Segment Routing and 5G – How Segment routing helps achieving 5G Transport network requirements

Segment Routing and 5G | Lets discuss how Segment Routing helps achieving 5G Transport network requirements .

5G Transport requirements 

  • Service provider Transport Network requires to have unified underlay forwarding plane architecture without multiple stitching points across core, edge , aggregation and access network. It should be able to provide any-to-any connectivity and should offer flexible service placement due to RAN dis-aggregation.
  • Network also requires to provide overlay services such as L3VPN, L2VPN, Service aware traffic engineering and network Slicing. 3GPP defines three types of 5G services eMBB, uRLLC and mmTC. Out of three, uRLLC is delay sensitive service whereas other services are either bandwidth hungry or need dense reachability.This requires Network Slicing to achieve  differential services . Please refer to my other post to read more details about Network Slicing Here are the links for that,


  • Another requirement of 5G transport network is SDN with hybrid intelligence and Service orchestration with reduce touch points of configuration. For that what needed is centralized SDN controller to have overall topology of the network and link state database . And also, orchestration layer is needed for service provisioning .

How Segment Routing Helps 
  • Segment Routing offers unified forwarding plane with single protocol to achieve this functionality which is IGP (ISIS/OSPF). It provides same underlay protocol across core, aggregation , edge and access part of the networks which not only exchange IP Prefix information with neighbours but also, exchange Segment id  (SID or label) as well.
  • Segment Routing overlay services such as SRTE (segment Routing traffic engineering) provides flexible way to achieve traffic engineering without RSVP. It provides per customer or per service SR policies , which can be static (always on)  or on-demand (ODN for L3VPN) . It provides efficient use of resources by providing ODN services (On-demand Next-hop). 
  • 3GPP defines three types of 5G services eMBB, uRLLC and mmTC. Out of three, uRLLC is    delay sensitive service, so this can be easily  steered to path or portion of the network which    can provide minimum end-to-end latency  calculated with the help of  Flex-algo with metric as  delay, and rest of traffic  can be sent across path calculated based on default metric. Here is the for more details on Flex-algo.


  • Another area where SR helps is SDN . SR is the foundation of Software defined networking which offers hybrid intelligence , both in centralized SDN controller and underlay routing devices . Routing devices still be responsible to run control plane protocols like IGP/BGP . SDN controller with the help of BGP-LS will have all topology and link state information. Through BGP-LS, SDN controller will have information regarding state of each link across different IGP or BGP domains, it will have real time metric , latency and bandwidth information. Headend or source node (PCC) leverages SDN controller  (PCE) for providing low latency path or high bandwidth path using path computation protocol (PCEP).
  • Another important  aspect is convergence to fulfil 5G business SLAs for mission critical services where link/node failure protection using TI-LFA comes into the picture and helps to provide under 50ms convergence.
In summary, Segment Routing has all ingredients which fulfil  5G transport network requirements being it SDN framework, convergence or  Network Slicing requirement. I hope this article is useful.

4 Comments on “Segment Routing and 5G – How Segment routing helps achieving 5G Transport network requirements

  1. Maps the requirements to solution in plain English . Simple as you can ever get. Excellent article Dinesh.

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