Wireless in the Metro-Packet Microwave Explained RAJESH KUMAR SUNDARARAJAN Assistant Vice President - Product Management, Aricent
www.aricent.com
WIRELESS IN THE METRO– PACKET MICROWAVE EXPLAINED
This whitepaper outlines the packet microwave technology, and its typical usage, benefits, applications, and deployment topologies. It also provides solutions to specific challenges posed by packet transport over microwave.
OVERVIEW
out cables throughout the MAN or RAN, and provides the
Across the world, communication networks have almost completely
microwave does present some unique challenges and obstacles,
adopted packetized infrastructure to leverage the benefits that
the innovative solutions to which are explored toward the end
Ethernet, IP, and MPLS offer in terms of efficiency, flexibility,
of this paper.
capability to create a network quickly and economically. However,
network utilization, and scalability. Two parts of the communication infrastructure that are seeing rapid conversion from circuit switched or leased-line infrastructure to packet-switched infrastructure are the Metropolitan Area Access Network (MAN) and the Radio Access Network (RAN).
MICROWAVE TRANSPORT APPLICATIONS The two most common use cases for packet microwave are:
Each of these networks is defined by common characteristics such as the density of connections, multiplication of bandwidth
MOBILE BACKHAUL (OR CELLULAR BACKHAUL)
demand, and the need to carry applications intolerant to delay
Used in RANs, Mobile Backhaul is the transport of traffic from
or loss. While some geographical areas already have abundant
cellular towers to the aggregation site, which is usually the Base
fiber infrastructure to deliver the required connectivity and
Station Controller (BSC).
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 microwave has emerged as an extremely attractive option, for both large and small operators.
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
Packet microwave refers to the mechanism of transmitting and
service provider network. It is typically used in MANs, usually
receiving packets (most commonly Ethernet, IP, or MPLS) over
for Internet connectivity or Virtual Private Networks (VPNs).
microwave links. The use of microwave eliminates the need to lay
Wireless in the Metro - Packet Microwave Explained
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TRANSPORTING PACKETS OVER MICROWAVE - USE CASES
Cellular antenna
Figure 3 shows the packetized nature of the transmission and Microwave antenna
reception over the microwave 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 microwave switch. The switch converts the TDM into Ethernet packets and transmits them over the microwave link. At the other end, another similar switch receives the signals
Cell tower
and converts the Ethernet 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.
Microwave antenna
Cell tower
BSC
Ethernet frames over microwave
Cellular antenna
TDM (T1/E1)
TDM (T1/E1) Packet microwave switch
Cell tower
BSC
Packet microwave switch
Figure 3: Packetized TDM over microwave from base station (cell tower) to BSC Figure 1: RAN cellular backhaul over microwave
But not all packet microwave switches are TDM-enabled. In such cases, a separate cell site router may be used to convert the TDM signals into Ethernet frames, which are then transported over
Microwave antenna
microwave by the packet microwave switch. Figure 4 shows this variation.
Microwave antenna Cellular antenna
University
Ethernet frames over microwave
Cell site router
TDM (T1/E1)
Ethernet Packet microwave switch
Office buildings
BSC
Ethernet Packet microwave switch
Figure 4: Packets over microwave from cell site router to BSC Microwave radio tower MTU/Residential Figure 2: MAN Ethernet backhaul over microwave
Wireless in the Metro - Packet Microwave Explained
In the case of LTE networks, the output from the base station is no longer a TDM line, but rather packets (Ethernet frames) that can be directly fed into an Ethernet port on the packet microwave switch (see Figure 5).
2
This is also a way to achieve redundancy for situations where
Microwave antenna
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 Ethernet frames over microwave
Cellular antenna Ethernet
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
Ethernet Packet microwave switch
Packet microwave switch
BSC
through the Link Aggregation Control Protocol (LACP) defined in IEEE 802.3ad.
Figure 5: LTE cell site to BSC connectivity over packet microwave
INSIDE THE PACKET MICROWAVE SWITCH Figure 6 shows a simplified view of Ethernet backhaul over
Figure 8 shows a typical packet microwave switch. Depending
microwave. Lines from individual subscribers (e.g., universities,
on the type of packets generated, the actual port type and
offices, and homes) are aggregated into the microwave switch
the number of ports may vary, while the basic nature of the
and transported over microwave to a service provider access
device remains the same. The optional TDM ports are required
router, where connectivity to the Internet or a VPN is established.
only when the device is used in cellular backhaul in 2G or 2.5G networks, where the connection to the base station is through
Service provider access router
Microwave antenna
TDM (T1/E1). The TDM or Ethernet ports connect to the source of the traffic to be transported. The ports go into an Ethernet switch that
Packet microwave switch
can switch and route traffic at line rates of 100 Mbps/1 Gbps/ 10 Gbps, the most common currently being 1 Gbps. An internal Packet microwave switch
port (usually Ethernet) is used to connect to the radio controller. In one direction, the radio controller converts the Ethernet frames into signals that the microwave radio transmits. In the other direction, the signals received by the microwave radio are converted
Modems or other devices in individual offices or homes
by the radio controller into Ethernet frames, which are then processed internally by a switching device.
