FAQ: Index

General (SDSL)

SDSL is the generic name for "Symmetrical" DSL (Digital Subscriber Line). Bulldog uses the latest ETSI and ITU standardised SDSL, more accurately called SHDSL. Equipment should therefore be compliant with ITU G.991.2 formally known as G.SHDSL. Unlike ADSL, SDSL requires a dedicated line that cannot be shared with a telephone service.

Bulldog SDSL is, an easy to install, modern alternative to a leased line. It can provide uncontended, leased line quality access and includes transit connection to the Internet. It is presently available throughout central London with a simple, flat rate structure. There is therefore no need to measure the distances to calculate price as with leased lines. Bulldog is unique in covering central London with a DSL network with full cross connect and remote line test capability and an underlying ATM network making sure your service is delivered with the highest quality and reliability. Bulldog, in conjunction with BT, can provide you with a new copper line over which to run your SDSL service or you may choose to transfer an existing phone or ADSL line over to us.

Actual throughput depends on what you're protocols you're using. For TCP/IP it is about 13% lower than the quoted speed. E.g. for 2 meg, the TCP rate is about 1.8 meg.

Bulldog's Central London SDSL is presented on a standard NTE5 with a BT phone socket. Therefore a standard modem cable is used. SDSL routers normally have an RJ11 SDSL socket just like a modem and indeed this is true of our Bulldog Shop supplied SDSL routers. Some other SDSL routers might use an RJ45 (same type as an Ethernet socket). So it is important to know what socket is used before you plan to install. Of course by buying a Bulldog managed installation service, there is no need to worry about this.

SDSL is targeted at businesses who use a separate phone line. SDSL is not designed to be shared with a phone line like ADSL is.

The two technologies are incompatible. You therefore need to make sure you use the right equipment. SDSL has the same upstream and downstream speeds up to 2 meg whereas ADSL has a faster downstream than upstream. ADSL can run up to 8 meg on very short copper lines or 6 meg is the practical limit.

The access routers used for both are similar, e.g. Cisco 1700 series. However, legacy leased lines up to 2 Mbps use a G.703/G704 transceiver but SDSL uses a G.991.2 annex B transceiver, so the equipment is different. SDSL provides you with an IP/Ethernet interface which can be a very cost-effective alternative.

A Virtual Private Network is a way of achieving private networking over the public Internet. It encrypts the data so that it cannot be intercepted and read by an unauthorised person on the Internet. The firewall behind the SDSL access router can provide private networking over SDSL.

ADSL is commonly used by the remote worker. They need to use an ADSL router with either:
VPN pass-through if using VPN client software on the PC
VPN client on the router if they do not wish to use PC based clients
Both client modes are supported by Bulldog. The head end at the corporate HQ should use Bulldog SDSL to supply the upstream bandwidth needed.