It is also used for quality of service (QoS) and available bandwidth calculations at the interface level.
However, the bandwidth command deals with the bandwidth label used by routing protocols to determine the cost of going through this interface. The clock rate command deals with the actual physical clocking and speed and bit rate. It does make sense though in routers connected back to back where one of them has to provide clocking. In real life, typically the DCE device, a CSU/DSU, would provide clocking and so you would not need this in a router. In that case, the router side would have to provide clocking, and so you use a clock rate command to define clocking. The clock rate command would only apply if the cable connected to the router was a DCE or data communications equipment. You would have to go into global configuration mode and then enter interface configuration mode for the serial interface. Configuring a Serial InterfaceĪll of these options could use serial interfaces, so let us take a look at the configuration commands to set up and initialize a serial interface. Twenty-eight DS1s would be bundled to get a DS3 line, also referred to sometimes as T3 with speed and bandwidth of 43.736 Mb/s. So a bundle of 24 DS0s would be a DS1 sometimes used interchangeably with the term T1. For example, European standards would use different bandwidths and frame structures in their E1s. This is true in the United States, but different in other countries.
Well, a bundle of DS0s would become a DS1, which is the bandwidth associated with a T1 line (1.544 Mb/s).
This was also the bandwidth required for an uncompressed digitized phone call using pulse code modulation. TDM networks will define the underlying physical technologies, but they also define the naming conventions for bandwidth parameters, so DS0 was the building block with 64 Kb/s. Cost is high and pricing is based on bandwidth – the more bandwidth, the more expensive. We know what the disadvantages of these were and are. The underlying network is based on T-carrier or E-carrier technologies and the typical components were a DTE and a DCE in the form of CSU/DSU. These were dedicated point-to-point services even though they would use multiplexing technologies within the service provider network, but still point-to-point and dedicated private networks nonetheless. Other options that would eventually use a serial interface were lease lines using TDM (Time Division Multiplexing) technology. Jumping to 56 Kb/s through digital connections was a big boom.Įven though PSTN is still low cost, highly available and relatively simple to configure and maintain, the low data rates provided by PSTN probably make it a non-option for the broadband requirements and high speed connectivity of today’s networks. PSTN was also used as a data transport network back in the day when the upper limit of around 33 Kb/s was actually considered good. The most common type of circuit switch to WAN is the PSTN, also referred to as the plain old telephone service or POTS, typically used for voice transport. The different options would use different encapsulation methods and so you could use PPP encapsulation on top of an ISDN transport or HDLC and/or PPP in asynchronous serial options. Under those options, a dedicated path was established and maintained and in fact terminated through a carrier network for each communication session. Later options like ISDN would not only represent backup dial-on-demand type connectivity but also the main connectivity for central offices. Back in the day of asynchronous serial interfaces with low bandwidth, those were the options of choice for wide area connectivity. Circuit SwitchingĬircuit switching options used to rule the world of wide area networks.
The lesson ends with a brief description of other layer 2 options like frame relay and ATM. We will explain some examples like the public switched telephone network and common connectivity options like point-to-point connections, leased lines, and various encapsulation methods for that type of connectivity.