backed” onto existing GSM networks. The fixed-band- width voice channels of the GSM network are then used for table look up (in the GSM’s Location Register data bases) to obtain a Packet Radio user profile.

The signaling and the data traffic are then sent through a separate radio channel that provides 8 timeslots. These timeslots can be used together (to provide a wide-bandwidth channel for a single user) or they can be parceled out among multiple users (to pro- vide several narrow-bandwidth channels).

By using multiple channel timeslots together, Packet Radio can provide mobile terminals with transmission speeds ranging from 14.4 Kbits/sec to 115 Kbits/sec. Because Packet Radio can pro- vide a wide range of bandwidths on demand, it can be configured to efficiently handle short “bursty” traffic (such as email and web browsing) as well as large volumes of data. In addition, different levels of service can be provided to different subscribers, billing them accordingly. By Robert Haim Once the user’s data has been sent over the radio channel times- lots, it is packetized for routing over an IP-based Public Land The volume of data traffic has been rapidly overtaking the Mobile Network. (Since these IP-based backbones are used to volume of voice traffic in fixed networks. Data traffic is expected interconnect wireless base stations within a local wireless system, to exceed voice traffic in fixed networks this year, and there is we will call them internal networks.) little doubt that wireless networks will follow soon after. However, second-generation wireless infrastructures were designed pri- Internal networks can be used to carry packets between mobile marily for voice communications, and will need to be replaced terminals within a local area. However, to allow a mobile terminal or enhanced to handle the anticipated data traffic. Third- to connect to a fixed terminal, the data packets are routed over generation wireless systems designed to handle a mix of voice Public Data Networks, such as ATM networks, X.25 networks, or and data traffic have been prototyped, but they have not yet been the . (Because these networks carry data outside the local deployed. An interim solution is to enhance existing second- wireless system, we will call them external networks.) generation wireless systems with hardware and that will allow them to carry data traffic. This article discusses how Packet Radio protocols and network components this is currently being done. To support Packet Radio operation, new protocols and new hard- ware components must be added to a GSM wireless network. Third-generation wireless systems (such as IMT-2000, UMTS) These are described in the next sections. have been designed to handle both voice and data traffic effi- ciently, taking into account the anticipated rise in data traffic, rel- Packet Radio Components ative to voice traffic. However, these new wireless systems are Two new major components are needed to: very complex, and that complexity has slowed the standardization process — international standards bodies have yet to approve all ■ Provide routing within and between internal networks of the needed standards. ■ Integrate the operation of the internal networks with an exist- ing (voice) GSM wireless network This complexity has also delayed full implementation and wide- ■ Provide routing between internal networks and external networks spread deployment of these third-generation systems. While there have been some proof-of-concept prototypes in Korea and Japan, These new components are called General Packet Radio Service third-generation wireless systems have yet to be deployed. Support Nodes. (We will call them simply Nodes.)

