Which protocols are used to exchange data packetsbetween nodes of a 4G network?
哪些协议用于在4G网络的节点之间交换数据包？
We know that IP is used but is it the only protocol?Just like Robinson Crusoe alone on his island? That is the question we are going to answer in this video.
我们知道使用IP但它是唯一的协议吗？就像他身上独自一人的鲁宾逊漂流记？ 这是我们将在本视频中回答的问题。
Remember encapsulation :when a packet that arrives from an external network, for example, the Internetit is taken up by the P Gateway, then placed in another IP packetthat is sent to the S Gatewayand once there, the S Gateway takes it inside and placesit in another packet sent to the eNode B.记住封装：当一个从外部网络到达的数据包，例如互联网，它被P网关接收，然后被放入发送到S网关的另一个IP数据包，然后在那里，S网关将其带入 并将其放入发 送给eNode B的另一个数据包中。
Between the P Gateway and the S Gateway, we have an IP network.在P网关和S网关之间，我们有一个IP网络。
If we take the entire stack of IP protocols,we get the idea, over IP, of a transport protocolbetween the endpoints.
如果我们采用整个IP协议栈，我们就可以通过IP获得端点之间传输协议的想法。
At this level, the endpoints arethe P Gateway and S Gateway.在此级别，端点是P网关和S网关。
There are two well-known transport protocols:TCP and UDP.有两种众所周知的传输协议：TCP和UDP。
TCP is used a lot, but is relativelycomplex due to reliability mechanisms such as theretransmission of lost packetsand also a complex congestion control.TCP被大量使用，但由于可靠性机制等原因而相对复杂重传丢失的数据包以及复杂的拥塞控制。
UDP has the advantage of being much simpler.UDP具有更简单的优点。
So, it’s UDP that was chosen as the transport protocol.因此，选择UDP作为传输协议。
If we need reliability and retransmission mechanisms,these will be placed over theuser IP protocol, in other words, between theserver and the mobile terminal:at that point, using UDP is a very good choice.如果我们需要可靠性和重传机制，这些将放在用户IP协议上，换句话说，放在服务器和移动终端之间：此时，使用UDP是一个非常好的选择。
So, UDP is used between the Serving Gateway and thePacket Gateway and between the Serving Gateway and the eNode B.因此，在服务网关和分组网关之间以及服务网关和eNode B之间使用UDP。
The moment you speak of a protocol, you’re speakingof headers that correspond to this protocol.在谈到协议的那一刻，您谈到的是与此协议相对应的标头。
So, IP packets include asource address (here the address of the P Gateway),a destination address (here the address of the Serving Gateway)and finally the UDP header with the port numbers.因此，IP分组包括源地址（这里是P网关的地址），目的地址（这里是服务网关的地址），最后是具有端口号的UDP报头。
We could easily say, “Let’s put our user IPpacket directly inside the IP datagram.”我们可以很容易地说，“让我们将用户IP数据包直接放在IP数据报中。”
But we know that there are several variations of theIP protocol: IPv 4, IPv 6, and so on;we want to keep the possibility of evolution and permitthe transport of other protocols.但我们知道IP协议有几种变体：IPv 4，IPv 6等等;我们希望保持进化的可能性并允许其他协议的传输。
To do this, we will develop anadditional protocol that’s called GTP: GPRS Tunneling Protocol.为此，我们将开发一种名为GTP的附加协议：GPRS隧道协议。
The idea is to add a format thatallows consistent processing for alluser protocols, whether they be IPv4 IPv6 or any other.我们的想法是添加一种格式，允许对所有用户协议进行一致处理，无论它们是IPv4 IPv6还是其他任何协议。
Therefore, we have different levels of headers, and on this diagramwe see the level of the additional header at the GTP layer.
因此，我们有不同级别的标头，在此图中我们看到GTP层的附加标头的级别。
We’ll explain in the next video what isin this GTP header.我们将在下一个视频中解释此GTP标头中的内容。
Now, if we look at thewhole protocol stack, we have, between the ServingGateway and the P Gateway, an IP network.现在，如果我们查看整个协议栈，我们在服务网关和P网关之间就有一个IP网络。
In accordance with the principlesof IP, the physical layer (1) and the data link layer (2)can be anything.根据IP的原理，物理层（1）和数据链路层（2）可以是任何东西。
The only thing that counts is having IP on the Serving Gatewayand the Packet Gateway.唯一重要的是在服务网关和分组网关上使用IP。
Above the IP layer we have UDP, above UDP, GTP.在IP层之上，我们有UDP，高于UDP，GTP。
To make it clear that we consider userpackets, for example the packets that contain the videostream if I’m watching a video on my smart phone,we talk of GTP-U, U stands for “user plane”.为了明确我们考虑用户数据包，例如我在智能手机上观看视频时包含视频流的数据包，我们谈到GTP-U，U代表“用户平面”。
Above GTP-U we find the user IP.在GTP-U之上，我们找到用户IP。
If we consider everything, we have the protocol stackthat we saw earlier between the Serving Gateway and thePacket Gateway, and we have the same protocolstack between the eNode Band the Serving Gateway.如果我们考虑所有事情，我们就拥有了之前在服务网关和分组网关之间看到的协议栈，并且我们在eNode B和服务网关之间拥有相同的协议栈。
GTP-U above UDP, above IPand above the physical and data link layers.GTP-U高于UDP，高于IP且高于物理和数据链路层。
We thus find GTP-U on the S1-Uinterface as well as on the S5/S8 interface.
因此，我们在S1-U接口以及S5 / S8接口上找到GTP-U。
To summarize, user IP packets are put in GTP-U packets, whichare themselves put in UDP packetstransported in IP packets!The protocol stack between the S-Gateway and theP-Gateway and between the S- Gateway and the eNodeBincludes IP/UDP/GTP-U/IP.总而言之，用户IP数据包被放入GTP-U数据包中，这些数据包本身被置于以IP数据包传输的UDP数据包中！S-Gateway与P-Gateway之间以及S-Gateway与eNodeB之间的协 议栈包括IP/ UDP/ GTP-U/ IP。
In the end, IP is not at all alone – unlike Robinson Crusoe.最后，IP并不孤单 - 与Robinson Crusoe不同。
转载于:https://www.cnblogs.com/sec875/articles/9990239.html
