Best Practices Guide for Cisco Network Converged Fronthaul Systems
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Best Practices Guide for Cisco Network Converged Fronthaul Systems
First Published: October 15, 2021
NOTE: This guide recommends best practices to deploy a Cisco Service Provider Packetized Converged Fronthaul system and is intended for an audience who is involved in the design or deployment of the Cisco NCS540-FH and Cisco N540-FH-AGG-SYS routers.
This guide is not intended to replace the Fronthaul configuration guide.
As the demand for Packet based Centralized RAN and Virtualized/Cloud RAN Architecture grows, migration to X-Haul (Fronthaul, Midhaul & Backhaul) Architecture is inevitable. Converged Packet-based Fronthaul extends to meet the needs of X-Haul for 4G and 5G Networks.
Market leader Cisco is not only helping provide secure, flexible, scalable, and proven solutions for Converged Fronthaul, but providing and recommending deployment options to optimize Converged Fronthaul implementations. Options that will improve user experience, provide better performance, reduce expenses and provide packet-based services to different generations of Mobile.
| Terms |
Recommendation |
| Capacity |
CPRI Rate-7 and Rate-8 for Structure Agnostic Tunnelling (Type-0) needs more than TenG core Capacity,25G and above are recommended. Bundling is not supported. |
| CPRI |
Common Public Radio Interference Apply values for CPRI Packet Length as recommended per rate for efficient bandwidth utilization, Custom header is based on availability of network clock. Set re-timer buffer to 0. CPRI Support for NCS540-FH is a bookended solution. |
| e-CPRI |
Enhanced-CPRI e-CPRI traffic is plain L2 Ethernet either Tagged or QnQ, only recommendation is to ensure the right tagging Filters and MTUs. |
| e-RAN |
Enterprise Radio Access Network Local Switching is deployed for Inter-DU communication across single hop e-RAN, EVPN is deployed for Multi Hop ERAN solution based on requirement. |
| EVPN |
Ethernet VPN EVPN Virtual Private Wire Service (VPWS) Single Homing is recommended with Pseudo wire class having a preferred path to disable fall-back. |
| GTP |
General Packet Radio Service (GPRS) Tunnelling Protocol GTP Load balancing mandates maximum of 3 MPLS Label Stack for Deep Lookup-Only for Midhaul. |
| L2VPN |
Layer 2 Virtual Private Network Though not recommended but if used needs to have Pseudo wire class for preferred path with fall-back disable |
| MTU |
Maximum Transmission Unit MTU of more than 9000 is recommended through the converged profile. |
| PM |
Performance Measurement The challenge of quickly updating the Dynamic Latency changes to IGP Database (Opaque LSA’s) is sorted by accelerating the advertisement of latency changes to IGP Database for Opaque LSAs |
| QoS |
Quality of Service Low-Delay Settings is recommended, Access RoE Traffic is default mapped to Traffic-Class 7, ensure explicit Traffic-Class 7 marking to the incoming core Labelled Traffic. |
| SR-TE |
Segment Routing-Traffic Engineering SR-TE policy without Flex-Algo is recommended to allow policy having constraint of both Affinity & bound Cumulative Latency. |
| Timing |
Centralized Clock is recommended. Converged 4G/5G Networks using Network Clock has to consider the Internal GNSS restrictions on NCS540-FH and plan PTP/Sync-E flow accordingly. |
Configuring CPRI
| Best Practice |
Example |
| Efficient throughput is achieved for CPRI Rate 3-5 with 8 Basic Frames. |
roe profile 108 packet-length 8 |
| Efficient throughput is achieved for CPRI Rate 6-8 with 4 Basic Frames. |
roe profile 108 packet-length 4 |
| Converged Packetized Fronthaul for 4G and 5G network, requires PTP (Network Clock) feed to 5G New Radio, henceforth a fronthaul network with PTP can have Sequence Number and Time Stamp both as Order Info for CPRI. |
roe profile 108 order-info SEQ-NUM-AND-TIMESTAMP |
| Retimer Buffer though available for Custom configuration is mandated to be 0 all the time for efficient de-jittering. |
roe profile 108 retimer-buf-size 0 |
Configuring Mapper and DeMapper Profiles
CPRI configurations need to match on Mapper and the De-Mapper to work, below is a graphical representation of which value to match and Mac values to reverse.
