WIRELESS IN THE METRO PACKET MICROWAVE EXPLAINED

WIRELESS IN THE METRO PACKET MICROWAVE EXPLAINED RAJESH KUMAR SUNDARARAJAN Assistant Vice President - Product Management, Aricent Group

WIRELESS IN THE METRO PACKET MICROWAVE EXPLAINED This whitepaper outlines the packet technology, and its typical usage, benefits, applications, and deployment topologies. It also provides solutions to specific challenges posed by packet transport over. OVERVIEW Across the world, communication networks have almost completely adopted packetized infrastructure to leverage the benefits that, IP, and MPLS offer in terms of efficiency, flexibility, network utilization, and scalability. Two parts of the communication infrastructure that are seeing rapid conversion from circuit ed or leased-line infrastructure to packet-ed infrastructure are the Metropolitan Area Access Network (MAN) and the Radio Access Network (RAN). Each of these networks is defined by common characteristics such as the density of connections, multiplication of bandwidth demand, and the need to carry applications intolerant to delay or loss. While some geographical areas already have abundant fiber infrastructure to deliver the required connectivity and services, many parts of the world do not. Delivering connectivity and services to these areas requires laying out a new network of cables, which brings with it a multitude of challenges: economic, logistical, and safety, among others. For such situations, packet has emerged as an extremely attractive option, for both large and small operators. refers to the mechanism of transmitting and receiving packets (most commonly, IP, or MPLS) over links. The use of eliminates the need to lay out cables throughout the MAN or RAN, and provides the capability to create a network quickly and economically. However, does present some unique challenges and obstacles, the innovative solutions to which are explored toward the end of this paper. MICROWAVE TRANSPORT APPLICATIONS The two most common use cases for packet are: MOBILE BACKHAUL (OR CELLULAR BACKHAUL) Used in RANs, Mobile Backhaul is the transport of traffic from cellular towers to the aggregation site, which is usually the Base Station Controller (BSC). ETHERNET BACKHAUL This refers to the transport of traffic from various subscriber sites like small enterprises, educational institutions, residences, multi-tenant units (MTUs), and multi-dwelling units (MDUs), to the service provider s access router for connectivity into the service provider network. It is typically used in MANs, usually for Internet connectivity or Virtual Private Networks (VPNs). Wireless in the Metro - Microwave Explained 1

Cellular antenna Cell tower TRANSPORTING PACKETS OVER MICROWAVE - USE CASES Figure 3 shows the packetized nature of the transmission and reception over the link in the case of the RAN. In the case of 2G or 2.5G networks, a TDM (T1/E1) line brings the signals to the packet. The converts the TDM into packets and transmits them over the link. At the other end, another similar receives the signals and converts the frames into TDM signals, which are then handed off to the BSC. An ATM circuit may be used in place of the TDM line for 3G networks. Cell tower BSC Cellular antenna frames over TDM (T1/E1) TDM (T1/E1) Cell tower BSC Figure 3: ized TDM over from base station (cell tower) to BSC Figure 1: RAN cellular backhaul over But not all packet es are TDM-enabled. In such cases, a separate cell site router may be used to convert the TDM signals into frames, which are then transported over by the packet. Figure 4 shows this variation. University Cellular antenna Cell site router frames over BSC TDM (T1/E1) Office buildings Figure 4: s over from cell site router to BSC MTU/Residential Figure 2: MAN backhaul over Microwave radio tower In the case of LTE networks, the output from the base station is no longer a TDM line, but rather packets ( frames) that can be directly fed into an port on the packet (see Figure 5). Wireless in the Metro - Microwave Explained 2

Cellular antenna frames over BSC This is also a way to achieve redundancy for situations where a radio or the port connected to it may fail, in which case the traffic can be carried through the other radio. The links may also be used in a purely redundant manner, with one link being placed in a standby state and activated when the other fails. Such activation, based on failure detection, can be achieved through the Link Aggregation Control Protocol (LACP) defined in IEEE 802.3ad. Figure 5: LTE cell site to BSC connectivity over packet Figure 6 shows a simplified view of backhaul over. Lines from individual subscribers (e.g., universities, offices, and homes) are aggregated into the and transported over to a service provider access router, where connectivity to the Internet or a VPN is established. Modems or other devices in individual offices or homes Service provider access router Figure 6: Internet or VPN connectivity through packet transport In this use case, the bandwidth requirement may be much higher. So, depending upon the need, multiple radios may be used to create multiple links to achieve this bandwidth requirement. INSIDE THE PACKET MICROWAVE SWITCH Figure 8 shows a typical packet. Depending on the type of packets generated, the actual port type and the number of ports may vary, while the basic nature of the device remains the same. The optional TDM ports are required only when the device is used in cellular backhaul in 2G or 2.5G networks, where the connection to the base station is through TDM (T1/E1). The TDM or ports connect to the source of the traffic to be transported. The ports go into an that can and route traffic at line rates of 100 Mbps/1 Gbps/ 10 Gbps, the most common currently being 1 Gbps. An internal port (usually ) is used to connect to the radio controller. In one direction, the radio controller converts the frames into signals that the radio transmits. In the other direction, the signals received by the radio are converted by the radio controller into frames, which are then processed internally by a ing device. Microwave radio When multiple radios are used to increase the bandwidth between two radios, a common technique called Link Aggregation or Link Capacity Aggregation Scheme (LCAS) is used to aggregate the links into a single, larger interfacecapacity trunk. Radio controller frames over s TDM ports ports Figure 8: Simplistic view of a packet Depending on the spectrum at which the is operated, a single link can deliver almost 1 Gbps throughput. This is sufficient to transport more than 50 T1/E1 lines. In practice, therefore, lines from multiple base stations may be transported over a single link. Figure 7: Bandwidth boosting and redundancy using Link Aggregation Wireless in the Metro - Microwave Explained 3

