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18

The SNR margin is the Signal to Noise Ratio margin. Signal to Noise Ratio is the relation between the data signal level and the noise level. Even the most perfect cable absorbs some noise. This "noise" is electromagnetic interference produced by: other cables running near the cable. Faulty connectors. Motors or transformers near the cable. Radio systems. ...


13

Another reason may be that PPPoE is a tunnelling protocol which is useful for security and hiding an ISPs infrastructure. A tunnel is created between the end user CPE and ISP’s centralised BRAS. The network in-between is hidden from the user and the user cannot interact with other users directly over the ISP’s distribution network until it reaches the BRAS ...


12

The very first Ethernet standards were designed for using a single, shared coax wire. There's no benefit in making the connection asymmetric in any way. Additionally, network nodes are generally viewed as equal peers from the technology design perspective (in contrast to specific network design). There's simply no motive in making a general-purpose network ...


10

Is ADSL's UDP packet forwarding rate strictly linear to packet size? The answer is "no, because of the variable nature of ATM AAL5 padding used in ADSL lines". Since you aren't sure what encapsulation is used on the ADSL modem, I'll assume it's PPPoE, most providers use PPPoE for customer connections. I also assume that you've measured the full ...


10

A few reasons. Firstly that is just the way it has always been and ISPs are loath to change a working setup. Secondly it's possible to create translators between different types of PPP. Just because what your router sees is PPPoE doesn't mean the path all the way back to your ISP is a simple ethernet network. You might have a setup that is PPPoE from your ...


9

Q: Why is ethernet symmetric (when compared to ADSL's asymmetry). A: This is best explained by looking the technical reason for ADSL's asymmetry. Quoting directly from wikipedia: There are both technical and marketing reasons why ADSL is in many places the most common type offered to home users. On the technical side, there is likely to be more ...


8

Yes, the "E" in PPPoE stands for ethernet. The PPP stands for Point-to-Point Protocol. PPPoE and PPPoA are often used with DSL. PPP was the original protocol which was allowed by the DSL Forum. PPP provides more options and security for the ISP than does DHCP. For instance, DHCP offers no authentication, but that is built into of PPP. Juniper has a ...


8

Twisted pair cable used for the local loop has a velocity factor of about .58 - each km of cable takes ca. 6 µs to travel, adding ca. 12 µs to latency. The rest of the Internet probably uses fiber with a VF of .67, resulting in ca. 10 µs or .01 ms latency per km. ADSL has a basic encoding latency of around 10 ms. However, your ISP may likely interleave DSL ...


8

You can't really compare those two technologies. ISDN is a network protocol encompassing practically the whole OSI model from physical to application layer. xDSL is a family of physical-layer line protocols running between two interfaces (point-to-point). There are ADSL and VDSL variants that allow the co-existence with POT and ISDN on the same line using ...


6

There are many things that can cause low SNR. If you put aside natural reasons such as attenuation caused by distance, most of the time problem lies in bad infrastructure. Bad cables (damaged shielding and exposed wires), ingress noise, crosstalk, impedance mismatches, bad connectors and micro-reflections, bad splitters and filters and stuff like that. It ...


6

You need to check a few things; DSL is an aggregation technology which is normally on 'shared' media (you will be sharing with other, both the media to the point of presence and aggregation devices such as DSLAM, LNS so there is always potential for oversubscription. It will also depend on latency, you need to ask the carrier for latency numbers for the ...


6

PPP doesn't use MAC addresses or ARP the way ethernet does, so no, there will not be ARP in PPP, but there may be ARP in the ethernet which carries the PPP frames. You will not see anything ethernet-related in the PPP. What you are looking at is the PPP, not the ethernet. ARP (Address Resolution Protocol) is used by some layer-2 protocols, e.g. ethernet, to ...


6

If I have a switch or laptop running a PPPOE server, could I go from ethernet-to-modem then connect the modem's WAN port to another modem's WAN port and have it connect via PPPOE? No. A DSL modem is the CPE part of a DSL link. You can't connect two CPEs, only CPE to COE, e.g. a DSLAM. DSLAMs usually require substantial infrastructure, so a lab environment ...


5

The ITU define the standard for basic ADSL in G.922.1: https://www.itu.int/rec/T-REC-G.992.1/en There is also a USA version defined by ANSI, T1.413


5

There are a number of possibilities here, not limited to, but including: The CPE's CPU is maxing out. (CPE=Customer Premesis Device) Check the specifications for the router you are using to make sure it can support the level of traffic you're trying to push. Try and graph the CPE's CPU if you are unsure. Bufferbloat in your ISP If your ISP has configured ...