Configuring e-CPRI
| Best Practice |
Example |
| eCPRI 5G Traffic is Radio Agnostic to Front Haul Router and treated as an ethernet traffic either single tagged or QnQ. No special recommendation except for proper Tag Filtering and MTU (Covered in MTU Section). NOTE: eCPRI is not bookended and in this section only L2 Interface Configurations are considered which is a pre-requisite for EVPN covered in later sections. |
interface TenGigE0/0/0/14.207 l2transport encapsulation dot1q 207 rewrite ingress tag pop 1 symmetric |
Configuring L2VPN VPWS
| Best Practice |
Example |
| L2VPN(VPWS) is not recommended but if used for P2P connections either with 5G or 4G Interfaces, Fall-back option has to be disabled with pseudo wire-class and Access interface MTU needs to be 9600. Configurations provided here consider SR-TE policy as the preferred path and hence SR-TE (Covered in later section) is a pre-requisite here,100G-Link is just a variable name signifying the 100G core link which is used here. Controller Optics and CPRI controller configurations with roe profile attached is a prerequisite for CPRIoE. NOTE Pseudo wire Grouping, Flow Label are not recommended for Radio Deployments. |
4G CPRI interface CPRIoE0/0/0/6 mtu 9600 l2transport
l2vpn pw-class 100G-Link encapsulation mpls preferred-path sr-te policy srte_c_109_ep_10.255.255.4 fallback disable
xconnect group 108 p2p 108 interface CPRIoE0/0/0/6 neighbor ipv4 108.108.108.1 pw-id 108 pw-class 100G-Link
5G eCPRI interface TenGigE0/0/0/6 mtu 9600 l2transport
l2vpn pw-class 100G-Link encapsulation mpls preferred-path sr-te policy srte_c_109_ep_10.255.255.4 fallback disable
xconnect group 109 p2p 109 interface TenGigE0/0/0/6 neighbor ipv4 108.108.108.1 pw-id 109 pw-class 100G-Link |
Configuring EVPN VPWS
| Best Practice |
Example |
| EVPN VPWS is the recommendation for Converged Packet Based Fronthaul deployments, Fall-back option has to be disabled with pseudo wire-class and Access interface MTU needs to be 9600. Configurations provided here consider SR-TE policy as the preferred path and hence SR-TE (Covered in later section) is a pre-requisite here,100G-Link is just a variable name signifying the 100G core link which is used here. Controller Optics and CPRI controller configurations with roe profile attached is a prerequisite for CPRIoE. NOTE Redundancy in RAN (N+1) is recommended via NSO. |
Global Configurations for BGP router bgp 108 bgp router-id 10.255.255.5 address-family l2vpn evpn ! neighbor 10.255.255.4 remote-as 108 update-source Loopback0 address-family l2vpn evpn
Global Configurations for EVPN evpn evi 108 ! evpn evi 109 ! 4G CPRI interface CPRIoE0/0/0/6 mtu 9600 l2transport
l2vpn pw-class 100G-Link encapsulation mpls preferred-path sr-te policy srte_c_109_ep_10.255.255.4 fallback disable
xconnect group evpn-vpws108 p2p evpn108 interface CPRIoE0/0/0/6 neighbor evpn evi 108 service 108 pw-class 100G-Link ! 5G eCPRI interface TenGigE0/0/0/6 mtu 9600 l2transport
l2vpn pw-class 100G-Link encapsulation mpls preferred-path sr-te policy srte_c_109_ep_10.255.255.4 fallback disable
xconnect group evpn-vpws109 p2p evpn109 interface TenGigE0/0/0/6 neighbor evpn evi 109 service 109 pw-class 100G-Link ! |
Configuring QoS
Figure 1. Sample Topology
| Best Practice |
Example |
| For 4G Traffic i.e. CPRI, Low-Delay settings are default enabled on Access. 5G Traffic i.e. eCPRI needs explicit marking for Low-Delay settings. From an end-to-end network perspective, both CPRI and eCPRI needs to be marked with appropriate MPLS Exp value for prioritization in the core network. This remarking disturbs Low-Delay settings for CPRI and henceforth setting Low-Delay for both CPRI and eCPRI is a best practice. Low-Delay settings need to be enabled on egress towards the RRU and RIU as well. In short Low-Delay settings is required bi-directional for Radio traffic. Marking QoS-Group sets the required MPLS Exp Value, marking traffic-class 7 ensures Low-Delay Settings. |
