C H A P T E R
1
Overview of the Cisco MWR 1941-DC Router
The MWR 1941-DC Mobile Wireless Edge Router is a networking platform optimized for use in mobile
wireless networks; specifically designed to be use at the cell site edge as a part of an IP Radio Access
Network (IP-RAN) or Cell Site Data Communications Network (DCN).
The MWR 1941-DC router offers high performance at a low cost while meeting the critical requirements
for deployment in cell sites, including small size, high availability, and DC input power flexibility.
This chapter includes the following sections:
•
Primary Uses of the MWR 1941-DC Router, page 1-1
•
Cisco IOS Software Features, page 1-4
•
Limitations and Restrictions, page 1-9
Primary Uses of the MWR 1941-DC Router
The MWR 1941-DC router is designed to be used at the cell site as part of an IP-RAN or Cell Site DCN
solution.
IP-RAN Solution
Note
Cisco IOS Release 12.3(11)T supports the Cisco IOS IP-RAN feature set (software image) for the MWR
1941-DC router.
In an IP RAN application, the MWR 1941-DC router extends IP connectivity to the cell site and Base
Transceiver Station (BTS). Through a FastEthernet interface to the BTS, the MWR 1941-DC router
provides bandwidth-efficient IP transport of voice and data bearer traffic, as well as maintenance,
control, and signalling traffic, over the leased line backhaul network between the BTS and leased line
termination and aggregation node via compression (cRTP/cUDP) and packet multiplexing (PPPmux and
MLPPP).
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Primary Uses of the MWR 1941-DC Router
Figure 1-1 shows the placement of and connections for the MWR 1941-DC router implemented in an
IP-RAN solution.
Figure 1-1
MWR 1941-DC Router in an IP-RAN Solution
Active
100BaseT
T1/E1 backhaul link to
IP RAN aggregation node
Standby
MWR 1900 IP BTS router pair
65827
pBTS
In the IP-RAN solution, the BTS site consists of a pair of MWR 1941-DC routers. The pair of
MWR 1941-DC routers provides for an active and standby router for redundancy. A failure of the active
MWR 1941-DC router causes the standby router to take over as the active router for the BTS site.
Each pair of MWR 1941-DC routers at the BTS site is identical in hardware configuration. They connect
to each other through the BTS via the Fast Ethernet interfaces. The individual backhaul links to an
MWR 1941-DC router are cabled from a single T1/E1 termination block in the BTS, connecting to both
the active and standby routers utilizing a “Y” cable. The redundancy design to control the active/standby
transitions of the router pair leverages HSRP to control the relays on the VWIC-2MFT-T1-DIR (or
VWIC-2MFT-E1-DIR) in each router to ensure that the relays on the active router are closed and the
relays on the standby router are open to avoid double termination of the T1 (or E1).
Cell Site DCN Solution
Note
Cisco IOS Release 12.3(11)T does not support the Cisco IOS Cell Site DCN feature set (software image)
for the MWR 1941-DC router.
In a Cell Site DCN, the MWR 1941-DC router can be used to extend a mobile operators DCN to the cell
site, providing the ability to manage radio and cell site equipment remotely from the operations center.
A cell site DCN minimizes the need to dispatch technicians for every problem that might occur at the
cell site by providing the ability to perform the following types of maintenance tasks remotely:
•
troubleshooting
•
diagnosis
•
repairs
•
control
•
upgrades
•
routine maintenance of the cell site devices
Additionally, the MWR 1941-DC router cell site DCN implementation also provides IP connectivity to
the cell site, enabling the use of IP-related applications that provide operation support (for example, web
camera for site surveillance, IP telephone for voice connectivity, and LAN extension to the cell site to
provide remote access to network applications, data, and access to the Internet and/or intranet).
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Primary Uses of the MWR 1941-DC Router
Cisco network modules and WAN interface cards used with the MWR 1941-DC router provide a variety
of connectivity options at the cell site.
