Evolution to Diameter
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Transcript of Evolution to Diameter
Keeping the SS7 Network Viable while Migrating to LTE/EPC/Diameter
© Copyright 2013 Performance Technologies, Inc. All Rights Reserved. 2
Table of Contents
Introduction ............................................................................................................ 3
SS7 Network Architecture Evolution ....................................................................... 4
SS7 Initial Implemention Phase ............................................................................... 4
North American SS7 Network Implementation .................................................. 4
International SS7 Network Implementation ....................................................... 4
SS7 Quasi Associated Network Phases .................................................................... 5
SS7 Core-Edge Network Architecture ................................................................ 5
SS7 Core Network Architecture ......................................................................... 5
SS7 High Speed Links ............................................................................................. 6
SS7 ATM Links .................................................................................................. 6
SS7 Annex "A" Links ........................................................................................ 6
SS7 SIGTRAN Links ........................................................................................... 7
SS7 Network Maturity ............................................................................................ 7
LTE/EPC/Diameter Network ................................................................................... 8
Diameter Network Transport (SCTP) ................................................................. 8
Diameter Mesh Network .................................................................................. 8
Diameter Router Network ............................................................................... 10
SS7 Maintainability and Evolution to Diameter Issues and Concerns ..................... 11
The SEGway® Solutions Advantage ....................................................................... 11
About PT ........................................................................................................... 13
About the Author ................................................................................................. 13
Acronyms ........................................................................................................... 14
Keeping the SS7 Network Viable while Migrating to LTE/EPC/Diameter
© Copyright 2013 Performance Technologies, Inc. All Rights Reserved. 3
IntroductionThe current status of today’s telecommunications signaling network can be described
by two important characteristics – the maturity of the Signaling System 7 (SS7)
Network and the evolution from SS7 signaling to Diameter signaling, each providing
benefits and challenges.
Over the past 25+ years the SS7 network has become the most reliable, secure, and
feature rich signaling methodology in telecommunications history. Any discussion
of the mature nature of the SS7 network should include its evolutionary phases:
mesh to quasi-associated network topology, Time Division Multiplexing (TDM)
links to high speed links, high speed links to IP-SIGTRAN links, and the benefits
each deliver to the SS7 network in general, and more specifically to the evolution to
Next-Generation Networks (NGN). The longevity of the SS7 protocol, its associated
network, and the equipment used within the network is exposing unforeseen
challenges to service providers and equipment vendors. These challenges directly
affect the core benefits of SS7 networks such as costs, reliability and maintainability
– all at a time when the desired focus is on the evolution to Diameter-based
signaling networks.
The evolution from SS7 to Diameter is being driven by advances in technology,
the service provider’s desire to monetize the networks, and the subscribers’
insatiable demand for applications and their bandwidth requirements. Since the
initial inception of SS7 there have been significant advances in telecommunication
network technology, including the introduction of Internet Protocol (IP) into service
providers’ networks thus driving the convergence between voice and data. This
convergence has opened telecommunications networks allowing them to take
advantage of protocol advances by the Internet Engineering Task Force (IETF)
including Stream Control Transmission Protocol (SCTP) and Diameter. As stated in
the report What is it worth? by Recon Analytics , "The decline in voice revenues is a
global trend. In eight out of the 14 countries analyzed, including the United States,
competition was so intense that the voice revenues declined, while subscriber
numbers increased and minutes of voice use remained roughly flat." The reduced
voice Annual Revenue per User (ARPU) is forcing service providers to monetize
their data network via evolution to Long Term Evolution/Evolved Packet Core (LTE/
EPC)/Diameter. Today, mobile network operators are faced with the challenges
Keeping the SS7 Network Viable while Migrating to LTE/EPC/Diameter
© Copyright 2013 Performance Technologies, Inc. All Rights Reserved. 4
of building Fourth Generation (4G) LTE/EPC/Diameter networks to meet the
demands of subscriber devices such as smartphones and tablets with the always-on
applications they support. This subscriber demand is referred to as the “Four Anys”
– get any information, from anywhere, at anytime, from any device.
This paper covers the evolution of the SS7 network and its subsequent evolution
to LTE/EPC/Diameter networks. Emphasis is placed on the maturity of the SS7
network, the age of its associated equipment, and the impact both of these factors
bring to the ongoing support of the network and its evolution to the LTE/EPC/
Diameter-based network.
