HDLC/PPP vs Frame relay/ATM

PeradPerad Posts: 7Member ■□□□□□□□□□
I know that Frame Relay works on Packet Switched connections, ATM on cell switched connections, also ATM can carry Frame Relay across networks.

Where are HDLC and PPP applied?


  • mikej412mikej412 Posts: 10,090Member
    Perad wrote:
    Where are HDLC and PPP applied?
    Point to point serial connections like leased lines
    :mike: Cisco Certifications -- Collect the Entire Set!
  • PashPash Posts: 1,601Member ■■■■■□□□□□
    Also many ADSL ISP connections are now PPPoATM.
    DevOps Engineer and Security Champion. https://blog.pash.by - I am trying to find my writing style, so please bear with me.
  • malcyboodmalcybood Posts: 900Member ■■■□□□□□□□
    HDLC is the standard encapsulation for cisco routers serial connections and does not have any authentication. It is an ISO standard that you can not use with mixed vendors routers. You do not have to "configure it" on a router out of the box

    PPP is used for CHAP & PAP authentication on a leased line connection i.e. ADSL, ISDN

    PPP is applied to the router interface

    PPP requires a Username and password to be configured on each router of the 2 that are connecting to each other over the direct link.

    RouterA wants to connect to RouterB. You would configure RouterA in the following way and RouterB vice versa (with RouterA's username and password)

    RouterA#config t
    RouterA(config)#username RouterB password cisco
    RouterA(config)#int s0
    RouterA(config-if)#encapsulation ppp
    RouterA(config-if)#ppp authentication chap pap

    Don't confuse username with the router hostname. These are different!....If you're not clear you should read up on the Cisco website or the Sybex book gives a good explanation

    For PPP think authentication over leased lines.

    HDLC standard encapsulation on Cisco routers that is a vendor specific so therefore it's not the same on say a Juniper router as a Cisco. You can't mix and match different makes of routers using HDLC as they all have different versions of HDLC. To get them to connect you would configure PPP or another protocol such as frame relay etc.
  • optimusoptimus Posts: 183Member
    PPP does not require any authentication. CHAP or PAP is optional.
  • NightShade1NightShade1 Posts: 431Member
    Most important things i think of PPP are
    1-Is not propietary protocol which means that if you dont have all cisco routers then you will need this encapsulation
    if i got a cisco router and got another router non of cisco suppose i try to configure HDLC encapsulation on both routers, it will not work because HDLC is a cisco propietary encapsulation

    2-PPP can trasnport different routed protocol such as IP,IPX

    Now you see you apply PPP when this happens i mean what i said above...

    Now for Frame relay help us in 2 ways as far i see
    1- Help us to save money!
    Instead bying dedicated connection for each point to point connection, you can multiplex different logical connection in one physical connection

    2- It Help you to save Addresses
    Having point to multi point connection and it save address because all the participating subinterfaces will be in the same subnetwork

    Well i hope this helps you :)
    Product Manager - ArubaNetworks
    Alternetworks Corp
  • Chivalry1Chivalry1 Posts: 569Member
    Great Topic. These WAN Technologies can be a bit confusing. AD
    "The recipe for perpetual ignorance is: be satisfied with your opinions and
    content with your knowledge. " Elbert Hubbard (1856 - 1915)
  • Johnny 5Johnny 5 Posts: 24Member ■□□□□□□□□□
    Couple notes:

    1) HDLC is an ISO standard, so you'll see some non-Cisco routers out there that support it. Most just use PPP though.

    2) PPP does better error/loop detection. One major "gotcha" I found from using HDLC is it will still report the interface as Up/Up even when the telco is doing a loopback test. You can change this behavior with the command "down-when-looped"
  • hectorjhrdzhectorjhrdz Posts: 127Member
    mmm porbably more than one misunderstood the question....

    lol, mike just said the right thing.

    in most cases is used when branch offices want internet access (for example), so they need a leased line such an E1, T1 to get access to the ISP network an then to the internet.

    So they both need to configure a encapsulation for that p-to-p link, wich can be HDLC or PPP. they both also decide what encap to use depending on their needings.

    Also you have to think about the cost v.s. benefit of using a leased line for getting access to a FR network(think multilink capacity; international links) or to get access to an ISP only.

    Sometimes an ADSL access tech can replace so good another WAN protocol.

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