Special Feature

Highly Reliable Edge Router Type-X40Yohji Ihara†, Akira Murashige, and Etsuji Kuraya
Abstract
Type-X40 is a highly functional edge router designed to accommodate various types of user networks.
One of the Type-X router family, it features high speed, high reliability, and high quality control. It lets
network designers build a sophisticated, large-scale, highly reliable MPLS (Multi-Protocol LabelSwitching) network.

1. Introduction
As well as fundamental aspects such as quality control and reliability, efficiency and flexible subscriber
accommodation are important requirements of edgerouters in an MPLS (Multi-Protocol Label Switching) network, especially in a highly reliable andlarge-scale (so-called “carrier-grade”) network. Our
Type-X40 router is a sophisticated edge router thathas various functions for accommodating diverse
user systems in addition to the functions available inType-X320 and X80, such as wire-speed packet forwarding, advanced quality-of-service (QoS) control,and reliability enhancement functions. The combination of edge routers (Type-X40), core routers (TypeX320/80), and X-OSS (Type-X operations supportsystem) can offer a scalable, highly reliable, and perfectly QoS-guaranteed MPLS network. Type-X40
provides high cost-performance and lets network
designers construct highly reliable MPLS networks
that are suitable for the required network scale.
2. Features
The Type-X40 router has four main features: i) highspeed, high reliability, and superior cost-performance, ii) advanced QoS control function as an edgerouter, iii) support for various types of network services to users and logical network configuration func† NTT Network Service Systems Laboratories
Musashino-shi, 180-8585 Japan
E-mail: ihara.yohji@lab.ntt.co.jp

58tions, and iv) maintenance and operation functions
for carrier-grade services. Table 1 shows its specifications.
2.1 High speed, high reliability, and superior
cost-performance
Figure 1 shows the hardware configuration of TypeX40. It consists of routing engine blade (REB) cards
that control the entire system, input/output controller(IOC) cards each with an interface to a maintenanceterminal and relay control signals between line interface (LINF) and REB cards, a switch blade (SWB)
that switches packets, and several LINF cards.
It has a switch capacity of 40 Gbit/s (input: 20Gbit/s, output: 20 Gbit/s), which is the smallest
among the routers in the Type-X family. By separating routing control and packet forwarding and by distributing forwarding tasks onto multiple LINF cards
and using a hardware-based execution mechanism(similar to Type-X320/80), Type-X40 achieves a highpacket processing speed of 48 Mpps (pps: packets persecond). Thanks to a content-addressable memory in
the forwarding processing part, its packet forwarding
performance is never degraded even if complex
denial or permission control is executed for eachpacket forwarding.
To ensure carrier-grade reliability, Type-X40 has
two levels of reliability enhancement measures. On
the router unit level, Type-X40 has a unique redundancy configuration for its common components(REB, SWB, and IOC), which resulted from our longexperience of switching system development. Whena running component fails, Type-X40 changes over to
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Special Feature

Table 1. Specifications of Type-X40.
System scaleLine interfaces

MPLS

QoS

Reliability

Switch capacity

40 Gbit/s

Maximum switch throughput

48 MppsNumber of line card slots

8Line interfaces

POS OC-48c/STM-16, POS OC-3/STM-1,
POS OC-12/STM-4*, ATM OC-3/STM-1,Gigabit Ethernet, Fast Ethernet,
T1 (by combining with interface unit)

LSP setup

Static, RSVP-TE, LDP*

Types of LSP

L2 (Ethernet/AAL5) over MPLS, L3 over MPLS, MPLS label stack

ATM QoS

CBR, VBR, UBR, VP/VC shaping

IP QoS

DiffServ (EF/AF4-AF1/BE, hardware processing), RSVP
1+1 configuration (SWB, REB, IOC, LINF*)

Redundancy

LSP protection switching

Interruption-free service function
Maintenance
operations

Protocols

Changeover of common components, software upgrading*Intermission-free service provisioning

Parameter changing (bandwidth, route etc.)

Fault detection

Audit function of LSP, notification of FCS error

Fault information gathering

Standby dump, failure data

NetworkIPv4, IPv6, IPv4/IPv6 dual stack (wire speed)

Routing

Static, OSPF, RIP, BGP4
Multicast, virtual router, VPN

IP service*: to be supported in 2003

High-speed lookup with CAM*,
DiffServ by hardware processing,
Separated composition of line cards,
High-performance network processor

High-speed
LINF ATM-OC3 (4 ports)

LINF ATM-OC3 (4 ports)
LIM
(ATM)

FM1

FM1

LIM(ATM)

High-speed packet processing at wire speed (48 Mpps)
LINF POS-OC3 (4 ports)
LINF FE (8 ports)
LIM(FE)FM1

FM1

LINF POS-OC48 (1 port)

LINF GbE (1 port)
LIM(GbE)

FM1

LIM(POS-OC3)

SWB

FM2

LIM
(POS-OC48)

LINF GbE (2 ports)
LIM(2p-GbE)

Changeover operation
without service
interruption

FM2REB
Dynamic routing control
distributing forwarding
task onto line cards

IOC

Information gatheringfunction when failure
occurs*CAM: content-addressable memory

Fig. 1. Hardware configuration of Type-X40.

