The objective of the 4G architecture was to separatethe various functions.4G架构的目标是分离各种功能。
First, control of the radio part between the eNodeB andthe terminal, and second, management of security andmobility in the MME.首先，控制eNodeB和终端之间的无线电部分，第二，管理MME中的安全性和移动性。
How do you permit an MME to manage only thesecurity and mobility part?您如何允许MME仅管理安全性和移动性部分？
How do you permit an eNodeB to concentrate on radio connection functions?您如何允许eNodeB专注于无线电连接功能？
These are the questions we will answer with this video.以下是我们将通过此视频回答的问题。
First, we have to keep in mind what the control plane is.首先，我们必须记住控制平面是什么。
The control plane can be defined as containing all theprotocols, mechanisms, and messages that permitconfiguration of the switches, routers or links toenable the effective delivery of a communication service.控制平面可以被定义为包含允许配置交换机，路由器或链路以允许有效传送通信服务的所有协议，机制和消息。
For example, the attachment mechanism stands inthe control plane. All the security exchanges, as well.例如，附着机制位于控制平面中。 所有的安全交流也是如此。
They are necessary for the network to work correctly, butthey do not transport any user data.它们是网络正常工作所必需的，但它们不传输任何用户数据。
In a general sense, you could say that the control planeconsists of signaling exchanges.在一般意义上，您可以说控制平面由信令交换组成。
So, the dialog between a terminal, a UE,and an MME is solely in the control planesince the MME will not pass on any packets of userdata; only control messages.因此，终端，UE和MME之间的对话仅在控制平面中，因为MME不会传递任何用户数据包; 只控制消息。
On the control plane, one can differentiatemanagement of mobility and of security, whichis taken care of by the MME andallocation of radio resources andestablishment of radio connections.在控制平面上，可以区分移动性和安全性的管理，其由MME和无线电资源的分配以及无线电连接的建立来处理。
These are exchanges between the UE and the eNodeB.这些是UE和eNodeB之间的交换。
These messages and protocols can be tightly linked withthe technology used on the radio interface.这些消息和协议可以与无线电接口上使用的技术紧密相关。
We saw that, between a terminal and the eNodeB,there is a radio connection and the terminalis identified by the RNTI, the Radio Network Temporary Identifier.我们看到，在终端和eNodeB之间存在无线电连接，并且终端由RNTI（无线电网络临时标识符）识别。
And that the LCID, or Logical Channel Identifier,is used to distinguish between user dataand signaling.并且LCID或逻辑信道标识符用于区分用户数据和信令。
More exactly, we will use different values, onefor signaling messages sent by theterminal to the MME and two othersfor messages exchanged with the eNodeB, 0 for urgentmessages and 1 for non-urgent messages.更准确地说，我们将使用不同的值，一个用于终端发送到MME的信令消息，另外两个用于与eNodeB交换的消息，0用于紧急消息，1用于非紧急消息。
We have seen the notion of the S1-AP connection:the messages sent by the terminalto the MME are transmitted on the radio connection andthen over the S1‑AP connection.我们已经看到了S1-AP连接的概念：终端发送给MME的消息在无线连接上传输，然后通过S1-AP连接传输。
Of course,the same thing happens in the other direction from the MME to the terminal.当然，从MME到终端的另一个方向也发生同样的事情。
All of these messages form the Non Access Stratum, or NAS.所有这些来自非访问层或NAS的消息。
NAS messages, and this is very important, are forwardedby the eNodeB, but their content isnever analyzed by the eNodeB.NAS消息非常重要，由eNodeB转发，但eNodeB从不分析它们的内容。
Which means that you can completely change the NASmessages, without having to change a single line of codein the eNodeB.这意味着您可以完全更改NAS消息，而无需更改eNodeB中的单行代码。
The A. S. or Access Stratum, includes all the messagesrelated to the radio technology, to the establishmentand management of the radio connection.A. S.或Access Stratum，包括与无线电技术相关的所有消息，以及无线电连接的建立和管理。
They are exchanged between the terminal and the eNodeB.它们在终端和eNodeB之间交换。
For example, the modification of a radiobearer is an A. S. message.例如，无线电承载的修改是A.S.消息。
If we now look at the protocol stack, we’verepresented here the UE, the eNodeBand the MME.如果我们现在看一下协议栈，我们在这里代表UE，eNodeB和MME。
Between the eNodeB and the MME, we havean IP network, so one given layer 1, onegiven layer 2 and the IP protocolas the network protocol.在eNodeB和MME之间，我们有一个IP网络，因此一个给定第1层，一个给定第2层，IP协议作为网络协议。
People who specified 4G networks decided touse a transport protocol that is neither TCP nor UDP.指定4G网络的人决定使用既不是TCP也不是UDP的传输协议。
UDP does not give reliability and TCP is abit too complex and, importantly, it’s not message oriented.UDP不提供可靠性，TCP有点过于复杂，重要的是，它不是面向消息的。
