Editing Measuring network throughput (section)

===Other low-level protocols===

Dedicated point-to-point links are not the only option for many connections between systems. [[Frame Relay]], [[Asynchronous Transfer Mode|ATM]], and [[Multiprotocol Label Switching|MPLS]] based services can also be used. When calculating or estimating data throughputs, the details of the frame/cell/packet format and the technology's detailed implementation need to be understood.<ref>Lydia Parziale, D. T. (2006). TCP/IP TUTORIAL AND TECHNICAL OVERVIEW</ref>

====Frame Relay====

Frame Relay uses a modified HDLC format to define the frame format that carries data.
<ref>Comer, D. E. (2008). Computer Networks and Internets 5th Edition</ref>

====ATM====

[[Asynchronous Transfer Mode]] (ATM) uses a radically different method of carrying data. Rather than using variable length frames or packets, data is carried in fixed size cells. Each cell is 53 bytes long, with the first 5 bytes defined as the header, and the following 48 bytes as payload. [[Computer networking|Data networking]] commonly requires packets of data that are larger than 48 bytes, so there is a defined adaptation process that specifies how larger packets of data should be divided up in a standard manner to be carried by the smaller cells. This process varies according to the data carried, so in ATM nomenclature, there are different [[ATM Adaptation Layers]]. The process defined for most data is named ATM Adaptation Layer No. 5 or [[AAL5]].

Understanding throughput on ATM links requires a knowledge of which ATM adaptation layer has been used for the data being carried.<ref>Comer, D. E. (2008). Computer Networks and Internets 5th Edition</ref>

====MPLS====

Multiprotocol Label Switching (MPLS) adds a standard tag or header known as a 'label' to existing packets of data. In certain situations it is possible to use MPLS in a 'stacked' manner, so that labels are added to packets that have already been labelled. Connections between MPLS systems can also be 'native', with no underlying transport protocol, or MPLS labelled packets can be carried inside frame relay or HDLC packets as payloads. Correct throughput calculations need to take such configurations into account. For example, a data packet could have two MPLS labels attached via 'label-stacking', then be placed as payload inside an HDLC frame. This generates more overhead that has to be taken into account that a single MPLS label attached to a packet which is then sent 'natively', with no underlying protocol to a receiving system.<ref>Smith, S. (2003). Introductions To MPLS. CISCO</ref>