Global Configurations for QoS class-map match-any exp5 match mpls experimental topmost 5 end-class-map ! policy-map Radio_Interface_Xhaul class class-default set traffic-class 7 set qos-group 5 ! end-policy-map ! policy-map Core_Interface_Xhaul class exp5 set traffic-class 7 ! end-policy-map ! 4G CPRI Access Interface interface CPRIoE0/0/0/0 mtu 9600 load-interval 30 ! l2transport service-policy input Radio_Interface_Xhaul ! 5G eCPRI interface TenGigE0/0/0/21 mtu 9600 service-policy input Radio_Interface_Xhaul
Xhaul Core Interfaces interface HundredGigE0/0/0/26 mtu 9600 service-policy input Core_Interface_Xhaul load-interval 30 ! |
Configuring SR-TE
Before you configure SR-TE, you must have already configured an IGP, either ISIS or OSPF with SR-MPLS and Distribute Link State enabled.
For latency-bound constraints in SR-TE, you must have dynamic link level Performance measurement. See the Configuring Performance Measurement section.
For more information, see the Segment Routing Configuration Guide for Cisco NCS 540 series Routers.
| Best Practice |
Example |
| SR-TE is best recommended for the Converged Fronthaul deployment due to the advantages of latency-based constraints. Flex-Algo does not support (&) operation of both Affinity and bound Cumulative latency. NOTE Latency constraint considered here is 150us, this can be customized. |
segment-routing traffic-eng interface TenGigE0/0/0/19 affinity name XENA ! policy XENA color 1008 end-point ipv4 10.255.255.5 candidate-paths preference 100 dynamic metric type igp ! ! constraints bounds cumulative type latency 150 ! ! affinity include-all name XENA ! ! ! affinity-map name XENA bit-position 3 ! |
Configuring Performance Measurement
| Best Practice |
Example |
| Latency Bound Traffic-Engineering with SR-TE is important for Converged Fronthaul deployment, Link level dynamic PM using TWAMP is enabled to achieve the same. Dynamic Latency changes to IGP Database (Opaque LSA’s) in real time is important to ensure stringent Latency budgets under all conditions. In order to achieve the same, accelerate the advertisement of latency changes to IGP Database for Opaque LSA’s. |
performance-measurement interface TenGigE0/0/0/15 delay-measurement ! delay-profile interfaces advertisement accelerated minimum-change 1 ! ! probe measurement-mode two-way protocol twamp-light ! ! |
| End to End transport delay measurement with Segment Routing as core can be achieved via SR-PM. SR-PM is Asymmetric 2-way Delay measurement. Use the show performance-measurement sr-policy brief command to display delay |
Segment-Routing Traffic-Eng policy SRPM binding-sid mpls 9002 color 9002 end-point ipv4 10.255.255.4 candidate-paths preference 100 explicit segment-list JB-BT-MT-TT-JT ! performance-measurement delay-measurement reverse-path label 9002 ! delay-profile name SRPM Global Configuration performance-measurement delay-profile sr-policy name SRPM probe measurement-mode two-way protocol twamp-light ! |
| For the CPRI delay measurement, use the show controllers cpRI 0/0/0/0 roe-stats command to display statistics. These statistics display one way delay measurement information that includes Packetizing Delay, Transport Delay and De-Jitter Buffer Delay. |
<truncated output> Packet Delay Variation : max/min/avg = 444 / 79 / 80
|
Configuring Timing
Figure 2. Sample Topology
For Standalone 4G Networks, SyncE can be retrieved from CPRI on the Proxy-Slave from REC (DU/BBU) but centralized clock is recommended.
