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

Six New Clocks for…

Jan 17, 2019
1061 More
Ultima Thule

New Year, New…

Jan 07, 2019
446 More

A Better Way to…

Dec 18, 2018
1446 More

Large USA Bank…

Nov 29, 2018
915 More

Low Risk and High…

Nov 06, 2018
728 More

What's Coming in…

Oct 17, 2018
468 More

What’s All This…

Oct 16, 2018
903 More

Latency in a Data…

Oct 03, 2018
2211 More

Testing Sync in…

Aug 14, 2018
633 More

Mobile Backhaul…

Aug 06, 2018
547 More

Related Blogs

banana skin

Will SD-WAN really be the savior?

Mar 13, 2019
The only way to prove it is to get validation on how it will perform against your needs…
836 Read more
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…
1676 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…
3063 Read more

Archived Blogs

Timing not Telecoms

Nov 08, 2016
385 More

5G Coming Soon

Aug 22, 2016
388 More

What is 1588 PTP?

Aug 04, 2016
483 More

5G on the Horizon

Aug 01, 2016
393 More
425 More

What is a PTP Clock?

Apr 09, 2016
488 More

What is Time Error?

Oct 21, 2015
405 More

LTE-A & VoLTE Rollout

Sep 22, 2015
381 More

LTE Picks Up Speed

Aug 22, 2015
380 More

What is the Time?

Aug 22, 2015
382 More

Mobile and Sync

Aug 22, 2015
373 More

What is SyncE?

Aug 22, 2015
571 More
416 More

Microwave Update

Aug 22, 2015
417 More

Unravelling Standards

Aug 22, 2015
410 More

Partial Progress?

Aug 22, 2015
386 More

Interpreting ITU

Aug 22, 2015
382 More

Confusion Rules!

Aug 22, 2015
381 More

Basestations Need Sync

Aug 22, 2015
399 More

ITSF 2015 Edinburgh

Aug 22, 2015
378 More

India to Follow China?

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

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