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rfc1256.ICMP Router Discovery Messages

Network Working Group S. Deering, Editor Request for Comments: 1256 Xerox PARC September 1991 ICMP Router Discovery Messages

Status of this Memo

This RFC specifies an IAB standards track protocol for the Internet

community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "IAB Official Protocol

Standards" for the standardization state and status of this protocol. This document is a product of the IETF Router Discovery Working

Group. Distribution of this memo is unlimited.

Abstract

This document specifies an extension of the Internet Control Message Protocol (ICMP) to enable hosts attached to multicast or broadcast

networks to discover the IP addresses of their neighboring routers.

Table of Contents

1. Terminology 1

2. Protocol Overview 3

3. Message Formats 5

4. Router Specification 7 4.1. Router Configuration Variables 7 4.2. Message Validation by Routers 9

4.3. Router Behavior 9

5. Host Specification 12 5.1. Host Configuration Variables 12 5.2. Message Validation by Hosts 13

5.3. Host Behavior 14

6. Protocol Constants 17

7. Security Considerations 17 References 18 Author’s Address 19

1. Terminology

The following terms have a precise meaning when used in this

document:

system a device that implements the Internet Protocol, IP [9].

router a system that forwards IP datagrams, as specified

Router Discovery Working Group [Page 1]

in [2]. This does not include systems that, though

capable of IP forwarding, have that capability turned

off. Nor does it include systems that do IP forwarding only insofar as required to obey IP Source Route

options.

host any system that is not a router.

multicast unless otherwise qualified, means the use of either IP multicast [4] or IP broadcast [6] service.

link a communication facility or medium over which systems

can communicate at the link layer, i.e., the protocol

layer immediately below IP. The term "physical

network" has sometimes been used (imprecisely) for

this. Examples of links are LANs (possibly bridged to

other LANs), wide-area store-and-forward networks,

satellite channels, and point-to-point links.

multicast link

a link over which IP multicast or IP broadcast service is supported. This includes broadcast media such as

LANs and satellite channels, single point-to-point

links, and some store-and-forward networks such as SMDS networks [8].

interface a system’s attachment point to a link. It is possible (though unusual) for a system to have more than one

interface to the same link. Interfaces are uniquely

identified by IP unicast addresses; a single interface may have more than one such address.

multicast interface

an interface to a multicast link, that is, an interface to a link over which IP multicast or IP broadcast

service is supported.

subnet either a single subnet of a subnetted IP network [7] or a single non-subnetted IP network, i.e., the entity

identified by an IP address logically ANDed with its

assigned subnet mask. More than one subnet may exist

on the same link.

neighboring having an IP address belonging to the same subnet. Router Discovery Working Group [Page 2]

2. Protocol Overview

Before a host can send IP datagrams beyond its directly-attached

subnet, it must discover the address of at least one operational

router on that subnet. Typically, this is accomplished by reading a

list of one or more router addresses from a (possibly remote)

configuration file at startup time. On multicast links, some hosts

also discover router addresses by listening to routing protocol

traffic. Both of these methods have serious drawbacks: configuration files must be maintained manually -- a significant administrative

burden -- and are unable to track dynamic changes in router

availability; eavesdropping on routing traffic requires that hosts

recognize the particular routing protocols in use, which vary from

subnet to subnet and which are subject to change at any time. This

document specifies an alternative router discovery method using a

pair of ICMP [10] messages, for use on multicast links. It

eliminates the need for manual configuration of router addresses and is independent of any specific routing protocol.

The ICMP router discovery messages are called "Router Advertisements" and "Router Solicitations". Each router periodically multicasts a

Router Advertisement from each of its multicast interfaces,

announcing the IP address(es) of that interface. Hosts discover the addresses of their neighboring routers simply by listening for

advertisements. When a host attached to a multicast link starts up, it may multicast a Router Solicitation to ask for immediate

advertisements, rather than waiting for the next periodic ones to

arrive; if (and only if) no advertisements are forthcoming, the host may retransmit the solicitation a small number of times, but then

must desist from sending any more solicitations. Any routers that

subsequently start up, or that were not discovered because of packet loss or temporary link partitioning, are eventually discovered by

reception of their periodic (unsolicited) advertisements. (Links

that suffer high packet loss rates or frequent partitioning are

accommodated by increasing the rate of advertisements, rather than

increasing the number of solicitations that hosts are permitted to

send.)

The router discovery messages do not constitute a routing protocol:

they enable hosts to discover the existence of neighboring routers,

but not which router is best to reach a particular destination. If a host chooses a poor first-hop router for a particular destination, it should receive an ICMP Redirect from that router, identifying a

better one.

A Router Advertisement includes a "preference level" for each

advertised router address. When a host must choose a default router address (i.e., when, for a particular destination, the host has not Router Discovery Working Group [Page 3]

been redirected or configured to use a specific router address), it

is expected to choose from those router addresses that have the

highest preference level (see Section 3.3.1 in the Host Requirements -- Communication Layers RFC [1]). A network administrator can

configure router address preference levels to encourage or discourage the use of particular routers as default routers.

A Router Advertisement also includes a "lifetime" field, specifying

the maximum length of time that the advertised addresses are to be

considered as valid router addresses by hosts, in the absence of

further advertisements. This is used to ensure that hosts eventually forget about routers that fail, become unreachable, or stop acting as routers.

The default advertising rate is once every 7 to 10 minutes, and the

default lifetime is 30 minutes. This means that, using the default

values, the advertisements are not sufficient as a mechanism for

"black hole" detection, i.e., detection of failure of the first hop

of an active path -- ideally, black holes should be detected quickly enough to switch to another router before any transport connections

or higher-layer sessions time out. It is assumed that hosts already have mechanisms for black hole detection, as required by [1]. Hosts cannot depend on Router Advertisements for this purpose, since they

may be unavailable or administratively disabled on any particular

link or from any particular router. Therefore, the default

advertising rate and lifetime values were chosen simply to make the

load imposed on links and hosts by the periodic multicast

advertisements negligible, even when there are many routers present. However, a network administrator who wishes to employ advertisements as a supplemental black hole detection mechanism is free to configure smaller values.

Router Discovery Working Group [Page 4]

3. Message Formats

ICMP Router Advertisement Message

0 1 2 3

0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Code | Checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Num Addrs |Addr Entry Size| Lifetime | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Router Address[1] | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Preference Level[1] | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Router Address[2] | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Preference Level[2] | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | . | | . | | . | IP Fields:

Source Address An IP address belonging to the interface

from which this message is sent.

Destination Address The configured AdvertisementAddress or the

IP address of a neighboring host.

Time-to-Live 1 if the Destination Address is an IP

multicast address; at least 1 otherwise.

ICMP Fields:

Type 9

Code 0

Checksum The 16-bit one’s complement of the one’s

complement sum of the ICMP message, start-

ing with the ICMP Type. For computing the

checksum, the Checksum field is set to 0. Router Discovery Working Group [Page 5]

Num Addrs The number of router addresses advertised

in this message.

Addr Entry Size The number of 32-bit words of information

per each router address (2, in the version

of the protocol described here).

Lifetime The maximum number of seconds that the

router addresses may be considered valid.

Router Address[i], The sending router’s IP address(es) on the

i = 1..Num Addrs interface from which this message is sent.

