Tag: LTE

Breaking the barrier to Service

Today, most businesses don’t need any convincing argument about how digital transformation can enhance their agility. The pressing question is how to onboard more and more consumers and how to provide improve service through differentiated offerings.

Given the pivotal role of networks in this era of cloud-powered enterprise, low-cost-per bit is central to creating digital transformation. This imperative is equally applicable from edge of the network to the core, as well the very data center that fuels  services.

The need for low-cost-per-bit at the Edge of Network

As applications are quizzing the network, demand for bandwidth is growing. Multi-media transport is a reality today and with that reality is the need  for faster response time. Service providers are now baffled with a two-prone challenge: How to improve differentiated service with faster response time and reduce the cost to service. Consumers are demanding better service at relatively cheaper price points for multi-media payload that fuels their need to stay connected, pushing the Petabytes of data to Internet that traverse through various service provider networks. The age-old infrastructure of service provider is simply inadequate to accommodate this demand for more bandwidth. Couple this with the traffic generated by billions of connected devices. Get the picture?

Welcome to the dawn of Zetabyte era! “If each petabyte in a zettabyte were a centimeter it would mean one can reach 12 times higher than world’s tallest tower Burj Khalifa”.[1]

Accommodating this pressing need for bandwidth means opening up the clogged pipe at the wireless and wired edge and web-scale network performance at the Edge of Network. There is no better technology than “Ethernet” and “Fiber” to open up clogged pipe at wired and Wireless Edge.

Unchoking Wireless Edge

You heard it right, wireless network across the globe is getting a shot in the arm as service providers are upgrading the first choking block where your wireless traffic runs down the tower to meet wired pipe. Perhaps you too have experienced this change to some extent while browsing Internet or watching YouTube video, there is no screeching halt or buffering of app in your smartphone. While this experience may be limited to users of certain service providers,  work is underway for all tiers of providers to unchoke their wireless edge. It is a dire need of their business.

When your data rides over RF frequency from your cell phone to reach the antenna of your mobile provider, it undergoes digitization at an “analog to digital” conversion device known as RRH (Radio Remote Head). From there, the bitstreams run down the pipe to meet its first transport gateway of packetization known as Baseband Unit or short BBU. Up until this point, the network is known as fronthaul. Please read more in my earlier article to know more about frounthaul at http://www.dhimanchowdhury.com/2018/01/13/hello-world/ .

In early days, constraints of interconnects choked this entry point of your data. However, new technologies made it possible to reshape the architecture of interconnects and moves the bulky pieces of equipment away from the tower base. Fiber is now rising up the tower upto RRH and allowing bigger pipe up to 20GbE to antenna base through a means of interconnect known as CPRI. Compare this to early days of coaxial interconnect that only allowed short distance interconnect and less than 100MBps of transfer rate. In my article about wireless and fiber convergence, I made a case for overhauling RRH with addition of Ethernet. If CPRI is limited to 20GbE bandwidth, having Ethernet at the very base of antenna the pipe could be enormous: 100GbE to 400GbE. IEEE already created an open and free standard to create ethernet transport at fronthaul known as ROE (Radio over Ethernet). While RoE promises the potential for fatter pipe at cheaper cost, it is still in research phase. What possible though is the bandwidth upgrade in the connectivity between BBU and operator’s packet network known as “mobile backhaul”.

Figure 1. Typical fronthaul and backhaul Network architecture

Many operators started to upgrade the pipe between BBU and backhaul aggregation using a device known as cell site router or sometimes referred to as cell site gateway. This creates a fatter pipe from 1GbE to 10GbE for each fronthaul endpoint. Prior to such upgrade many deployments had 10/100Mbps at this level connectivity. Now the 4G fronthaul service can use 1GbE pipe while 5G 10GbE. This is just an example of upgrade underway. The important conduit to this upgrade is whitebox open networking platform. As such cell site router not only endows the benefits of an unlocked system, it innately reduced the cost per bit and improve services.

Unleashing the power of open networking at Wireless Edge

The Cell Site Router (please refer to figure 1) is not a new concept, there are many deployments of it using OEM switches. However, the cost of OEM switches is extremely high. It also poses challenge that inherent of vendor locked system making it difficult for operator to deploy in massive scale. This constraint can be completely eliminated by deploying “Whitebox Cell Site Router” that utilizes state of the art merchant silicon while offering the benefit of low cost per bit and the choice of hardware and software. The TIP (Telecom Infra Project) initiative for open networking infrastructure product to serve telecom service provider has undertaken activities around the same concept known as DCSG (Disaggregated Cell Site Router)[2]. The term “whitebox CSR (Cell Site Router)” and DCSG are synonymous. Central to this concept is separation of hardware and software as in whitebox but applied to Cell Site Router for specific deployments in mobile backhaul. There can be variations of DCSG devices ranging from 12 ports of 1/10GbE to 48 ports of 10GbE with 2 to 6 ports of 100GbE.

Figure 2. Whitebox Cell Site Router or DCSG (Disaggregated Cell Site Router) Architecture.

