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QoS General Overview

Quality of Service (QoS) is a data network solution that prioritises network traffic, to ensure that key traffic has precedence over less important traffic during times of congestion.

QoS on N3

The N3 Network has a 6 layer QoS (Quality of Service) scheme. The diagram below shows the set-up. The grey pipe is the overall bandwidth available for a given section of the network. Each QoS class of traffic has a priority and a contracted bandwidth - a percentage of the overall bandwidth (data rate), shown by the smaller coloured pipes. When the network or parts of it are congested - operating close to or at maximum bandwidth - QoS decides how traffic is handled.

 Diagram of QoS 

The layers are often known as QoS classes and they're designed to cater for the wide variety of traffic types found on a network such as N3, where they're used as follows:

EF - VoIP Telephony
The highest priority class - provides a (normally) small amount of dedicated bandwidth with an assured performance for telephony.

AF1 - Bulk Data Transfer
Used for applications that mainly move large volumes of data or data that is not ‘real time' critical. Examples include:

  • PACS
  • NHSmail
  • Overnight server backups to data centres

AF2 - Community Applications
Used within a local or regional NHS natural community for transactional (interactive) applications. Examples include:

  • Locally hosted GP Systems
  • SBS Finance System (Shared Business Services)
  • IPSEC (N3 VPN) local site to local site

AF3 - National Applications
Used for strategically significant transactional (interactive) applications. Examples include:

  • NCRS (National Care Record Service) to and from the BT NASP data centre, including, but not limited to:
    • SSB (Spine Security Broker)
    • IA (Identity Agent)
    • PSIS (Personal Spine Information Service)
    • EBS (Electronic Booking Service) a.k.a. Choose and Book
  • LSP CRS (Care Record Service applications offered by each LSP) including, but not limited to:
    • PAS
    • GP EPR
    • Clinical Systems
    • Emergency bundles
    • RIS
    • https
    • Ad-Hoc image requests
    • ESR (Electronic Staff Record)
    • Remotely hosted GP Systems

AF4 - Media Streaming (Multimedia + VoIP signalling)
Used for e.g. video-conferencing traffic.

DE - Default (all other traffic not assigned to a QoS Layer)
The remainder of traffic not assigned to any QoS class and thus the lowest priority traffic. Internet Gateway traffic is carried as DE across the N3 network.

Optimising QoS

QoS manages available bandwidth by prioritising certain traffic over other traffic. the Health and Social Care Information Centre sets the overall QoS policies applied to different parts of the N3 network. There is an annual ‘QoS Refresh' programme, where the Health and Social Care Information Centre work with N3SP to ensure the QoS policies remain optimal for NHS clinical and business operations.