Preference Level[i], The preferability of each Router Address[i] i = 1..Num Addrs as a default router address, relative to

other router addresses on the same subnet.

A signed, twos-complement value; higher

values mean more preferable.

ICMP Router Solicitation Message

0 1 2 3

0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

Source Address An IP address belonging to the interface

from which this message is sent, or 0.

Destination Address The configured SolicitationAddress.

Time-to-Live 1 if the Destination Address is an IP

multicast address; at least 1 otherwise.

ICMP Fields:

Type 10

Code 0

Router Discovery Working Group [Page 6]

Checksum The 16-bit one’s complement of the one’s

complement sum of the ICMP message, start-

ing with the ICMP Type. For computing the

checksum, the Checksum field is set to 0.

Reserved Sent as 0; ignored on reception.

4. Router Specification

4.1. Router Configuration Variables

A router that implements the ICMP router discovery messages must

allow for the following variables to be configured by system

management; default values are specified so as to make it unnecessary to configure any of these variables in many cases.

For each multicast interface:

AdvertisementAddress

The IP destination address to be used for multicast

Router Advertisements sent from the interface. The

only permissible values are the all-systems multicast

address, 224.0.0.1, or the limited-broadcast address,

255.255.255.255. (The all-systems address is preferred wherever possible, i.e., on any link where all

listening hosts support IP multicast.)

Default: 224.0.0.1 if the router supports IP multicast on the interface, else 255.255.255.255

MaxAdvertisementInterval

The maximum time allowed between sending multicast

Router Advertisements from the interface, in seconds.

Must be no less than 4 seconds and no greater than 1800 seconds.

Default: 600 seconds

MinAdvertisementInterval

The minimum time allowed between sending unsolicited

multicast Router Advertisements from the interface, in seconds. Must be no less than 3 seconds and no greater than MaxAdvertisementInterval.

Default: 0.75 * MaxAdvertisementInterval

Router Discovery Working Group [Page 7]

AdvertisementLifetime

The value to be placed in the Lifetime field of Router Advertisements sent from the interface, in seconds.

Must be no less than MaxAdvertisementInterval and no

greater than 9000 seconds.

Default: 3 * MaxAdvertisementInterval

For each of the router’s IP addresses on its multicast interfaces:

Advertise

A flag indicating whether or not the address is to be

advertised.

Default: TRUE

PreferenceLevel

The preferability of the address as a default router

address, relative to other router addresses on the same subnet. A 32-bit, signed, twos-complement integer,

with higher values meaning more preferable. The

minimum value (hex 80000000) is used to indicate that

the address, even though it may be advertised, is not

to be used by neighboring hosts as a default router

address.

Default: 0

The case in which it is useful to configure an address with a

preference level of hex 80000000 (rather than simply setting its

Advertise flag to FALSE) is when advertisements are being used for

"black hole" detection, as mentioned in Section 2. In particular, a router that is to be used to reach only specific IP destinations

could advertise its address with a preference level of hex 80000000

(so that neighboring hosts will not use it as a default router for

reaching arbitrary IP destinations) and a non-zero lifetime (so that neighboring hosts that have been redirected or configured to use it

can detect its failure by timing out the reception of its

advertisements).

It has been suggested that, when the preference level of an address

has not been explicitly configured, a router could set it according

to the metric of the router’s "default route" (if it has one), rather than defaulting it to zero as suggested above. Thus, a router with a better metric for its default route would advertise a higher

preference level for its address. (Note that routing metrics that

are encoded such that "lower is better" would have to be inverted Router Discovery Working Group [Page 8]

before being used as preference levels in Router Advertisement

messages.) Such a strategy might reduce the amount of ICMP Redirect traffic on some links by making it more likely that a host’s first

choice router for reaching an arbitrary destination is also the best choice. On the other hand, Redirect traffic is rarely a significant load on a link, and there are some cases where such a strategy would result in more Redirect traffic, not less (for example, on links from which the most frequently chosen destinations are best reached via

routers other than the one with the best default route). This

document makes no recommendation concerning this issue, and

implementors are free to try such a strategy, as long as they also

support static configuration of preference levels as specified above.

4.2. Message Validation by Routers

A router must silently discard any received Router Solicitation

messages that do not satisfy the following validity checks:

- IP Source Address is either 0 or the address of a neighbor

(i.e., an address that matches one of the router’s own

addresses on the arrival interface, under the subnet mask

associated with that address.)

- ICMP Checksum is valid.

- ICMP Code is 0.

- ICMP length (derived from the IP length) is 8 or more

octets.

The contents of the ICMP Reserved field, and of any octets beyond the first 8, are ignored. Future, backward-compatible changes to the

protocol may specify the contents of the Reserved field or of

additional octets at the end of the message; backward-incompatible

changes may use different Code values.

A solicitation that passes the validity checks is called a "valid

solicitation".

A router may silently discard any received Router Advertisement

messages. Any other action on reception of such messages by a router (for example, as part of a "peer discovery" process) is beyond the

scope of this document.

4.3. Router Behavior

The router joins the all-routers IP multicast group (224.0.0.2) on

all interfaces on which the router supports IP multicast.

Router Discovery Working Group [Page 9]

The term "advertising interface" refers to any functioning and

enabled multicast interface that has at least one IP address whose

configured Advertise flag is TRUE. From each advertising interface, the router transmits periodic, multicast Router Advertisements,

containing the following values:

- In the destination address field of the IP header: the

interface’s configured AdvertisementAddress.

- In the Lifetime field: the interface’s configured

AdvertisementLifetime.

- In the Router Address[i] and Preference Level[i] fields:

all of the interface’s addresses whose Advertise flags are

TRUE, along with their corresponding PreferenceLevel

values. (In the unlikely event that not all addresses fit

in a single advertisement, as constrained by the MTU of the

link, multiple advertisements are sent, with each except

the last containing as many addresses as can fit.)

The advertisements are not strictly periodic: the interval between

subsequent transmissions is randomized to reduce the probability of

synchronization with the advertisements from other routers on the

same link. This is done by maintaining a separate transmission

interval timer for each advertising interface. Each time a multicast advertisement is sent from an interface, that interface’s timer is

reset to a uniformly-distributed random value between the interface’s configured MinAdvertisementInterval and MaxAdvertisementInterval;

expiration of the timer causes the next advertisement to be sent from the interface, and a new random value to be chosen. (It is

recommended that routers include some unique value, such as one of

their IP or link-layer addresses, in the seed used to initialize

their pseudo-random number generators. Although the randomization

range is configured in units of seconds, the actual randomly-chosen

values should not be in units of whole seconds, but rather in units

of the highest available timer resolution.)

For the first few advertisements sent from an interface (up to

MAX_INITIAL_ADVERTISEMENTS), if the randomly chosen interval is

greater than MAX_INITIAL_ADVERT_INTERVAL, the timer should be set to MAX_INITIAL_ADVERT_INTERVAL instead. Using this smaller interval for the initial advertisements increases the likelihood of a router being discovered quickly when it first becomes available, in the presence

of possible packet loss.

