SS7 evolution-to-diameter.pdf

White Paper: SS7 Maintainability and Evolution to Diameter

© Copyright 2012 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



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



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



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.



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.



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



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



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

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MME

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Diameter Router Network

A network deployment including Diameter Routing Agents at both the core and

edge of the network provides a more effi cient 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

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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.



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.

Upcoming PaperMore information on the subject of maintaining the integrity of SS7 networks while

evolving to LTE/EPC/Diameter will be provided in an upcoming Whitepaper titled

“Cap and Evolve – A cost effective, efficient strategy for maintaining the integrity

of the SS7 network while evolving to Next-Generation Networks (LTE/EPC/

Diameter)”.

For more information about PT and the SEGway signaling solutions, or to schedule

a demonstration, please contact [email protected].



About PT (www.pt.com) PT (NASDAQ: PTIX) is a global supplier of advanced network communications

solutions to the service provider, government, and OEM markets. PT’s portfolio

includes IP centric network elements and applications designed for high availability,

scalability, and long life cycle deployments. The industry-leading Monterey

MicroTCA and IPnexus® Application-Ready Platforms anchor the company’s

broad range of offerings. PT’s SEGway® Signaling Solutions provide affordable,

high-density signaling, advanced Diameter routing for LTE and IMS applications,

IP migration, gateway capabilities, and core-to-edge distributed intelligence, as

well as features such as Number Portability and SMS Spam Defense. The SIP-

based Xpress product family enables service providers to provision a wide range

of revenue generating and churn-reducing applications in either cloud-based or

captive architectures. PT is headquartered in Rochester, NY and maintains sales and

engineering offices around the world.

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].



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

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