Lines Matching defs:circuit
159 We use virtual circuit switching in order to multiplex multiple multi-hop channels over the available ICD links. Virtual circuit switching has several advantages over a packed-switched approach. It ensures that all messages take the same path and thereby FIFO delivery of messages (as long as the underlying ICD links provide FIFO delivery). Moreover, it allows to create per-circuit state on the nodes of a virtual circuit.
165 The virtual circuit switching approach would also allow to reserve some resources on the nodes for each channel. Per-channel reserved resources could include buffer space to save received, but not yet forwarded messages, or bandwidth on the ICD links. This is potentially very useful for congestion and flow control. Note that we cannot simply drop messages in case of congested links, as we want to provide a reliable messaging service. As of now, we do not reserve resources on the nodes, but allocate required resources dynamically.
180 \section{Virtual circuit identifiers}
182 Multi-hop messages carry a virtual circuit identifier (VCI). Virtual circuit identifiers allow nodes to identify the particular multi-hop channel a message belongs to. Each node on a multi-hop channel maintains a forwarding table, which maps VCIs to the next hop on that particular channel. A node forwards multi-hop messages based on this forwarding table. At channel end-points, a VCI allows to identify the binding belonging to the multi-hop channel the message was sent over. Virtual circuit identifiers are not only local to a specific link, but also to a direction on that link. Figure~\ref{fig:vci} shows an example assignment of VCIs.
184 We assign virtual circuit identifiers at random. At each node, we use a hash table to map virtual circuit identifiers to a pointer to the channel state. The use of a hash table allows efficient message forwarding. When a message arrives, it can be determined where to forward this message by means of a simple look-up in the hash table. The complexity of this lookup is linear in the number of virtual circuit identifiers that map to the same hash bucket (the number of buckets in the hash table is a compile time constant).
186 An attacker sending messages with manipulated virtual circuit identifiers may be able to send messages on channels not belonging to him. By assigning virtual circuit identifiers at random, we make it very unlikely for an attacker to find valid virtual circuit identifiers of channels not belonging to him.
188 This design requires that each node on a multi-hop channel tells its neighbours what virtual circuit identifier they should use for messages sent over that particular channel. This happens in the set-up phase of a multi-hop channel (see section~\ref{section: set-up}).
193 \caption{Virtual circuit identifiers} \label{fig:vci}
209 \item A client dispatcher initiates the set-up process by calling the bind function of the multi-hop interconnect driver. This function forwards the bind request to the monitor running on the client dispatcher's core. The bind request includes various parameters, including the \emph{iref} of the service and the client's (ingoing) virtual circuit identifier.
225 As described in section~\ref{section:vcis}, it is necessary that each node on the multi-hop channel tells its neighbouring nodes what virtual circuit identifier they should use for messages sent over that particular channel. Therefore, each message contains the virtual circuit identifier of the sender. The two response-messages additionally contain the VCI of the receiver. This allows the receiver of a response-message to identify the multi-hop channel the message belongs to.