Facilitating IP Applications over HF Networks
Icon-PEP supports implementing IP applications over high-frequency (HF) networks using the STANAG 5066 link layer as the connection interface.
Icon-PEP offers two primary services:
- Generic Switching of IP Packets: This enables the HF network to function as an IP subnet, supporting many IP applications.
- Enhanced TCP Support: A Performance Enhancing Proxy (PEP) optimises TCP performance across HF networks, enabling applications like web browsing to operate effectively. Although theoretically, any application can be used, the selection is limited in practice due to the restricted bandwidth and significant latency associated with HF communications.
IP Switching & PEP
Icon-PEP’s first service focuses on switching IP packets, adhering to STANAG 5066 Annex U “IP Client” for managing an IP subnet over HF. This service promotes IP packets and allows controls based on the IP protocol and its ports (e.g., ICMP, UDP). Packets are variously manageable based on these protocols, consisting of options for blocking or opting for ARQ versus non-ARQ transmission.
Icon-PEP is compatible with both IPv4 and IPv6 in connection with STANAG 5066 Annex U. The second service utilises a proxy architecture to boost the performance of TCP applications.
TCP connections from applications end at the point of interaction with Icon-PEP instead of continuing to the other application. Icon-PEP then transmits data over HF using the HF-PEP protocol detailed in [HF-PEP: STANAG 5066 TCP Performance Enhancing Proxy Protocol (S5066-APP9)]. This method makes sure that only the data stream is sent over HF, not including the overhead of the entire TCP protocol, such as acknowledgments and window management. By avoiding the challenges of running TCP over IP Client, the PEP approach brings important improvements in performance and reliability.
HF-PEP operates over SLEP (SIS Layer Extension Protocol) as outlined in S5066-APP3. SLEP offers stream services for HF-PEP, including data compression. It communicates over STANAG 5066 by connecting to the local STANAG 5066 SIS (Subnet Interface Service). Icon-PEP is optimised for HTTP usage, allowing typical small data transfers to be completed with a single round trip in HF.
Icon-PEP operates as an IP router and facilitates two models of IP routing:
- Fixed Routing: Icon-PEP establishes IP networks linked to each peer STANAG 5066 node, directing IP traffic accordingly, including a default route permitting mobile units to send all traffic to a shore node automatically.
- NAT Mode: Aimed at shore nodes, this enables traffic support from any mobile unit without the shore node needing to recognise the IP networks used by the mobile unit. This is achieved through Network Address Translation (NAT), though it only accommodates IP traffic initiated by a mobile unit, with traffic originating from Icon-PEP instead of using GRE.
Icon-PEP supports establishing IP and TCP traffic rules to manage and control data flow. These rules can be formed according to:
- Protocol (for TCP: the port; for IP: the protocol/port).
- Source and Destination IP addresses are matched against lists of IP subnetworks.
The rules can be used to:
- Block matching traffic.
- Set custom parameters for traffic that meets the criteria.
- Specify ARP/Non-ARQ preferences for IP traffic.