REDUNDANCY PROVISIONING FOR RELIABLE SERVICE DELIVERY Microwave transmission and reception is susceptible to weather and climatic conditions. In these situations, in order to provide service assurance for users, operators may provision redundancy by providing alternate links/paths (see Figure 9). User data is normally transported on the working path, or when that fails, to the protection path. The failure is detected by constantly monitoring the path. A standard way to implement protection ing is through the mechanisms specified in the ITU-T G.8031 specification for Link Protection Switching, which in turn uses the mechanisms specified in the ITU-T Y.1731 specification for path monitoring. Working path Protection path Figure 10: Microwave Ring SPECIAL PROBLEMS AND SOLUTIONS When used for packet transport, links pose some unique problems that must be addressed for a reliable and viable networking solution. Figure 9: Service assurance through redundancy MICROWAVE RINGS A packet network may be laid in different topologies. Figure 1 shows the simplest point-to-point. Figure 9 shows a nodal or mesh topology. In Figure 10 below, the ring network topology popular in access and aggregation networks is shown, as applied to packet in the RAN. Rings are an efficient way of provisioning redundancy while maximizing capacity utilization. A standard way to implement redundancy and protection ing is through the mechanisms specified in the ITU-T G.8032 specification for Ring Protection Switching, which in turn uses the mechanisms specified in the ITU-T Y.1731 specification for path monitoring. LINK SPEED Microwave links are typically much slower than wires. As a result, efficiency and utilization must be maximized in order to use the available speeds and capacity effectively. The standard Quality of Service (QoS) mechanisms applied to other devices that transmit packets can also be used in devices. These include ingress priority classification, rate limiting, queuing, policing, marking, and rate shaping. Although these mechanisms are the same, they take on much more importance in the case of links. LINK MONITORING OR SERVICE MONITORING Microwave links are susceptible to climate and weather conditions, much more so than cables, which can be better protected. Therefore, in order to realize a reliable service, the links must be constantly monitored. A very reliable and popular technique is to use the monitoring mechanism defined in the ITU-T Y.1731 specification for connectivity and fault management. The technique is similar to that applied to links or services, but takes on far more importance due to the higher possibility of link failure. Wireless in the Metro - Microwave Explained 4

TIMING AND TIME SYNCHRONIZATION Microwave links are also susceptible to differing delays in transmission. This is a particularly critical issue for TDM transport because it relies on clock synchronization between the two ends of the TDM channel. The most reliable and popular technique to address this is to use the IEEE 1588 specification for Precision Time Protocol (PTP). The protocol provides a highly accurate and very reliable mechanism for time synchronization over packet networks. ARICENT INTELLIGENT SWITCH SOLUTION (ISS) FOR PACKET MICROWAVE SWITCHES As part of its comprehensive portfolio of networking products, Aricent offers a licensable software framework for a variety of ing applications, including packet. This industryleading framework caters to the needs of Carrier and Metro infrastructure. The software is available through pre-integration on reference designs from leading silicon manufacturers. The high level of integration, in addition to the mature and ready software, offers compelling advantages of cost and time to network equipment manufacturers and network operators worldwide. Aricent provides a variety of services, including product definition, design, development, system integration, testing, validation, and sustenance to customers across the world, offering unmatched efficiencies and value. RAJESH KUMAR SUNDARARAJAN is Assistant Vice President for Data Communication products at Aricent, focusing on routing and ing solutions including Aricent s ISS. He has over 16 years of industry experience in strategizing and managing software for communications. rajeshkumar.sundararajan@aricent.com Software Sustenance & Enhancement System Integration & Release Testing Aricent Software Services UI Development or Adaptation System Infrastructure Adaptation QoS - /IP/MPLS Add & Customize Customer Applications MPLS, MPLS-TP IP Security Aricent Software Frameworks Aricent ISS Device Integration Layer (SDK) IPv4/v6 Routing - Unicast + Multicast OAM - /MPLS Product Launch and Maintenance Driver Adaptation to Custom Hardware (L2) Control Plane MAC Security Switch Infrastructure Aricent Hardware Services BSP OS Port SDK Port Drivers Aricent ISS - Licensable pre-integrated, platform-ready software Custom Platform Board/Prototype Design Figure 11: Aricent ISS Wireless in the Metro - Microwave Explained

INNOVATION SERVICES FOR THE CONNECTED WORLD The Aricent Group is a global innovation and technology services company that helps clients imagine, commercialize, and evolve products and services for the connected world. Bringing together the communications technology expertise of Aricent with the creative vision and user experience prowess of frog, the Aricent Group provides a unique portfolio of innovation capabilities that seamlessly combines consumer insights, strategy, design, software engineering, and systems integration. The client base includes communications service providers, equipment manufacturers, independent software vendors, device makers, and many other Fortune 500 brands. The company s investors are Kohlberg Kravis Roberts & Co., Sequoia Capital, The Family Office, Delta Partners, and The Canadian Pension Plan Investment Board.