Figure 1-2 shows an example placement and connections for the MWR 1941-DC router implemented in
a Cell Site DCN solution.
Figure 1-2
MWR 1941-DC Router in an Cell Site DCN Solution
BTS Node B
T1/E1
BSC/RNC
MWR 1941-DC, 7200, 1/0 DACS
Voice circuits
10/100 Base-T
T1/E1
Cisco MWR
1941-DC
Network Operations
Center
Drop
and
Insert
RS-232
DCN traffic
T1/E1
RF monitoring Unit
Microwave Equipment
Tower Light Controller
Battery System
Email access for trouble tickets
OSS network access
Database access for inventory and technical knowledge
Cisco IP SoftPhone or FXO/FXS VoIP for tech and support services
Web camera for Security
Local data archival
101070
10/100 Base-T
In the Cell Site DCN solution, the MWR 1941-DC router provides a channelized T1/E1 interface to the
BTS and routes management and control traffic via one DS0 from a T1. Additionally, the
MWR 1941-DC router supports a variety of interfaces to monitored and controlled devices using Cisco
network modules installed in the MWR 1941-DC router.
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Cisco IOS Software Features
Cisco IOS Software Features
There are two versions of software available for the Cisco MWR 1941-DC router. One version of
software is required for implementing the Cisco MWR 1941-DC router in an IP RAN; the other for
implementing the router in a Cell Site DCN.
The software features vary depending on the version of software running on the MWR 1941-DC router.
•
Software Features for the IP-RAN Implementation, page 1-4
•
Software Features for the Cell Site DCN Application, page 1-8
Software Features for the IP-RAN Implementation
The software required for implementing the MWR 1941-DC router in an IP-RAN consists of two
components: Cisco IOS software running on the MIPs-based route processor portion of the
MWR 1941-DC router hardware, and microcode running on the Cisco network processor, also known as
“Parallel eXpress Forwarding (PXF).” When deployed in an IP-RAN, the MWR 1941-DC router is
customized for performance, high availability, quality of service, and link efficiency.
Cisco IOS software functions added to the MWR 1941-DC router for the IP-RAN implementation
include:
•
Redundancy logic—For monitoring Hot Standby Routing Protocol (HSRP) information to
determine the active and standby router and control T1 termination.
•
Failover logic—To force a switchover for hardware failures or an over-temperature condition.
•
Relay control—To open and close the T1/E1 interfaces on the active and standby routers.
•
Diagnostic functions—To monitor the “health” of the standby MWR 1941-DC router.
This section contains the following information:
•
MIPs-Based Software Features, page 1-4
•
Network Processor (PXF) Software Features, page 1-5
•
Redundancy Support, page 1-6
•
IP-RAN Implementation Updates, page 1-7
MIPs-Based Software Features
Standard Cisco IOS software features supported in the MWR 1914-DC router for the IP-RAN
implementation include:
•
IP Fragmentation
•
IP Multicast
•
IGMP
•
MLP, PPP Control Path (IPCP, NCP, LCP, CLNS)
•
ACFC and PFC Handling During PPP Negotiation
•
HSRP
•
OSPF
•
DHCP
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Cisco IOS Software Features
•
CDP
•
NTP
•
SNMP
Network Processor (PXF) Software Features
To achieve the required efficiency, when implemented in an IP-RAN, the MWR 1941-DC router
additionally has microcode running on the network processor to offload the fast-path processing of
packets. This allows the MWR 1941-DC router to support the traffic of up to 4 T1s or E1s (up to 60,000
packets per second) at a targeted 80% processor utilization while performing UDP/RTP header
compression/decompression (cUDP/cRTP) and PPPmux.
