We saw in a previous video the importance of the TEID, the ID of the endpoint of a tunnel.
我们在之前的视频中看到了TEID的重要性，即隧道端点的ID。
How do we establish a tunnel and ensure that bothendpoints are aware of both TEIDs?How are packets processed once the tunnel has been established?These are the questions we’re going to answer in this video.我们如何建立隧道并确保两个端点都知道这两个TEID？隧道建立后如何处理数据包？这些是我们将在本视频中回答的问题。
If we look at initializing a tunnel, the Serving Gateway,for example, will choose a new, unique TEIDvalue: 102.
如果我们查看初始化隧道，例如，服务网关将选择一个新的唯一TEID值：102。
It will send a request to establish a tunnel, saying:“New tunnel with the TEID 102”.
它将发送建立隧道的请求，说：“具有TEID 102的新隧道”。
The P-Gateway will choose a new TEID valuethat will be unique for it, in this example:16,538.P-Gateway将选择一个新的TEID值，在此示例中为16,538。
The P-Gateway stores the address ofthe sender, here, the address of the Serving Gateway andalso stores the value of the TEID it received.P-Gateway存储发送方的地址，这里是服务网关的地址，还存储它收到的TEID的值。
And it creates a link between 16,538 and 102.它创建了一个介于16,538和102之间的链接。
The P Gateway sends anacknowledgement message with both TEIDs.P网关发送带有两个TEID的确认消息。
This way, theServing Gateway knows the correspondence between itstunnel ID and the tunnel ID allocated by the P-Gateway.这样，服务网关知道其隧道ID与P网关分配的隧道ID之间的对应关系。
At the end of this exchange, a tunnel has beenestablished wit, at one end, a TEID of 102,102 and, at the other end, 16,538.
在这次交换结束时，已经建立了一条隧道，一端是TEID 102,102，另一端是16,538。
Note that, at the end of this exchange, each end knowsthe TEID allocated by the opposite node.注意，在该交换结束时，每一端都知道由相对节点分配的TEID。
Let’s go a little further to see what processing is donein the Serving Gateway.让我们再进一步了解服务网关中的处理过程。
We’ll see that the processing is relatively simple,once a table has been set up.一旦设置了表格，我们就会看到处理相对简单。
The following explanation is valid to illustrate the principle.以下说明有效说明原理。
I’m not saying that the real implementation in theServing Gateway is exactly like this, but it helpsto really understand how the TEIDs are managed and howtwo tunnels are appended.我不是说服务网关中的实际实现与此完全相同，但它有助于真正理解如何管理TEID以及如何附加两个隧道。
We have, in the Serving Gateway table, theTEID values, the actions to becarried out, perhaps details about theseactions and we’ll indicate which isthe tunnel of the peer node.我们在Serving Gateway表中有TEID值，要执行的操作，可能有关这些操作的详细信息，我们将指出哪个是对等节点的隧道。
An example: when the Serving Gateway establishes thetunnel, it indicates TEID 102, so we’ll createan entry in row 102 of the table ofthe Serving Gateway.示例：当服务网关建立隧道时，它指示TEID 102，因此我们将在服务网关的表的行102中创建条目。
The S-Gateway knows the IP address of the P-Gateway.S-Gateway知道P-Gateway的IP地址。
Once the P Gateway has responded, theS-Gateway knows that the P-Gateway has allocated 16,538for the tunnel and for the TEID of that tunnel.一旦P网关响应，S网关就知道P网关已为隧道和该隧道的TEID分配了16,538。
This TEID is stored in row 102.该TEID存储在行102中。
The tunnel has been established.隧道已经建立。
Now we can have a tunnel between the Serving Gateway and the eNodeB.现在我们可以在服务网关和eNodeB之间建立隧道。
This tunnel, for example, is established using103 as the TEID: the corresponding address will bebe the address of the eNodeB,eNodeB 2 in our example, andthe TEID is 101.例如，使用103作为TEID建立该隧道：对应的地址将是eNodeB的地址，在我们的示例中是eNodeB 2，并且TEID是101。
This is the TEID that was chosenby eNodeB 2.这是eNodeB 2选择的TEID。
Every packet arriving on tunnel 103 must be re-sent to tunnel 102.到达隧道103的每个分组必须重新发送到隧道102。
The action of retransmission is called “Forwarding”.重传的动作称为“转发”。
In the table, column Detail indicates thatwe forward packets from tunnel 103 to tunnel 102.在表中，列Detail表示我们将数据包从隧道103转发到隧道102。
If we look at the processing, that means that a packet arriving from,for example, eNodeB 2 will contain TEID 103.如果我们查看处理，这意味着从例如eNodeB 2到达的分组将包含TEID 103。
The Serving Gateway looks at 103, it sees,“I have to forward the packet, I forward it to tunnel 102",and what does tunnel 102 correspond to?It corresponds to tunnel 16,538 for thisPacket Gateway.服务网关查看103，它看到，“我必须转发数据包，我将其转发到隧道102”，隧道102对应的是什么？它对应于此数据包网关的隧道16,538。
So, every packet that Ireceive with TEID 103, I resend it to the PacketGateway with the TEID 16,538.因此，我使用TEID 103接收的每个数据包，我将其重新发送到TEID为16,538的数据包网关。
The principles governing tunnels and their usefor uplink packets are also validfor downlink packets.管理隧道及其用于上行链路分组的原理对于下行链路分组也是有效的。
Packets from tunnel 102 areforwarded to tunnel 103.来自隧道102的分组被转发到隧道103。
We have seen how packets in the user plane areprocessed by the nodes of a 4G network:each packet received by a node through a tunnelincludes the local TEID of that tunnel.来自隧道102的分组被转发到隧道103。
As the TEID is unique, it ispossible to define a lookup table in the nodewhere the TEID is the entry and to indicate how toprocess the packet.由于TEID是唯一的，因此可以在TEID作为条目的节点中定义查找表，并指示如何处理该数据包。
Processing a packet is very simple.
处理数据包非常简单。
It is thus possible to manage a huge number of tunnels.
因此可以管理大量隧道。
Furthermore, a levelof quality of services can be associated to a tunnel.此外，服务质量水平可以与隧道相关联。
The association of a data tunneland a quality of service levelis called a data bearer.数据隧道和服务质量等级的关联称为数据承载。
转载于:https://www.cnblogs.com/sec875/articles/10008442.html
