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iPCA Makes Quality Awareness on IP Networks Easy
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iPCA Makes Quality Awareness on IP Networks Easy
— What Advantages Does an Agile Network Bring? (Issue 3)
By Swift Liu, President
Enterprise Networking Product Line
Huawei Enterprise Business Group
Agile means quick and nimble.
New services such as mobility, cloud computing, social media, Big Data, and the Internet of Things (IoT) bring
higher requirements for real-time service transmission, network mobility and scalability, as well as improved user
experience. Huawei Agile Network Solution focuses on ways to cope with the challenges brought by these new
services and quickly solve problems they create for traditional networks.
This article discusses how to monitor the quality of IP networks and facilitates network operation and maintenance
(O&M).
1 Challenges to Enterprise Networks Brought by Social Media
and Multi-Service
Social media is a challenge to network capacity.
Different services place different requirements on network quality. For example, the packet loss ratio of voice
service should be smaller than 10-2 and that of High Definition (HD) video service should be smaller than 10-6.
That is, voice quality degrades if one packet is lost among 100 packets, and video pixelation will appear if one
packet is lost among 1 million packets.
On traditional enterprise networks, the data traffic of voice and video services is small. With the development of
interactive services, real-time traffic increases quickly. Moreover, the services requiring data interaction have high
requirements on network quality.
Low data traffic of voice and video has little impact on networks, but bursts of traffic will affect networks. Take
TV stations for example, where multiple HD channels access multiple studios. If six channels access the same
studio, traffic bursts will be generated. A switch’s buffer may fill quickly, which causes congestion that loses
packets. Gaming companies provide another example, because traffic bursts of HD video are much larger. The
biggest challenge of social media is the impact of multi-service on networks. A network needs to transport
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services that have different quality requirements and limits on traffic bursts. How can a network transmit all these
services and still guarantee service quality?
For enterprises, pixilation during video conferences is a big problem; however, the pixilation disappears quickly.
How do we locate the fault? Did the problem occur in the video conferencing system or the network? Is there a
faulty network link or device? Which card failed? Traditional IP networks cannot locate the fault. Therefore, in
most cases, users just endure experience degradation. An agile network should be able to transport all these
services and facilitate network operation and maintenance.
2 Innovation 3: IP Quality Awareness
IP is a connectionless protocol, and is unaware of network quality. Therefore, fault location is difficult for IP
networks and a problem for carriers. However, IP is still widely used. IP was invented by the U.S military during
the Cold War, but civilians have made wide use of IP. Basically, IP is reliable because every node on an IP
communications path is intelligent. For example, when a serious typhoon assaulted the east coast of the U.S in
2008, all mobile phones and fixed phones were unavailable. The only available communication channel was
email.
Although IP is a connectionless protocol, many connection-oriented technologies have been introduced so that the
Internet Service Provider (ISP) networks can transmit voice as well as data. To monitor IP network quality, people
invented many technologies. One method is to continuously send detection packets to test whether a link is normal;
that is, a network node continuously sends detection packets to another node. If one packet is lost, an alarm is
generated. If three consecutive packets are lost, the system considers that the link is broken, and switches services
to a backup link or takes other measures.
Huawei has invented a new method — Internet Packet Conservation Algorithm (iPCA) — to implement IP quality
awareness.
With the traditional method, devices A and B are directly connected, and device C is a tester. Tester C may send
10,000 packets to A and B. Count the packets received by interfaces A1, A2, B1, and B2. If an interface receives
9999 packets, one packet has been lost. The counters on A1, A2, and B1 show that both A1 and A2 have received
10000 packets, but B1 received 9999 packets. Obviously, one packet has been lost on the link between A1 and B1.
Why can’t the counters be used to detect packet loss? Because each interface has a large number of counters, we
can only view the counters at a specified moment. However, a real service interface, for example, a 10G interface,
sends several millions of packets within one second. We cannot obtain the counters of sent and received packets at
the same time. Even if the time difference is 1 second, the error may reach several million packets. Therefore, if
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we cannot see the values of all counters at the same time, we cannot determine whether a packet has been lost. In
addition, the transmission/receive time of different devices may not be the same even if the 1588v2 protocol is
used.
iPCA can address these problems. It uses a reserved bit in IP packets to monitor service quality. The device sets
the reserved bit to 0 in an interval, and to 1 in the next interval, and marks, or colors, the packets. Then the device
detects the reserved bits in IP packets and calculates the packets. Therefore, the time difference will not affect the
calculation result. The simplest Network Time Protocol (NTP) synchronization can meet transmission
requirements.
iPCA provides the following benefits:
1.
Quality monitoring for WAN dedicated lines
Most enterprises lease dedicated lines from ISPs to connect their WANs. Actually, a dedicated line is not
merely a fiber. It passes many routers and switches on an ISP network. The line may be a L3VPN or L2VPN
line. A large number of packets are lost on the dedicated lines. Why are users unaware of the packet loss? As
we know, TCP has a retransmission mechanism, and so does the application layer. Therefore, services are not
interrupted. However, service quality will still degrade. In this situation, iPCA can be deployed on the egress
and ingress of a dedicated line so that all lost packets are recorded.
2.
Link quality control on an HD video conference network
On a video conference network, the customer is clear about the network structure. After iPCA is deployed,
the customer knows where the packets are lost. Therefore, the network administrator can monitor the quality
of video conferences, quickly detect faults or potential faults, and take measures to rectify them.
3.
Campus network quality control
Generally, the switches on a campus network have small buffers. When congestion occurs, packets are lost.
The upper-layers (TCP or application layer) have a retransmission mechanism, so the loss of a few packets
can be ignored. User experience degrades only occasionally. In this situation, network administrators cannot
find problems on the network. Most customers endure this problem because it happens so often.
Packet loss occurs frequently, but cannot be located. Huawei iPCA can help network administrators locate
the problem on a specific device or link. With iPCA, customers can monitor service quality on campus
networks and eliminate potential risks.
iPCA is an innovative technology. In addition to monitoring links, it can detect faults on cards and chips,
determine packet loss locations and reasons on network nodes.
On a card, all service interfaces that receive data are inbound interfaces, and all interfaces that forward data to the
Switch Fabric Unit (SFU) are egress interfaces. iPCA compares the counters on inbound and outbound interfaces.
If the two counters are different, packets have been lost on the card. Similarly, an interface receiving data on a
chip is the inbound interface and an interface sending data is the outbound interface. iPCA compares the counters
on inbound and outbound interfaces. If the two counters are different, packets have been lost on the chip. On a
device, iPCA compares the counters on all inbound interfaces with the counters on all outbound interfaces to
determine whether packets are lost on the device.
Therefore, iPCA can detect faults on links, devices, cards, and even chips. Many scenarios will require iPCA.
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There is another problem. Non-Huawei devices do not support iPCA. Do we need to replace all devices with
Huawei devices? The answer is "no." All devices communicate with each other through IP packets. iPCA just
utilizes a reserved bit in the IP packets. Customers need only deploy Huawei agile devices and iPCA on key nodes.
This facilitates network reconstruction and protects customers’ investments. Basically, iPCA helps IT
administrators monitor IP network quality and makes network operation and maintenance easier.
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