This document discusses the use of Ethernet in optical fronthaul networks to support the deployment of white-box solutions in telecom network transformation. It covers digital radio over fiber (D-ROF) techniques like CPRI, OBSAI, and ORI that allow separating the baseband and radio units. The IEEE P1914.3 standard for radio over Ethernet is described, which enables transporting digitized radio signals over Ethernet. This paves the way for implementing white-box switches that support radio over Ethernet, providing cost savings and flexibility to mobile network operators.

1. Dhiman Deb Chowdhury
http://www.dhimanchowdhury.blogspot.com
Does support of Ethernet in Front-haul
Mobile Networks help increase
deployment of White-box in Telecom
transformation?

2. Copyrights, ©2017 Dhiman Deb Chowdhury: All Rights Reserved.
Contact: Dhiman Deb Chowdhury
Web: dhimanchowdhury.blogspot.com
Email: dhiman.chowdhury@yahoo.com

3. Contents
1.0 D-ROF (Digital Radio over Fiber) .............................................................................................................3
1.1 Common Public Radio Interface (CPRI)...............................................................................................4
1.2 Open Base Station Architecture Initiative (OBSAI) .............................................................................6
1.3 Open Radio Interface (ORI).................................................................................................................7
2.0 Radio over Ethernet (RoE).......................................................................................................................7
3.0 Ethernet at Optical Front haul Network: The case for White-box..........................................................9
4.0 Reference:...............................................................................................................................................9

4. Gothenburg is a port city nestled within the unique Kattegat (a sea area considered neither North Sea
nor the Baltic Sea, a contradiction in itself) nearly 290 miles northwest of Stockholm, capital of Sweden.
The days are gloomy here specifically in the fall season and in the winter, fortunate to have a glance of
sun if you are lucky yet the city has much to offer. Gothenburg’s panoramic beauty is certainly
something to behold. From its historic buildings to classic culinary, this largest port city of Nordic region
has something to offer for everyone. However, I am not here to indulge in her beauty rather in a quest
to learn about technological trend in optical networking and present whitebox open networking
solutions in telecom network transformation at the European Conference on Optical Communication
(ECOC 2017). I was quite amazed by noting the advances in photonic technologies, more importantly
available technologies for 200GbE to 600GbE transports and how optical networking is paving the way
for mobile networks to accommodate higher bandwidth. For mobile networks, optical networking now
starts at the cell tower and D-ROF (Digital RF over Fiber) techniques used for transport. In fact, wireless
and fiber convergence is something interesting and will shape the LTE-A, 5G transport networks, thanks
to the advances in D-ROF technologies.
1.0 D-ROF (Digital Radio over Fiber)
The D-ROF techniques allows a split architecture in which BBU (Baseband Unit) and Radio Remote Head
(RRH) can be separated contrary to traditional deployment where BS (Base Station) includes both RRU
(Radio Remote Unit) or RRH and BBU.
Figure 1. Traditional Cell tower with coaxial cabling system.
Now, RRH performing analog processing is mounted in the Cell tower due to smaller size and weight and
BBU performing baseband digital processing can be placed at the base of the tower or in a remote
location connected through fiber. D-ROF was developed around year 2000 and since then it has received
significant interest. Its counterpart A-ROF (Analog Radio over Fiber) did not get standardize due to