The following features are supported in the network processor:
•
MAC Classify
•
ICMP
•
FIB (CEF)
•
Load-balancing
•
MAC Rewrite
•
QoS Matching, including IP Access Lists (Input/Output Security ACLs are not supported), QoS
Group, IP Precedence, IP DSCP, and Input Interface
•
QoS Actions, including Set IP Precedence, Set IP DSCP, Set QoS Group, Traffic Shaping, Class
Based WFQ (CB-WFQ), and Low Latency Queuing (LLQ)
•
Maintenance of statistics, such as Forwarding, Drop, and Interface
•
IPv4
•
MLPPP, MLP, PPP Data Path (MLP LFI is not supported)
•
PPPmux
•
cRTP/cUDP
•
Link Noise Monitoring (LNM) provides configuration monitoring of individual T1/E1 circuit
quality
PPP Multiplexing/Demultiplexing
Encapsulated PPP frames contain several bytes of header information, which adds overhead to a network
that is used to transport PPP frames.
RFC 3153 describes a way to overcome this overhead. On the sending end, a multiplexor concatenates
multiple PPP frames (subframes) into a single, multiplexed frame (superframe). One header is included
in the superframe and the individual PPP subframes are separated by delimiters. On the receiving end, a
demultiplexor uses the delimiters to separate the individual PPP subframes.
The MWR 1914-DC router network processor software conforms to this specification and acts as both a
multiplexor and a demultiplexor.
RTP/UDP Header Compression
RTP is a protocol used for carrying packetized audio and video traffic over an IP network. RTP, described
in RFC 1889, is not intended for data traffic, which uses TCP or UDP. Instead, RTP provides end-to-end
network transport functions intended for applications with real-time requirements (such as audio, video,
or simulation data) over multicast or unicast network services.
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Cisco IOS Software Features
In an RTP frame, there is a minimum 12 bytes of the RTP header, combined with 20 bytes of IP header,
and 8 bytes of UDP header. This creates a 40-byte IP/UDP/RTP header. By comparison, the RTP packet
has a payload of approximately 20 to 160 bytes for audio applications that use compressed payloads.
Given this ratio, it is very inefficient to transmit the IP/UDP/RTP header without compressing it.
Figure 1-3
RTP Header Compression
Before RTP header compression:
20 bytes
IP
8 bytes 12 bytes
UDP
RTP
Header
Payload
20 to 160 bytes
After RTP header compression:
2 to 4 bytes
IP/UDP/RTP header
20 to 160 bytes
12076
Payload
RFCs 2508 and 2509 describe a method for compressing not only the RTP header, but also the associated
UDP and IP headers. Using this method, the 40 bytes of header information is compressed into
approximately 2 to 4 bytes, as shown in Figure 1-3. Because the frames are compressed on a link-by-link
basis, the delay and loss rate are lower, resulting in improved performance.
The MWR 1914-DC router network processor offloads both the compression and decompression of RTP
frames from the Cisco IOS software.
Note
The MWR 1941-DC router can be configured to perform only IP/UDP compression, in which case the
header is reduced from 28 bytes to 2 to 4 bytes.
Redundancy Support
In an IP-RAN application, to ensure availability, the backhaul links to an MWR 1941-DC router are
redundantly cabled to the VWIC-2MFT-T1-DIR/ VWIC-2MFT-E1-DIR cards. This card, designed
specifically for the MWR 1941-DC router, is a modified 2-port T1/E1 Multiflex VWIC with Drop and
Insert.The modifications include the addition of relays to activate the T1/E1 ports. The relays allow “Y”
cabling for router redundancy where the T1/E1 link is not redundant and default to open. The relays are
controlled by HSRP/redundancy protocol between the two routers connected to the same T1/E1.
Note
If you choose to use the MWR 1941-DC router in a non-redundant configuration, you must close the
relays on the card using the standalone subcommand. Also, redundancy parameters are processed when
the router is booted up. These parameters cannot be changed “on the fly.”
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Cisco IOS Software Features
HSRP
Cisco’s Hot Standby Router Protocol (HSRP) is used to control which router is active and which is
standby. HSRP uses a priority scheme to determine which HSRP-configured router is to be the default
active router. Priority is determined first by the configured priority value, and then by the IP address. In
each case a higher value is of greater priority.