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Special Feature

another component without any service intermission(not ever a small one).
Further reliability enhancement measures will beprovided by software upgrades without service intermission and the redundant configuration for LINF
(1+1 redundancy). As for path-level redundancy,
Type-X40 supports LSP (Label Switched Path) protection switching. When a failure occurs, a failure
notification is sent to an ingress router, which quickly switches packet flows from the primary LSP to thesecondary LSP.
The hardware composition of Type-X40 is based on
the high-density mounting method using highly integrated, high cost-performance devices. This makes
Type-X40 so small that two type-X40 systems can bemounted in one cabinet. Its superior cost-performance compared with other routers of the same classderives from such implementation technology.
2.2 Advanced QoS control function at an edge
routerAn edge router needs to have more finely tunable
QoS control functions to meet various user traffic
requirements than a core router. For ATM QoS functions, Type-X40 provides a layered shaping function
for virtual paths and channels in addition to general
QoS functions of ATM. These functions make it possible to design a network that provides well-adjusted
QoS capabilities for each user’s conditions.
Type-X40, like Type-X320/80, provides a DiffServ(Differentiated Services) function. DiffServ technology in a router consists of six transfer quality classes,with the highest quality class being Expedited ForVoIP servers
SGCA

warding (EF). This technology achieves fine tuningfor various types of traffic, for example VoIP and data
communication. To complete DiffServ control, thequeuing control of Type-X40 has an outstanding
hardware mechanism that simultaneously performs
priority read-out control in the Assured Forwarding(AF) class and priority control between classes,
which other routers do not do. Furthermore, its DiffServ function can be set not only to a physical circuit
but also to each logic interface, such as an ATM virtual channel or virtual LAN. In addition to the DiffServ function, interworking with the QoS servers
makes it possible to operate a network where thebandwidth of all LSPs is completely guaranteed.
2.3 Support for various types of network services
to users and logical network configuration
functions
For a large-scale MPLS network such as a carrier’s
network, it is important how scalable the network is,
how many network services can be provided to users
systems, and how flexibly logical network resources
can be handled by the network designer. The various
network services and logical network configuration
examples supported by Type-X40 are shown in Fig.
2. Type-X40 provides various types of circuit interfaces such as POS, ATM, FE, and GbE, so it can deal
with the various interface requirements of each user
system accommodated. The LINF cards are divided
into line interface modules (LIMs) and forwardingmodules (FMs) in Type-X40, unlike in the core router
Type-X 320/80. This composition, aimed at common
use of FM cards, enables the circuit type to be easily
High-quality IP telephoneservice with low latency andbandwidth guarantee

Services accommodated
by various interfaces

PSTN

IP phone

Bandwidth-guaranteed VPN
service for business use

MG
Company LAN Company LAN
Company LANATM
FE

IPv6 network

VRF
VRF
VRF

L3 over MPLS
IPv4/v6 tunneling

VRF
VRF
VRF

IPv6 users
IPv6 network

ATM
Digital leasedline network

20

VLAN
VLAN

10VLAN

GbE
FE

VRF
VRF

L2 (Ethernet/AAL5) over MPLS

Subscriber accommodation expansion
by VLAN tag replacement
LSP label stack

VRF

VLAN

Highly reliable MPLS network
ISPISP

Leased line service
where delay, bandwidth,and high reliability areguaranteed
VRF

ISPUsers

ISP access service that
accommodates many users FE: Fast Ethernet
GbE: Gigabit Ethernet

Fig. 2. Various network services and logical network configuration examples supported by Type-X40.

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Special Featurechanged by replacing an LIM card with another typeof LIM card. This is very useful for coping with not
only card failures but also changes in user requirements.
One of the features of Type-X40 as a user accommodation router is its ability to establish data links,
such as ATM-AAL5 and Ethernet (including taggedVLAN), on an IP network with an LSP. Long-distance data links over LSPs give users a free hand indesigning their own networks. These LSPs canaccommodate many users with various traffic types inthe same router by applying QoS control. An MPLS
label stack function enables the network to accommodate many data-links in an LSP. Therefore, evenwhen accommodating many users at a low speed, it ispossible to establish an efficient MPLS network withthe increase in the number of MPLS paths kept to theminimum. Furthermore, to establish many more Ethernet-links in a network, Type-X40 as an MPLS
egress router replaces the VLAN-TAG of the Ethernet-frame. This expands the number of VLANs thatcan be accommodated in the whole network.
Another feature of Type-X40 is abundant service
functions which are essential for promising commercial services, such as IPv6 and VPN (Virtual PrivateNetwork) function. Type-X40 enables these services
without the routers being set up service by service. Ofcourse, such functions can cooperate with the highly
reliable and high-quality controlled MPLS edge functions.

