PROTELECON
What You Will Learn
With the advent of small cells and increasing use of data devices in
mobile networks, many operators now seek to optimize their microwave
infrastructure to address these new challenges in the radio access
network (RAN).
Cisco and SIAE MICROELETTRONICA developed the Microwave Adaptive
Bandwidth (MAB) feature to provide reliable quality of service (QoS)
management and optimized performance for both ring-based and
non-ring-based topologies, even under worst-case radio propagation
conditions. Although the MAB feature is generic, this document describes
it with specific application to mobile backhaul network architectures.
Introduction
Traditional time-division multiplexing (TDM) allowed mobile
operators to deploy stable networks with well-defined deterministic
traffic flows and fixed bandwidth circuits. Although ideal for voice
traffic, this model cannot support the recent rapid growth in data
traffic. Packet networks, the only solution to this problem, are
characterized by QoS-based traffic flows and variable bandwidth
circuits. This shift requires a unified RAN environment and new features
to integrate different network elements (Figure 1).
Figure 1. Unified RAN
With the advent of small cells and cloud RAN (CRAN) models in mobile
networks, many operators want to reuse their installed microwave
infrastructure to address new challenges and opportunities. In many
mobile networks, microwave equipment is a very significant portion of
the backhaul network, at times representing a large majority of base
station interconnections. Operators are looking for high-capacity
solutions to address the increased capacity requirements of data traffic
from small cell long term evolution (LTE) deployments and fiber
extension connectivity.
The migration of data networks, coupled with data growth caused by
densely deployed base stations with small cell deployments, promotes the
use of ring architectures to provide better network protection. Until
now, microwave ring architectures were implemented with fixed microwave
modulation schemes, because ring protocols are not designed to react to
dynamic bandwidth changes. In traditional fixed modulation schemes, any
degradation in wave propagation (for example, due to adverse weather
conditions such as heavy fog or rain) led to a complete loss of signal
and a disruption of traffic. Using fixed modulation, the microwave radio
link was either "available" (on) or "unavailable" (off).
More advanced microwave radios can use adaptive modulation schemes.
The radio changes its modulation to a more robust scheme when the
microwave link degrades due to adverse weather conditions (in this case,
bandwidth is also reduced). The radio continues to transmit,
maintaining connectivity, and forwards traffic in proportion to the
adopted modulation scheme. As a result, the radio link can be in several
capacity or bandwidth states, not just on or off.
In an Ethernet ring, capacity degradation can affect one part of the
ring, while the rest remains unaffected. If congestion occurs, the
microwave radio frequently uses QoS to prioritize the Ethernet traffic
with higher importance, helping ensure that those packets get a fixed
amount of the available bandwidth.
Traffic shaping is required in the packet transport network to
optimize bandwidth and avoid traffic overflow resulting from bursty LTE
traffic. Unlike ring topologies, other topologies (chain, star, tree,
and so on) do not have alternate paths for forwarding traffic when
adverse conditions occur in one part of the network. Traffic shaping and
QoS are widely used to manage traffic flows. In these cases, changes in
microwave modulation must be reported to upstream Ethernet switches or
routers, which in turn must adapt traffic shaping and forwarding rules
to the new network conditions.
Cisco and SIAE MICROELETTRONICA have developed a generalized MAB
feature to provide reliable QoS management and optimized performance,
even under worst-case radio propagation conditions, for both ring-based
and non-ring-based topologies. This solution is generic, although the
following description highlights its applicability to mobile backhaul
networks.
Cisco and SIAE MICROELETTRONICA Solution
The joint solution addresses the consequences of microwave variable
bandwidth techniques, in relation to traffic shaping and QOS
configuration in networking equipment and dynamic ring topology
reconfiguration. The solution allows operators to take advantage of the
maximum available air bandwidth under any atmospheric conditions,
because they can deploy ring topology or non-ring topology backhaul
networks in the RAN, while cooperating with adaptive modulation radios.
The MAB feature is based on IEEE 802.1ag Connectivity Fault
Management (CFM) and ITU-T Y.1731 protocols, and it uses Cisco IOS
®
Embedded Event Manager (EEM), a powerful and flexible subsystem that
provides real-time network event detection to trigger traffic changes. A
CFM vendor-specific message (VSM) has been defined to communicate
between SIAE MICROELETTRONICA microwave radios and Cisco
® switches and routers.
When the microwave radio detects signal degradation, the radio
triggers a modulation change, notifies the adjacent Cisco equipment
using specially designed VSMs, and periodically sends updates until the
standard maximum bandwidth is restored. The switch receives these VSMs
from the microwave radio port and notifies the Cisco IOS EEM subsystem
of a signal degradation event.
The subsystem checks new available bandwidth values from the signal
degradation event information against configured thresholds. If the new
value crosses a defined threshold, traffic forwarding is managed
according to the topology (ring) or hierarchical QoS (HQoS) shaping
application. If a complete link failure causes a loss of microwave
signal, a signal failure event is signaled. Signal failure events take
priority over signal degradation events.
Ring Topology Application
The MAB feature developed by Cisco and SIAE MICROELETTRONICA allows
operators to benefit from adaptive modulation, even in a ring topology
(Figure 2). The feature extends the capabilities of the G.8032 Ethernet
Ring Protection Switching (ERPS) mechanism and Ethernet CFM to achieve
this benefit.