Additionally, the DCSG or Whitebox CSR provides SyncE and PTP (1588) clocking capabilities. It will help synchronize between GPS clock and packetized clocking information retrieved from packet network. Clocking is essential part of mobile backhaul transport. There are varied deployments using DCSG or whitebox CSR ranging from Ring interconnect to CLOS fabric interconnects. For example, the figure below shows typical ring interconnect allowing various RAN (Radio Access Network) configurations in MPLS network. Such configuration allows wider area coverage for various RANs including 5G and migration path from 4G to 5G for operators.

Figure 3. Typical Ring topology of interconnect for mobile backhaul.

For migration path from 4G to 5G, network operator benefits from utilizing same DCSG based network for both 4G and 5G. As shown in figure 3, 5G base station Distributed Unit (DU) [3][4] can be connected to same DCSG where 4G base station is connected. 5G deployment requires a spit of base station in two parts distributed unit (DU) and Central Unit (CU) [3][4] for which DU may reside on or near the tower and CU is placed in 5G core network. The CU is then connected to servers to provide various network functions through NFV (Network Function Virtualization). Please note DU can provide upto 100GbE link and RoE capabilities making it easier to integrate into your packet network. Within the DCSG based MPLS network primary and secondary path can be created easily making fail over faster and reliable. Other variation of this network could be DWDM based long distance interconnect between MPLS mobile backhaul (BMH) Ring and MBH aggregation (please refer figure 3).

Passive Optical Network for Wireless Edge

With the advent of whitebox OLT (Optical Line Terminator), Passive Optical Network (PON) can now be extended to fronthaul. The benefit of such deployment is that same fiber can carry mixed set of traffic allowing fronthaul connection and residential/business fixed line services over the same fiber. As such overall TCO (total cost of ownership) will be drastically reduced.

Figure 4. Mixed Traffic PON for MBH and fixed line services.

In figure 4, a typical example of mixed traffic PON deployment is shown. There can be two types of OLT deployments using whitebox solutions: whitebox OLT device and whitebox Ethernet switch with OLT transceivers.

For the first, OLT functions are realized through virtualized solution known as VOLTHA. In this scenario, mixed traffic from MBH, residential and enterprises are carried over single fiber depending upon split ratio. Typical split ratio is 1:32 meaning 32 ONUs can be connected to single incoming fiber. For the second solution, OLT transceivers can be used with standard whitebox ethernet switch. These OLT transceivers are available in SFP+ form factor making it easier to plug it in a 10GbE SFP+ port socket of the whitebox switch. OLT functions can be virtualized with VOLTHA or it can be implemented in the Ethernet switch itself. IP Infusion, a leader of independent NOS (Network Operating System) for whitebox platform, implements OLT functions through a container within its OcNOS™ software. Third-party OMCI stack that provides OLT functionalities can be integrated within OcNOS container for which Netconf API provides EMS (Element Management System) based configuration and management capabilities including provision of ONUs.

Solutions such as these reduce overall TCO for operators and offers the choices and benefits of open networking. Low-cost-per-bit is essential today for operators to improve service and maximize ROI.

 

Reference:

  1. Cisco, 2016. The Zettabyte Era Officially Begins (How Much is That?). Available at https://blogs.cisco.com/sp/the-zettabyte-era-officially-begins-how-much-is-that
  2. Lightwave, 2018. Telecom Infra Project targets disaggregated cell site gateways. Available at https://www.lightwaveonline.com/articles/2018/10/telecom-infra-project-targets-disaggregated-cell-site-gateways.html .
  3. Microsemi, 2019. 5G LTE Base stations. Available at https://www.microsemi.com/applications/5g-mobile-infrastructure/5g-lte-base-stations .
  4. Techplayon, 2017. 5G NR gNB Logical Architecture and Its Functional Split Options. Available at http://www.techplayon.com/5g-nr-gnb-logical-architecture-functional-split-options/

Front haul wireless-fiber convergence: Does Ethernet at front haul help the case for increase white box deployment in Telecom Network transformation?

All Rights Reserved. © 2017: Dhiman Deb Chowdhury
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.

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 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.

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 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.
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.
Figure 4. eCPRI Protcol stack overview (eCRPI, 2017).
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.

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.
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 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).

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.
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).

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 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.
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.

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.
Reference:
  1. Altera, 2011. OBSAI Reference Design Datasheet. Available at https://www.altera.com/en_US/pdfs/literature/ds/ds01026.pdf .
  2. 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 .
  3. eCPRI, 2017. eCRPI Specification V1.0. Ericsson AB, Huawei Technologies, NEC Corporation and Nokia. Available online at http://www.cpri.info/spec.html .
  4. 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.
  5. 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.
  6. IEEEP1914.3, 2017. IEEE P1914.3™/D2.0: Draft Standard for Radio over Ethernet Encapsulations and Mappings. Institute of Electrical and Electronics Engineers, Inc.
  7. Tornatore, M., Chang, G., & Ellinas, G., 2017. Fiber-Wireless convergence in Next-Generation Communication Networks. Springer.