In addition to the periodic, unsolicited advertisements, a router

sends advertisements in response to valid solicitations received on

any of its advertising interfaces. A router may choose to unicast Router Discovery Working Group [Page 10]

the response directly to the soliciting host’s address (if it is not zero), or multicast it to the interface’s configured

AdvertisementAddress; in the latter case, the interface’s interval

timer is reset to a new random value, as with unsolicited

advertisements. A unicast response may be delayed, and a multicast

response must be delayed, for a small random interval not greater

than MAX_RESPONSE_DELAY, in order to prevent synchronization with

other responding routers, and to allow multiple, closely-spaced

solicitations to be answered with a single multicast advertisement.

If a router receives a solicitation sent to an IP broadcast address, on an interface whose configured AdvertisementAddress is an IP

multicast address, the router may send its response to the IP

broadcast address instead of the configured IP multicast address.

Such an event indicates a configuration inconsistency, and should be logged for possible corrective action by the network administrator.

It should be noted that an interface may become an advertising

interface at times other than system startup, as a result of recovery from an interface failure or through actions of system management

such as:

- enabling the interface, if it had been administratively

disabled and it has one or more addresses whose Advertise

flag is TRUE, or

- enabling IP forwarding capability (i.e., changing the

system from being a host to being a router), when the

interface has one or more addresses whose Advertise flag is

TRUE, or

- setting the Advertise flag of one or more of the

interface’s addresses to TRUE (or adding a new address with

a TRUE Advertise flag), when previously the interface had

no address whose Advertise flag was TRUE.

In such cases, the router must commence transmission of periodic advertisements on the new advertising interface, limiting the first few advertisements to intervals no greater than MAX_INITIAL_ADVERT_INTERVAL. In the case of a host becoming a router, the system must also join the all-routers IP multicast group on all interfaces on which the router supports IP multicast (whether or not they are advertising interfaces). An interface may also cease to be an advertising interface, through actions of system management such as:

- administratively disabling the interface,

Router Discovery Working Group [Page 11]

- shutting down the system, or disabling the IP forwarding

capability (i.e., changing the system from being a router

to being a host), or

- setting the Advertise flags of all of the interface’s

addresses to FALSE.

In such cases, it is recommended (but not required) that the router

transmit a final multicast advertisement on the interface, identical to its previous transmission but with a Lifetime field of zero. In

the case of a router becoming a host, the system must also depart

from the all-routers IP multicast group on all interfaces on which

the router supports IP multicast (whether or not they had been

advertising interfaces).

When the Advertise flag of one or more of an interface’s addresses

are set to FALSE by system management, but there remain other

addresses on that interface whose Advertise flags are TRUE, it is

recommended that the router send a single multicast advertisement

containing only those address whose Advertise flags were set to

FALSE, with a Lifetime field of zero.

5. Host Specification

5.1. Host Configuration Variables

A host that implements the ICMP router discovery messages must allow for the following variables to be configured by system management;

default values are specified so as to make it unnecessary to

configure any of these variables in many cases.

For each multicast interface:

PerformRouterDiscovery

A flag indicating whether or not the host is to perform ICMP router discovery on the interface.

Default: TRUE

SolicitationAddress

The IP destination address to be used for sending

Router Solicitations from the interface. The only

permissible values are the all-routers multicast

address, 224.0.0.2, or the limited-broadcast address,

255.255.255.255. (The all-routers address is preferred wherever possible, i.e., on any link where all

advertising routers support IP multicast.)

Router Discovery Working Group [Page 12]

Default: 224.0.0.2 if the host supports IP multicast on the interface, else 255.255.255.255

The Host Requirements -- Communication Layers RFC [1], Section

3.3.1.6, specifies that each host implementation must support a

configurable list of default router addresses. The purpose of the

ICMP router discovery messages is to eliminate the need to configure that list in hosts attached to multicast links. On non-multicast

links, and on multicast links for which ICMP router discovery is not (yet) supported by the routers or is administratively disabled, it

will continue to be necessary to configure the default router list in each host. Each entry in the list contains (at least) the following configurable variables:

RouterAddress

An IP address of a default router.

Default: (none)

PreferenceLevel

The preferability of the RouterAddress as a default

router address, relative to other router addresses on

the same subnet. The Host Requirements RFC does not

specify how this value is to be encoded; to allow the

preference level to be conveyed in a Router

Advertisement or configured by system management, it is here specified that it be encoded as a 32-bit, signed, twos-complement integer, with higher values meaning

more preferable. The minimum value (hex 80000000) is

reserved to mean that the address is not to be used as a default router address, i.e., it is to be used only

for specific IP destinations, of which the host has

been informed by ICMP Redirect or configuration.

Default: 0

5.2. Message Validation by Hosts

A host must silently discard any received Router Advertisement

messages that do not satisfy the following validity checks:

- ICMP Checksum is valid.

- ICMP Code is 0.

- ICMP Num Addrs is greater than or equal to 1.

- ICMP Addr Entry Size is greater than or equal to 2.

Router Discovery Working Group [Page 13]

- ICMP length (derived from the IP length) is greater than or

equal to 8 + (Num Addrs * Addr Entry Size * 4) octets.

The contents of any additional words of per-address information

(i.e., other than the Router Address and Preference Level fields),

and the contents of any octets beyond the first 8 + (Num Addrs * Addr Entry Size * 4) octets, are ignored. Future, backward-compatible

changes to the protocol may specify additional per-address

information words, or additional octets at the end of the message;

backward-incompatible changes may use different Code values.

An advertisement that passes the validity checks is called a "valid

advertisement".

A host must silently discard any received Router Solicitation

messages.

5.3. Host Behavior

On any interface on which the host supports IP multicast, the host

will be a member of the all-systems IP multicast group (224.0.0.1).

This occurs automatically, as specified in [4]; no explicit action is required on the part of the router discovery protocol implementation.

A host never sends a Router Advertisement message.

A host silently discards any Router Advertisement message that

arrives on an interface for which the host’s configured

PerformRouterDiscovery flag is FALSE, and it never sends a Router

Solicitation on such an interface.

A host cannot process an advertisement until it has determined its

own IP address(es) and subnet mask(s) for the interface on which the advertisement is received. (On some links, a host may be able to use some combination of BOOTP [3], RARP [5], or ICMP Address Mask

messages [7] to discover its own address and mask.) While waiting to learn the address and mask of an interface, a host may save any valid advertisements received on that interface for later processing; this allows router discovery and address/mask discovery to proceed in

parallel.

To process an advertisement, a host scans the list of router

addresses contained in it. It ignores any non-neighboring addresses, i.e., addresses that do not match one of the host’s own addresses on the arrival interface, under the subnet mask associated with that

address. For each neighboring address, the host does the following: - If the address is not already present in the host’s default

Router Discovery Working Group [Page 14]

router list, a new entry is added to the list, containing

the address along with its accompanying preference level

and a timer initialized to the Lifetime value from the

advertisement.

- If the address is already present in the host’s default

router list as a result of a previously-received

advertisement, its preference level is updated and its

timer is reset to the values in the newly-received

advertisement.

- If the address is already present in the host’s default

router list as a result of system configuration, no change

is made to its preference level; there is no timer

associated with a configured address. (Note that any

router addresses acquired from the "Gateway" subfield of

the vendor extensions field of a BOOTP packet [11] are

considered to be configured addresses; they are assigned

the default preference level of zero, and they do not have

an associated timer. Note further that any address found

in the "giaddr" field of a BOOTP packet [3] identifies a

BOOTP forwarder which is not necessarily an IP router; such

an address should not be installed in the host’s default

router list.)

