Solved: WAN technologies confusion

a.azab · ‎06-02-2017

Hello Experts,

I am still new to WAN, where my expertise lies in LAN, IPS and FWs. I have been reading about WAn and got a bit confused.

1- For leased lines, we connect our router via a serial cable to a CSU/DSU, where it connects to the ISP/phone company. Inside the WAN cloud, do packets route using routers or switches?

2- Do we need Internet access for leased lines to connect two sites? If no, can we use leased line technology to connect to the Internet?

3- Nowadays, what is the physical cables that we use for leased lines?

4- Same as question 1 but for frame relay, do packets connect via routers inside the WAN cloud?

5- What if we need to connect two sites using leased lines that are in different countries. Do we have to pay for a dedicated paths?

6- If DSL is circuit switching technology (have your own path), how come this happen although the Internet is shared with other users around the globe?

7- In internet connection, do ISPs use Frame relay, leased lines and other WAN technologies to route the packets?

8- Finally, if leased lines are used to connect to the Internet, how come we use circuit switching to connect over a shared WAN infrastructure?

Note: pictures would be highly appreciated, as they say a picture is better than a thousand words.

Thanks!

Joseph W. Doherty · ‎06-02-2017

#1 Your data packets are converted, by a DSU/CSU to travel across an analog voice network, but most modern voice networks are digital. So your digital to analog is converted again to digital, but the latter doesn't "see" your original data packet. The voice carrier might be switch/routing your their traffic, but again, that has nothing to do with your switching/routing.

Since newer voice networks are digital newer hand offs to them are also digital.

#2 No, yes.

#3 On your side or the carrier side of demarc? For either all kinds of cable might be used, much depends on a physical media.

#4 Frame-relay is a digital L2 network. I don't recall what it used for the hand-off, but it shouldn't be a DSU/CSU. If also, as name implies switches frames, it doesn't "see" packets. (Much like a L2 LAN switch.)

#5 Normally yes, which is why LL can be so expensive. Your built you own dedicated analog circuit.

#6 Because like LL, it doesn't have to be end-to-end. DSL get you to the ISP. LLs can be just to a WAN cloud provider. For example, I've supported WANs where a site has a LL line to a frame-relay vendor, same vendor moves frame across their cloud (probably over MPLS), converts it to ATM, and you have another LL from vendor's ATM cloud to your site. I.e. you have a LL on each end that connects to the WAN cloud vendor, vs. have a LL between your sites. Often much, much less expensive than a LL end-to-end.

#7 Internet use IP. Large ISP might be running IP on top of MPLS. I.e. they might be doing both L3 routing and MPLS switching.

#8 You don't have to use LL to connect to Internet. There's also wireless and cable.

Not all depends on circuit switching, and that that currently exists if often logical circuit switching over a digital network of some kind. But remember telco infrastructures were originally designed for analog circuit switching. Today, telco will support prior circuit switching logically. (Much like we often support LAN logically using VLANs.)

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Joseph W. Doherty · ‎06-02-2017

#1 Your data packets are converted, by a DSU/CSU to travel across an analog voice network, but most modern voice networks are digital. So your digital to analog is converted again to digital, but the latter doesn't "see" your original data packet. The voice carrier might be switch/routing your their traffic, but again, that has nothing to do with your switching/routing.

Since newer voice networks are digital newer hand offs to them are also digital.

#2 No, yes.

#3 On your side or the carrier side of demarc? For either all kinds of cable might be used, much depends on a physical media.

#4 Frame-relay is a digital L2 network. I don't recall what it used for the hand-off, but it shouldn't be a DSU/CSU. If also, as name implies switches frames, it doesn't "see" packets. (Much like a L2 LAN switch.)

#5 Normally yes, which is why LL can be so expensive. Your built you own dedicated analog circuit.

#6 Because like LL, it doesn't have to be end-to-end. DSL get you to the ISP. LLs can be just to a WAN cloud provider. For example, I've supported WANs where a site has a LL line to a frame-relay vendor, same vendor moves frame across their cloud (probably over MPLS), converts it to ATM, and you have another LL from vendor's ATM cloud to your site. I.e. you have a LL on each end that connects to the WAN cloud vendor, vs. have a LL between your sites. Often much, much less expensive than a LL end-to-end.

#7 Internet use IP. Large ISP might be running IP on top of MPLS. I.e. they might be doing both L3 routing and MPLS switching.

#8 You don't have to use LL to connect to Internet. There's also wireless and cable.

Not all depends on circuit switching, and that that currently exists if often logical circuit switching over a digital network of some kind. But remember telco infrastructures were originally designed for analog circuit switching. Today, telco will support prior circuit switching logically. (Much like we often support LAN logically using VLANs.)