Computer Network (xix) other IP related technologies

1.IP multicast technologies

In multicast communication, a receiving end to confirm whether or not there is very important.
To confirm whether the receiving end, to be achieved by MLD. It is one of the important functions of the IPv4 IGMP and IPv6 in the IGMPv6.
IGMP (MLD) has two main functions:
1. indicate to the router wants to receive multicast messages (and would like to receive notification of multicast address).
2. To notify the switching hub receives multicast address.
First of all, the first router based on a role, learned wants to receive multicast host, and will inform this information to other routers, ready to receive multicast messages.
The second effect is also called IGMP (MLD) snooping. Switching hub usually only learned unicast addresses. The multicast frame is the same as with the broadcast frames are not filtered will all be copied to the port.
IGMP (MLD) is employed as the second action snoop. Support IGMP (MLD) snooping switching hub multicast frame may be filtered, so that the load on the network can be reduced.
In the IGMP (MLD) snooping, the switching hub to the IGMP (MLD) is monitored by the packet. Since known multicast address and the port sent from the IGMP (MLD) packet, the port will no longer transmitted so that nothing multicast frame.

2.IP anycast

IP任播主要用于报警电话110与消防电话119系统。
IP任播是指为那些提供同一种服务的服务器配置同一个IP地址，并与最近的服务器进行通信的一种方法。它可适用于IPv4和IPv6。
在IP任播的应用当中最为有名的当属DNS根域名服务器，使用IP任播可以让更多的DNS根域名服务器散布到世界的各个角落。因此，当发送一个请求包给DNS根域名服务器时，一个适当区域的IP地址也将被发送出去，从而可以从这个服务器获得应答。

IP任播机制虽然听起来非常方便， 实际上也有不少限制。例如，它无法保证将第一个包和第二个包发送给同一个主机。

3.通信质量控制

通信线路上的拥塞也叫做收敛。当网络发生收敛时，路由器和集线器 （交换集线器）的队列" (Buffer) 溢出，会出现大量的丢包现象，从而极端影响通信性能。

a.控制通信质量的机制

控制通信质量的工作机制类似于高速公路上的VIP通道。对于需要保证通信质量的包，路由器会进行特殊处理，并且在力所能及的范围之内对其进行优先处理。
通信质量包括带宽、延迟、时延波动等内容。
路由器在内部的队列（缓存）中可以优先处理这些要求保证通信质量的包，有时甚至不得不丢弃那些没有优先级的包以保证通信质量。
为了控制通信质量，人们提出了RSVP技术，它包括两个内容：
1.提供点对点的详细优先控制(lntServ)
2.提供相对较粗粒度的优先控制(DiffServ)

b.IntServ

IntServ是针对特定应用之间的通信进行质最控制的一种机制。
特定应用是指源IP地址、目标IP地址、源端口、目标端口以及协议号五项完全内容一致。
lntServ所涉及的通信并非一直进行，只是在必要的时候进行。
只有在必要的时候才要求在路由器上进行设置，这也叫 “流量设置”。实现这种流量控制的协议正是 RSVP。
RSVP中在接收端针对发送端传送控制包，并在它们之间所有的路由器上进行有质量控制的设定。
路由器随后就根据这些设置对包进行有针对性的处理。
RSVP的机制相对复杂，在大规模的网络中实施和应用比较困难。

c.DiffServ

IntServ针对应用的连接进行详细的通信质量控制。DiffServ则针对特定的网络进行较粗粒度的通信质量控制。
进行DiffServ质量控制的网络叫做DiffServ域。在DiffServ域中的路由器会对所有进人该域IP包首部中的DSCP字段进行替换。
对于期望被优先处理的包设置一个优先值，对于没有这种期望的包设置无需优先的值。
DiffServ域内部的路由器则根据IP首部的DSCP字段的值有选择性地进行优先处理。在发生网络拥塞时还可以丢弃优先级较低的包。
IntServ中每进行一次通信都要设置一次流量设置。而DiffServ则根据供应商的合约要求以比较粗粒度进行质量控制，机制相对简单，实用性较好。

4.显式拥塞通知

当发生网络拥塞时，发送主机应该减少数据包的发送量。
在IP层新增了一种使用显式拥塞通知的机制，即ECN。
ECN为实现拥塞通知的功能，将IP首部的TOS字段置换为ENC字段，并在TCP首部的保留位中追加CWR标志和ECE标志。
通知拥塞的时候，要将当前的拥塞情况传达给那个发送数据包的源地址主机。
ECN的机制概括起来就是：
在发送包的IP首部中记录路由器是否遇到拥塞，并在返回包的TCP首部中通知是否发生过拥塞。
拥塞检查在网络层进行，而拥塞通知则在传输层进行，这两层的互相协助实现了拥塞通知的功能。

5.Mobile IP

a.Mobile IP的定义

IP地址由 “网络地址” 和 “主机地址” 两部分组成。
Mobile IP：这种技术在主机所连接的子网IP发生变化时，主机IP地址仍保持不变。应用不需要做任何改动，即使是在IP地址发生变化的环境下，通信也能够继续。

b.IP隧道与Mobile IP

1. mobile host (MH: Mobile Host)
are those that move the location, IP address, but the same device.
When we do not move, the network connection is called a home network, IP addresses known home address. Home address as a person's residence, movement will not change the address.
Even if the mobile will be set to the IP address which subnet. This address is called a mobile address (CoA: Care-of Address) .
2. The home agent (HA: Home Agent)
is in the home network, monitoring the location of the mobile device, and forwards the data packet to the mobile host.
3. The foreign agent (FA: Foreighn Agent)
used for supporting a mobile host in a mobile device. All mobile host needs access network requires it.
Watching the mobile host from the application layer, you will find it always use the home address for communication. However, in practice the use of Mobile IP care-of address to forward packets.

c.Mobile IPv6

In Mobile IP, there are some problems:
1. There is no communication with the external network can not agent.
2.IP triangular path is forwarded packet therefore inefficient.
3. In order to improve safety, a domain may do so provided that if the source address of the packet transmitted to the outside from the own domain is not present in the domain of IP addresses, the packet is discarded. Destination router may discard the packet.
In Mobile IPv6 above problem has been appropriate to address:
1. External agents are assumed by the mobile host cities and counties of Mobile IPv6 own.
2. Consider the path optimization, it can not communicate directly through the home agent.
3.IPv6 header source address in the address assigned to the mobile, not dropped by the firewall.
Mobile host and correspondent host side need to support all of Mobile IPv6 in order to use these functions.