Whenever the timer expires in any entry that was created as a result of a received advertisement, that entry is discarded.

To limit the storage needed for the default router list, a host may

choose not to store all of the router addresses discovered via

advertisements. If so, the host should discard those addresses with lower preference levels in favor of those with higher levels. It is desirable to retain more than one default router address in the list so that, if the current choice of default router is discovered to be down, the host may immediately choose another default router, without having to wait for the next advertisement to arrive.

Any router address advertised with a preference level of hex 80000000 is not to be used by the host as default router address; such an

address may be omitted from the default router list, unless its timer is being use as a "black-hole" detection mechanism, as discussed in

Section 4.1.

It should be understood that preference levels learned from

advertisements do not affect any of the host’s cached route entries. For example, if the host has been redirected to use a particular

router address to reach a specific IP destination, it continues to

use that router address for that destination, even if it discovers Router Discovery Working Group [Page 15]

another router address with a higher preference level. Preference

levels influence the choice of router only for an IP destination for which there is no cached or configured route, or whose cached route

points to a router that is subsequently discovered to be dead or

unreachable.

A host is permitted (but not required) to transmit up to

MAX_SOLICITATIONS Router Solicitation messages from any of its

multicast interfaces after any of the following events:

- The interface is initialized at system startup time.

- The interface is reinitialized after a temporary interface

failure or after being temporarily disabled by system

management.

- The system changes from being a router to being a host, by

having its IP forwarding capability turned off by system

management.

- The PerformRouterDiscovery flag for the interface is

changed from FALSE to TRUE by system management.

The IP destination address of the solicitations is the configured

SolicitationAddress for the interface. The IP source address may

contain zero if the host has not yet determined an address for the

interface; otherwise it contains one of the interface’s addresses.

If a host does choose to send a solicitation after one of the above

events, it should delay that transmission for a random amount of time between 0 and MAX_SOLICITATION_DELAY. This serves to alleviate

congestion when many hosts start up on a link at the same time, such as might happen after recovery from a power failure. (It is

recommended that hosts include some unique value, such as one of

their IP or link-layer addresses, in the seed used to initialize

their pseudo-random number generators. Although the randomization

range is specified in units of seconds, the actual randomly-chosen

value should not be in units of whole seconds, but rather in units of the highest available timer resolution.)

A host may also choose to further postpone its solicitations,

subsequent to one of the above events, until the first time it needs to use a default router.

Upon receiving a valid advertisement containing at least one

neighboring address whose preference level is other than hex

80000000, subsequent to one of the above events, the host must desist from sending any solicitations on that interface (even if none have Router Discovery Working Group [Page 16]

been sent yet), until the next time one of the above events occurs.

The small number of retransmissions of a solicitation, which are

permitted if no such advertisement is received, should be sent at

intervals of SOLICITATION_INTERVAL seconds, without randomization.

6. Protocol Constants

Router constants:

MAX_INITIAL_ADVERT_INTERVAL 16 seconds

MAX_INITIAL_ADVERTISEMENTS 3 transmissions

MAX_RESPONSE_DELAY 2 seconds

Host constants:

MAX_SOLICITATION_DELAY 1 second

SOLICITATION_INTERVAL 3 seconds

MAX_SOLICITATIONS 3 transmissions

Additional protocol constants are defined with the message formats in Section 3, and with the router and host configuration variables in

Sections 4.1 and 5.1.

All protocol constants are subject to change in future revisions of

the protocol.

7. Security Considerations

This extension of ICMP makes it possible for any system attached to a link to masquerade as a default router for hosts attached to that

link. Any traffic sent to such an imposter is vulnerable to

eavesdropping, to denial of forwarding service, and to modification

by insertion, deletion, or alteration of packets. It should be noted that, on most multicast or broadcast links on which this protocol is expected to operate, eavesdropping is already possible by any system attached to the link, and the Address Resolution Protocol (ARP) used on those links offers a similar opportunity for service denial and

message stream modification. For environments where those threats

are deemed unacceptable, there are configuration variables to disable dynamic router discovery by hosts.

The Router Advertisement message format is defined so as to allow

additional information to be added to the message in a backward-

compatible manner. One possible use of that capability is to add Router Discovery Working Group [Page 17]

digital signatures or some other form of authentication information

to the advertisements, to enable hosts to verify their authenticity. This is FOR FURTHER STUDY.

References

[1] Braden, R., Editor, "Requirements for Internet Hosts --

Communication Layers", RFC 1122, USC/Information Sciences

Institute, October 1989.

[2] Braden, R., and J. Postel, "Requirements for Internet Gateways", RFC 1009, USC/Information Sciences Institute, June 1987.

[3] Croft, B, and J. Gilmore, "Bootstrap Protocol (BOOTP)", RFC 951, Stanford and SUN Microsystems, September 1985.

[4] Deering, S., "Host Extensions for IP Multicasting", RFC 1112,

Stanford University, August 1989.

[5] Finlayson, R., Mann, T., Mogul J., and M. Theimer, "A Reverse

Address Resolution Protocol", RFC 903, Stanford University, June 1984.

[6] Mogul, J., "Broadcasting Internet Datagrams", RFC 919, Stanford

University, October 1984.

[7] Mogul J., and J. Postel, "Internet Standard Subnetting

Procedure", RFC 950, USC/Information Sciences Institute, August

1985.

[8] Piscitello D., and J. Lawrence, "Transmission of IP datagrams

over the SMDS Service", RFC 1209, Bell Communications Research,

March, 1991.

[9] Postel, J., "Internet Protocol - DARPA Internet Program Protocol Specification", RFC 791, DARPA, September 1981.

[10] Postel, J., "Internet Control Message Protocol - DARPA Internet

Program Protocol Specification", RFC 792, USC/Information

Sciences Institute, September 1981.

[11] Reynolds, J., "BOOTP Vendor Information Extensions", RFC 1084,

USC/Information Sciences Institute, December 1988.

Router Discovery Working Group [Page 18]

Author’s Address

Stephen E. Deering

Xerox Palo Alto Research Center

3333 Coyote Hill Road

Palo Alto, CA 94304

Phone: (415) 494-4839

EMail: deering@https://www.wendangku.net/doc/3718461906.html,

Or send comments to gw-discovery@https://www.wendangku.net/doc/3718461906.html,.