5

I'd remove the Ericsson box. It isn't a BRAS. From your diagram it looks like you'd be using it as a aggregation switch and the Linux PPP Server would be your BRAS. Personally, for lab purposes I'd also remove the Linux PPP Server and hook the DSLAM up to a Cisco 3825 or 7200 configured as a BRAS. If you really want the Linux element set up a FreeRADIUS ...


5

Fundamentally, loss of signal and/or increase in noise. If your SNR is always low and has always been low, it may simply be near the distance limit. Then again, it could be that it's always run over a lousy chunk of cable or bad splice. A few years back I had two ADSL circuits to campus, which took different routes - one significantly longer. Both cost the ...


5

The first diagram will not work, and in fact may result in damage to your router. The AUX port is a regular RS232 serial port, which is completely incompatible with ADSL. Don't do it. The second diagram should work, provided your D-Link modem can operate in bridged mode.


5

What is Local Loop? The portion of the telephone system that connects your home or office to the nearest central office (CO) of your local telco. The wiring used in the local loop is usually unshielded twisted-pair (UTP) cabling, the transmission method is analog transmission, and the maximum distance from the telco’s CO to the subscriber’s customer ...


5

Ethernet is a local area network technology, and it was designed with no assumption that traffic will be higher in one direction than the other. It was developed long before the web or Internet was available.


5

The cabling for ADSL uses telephone grade cabling and upstream and downstream traffic share the same copper pair. As there is limited bandwidth, the designers chose to give the downstream more capacity to make more efficient use of the bandwidth, something that fits the usage patterns of home users. ADSL was designed for a specific use case – to connect ...


5

According to the German Wikipedia the bit rates used in the time when ADSL was invented was the reason: At that time the backbones of the telephone and internet providers operated at 1-40 MBit/s while today rates above 10 GBit/s are used. At 2 MBit/s a packet of 1000 bytes length would take 4ms time for transmission; at 1 MBit/s a packet of 1500 bytes ...


5

They are just all mixed together. No, they're not. Each pair must be kept together at all times; if you separate or recombine the single wires crosstalk goes through the roof and all is lost. Depending on how the trunk is actually deployed, crosstalk might be a non-issue. Vectoring is required when numerous links run in parallel for some distance - looking ...


4

Except the 1750 only has one fastethernet port. A WIC-1ENET is 10m, WIC-4ESW a 4 port switch... but they both live on the WIC bus that'll top out about 6-8m. Depending on your DSL speed, this may not be a problem. I use a WIC-1ADSL (and WIC-4ESW) in a 1720, but the DSL line is 6m anyway. (and neither the 1720 nor 1750 support dot1q; that's a feature of ...


4

The Ethernet connections are full duplex, and in this sense there shouldn't be usually problem on a path from end user to switch, and in most of the time, from switch to ADSL router. However, depending on your end user traffic patterns (applications, time, and so on), the bandwidth available on both upstream and downstream of your ADSL service may be ...


4

I think you are confused with the terms Point to Point and TR-069 here. An ISP normally uses IPOE/PPPOE/PPPOA for establishing the connectivity between CPE(Modem/Gateway) and their BRAS. They also use their own radius server to authenticate the PPP connection for obvious reasons. TR-069 is a mechanism to provision a Gateway/Modem with the respective plan(...


4

The particular device you have listed is required to be used as a pair. This is for someone who want to extend a network across voice cabling, or for a small ISP to use to connect to customers. It doesn't work as a general replacement for a DSL modem. This is explained in the device description (my emphasis): The VC-231 provides CPE and CO mode for ...


4

The DSL line runs for hundreds or even thousands of meters on plain telephone cable (Cat-3ish). A few meters of Cat-6 will change nothing to improve signal integrity. Just use any pair. Don't interconnect pairs. Note that your middle drawing will degrade the signal significantly due to not using the twisted pairs. The bottom drawing improves nothing but ...


3

I don't know where you are based, but I'm in the UK. Here ADSL is "contended" in other words you are potentially sharing your connection with a number of other users this can hammer performance at peak times http://en.wikipedia.org/wiki/Contention_ratio A leased line isn't shared (1:1 contention ratio) so you get all the bandwidth all the time so can be ...


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