is the default for Cisco Sync serial. It's Cisco proprietary, and it's used for point-to-point links (like dedicated leased lines, like a T1/DS1)

PPP is used over point-to-point circuits for interoperability with other vendor's serial links (like Cisco <--> Nortel {Juniper, Adtran, etc}. PPP can also be used for dial-up, or as a transport for ISDN circuit-switches links. PPP can join multiple channels to make one logical, larger chunk of bandwidth (Multi-Link PPP ...MLPPP)

ISDN is more of an infrastructure technology (like a T1/DS1 would be for data). The two most common forms (in North America) are BRI (Basic Rate) (two bearer channels, one delta channel, 2B+D, 128/144Kbps) ... a PRI (Primary Rate) is 23 Bearer chanels, one Delta channel, 23B+D, ~1.5Mbps, but usually "channelized" ... each B channel is 56 or 64K and carries one voice call. PRIs aren't usually used to carry data on aggregated bandwidth (1.5M) ... it usually carries data on each channel. MLPPP can also be used to create a link of greater than 64Kbps with multiple channels of the PRI.

Frame-Relay permits many endpoints (locations) to share a common WAN fabric. Because many customers are served by the same WAN "cloud," the carrier saves money in infrastructure ... and that is passsed on to the consumer (FR is generally less expensive to implement than a full mesh of point-to-point links).

Each location gets one physical connection (like a T1/DS1), but each physical connection can carry multiple logical ("Virtual") circuits ... in the form of a "Permenant Virtual Circuit." Each PVC usually connects to different far-end endpoints (and / or the Internet). SO, instead of having 10 Point-to-Point dedicated lines (each to a different location), with frame relay, there's a single physical connection with ten PVCs (each connected "through the cloud" to the other locations). Each PVC gets a label, called a Data Link Circuit Identifier (DLCI) so the local router can figure out which DLCI to put the data on to get to the other locations. DLCIs are usually mapped to an IP address / subnet.

ATM was developed to be a Multi-Service, Multi-protocol transport. Is operates in a switched cloud, like Frame-Relay (with the same advantages), but ATM uses very small frames (called "Cells", each are fixed-size of 53 bytes long ... 5 Header bytes, 48 payload bytes)

The smaller frame size gives each frame/cell the same transmission characteristics, so it's easy to switch and get through the cloud.

ATM was designed to offer "quality of service" (QOS) from end-to-end through a shared architecture.

Here's a link to Cisco's Internetworking Guide. This is an online (free) version of a very large book ($$$). IT is excellent at covering all of the LAN/WAN technologies.

http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/index.htm

Hope this helps, welcome to NetPro!

Good Luck in your studies.

Scott

kmerchant Thu, 03/01/2007 - 19:51

Thanks a lot for such a detailed answer scott.. my basic confusion was whether HDLC is a WAN technology used independently or whether it is an encaptulation method used in conjunction with one of the WAN technologies (i.e. PPP, frame relay etc.)

At least one thing is clear.. it is cisco proprietry.. but my original question remains -- is it an encaptulation technique or a WAN technology??

and thanks for the link, i'm going thru it at the moment.. looks like a huge collection of wealth of info... thanks for that..

and scott, could u also pls suggest any simulation program to practice for CCNA labs as i'm struggling find one??

thanks once again.. take care..

avillalva Thu, 03/01/2007 - 22:36

Hi,

I think I may be able to help...

Both PPP and HDLC are layer 2 protocols that are used to establish a direct connection between 2 nodes.

ISDN, Frame-relay, ATM etc. are types of packet (or circuit) switching technlogies. They have their own signalling and their own methods of getting packets from A to B.

You can, and do, for example run PPP over ISDN. Or HDLC over ISDN. These days, PPPoE (That is PPP over Ethernet) is popular with DSL broadband solutions.

PPP is not required over Frame relay because frame creates "frame maps" which in a broader sense perform the function that ppp would otherwise be used for.

Hope that helped,

Andres

kmerchant Thu, 03/01/2007 - 22:53

Andres, you pretty much answered what i wanted to know.. thanks a lot mate.. as u said both PPP and HDLC are yer 2 protocols that are used to establish a direct connection between 2 nodes. does that mean their whole and sole use is to just establish the connection?? and if so then i assume we may be doing that on some of the WAN technologies like ISDN.. so in essence PPP over ISDN... and what abt data transfer?? that's taken care by WAN technologies like ISDN, fram relay.. is it??

And according to Scott, HDLC is cisco propritery protocol so i believe u can use it only when u have two or more cisco devices wanting to communcate with each other.

I have one more question to ask if i may. u said ISDN, frame relay are types of packet (or circuit) switching technlogies. They have their own signalling and their own methods of getting packets from A to B. Does that mean they can establish direct connection between A and B on their own without the need of PPP or HDLC?? If yes, then why would we have a scenario like PPP over ISDN or something like that?? i am being very specific here and pestering all of u because of my extremely poor understanding..

thanks for all the reply.. take care..

- Kervin

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