Router Discovery Working Group [Page 19]

TEMSDiscovery2.5操作指南概论

TEMS DISCOVERY DISCOVERY的几大功能：一：数据展示（地理化窗口/layer 3/图形化显示）都是在project中可以直接打开显示的。二：出报告三：地理化的差值分析/平均分析 Discovery和TI导入数据的想法不一样,TI是用logfile进行导入后分析,discovery是通过PROJECT形式导入各种数据（.cel/map/log这些数据是基于project）第一步:新建一个project:点击project explorer---new

上图中我们需要给project定义一个project name。然后SAVE一下。（再导入cell/map之前GIS/CELL CONFIGATION是空的，导入之后这里会有相应的显示） UDR:uers defined region(用户自定义区域) 第二步: 导入数据路测数据地理化数据

小区数据天线数据(天线的主瓣旁瓣) 覆盖图(planning tools导出来的)

在导入.cel(小区数据) 文件时的选项:要定义小区数据是属于哪一个project(define target project),然后Browse小区数据。导入过程中，我们会在TASK WINDOW中看到相应的project/.cel导入信息。导入好小区数据之后我们会在project Explorer中看到我们新建的project (20100801)中会出现Composite（组合）/datasets（数据组）,现在这里还是空的,然后我们右键project(比如:20100801)—view/edit properties会看到我们cell configuration已经存在CELL文件了。 ,

Deep Learning for Human Part Discovery in Images

Deep Learning for Human Part Discovery in Images Gabriel L.Oliveira,Abhinav Valada,Claas Bollen,Wolfram Burgard and Thomas Brox Abstract—This paper addresses the problem of human body part segmentation in conventional RGB images,which has several applications in robotics,such as learning from demon-stration and human-robot handovers.The proposed solution is based on Convolutional Neural Networks(CNNs).We present a network architecture that assigns each pixel to one of a prede?ned set of human body part classes,such as head, torso,arms,legs.After initializing weights with a very deep convolutional network for image classi?cation,the network can be trained end-to-end and yields precise class predictions at the original input resolution.Our architecture particularly improves on over-?tting issues in the up-convolutional part of the network.Relying only on RGB rather than RGB-D images also allows us to apply the approach outdoors.The network achieves state-of-the-art performance on the PASCAL Parts dataset.Moreover,we introduce two new part segmentation datasets,the Freiburg sitting people dataset and the Freiburg people in disaster dataset.We also present results obtained with a ground robot and an unmanned aerial vehicle. I.INTRODUCTION Convolutional Neural Networks(CNNs)have recently achieved unprecedented results in multiple visual perception tasks,such as image classi?cation[14],[24]and object detection[7],[8].CNNs have the ability to learn effective hierarchical feature representations that characterize the typical variations observed in visual data,which makes them very well-suited for all visual classi?cation tasks.Feature descriptors extracted from CNNs can be transferred also to related tasks.The features are generic and work well even with simple classi?ers[25]. In this paper,we are not just interested in predicting a single class label per image,but in predicting a high-resolution semantic segmentation output,as shown in Fig.1. Straightforward pixel-wise classi?cation is suboptimal for two reasons:?rst,it runs in a dilemma between localization accuracy and using large receptive?elds.Second,standard implementations of pixel-wise classi?cation are inef?cient computationally.Therefore,we build upon very recent work on so-called up-convolutional networks[4],[16].In contrast to usual classi?cation CNNs,which contract the high-resolution input to a low-resolution output,these networks can take an abstract,low-resolution input and predict a high-resolution output,such as a full-size image[4].In Long et al.[16], an up-convolutional network was attached to a classi?cation network,which resolves the above-mentioned dilemma:the contractive network part includes large receptive?elds,while the up-convolutional part provides high localization accuracy. All authors are with the Department of Computer Science at the University of Freiburg,79110Freiburg,Germany.This work has partly been supported by the European Commission under ERC-StG-PE7-279401-VideoLearn, ERC-AG-PE7-267686-LIFENA V,and FP7-610603-EUROPA2. (a)PASCAL Parts(b)MS COCO (c)Freiburg Sitting People(d)Freiburg People in Disaster Fig.1:Input image(left)and the corresponding mask(right) predicted by our network on various standard datasets. In this paper,we technically re?ne the architecture of Long et al.and apply it to human body part segmentation,where we focus especially on the usability in a robotics context.Apart from architectural changes,we identify data augmentation strategies that substantially increase performance. For robotics,human body part segmentation can be a very valuable tool,especially when it can be applied both indoors and outdoors.For persons who cannot move their upper body, some of the most basic actions such as drinking water is rendered impossible without assistance.Robots could identify human body parts,such as hands,and interact with them to perform some of these tasks.Other applications such as learning from demonstration and human robot handovers can also bene?t from accurate human part segmentation.For a learning-from-demonstration task,one could take advantage of the high level description of human parts.Each part could be used as an explicit mapping between the human and joints of the robot for learning control actions.Tasks such as human-robot handovers could also bene?t.A robot that needs to hand a tool to its human counterpart must be able to detect where the hands are to perform the task. Human body part segmentation has been considered a very challenging task in computer vision due to the wide variability of the body parts’appearance.There is large variation due to pose and viewpoint,self-occlusion,and clothing.Good results have been achieved in the past in conjunction with depth sensors[22].We show that CNNs can handle this variation very well even with regular RGB cameras,which can be used also outdoors.The proposed network architecture yields correct body part labels and also localizes them precisely. We outperform the baseline by Long et al.[16]by a large

中国电视纪录片发展现状研究

中国电视纪录片发展现状研究本文的目的在于研究中国电视纪录片发展现状。新中国成立以来电视纪录片的的发展经历了四个阶段新闻纪录、专题纪录、创新纪录、媒介融合。从研究历史出发通过对当下纪录片生态环境、市场化问题、话语权三大问题的现状分析归纳出体制内外纪录片发展中共同面临的问题。世纪在新的传播环境和传播语境下中国当下的电视纪录片依托传播学的理念从自身改造突破问题寻找出路。关键词电视纪录片市场化问题话语权传播过程引言引言研究缘起在年第届奥斯卡金像奖提名名单中华人女导演杨紫烨凭借执导的环保题材纪录短片《仇岗卫士》成功入围最佳纪录短片提名。杨紫烨接受采访时说“现在是中国纪录片最好的时代。与“最好时代”不相称的是纪录片现状的尴尬局面翻阅电视报几乎找不到它的身影即使找到了也被安排在午夜等非黄金时段相亲节目选秀节目竟猜节目……充斥于荧屏成为了老百姓茶余饭后的谈资。与二十世纪九十年代的辉煌相比电视纪录片节目渐渐冷清甚至已淡出人们的视线。纪录片遇到了怎样的困境把电视台的资源拱手让于其他节目电视纪录片在中国为何会有此境遇它的出路又在哪里这就是笔者写作的缘起也是重点研究的问题。纪录得益于电影。年月日法国卢米埃尔兄弟开创了电影的先河,工厂大门》、火车到站》、《婴儿进餐》等影片的公开收费放映使得电影真正走入了人类世界展示出独有的光影魅力。这些影片就像一幅幅活动的相片带有很大程度的纪实性质。而就在年电影很快登陆中国。上海、北京、香港、

台湾陆续出现电影但放映的都是外国人的影片。直到年北京丰泰照相馆的老板任庆泰以著名京剧艺术家谭鑫培作为拍摄对象拍下了他表演定军山》的几个片断观众反响热烈。这预示了中国纪录片的萌芽。而国际上公认的第一部纪录电影是罗伯特?弗拉哈迪在年拍摄的北方的纳努克》这也是他的第一部电影。直到今天这部电影仍然充满着无穷的魔力被热爱纪录片的专家学者作为研究欣赏图本。原因就在于他开创了纪录片的拍摄手法。纪录片依托电影发展壮大在电影和电视界闯下了一番天地被全世界人民所认同。从年电视发明以后人们就可以足不出户了解世界新闻、博览社会百态。影视合流成了趋势。电视纪录片应电视技术的成熟、媒体力量的聚合诞生了。美国国家地理频道、探索频道依托纪录片而崛起、发展英国的日本的在世界上在纪录片的专属领域中享有美誉。中国的电视杨紫烨现在是中国纪录片最好时代新浪网? 引言纪录片发从年起步至今已走过了五十三年的历史现状又是如何呢研究的目的和意义选择中国电视纪录片的现状作为论文的研究对象其目的和意义在于第一新千年已进入第十一个年头科学技术日新月异中国电视纪录片自身在承载内容和外在形式上都表现出个性化、丰富化的特点通过回顾半个世纪的电视纪录史分析出每个时期电视纪录片的共性站在历史的肩头才能更好的审视现在展望未来。第二电视生态环境与纪录片发展息息相关在市场经济时代纪录片面临着哪些问题又该如何把握自己的话语权这些问题的探讨是纪录片现状生存必须面对的课题。第三电视纪录片是一个复杂动态的