General Packet Radio Service There are two types of Nodes: Because of the delays in implementing third-generation wireless ■ Serving Nodes ■ Gateway Nodes systems, General Packet Radio Service (GPRS) has been intro- duced as an interim method for sending data at high-speeds over Serving Nodes current wireless network infrastructures, such as: Serving Nodes on an internal network collectively perform sev- eral functions within their service area: ■ Global Systems for Mobile communications (GSM) wireless networks ■ They detect the presence of any new Packet Radio mobile station. ■ TDMA-based wireless networks ■ They process the registration of the new mobile subscriber, and keep a record of its location. Note: The term General Packet Radio Service is quite a mouthful, ■ They send queries to Home Location Registers, to obtain pro- so we will simply call it Packet Radio in this article. file data for each Packet Radio subscriber. ■ They deliver packets to the mobile stations. How Packet Radio works A voice-based wireless link provides a fixed bandwidth that is Gateway Nodes adequate for voice communication. However, different types of A Gateway Node also performs several functions: require different bandwidths — often much more bandwidth than a voice channel can provide. To provide ■ It provides an interface between an internal network and an the additional bandwidth, Packet Radio systems can be “piggy- external network. ■ It maintains the routing information that is needed to “tunnel” ■ The System General Packet Radio Service Protocol Data Units (PDUs) between internal networks, allow- Protocol (BSSGP) communicates with its counterpart in the ing the Serving Nodes in one internal network to exchange Serving Node, to allow processing of routing and quality of data with those in another internal network. service information. The base station protocol uses the Frame ■ It provides network and subscriber screening, and address Relay Q.922 core protocol as its transport mechanism. mapping between internal networks and external networks. There are also special protocol layers that run on the Serving Network enhancements Nodes (see Figure 3). In addition to adding the Serving and Gateway nodes to the GSM wireless network (to provide high-speed data paths), the existing GSM infrastructure must also be enhanced to support Packet Serving Node protocol stacks Radio as follows: SNDCP GMM GTP ■ The GSM base stations must be enhanced to communicate LLC TCP/UDP with the Serving Node that is handling the wireless data com- munications within its coverage area. BSSAP+ BSSGP ■ The GSM Home Location Registers must be enhanced to register Packet Radio user profiles, and to respond to queries SCCP Network IP originating from Serving Nodes regarding these profiles. MTP3 Service Packet Radio MTP2 Q.922 (core) L2 network protocols Base station Application software running protocol stacks MTP1 HDLC PHY on a mobile terminal commu- Application nicates by making API calls Figure 3 to a standard network-level protocol, such as IP or X.25. IP or X.25 Below this network-level pro- GMM SNDCP ■ The Base Station System General Packet Radio Service tocol are layers that provide Protocol (BSSGP) communicates with its counterpart in the special data and signaling LLC base station, and processes routing and quality of service infor- protocols that are used to mation. The base station protocol uses the Frame Relay Q.922 communicate with GSM base RLC core protocol as its transport mechanism. stations and Serving Nodes. MAC ■ The BSSAP+ software manages paging for voice and data (See Figure 1) connections, and optimizes paging for mobile subscribers. PHY BSSAP+ is also responsible for location and routing updates, ■ The Sub-Network De- as well as mobile station alerting. pendent Convergence Pro- Figure 1 ■ The Logical Link Control (LLC) layer communicates with its tocol (SNDCP) is a special counterpart in the mobile terminal to assure reliable transfers layer below the network-level protocol that communicates with between the mobile terminal and the Serving Node across the its counterpart in the Serving Node. SNDCP also provides data wireless link. compression, data segmentation, and multiplexing of network- layer messages onto the radio link connection. There is also a special protocol layer ■ The Logical Link Control (LLC) is a special data link layer that runs on the Gateway Nodes (see Gateway Node protocol for Packet Radio that is similar to Link Access Figure 4). protocol stack Protocol -D (LAPD). This protocol layer communicates with its counterpart in the Serving Node to assure reliable transfers ■ The Tunnel Protocol (GTP) adds IP or X.25 between the mobile terminal and the Serving Node across the routing information to protocol wireless link. data units for Node-to-Node deliv- GTP ■ The Packet Radio Mobility Management (GMM) software ery through the IP backbone. The TCP/UDP is used for signaling, and handles mobility issues such as Tunnel Protocol operates on top of roaming, authentication, and selection of encryption algo- TCP/UDP over IP. IP rithms. Packet Radio L2 (IP/ATM) There are also several special network operation PHY protocol layers that run on Base station In Packet Radio communication, a the GSM base stations (see protocol stacks new network connection is estab- Figure 4 Figure 2). lished for each data transaction, and LLC Relay then released once that transaction is completed. However, these ■ The Network Service proto- connections are established so quickly that the user is given the BSSGP col manages the conver- RLC impression of always being “connected”. The process used to gence sublayer that operates Network establish and sever connections in real time requires several between the base station Service steps: protocol and the Frame MAC Relay Q.922 Core by map- Q.922 (core) ■ Network access ping the base station proto- ■ Routing and data transfer col’s service requests to the PHY ■ Mobility management appropriate Frame Relay services. Figure 2 These steps are described on next pages. a long time before widespread demand is apparent. As a result, leading-edge technology providers often face substantial risks when introducing new products.

