IP best effort networks (Figure 8.17). It is also confirmed when looking at the need for information at the start of a packet communication after attaching, let us say a mobile terminal in GPRS to a packet network. The information referred to is called PDP (packet data protocol) context. It might be a logical association between a mobile station and a public data network running across a GPRS network. The context may define aspects such as routing, QoS, security, billing, type of network, network address, access point name and radio priority. Largely, we are again back to the fundamental plans. Service Implementation PS domain transport, IP end-to-end CS domain transport Header PAYLOAD bytes UDP/TCP Common transport for the Header CS & PS PAYLOAD bytes domain (AMR) Transport backbone Figure 8.15 Packets travelling in the network, example The basic packet typically consists of: Checksum Payload Address Control OSI 2 OSI 4 -7 OSI 2, 3 OSI 2 Checksum Payload Address Control Figure 8.16 Basic packet composition IP infrastructure The overall requirements on an IP backbone is to provide connectivity services embracing: - IP address assignment DHCP/RADIUS - domain name translation - routing Routers - address transparency (tunnelling) NAT, NAS - user authentication RADIUS, certificate server - user authorization RADIUS, firewall, proxies - accounting RADIUS - data authentication (digital signature, key management) Security gateway - data confidentiality (encryption, key management) Security gateway - data integrity (hash algorithms) Security gateway - filtering, proxies Proxies Figure 8.17 IP network support functions Understanding Changing Telecommunications - Building a Successful Telecom Business 8.6 THE ROLE OF FUNDAMENTAL TECHNICAL PLANS IN PACKET DESIGN From Figures 8.15 and 8.17 it is easy to recognize the following fundamental technical plans: routing, QoS (= checksum), numbering/addressing, security, charging and accounting. When extending the capabilities the QoS plan is even more important. From the PDP (packe