用STM32F4-Discovery套件自带调试器烧录STM32芯片

用STM32F4-Discovery套件自带调试器烧录STM32芯片碧云天书 STM32F4-Discovery自带了SWD调试连接器，可以用来调试和烧录STM32芯片和开发板。一般STM32开发板上的调试接口为20脚的JTAG接口，而STM32F4-Discovery板载的SWD调试连接器为6教SWD接口，可以用一条20脚转6脚的连接线将SWD调试器连接到开发板的JTAG接口上。一、硬件连接下图是JLink接口的SWD端口配置图，可以作为连接参考。引脚编号为简易牛角座顶视图对应的编号。红线标识的引脚对应着ST-LINK/V2调试连接器CN2的6个引脚。表1STM32F4-Discovery自带的ST-LINK/V2调试连接器CN2引脚定义(SWD) 引脚CN2说明 1VDD_TARGET来自应用的VDD 2SWCLK SWD时钟 3GND地线 4SWDIO SWD数据输入/输出 5NRST目标MCU的复位 6SWO保留（TRACESWO，连接目标MCU的PB3，可以不接）由于使用ST-LINK/V2上的NRST就得断开SB11锡桥，因此不使用NRST线。需要连接剩下的5根线，分别是VCC,SWDIO,SWCLK，SWO，GND。其中SWO也可以不接，这样就只需要连4条线。下面的表2总结了连线方式。表2连接STM32F4-Discovery自带的ST-LINK/V2调试连接器到开发板JTAG接口的连线 VDD SWCLK GND SWDIO SWO(可省略） 12346 ST-LINK/V2 （CN2） JTAG接口194713

连接线实物使用STM32F4-Discovery自带的ST-LINK/V2调试连接器时，需要把CN3上的跳线拔掉，这时板载的ST-LINK/V2处于调试外部开发板状态。如下图：

Discovery纽约时代广场探索博物馆EB-5项目

Discovery纽约时代广场探索博物馆EB-5项目项目概况探索频道（Discovery Channel）于1985年在美国创立，探索频道目前覆盖全球超过160个国家、4亿5千万个家庭，探索公司同时也是美国的上市公司，是美国最大的主流媒体之一。 Discovery博物馆（mDiscovery Times Square）成立于2009年，是探索频道（Discovery）的官方合作伙伴，为纽约市的前五大的博物馆。地处于时代广场核心的44街与第七第八大道中间，过去成功展出：泰坦尼克号、哈利波特、法老王和兵马俑等世界知名展览，已接待超过数百万人次的游客。继成功推出纽约时代广场第一期娱乐项目“百老汇4D剧院”项目（进展顺利，投资者均取得I-526移民申请通过）后，曼哈顿区域中心（MRC）又重磅推出位于纽约时代广场的第二期娱乐项目Discovery博物馆——探索纽约项目，该项目与第一期4D剧院项目仅隔一街距离。

项目特点独一无二的地理优势纽约时代广场在2013年迎接了5340万次游客，游客总消费超过了400亿美金，旅游消费预计将会在未来4年每年以8.5%的速度增长。良好的发展前景——纽约市的旅游统计表

足够的就业机会创造依照Michael Evans所做出的就业人数计算（即RIMS Ⅱ计算方式，该计算方法为美国移民局比较推荐的就业机会计算方式），该项目预计产生593个新的就业机会。远远超过EB-5所需的240个就业机会空间高达60%。银行专户还款 Discovery博物馆参观门票预计价格为22美元，娱乐产业一直以来都是现金流十分可观的产业，依照与其他时代广场相似项目比较并且保守评估推算，每年项目净利润预计高达一千万美元以上，项目承诺在营运方面将保留60%的现金存放至还款账户中，专款专户作为未来贷款五年还款准备。资金结构

DAVID使用方法介绍

DAVID使用说明文档一、DAVID简介 DA VID （the Database for Annotation，Visualization and Integrated Discovery）的网址是https://www.wendangku.net/doc/3718461906.html,/。DA VID是一个生物信息数据库，整合了生物学数据和分析工具，为大规模的基因或蛋白列表（成百上千个基因ID或者蛋白ID列表）提供系统综合的生物功能注释信息，帮助用户从中提取生物学信息。 DA VID这个工具在2003年发布，目前版本是v6.7。和其他类似的分析工具，如GoMiner，GOstat等一样，都是将输入列表中的基因关联到生物学注释上，进而从统计的层面，在数千个关联的注释中，找出最显著富集的生物学注释。最主要是功能注释和信息链接。二、分析工具： DAVID需要用户提供感兴趣的基因列表，在基因背景下，使用提供的分析工具，提取该列表中含有的生物信息。这里说的基因列表和背景文件的选取对结果至关重要。 1.基因列表：这个基因列表可能是上游的生物信息分析产生的基因ID列表。对于富集分析而言，一般情况下，大量的基因组成的列表有更高的统计意义，对富集程度高的特殊Terms有更高的敏感度。富集分析产生的p-value在相同或者数量相同的基因列表中具有可比性。 DAVID对于基因列表的格式要求为每行一个基因ID或者是基因ID用逗号分隔开。基因列表的质量会直接影响到分析结果。这里定性给出好的基因列表应该具有的特点，一个好的基因列表至少要满足以下的大部分的要求：（1）包含与研究目的相关的大部分重要的基因（如标识基因）。