IP-RAN Implementation Updates
This section lists MWR 1941-DC router product updates:
•
Traffic Recovery Over MLP After T1 Failure
With Cisco IOS Release 12.2(8)MC2b and later, you can use the keepalive interface configuration
command to configure traffic over an MLP link to recover within 6 second if a T1 failure should
occur.
•
ACFC and PFC Support on PPP Multilink Interfaces
With Cisco IOS Release 12.2(8)MC2c and later, by default, Address and Control Field Compression
(ACFC) and Protocol Field Compression (PFC) are enabled on PPP interfaces. Both features are
always enabled and will be negotiated on all serial interfaces.
Note
•
If upgrading for this support, ensure that you upgrade the MGX-RPM-1FE-CP back card
images first. After doing so, immediately upgrade all MWR 1941-DC routers connected to
the MGX-RPM-1FE-CP back card.
Ignore IP ID Field Delta in cUDP Packet Flows
With Cisco IOS Release 12.2(8)MC2c and later, by default, the ability to ignore IP ID field delta in
cUDP traffic flows is enabled. This ability eliminates the need to send information about the IP
header ID field in compressed packets. The decompressor saves the original ID field from the full
header packet and generates an ID field by incrementing it by one for each decompressed packet.
This feature improves processing efficiency; helping to minimize dropped packets and link
saturation.
•
Link Noise Monitor
Noise on T1 and E1 links that span between the BTS and central office can affect voice quality for
mobile users to the point where it becomes unacceptable. Therefore, with Cisco IOS release
12.2(8)MC2d and later, you can configure the Link Noise Monitor (LNM) on the MWR 1941-DC
router to monitor the quality of individual links in a multilink bundle. The LNM provides the ability
to detect, alert, and remove noisy links from a bundle based on user-defined thresholds and
durations. For more information on the LNM feature, see “Configuring the Link Noise Monitor”
section on page 4-21.
•
First Two Packets Sent with Full cUDP Headers
With Cisco IOS Release 12.2(8)MC2d and later, at the start of a call flow, the MWR 1941-DC router
and the MGX 8850 RPM-PR back card send the first two packets of the flow with full headers. This
feature helps to minimize the loss of cUDP headers (and therefore misrouted packets) in noisy
and/or congested networks.
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Cisco IOS Software Features
Software Features for the Cell Site DCN Application
The software required for implementing the MWR 1941-DC router in a Cell Site DCN runs on the
MIPs-based router processor portion of the MWR 1914-DC router hardware.
Standard Cisco IOS software features supported in the MWR 1914-DC router for the Cell Site DCN
implementation include:
•
Standard and extended Access Control Lists
•
IP Fragmentation
•
IP Multicast
•
IGMP
•
MLPPP
•
PPPo HDLC
•
HSRP
•
OSPF
•
DHCP
•
IP Precedence
•
cRTP/cUDP
•
CB-WFQ
•
Traffic shaping
•
TDM Drop & Insert
•
DS0-level grooming
•
NTP
•
SNMP
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Limitations and Restrictions
MIB Support
The MWR 1914-DC router supports the following MIBs:
•
CISCO-ACCESS-ENVMON-MIB
•
CISCO-TCP-MIB
•
CISCO-CDP-MIB
•
ENTITY-MIB
•
CISCO-CLASS-BASED-QOS-MIB
•
IF-MIB
•
CISCO-CONFIG-COPY-MIB
•
IGMP-MIB
•
CISCO-CONFIG-MAN-MIB
•
IPMROUTE-MIB
•
CISCO-ENVMON-MIB
•
OLD-CISCO-CHASSIS-MIB
•
CISCO-FLASH-MIB
•
OLD-CISCO-FLASH-MIB
•
CISCO-HSRP-EXT-MIB
•
OLD-CISCO-INTERFACES-MIB
•
CISCO-HSRP-MIB
•
OLD-CISCO-IP-MIB
•
CISCO-ICSUDSU-MIB
•
OLD-CISCO-SYSTEM-MIB
•
CISCO-IMAGE-MIB
•
OLD-CISCO-TS-MIB
•
CISCO-IP-STAT-MIB
•
RFC1213-MIB
•
CISCO-IPMROUTE-MIB
•
RFC1253-MIB
•
CISCO-MEMORY-POOL-MIB
•
RFC1406-MIB
•
CISCO-MOBILE-IP-MIB
•
TCP-MIB
•
CISCO-PROCESS-MIB
•
UDP-MIB
•
CISCO-QUEUE-MIB
•
CISCO-SYSLOG-MIB
The MWR 1914-DC router uses the same software base as the Cisco 10000. As such, it shares the same
QoS MIB limitations of the Cisco 10000. For information about the Cisco10000 MIB support, see the
Cisco 10000 Series ESR MIB Specifications Guide on CCO at
http://www.cisco.com/univercd/cc/td/doc/product/aggr/10000/10kmibs/specgdll/index.htm.