5. physical layer impairment over long distance (Haddad & Gagnaire, 2014). Radio signals are digitized at
RRH and then transmitted over fiber to BBU according to one of the protocol mechanisms listed below:
• CPRI (Common Public Radio Interface)
• OBSAI (Open Base Station Architecture Initiative)
• ORI (Open Radio Interface)
D-ROF creates a potential for high bandwidth support as needed for 5G despite some of the challenges
in standardization and connecting multi-vendor BBUs. Overall, it offers the promise of CAPEX and OPEX
reduction.
1.1 Common Public Radio Interface (CPRI)
The CPRI is an important element of mobile fronthaul networks. It connects RRH (Radio Remote Head)
and BBUs with fiber instead of traditional copper or coaxial cable. As of today, traditional co-axial based
cell towers are undergoing complete overhaul from bulky, expensive and power hungry cabling system
to fiber optic cabling for longer-reach distances and more capacity.
The CPRI initiative started in November, 2003 as a cooperation between five companies: Ericsson,
Huawei, NEC, Nortel Networks and Siemen’s mobile (CPRI, 2015). As of writing this article, only four
organization currently involved in this evolving specification: Ericsson, Huawei, NEC and Nokia (CPRI,
2015). The specification only defines the key criteria for interfacing transport, connectivity and control
communications between the BBU and RRU. It is one of the protocols for D-ROF (Frigerio, Lometti &
Sestito, 2017) and considered more efficient than OBSAI and ORI (Haddad & Gagnaire, 2014).
Figure 2. Common Public Radio Interface.
CPRI defines layer 1 and 2 protocols for user, control, synchronization and management. Layer 1 is
related to Time division multiplexing of data flows, low level signaling and electrical and optical

6. characteristics while layer 2 is about MAC (Media Access Control), Flow control and data protection of
the control/management flow. The protocol interface supports upto 24Gbps transfer rate and round
Trip Delay is limited to 5 µS (Tornatore, Chang & Ellinas, 2017). Additionally, Two different layer 2
protocols are supported in CRPI: a subset of HDLC & Ethernet.
User Plane
Control & Management
Plane
Sync
I/Q Data
Vendor
Specific
Ethernet HDLC
L1
inband
protocol
Time Division Multiplexing
Electrical Transmission Optical Transmission
Figure 3. Overview of CPRI protocol.
The eCPRI specification 1.0 claims it suitability for 5G mobile transmission and intended for packet based
fronthaul transport network like Ethernet and IP. The following diagrammatical representation depicts
eCRPI protocol stack over IP/Ethernet Networks.
User
Data
Connection
OAM
C
&
M
UDP
eCPRI Protocol Layer
Synchro-
nization
IP
IPSEC
Ethernet PHY
Ethernet OAM
Ethernet MAC [ VLAN Priority Tag/MAC Sec]
ICMP
Real-
Time
Control
Other
Services
SyncEPTP
SN
MP
UDP,
TCP,
SCTP
UDP
Figure 4. eCPRI Protcol stack overview (eCRPI, 2017).

7. The eCPRI is compatible to point-to-point and Point to multi-point legacy CRPI as well multipoint to
multipoint transport. More importantly, eCPRI enables the possibility of extending IP based Ethernet
transport network to fronthaul at the Cell tower.
1.2 Open Base Station Architecture Initiative (OBSAI)
Unlike CPRI, OBSAI is an initiative for open base station but also defines interface between RRH and
baseband unit. The OBSAI forum started by Hyundai, LG Electronics, Nokia, Samsung Electronics and ZTE
Corporation in 2002. Its goal is to create an open market for cellular base stations (BTS). There are four
components to OBSAI architecture: RRH block, Base Band block, Control & Clock block and transport
block.
Control & Clock Block
RP1
Figure 5. OBSAI Architecture depicting four blocks and interfaces.
The RP3-01 interface is similar to CPRI and supports bit rates from 768 Mbps to 6.1Gbps. Both CPRI and