教你DIY中文增强版Geexbox

教你DIY中文增强版Geexbox Geexbox是一款可以从光盘上直接启动的Linux多媒体操作系统【当然也可以从硬盘和USB闪存上启动】，它是基于Linux和MPlayer进行开发应用的，它可以让你不用进windows 就可以欣赏大片。它几乎支持大部分主流媒体格式，包括AVI、RM、RMVB、MPEG-4、MP3及外挂中文字幕，可以让旧电脑变成强悍的媒体中心。可惜官方提供的只有英文的ISO 镜像，因此网上也出现了不少网友定制的中文版。他们是怎么做的呢？其实很简单。利用官方提供的GeeXboX ISO Generator，你也可以轻松DIY属于自己的Geexbox中文增强版。还犹豫什么呢？下面就和笔者一起来体会DIY的乐趣。一、GeeXboX ISO Generator初上手 “工欲善其事，必先利其器”，首先，请你到Geexbox的官方网站（https://www.wendangku.net/doc/3718461906.html,/en/downloads.html）下载最新的GeeXboX ISO Generator。然后将下载到的geexbox-generator-1.0.i386.tar.gz用Winrar解压到硬盘中（本文以“D：\geexbox”为例进行说明）。进入解压目录，双击generator.exe运行软件(这个镜像生成器还包括在Linux和Macosx下使用的程序)。进入程序界面，你可以看到八个标签页，它们分别是：界面设置(Interface)、音频设置（Audio)、视频设置(Video)、遥控设置（Remote control）、网络设置（Network）、服务设置（Services）、液晶显示设置（Lcd display）、套件设置（Packages）。接下来，请你单击“Packages“，进入套件设置项。这里列出的都是一些非常有用却没有包含在压缩包中的解码器（Codecs）、固件（Filmwares）、字体（Fonts）和主题（Themes）。建议你选中所有的解码器、固件、主题以及字体——“Chinese Simplified-GB2312”，然后点击”DownlOad”按钮下载。好啦，沏杯热茶慢慢等，Generator自己会通过网络把相应的文件下载到本地硬盘中。（如图1）心急的朋友如果受不了牛速，你也可以直接进入官方ftp下载所需资源： ⑴.解码器：https://www.wendangku.net/doc/3718461906.html,/codecs/ 将下得的压缩包解压至 D：\geexbox\iso\GEEXBOX\codec\即可。 ⑵.固件：https://www.wendangku.net/doc/3718461906.html,/firmwares/ 将下得的压缩包解压至 D：\geexbox\iso\GEEXBOX\firmwares\即可。 ⑶.字体：https://www.wendangku.net/doc/3718461906.html,/fonts/ 将下得的压缩包解压至 D：\geexbox\i18n\fonts\即可。

discovery软件在测井资料标准化中的应用

discovery软件在测井资料标准化中的应用趋势而分析方法是依据物质的某一物理参数的测量值来研究幷空间分布特点及变化规律的方法。任何汕出实际地质参数在横向上差不多上具有某种规律性渐变，即可看作是趋势面变化。趋势而分析的差不多思路确实是对标准层的测井响应多项式趋势面作图，并认为与地层原始趋势而具有一致性。若趋势面分析的残差图仅为随机变量，则是测井刻度误差造成的，若存在一组专门残差值，则认为是岩性变化导致的0 1981年J H Doveton和E?Bomcman 进一步用趋势而分析来描述这一标准化过程，1991年石汕大学熊绮华教授在进行牛庄洼陷万全汕田油藏描述研究过程中采纳该方法对测井曲线进行标准化。 Discovery软件是应用较为广泛的油藏描述软件，该软件在用趋势面分析方法进行测井曲线标准化方而具有操作简单、图形化输出及运算等特点，使得测井曲线标准化变得专门方便。 1 Discovery软件的趋势面分析方法 1.1趋势面分析方法的数学原理若趋势而分析的残差图仅为随机变量，则是测井刻度误差造成的，若存在一组专门残差值，则认为是岩性变化导致的。它的数学方法概述如下: 设用z(x,y)表示所研究的地质特点，其中(x,y)是平面上点的坐标.则趋势值和剩余值用下式表示: z(x,y)= Z (x,y)+e 其中：2(xj)为趋势值，C为剩余值。关于已知的数据：z,x\yiJH2 No 通常用回来分析求出趋势值和剩余值，即依照已知的数据求出回来方程f(x?y),使得: N 2 =乞忆一/(兀，片)] r-l 达到最小。实际上这确实是最小二乘意义下的曲面拟合咨询题，即依据运算值z(xj)用回来分析方法求出一个回来而: 对应于回来而上的值Z = 为趋势值，残差z，.名为剩余值。

纪录片制作机构

探索频道（Discovery Channel）是由探索传播公司（Discovery Communications, Inc./DCI；NASDAQ：DISCA，旗下拥有197多家全球性电视网，包括Discovery探索频道、动物星球频道、Discovery科学频道和Discovery高清视界频道等）于1985年创立的，总部位于美国马里兰州蒙哥马利县银泉市。探索频道主要播放流行科学、科技、历史、考古及自然纪录片。探索频道自1985年在美国启播后、现今已成为世界上发展最迅速的有线电视网络之一、覆盖面遍及全国百分之九十九的有线电视订户、在全球145个国家和地区有超过14400万个家庭订户。探索频道是全球最大的纪录片制作及买家、它吸引全球最优秀的纪录片制作人、所以探索频道的节目均被认为是世界上最优秀的纪实娱乐节目。也是世界上发行最广的电视品牌，目前到达全球160多个国家和地区的30600多万家庭，以35种不同语言播出节目。探索频道在世界主要国家地区均有落地，但探索频道会因应不同地区设立不同版本，加上字幕或配音。美国版本主要播放写实电视节目，如著名的流言终结者系列。亚洲探索频道除着重播放写实节目之外，也播放文化节目，如介绍中国、日本文化的一系列节目。亚洲探索频道于1994年成立，总部在新加坡，为美国Discovery传播公司（DCI）的全资附属机构，提供二十四小时精彩的纪实娱乐节目。据2005年泛亚媒体调查（PAX）的结果显示，探索频道在富裕成人中连续9年被公认为亚洲地区收视人口最多的有线及卫星电视频道。在新加坡举办的2004年“亚洲电视大奖”评选中，探索频道还荣膺“年度最佳有线及卫星电视频道”。中国国际电视总公司（中央电视台全额投资的大型国有独资公司，成立于1984年，是中国内地规模最大、赢利能力最强的传媒公司）境外卫星代理部接收探索频道信号，通过亚太6号卫星（东经134度）发射KU波段信号。该服务一般只提供给三星级或以上的涉外宾馆酒店，外国人居住区，领事馆及大使馆。中国大陆各省市的地方电视台会转播或播放探索频道制作的节目。同时，还与浙江华数集团成立合资公司，向由杭州电视台开办的四个面向全国播出的高清付费电视频道（求索纪录、求索生活、求索科学、求索动物）提供绝大多数的节目内容。

discover微波操作手册

微波合成仪标准操作手册一、操作流程 1、例行检查：仪器开机前，首先检查仪器整体是否正常；反应腔及内衬溢出杯是否清洁；检查自动压控装置APD是否清洁；自动进样器是否在正常位置；仪器电源线、数据线、气体管路连接情况是否正常。经检查一切正常方可开机。如内衬、APD不清洁或其它问题未经处理而运行仪器所造成的损害，属于非正常操作范畴。 2、开机顺序：先打开计算机电源，再打开Discover主机电源，然后运行Synergy软件（在计算机桌面上）。最后打开空压机电源。 3、登记制度：检查、开机均正常，请认真按规定填写仪器使用记录，记录信息不全将承担后续使用问题的责任。检查、开机、运行过程中，发现任何问题请及时联系管理员。 4、启动软件：运行Synergy软件，选择用户名并输入密码，进入软件操作界面后，可从屏幕右下方工具栏察看Discover和Explorer的联机情况。 5、放入样品：按要求装配好微波反应管（详见第六部分），放入仪器衰减器。 6、选择方法：打开软件界面中相应用户的“M ethod”文件夹图标，选择所需方法，单击鼠标左键拖拽到相应样品位置，如有需要，可新建方法或对方法进行修改（详见第四部分） 7、运行前检查：检查衰减器是否处于锁定状态；察看屏幕右侧温度、压力的显示是否正常。 8、运行方法：点击软件界面上部工具栏中的“P lay”按钮，仪器自动运行。二、禁止的操作项 1、严禁频繁开关机；开机后1min内关机；关机后1min内开机。 2、严禁修改电脑系统设置如注册表项等内容。 3、严禁使用破损的、有裂痕的、划痕严重的反应瓶。 4、严禁使用变形的样品盖。 5、反应瓶盖必须严格按要求装配，禁止未经过检查就放置于自动进样器架上。 6、严禁将标签纸粘贴在反应瓶的任何部位。 7、严禁将文献中多模微波仪器（特别是家用微波炉）的反应条件直接用于该仪器。 8、严禁长时间无人值守，仪器运行过程中，必须每2小时进行巡视查看，并做好检查记录。 9、微波程序运行过程中，严禁非仪器管理员在线修改反应参数。 10、仪器登陆用户只有管理员的权限可以设置为“Admin”其他均设置为“User”。 11、仪器各登陆用户的参数设置应符合仪器要求（详见第三部分），禁止修改。