Microwave links are often deployed in redundant ring topologies that
use ERPS techniques based on ITU-T G.8032. Typically, adaptive
modulation is not activated in these deployments, because capacity
variation within a ring was not foreseen by protocols such as ERPS.
Nevertheless, using adaptive modulation can bring tremendous advantages,
by allowing operators to couple protection with full use of the
available bandwidth.
For microwave links with adaptive modulation, the normal operation,
administration, and maintenance (OAM) protocols used by ring protection
protocols cannot make the best use of the available bandwidth for the
following reasons:
• If the OAM protocol used for failure detection is tagged as
high-priority traffic, frames bypass degraded (congested) microwave
links, and no protection switching is triggered.
• If the OAM protocol used for failure detection is tagged as
low-priority traffic, then momentary congestion over the native Ethernet
links could lead to loss of continuity and spurious protection
switching.
In general, the network topology must be provisioned with enough
redundant bandwidth to handle a complete failure. In certain situations,
however, when the service committed information rate (CIR) is very low,
forwarding as much traffic above the CIR as possible still represents
an important value. Treating bandwidth degradation as a complete failure
is not desirable.
Figure 2. Ring Topology
As bandwidth capacity changes because of switching to a different
modulation scheme, the MAB feature triggers a CFM notification to the
Cisco Ethernet switches within the ring. This allows the switches to
optimize the traffic-forwarding rules of the affected traffic. Instead
of reconfiguring the ring to switch all traffic to an alternate path,
the MAB feature selects a more efficient ring configuration that
increases traffic throughput. A complete rerouting of traffic occurs
only if the switches detect a complete loss of continuity, for example,
through the complete absence of connectivity connection messages (CCMs)
from CFM.
With the MAB feature, G.8032 ERPS mechanisms can be used as a
control mechanism in response to bandwidth degradation (such as an SD
indicator) on microwave links. Ethernet CFM interacts with the microwave
system to continuously monitor the quality and bandwidth of the
microwave link. When microwave link degradation is detected, CFM
notifies the Cisco IOS EEM facility on the Cisco switch to invoke G.8032
ERPS mechanisms. Based on service-level agreement (SLA) information and
configured thresholds, some ERPS instances can be switched to an
alternate path (for example, when the instances are based on VLAN),
while other ring instances carrying high-priority traffic may still be
switched through the degraded microwave link.
HQoS Traffic Shaping Application
The adaptive modulation of SIAE MICROELETTRONICA microwave radios
can be used to help ensure that high-priority Ethernet traffic continues
to pass through a degraded link, even under the worst weather
conditions. When SIAE MICROELETTRONICA microwave links and Cisco
switches are in daisy-chain or star topologies, the MAB feature
dynamically controls HQoS class-based traffic shaping (Figure 3).
Figure 3. HQoS Traffic Shaping
As in the ring topology, Ethernet CFM continuously monitors the
quality and bandwidth of the microwave link. When bandwidth capacity
changes due to changes in the modulation scheme, Ethernet OAM triggers a
CFM notification to the Cisco switches, so they can optimize
traffic-forwarding rules for the affected traffic flow. However, in this
case, instead of changing the ERPS ring configuration, Ethernet CFM
modifies HQoS traffic-shaping rules to dynamically increase high-value
traffic throughput across the degraded link.
This mechanism is achieved with the following steps:
• The operator specifies a rate for traffic shaping, on the Cisco
router, that avoids bottlenecks and packet loss on the SIAE
MICROELETTRONICA microwave links during normal operation.
• Traffic shaping is configured in a hierarchical policy map structure
to help ensure that a packet acts according to a stipulated contract,
based on available bandwidth. The structure includes primary (parent)
and secondary (child) policy maps.
• The Cisco switch or router is also configured with alternative
traffic-shaping rules that are appropriately tuned for circumstances in
which microwave links run in a degraded or constrained state.
• The alternative traffic-shaping rules are defined to improve the
value and use of newly determined available resources. This means that
microwave equipment will be presented only with high-value traffic and
with only the amount of traffic that can be handled without dropping.
• As bandwidth changes on microwave links, the SIAE MICROELETTRONICA
radio will use a CFM message to initiate an signal degradation event in
the Cisco IOS EEM facility on the Cisco switch, which then reconfigures
HQoS to switch to alternate traffic-shaping rules.
Conclusion
Operators have invested substantial resources in building robust and
highly capable RAN backhaul networks based on microwave radio.
Additionally, SIAE MICROELETTRONICA has substantial experience in
designing and delivering sophisticated adaptive modulation techniques
that significantly improve use of available bandwidth and capabilities
under adverse conditions. What has been missing, until now, is the
ability to apply new intelligence in backhaul applications.
With the MAB feature developed by Cisco and SIAE MICROELETTRONICA,
operators can use adaptive modulation to optimize the use of available
resources, so that subscribers experience improved service under
challenging conditions. The MAB feature allows high-priority, high-value
traffic to be forwarded under conditions that would normally lead to
service outages and promotes much more intelligent use of available
resources.
For More Information
https://www.siaemic.com/index.php/applications/mobile-backhaul/28-applications/238-ip-multi-vendor-environment
Source : http://www.cisco.com/c/en/us/solutions/collateral/service-provider/unified-ran-backhaul/white_paper_c11-728355.html
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