The NDN Interest packet is a TLV defined as follows:
Interest = INTEREST-TYPE TLV-LENGTH Name [CanBePrefix] [MustBeFresh] [ForwardingHint] [Nonce] [InterestLifetime] [HopLimit] [ApplicationParameters [InterestSignature]]
Name is the only required element in an Interest packet.
Nonce is required when an Interest is transmitted over the network links, i.e., a compliant forwarder must augment the Interest with the
Nonce element if it is missing.
ForwardingHint are optional elements to guide Interest matching or forwarding.
Interest can also include an optional
If an Interest contains
InterestSignature, it is considered a Signed Interest.
See Signed Interest section for details.
As recommended by TLV evolvability guidelines, unrecognized non-critical TLV elements may appear in the Interest packet.
However, they must not appear before the
See Name for details.
Name element that can be put in the Interest is further restricted to have at least one name component.
Interests that include Name TLV that has zero name components MUST be discarded.
CanBePrefix = CAN-BE-PREFIX-TYPE TLV-LENGTH ; == 0
Name element in the Interest is a prefix, exact, or full name of the requested Data packet.
When not present, the
Name element is either exact or full name of the Data packet:
if the last component of the
ImplicitSha256DigestComponent, Interest can be matched only to a Data packet with full name that includes the implicit digest component;
if the last component has any other type, Interest is matched to Data if all name components in Interest’s
Nameelement equal to components in Data’s
Nameelement, without consideration of the implicit digest component.
MustBeFresh = MUST-BE-FRESH-TYPE TLV-LENGTH ; == 0
The presence or absence of the
MustBeFresh element indicates whether a content store may satisfy the Interest with stale Data.
See FreshnessPeriod for more information.
ForwardingHint = FORWARDING-HINT-TYPE TLV-LENGTH 1*Name
The ForwardingHint element contains a list of Names (“delegations”).
Presence of the forwarding hint implies that Data can be retrieved by forwarding the Interest over path(s) pointed by the listed Names.
Specifics of the forwarding logic for Interests with
ForwardingHint will be defined in a separated document.
Nonce = NONCE-TYPE TLV-LENGTH ; == 4 4OCTET
The Nonce carries a randomly-generated 4-octet long byte-string. The combination of Name and Nonce should uniquely identify an Interest packet. This is used to detect looping Interests.
InterestLifetime = INTEREST-LIFETIME-TYPE TLV-LENGTH NonNegativeInteger
InterestLifetime indicates the (approximate) time remaining before the Interest times out.
The value is the number of milliseconds. The timeout is relative to the arrival time of the Interest at the current node.
Nodes that forward Interests may decrease the lifetime to account for the time spent in the node before forwarding, but are not required to do so. It is recommended that these adjustments be done only for relatively large delays (measured in seconds).
It is the application that sets the value for
InterestLifetime element is omitted, a default value of 4 seconds is used (4000).
The missing element may be added before forwarding.
HopLimit = HOP-LIMIT-TYPE TLV-LENGTH ; == 1 OCTET
HopLimit element indicates the number of hops the Interest is allowed to be forwarded. The value is encoded as a 1-byte unsigned integer value in the range [0, 255].
If element is present:
HopLimitvalue is larger than or equal to 1, a node should accept the packet and decrease the encoded value by 1.
HopLimitvalue becomes 0, a node can satisfy this Interest locally (cache or applications bound to local faces), but must not forward the Interests to any non-local faces.
HopLimitis 0, a node must drop the packet
a node should accept the packet;
when desired, a node can augment the Interest with the
ApplicationParameters = APPLICATION-PARAMETERS-TYPE TLV-LENGTH *OCTET
ApplicationParameters element can carry any arbitrary data that parameterizes the request for Data.
The Interest’s name MUST include a Interest parameters digest component to ensure uniqueness and integrity of the parameterized Interest (see Parameters Digest Component for additional details).
See Interest Signature.