Maritime Monday: A Question of Time
Guest Blogger: Will Kraus, Director, Maritime Business & Product Management
Frequently, maritime service providers will talk about bandwidth – bigger bandwidth equals a better user experience. Whilst some of this is true, latency can have a more dramatic effect upon the perception of how fast a network connection actually is. You may have experienced webpages loading slowly on a public Wi-Fi network, despite your laptop/phone reporting that the Wi-Fi link is fast – this is a similar effect to a high latency connection. Crew members on a ship often complain about the Internet speed, with both over-use and high latency causing frustration. Over-use of a satellite link can be managed, but the physics of transmitting a signal from a vessel 36,000km cannot be overcome. Remember, captain, ‘Ye cannae change the laws of physics”!
Latency describes the amount of time it takes for a data packet to be transmitted and returned back to its source. The total time for the round trip is known as latency and is normally expressed in milliseconds (ms). For example, your LTE mobile phone will have a latency of about 20ms compared against a geosynchronous L-band satellite with 1,100ms. A maritime VSAT service would typically experience around 700ms latency. Higher latency figures can play havoc with applications that communicate over networks. If an application is not optimised for satellite communications, it can lead to retransmission of data packets. This in turn makes data communications less efficient, perhaps increasing costs in particular on volume-based plans (e.g. 1GB per month). Additionally, some network applications require the link’s latency to be under a specified time.
Optimisation of the ship’s Wide Area Network (WAN) satellite links can both improve the user experience of browsing and provide management of data traffic passing over the link. For example, classifying outbound network traffic with a priority allows the satellite modem to determine which data should be sent first. This allows for time critical applications and services to pass over the satellite link first, with lower priority traffic such as crew Internet browsing waiting its turn. Restricting which traffic is allowed to pass over the satellite link is also recommended, as operating system updates can be very large. Many service providers have smart boxes that can automatically perform these tasks, and allow only desired applications and services onto the WAN link.
Working hand in hand with our Service Provider (SP) network, Iridium ensures that the Iridium CertusSM service is always optimised. Our Low-Earth-Orbit (LEO) network’s latency is greatly reduced compared to Geostationary (GEO) satellite constellations. When combined with our inter-satellite links, the net effect is lower latency with less packet retransmission, making Iridium® more attractive for applications with critical timing requirements.
Learn more about what Iridium Certus can offer you at www.IridiumCertus.com.