Converged 4G/5G Networks using Network Clock has to consider the Internal GNSS restrictions on NCS540-FH.
In a 5G Network, NR needs a PTP Feed via the Fronthaul Router, EVPN endpoints on FH Router towards 5G BBU loops PTP packet to NR and hence has to be dropped by making the interface as a PTP client.
| Detail |
Example |
| T-GM: NCS540-FH does not support Internal GNSS, henceforth Back Haul CSR can be T-GM driving network clock to Front Haul Routers. Or, any other router supporting internal GNSS can be used. |
T-GM Global Configuration ptp clock domain 24 profile g.8275.1 clock-type T-GM timescale PTP time-source GPS clock-class 6 ! profile slave transport ethernet sync frequency 16 announce frequency 8 delay-request frequency 16 ! profile master multicast target-address ethernet 01-1B-19-00-00-00 transport ethernet port state master-only sync frequency 16 clock operation one-step announce frequency 8 delay-request frequency 16 ! physical-layer-frequency !
On the T-GM: gnss-receiver 0 location 0/RP0/CPU0 constellation gps cable-delay compensation 1230 frequency synchronization selection input wait-to-restore 0 time-of-day-priority 1 ! !
frequency synchronization |
| T-GM: Backhaul CSR router running internal GNSS is the Master providing clock to BBU. Centralized Clock to the entire RAN network is via this Backhaul CSR. |
T-GM TN Ports to Backhaul interface TenGigE0/0/0/22 description To_BBU(TN) mtu 9010 ptp profile master multicast target-address ethernet 01-1B-19-00-00-00 transport ethernet port state master-only sync frequency 16 local-priority 10 clock operation one-step announce frequency 8 delay-request frequency 16 ! frequency synchronization wait-to-restore 0 ! |
| T-GM: Centralized Clock to the entire RAN network is via this Backhaul CSR, here it serves as Master to the Fronthaul CSR. |
T-GM Ports to Fronthaul interface HundredGigE0/0/1/2 description To_FrontHaul_Router ptp profile master multicast target-address ethernet 01-1B-19-00-00-00 transport ethernet port state master-only sync frequency 16 local-priority 10 clock operation one-step announce frequency 8 delay-request frequency 16 ! frequency synchronization wait-to-restore 0 ! |
| T-BC (Proxy-Slave): NCS540-FH here is the Endpoint towards BBU for Converged 4G(CPRI) and 5G(e-CPRI) Fronthaul packet-based solution. 8275.1 T-BC profile is used here. This Endpoint is Proxy-Slave connecting to 4G BBU(LTE). In this converged profile, this same node is the endpoint for 5G BBU(NR-Cell). Note:8275.1 requires Sync-E to be locked as well for Phase Lock. |
T-BC Proxy-Slave Global ptp clock domain 24 profile g.8275.1 clock-type T-BC time-source PTP ! profile slave transport ethernet sync frequency 16 announce interval 8 delay-request frequency 16 ! profile master multicast target-address ethernet 01-1B-19-00-00-00 transport ethernet port state master-only sync frequency 16 clock operation one-step announce interval 8 delay-request frequency 16 ! physical-layer-frequency !
|
| T-BC (Proxy-Slave): As part of the Converged Fronthaul profile, EVPN for e-CPRI traffic is established between the endpoints.
This endpoint connecting to BBU receives PTP packets from BBU and transparently switches over EVPN to the remote end causing PTP failure.
