LES circuits have become increasingly common in recent years for providing high speed WAN links between two sites, usually either between two company offices or between a client site and an ISP PoP (Point of Presence), where it is used to provide Internet connectivity. The limiting factor is usually distance to the nearest PoP as the LES circuit cannot cover more than about 15km so they tend to be limited to city environments. It is based on fibre optic technology but the end connections are presented as standard RJ45 network ports, standard speeds are 10 or 100Mbps, so for practical purposes it is the same as a long CAT5 cable.

There are however a couple of things to look out for when setting up a LES circuit, and there is little documentation generally available:

Several telcos can provide LES circuits in the UK, who you get will usually depend on which has a suitablly equipped PoP nearby, but the basic equipment is the same. You should normally expect it to take at least 3 months to get your LES installed as it will require several engineer visits, they will require approx. 4U of rackspace for their termination equipment. Once installed you will have a new fibre connection coming into your rack and a couple of new boxes. For a straight site to site link they will leave it terminated on the LES box itself, you will have a single RJ45 socket ready to plug into. Should your LES be providing you with Internet bandwidth then your ISP will normally connect their own router to that socket and you can then connect your firewall to that router.

 The second scenario is easy to setup as it is in effect no different to connecting to a DSL router, and if you experience any problems you can expect some assistance from the ISP. The first scenario can be more complicated as you are pretty much left alone to figure it out yourself.

Although you could actually connect the LES direct to the LAN at each site and create one big LAN you will probably want to implement a router at one end. This will allow you to control the traffic over the LES and thus make the best use of the available bandwidth. A basic router such as a Cisco 800 series will be fine, and the configuration for routing between 2 sites/subnets is simple enough. You may want to consider using QoS if you are routing delay sensitive traffic such as VoIP over your link.

There is one big potential problem to be aware of though, and it usually goes like this; you have everything setup and routing fine but once you go live you discover the bandwidth is nothing like that advertised. On a LES100 you should be able to get 80+Mbps sustained transfer but you may find in reality its less than 10Mbps. The reason for this is that the LES is very sensitive to port duplex and speed settings, and if you leave the router port set to the default auto/auto then it will probably get it wrong. Your LES provider should give you documentation stating how the port is set, it will usually be full duplex/10 or 100. All you need to do is make sure your router port is manually set to the required setting and everything will magically speed up, although you may need to switch the router off for a couple of minutes first to give the LES time to resync.