SS7 Network Architecture EvolutionSince its initial deployment in the mid 1980s the SS7 network architecture
evolved over time to address problems encountered with the network-based
routing methodology. This evolution can be described in phases including: initial
implementation, quasi-associated signaling, and high speed link. The initial
phase of SS7 network deployment can be segmented in to the North American
Implementation Phase and the International Implementation Phase due to
regulatory and network topology issues.
SS7 Initial Implementation PhaseNorth American SS7 Network Implementation
The initial deployment of SS7 in North America was characterized by network
topology that included STPs for the routing of SS7 messages. This network
architecture is discussed in the Quasi Associated Network section of this paper.
International SS7 Network Implementation
The track of international signaling evolution is quite different from that of
North America due, in part, to the size of the networks, the starting point of the
network, and the design of network elements. Typically, the size of the individual
international telecommunications networks was much smaller than those in North
America. The international switching equipment vendors incorporated some STP
functionality into the each of the network elements. The network size, coupled
with the differences in switching equipment, facilitated the implementation of an
associated or mesh network. In the initial international implementation phase of
Keeping the SS7 Network Viable while Migrating to LTE/EPC/Diameter
© Copyright 2013 Performance Technologies, Inc. All Rights Reserved. 5
SS7, network elements were interconnected directly with each other to create a
fully meshed network. As the network continued to grow with more traffic and
more interconnected elements, network operators found that the management and
administration of this meshed network became untenable and fraught with human
related errors affecting network routing, address assignment, and security when
interconnected to foreign networks.
SS7 Quasi-Associated Network PhasesThe quasi-associated phase of SS7 network evolution is identified by the presence
of STPs being incorporated within the network. Like most phases of SS7 network
evolution this phase can also be subdivided for clarity. The two sub-phases of
this evolutionary category are the more distributed Core-Edge topology and the
centralized Core routing topology.
SS7 Core-Edge Network Architecture
This phase was built on a distributed architectural concept including network (core)
and local (edge) STP pairs. The core STP pairs provided access to the company-
wide database services, aggregated connectivity to local STPs, and served as
access points to other service providers. The edge STPs provided SS7 services
and connectivity to all end offices and tandems within a geographical region. All
requests for services that required database intervention were routed from the edge
STPs to the core STPs and then to the appropriate database.
SS7 Core Network Architecture
The final phase of network evolution, today’s network architecture, is totally
centralized and is comprised of large core STPs providing all SS7 connectivity
and database services such as 800, Number Portability (NP), Intelligent Network
(IN), and Calling Name (CNAM). The evolution to this network configuration
was influenced by governmental mandates to implement NP in both the wireline
and wireless telecommunications market segments. The NP service required
extremely large and fast databases that could be accessed from every end office
in the network. To accomplish these requirements, a solution was developed
that integrated the database within STP functionality. The operating companies
determined that a large core STP with an included database was the most cost-
effective use of this expensive technology.
Keeping the SS7 Network Viable while Migrating to LTE/EPC/Diameter
© Copyright 2013 Performance Technologies, Inc. All Rights Reserved. 6
SS7 High Speed LinksAs the number of SS7 network users and the amount of traffic continued to grow,
the network became bandwidth and facility constrained due to the low speed link
capabilities and the 16 link per linkset limit imposed by the protocol. The solution to
this problem was to implement technological advances to overcome the limitation
of TDM/DS0 based links. On the surface, the implementation of high speed links
was simple “just increase the bandwidth of the transmission facilities.” However,
because the SS7 protocol defines the entire message delivery mechanism from
physical layer to the application layer, modifications to the protocol had to be made
at both the physical and transport layers.
SS7 ATM Links
One methodology used for high speed links was to carry SS7 information using
Asynchronous Transfer Mode (ATM). This methodology required the replacement
of SS7 Physical Layer (Message Transfer Part 1) with ATM, and the replacement of
the SS7 Transport Layer (Message Transfer Part 2) with Signaling ATM Adaptation
Layer (SAAL). Based on the fixed width of ATM cells, the efficiency of ATM high
speed links varied based on SS7 message size.
� Short SS7 Messages are inefficient
� Messages approaching 48 octets are efficient
� Messages in excess of 48 octets are not as efficient
SS7 Annex “A” Links
Another high speed link methodology was to utilize the entire bandwidth of a T1
(1.536 Mbit/s) or E1 (1.984 Mbit/s) transmission facility for the transport of a
single SS7 signaling data link. This solution also requires modification to the SS7
protocol including Physical Layer (Message Transfer Part 1) and SS7 Transport
Layer (Message Transfer Part 2) to accommodate the full bandwidth of the
transport facility and a larger quantity of messages for both acknowledgment and
retransmission.