Packet Radio is a good example of this. The technology requires a very substantial initial investment in a new infrastructure, and the payoff might be a while coming. Timing is vital. With the explosive growth of data traffic in fixed networks (due to the Internet) the ques- Network access tion is not whether there will be a substantial demand for Packet When a Packet Radio mobile station is powered up, it “intro- Radio, but when (and how fast) that demand will materialize. duces” itself to the network by sending an “attach” request. As in cellular wireless networks, several administrative functions are Anticipated use of Packet Radio by service suppliers performed to validate a user: Although Packet Radio was originally promoted by communica- tions equipment suppliers, it has also generated strong interest ■ User Registration uses the mobile ID to determine the user’s among wireless service providers because of its potential to pro- packet data protocol and the user’s address within the internal vide increased revenue, due to data traffic. Figure 5 provides a network. Within the home area of the mobile station, tradi- market overview, showing where Packet Radio can be used at tional Home Location Registers are used. (These registers are various points within the communication network, along with enhanced to support Packet Radio.) projections of when deployments will take place. ■ Authentication ensures the validity of the Packet Radio mobile station, and determines its associated services. Mobility man- Mobile high-speed Internet access — micro web browsers; Email; agement functions are used for this part of signaling. Wireless Virtual Private Networks; New IN services, such as “uni- ■ Call Admission Control determines the network resources fied messaging”; electronic commerce; education and entertain- needed to provide the requested quality of service. If those ment services resources are available, they are reserved. Market Anticipated Routing and data transfer participant Benefits availability Once a mobile station begins its data transmission, the Serving Nodes and the Gateway Nodes use the destination address in each End-user Mobile high-speed Internet access — message header to route the messages through the internal net- micro web browsers; Email; Wireless works, on a hop-by-hop basis. Depending on the destination, the Virtual Private Networks; New IN data might be: services, such as “unified messaging”; electronic commerce; education and ■ Forwarded from one Serving Node to another, within the inter- entertainment services Q4 2000 nal network Wireless New sources of revenue with data ■ Tunneled, to transfer the data from one internal network to another service traffic through existing GSM and providers TDMA infrastructure; Charge on a The Tunnel Protocol layer also converts each external network packet-volume basis; Expansion of Deployment address to an address that can be used for routing within the inter- market to accommodate data traffic, and testing nal networks. as well as voice traffic by Q2 2000 The data itself might also go through several transformations as “Inside the Opportunities for existing equipment it travels through the internal networks. For example, the data network” and development of new equipment, might be: equipment such as GGSN, SGSN and test vendors equipment. Immediately ■ Compressed to use the radio path in a more efficient manner “Outside the Opportunities to develop Packet- (Special, compression algorithms are sometimes used by man- network” Radio-enhanced handheld devices ufacturers to differentiate themselves. These algorithms can equipment and appliances offering a range cause interoperability problems in heterogeneous networks.) Vendors of capabilities. Immediately ■ Encrypted to protect the mobile station from eavesdropping (Encryption algorithms are also used as a differentiating feature.) Figure 5

Mobility management Trillium’s General Packet Radio Service As a user’s mobile station moves from one area to another, mobil- (GPRS) Solutions ity management software tracks its location within the internal Trillium Digital Systems has developed software that implements network, and Serving Nodes communicate with each other, to all of the GPRS protocol layers needed to support every node in a update the user’s location. This allows a continuous logical link GSM wireless network. (Software to support TDMA-based wire- to be maintained between the mobile station and some Serving less networks is currently being developed.) This code has been Node within the internal networks. At the end of transmission this implemented in , and has been optimized for both high perfor- logical link is severed, and the resources associated with it are mance and for a minimum memory footprint. made available for reallocation. Each protocol layer is designed to support both ends of any Packet Market trends Radio connection. For example, a single instance of SNDCP can Popular wisdom says that, to be successful, a new product must be simultaneously support the Serving Node side, as well as mobile customer-driven — not supplier-driven. However, emerging tech- terminal side. This is very useful for testing purposes during sys- nologies often allow the design of innovative new products before tem development. When a Serving Node is being built, the code potential users can fully appreciate their value. While a few for a mobile station can be included (for test purposes) and then sophisticated users might see the value immediately, it might take switched out of the compilation in the final product. The Packet Radio protocol stack software is also designed to Robert Haim is Marketing Manager for Trillium Digital Systems. allow multiple copies of each layer to be distributed (and simulta- neously executed) among multiple processors. This allows a sin- For more information about Trillium’s General Packet Radio gle multiprocessor system to handle large volumes of data. It also Service software products, you can contact Trillium at: allows for future scaling up of Packet Radio equipment as data Trillium Digital Systems, Inc. loads increase. 12100 Wilshire Blvd., Suite 1800 Los Angeles, CA 90025-7118 Figure 6 shows the Packet Radio stacks and layers that are avail- Phone: 310-442-9222 • Fax: 310-442-1162 able, along with the unique features of each. Email: [email protected] Web: http://www.trillium.com

