CPRI and Slicing the Network

The dark fibre used by CPRI connections is expensive to install, nor is it fully utilised by a CPRI connection. Some proposals were made to carry CPRI over WDM, enabling sharing of fibres between closely sited RRUs. However, the next major step in the evolution of fronthaul was to consider if the CPRI protocol could be transported across a shared network such as Ethernet.

The CPRI consortium created a new specification called eCPRI. They don’t actually specify what the “e” stands for, it could be for Ethernet (but it also works over IP), Evolved (but this was the term used to denote 4G over 3G) or Enhanced (which is my personal favourite). The eCPRI specification defines how to carry radio signals over a packet network. The underlying networks are not defined, but can include IP/UDP and/or Ethernet.

The IEEE are also in the process of creating an open standard for the same thing, designated IEEE1914. This is split into two parts, the radio over packet protocol (IEEE1914.4) and the requirements on the underlying transport network (IEEE1914.1).

The main feature of both of these is that the functions of the basestation are split into three parts – the CU (Centralized Unit), the DU (Distributed Unit) and the RRU. One reason for this is that carrying a radio signal across a packet network is very inefficient, especially for 5G where the data rates are very high. The RRU connection may require a data rate of 25Gb/s or higher. The DUs can be located out in the network close the to RRUs. The connection from the CU to DU can be lower bandwidth, because carrying the raw data is more efficient than the encoded radio signal. This connection is sometimes referred to as the “middlehaul”.

A second reason is that some functions are very latency sensitive, limiting the length of the connection to a few kms, as with the original CPRI interface. If those functions are located in the DU, the less latency sensitive portions of the basestation function can be located further back in the network. This last piece enables the transition from Centralized RAN to Cloud RAN – the CUs can be located anywhere in the network, not just in a localized “baseband hotel”.

Tim Frost
Strategic Technology Manager, Calnex Solutions.

Recent Blogs

Related Blogs

Four Boardroom Members

How to Optimise Your IT Network and Spend

Feb 06, 2019
Network emulation can be a key tool to overcome barriers in getting the most out of your…
4846 Read more

Responding to IT Network Issues

Jan 22, 2019
If simple remedial scripts are not enough to fix an IT network issue, a more…
5474 Read more

Keeping Audiences 'In the Moment'

Nov 16, 2018
Today’s broadcast audiences are seeking more. They want user defined, on demand content.…
1831 Read more

Archived Blogs

1626 More
1818 More

Timing not Telecoms

Nov 08, 2016
1216 More

5G Coming Soon

Aug 22, 2016
1225 More

What is 1588 PTP?

Aug 04, 2016
1637 More

5G on the Horizon

Aug 01, 2016
1250 More
1242 More

What is a PTP Clock?

Apr 09, 2016
1529 More

What is Time Error?

Oct 21, 2015
1241 More

LTE-A & VoLTE Rollout

Sep 22, 2015
1190 More

LTE Picks Up Speed

Aug 22, 2015
1170 More

What is the Time?

Aug 22, 2015
1194 More

Mobile and Sync

Aug 22, 2015
1166 More

What is SyncE?

Aug 22, 2015
2374 More
1301 More

Microwave Update

Aug 22, 2015
1266 More

Unravelling Standards

Aug 22, 2015
1245 More

Partial Progress?

Aug 22, 2015
1161 More

Interpreting ITU

Aug 22, 2015
1182 More

Confusion Rules!

Aug 22, 2015
1234 More

Basestations Need Sync

Aug 22, 2015
1227 More

ITSF 2015 Edinburgh

Aug 22, 2015
1173 More

India to Follow China?

Aug 07, 2015
1190 More
HOW CAN CALNEX HELP YOU FURTHER?

Click your area of interest below for more tutorials and real-world case studies.