Introduction

Voice networks are evolving from traditional circuit switched networks to IP-based networks. As part of this evolution, legacy switches are being replaced by softswitches and application servers.

 

Service providers are moving away from the big monolithic cluster-based servers and moving towards smaller and more flexible designs. Hardware is now deployed in cost-effective increments using a "rack and stack" server farm concept, where capacity can be added on a per need basis.

 

Challenges

The replacement of legacy switches represents several significant challenges to the service providers. Typically a switch is migrated in several steps:

1. The new switch is introduced and provisioned
2. The SS7 network is updated to allow routing to the new switch
3. Trunks are gradually migrated from the legacy switch to the new switch
4. The interconnecting switches must be updated for each trunk that is migrated

 

This transition poses a considerable operational effort and challenge, and it has to be carefully coordinated across all carriers in order to ensure uninterrupted service during the transition

 

Another issue in this transition is that the new switch will require a new point code assignment, and as can often be the case in many networks, network point codes can be a scarce resource, making them difficult to obtain.

 

Solution

Interestingly enough, the IP network addressed these problems a long time ago by using a Network Address Translator (NAT). Typically the NAT creates a private network by transparently re-mapping IP addresses. A company can map its local, inside network addresses to one or more global outside IP addresses. The global IP addresses on incoming packets can be unmapped back into local IP addresses. This not only helps ensure security, but also reduces the number of global IP addresses that a company requires. Utilization of a NAT enables a company to use a single IP address in its communication with the outside world. What happens inside the private network is invisible to the public network.

 

Using this kind of technology rather than IP addresses for point codes enables a number of switches in a private network 'behind' the ISUP NAT to share the same public network point code. Routing to and from these switches will be based upon CIC tables. The ISUP NAT will then perform the appropriate routing as well as the necessary point code swapping. A new switch can be introduced seamlessly behind the ISUP NAT and trunks can be gradually moved from a legacy switch to the new switch by provisioning the appropriate CIC routing tables.

 

Ulticom nSignia eSTP

Ulticom's nSignia^® eSTP offers a Point Code Emulation feature, which greatly simplifies the switch migration. The Point Code Emulation uses nSignia eSTP's unique multiple networks feature in order to create a private network where multiple switches can share the same outside (public network) point code. Routing to the individual private network switches is done according to the CIC codes (trunk identifiers) handled by each switch.

 

Figure 1 illustrates how a legacy switch can be gradually migrated to one or more new switching elements. First, nSignia eSTP replaces the legacy switch in the public network (same point code). nSignia eSTP will then serve as a front end to the new switching elements, including the legacy switch (now in the private network).

 

There are no changes required in the public network; it still appears as if the legacy switch is handling all of the traffic. nSignia eSTP will route to the private network (new switches) based upon CIC value provisioning (trunk identifier). Trunks can be moved from the legacy switch to one of the new switches simply by changing the CIC routing tables on nSignia eSTP (and moving the physical trunks). From the standpoint of the public network, nothing appears to have changed.

 

In addition to the ability to migrate legacy equipment, this feature also enables service providers to gradually grow the switch capacity without requiring SS7 network reconfiguration - all traffic simply continues to go through the same point code even though new equipment is installed in the private network.

 

Key Business Benefits

Facilitates new legacy switch replacement by allowing:

• New switches to share the same public network point code trunks to be smoothly migrated from the legacy switch to a new switch
• Improves cost/performance ratio. New switch equipment can be introduced without any network changes
• Reduces point code consumption by allowing many switches to share the same point code
• Optimizes service scaling using the Internet model. Using nSignia eSTP will enable the addition of more trunks without changing the network infrastructure
• Lower cost of initial deployment (flexible growth). As additional trunks are required, new switching equipment can be added without impacting the public network