2.4 Maintenance and operation functions for
carrier-grade services
To minimize service intermissions caused by maintenance operations, not only router reliability functions but also advanced maintenance and operation
functions are needed. In particular, the edge routerneeds a function for performing flexible operations
corresponding to various user demands because edge
router intermission immediately causes user communication intermission. The maintenance and operation functions provided by Type-X40 are shown inFig. 3.
Type-X40 has a function for changing various service provisioning data without service intermission.
LSP bandwidth and forwarding route are typicalexamples of such data. For MPLS, it also has intermission-free service provisioning functions that canchange an LSP route or QoS parameter without any
service intermission. Moreover, Type-X40 canchange the ATM bandwidth without service intermission in order to cope with the need to change user
bandwidth quickly.
Type-X40 can configure line-card data before
mounting and remove or insert a card while operating, so maintenance operations such as adding a newline card can be done efficiently.
Another important element for a carrier-grade network is to avoid or minimize service intermission
caused by a network-level failure. For this purpose, it
is very important to display latent network disorderand recover from a failure at an early stage. For early
X-OSS

By comparing Type-X40 with X-OSS in terms
of provisioning data (route, bandwidth etc.),
latent inconsistencies can be found.
Collation of the data
between router and OSS
Type-X40

Type-X40LSPUser networkCorerouter
Alarm is issued whenerrored frame occurs.

Change in LSP
route without
service intermission
Type-X40

User network

alarm•••

In-service

Existing network

Highly reliable MPLS network

failureEthernet

User network

Corerouter
Change in QoS
parameters without
service intermission

dataCore router
Failureinformation Information gathering
for memory data andfault information
Remote operation terminal

Existing network

LSP
LSP

Core router

Unmounting

Newly establishednetwork

Configuration before
card mounting

Fig. 3. Maintenance and operation functions of Type-X40.

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Special Featuredetection of provisioning data inconsistencies, TypeX40/80 and X-OSS have LSP data audit functions
which are achieved by comparing the provisioning
data in Type-X40/80 and X-OSS. Surveillance andnotification functions for an errored frame on Ethernet are also provided for early detection of failures
hidden in an Ethernet segment.
Even when a complicated failure like a software
failure occurs, it should not persist for long, and any
affect on the whole network must be avoided. TypeX40 has a function for gathering various data, such as
memory data and fault information at the instant a
failure occurs. Therefore, as in a switching system,
the cause of the fault can be identified and the fault
can be corrected. Speedy investigation into the causeof failure and complete recovery are possible thanks
to these data collecting functions.
3. Conclusion
Development of the basic functions of Type-X40
was completed in the 2nd quarter of 2002, the second
step of developing functions dealing with a largescale network was completed in the 4th quarter of2002, and Type-X40 is now in a stable operating condition. Demand for a highly reliable service network
based on MPLS technology is increasing more andmore. We plan further improvements, such as reliability enhancement or high-speed rebooting without
hardware initialization, and further development of
new service functions, such as IP multicasting.

62

Yohji Ihara
Senior Research Engineer, Second Promotion
Project, NTT Network Service Systems Laboratories.
He received the B.E. and M.E. degrees in electrical and electronic engineering from Hiroshima
University, Hiroshima, in 1986 and 1988, respectively. In 1988, he joined NTT and engaged in
the development of digital switching systems.
Currently, he is developing carrier-grade routers.

Akira Murashige
Senior Research Engineer, Supervisor, SecondPromotion Project, NTT Network Service Systems Laboratories.
He received the B.E. and M.E. degrees in system engineering from Hiroshima University,
Hiroshima, in 1981 and 1983, respectively. Sincejoining NTT Yokosuka Laboratories he has
mainly been engaged in research and development of private-use data communication systems
and their operating systems. Currently, he isengaged in research and development of carriergrade routers.

Etsuji Kuraya
Development Project Leader, Second Promotion Project, NTT Network Service Systems Laboratories.
He received the B.E. and M.E. degrees in electrical systems engineering from Osaka Prefecture
University, Osaka, in 1978 and 1980, respectively. In 1980, he joined NTT Musashino ElectricalCommunications Laboratories and engaged inresearch and development of digital switchingsystems. Currently, he is engaged in research anddevelopment of integrated IP edge systems. He isa member of the Institute of Electronics, Information and Communication Engineers (IEICE)of Japan.

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