8. OBSAI now supports Ethernet transport at RRH level. For example, Intel’s Altera® FPGA OBSAI reference
architecture supports Ethernet communication interface at RP3-01 (Altera, 2011).
1.3 Open Radio Interface (ORI)
Although both CPRI and OBSAI attempted to created open industry standard for D-ROF including
support for Ethernet communication interface, both are still considered “semi proprietary” in nature.
This led to creation of ORI standard by ETSI (European Telecommunication Standard Institute) in2010 to
provide more flexibility and choice of BBU and RRH suppliers. The ORI standard is the result of
requirements work undertaken by NGMN (Next-Generation Mobile Network) alliance.
User Plane
Control & Management
Plane
Sync
I/Q Data
Vendor
Specific
Ethernet HDLC
L1
inband
protocol
Time Division Multiplexing
Electrical Transmission Optical Transmission
Scope of ORI by ETSI
Figure 6. Open Radio Interface (ORI) standards that essential augments some parts of CPRI reference architecture.
The ORI standards actually augments some parts of CPRI reference architecture as shown in figure 6
(Tornatore, Chang & Ellinas, 2017).
2.0 Radio over Ethernet (RoE)
Parallel to the work of CPRI, OBSAI and ORI to support Ethernet, IEEE initiated P1914.3 project to
standardize Radio over Ethernet (RoE) encapsulation and mapping capabilities for the front haul
transport between RRH and BBU and applicable to RF interfaces like CPRI, OBSAI and ORI. The standard
specifies: a) encapsulation of digitized I/Q (In-phase Quadrature) payload, vendor specific and control
data/flow into Ethernet payload, b) header frame format both structure-aware and structure-agnostic
encapsulation of existing digitized radio transport formats, and c) A structure-aware mapper for
Common Public Radio Interface (CPRI) frames and payloads to/from Ethernet encapsulated frames
(IEEE, n.b.). Though IEEE P1914.3 standard is yet to be ratified, it creates possibility for wider adoption

9. due to strong industry support of IEEE standards for Ethernet. The typical packet format for RoE is
shown in figure below; Ethernet frame format remain unchanged.
Preamable SFD DA SA Ethtype Payload FCS IPG
RoE EthType
subType flowID length Orderinginfo RoE Payload
RoE Header
Figure 7. Proposed RoE Packet Format (IEEEP1914.3, 2017).
According to IEEE P1914.3 draft, various Ethernet based topologies will be supported at CPRI which
includes point-to-point, point-multi-point, multipoint-to-point, ring, tree and chain. Timing
synchronization is possible through protocol such as IEEE1588 (ptp).
Figure 8. IEEE P1914.3 implementation for C-RAN.
Interestingly, RoE allows encryption and decryption of links and flows. However, technique for this
implementation is not specified in the standard.

10. 3.0 Ethernet at Optical Front haul Network: The case for White-box
The advances in D-ROF technologies such CPRI, OBSAI and ORI in separating RRH and BBU to be
deployed over long distance is essentially creating possibilities for mobile operators to be benefits from
CAPEX and OPEX reduction. More importantly, IEEE P1914.3 standard will make it easier for industry
wide acceptance of fronthaul Ethernet network. As such, it is expected that with support from merchant
silicons white-box suppliers will support implementation of RoE in their switches. Moreover, some of the
whiteboxes, e.g. Agema’s AGC7648A already offers SyncE and 1588 support with advance buffering
technique that will be ideal in such deployment. In addition to significant cost savings offered by white-
box, this disaggregation model would pave the way for further development in multi-tenant services at
cell tower level. Similarly, the deployment will also benefit telecom infrastructure to support higher
bandwidth capabilities for 5G and improve service offerings.
4.0 Reference:
Altera, 2011. OBSAI Reference Design Datasheet. Available at
https://www.altera.com/en_US/pdfs/literature/ds/ds01026.pdf .
CPRI, 2015. CPRI Overview: Input requirement for CPRI. Available online at
http://www.ieee802.org/1/files/public/docs2015/liaison-CPRI_Tdoc_1124_presentation-0315.pdf .
eCPRI, 2017. eCRPI Specification V1.0. Ericsson AB, Huawei Technologies, NEC Corporation and Nokia.
Available online at http://www.cpri.info/spec.html .
Frigerio, S., Lometti, A. & Sestito, V., 2017. Overview of Standardization for D-RoF. In Fiber-Wireless
Convergence in Next-Generation Communication Networks pp 127-156. Springer.
Haddad, A. & Gagnaire, M., 2014. Radio over Fiber (ROF) for mobile backhauling: A technical and
economic comparison between Analog and Digitized ROF. ONDM, 2014. Stockholm, Sweden.
IEEEP1914.3, 2017. IEEE P1914.3™/D2.0: Draft Standard for Radio over Ethernet Encapsulations and
Mappings. Institute of Electrical and Electronics Engineers, Inc.
Tornatore, M., Chang, G., & Ellinas, G., 2017. Fiber-Wireless convergence in Next-Generation
Communication Networks. Springer.