Information Technology Reference
In-Depth Information
Each RTP packet has a 4-byte header consisting of the following 1-byte fields:
Operation type —Indicates the packet type.
Node type —Indicates whether the packet came from a service node or a nonservice node.
Controller type —Indicates whether the controller in the node transmitting the RTP packet has a
multibuffer controller.
Machine type —Indicates whether the processor in the RTP sender is fast or slow.
Both the controller type and the machine type fields are used for pacing.
ARP
ARP entities are classified as either address resolution clients or address resolution services. Address
resolution clients are usually implemented in client nodes, whereas address resolution services are
typically provided by service nodes.
An ARP packet has an 8-byte header consisting of a 2-byte packet type, a 4-byte network number, and
a 2-byte subnetwork number. There are four packet types: a query request, which is a request for an ARP
service; a service response, which is a response to a query request; an assignment request, which is sent
to an ARP service to request a VINES internetwork address; and an assignment response, which is sent
by the ARP service as a response to the assignment request. The network number and subnet number
fields have meaning only in an assignment response packet.
ARP clients and services implement the following algorithm when a client starts up. First, the client
broadcasts query request packets. Then, each service that is a neighbor of the client responds with a
service response packet. The client then issues an assignment request packet to the first service that
responded to its query request packet. The service responds with an assignment response packet
containing the assigned internetwork address.
ICP
ICP defines exception notification and metric notification packets. Exception notification packets
provide information about network-layer exceptions; metric notification packets contain information
about the final transmission used to reach a client node.
Exception notifications are sent when a VIP packet cannot be routed properly, and the error subfield in
the VIP header's transport control field is enabled. These packets also contain a field identifying the
particular exception by its error code.
ICP entities in service nodes generate metric notification messages when the metric subfield in the VIP
header's transport control field is enabled, and the destination address in the service node's packet
specifies one of the service node's neighbors.
The Transport Layer
VINES provides three transport-layer services:
Unreliable datagram service —Sends packets that are routed on a best-effort basis but not
acknowledged at the destination.
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