Technical Overview System Architecture and Protocol Guide System Architecture and Protocol Guide – 9-05 1 © 2005 SkyPilot Networks, Inc.
Table of Contents Introduction .................................................................................................................................... 3 System Components ................................................................................................................. 3 Network Topologies....................................................................................................................... 4 Point-to-Point/Multipoint .............................................
Introduction The SkyPilot Carrier-Class Broadband Wireless System supports an innovative architecture offering point-to-point, point-tomultipoint and mesh topologies. Automatic network discovery and connectivity allows an operator to quickly build a network offering high levels of coverage and redundancy. The system implements a sophisticated and flexible Layer 2 network. Rate control and packet prioritization enables multiple service offerings, including high-quality voice over IP (VoIP) support.
Network Topologies The SkyPilot Carrier-Class Broadband Wireless System supports point-to-point, point-to-multipoint and mesh topologies. An operator has the flexibility to start with a simple point-to-point/multipoint configuration and add SkyExtenders as subscriber demand requires to create a more robust mesh topology over time. Point-to-Point/Multipoint In a typical point-to-multipoint configuration, a SkyGateway is installed on a cell-tower, tall building or other height-advantaged location.
this message records the link on which the message was received, the SkyGateway identifier and the associated cost. These SkyExtender and SkyConnector nodes utilize this cost data to select the optimal, lowest cost link on which to forward data. Every SkyExtender forwards a message specifying its lowest cost path to a given SkyGateway. In the case of a network with multiple SkyGateways, each SkyExtender forwards a cost message for each SkyGateway.
Routing Example Example of mesh routing based on lowest link cost. • SkyExtender A – This node, the first one deployed, receives a cost of 23 directly from the SkyGateway. The node selects to route over this 36/24 Mbps link. • SkyExtender B – This node receives a cost of 30 directly from the SkyGateway, and it selects to route over this 24/24Mbps link. • SkyExtender C – This node receives two cost messages, one from SkyExtender A advertising a cost of (23*1.
Rerouting A rerouting decision is made either due to an active route failure or because a significantly lower cost route is consistently available. There are four scenarios that cause a reroute operation: 1. A failure in the link or a SkyGateway/SkyExtender system along the selected route. 2. A failure in the link or a SkyGateway/SkyExtender further along the route to the SkyGateway. 3.
Spectral Management SkyExtenders and SkyConnectors require no pre-configuration and automatically search or “hunt” among all supported frequencies and, in the case of the SkyExtender, all antennas. When a SkyExtender or SkyConnector is powered up, it checks non-volatile memory for a Preferred Frequency. This is the frequency that should be favored in any search, and is set after a successful connection to the network or by operator configuration.
Link Management The SkyPilot system supports variable modulation types and encoding rates. Differing rates can be utilized for each individual link within the network, including each of the multiple individual links possible for any given node. The various modulation types and rates are shown in the table below. Note that the payload traffic capacity will be less than the stated data rates due to packet header and protocol overhead.
Initial Link Optimization The SkyPilot Synchronous Mesh Protocol (see separate section) implements an Automatic Repeat reQuest (ARQ) mechanism that allows for the rapid retransmission of errored packets. This feature operates transparently to the all protocols (such as TCP/IP) transmitted over a SkyPilot system.
SkyPilot Mini-Slots All SkyPilot nodes are synchronized to the same 1 second timing frame. The SkyGateway and SkyExtender nodes house a GPS receiver that provides a standard, highly accurate 1 Pulse Per Second (PPS) clock. SkyConnectors derive the 1 second frame from timing messages exchanged with the connected SkyGateway or SkyExtender.
Receiving Data from a Child If a child node has data queued for transmission upstream and is not in active communication with its parent, it will signal the need by transmitting a Bandwidth Request message in the next contention slot. The details of the Bandwidth Request, including the priority of the data queued, is stored by the parent node and accessed by the scheduler. In the current SkyPilot system, child status is polled by the parent.
The operator can use a range of classifiers to control prioritize packets. For instance, an operator may assign a high priority to packets matching a range of IP addresses and having a defined ToS field setting. Any packets not matching this classification will be assigned a low priority. The resulting classification is tagged (in the SkyPilot protocol header) so that any intermediary SkyExtenders can maintain the prioritization.
Security Provisions A SkyPilot Carrier-Class Broadband Wireless System operates as an intelligent, virtual Ethernet switch, with a full learning bridge implemented at both the subscriber interface (SkyConnector or SkyExtender) and the networking interface on the SkyGateway. This Layer 2 network architecture allows subscribers to have full mobility between SkyGateways without the need to update IP addresses.
VLANs The SkyPilot system allows an operator to partition subscriber traffic through the use of Virtual LANs. VLANs limit the scope of broadcast and multicast traffic, and facilitate the segmentation of traffic in the backbone network. An individual subscriber can be configured to a single VLAN. In this mode all Ethernet packets received on the subscriber interface of the SkyConnector or SkyExtender are tagged with the configured VLAN ID.
4. When Node A receives the SP_AUTH_CHALLENGE message, it verifies Node B’s Identification Certificate using its root public key. Node A decrypts Node B’s random number using its private key and shared static key. Node A then computes its own random number. Using the two random numbers it computes the secret session key. 5. Node A encrypts its random number using the shared static key. It then encrypts this ciphertext along with Node B’s decrypted random number using Node B’s public key.
SNMP Each SkyPilot node has an SNMP Agent. This agent allows an operator to query system configuration, and to monitor status and statistics. SNMP provides a predominately read-only interface with only the reload and reboot write attributes. Reload causes the configuration file to be downloaded and any changes in provisioning parameters to be completed. Reboot will cause the node to be reset and reconnect with the network.