Component Protocol stacks Unique features GPRS — GMM, SNDCP, LLC, Network Service, ■ One instance of each protocol stack can service thousands of mobile and GTP stations (configurable by the operator). SS7 — MAP, TCAP, BSSAP+, SCCP, MTP Level 3, ■ Provides load balancing among active logical interfaces (virtual Serving GPRS MTP Level 2 and MTP Level 1 channels). Support Node Frame Relay — Q.922 Core and LMI ■ Traffic distribution can be configured per logical interface, and can (SGSN) be used for providing dissimilar services to different users. ■ Uses the “Precedent Class” to prioritize messages from various Packet Data Protocols (PDP) contexts when congestion occurs. GPRS – GTP ■ Supports socket interfaces with a generic TCP/UCP stack; One Gateway GPRS X.25 – X.25 and LAPB instance of GTP software can support multiple GSNs at the same time. Support Node ■ Can transparently pass user-defined messages; private messages (GGSN) and information elements can easily be added. ■ Can directly interwork with Trillium’s X.25 products. GPRS – LLC Relay, the base station protocol, ■ Supports point-to-point connections. Base and Network Service ■ Both static and dynamic mapping of BSS Virtual circuits to Network Station System SS7 – SCCP, MTP Level 3, MTP Level 2, and MTP Service Virtual circuits are provided (BSS) Level 1 Frame Relay – Q.922 Core and LMI GPRS – BSSAP+ ■ Existing equipment can be upgraded to accommodate GPRS by Home Location SS7 – MAP (GSM Phase II+), TCAP, porting BSSAP+ whether a Trillium or a non-Trillium SS7 stack is Register currently in operation. (HLR) SCCP, ISUP, MTP Level 3, MTP Level 2 and MTP Level 1

Mobile GPRS – GMM, SNDCP, LLC ■ Small code footprint to accommodate low memory devices. Terminal X.25 – X.25 and LAP Figure 6

Summary Until third-generation IMT-2000 systems become a reality (and About Trillium perhaps even long afterward) General Packet Radio Service will thrive wherever high-speed data transmission over wireless net- Trillium Digital Systems was founded in 1988 and has provided works is needed. Since any current GSM wireless network user can upgrade to handle high-speed data, Packet Radio will greatly leading-edge software technology to the communications industry increase wireless data traffic volume, thus generating new revenue for over 11 years. The company develops, licenses, and supports for GSM service providers standards-based communications software solutions for SS7, ATM, General Packet Radio Service has already been deployed in: H.323, V5, ISDN, Frame Relay, IP, X.25/X.75, fault-tolerance/ high-availability, and interworking technologies, and is currently ■ Europe by Telfort in Holland, One 2 One in England, and T-Mobil in Germany developing solutions for wireless, mobility, software on silicon, ■ Asia by SmarTone Mobile Communications, Ltd. in Hong Java, and other emerging technologies. Trillium has licensed its Kong ■ US by Omnipoint software to more than 250 companies, for use in more than 400 projects worldwide. Trillium provides its products in the Trillium provides all of the necessary software components for upgrading GSM wireless networks to support Packet Radio. C programming language, along with documentation, training, and Each protocol stack is comprised of layers that can be used inde- support as standard deliverables. Additional company and product pendently. Because the stack is platform independent, it can be ported to any , to any processor or to any system information is available on the Web at http://www.trillium.com. architecture.