NMS AccessGate

Optimizing bandwidth utilization has become more critical even though simultaneously technology is evolving to improve bandwidth throughput — whether it’s wireless, over copper (DSL, T1, E1, etc.) or fiber. The reason is simply cost and the resultant margins. In an increasingly competitive telcom/datacom landscape, keeping your costs low with the highest possible profit margin is critical. In most wireless networks, operators bear the recurring cost of traffic backhauling in order to connect geographically dispersed cell sites with their core networks. As access networks have been built out to support wireless services, each newly deployed service has required additional dedicated transmission equipment (such as leased lines, satellite trunks, or microwave links) between the base station and the base station controller. According to NMS Communications, this backhaul cost can represent up to 20–30 percent of total network operating expenses (OpEx). By reducing the number of these connections, operators can eliminate a significant portion of network OpEx.

NMS’ AccessGate is a backhaul optimizer that reduces the backhaul OPEX expense in GSM networks. NMS’s AccessGate provides up to 2:1 bandwidth savings, drastically lowering operating expenses and according to NMS, it typically allows wireless operators to recover their investment (ROI) in less than 12 months. According to NMS, the ROI is less than 12 months for T1/E1 when monthly link costs are $400–$1,000 and less than four months for expensive satellite links. Additional savings can be achieved in specific cell site configurations, such as those involving TDMA, EDGE, and UMTS. AccessGate is specifically designed for radio access networks (RANs) and consists of systems installed at the central office (CO) that are connected to units deployed in the cell sites.

NMS actually pioneered unique aggregation and bandwidth reduction techniques that enable wireless operators to maximize network utilization, while still preserving call quality and only adding an impressive less than 9 ms end-to-end latency. The NMS wireless backhaul optimizer not only recovers unused DS0s, but it also recovers inactive bandwidth at the subchannel level through intelligent processing of network traffic. This “freed up bandwidth” can then be used to offer additional services. The AccessGate product uses A.bis multiplexing and optimization techniques and will operate in existing radio access infrastructure and integrates easily with legacy radio systems.

One important note is that AccessGate does not perform vocoding, so it actually preserves audio quality and data integrity. Interestingly, some of the product’s heritage came from NMS’s expertise in their VoIP product line — in particular their packet optimization within their VoIP products.

So How Does It Work?
Essentially what the product does is create its own HDLC packet that contains the optimized payload. Silence is removed completely which alone can save 40 percent on bandwidth. Typically when a E1/T1 channel is idle, signaling is still sent, however with AccessGate, it eliminates these idle packet payloads. Similarly, with GPRS or EDGE data, if no data is being sent, the AccessGate with keep the connection alive with reduced payload.

The system located at the cell site is a small, cost-effective device designed to optimize the bandwidth utilization of 2G, 2.5G, and 3G mobile traffic. The device optimizes, aggregates, and multiplexes mobile traffic from multiple cell site services onto a common backhaul to an AccessGate system at the CO, and performs the reverse operation for traffic coming from the CO to the cell site. By enabling operators to backhaul traffic over a reduced number of leased lines, AccessGate reduces current operating expenses.
At the CO, AccessGate is a high-performance, carrier-class, scalable platform that terminates multiplexed streams (backhaul connections) from multiple AccessGate cell site gateways. The CO system processes traffic from each cell site to reconstruct frames and channels. The original frame is then delivered to the base station controller (BSC) and, where applicable, to the 3G radio network controller (RNC).

One interesting feature is the ability to pass SNMP traffic over the backhaul link essentially using an IP packet to be able to remotely manage remote cell sites. In fact, the administrative interface (See Figure 1) is a Java application that transmits the SNMP signals to and from the interface over the backhaul link. The management tool application can run from PCs with access to a LAN on which Central Office AccessGate systems are running. The tool can be launched as a native application, or integrated with HP OpenView or with the operator’s OSS (using its embedded SNMP agent). The AccessGate management tool’s main functionality includes the ability to configure and view system, trunk, timeslot, and sub-channel parameters, remotely upgrade system software, acknowledge and delete system alarms, monitor and view charted data for key performance indicators (KPIs), and more.

Figure 1

The cell site unit (BTS) is a 1U server with DC power, 50 watts, and currently eight T1s/E1s with a 16 T1/E1 version called the AccessGate 1000 which will be available shortly. The BSC unit is a CompactPCI chassis with N+1 redundancy, 12U, STM-1, OC-3, etc. You can configure certain trunks to be backhaul, Iub, or A.bis. One really nice feature is that the product has a bypass feature that detects if the box fails due to power failure or software failure and it then triggers a relay switch to connect the BSC straight through to the BTS. The relay switch connects the two at the physical “copper” level, so although you lose the optimization techniques, you minimize potential outages. NMS claims five nines (99.999%) reliability with pass-through enabled.

Another nice feature is that you can set by subchannel or timeslot the ability to NOT optimize traffic, i.e., for sensitive traffic. Another nice feature is that you can remotely upgrade the units at the same time. It has QoS so that if channels are busy, in the event of any congestion, the upgrade download will continue but at a slower throughput. Essentially IP gets a lower priority over voice. Also, when rebooting the unit during an upgrade, the relay switch previously mentioned “kicks in” until the unit has completely booted up, so your backhaul links still go through.

Migration Path
AccessGate provides a cost-effective migration to EDGE and 3G. AccessGate provides cost saving and benefits during the rollout of EDGE and 3G radio access networks AccessGate aggregates and optimizes EDGE traffic to form a reduced and “pooled” backhaul link group. When introducing UMTS, Node B systems are added to GSM cell sites, requiring an additional E1/T1 connection to accommodate minimal additional network traffic — but not if operators use AccessGate. AccessGate can accommodate both 2G (A.bis) and 3G (Iub) interfaces in a single system. The AccessGate cell site system aggregates traffic from the Node B (Iub interface), utilizing bandwidth made available by compressing the GSM traffic. Wireless operators can avoid both the installation and recurring costs of E1/T1 lines as 3G RAN is deployed, until bandwidth is more fully utilized.

Features
Aggregates T1/E1 communications onto a common backhaul between the cell site and the MSO. It also performces statistical multiplexing which suppresses idle frames and idle channels for 2G services, making the most of backhaul bandwidth.
Other features:

• Bandwidth savings: Achieves a bandwidth savings ratio of up to 2:1.
• Backhaul media: Satellite, leased lines, and microwave.
• Network interfaces: Supports interfaces for 2G, EDGE, and 3G networks.
• OAM&P: Offers simple management and provisioning; SNMP MIB.
• High availability: Provides five nines reliability on the CO system, with pass-through.
• Network interoperability: Supports 2G, 2.5G, and 3G networks.
• Scalability: Up to eight T1/E1 lines in a flexible configuration for cell site systems, and up to 120 T1/E1 interfaces for the CO system.

Conclusion
Simply put, AccessGate reduces the number of E1/T1 connections to the CO resulting in improved efficiency in 2G networks today that can also be applied as 3G and EDGE are deployed. AccessGate was designed from the ground up to address the critical requirements of telecom operators, including reliability (Five 9’s) and low latency. With a common backhaul, provisioning and management is easy, and these systems integrate with the operator’s existing infrastructure. TMC Labs can say unequivocally that NMS Communications is the true pioneer in backhaul optimization that others have copied, but never truly duplicated. IT

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