How can we transmit efficiently and very rapidly packetsthat can arrive from different PGateways and which areintended for different terminals?
我们如何有效和快速地传输可以从不同PGateways到达并且针对不同终端的数据包？
There’s a chance we will have to send them to differenteNodeBs, so, how can we quickly handle anddirect these packets towards the correct eNB?That is the question we are going to answer in this video.
我们有可能将它们发送到不同的eNodeB，那么，我们如何快速处理并将这些数据包指向正确的eNB？这是我们将在本视频中回答的问题。
To truly understand this question, we need to rememberthat we have millions of users.要真正理解这个问题，我们需要记住，我们有数百万用户。
They’re not all on the same eNode B.它们并非都在同一个eNode B上。
We have thousands or tens of thousands of eNode Bs.
我们有成千上万的eNode B。
They’re not all served by the same serving gateway.它们并非全部由同一服务网关提供服务。
But we have only a few packet gateways, in general2 or 3, perhaps up to 10.但我们只有几个分组网关，一般为2或3，可能高达10。
We have to be able to manage different tunnels.我们必须能够管理不同的隧道。
In this simple example,we can see that, between the P-Gateway and the S-Gateway,there are 2 tunnels.在这个简单的例子中，我们可以看到，在P-Gateway和S-Gateway之间，有2个隧道。
Packets for UE2should be forwarded by the SGW throughthe upper tunnel, which will lead to eNode B2and the packets for UE1 should beforwarded through the lower tunnel towards eNode B1.UE2的分组应该由SGW通过上层隧道转发，这将导致eNode B2，并且UE1的分组应该通过下层隧道转发到eNode B1。
Therefore, the processing for packets coming from the Packet Gatewayshould be specific to the tunnel along which they are sent.因此，来自分组网关的分组的处理应该特定于它们被发送的隧道。
We want to be able to do this processing very rapidly.我们希望能够非常迅速地进行这种处理。
If we leave the world of telecommunications for a moment… We know that, when businesses communicate, eachassigns a reference or file number to each communication.如果我们暂时离开电信世界......我们知道，当企业进行通信时，每个人都会为每个通信分配一个参考号或文件号。
When they write to each other regarding acertain subject, they add “Your reference”, the referenceof the recipient and“Our reference”, the reference of the sender.当他们互相写关于某一主题时，他们会添加“您的参考”，收件人的参考和“我们的参考”，即发件人的参考。
In a way, we’ll follow the same principle in mobile networks.在某种程度上，我们将在移动网络中遵循相同的原则。
Each business can be seen as a node, for example, the Serving Gateway.每个企业都可以被视为一个节点，例如服务网关。
The Serving Gateway has a certainnumber of tunnels that can be coming from otherpieces of equipment.服务网关有一定数量的隧道可以来自其他设备。
It will number the endpoint of each tunnel witha unique number, in this case 101-102-103-104 forthe 4 tunnels.它将使用唯一编号对每个隧道的端点进行编号，在这种情况下，对于4个隧道，为101-102-103-104。
This number is called the TEID or Tunnel Endpoint Identifier.
此号码称为TEID或隧道端点标识符。
Each tunnel therefore has2 identifiers because each tunnel has two endpoints.因此，每个隧道具有2个标识符，因为每个隧道具有两个端点。
For example, consider this tunnel betweenthe Serving Gateway and the Packet Gateway.例如，考虑服务网关和分组网关之间的此隧道。
From the point of view of the Serving Gateway, the TEID is 101.从服务网关的角度来看，TEID是101。
From the point of view of the Packet Gateway, it is 32,000.从分组网关的角度来看，它是32,000。
The numbering that each piece of equipment uses isunique, but there’s nothing preventing thesame number being used by two different nodes.每台设备使用的编号是唯一的，但没有什么能阻止两个不同节点使用相同的编号。
The TEID is coded over 32 bits or 4 bytes.TEID编码为32位或4字节。
It should be put in each packetto facilitate processing.它应该放在每个数据包中以方便处理。
The first solution that we will see is to put the TEIDallocated by the transmitter in the GTP header.我们将看到的第一个解决方案是将发送器分配的TEID放在GTP头中。
If we take for example, a packet arriving atthe P-Gateway, this packet is put into another packetand, on the GTP level, we will put thetunnel number in the header.例如，如果我们拿到一个到达P-Gateway的数据包，则将该数据包放入另一个数据包，在GTP级别，我们将隧道号放入标头中。
If we put 16,538,the receiving entity, here the S-Gateway, shouldidentify where the packet came from, since we’veused the identification of the sender.