Keeping the SS7 Network Viable while Migrating to LTE/EPC/Diameter
© Copyright 2013 Performance Technologies, Inc. All Rights Reserved. 7
SS7 SIGTRAN Links
The final phase of network evolution was driven by a multitude of factors including
ongoing bandwidth demands, need for facility cost reduction and migration to
Next-Generation Networks. There were many issues that had to be addressed in
order to place a real-time, network critical protocol over IP. The first obstacle was
“What transport protocol would be used on top of IP?” Since, Transmission Control
Protocol (TCP) had been around for quite a while it was the first to be investigated.
A close look at TCP revealed the “Head of the line blocking issue” which would
have to be overcome before using TCP for a 5 nines, real-time protocol. The next
transport protocol studied was User Datagram Protocol (UDP). It was quickly
determined that there would be too much work involved to overcome UDP’s lack
of guaranteed delivery. The final answer was to use the new IETF specified Stream
Control Transmission Protocol (SCTP). SCTP provided a solution to the problems
of both TCP and UDP and addressed the needs to transport SS7 data using an IP
centric methodology. The advantages of SCTP include the following:
� Acknowledged Error Free Non Duplicated transfer of data
� Data Fragmentation – single data message may be split into multiple
SCTP messages
� Sequence Delivery of User Messages within Multiple Streams
� Bundling of Multiple User Messages into a Single SCTP Message
� Network Fault Tolerance using Multi-homing at either end or both
This solution also included the use of SS7 adaption layers to maintain the primitive
interfaces to upper layers of the SS7 protocol eliminating the need to totally rewrite
the SS7 protocol handling software. The SS7 network became the first large scale
commercial network deployment of the SCTP protocol.
SS7 Network MaturityThe SS7 network, including its transport capabilities and protocol technologies, are
mature, well established, and understood by telecommunications service providers
worldwide. SS7 remains the preeminent standard of signaling for many operators
providing network-based, revenue-generating services. With the large installed
base, any change from the legacy SS7-managed networks to Next-Generation
Networks such as LTE/EPC/Diameter or IP Multimedia Subsystem (IMS) will be
Keeping the SS7 Network Viable while Migrating to LTE/EPC/Diameter
© Copyright 2013 Performance Technologies, Inc. All Rights Reserved. 8
evolutionary, not a revolutionary. As a result of this prolonged technological shift,
hybrid networks combining parts of both network SS7 and LTE/EPC/Diameter will
be the standard for the near term.
LTE/EPC/Diameter NetworkThe mobile subscriber’s ever increasing demand for large volumes of bandwidth
is driving the deployment of LTE/EPC/Diameter networks globally. Subscriber
devices, such as smartphones and tablets with the always-on applications they
support, are having a huge impact on a mobile operator’s ability to keep up with
bandwidth demands and the associated signaling requirements. Eros Spadotto,
of Telus, explained the signaling and bandwidth issues in his keynote speech for
the IEEE conference in Ottawa, June 12, 2012. He said, “The reality is that while
our megabytes of traffic are increasing, the signaling from these devices is greatly
overwhelming that. In fact, we can look at a period of time where our growth has
been 100% year over year on payload, on how many megabytes, but our signaling
has grown 2,700%.” This signaling increase is changing the entire LTE/EPC/
Diameter deployment paradigm.
Diameter Network Transport (SCTP)
The first step in the planning and design of the LTE/EPC/Diameter network was
to decide which transport protocol to use. Because the IEFT designed Diameter
protocol to use the services of either TCP or SCTP on top of IP, network operators
and vendors alike had to choose between the two. The reliability and survivability
required in EPC made this choice relatively easy. Because the network required real-
time, guaranteed sequence delivery of messages, the only choice was SCTP. SCTP
also provided the added benefit of multi-homing thus adding to the reliability of the
network.
Diameter Mesh Network
The architecture of the LTE/EPC/Diameter network (Figure 1) defines a large
quantity of network elements, each with its own functionality. Each network
element can have multiple interfaces to other elements based on the procedures
and information exchanged. Additionally, the peer concepts of the Diameter
protocol and the connection-oriented methodologies of SCTP, significantly increase
the complexity and quantity of routing rules within the network. As the network
Keeping the SS7 Network Viable while Migrating to LTE/EPC/Diameter
© Copyright 2013 Performance Technologies, Inc. All Rights Reserved. 9
continues to evolve and grow additional routing rules have to be provisioned
in every network element. The routing complexity inherent within this mesh-
type network presents a twofold problem. First, the large task of maintenance
and administration of the routing rules on individual nodes directly affects the
consistency and scalability of the network. Second, placing the routing responsibility
on the individual network elements can degrade the network element’s ability to
perform its primary function.