Henceforth recommendation is to make this interface connected to BBU as PTP client to discard PTP frames. |
T-BC e-CPRI from 5G BBU (Discard PTP) interface TenGigE0/0/0/21 description Dummy-PTP-Client-eCPRI ptp profile master multicast target-address ethernet 01-1B-19-00-00-00 transport ethernet port state master-only sync frequency 16 local-priority 10 clock operation one-step announce frequency 8 delay-request frequency 16 ! frequency synchronization wait-to-restore 0 ! |
| T-BC(Proxy-Slave): For the 4G LTE traffic, Sync-E is derived from a common clock source(T-GM) driving BBU. For the 5G Traffic PTP is derived from a common clock source(T-GM) driving BBU. NOTE 8275.1 requires Sync-E to be locked as well for Phase Lock. |
T-BC Proxy-Slave connecting T-GM interface HundredGigE0/0/0/26 description From_T-GM ptp profile slave multicast target-address ethernet 01-1B-19-00-00-00 transport ethernet port state slave-only local-priority 10 ! frequency synchronization selection input priority 1 wait-to-restore 0 ssm disable quality receive exact itu-t option 1 PRC ! ! |
| T-BC(Proxy-Slave): This NCS540-FH has to relay PTP per hop to the downstream neighbours all the way up to the NCS540-FH(Proxy-Master) for the 5G NR. NOTE In this Design we are considering back-to-back nodes for simplicity, it can be more than a hop if within the latency budgets. |
T-BC Proxy-Slave Towards Proxy-Master interface HundredGigE0/0/0/27 description To_T-BC Felidae Proxy-Master ptp profile master multicast target-address ethernet 01-1B-19-00-00-00 transport ethernet port state master-only sync frequency 64 clock operation one-step announce frequency 16 delay-request frequency 64 ! frequency synchronization wait-to-restore 0 |
| T-BC(Proxy-Master): NCS540-FH here is the Endpoint towards RRH for Converged 4G(CPRI) and 5G(e-CPRI) Fronthaul packet-based solution. 8275.1 T-BC profile is used here. This Endpoint is Proxy-Master connecting to 4G LTE RRH. In this converged profile, this same node is the endpoint for 5G NR. NOTE 8275.1 requires Sync-E to be locked as well for Phase Lock. |
T-BC Proxy-Master Global Configuration ptp clock domain 24 profile g.8275.1 clock-type T-BC time-source PTP ! profile slave transport ethernet sync frequency 16 announce interval 8 delay-request frequency 16 ! profile master multicast target-address ethernet 01-1B-19-00-00-00 transport ethernet port state master-only sync frequency 16 clock operation one-step announce interval 8 delay-request frequency 16 ! physical-layer-frequency ! |
| T-BC(Proxy-Master): For the 4G LTE traffic, Sync-E is derived all the way from upstream nodes getting a common clock source from T-GM feeding BBU. For the 5G Traffic PTP is derived all the way from upstream nodes getting a common clock source from T-GM feeding BBU. NOTE 8275.1 requires Sync-E to be locked as well for Phase Lock |
T-BC Proxy-Master from Proxy-Slave interface HundredGigE0/0/0/27 description From_ T-BC Felidae Proxy-slave ptp profile slave multicast target-address ethernet 01-1B-19-00-00-00 transport ethernet port state slave-only local-priority 10 ! frequency synchronization selection input priority 1 wait-to-restore 0 ssm disable quality receive exact itu-t option 1 PRC ! ! |
| T-BC (Proxy-Master): For the 5G Traffic PTP needs to be delivered to 5G NR, This interface is already part of the EVPN Circuit for e-CPRI traffic and PTP profile for Master is executed. T-BC (Proxy-Master): For the 5G Traffic PTP needs to be delivered to 5G NR. This interface is already part of the EVPN Circuit for e-CPRI traffic and PTP profile for Master is executed. |
T-BC Proxy-Master to 5G NR interface TenGigE0/0/0/18 description <<< ECPRI-To-5G-NR >> ptp profile master multicast target-address ethernet 01-1B-19-00-00-00 transport ethernet port state master-only sync frequency 64 clock operation one-step announce frequency 16 delay-request frequency 64 ! frequency synchronization wait-to-restore 0 ! |