SuperScan 使用教程

扫描工具SuperScan使用教程（如何使用SuperScan） SuperScan 是由Foundstone开发的一款免费的，但功能十分强大的工具，与许多同类工具比较，它既是一款黑客工具，又是一款网络安全工具。一名黑客可以利用它的拒绝服务攻击（DoS，denial of service）来收集远程网络主机信息。而做为安全工具，SuperScan能够帮助你发现你网络中的弱点。下面我将为你介绍从哪里得到这款软件并告诉你如何使用它。如何获得SuperScan SuperScan4.0是免费的，并且你可以在如下地址下载： https://www.wendangku.net/doc/3718461906.html,:81/up/soft3_2010/SuperScan.rar 因为SuperScan有可能引起网络包溢出，所以Foundstone站点声明某些杀毒软件可能识别SuperScan是一款拒绝服务攻击（Dos）的代理。 SuperScan4.0只能在Windows XP或者Windows 2000上运行。对一些老版本的操作系统，你必须下载SuperScan3.0版。 SuperScan的使用给SuperScan解压后，双击SuperScan4.exe，开始使用。打开主界面，默认为扫描（Scan）菜单，允许你输入一个或多个主机名或IP范围。你也可以选文件下的输入地址列表。输入主机名或IP范围后开始扫描，点Play button，SuperScan开始扫描地址，如下图A。

图A：SuperScan允许你输入要扫描的IP范围。扫描进程结束后，SuperScan将提供一个主机列表，关于每台扫描过的主机被发现的开放端口信息。SuperScan还有选择以HTML格式显示信息的功能。如图B。

美国探索教育视频资源服务平台

1、美国探索教育视频资源服务平台平台内容及意义大众文化的流行，娱乐学习一体化的浪潮席卷全球。同时随着社会发展，多学科交叉融合，使得社会对大学生综合能力要求颇高。在某一个方面出类拔萃的复合型人才，越来越受到企业社会的青睐。综合性人才在当今社会炙手可热，因此学校在重视专业课的同时，加强对课外知识的普及符合当今教育时代的发展需求。美国探索教育视频资源服务平台坚持以“科教兴国”为总方略，以提高在校师生综合素质、开拓师生眼界为宗旨；以教育、科学、文化、历史、探险等为题材的多学科交叉融合的教育视频资源服务平台。平台始终坚持科学研究与教学理论相统一，历史知识和文化教育相结合，以求达到师生即使足不出户，亦能知大千世界之神奇、能知世界各地前沿性科学技术，能解世间万物之疑惑。此平台已经成为西安数图网络科技有限公司一个独具特色的教育资源服务平台。平台特色美国探索教育视频资源服务平台，结合高校科学教育及科普知识所需，精选整合美国探索频道（Discovery）和美国国家地理频道（National Geography）两大世界知名频道近年来的最新节目，精心制作而成。 1、美国探索频道（Discovery） 1985年开播使用客户在全球达到160多个国家，3亿零6百多万家庭。通过15颗卫星用36种语言、24小时播放来源于全球不同地方摄制的精彩高品质纪实节目 2、美国国家地理频道（National Geography）遍布全球达171个国家及地区通过48种语言收看荣获1次奥斯卡金像奖和2次金像奖提名，129座艾美奖平台分类自然科学，历史人文，科学发现，生命科学，旅游风光，体育探索，军事侦探，交通机械，工程建筑

discovery教程

第一章：前言 (1) 第二章：微机油藏描述系统集成 (3) 一、Landmark公司微机油藏描述系统发展历程 (3) 二、微机油藏描述系统各模块集成 (4) （一）工区、数据管理系统（二）GESXplorer地质分析与制图系统（三）SeisVision 2D/3D二维三维地震解释系统（四）PRIZM 测井多井解释系统（五）ZoneManager层管理与预测（六）GMAPlus正演建模三、Discovery微机油藏描述系统软件特色 (12) 第三章：微机三维地震解释系统软件应用方案研究 (13) 一、工区建立 (13) （一）工区目录建立（二）一般工区建立（三）工区管理二、数据输入 (20) （一）地质数据输入 1 井头数据输入 2 井斜数据输入 3 分层数据输入 4 试油数据输入 5 生产数据加载 6 速度数据输入（二）测井数据输入 1 ASCII格式测井数据输入 2 LAS格式测井数据输入（三）地震数据输入 1 SEG-Y三维地震数据输入 2 层位数据输入 3 断层数据输入

三、微机地质应用 (31) （一）微机地质应用工作流程工作流程 1 地质分析工作流程 2 沉积相分析工作流程（二）微机地质应用 1 井位图建立 2 等值线图(isomap)建立 3 各种剖面图(Xsection)建立 4 生产现状图制作 5 沉积相图制作四、微机三维地震解释综合应用 (48) （一）微机三维地震解释工作流程 1 合成记录及层位工作流程 2 地震解释工作流程 3 速度分析工作流程（二）微机三维地震解释综合应用 1 地震迭后处理－相干体 2 合成记录制作及层位标定 3 层位和断层建立、解释 4 三维可视化 5 速度分析与时深转换 6 构造成图 7 地震测网图建立 8 地震属性提取五、微机单井测井解释及多井评价 (104) （一）微机单井测井解释及多井评价工作流程 1 测井曲线环境校正与标准化工作流程 2 测井分析流程（二）微机单井测井解释及多井评价 1 打开测井曲线 2 测井曲线显示模板制作 3.测井曲线显示、编辑与预处理 4.交会图制作与分析 5 测井解释模型建立与解释 6 测井解释成果报告

BBC一百多部记录片

BBC一百多部记录片 BBC.生物记录片.细胞 https://www.wendangku.net/doc/3718461906.html,/cszGSiqUkU9cr（访问密码：e215）自然风光喜马拉雅山脉 https://www.wendangku.net/doc/3718461906.html,/cs4iYcAeiHKIn 提取码：28c1自然风光巴厘岛 https://www.wendangku.net/doc/3718461906.html,/csizn3trNnCGv 提取码：e5edBBC纪录片《野性水域终极挑战》[MKV] https://www.wendangku.net/doc/3718461906.html,/Qi24t6zR3TyCK （提取码：bbcb）[历史地理] 詹姆斯·卡梅隆的深海挑战. https://www.wendangku.net/doc/3718461906.html,/lk/cJxR8pIvfSvR8 访问密码4076远方的家-边疆行全100集 https://www.wendangku.net/doc/3718461906.html,/cszGATNBFhjjw（访问密码：52c6）美丽中国湿地行50集

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