Figure 1. LTE/EPC Network
IMSHPMN
VPMN
Non-3GPP
Gxb
Rx
Rf
Ro
Sh
Ro
S6d S6a
S13
S6a
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OCS
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H-PCRF
V-PCRF
ePDGSGSN
AAA
3GPPAAA Proxy
P-GW
S-GW
AS
S-CSCF
I-CSCF
P-CSCF
Non TrustedNon-3GPP
TrustedNon-3GPP
MME
EIR
MME
HSS
Keeping the SS7 Network Viable while Migrating to LTE/EPC/Diameter
© Copyright 2013 Performance Technologies, Inc. All Rights Reserved. 10
Diameter Router Network
A network deployment including Diameter Routing Agents at both the core and
edge of the network provides a more efficient and scalable architecture. By placing
the Diameter Router in the core of the network, routing is centralized to reduce the
quantity and complexity of inter-network and intra-network routing. Also, because
the routing responsibility is removed from individual network elements, expensive
resources are freed to perform their primary function – thus reducing network wide
capital expenditures.
Figure 2. LTE/EPC Network with SEGway® UDR™
HPMN
VPMN
Non-3GPP
S6d
S6a
Gx
Gxc
S9
IMS
STaGxa
SWa
SWd
Non TrustedNon-3GPP
TrustedNon-3GPP
S6a
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GzShRo
CxRo
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S-GW
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UDR
AS
S-CSCF
I-CSCF
P-CSCF
HSS
Keeping the SS7 Network Viable while Migrating to LTE/EPC/Diameter
© Copyright 2013 Performance Technologies, Inc. All Rights Reserved. 11
SS7 Maintainability and Evolution to Diameter Issues and ConcernsThe age of the SS7 signaling network and its associated equipment are of great
concern to network operators. These concerns are paramount to maintainability
of the network and its service/revenue generating capabilities, all while the
network is evolving to the NGN network model of LTE/EPC/Diameter. From the
service provider’s point of view, these concerns are characterized by the following
questions:
� Has my current STP reached End of Life?
� Is my current STP vendor continuing to provide SS7/STP solutions?
� Is my current STP vendor requiring upgrades to their systems?
- Are these upgrades incremental?
- Are these upgrades extensive?
- Do these upgrades provide me an evolutionary path to NGN networks
(LTE/EPC/Diameter)?
� Am I facing ongoing support issues for my existing STPs?
The answers to these questions affect the core values of the SS7 network; the most
reliable, secure, and feature rich signaling methodology in telecommunications history.
The SEGway® Solutions Advantage
PT’s SEGway® portfolio includes IP-centric network elements and applications
designed for high availability, scalability and long life cycle deployments. These
solutions offer carriers and service providers extensive IP networking options,
unrivaled in the industry with features such as high density signaling, advanced
routing, IP migration, gateway capabilities, SIP bridge, and core-to-edge distributed
intelligence. In addition, these carrier grade solutions provide lower cost of owner-
ship from initial purchase through their entire product life-cycle deployment. The
SEGway product portfolio provides the following unique advantages:
Designed and architected for IP deployment: SEGway products are designed to
be simply an extension of the IP network. The internal architecture of SEGway
platforms includes intelligent IP backplanes for both internal and external
communications. Also included in the design is an integrated, five-nines-reliable,
gigabit Ethernet switch. The inclusion of the carrier grade Ethernet switch reduces
the requirement for an expensive, external Ethernet switch or IP router ports.
Keeping the SS7 Network Viable while Migrating to LTE/EPC/Diameter
© Copyright 2013 Performance Technologies, Inc. All Rights Reserved. 12
Evolution to NGN networks: The addition of the SEGway® Universal Diameter
Router™ (UDR™) to the SEGway product portfolio provides the most efficient, cost
effective and high capacity evolution path from SS7 to LTE/EPC/Diameter-based
networks.
High processing capabilities: PT’s SEGway STP platforms meet a variety of
network requirements from very small to large and can support up to 4,536 links.
Most environmentally friendly: The SEGway product portfolio has the lowest
power consumption and heat generation of any signaling product available, thus
reducing its carbon footprint.