Here, what we want is to exchangesignaling messages reliably.在这里，我们想要的是可靠地交换信令消息。
The protocol that meets our needs is SCTP,or Stream Control Transmission Protocol.满足我们需求的协议是SCTP或流控制传输协议。
This protocol is reliable and avoids unnecessaryretransmissions by the upper layer.该协议是可靠的并且避免了上层的不必要的重传。
Why use this protocol?为什么使用这个协议？
Well, sometimes the eNodeB can be connected withmicrowave links that are not necessarily very reliable.好吧，有时eNodeB可以连接不一定非常可靠的微波链路。
So, using a protocolthat manages retransmission of lost messages is a good idea.因此，使用管理丢失消息重传的协议是个好主意。
Above SCTP,we have the S1-AP protocol.在SCTP之上，我们有S1-AP协议。
This protocol is connection oriented and there are asmany connections as there are terminals managed bythe MME.该协议是面向连接的，并且存在与由MME管理的终端一样多的连接。
If we look at the radio interface side,we’ll see a few things we’re familiar with: the physicallayer here called layer 1, the Medium Access Control,(MAC); the Radio Link Control (RLC);the Packet Data Convergence Protocol(PDCP) and, above,RRC to establish radio connections.如果我们看一下无线电接口方面，我们会看到一些我们熟悉的东西：这里称为第1层的物理层，媒体访问控制，（MAC）; 无线链路控制（RLC）;分组数据汇聚协议（PDCP）以及上面建立无线连接的RRC。
All RRC messages are exchanged between the UE and the eNodeB.在UE和eNodeB之间交换所有RRC消息。
NAS messages aresent by the UE to theMME or by the MME to the UE.NAS消息由UE发送到MME或由MME发送到UE。
These NAS messages are transported in RRC messages.这些NAS消息在RRC消息中传输。
We have two NAS protocols: EMM, for EvolvedMobility Management and ESM for Evolved Session Management.我们有两个NAS协议：EMM，用于演进移动性管理，ESM用于演进会话管理。
Let’s look now on the user plane.现在让我们看看用户平面。
Data are transported in tunnels,also called bearers.数据在隧道中传输，也称为承载。
There should be a minimum of control to set up these tunnels.设置这些隧道应该有最低限度的控制。
Because of that, we will alsoset up control tunnels.因此，我们还将设置控制隧道。
Each control tunnel is identified by apair of TEIDs, justlike the data tunnels, but the values are different.每个控制隧道由一对TEID标识，就像数据隧道一样，但值不同。
There are control tunnels between the Serving Gateway andthe P-Gateway and between the MME and the Serving Gateway and the MME.服务网关和P网关之间以及MME和服务网关以及MME之间存在控制隧道。
These control tunnels are used for GTP-C exchanges.这些控制隧道用于GTP-C交换。
GTP‑C standsfor GPRS Tunnel Protocol in the Control Plane.GTP-C代表控制平面中的GPRS隧道协议。
These are all the messages necessary to set up, maintainand release data tunnels.这些是设置，维护和释放数据隧道所需的所有消息。
We have the protocol stack that we’ve already seen a bitfor the user plane.我们已经看到了用户平面的协议栈。
Here, for the control plane, it is IP and above that, UDPand GTP-C, whether it’s between the Serving Gateway andthe P-Gateway or between the Serving Gateway and the MME.这里，对于控制平面，它是IP以及UDP和GTP-C，无论是在服务网关和P网关之间，还是在服务网关和MME之间。
If we try to pull back and have a largerview, still on the control plane, we have the figure herethat you can take your time looking at with the slides.如果我们试图拉回并拥有更大的视图，仍然在控制平面上，我们在这里有一个数字，你可以花时间看幻灯片。
This figure symbolizes everything we haveseen in the previous slides.这个数字象征着我们在之前的幻灯片中看到的一切。
There’s not just the control plane, there’s also the user plane.不仅有控制平面，还有用户平面。
We can depict it in the diagram.我们可以在图中描述它。
It appears here and this gives us an overall viewof the set of protocols between theUE, the eNodeB, the MME,the S-Gateway the P-Gateway and a corresponding node, an external host.这里看起来并且这给出了UE，eNodeB，MME，S网关，P网关和相应节点（外部主机）之间的协议集的整体视图。
We’ve used blueto depict the control plane and pinkfor the user plane.我们使用蓝色来描绘用户平面的控制平面和粉红色。
The NAS, or Non Access Stratum, messages are thosewhich are exchanged between the eNodeB and the MME butwhich are in fact forwarded bythe eNodeB.NAS或非接入层消息是在eNodeB和MME之间交换但实际上由eNodeB转发的消息。
To summarize, A. S.总结一下，A。S.
control messages, NAS control messagesand data packets are transported on different logicalchannels, different LCID, over the radio interface.控制消息，NAS控制消息和数据分组通过无线电接口在不同的逻辑信道（不同的LCID）上传输。
A.S. messages are processed by theeNodeB, NAS messages are forwarded by the eNodeBto the MME on the S1-AP connections.如。 消息由eNodeB处理，NAS消息由eNodeB转发到S1-AP连接上的MME。
Data messages are sent through tunnels.数据消息通过隧道发送。
转载于:https://www.cnblogs.com/sec875/articles/10027923.html