Limitations and Restrictions
Caution
The Cisco MWR 1941-DC router does not support online insertion and removal (OIR) of WAN interface
cards. Any attempt to perform OIR on a card in a powered up router might cause damage to the card.
Caution
Removing the compact flash from the Cisco MWR 1941-DC router during a read/write operation might
corrupt the contents of the compact flash, rendering it useless. To recover from an accidental removal of
or corruption to the compact flash, a maintenance spare with the appropriate bootable Cisco IOS
software image might be needed.
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Limitations and Restrictions
IP-RAN Implementation Limitations and Restrictions
The following list of restrictions applies when implementing the MWR 1941-DC router in an IP-RAN.
Cisco IOS Software Features not Supported on the MWR 1941-DC Router
The Cisco MWR 1941-DC router requires a special version of Cisco IOS software. Not all Cisco IOS
software features can be used with the Cisco MWR 1941-DC router as the core routing is handled by the
network processor. A list of supported features is included in the “Cisco IOS Software Features” section
on page 1-4. The following standard Cisco IOS software features are not supported on the Cisco
MWR 1941-DC router:
•
Security Access Control Lists
•
MPLS
•
802.1Q VLANs
•
Frame Relay (FR)
•
MLP LFI
•
ATM
•
Use of additional WICs. The only supported WIC is the VWIC-2MFT-T1DIR/VWIC-2MFT-E1DIR.
(IP-RAN implementation only.)
Upgrading the VWIC-2MFT-T1-DIR Microcode
When upgrading the image on your Cisco MWR 1941-DC router, power cycle the router or perform a
microcode reload on the VWIC-2MFT-T1-DIR to ensure that the firmware for the VWIC-2MFT-T1-DIR
is updated during the upgrade.
Disabling PPP Multiplexing
To fully disable PPP multiplexing (PPPMux), issue the no ppp mux command on the T1 interfaces of
the routers at both ends of the T1 link. If PPP multiplexing remains configured on one side of the link,
that side will offer to receive PPP multiplexed packets.
MLP LFI Support
MLP LFI is not supported by the Cisco MWR 1941-DC router. Therefore, MLP LFI must be disabled on
peer devices connecting to the Cisco MWR 1941-DC router T1 MLP connections.
ACFC and PFC Support on PPP Interfaces
If upgrading to Cisco IOS Release 12.2(8)MC2c or later for the ACFC and PFC support on PPP
interfaces, ensure that you upgrade the MGX-RPM-1FE-CP back card image first. After doing so,
immediately upgrade all MWR 1941-DC routers connected to the MGX-RPM-1FE-CP back card.
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New Features in Cisco IOS Release 12.2(15)MC2h
Cell Site DCN Implementation Limitations and Restrictions
The following list of restrictions applies when implementing the MWR 1941-DC router in a Cell Site
DCN.