World Class Support: PT provides a vast array of support services including:
network planning, engineering, installation, and training. These services are offered
on an a la carte basis and can be tailored to meet individual customer requirements.
The SEGway signaling solutions have been deployed international and domestic
applications in wireless and wireline configurations all over the world, including
the United States, Canada, France, United Kingdom, Netherlands, Brazil, Mexico,
Azerbaijan, Japan, China, Africa, and many others. Vast arrays of standards-based
protocols are supported including: SCTP, M2PA, M2UA, M3UA and SUA. Also
supported are traditional TDM, ATM Annex “A.”, SIP and Diameter.
For more information about PT and the SEGway signaling solutions, or to schedule
a demonstration, please contact [email protected].
Keeping the SS7 Network Viable while Migrating to LTE/EPC/Diameter
© Copyright 2013 Performance Technologies, Inc. All Rights Reserved. 13
About PT (www.pt.com) PT (NASDAQ: PTIX) is a global supplier of advanced, high availability network
communications solutions. Its SEGway® Diameter and SS7 Signaling Systems
provide tightly integrated signaling and advanced routing capabilities and
applications that uniquely span the mission critical demands of both existing
and next-generation 4G LTE and IMS telecommunications networks. The
Company’s IPnexus® Multi-Protocol Gateways and Servers enable a broad range
of IP-interworking in data acquisition, sensor, radar and control applications for
aviation, weather and other infrastructure networks. Established in 1981, PT is
headquartered in Rochester, NY and markets and sells its products worldwide
through its direct sales organization as well as through channel partners that include
major telecommunications equipment vendors, government prime contractors and
value-added resellers.
About the Author Tom Jenkins has over 42 years of experience in telecommunications. During his
career, he has held positions related to SS7 Signaling including: Technical Support
Manager, Manager of Product Management for STPs, International Sales Director
for SS7 Test Equipment, and Vice President Sales and Marketing for SS7 Test
Equipment. In 1997 Tom started Center Point Consulting, Inc., providing SS7,
SIGTRAN, and SIP training to over 2500 students worldwide. Tom has been actively
involved with telecommunications signaling including SS7, SIGTRAN, SIP and
Diameter for 26 years. Tom has been working directly with the Diameter Protocol
since 2008. Today, Tom is currently the Senior Director of Marketing at PT. You can
contact Tom at [email protected].
Keeping the SS7 Network Viable while Migrating to LTE/EPC/Diameter
© Copyright 2013 Performance Technologies, Inc. All Rights Reserved. 14
Acronyms
3GPP Third Generation Project Partnership
4G Fourth Generation
AAA Authentication Authorization Accounting
AS Application Server
ATM Asynchronous Transfer Mode
CNAM Calling Name
DS0 Digital Signal 0, 64kbps
E1 2.048Mbps
EIR Equipment Identity Register
EPC Evolved Packet Core
ePDG Evolved Packet Data Gateway
H-PCRF Home Policy Control Rules Function
HPMN Home Public Mobile Network
HSS Home Subscriber Server
I-CSCF Interrogating Call Session Control Function
IEEE Institute of Electrical and Electronics Engineers
IETF Internet Engineering Task Force
IMS IP Multimedia Subsystem
IN Intelligent Network
IP Internet Protocol
LTE Long Term Evolution
M2PA MTP2 User Peer-to-peer Adaptation Layer
M2UA MTP2-User Adaptation
M3UA MTP3-User Adaptation
MME Mobility Management Entity
mTCA Micro Telecom Computing Architecture
MTP1 Message Transfer Part 1
MTP2 Message Transfer Part 2
NGN Next Generation Network
NP Number Portability
OCS Online Charging System
OEM Original Equipment Manufacturer
OFCS Off Line Charging System
P-CSCF Proxy Call Session Control Function
P-GW PDN Gateway – Packet Data Network Gateway
SAAL Signaling ATM Adaptation Layer
SCCP Signaling Connection Control Part
S-CSCF Serving Call Session Control Function
SCTP Stream Control Transmission Protocol
SGSN Serving GPRS Support Node
S-GW Serving Gateway
SIGTRAN Signaling Transport
SIP Session Initiation Protocol
SS7 Signaling System 7
STP Signaling Transfer Point
SUA SCCP User Adaptation Layer
T1 T-carrier 1, 1.544 Mbps
TCP Transmission Control Protocol
TDM Time Division Multiplex
UDP User Datagram Protocol
UDR Universal Diameter Router
V-PCRF Visited Policy Control Rules Function
VPMN Visited Public Mobile Network