如果我们放16,538，接收实体（这里是S-Gateway）应该识别数据包的来源，因为我们已经使用了发送者的标识。
Because each sender has his ownidentification system, the S-Gateway needs to find thesender of the packet, and the local tunnel identifiercorresponding to this pair.因为每个发送者都有自己的识别系统，所以S-Gateway需要找到该分组的发送者，以及与该对相对应的本地隧道标识符。
The processing is complicated because the receiver has toknow the TEID used by the node at theother end of the tunnel.处理很复杂，因为接收器必须知道隧道另一端节点使用的TEID。
It must therefore analyze the TEIDand the source address.因此，它必须分析TEID和源地址。
This isn’t a very good method.这不是一个很好的方法。
Let’s look at the second possibility, which would be to put the TEIDallocated by the receiver in the header.让我们看看第二种可能性，即将接收器分配的TEID放在标头中。
Here we have a process that is managed by the sender.这里我们有一个由发件人管理的流程。
If the sender wants to send a packetin a tunnel locally identified as 16,538,he should find the corresponding TEID allocated bythe Serving Gateway.如果发送方想要在本地标识为16,538的隧道中发送分组，则应该找到由服务网关分配的相应TEID。
In my example it converts 16,538 into102 in order to transmit a packet withthe TEID that the receiver uses.在我的例子中，它将16,538转换为102，以便传输具有接收器使用的TEID的数据包。
The advantage of this solution is that the receiver hasno conversion to do.此解决方案的优点是接收器无法进行转换。
It receives the packet on tunnel 102 and can process it.它在隧道102上接收数据包并可以处理它。
We can note that, here, there is necessarily uniqueness.我们可以注意到，这里必然存在唯一性。
Because 102 was allocated bythe Serving Gateway, there will only be one 102 valuefor a given tunnel arriving at the Serving Gateway.因为102是由服务网关分配的，所以到达服务网关的给定隧道只有一个102值。
There is a slight increase in complexity for thetransmitter but considerable simplificationfor the receiver.发射机的复杂性略有增加，但接收机的大大简化。
The third possibility is the one we saw in the examplewith the letters: put two TEIDs: 102 and 16,538.第三种可能性是我们在示例中看到的字母：放两个TEID：102和16,538。
Because we’ve put both,on the receiver side, we can just use the recipient one: 102.因为我们在接收器端放置了两个，我们可以只使用接收者：102。
So, we have simple processing on the receiver side,that the header is a bit longer.因此，我们在接收器端进行了简单的处理，标头有点长。
The advantage is, if one piece of equipment wants tochange the value of TEID on the fly, it can do itwithout additional processing.优点是，如果一件设备想要动态改变TEID的值，它可以在没有额外处理的情况下完成。
In other words, if the PGW wants to go from 16,538to 33 for some reason or other, it just needs toreplace 33 in the header and the receiver will say, “Aha!The other endpoint has changed.I’ll store this new value for the tunnel”.换句话说，如果PGW由于某种原因想要从16,538转到33，它只需要在标题中替换33并且接收器会说：“啊哈！另一个端点已经改变。我将存储这个新的 隧道的价值“。
This solution is not retained for GTP but it is used in aprotocol between the eNode B and the MME that we will seein another video.
GTP不保留此解决方案，但它用于eNode B和MME之间的协议，我们将在另一个视频中看到。
To summarize, each end of each tunnel is identified by a TEID, Tunnel Endpoint Identifier.总而言之，每个隧道的每一端都由TEID隧道端点标识符标识。
The TEID is allocated by the node that corresponds toeach end of the tunnel and is locally unique.TEID由对应于隧道的每一端的节点分配，并且是本地唯一的。
When a packet is sent through a tunnel,the TEID allocated by the receiver is put in theGTP header by the sender.当通过隧道发送数据包时，接收方分配的TEID由发送方放入GTP报头中。
转载于:https://www.cnblogs.com/sec875/articles/10002205.html