Caution
The Cisco MWR 1941-DC router does not support online insertion and removal (OIR) of network
modules. Any attempt to perform OIR on a card in a powered up router might cause damage to the card.
Using the 1-port T3/E3: NM-1T3/E3(=)
When using the 1-port T3/E3 network module in your MWR 1941-DC router configuration, note that E3
mode is not supported with Cisco IOS Release 12.2(15)MC1a. E3 mode is supported with Cisco IOS
Release 12.2(15)MC1b and later.
Also, when used with the MWR 1941-DC router, the NM-1T3/E3 supports line rate throughput for traffic
with packet sizes of 1500 bytes. For traffic with smaller packet sizes, degradation in throughput will be
seen.
Upgrading the VWIC-2MFT-T1-DIR Microcode
When upgrading the image on your Cisco MWR 1941-DC router, power cycle the router or perform a
microcode reload on the VWIC-2MFT-T1-DIR to ensure that the firmware for the VWIC-2MFT-T1-DIR
is updated during the upgrade.
New Features in Cisco IOS Release 12.2(15)MC2h
The following new features are implemented in Cisco IOS Release 12.2(15)MC2h and later releases:
•
Support for 6 T1/E1 interfaces per/MWR
•
Support for 1800 Context IDs (CIDs) per/MWR
•
Support for enhanced Link Noise Monitoring (LNM)
Support for 6 T1/E1 Interfaces per/MWR
The new MWRs support up to 6 T1/E1 interfaces on the platform. These interfaces are configured by
IOS software as controller t1 0/4 and controller t1 0/5 for the T1 interface, and as controller e1 0/4 and
controller e1 e1 0/5 for the E1 interface. In effect, the multilink interface can now be configured with 6
T1 or 6 E1 interfaces under it. Also, the number of serial interfaces can increase depending upon how
the T1/E1 interfaces are split up by the configuration. All controller specific commands are applicable
to the new T1/E1 interfaces.
Support for 1800 CIDs per/MWR
With Cisco IOS Release 12.2(15)MC2h, the maximum number of connections is increased to 1800 for
the interface configuration command ip rtp compression-connections. This command is also used to
specify the total number of Real-Time Transport Protocol (RTP) header compression connections that
can exist on an interface. The default is 16 CID connections.
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New Features in Cisco IOS Release 12.2(15)MC2h
Command
Purpose
Router(config-if)# ip rtp compression-connections
number
Number of RTP header compression connections the cache
supports in the range of 3 to 1800.
To restore the default value, use the no form of this command.
Support for Enhanced Link Noise Monitoring (LNM)
With Cisco IOS Release 12.2(15)MC2h, LNM algorithm support has been changed or updated. There is
no longer support for the existing or previous LNM algorithm. The enhanced LNM algorithm is now
supported by default. However, the existing or previous LNM CLI is still used to set the threshold and
duration values.
The averaging algorithm is responsible for maintaining the simple moving average of link quality Bit
Error Rate (BER), Line Code Violation/Path Code Violation (LCV/PCV) values as and when noise
samples arrive. The noise is calculated as a simple moving average for the duration configured. The
average noise at any time represents the noise average for the last configured duration in seconds. It is
recalculated each second as the noise samples arrive each second. Basically, it’s a sliding window of
noise averages for the last duration in seconds.
The Benefits of this new algorithm are the following:
•
Improves CDMA backhaul link robustness by detecting noisy spans and removing them out of
service 100 percent of the time and restoring them back 100 percent of the time when the link quality
reaches an acceptable value.
•
Improves CDMA Link Noise Monitoring Capability through intelligent threshold setting by using
the averaging algorithm and providing better detection at a wide range of Bit Error Rate levels.
•
100 percent detection at the Threshold which the customer sets to.
•
Alerts the customer 100 per cent of the time about the quality of the spans.
•
Removes the degraded span effectively and having only acceptable spans in service.
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