Configuring e-RAN
| Best Practice |
Example |
| Local Switching is deployed for Inter-DU communication across single hop e-RAN. EVPN is deployed for Multi Hop ERAN solution based on requirement
|
EVPN evpn evi 1000 advertise-mac ! l2vpn bridge group ERAN bridge-domain ERAN-A1 interface TenGigE0/0/0/16.1000 ! interface TenGigE0/0/0/18.1000 ! evi 1000 ! Local Switching l2vpn xconnect group 20 p2p 20 interface TenGigE0/0/0/16 interface TenGigE0/0/0/18 |
Configuring GTP for Midhaul
| Best Practice |
Example |
| Load balancing based on GTP in Labelled core network helps avoid polarization of traffic in the Midhaul GTP Load balancing mandates maximum of 3 MPLS Label Stack for Deep Lookup. |
hw-module profile load-balance algorithm gtp-mpls |
Configuring MTU
| Best Practice |
Example |
| For 5G eCPRI, TCP based OAM are exchanged on the wire between RU and BBU, so the minimum size required is 1522.This may increase with additional transport overheads. For 4G CPRI, increased number of basic Frames adds to the Frame Size. Henceforth as a best Practice MTU 9600 is recommended on Access and Core in the entire network. |
5G eCPRI Access Interface interface TenGigE0/0/0/17 mtu 9600 4G CPRI Access Interface interface CPRIoE0/0/0/0 mtu 9600 Core Interface. interface HundredGigE0/0/0/26 mtu 9600 |
Planning Capacity
| Best Practice |
Example |
| CPRI Rate 3-6 in Structure Agnostic Tunnelling mode with Ethernet and Transport overhead, requires less than 10G Bandwidth. But CPRI Rate 7 and 8 in Structure Agnostic Tunnelling mode with Ethernet and Transport overhead, requires more than 10G Bandwidth. Bundle is not supported/recommended for CPRI bandwidth Aggregation in Core Network. |
Individual CPRI Rate 3-6 in Type-0 10G Core Interface Individual CPRI Rate 7-8 in Type-0 25G/100G Core Interface
Individual CPRI Rate 3-7 in Type-1 10G Core Interface
Individual CPRI Rate 8 in Type-1 25G/100G Core Interface |
Frequently Asked Questions
1. CPRI is supported on Ports 0-11; Ports 8-11 are universal ports and can function as Ethernet and CPRI both.
2. CPRI Rate 3-8 are supported, however, 7A is not supported.
3. Two TSN ports are supported in 10G and 25G mode.
4. 8*1/10G, 4*10/25G and 2*100G Ethernet ports are supported.
| Question |
Answer |
| Do we support Type-1 in CPRI?
|
Yes, we support both Structure Agnostic Tunneling(Type-0) and Line Code Aware (Type-1) over Ethernet/IP as per CPRI Specifications 1914.1 and 1914.3. |
| Do we support Custom Header? |
Yes, if PTP is configured Time Stamping and Sequencing both (1914.3a) are supported. |
| Do we handle the PDV introduced due to packet based network in Fronthaul? |
Yes, NCS540-FH will do the de-jitter of data before doing bit stream on CPRI. |
| Does Inter-op work on NCS540-FH for CPRI? |
No, CPRI is a book-ended solution on NCS540-FH and does not support Inter-Op with different vendor FHR. |
| Is NCS540-FH Class-C compliant? |
Yes |
| Do we support GNSS Receiver on NCS540-FH? |
Internal GNSS is not supported, only external GNSS is supported. |
| Is EVPN Multi-Homing for CPRI supported? |
No |
| Is TSN supported on NCS540-FH? |
Yes. Supported from Cisco IOS XR 7.3.2 |
| Is Hot Standby Supported for CPRI? |
No |
| Is Structure Aware mode supported for CPRI? |
No |
| Is CPRI over SRv6 Supported? |
No |
| Is Auto-Negotiation for CPRI Supported? |
No |
| Will Load-Sharing over bundle for CPRI work? |
This will not work and is not recommended for Radio Deployments. |
| How do I achieve Radio Redundancy if Multi-Homing & Hot Standby is not supported? |
Through NSO |
| Do we support underrun and overrun counters for CPRI? |
No |
| Do we support Statistics for ROE packets? |
Rate is not supported in bits per second, packets per second is supported. |
| Do we support Alarm Statistics? |
No |
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