Figure 6: Internet or VPN connectivity through microwave packet transport Microwave radio
In this use case, the bandwidth requirement may be much higher. So, depending upon the need, multiple radios may be used to create multiple microwave links to achieve this bandwidth requirement. When multiple radios are used to increase the bandwidth
Radio controller
between two microwave radios, a common technique called Link Aggregation or Link Capacity Aggregation Scheme (LCAS)
Ethernet frames over microwaves
Ethernet
is used to aggregate the links into a single, larger interfacecapacity trunk. TDM ports
Packet microwave switch
Ethernet ports
Figure 8: Simplistic view of a packet microwave switch
Depending on the spectrum at which the microwave is operated, a single microwave link can deliver almost 1 Gbps throughput. Packet microwave switch
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 microwave link.
Figure 7: Bandwidth boosting and redundancy using Link Aggregation
Wireless in the Metro - Packet Microwave Explained
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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 switching 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 Packet microwave switch Protection path Figure 10: Microwave Ring Packet microwave switch
SPECIAL PROBLEMS AND SOLUTIONS Packet microwave switch
When used for packet transport, microwave links pose some unique problems that must be addressed for a reliable and viable networking solution.
Figure 9: Service assurance through redundancy
LINK SPEED
MICROWAVE RINGS A packet microwave network may be laid in different topologies. Figure 1 shows the simplest point-to-point microwave. 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 microwave in the RAN. Rings are an efficient way of provisioning redundancy while maximizing capacity utilization. A standard way to implement redundancy and protection switching is through the mechanisms specified in the ITU-T G.8032 specification for Ring Protection
Microwave links are typically much slower than Ethernet 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 microwave 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 microwave links.
Switching, which in turn uses the mechanisms specified in the
LINK MONITORING OR SERVICE MONITORING
ITU-T Y.1731 specification for path 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 Ethernet links or services, but takes on far more importance due to the higher possibility of link failure.
Wireless in the Metro - Packet Microwave Explained
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TIMING AND TIME SYNCHRONIZATION
pre-integration on reference designs from leading silicon
Microwave links are also susceptible to differing delays in
manufacturers. The high level of integration, in addition to the
transmission. This is a particularly critical issue for TDM transport
mature and ready software, offers compelling advantages of
because it relies on clock synchronization between the two ends
cost and time to network equipment manufacturers and network
of the TDM channel. The most reliable and popular technique to
operators worldwide. Aricent provides a variety of services,
address this is to use the IEEE 1588 specification for Precision
including product definition, design, development, system
Time Protocol (PTP). The protocol provides a highly accurate
integration, testing, validation, and sustenance to customers
and very reliable mechanism for time synchronization over
across the world, offering unmatched efficiencies and value.
packet networks. RAJESH KUMAR SUNDARARAJAN
ARICENT INTELLIGENT SWITCH SOLUTION (ISS) FOR PACKET MICROWAVE SWITCHES
is Assistant Vice President for Data
As part of its comprehensive portfolio of networking products,
solutions including Aricent’s ISS. He has
Aricent offers a licensable software framework for a variety of
over 16 years of industry experience in
switching applications, including packet microwave. This industry-
strategizing and managing software
leading framework caters to the needs of Carrier Ethernet and
for communications.
Metro Ethernet infrastructure. The software is available through
rajeshkumar.sundararajan@aricent.com
Communication products at Aricent, focusing on routing and switching
Software Sustenance & Enhancement System Integration & Release Testing Aricent Software Services
UI Development or Adaptation System Infrastructure Adaptation
QoS - Ethernet/IP/MPLS
Add & Customize Customer Applications
MPLS, MPLS-TP IP Security IPv4/v6 Routing - Unicast + Multicast
Aricent ISS
Aricent Software Frameworks
OAM - Ethernet/MPLS
Device Integration Layer (SDK) Driver Adaptation to Custom Hardware
Ethernet (L2) Control Plane MAC Security Switch Infrastructure
Aricent Hardware Services
BSP
OS Port
SDK Port
Drivers
Custom Platform Board/Prototype Design
Figure 11: Aricent ISS
Wireless in the Metro - Packet Microwave Explained
Aricent ISS - Licensable pre-integrated, platform-ready software
Product Launch and Maintenance
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.
Engineering excellence.Sourced Aricent is the world’s #1 pure-play product engineering services and software firm. The company has 20-plus years experience co-creating ambitious products with the leading networking, telecom, software, semiconductor, Internet and industrial companies. The firm's 10,000-plus engineers focus exclusively on software-powered innovation for the connected world. frog, the global leader in innovation and design, based in San Francisco is part of Aricent. The company’s key investors are Kohlberg Kravis Roberts & Co. and Sequoia Capital. info@aricent.com
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